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Plate Tectonic and Sediments - graphics SEDIMENTS 1. What Sediments Look Like 2. Classifying Sediments by Particle Size 3. Classifying Sediments by Source (Origin) 4. The Distribution of Marine Sediments 5. The Sediments of Continental Margins 6. The Sediments of Deep-Ocean Basins 7. Sediments: A World Ocean View 8. The Economic Importance of Marine Sediments Sediments I. Sediment a. Sediment is particles of organic or inorganic matter that accumulate in a loose, unconsolidated form. i. The particles originate from 1. the weathering and erosion of rocks, 2. the activity of living organisms 3. volcanic eruptions 4. chemical processes within the water itself 5. space ii. Marine sediments occur in a broad range of sizes and types 1. Beach sand is sediment 2. Mud in quiet bays is sediment iii. The origin and distribution of materials depends on a combination of biological, chemical and physical processes b. What do sediments look like? i. Surface 1. Could be smooth 2. May be rippled where there is a strong current ii. Color 1. Biological sediments are white or cream-colored 2. Clays range in color from tan to chocolate brown 3. Nearshore sediments are dark and contain organic matter and smell of hydrogen sulfide (rotten eggs) c. Where do you find sediments? i. Almost everywhere ii. If an area looks like it doesnЎ¦t have sediments itЎ¦s because the current there is moving the smaller particles away and leaving behind only the larger ones d. Classifying Sediment by Particle Size i. Particle size is frequently used to classify sediments 1. Most marine sediments are made of sand, silt and clay ii. The smaller the particle the more easily it can be transported by streams, waves and currents. 1. As sediment is transported it tends to be sorted by size a. Coarser grains, which are moved only by strong, turbulent flow, tend not to travel as far as finer grains. 2. Clays, particles < 0.004 millimeter in diameter, can remain suspended for very long periods and may be transported great distances by ocean currents before they are deposited. iii. A layer of sediment can contain particles of similar size, or it can be a mixture of different-sized particles 1. Sorting of sizes depends on the energy of the environment 2. Well-sorted sediments are composed of particles of one size and occur in environments where energy fluctuates within narrow limits a. Sediments from the deep ocean tend to be well-sorted 3. Poorly-sorted sediments have a mixture of sizes and are found in environments where energy fluctuates over a wide spectrum a. The mix of rubble at the base of rapidly eroding shore cliffs is an example of poorly-sorted e. Classifying Sediments by Source i. Can also classify sediments by their origin 1. Terrigenous Sediments are the most abundant and originate on the continents or islands near them. a. The most familiar continental igneous rock is granite, the source of quartz and clay, the two most common components of terrigenous sediments i. Quartz, an important mineral in granite, is hard, durable and cans withstand weathering and long transport. 1. Quartz sands are important components of sediments along continental margins b. Estimated that 15 billion metric tons of terrigenous sediments is transported in rivers to the sea each year i. 100 million metric tons is transported by air. 2. Biogenous Sediments are the next most abundant and they come from the living organisms a. The siliceous and calcareous compounds used by the organisms originally came from rivers or mid ocean ridges b. The plants and animals precipitated these minerals and used them to form their shells and skeletons. c. Most abundant in areas of high productivity i. Over millions of years they can form oil and natural gas 3. Hydrogenous Sediments are minerals that have precipitated directly from seawater a. The sources of dissolved minerals include submerged rock and sediment, leaching of the fresh crust at oceanic ridges, material issuing from hydrothermal vents and substances flowing to the ocean in river runoff. b. Also called authigenic sediments because they were formed in the place they currently occupy. 4. Cosmogenous Sediments are of extraterrestrial origin and are the least abundant a. Typically greatly diluted by other sediment components. b. Come from two major sources i. Interplanetary dust 1. Silt and sand sized micrometeoroids that come from asteroids and comets or from collisions between asteroids 2. About 15,000 to 30,000 metric tons of interplanetary dust enters earthЎ¦s atmosphere every year ii. Rare impacts by large asteroids and comets 1. Very rare 2. 65 million years ago an asteroid 10 km in diameter struck earth on what is now the northern coast of the Yucatan. ii. Sediment Mixtures 1. Sediments on the ocean floor only rarely come form a single source; most are a mixture of biogenous and terrigenous particles f. Distribution of Marine Sediments i. Sediments on continental shelves are often different from those on the deeper basin floors 1. Continental shelf sediments, neritic sediments, consist primarily of terrigenous material. a. 72% of all marine sediment is on continental slopes and rises 2. Deep ocean floors are covered by finer sediments than those of the continental margins. a. Pelagic sediments come from the sea ii. Sediments of the Continental Margins 1. In general, coarser sediments are found closer to land, and they become finer as one moves farther off the coast. a. Exceptions occur during glaciations when glaciers deposit poorly sorted sediments b. Also, when sea levels were lower rivers carried sediments right to the shelfЎ¦s edge 2. Biological productivity is also high along continental shelves, thus adding a lot of biogenous sediments as well. 3. Sediments can undergo lithification, and be converted into sedimentary rock if they get deep enough a. This type of rock can be found at the top of Everest or on the Colorado plateau iii. Sediments of the Deep-Ocean Basins 1. Sediment thickness vary greatly from place to place a. Atlantic = 1 km deep b. Pacific = 0.5 km deep c. Three reasons i. Atlantic is smaller in area ii. Atlantic is fed by a greater number of rivers laden with sediment iii. Pacific has many trench that trap sediments moving toward basins d. Sediments are thickest on the abyssal plains and thinnest (or absent) on ridges 2. Turbidites a. Underwater avalanches of thick muddy fluid help cut canyons and end up transporting continental sediments onto the abyssal plain. b. The deposits are called turbidites and are graded layers of terrigenous sand interbedded with the finer sediments of the deep sea floor. 3. Clays a. About 38% of the deep-sea is covered by clays and other fine terrigenous particles b. Terrigenous sediment accumulation on the deep-ocean floor is typically about 2 mm/thousand years 4. Oozes a. Seafloor samples taken farther from land usually show a greater proportion of biogenous sediments than those found near the continental margins because there is less terrigenous material far from shore. b. Deep ocean sediment with at least 30% biogenous material is called ooze i. Mostly made up of skeletons and shells of dead marine plants and animals. c. Oozes accumulate at about 1 ЎV 6cm/ thousand years d. Calcareous oozes form mainly from shells of foraminifera, pteropods and coccolithophores i. At great depth sea water contains more CO2 and is therefore slightly more acidic. This means that below a certain depth calcareous oozes wonЎ¦t form because itЎ¦s too acid. ii. This level is called the Calcium Carbonate Compensation Depth (CCD). iii. About 48% of the surface of the deep-ocean basins is covered by calcareous oozes. e. Siliceous oozes predominate at greater depths and in colder polar regions. i. They are the remnants of radiolarians and diatoms, which both use silica (opal) to make their shells. ii. Silica also dissolves in seawater, but very slowly iii. About 14% of the surface of the deep-ocean floor is covered by siliceous oozes. f. The very small particles that make up most of the deep-ocean sediments would need between 20 and 50 years to sink to the bottom, but they get there faster (about 2 weeks) because they are packaged in fecal pellets. g. Some deep sea oozes have been uplifted to form such deposits as the White Cliffs of Dover 5. Hydrogenous sediments originate from chemical reactions that occur on particles of the dominant sediment a. Manganese nodules are made of manganese and iron oxides and grow about 1 ЎV 10 mm/ million years. i. Between 20% and 50% of the Pacific ocean may be strewn with nodules iv. Sampling Sediments 1. Historically most sediments have been sampled by clamshell samplers and deeper samples by piston corers 2. Pretty straightforward and dirty v. Sediments as Historical Records 1. Stratigraphy uses the premise that older sediments are below younger ones, which allows us to determine a historical record of events that happened in the distant past. 2. Researchers can therefore analyze different layers, strata, in the sediments and determine what ocean conditions were when the sediments were laid down. This allows for a historical record of things like global climate or productivity. Plate and Ocean Course Content: AN OCEAN WORLD 1. One World Ocean 2. The world Ocean: two views 3. The Nature of Science 4. What is Marine Science? 5. The Origin of Earth 6. Earth and Ocean 7. The Origin of Life A HISTORY OF MARINE SCIENCE 1. Voyaging Begins 2. Science for Voyaging 3. Voyages for Science 4. Scientific Expeditions 5. Twentieth-Century Voyaging for Science 6. The Rise of Oceanographic Institutions 7. Current and future Oceanographic Research EARTH STRUCTURE AND PLATE TECTONICS 1. A Layered Earth 2. Towards an Understanding of Earth 3. Plate Tectonics: A Closer Look 4. The Confirmation of Plate Tectonics 5. Problems and Implications CONTINENTAL MARGINS AND OCEAN BASINS 1. The Topography of Ocean Floor 2. Continental Margins 3. Deep-Ocean Basins SEDIMENTS 1. What Sediments Look Like 2. Classifying Sediments by Particle Size 3. Classifying Sediments by Source (Origin) 4. The Distribution of Marine Sediments 5. The Sediments of Continental Margins 6. The Sediments of Deep-Ocean Basins 7. Sediments: A World Ocean View 8. The Economic Importance of Marine Sediments SEAWATER CHEMISTRY 1. The Water Molecule 2. The Dissolving Power of Water 3. Seawater 4. Dissolved Gases OCEAN PHYSICS 1. Water and Heat 2. Global Thermostatic Effects 3. Temperature, Salinity, and Water Density 4. An Overview of the Ocean Surface Conditions 5. Refraction, Light and Sound ATMOSPHERIC CIRCULATION AND WEATHER 1. Composition and Properties of the Atmosphere 2. Weather and Climate 3. Wind Patterns OCEAN CIRCULATION 1. The Forces That Drive Currents 2. Surface Currents 3. Wind-Induced Vertical Circualtion 4. Thermohaline Circulation LIFE IN THE OCEAN 1. The Organization of Communities 2. Classification of the Marine Environment 3. The Flow of Energy and Materials 4. Marine Productivity 5. Fisheries Resources graphics for ocean basin and plate tectonics OCEAN BASINS Bathymetry Echo Sounding Multibeam Systems Satellite Altimetry The Shape of Ocean Floors Continental Margins Continental Shelves Continental Slopes Submarine Canyons Continental Rises Deep-Ocean Basins Oceanic Ridges Hydrothermal Vents Abyssal Plains and Abyssal Hills Seamounts and Guyots Trenches and Island Arcs The Grand Tour Tectonic forces greatly influence the shape and location of continental margins Passive margins Atlantic-type Active margins Pacific-type Shelf ЎV continental shelves Slope ( common vertical exaggeration 50:1 for profiles) Ice age Near shore, the features of the ocean floor are similar to those of the adjacent continents because they share the same granitic basement. The transition to basalt marks the true edge of the continent. Continental slopes Shelf break Submarine Canyons (Hudson canyon) Turbidity currents, canyon heads, distribution channel, deep-sea fan The submerged outer edge of a continent is called the continental margin. Features of continental margins include continental shelves, continental slopes, submarine canyons, and continental rises. DEEP-OCEAN BASIN Oceanic Ridges, transform faults, fracture zones Hydrothermal vents, black smokers Abyssal Plains and Abyssal Hills Seamounts and Guyots Oceanic trenches and Island Arcs: Aleutian Trench, Hawaiian Islands, Juan de Fuca Ridge, Clipperton Fracture zone, Peru-Chile Trench, East Pacific Rize, Marian Trench, Mid-Atlantic Ridge, South Sandvich Trench, Red Sea, Easter IslandGalapagos Rift, Iceland, Gulf of Aden, Pacific-Antarctic Ridge, Azores, Tristan de Cunha, Kermadec Trench, Hatteras Abyssal Plain, Grand Banks, Mid-Indian Ridge, Atlantic-Indian Ridge, Maldive Islands, Eltanin Fracture Zone, Emperor seamounts, Java Trench, Great Barrier Reef, Kuril Trench, Japan Trench Age of Ocean ORIGINS Marine Science, Oceanography, and the Nature of Science Origins Galaxies and Stars The Formation of the Solar System The Origin of Life The Distant Future of Earth OTHER OCEAN WORLDS Europa ЎV the moon of Jupiter (the photo of the icy surface of Europa) Mars Titan Extrasolar Planets Other planets in our solar system may have ЎV or may have had ЎV oceans. Mars was once wetter than it is today (valleys). Life The relative amount of water in various locations on or near EarthЎ¦s surface.97% - ocean, 1.7% -ice, 0.8% - groundwater, 0.007% - rivers and lakes. 0.001% - the atmosphere. Some Statistics of World Ocean An outline of the scientific method, as a systematic process of asking questions about the observable world. THE ORIGIN OF LIFE Life probably arose on Earth shortly after its formation, about 4 billion years ago. Life may have arisen in the deep ocean. Weak sunlight and unstable conditions on EarthЎ¦s surface may have favored the origin of life on mineral surfaces near deep-ocean hydrothermal vents. Fossil of a bacteria-like organism that photosynthesized and released oxygen into the atmosphere. The microscopic filament from northwestern Australia is about 3.5 billion years old. Sediments can tell story: Ocean Drilling Program science at the SmithsonianЎ¦s National Museum of Natural History Deep-sea core shows impact - One bad day, 65 million years ago...Meteorite Impact • K-T* meteorite crater off Yucatan Peninsula • Tektites & spherules found in marine sediments • Shocked quartz in marine sediments An asteroid nearly 10 km (6 mi) wide slammed into what is now MexicoЎ¦s Yucatan Peninsula and blasted debris into the atmosphere. When the dust cloud settled, a 177 km (110 mi) wide crater scarred the Earth. A large number of marine and terrestrial creatures became extinct. Treasure Chest--Leg 171 | JOIDES Resolution Annual Report PGP see Internet Paleobiologist Richard Norris investigates events surrounding the dinosaursЎ¦ demise Anatomy Of A Disaster By John Lauerman Only tiny, less ornate foraminifera microfossils are found in the core after the impact. Note the difference in size of the foraminifera shown above compared to those shown in the bottom photo from before the impact. (The largest specimens above are approximately 1/5 millimeter in diameter.) Ejecta including tektites, glassy spherules condensed from the hot vapor cloud produced by the asteroid impact, are found in this layer of the core. Debris thrown into the atmosphere by the impact rained down on the earth for days to months after the event. The impact and ensuing global climatic changes had disastrous consequences, wiping out 95 percent of the oceansЎ¦ free-floating foraminifera. (The glass spherule is approximately 1/5 millimeter in diameter.) Integrated Ocean Drilling Program Marine Sediments Ocean sediment includes particles from land, from chemical processes, from biological activity, and from space. * Ocean sediment is thickest over continental margins and thinnest over active oceanic ridges. * Sediment deposited on a quiet seafloor can provide a sequential record of recent events in the water column above. Sediments may be recycled into the Earth at subduction zones. * Sediments are an important source of crude oil and natural gas, food materials, and manganese and other economically important materials What is sediment, and who cares? " Sediment = Layers of loose material on ocean bottoms (or elsewhere). ЎЎ±Marine snowЎЁ. " Records Earth history (mineral composition, sediment texture). ЎЎ±ForensicsЎЁ. ЎV Past climate ЎV Age of seafloor ЎV Plate motions ЎV Fossil evolution & extinction Types of Sediments By particle siize ((ttextture)) • By oriigiin ((fformattiion)):: ЎV Terrigenous (Lithogenous) ЎV Biogenous (Biogenic) ЎV Hydrogenous (Authigenic) ЎV Cosmogenous (Cosmogenic) Terrigenous (Lithogenous) • Rock fragments from land • Transported to oceans by: ЎV Rivers ЎV Ice ЎVWind ЎV!Gravity flows • Mainly quartz (SiO2) ЎV Chemically stable ЎV Abrasion resistant • Most accumulates near continental margins • Wind-blown dust makes abyssal clay Distribution of Terrigenous Sediments • Neritic = near-shore ЎV Mainly from breakdown of continental rocks ЎV Coarser particles closer to shore ЎV Beach sands, continental shelf deposits, turbidite deposits, glacial deposits ЎV Shelf sediments may be converted to rock via lithification • Pelagic = deep ocean ЎV Finer particles farther from land ЎV Wind blown or distal turbidite Biogenous (Biogenic) • Hard parts of once-living organisms (shells, teeth, bones, and even poop!) • Callcareous (CaCO3) = calcium carbonate • Siilliiceous (SiO2) = silica • ЎЎ±OozeЎЁ is >30% biogenic material Distribution of Biogenous Sediments • Neritic = near-shore ЎV Carbonates in shallow, warm ocean • Coral reefs, ooid shoals, beach sands ЎV Stromatolites (carbonate, cyanobacteria, algae) • Pelagic = deep ocean ЎV SiO2 ooze under areas of surface ocean upwelling (high biologic productivity) ЎV CaCO3 ooze on seafloor <4500 m deep • CaCO3 dissolves in cold seawater The depth below which carbonate readily dissolves. Only non-calcareous sediments accumulate below the CCD. Factors in distribution of biogenous sediments: ЎVBiologic productivity ЎVDissolution as shells settle through ocean ЎVЎЎ±DilutionЎЁ by non-biogenic material Hydrogenous (Authigenic) Dissolved ions precipitate from seawater ЎVManganese nodules ЎV Inorganic carbonates ЎVPhosphates ЎVMetallic sulfides ЎVEvaporites Nodules - Very sllow ratte off accumullattiion • Larger nodulles grow llarger ffastter • Oriigiin iis unknown Cosmogenous (Cosmogenic) Extraterrestrial fragments ЎVGlassy tektites ЎVFe-Ni micrometeorites ЎVFound in deep ocean where other sediments accumulate very slowly Mixtures of Sediment Types • Most marine sediments are mixtures of the 4 types of sediment • Usually one sediment type is dominant Classification systems In general, geologists have attempted to classify sedimentary rocks on a natural basis, but some schemes have genetic implications (i.e.,knowledge of origin of a particular rock type is assumed), and many classifications reflect the philosophy, training, and experience of those who propound them. No scheme has found universal acceptance, and discussion here will centre on some proposals. The book Rocks and Rock Minerals by Louis V. Pirsson was first published in 1908, and it has enjoyed various revisions. Sedimentary rocks are classified there rather simplistically according to physical characteristics and composition into detrital and nondetrital rocks Terms designating composition and physical characteristics Detrital rocks Rudites (coarse) conglomerates (rounded clasts) breccias (angular clasts) basal, or transgression fanglomerates (in alluvial fans) tillites (glacially transported) Arenites (medium-grained) sandstone arkose (feldspar-rich) graywacke (sandstone with mud matrix) quartzite (orthoquartzite) Lutites (fine-grained) siltstone shale mudstone or claystone argillite loess (transported and deposited by wind) Nondetrital rocks Precipitates chemical precipitates (rocks formed by precipitation from seawater or fresh water) evaporites (products of evaporation from saline brines) duricrust rocks (hardened surface or mean-surface layer of any composition) Organic zoogenic (made up of hard parts of animals; e.g., crinoidal limestone) phytogenic (made up of plant remains; e.g., algal limestone Classifying Sediments Impact event Cataclysms Fornation of Universe, Solar System, Earth and Ocean All about GIS (Geography) http://www.geo.hunter.cuny.edu/programs/ma_courses.html#gtech711 ORIGINS Big Bang occurred 14 billions years ago. All of the mass and energy of the universe is through to have been concentrated at a geometric point at the beginning of space and time, the moment when the expansion of the universe began. We donЎ¦t know what initiated the expansion, but it continues today and will probably continue for billions of years, perhaps forever. The very early universe was unimaginably hot, but as it expanded, it cooled. About a million years after the big bang, temperatures fell enough to permit the formation of atoms from the energy and particles that had predominated up to that time. Most of these atoms of matter in the universe/ About a billion years after the big band , this matter began to congeal into the first galaxies and stars. A galaxy is a huge , rotating aggregation of stars, dust, gas, and other debris held together by gravity. Our galaxy is named a Milky Way. The stars that make up a galaxy are massive spheres of incandescent gases. Protostars, red giant. The solar system was formed 5 billion years ago from a thin cloud that had been enriched by heavy elements made in exploding stars. Solar nebula, planets, accretions. Earth is density stratified. During its formation heavy materials fell inward to form the core, and lighter substances rose to become the outer layers. Ocean and atmosphere are the least dense of these layers. Sources of the ocean: outgassing: volcanic gases emitted by fissures add water vapor, carbon dioxide, nitrogen, and other gases to the atmosphere. Volcanism was a major factor in altering EarthЎ¦s origin atmosphere; the action of photosynthetic plants was another. Comets may have delivered something bombard Earth bogy probably about 3.8 billion years ago. Earth first had a solid surface about 4.5 billion years ago. The ocean formed later when EarthЎ¦s surface became cool enough to allow clouds of steam and water vapor to condense and rest on the surface. Primitive atmosphere. 13 billion years ago ЎV Big Bang 11 billion years ago ЎV First galaxies form 5.5 billion years ago ЎV Solar nebula 4.6 billion years ago ЎV Earth 4.2 billion years ago ЎV ocean forms 3.8 billion years ago ЎV Oldest dated rocks 3.6 billion years ago ЎV First evidence of life 2 billion years ago ЎV Oxygen revolution begins 0.8 billion years ago ЎV Ocean and atmosphere reach steady state as today 800 millions of years ago ЎV First animals arise 510 millions of years ago ЎV First fishers appear 210 millions of years ago ЎV Pangaea breaks apart 66 millions of years ago ЎV end of dinosaurs 50 millions of years ago ЎV First marine animals 3 millions of years ago ЎV Humans appear Today 3.5 billions of years in the future ЎV SunЎ¦s output too low for liquid water ocean 5 billions of years in the future ЎV The sun swells, planets destroyed THE ORIGIN OF LIFE Life probably arose on Earth shortly after its formation, about 4 billion years ago. Life may have arisen in the deep ocean. Weak sunlight and unstable conditions on EarthЎ¦s surface may have favored the origin of life on mineral surfaces near deep-ocean hydrothermal vents. Fossil of a bacteria-like organism that photosynthesized and released oxygen into the atmosphere. The microscopic filament from northwestern Australia is about 3.5 billion years old. Ocean explorer HISTORY OF OCEANOGRAPHY James Cook 1778 Matthew Maury 1847 Charles Wilkes 1431 The Challenger Expedition 1831-36 The German Meteor expedition 1925 The Rise of Oceanographic Institutions the Japan Marine Science and Technology Center 1971 The Woods Hole Oceanographic Institution on Cape Cod The Scripps Institution of Oceanography in La Jolla NASA TOPEX/Poseidon Global Positioning System Alvin Echo sounding EXPLORING THE OCEAN BASINS WITH SATELLITE ALTIMETER DATA The surface of the ocean bulges outward and inward mimicking the topography of the ocean floor. The bumps, too small to be seen, can be measured by a radar altimeter aboard a satellite. Over the past year, data collected by the European Space Agency ERS-1 altimeter along with recently declassified data from the US Navy Geosat altimeter have provided detailed measurements of sea surface height over the oceans. These data provide the first view of the ocean floor structures in many remote areas of the Earth. For scientific applications, the Geosat and ERS-1 altimeter data are comparable in value to the radar altimeter data recently collected by the Magellan spacecraft during its systematic mapping of Venus The geologic and topographic structures of the ocean floor primarily reflect plate tectonic activity that has occurred over the past 150 million years of the 4.5 billion year age of the Earth. Seafloor geology is far simpler than the geology of the continents because erosion rates are lower and also because the continents have suffered multiple collisions associated the opening and closing of ocean basins (Wilson Cycle). Despite their youth and geologic simplicity, most of this deep seafloor has remained poorly understood because it is masked by 3-5 km of seawater. For example, the Pacific-Antarctic rise, which has an area about equal to South America, is a broad rise of the ocean floor caused by sea floor spreading between two major tectonic plates (see Poster southeast of New Zealand). To the west of the ridge lies the Louisville seamount chain which is a chain of large undersea volcanoes having a length equal to the distance between New York and Los Angeles. These features are unfamiliar because they were discovered less than 20 years ago. The Louisville seamount chain was first detected in 1972 using depth soundings collected along random ship crossings of the South Pacific. Six years later the full extent of this chain was revealed by a radar altimeter aboard the Seasat (NASA) spacecraft. Recently, high density data collected by the Geosat (US Navy) and ERS-1 (European Space Agency) spacecraft data show the Pacific-Antarctic Rise and the Louisville Ridge in unprecedented detail. In an age when we are mapping the surfaces of Venus and Mars, it is difficult to believe that so little is known about our own planet. Plate Tectonics Laboratory for Satellite Altimetry TOPEX/Poseidon Altimetry Ocean Surface Topography from Space Satellite Geodesy Global Sea Floor Topography from Satellite Altimetry and Ship SATELLITE OCEANOGRAPHY Side-scan sonar Sonar Oceanographic and Geophysical Tomography Gulf of Mexico Gas Hydrates Seafloor Observatory Project Continental Drift and Plate Tectonics Earthquakes and earthquake waves Some seismic waves ЎV energy associated with earthquakes ЎV can pass through Earth reflecting from boundaries and telling about inner part of our planet. A Layered Earth Crust Oceanic crust Basalt Continental crust Granite Mantle Lithosphere Asthenosphere Lower mantle Core Internal Heat Radioactive decay Conduction Convention Isostatic Eguilibrium Large redions of EarthЎ¦s continents are held above sea level by isostatic equilibrium, a process analogous to a ship floating in water. Curious Coincidences? Continental Drift - http://ourworld.compuserve.com/homepages/dp5/tecto.htm Alfred Wegener Pangaea Triassic 210 Ma The Idea Transformed The Breakthrough: From Seafloor Spreading to Plate Tectonics Plate Boundaries Divergent Plate Boundaries ЎV Forming Ocean Basin Convergent Plate Boundaries ЎV Recycling Crust, descending slab, Wadati-Benioff zoneBuilding Island Arcs and Continents Transform Plate Boundaries ЎV Fracturing Crust ( Queen Charlotte Fault, Cascadian Subduction Zone, Mendocino Fracture Zone, Rivera Fault) Plate Interactions The Hawaiian chain (1 Ma) ЎV Emperor Seamounts (50 Ma) Meiji Seamonth (70 Ma) ЎV and the bend in the chain shows that the plate changed direction about 40 Ma. The Conformation of Plate Tectonics Hot Spot Terranes - buoyant continental and oceanic plateaus, fragments of granitic rock and sediments can be rafted along with a plate and scraped off onto a continent when the plate is subducted. plateaus, isolated segments of seafloor, oceanic ridges, ancient island arcs, and parts of continental crust are called terranes. The thinckness and low density prevent their subduction. Fragments of oceanic plateau or microcontinent, seamount or inactive oceanic ridge that can do accretion over zone of subduction and future faults and exotic terranes. Terrane formation. Oceanic plateaus usually composed of relatively low-density rock are not subducted into the trench with the oceanic plate. Instead, they are ЎЎ±scraped offЎЁ , causing uplifting and mountain building as they strike a contient. Though rare, assemblages of subducting oceanic lithosphere can also be scraped off (obducted) into the edges of continent. These dence, mineral-rich assemblages are known as ophiolites after their serpent-like shapes. Rich ore depositsare found in them. Paleomagnetism earthquake explorer possible paths of seismic waves through earth paths of earthquake waves The layers of the Earth The layers of the Earth Terrane Terrane accretion is the process of continent building in which smaller units of exotic crust (both oceanic and continental) collide and become welded to a larger continental craton. Terranes differ sufficiently from the craton petrologically and stratigraphically and are often bounded by known or suspected faults. Terrane is a general term for an exotic geologic unit, and they need not possess specific characteristics, except that they differ from the craton. Often, terranes are separated by clear physical boundaries between rock groups and breaks in stratigraphy that cannot be explained by conventional facies changes or unconformity (Coney et al., 1980). Many terranes display sedimentary or volcanic rock characteristics that are of oceanic origin rather than continental, but some simply are of a different continental origin than the one to which they are accreted. Paleomagnetic data are sometimes used to differentiate between terranes and craton. When available, faunal variations can be clues to terrane classification. Terrane accretion during primarily Mesozoic to early Cenozoic time into the Cordillera of western North America extended the continental margin to the west by over 500 km in some areas and caused deformation as far east as the Great Plains. The terranes were accreted as a result of the closing of the Paleozoic Pacific Ocean and consist of pieces of oceanic and possibly continental crust, as well as some oceanic arcs (Coney et al., 1980). Terranes collide and accrete onto continents at convergent plate boundaries. The terranes ЎЎ±rideЎЁ along the subducting slab until they are scraped off by the over-riding plate. This causes folding and faulting in both the terrane and the continent. While the terrane is more buoyant than the subducting lithospheric slab, and most of it remains near the surface, some of the terrane may, in fact, be partially subducted with the slab beneath the over-riding plate. This partial subduction of oceanic or continental crust exposes those rocks to increased temperature and pressure. If the leading edge of the lithospheric slab were to neck and release from the system, removing the main driving force of the subduction, these metamorphosed crustal rocks could be re-exposed as the positively buoyant material rises back towards the surface. This bouyant re-surfacing also leads to uplift and seismic activity in the over-riding continental plate. The silicone putty-flubber-corn syrup analog model in this study attempts to simulate this partial subduction and subsequent re-surfacing of the terrane in an oceanic-continental subduction zone. A second model created an idealized subduction zone with a manually plunged Plexiglas slab that allowed for the mathematical and graphical displays of flow and strain components in the mantle, which lead to observable deformation in the back-arc region of the over-riding continental plate. Late Mesozoic and Early Cenozoic terrane translation along western North America: The Baja-BC hypothesis An on-going controversy is the extent of large-scale (> 1,000 km) translation of exotic terranes along the western margin, between Baja California (northern Mexico) and British Columbia (Canada). A controversial proposal is that in the early Cenozoic, terranes were transported several thousand kilometers from the latitude of Baja California, to Canada - the "Baja-BC hypothesis". Such translation would have had to occur in the early Cenozoic, long before the current tectonic setting of the western U.S. was established (see 3D topographic/bathymetric image on the left). Our approach is to combine isotopic, geochronologic, and paleomagnetic studies on the same strata to determine a complete characterization of sediment provenance and paleo-latitude of the basin during deposition. Our primary targets are the Cretaceous coastal basins in Oregon and California - including the Gold Beach (Oregon), Coastal Franciscan (California), and Gualala (California) - which previous paleomagnetic data suggest are allocthonous. In addition, our work on the Hornbrook Formation (Oregon) will provide a "control" basin that is expected to be in-place relative to the Klamath Mountains. geologic time mass extinction structural geology Accretion tectonics and geodynamics of Kamchatka-Sakhalin region Abstract. Tectonic structure of the Sea of Okhotsk bottom is problematic and different tectonic models are proposed to explain its origin. New geological materials on the composition of pre-Cenozoic complexes of Kamchatka and Sakhalin gave the evidence of accretionary framework of the periphery of the Okhotsk plate. Main role in the producing of modern tectonic structure played terrane accretion because both regions composed of a mosaic of terranes accreted to Siberia and experienced complex history of subduction, collision and strike-slip tectonics. The dredged samples from outcrops of pre-Cenozoic basement showed the similarity with rocks of neighboring onshore areas. These data also as geophysical materials allow to suppose that tectonic structure of the Sea of Okhotsk bottom, also, has partly accretionary origin. The structural mode of the arrangement of above terranes indicates long discrete process of continental margin generation. The ancient stages of this process are marked in Sakhalin where very intensive tectonic movements took place in Campanian and Maastrichtian time. The tectonic framework of Sakhalin turned into collage of different terranes in the end of Cretaceous - very beginning of Paleogene. In Kamchatka, problematic Campanian, Early Paleogene (?), very intensive Middle Eocene and Late Miocene episodes of accretion and continental growth are determined. Cenozoic history of Sakhalin connected with tectonic evolution of Sea of Okhotsk and Japan sea, but the history of Kamchatka - with the subduction of the Pacific plates. Available seismic and geologic data on age and composition of the sedimentary cover of Okhotsk plate donЎ¦t supply reliable correlation between main tectonic events in offshore and onshore regions. The basement of the Sea of Okhotsk bottom is unconformably covered by Cenozoic sedimentary cover composed of Lower Paleogene, Paleogene-Miocene and Pliocene-Quaternary sequences the dating of which is based on the general correlationЎ¦s with onshore areas. There is the correlation between accretion episodes and rifting processes in Sea of Okhotsk region also as reorganizations of movements of Pacific ocean plates. Accretion tectonics and geodynamics of Kamchatka-Sakhalin region Introduction The Sea of Okhotsk region (Figure 1) includes, besides marine basin, bordering land area, because the most part of tectonic units of this sea frame is traced to shelf. The marine basin is bounded by the Kurile island arc to the south, by Kamchatka to the east, by the Asian continental margin to the north and northwest and Sakhalin and Hokkaido to the west. This basin has very complex structure and consists of crust blocks of different types: typically oceanic (South Okhotsk Basin), suboceanic (Derugin Deep) and continental (shelf areas). The mosaic pattern of these blocks results from the junction in this region of tectonic units of different age and origin. The Kurile island arc intersects the Sakhalin-Hokkaido accretionary belt at almost right angle. The continuation of tectonic units of Sakhalin to the north is uncertain. The Okhotsk-Chukotsk volcanic belt borders this region in the north where it overlaps a basement consisting from different tectonic units (Okhotsk and Taigonos massifs of Precambrian and younger rocks, Verkhoyansk folded belt, Uda-Murgal volcanic belt). Tectonic units of Kamchatka are continued to north in Koryak highlands and occupy large part of neighboring shelf. New geological materials on the composition of pre-Cenozoic complexes of Kamchatka [Zinkevich and Tsukanov, 1993] and Sakhalin [Rikhter, 1986] has demonstrated that both regions are composed of a mosaic of terranes accreted to Siberia at various times mainly in Late Cretaceous and Early-Middle Cenozoic. These terranes (fragments of island arc chains, back-arc basins, and oceanic plateaus) experienced a complex history of subduction, collision and strike-slip tectonics and played main role in the producing of the modern tectonic structure of the region. The evidence of the accretionary framework of the periphery of Okhotsk plate gives us a possibility to analyze the tectonic history of Sea of Okhotsk region from the point of view of accretionary tectonics. The specific aims of this paper are to (1) outline the new materials on tectonics of Kamchatka and Sakhalin; (2) discuss tectonic style of offshore and onshore parts of Sea of Okhotsk region; (3) present possible model for tectonic evolution of the region. Kamchatka-Sakhalin region: The frame of the Sea of Okhotsk region consists of structural elements of different ages and origin Uda-Murgal volcanic belt consists mainly of Upper Jurassic to Lower Cretaceous (Hauterivian), chiefly basaltic to andesitic, rarely dacitic volcanic rocks that extend from western coast of Sea of Okhotsk to Taigonos peninsula and far to north, to Koryak highlands. Parfenov [1984] gives the evidence of more ancient (Triassic, possibly Permian) age of southern part of this belt. The volcanics are associated with shallow water sediments of various facies. Despite the discontinuous distribution of volcanic rocks in the Uda-Murgal belt, the calc-alkaline composition of volcanic rocks indicates a genetic link with subduction of an oceanic crust. Parfenov [1984] showed that Uda-Murgal volcanic belt was related with Benioff zone dipped at approximately 65o-70o to the northwest. Uda-Murgal volcanic belt is interpreted to have formed as volcanic arc within Eurasian continental margin. Okhotsk-Chukotsk volcanic belt consists predominantly of subaerial calc-alkalic andesitic-basalt to ignimbritic and rhyolitic flows, tuff, agglomerate, and breccia, with minor amount of basalts and volcaniclastic rocks intruded by gabbro and granitoid intrusions of Cretaceous age. The volcanics erupted during 25 Ma from mid-Albian to early Senonian [Belyi, 1994]. Belyi [1994] divides this belt along its continuation at three parts. It depends, in his opinion, of the heterogeneity of its basement because this belt lies on the different tectonic units. He distinguishes, also, outer and inner zones. The former is superimposed on Mesozoides and pre-Riphean continental block. The latter overlies the structures of Uda-Murgal volcanic belt. Highly aluminous basalt, andesite, diorite, tonalite, and granodiorite prevail in the inner zone; andesite, rhyolite, granodiorite, quartz monzonite, and granite - in the outer one. Okhotsk massif, roughly triangular in outlines is exposed in northern part of region among terrigenous complexes of Mesozoides. It is confined by complexly formed fault zones to the north-west and north-east [Chikov, 1970]. The southern boundary of this massif is uncertain. The massif consists of the Archean crystalline basement and Proterozoic-Paleozoic and Mesozoic sedimentary cover. The basement rocks are composed of amphibolite-facies gneiss, schist, and amphibolite, rarely by calciphyre, marble, and quartzite. The sedimentary cover unconformably overlying crystalline complex consists of Proterozoic quartzite, slate, and limestone; Late Cambrian limestone, sandstone, and slate; Lower Ordovician limestone, dolomites, carbonatous sandstone; Silurian limestone and sandstone and Middle-Upper Devonian tuffaceous sandstone, slate, limestone, gravelstone, alternated andesite, rhyolite, and tuff. Mesozoic rocks represented by Upper Triassic and Lower-Middle Jurassic terrigenous formations and Upper Jurassic and Neocomian volcanic and coarse-sedimentary complexes. The widespread late Lower Cretaceous and Upper Cretaceous rocks represented by mainly siliceous and intermediate, rarely mafic volcanics. Balygichansky massif is situated in the north-eastern part of the region. Its existence is proposed because terrigenous rocks of Verkhoyansk Complex very gently lie in this area [Tilman and Bogdanov, 1992]. The outcrops of ancient rocks similar to those of Okhotsk and Omolon massifs are absent. Omolon massif. It is exposed only little part of this continental block in this area. The massif consists of Archean crystalline basement overlapped by Riphean and Ordovician - Jurassic carbonate-terrigenous, volcanic-sedimentary and terrigenous sequences [Terekhov, 1979]. Archean (or Lower-Middle Proterozoic) rocks are represented by gneiss and plagiogneiss, crystalline schist, quartzite, and plagiogneiss, minor amphibolite, eclogite, migmatite, and pegmatoid granite. Upper Proterozoic sequence is made up of carbonate-terrigenous rocks (quartzite, quartz sandstone, and shale). Ordovician rocks are composed of limestone, carbonatous siltstone, dolomite, minor siltstone, sandstone. The sequence represented by subaerial volcanics (rhyolite and dacite) of Devonian age unconformably rest on underlying complexes. Devonian-Carboniferous rocks are represented by arcose and polymict sandstone, gravelstone, and conglomerate, minor limestone, and carbonate sandstone. Permian sequence consists of conglomerate, gravelstone, sandstone, mudstone, slate, minor argillite, limestone, siliceous argillite. Triassic sequences are represented by terrigenous rocks (siltstone, mudstone, argillite, minor limestone). Latest Triassic sequence includes also conglomerate and gravelstone. Lagoon-continental Jurassic sequence consists of sandstone, gravelstone, siltstone, minor conglomerate, tuff, tuffite. Lower Cretaceous sequence is represented by continental sedimentary rocks. Paleozoic-Mesozoic rocks characterize a gradual subsidence with accumulation of thick shelf and terrace wedge sequences. Mesozoides are composed of Verchoyansk Complex rocks including thick Carboniferous, Permian, Triassic and Jurassic terrigenous sequences. The marine terrigenous rocks (siltstone, mudstone, sandstone) are more widespread, but continental, lagoon and shallow-marine sandstone occur near large outcrops of ancient continental basement. The rocks of Verchoyansk complex were accumulated within passive continental margin environment at a broad shelf submerged to north-eastward direction. The general change from carbonatous to terrigenous sedimentation occurred between Middle and Late Paleozoic possibly is connected with a change of climatic environment during the displacement of the region from equatorial latitudes to northern ones [Parfenov, 1984]. Sikhote-Alin and Mongol-Okhotsk Accretionary Systems. Western part of the region, to south of Siberian craton, includes Mongol-Okhotsk and Sikhote-Alin accretionary systems. The former was connected with closure of Mongol-Okhotsk paleo-ocean and, later, with collision of Siberian craton and Burein massif in Middle-Late Jurassic. Galam and Ulban terranes is exposed here as only little part of this system (Figure 1, figure 2). The latter is usually interpreted as a packet of Mesozoic accretionary complexes formed near eastern margin of Asia during subduction of Pacific plates in Late Mesozoic. It consists of Gorinsky, Nizhne-Amur, Sergeevsky, Hungarian, Kemsky, Samarsky and Zhuravlesky terranes (Khanchuk, 1993) emplacing at their present position by left-lateral strike-slip faults. We characterize these terranes very briefly after Khanchuk [1993] and Parfenov, [1984] because the description of these tectonic units is necessary only for general understanding of the aims of this paper. Galam terrane consists of Cambrian, Silurian-Middle Devonian, Middle Devonian-Lower Carboniferous, and Upper Permian complexes with uncertain relationships [Parfenov, 1984]. Cambrian complex is composed from jasper, chert, graywacke, tholeiitic and alkaline basalts, blocks of reef limestone and dolomite. Silurian-Middle Devonian complex is represented by deep-water siliceous-terrigenous rocks with mafic volcanics and shallow-marine arcose and graywacke sandstone. There are of limestone olistolites Early Ordovician, Cambrian and Late pre-Cambrian ages. Middle Devonian-Lower Carboniferous complex consists of flyschoid sequences, minor breccia, gravelstone, conglomerate, siliceous shale, basalt. Upper Permian sequence forms little tectonic blocks in tectonic zones. It is composed of continental and shallow- marine conglomerate and sandstone with interlayers of siliceous and carbonatous rocks. Mesozoic sequences unconformably rest on Paleozoic rocks. They include Upper Triassic-Jurassic shallow-marine coarse-terrigenous rocks which are overlain without angular unconformity by Neocomian continental terrigenous rocks with interlayers of silicic lava and tuff. The source of volcanic material was likely Uda-Murgal volcanic arc [Parfenov, 1984]. Ulban terrane is situated to south of the Siberian platform. Its boundaries with Galam and Gorinsky terranes are thrust faults. Ulban terrane is composed of graywacke, flysch packets, chert, and minor basalt with general thickness up to 10000 m. [Parfenov, 1984]. The rocks are intensively deformed in different folds and are broken by faults, including thrust faults. Jurassic rocks of this terrane deposited as turbidites in deep marine environment near continental slope. Gorinsky terrane has a melange-type structure consisting of sheets and blocks composed of Triassic and Jurassic chert, basalt, gabbro, limestone of Late Carboniferous, Permian, and Late Triassic ages, metamorphic schist, and Titonian-Valanginian sandstone and siltstone. The matrix is composed of sandstone and siltstone of Early Hauterivian - Early Barremian age. Nizhne-Amursky terrane consists of tectonic sheets composed of Upper Jurassic to Lower Cretaceous chert and limestone overlaying on oceanic basalt. Upper parts of these sheets are composed by Aptian-Albian turbidites [Khanchuk, 1993]. Samarkinsky terrane in central Sikhote-Aline is in fault contact with Hungarian and Nizhne-Amursk terranes. It composed of the olistostrome complex that looks as a gigantic sedimentary melange containing allochthonous blocks. These blocks consist of: 1) fragments of ophiolite, which basalts of are overlain by Upper Devonian to Lower Permian chert and Lower Carboniferous to Lower Permian limestone; 2) basalt overlain by Upper Permian chert; 3) Middle to Upper Triassic chert, sometimes in association with basalt; 4) Lower Jurassic siliceous-terrigenous sediments; 5) Upper Permian and Triassic-Jurassic sandstone; 6) pycrite and basalt of uncertain age; 7) greenschist and amphibolite facies metamorphic rocks formed from ophiolite; 8) greenschist and glaucophane schist formed from meta-pelites and high-titanium meta-basites (in upper part of Samarsky terrane and in the basement of Sergeevsky terrane). Among turbidite matrix of Callovian-Early Cretaceous age, there are also extended at tens kilometers tectonic sheets of more ancient chert that are not connected with olistosrome. The turbidite and olistostrome sequences are unconformably overlain by coarse-clastic coal-bearing sedimentary strata of Late Valanginian - Albian age. Samarsky terrane is considered as a fragment of the Middle Jurassic-Berriasian accretionary prism [Khanchuk, 1993]. Hungarian terrane consists of tectonic sheets composed of Middle-Upper Triassic chert and pelagic limestone with minor intraplate basalt also as of Lower to Middle Jurassic siliceous and terrigenous rocks and turbidites of Late Jurassic-Berriasian age. Zhuravlevsky terrane, in central and southern Sikhote-Aline, is made up by complexly deformed Early Cretaceous (from Valanginian to Albian) turbidite. It is very thick (up to 6000 m) flyshoid sequence containing shallow-marine fauna of Barremian-Early Senonian age [Parfenov, 1984]. To the east, sequence includes tuff and andesite. The rocks of Zhuravlevsky terrane are interpreted as sediments of turbidite basin [Khanchuk, 1993]. Kemsky terrane is exposed in eastern part of Sikhote-Alin (Figure 2) among flat-laying volcanics of East Sikhote-Alin belt. It is composed of complexly deformed shallow-water marine and continental volcanics and sedimentary rocks (up to a few kilometers thickness). Volcanics include andesite, andesite-basalt, basalt, minor rhyolite). These rocks are interpreted as Aptian-Albian island arc [Khanchuk, 1993; Melankholina,, 1988;]. Koryak Accretionary System Discussed region covers only little part of Koryak accretionary system exposed in the Taigonos peninsula and in south-west Koryak highlands (Figure 1). In general, tectonic framework of this system consists of accreted of Mesozoic margin terranes of island arc and oceanic origin. In Taigonos peninsula, the ancient craton complex (from Archean to Riphean - Lower Paleozoic) is exposed in its northern part [Nekrasov, 1976]. To north, ancient rocks of Taigonos continental block contact along thrust fault with folded volcaniclastic and sedimentary assemblages of Early Paleozoic to Jurassic age. The volcanics and volcanoclastic rocks of Uda-Murgal volcanic belt are exposed in narrow north-east trending zone in southern Taigonos peninsula. Two small specific complexes are exposed in south-eastern part of this peninsula [Chekhov, 1994]. Povorotny Cape Complex includes the imbricated ophiolite assemblage from Triassic to Jurassic age, same as Kuyul ophiolite in Koryak highlands. It composed of tectonic sheets consisting from serpentinite melange, eclogite, amphibolite, greenschist, chert, and pillowed basalt. Another complex consists of thick mafic and ultramafic rocks and diorites overlying folded greenschist and blueschist complex. Also, there are phyllites containing Middle Ordovician conodonts. All complexes of Taigonos peninsula underwent intense deformations as well as metamorphism related to the formation of the Uda-Murgal volcanic belt. Sakhalin-Hokkaido Accretionary System There are apparently similarities between the geology of Sakhalin and Hokkaido indicating that the main tectonic units of both islands constitute uniform accretionary system. Their comparison was held not so far ago [Kimura et al., 1983; Dobretsov et al., 1994]. Sakhalin Island consists of the Western terrane, Aniva-Central-Sakhalinsky and Eastern composite terranes (Figure 3, figure 4). Western terrane consists of Lower Cretaceous - Miocene formations (thickness about 10 km). It is bounded from east by the system of right strike-slip faults and thrusts. Lower Cretaceous sequence (from Berriasian - to Albian, thickness 120 m) is composed of radiolarite, chert, siliceous argillite interbedded with alkaline basalt. Siliceous rocks were deposited in oceanic environment, like as modern radiolarian muds and deep-sea red clays. The Lower Cretaceous rocks are concordantly overlain by Upper Cretaceous (Albian-Turonian) deep-sea terrigenous turbidites (thickness 3500 m), and more shallow-marine Late Cretaceous and Cenozoic terrigenous rocks. Upper Cretaceous and Cenozoic sediments, containing interlayers of andesite and silicic tuff, probably were accumulated near continental East-Sikhote-Alinsky volcano-plutonic marginal belt. Aniva-Central-Sakhalinsky composite terrane consists of Central - Sakhalinsky, Mereisky, Gomonsky, Anivsky, Langeriysky, and Susunaysky terranes. Central - Sakhalinsky terrane in the central Sakhalin Island is overthrusted by Langeriysky or Gomonsky terranes from east and by Western terrane from the west. It made up of Upper Permian limestone and mafic volcanics, of Triassic to Lower Cretaceous volcanics and chert, and Upper Cretaceous terrigenous formations. Upper Permian basalts and reef limestones are small boulders in Albian-Cenomanian sequence, while Triassic-Lower Cretaceous rocks form homogeneous sequences. Triassic part of the sequence consists of oceanic tholeiitic basalt, Okhotsk Basin and Kuril arcs Kurile Island Arc Kurile Island arc consists of the Great Kurile and Lesser Kurile Island chains separated off Pacific ocean by Kurile-Kamchatka trench. Great Kurile Islands are composed of volcanics originated due to subduction of the Pacific plate. The oldest rocks recovered from this typical volcanic belt are of Neogene. The modern geophysical data [Ermakov et al., 1989, Zlobin, 1987] show that earth crust along Kurile arc has similar affinities and thickness (30-40 km). Granite layer exists in whole island arc but varies in the thickness and velocities of seismic waves. The intensive volcanism occurred at Islands of the Great Kurile range in Miocene, Pleistocene and Recent time. The concentration of alkalic volcanics is higher in western part of Great Kurile than in eastern one that is corresponded with the depth to the Benioff zone. There is the zoning in the distribution of isotopes Sr along and across this island arc [Volynetz et al., 1988] and Ne and Sr [Zhuravlev et al., 1985]. Recent lavas contain 10 Be isotope that gives the evidence of the influence of modern sediments in the magma genesis of Kurile volcanic arc. Great Kurile range is accompanied off Pacific side by nonvolcanic submarine range (Vityaz Rise), the southwestern part of which is the Lesser Kurile island chain exposed also at Hokkaido island, in Japan. The Lesser Kurile range consists of Upper Cretaceous - Lower Paleogene mainly shallow-marine and subaerial volcanic, tuffaceous-sedimentary and terrigenous complexes intruded by mafic to siliceous sills and dikes Main Features of Sea of Okhotsk Bottom The most part (40%) of the Sea of Okhotsk basin is shelf with depth up to 200 m and only 11% of its bottom has depth more 2000 m. On the north-west of this bottom, there is stretched from west to east the North-Okhotskan system of troughs divided by local structural rises. The large rift basin (TINRO) is situated between Kamchatka and PЎ¦yagina peninsula. Near Kamchatka, there is the West-Kamchatkan system of north-trending troughs. Large Institute of Oceanology and Academy of Sciences of USSR Rises divided by Makarov trough occur in the center of Sea of Okhotsk bottom and deep abyssal Deryugin, South-Okhotsk Basins present in its southern and western parts (Figure 1, figure 8). Seismic refraction studies have revealed crustal thickness and velocities in different parts of the Sea of Okhotsk bottom that are typical to continental, subcontinental and suboceanic types of an earth crust [Markov et al., 1967]. The continental type characterizes the northern part of Sea of Okhotsk bottom, where the crust thickness is up to 28-32 km (the thickness of granite layer changes from 2 to 16 km). The subcontinental type of the crust occur in the central part of Sea of Okhotsk bottom (Institute of Oceanology and Academy of Sciences of USSR Rises). Suboceanic type with thickness up to 15-20 km (without granite layer) underlies South-Okhotsk Basin and Derugin Deep [Markov et al., 1980]. Okhotsk Arch is distinguished in the north-western Sea of Okhotsk bottom. It differs of another tectonic structures of Sea of Okhotsk bottom by its orientation, homogeneity of the sedimentary cover and basement as well as homogenous gravity and magnetic fields. The flat surface of the acoustic basement of Okhotsk Arch sometimes has minor folded structure that, probably, connected with marine volcanics. The thickness of Cenozoic cover usually does not prevail 1 km. The Institute of Oceanology Rise is gently sloping tectonic unit with rounded form in center of Sea of Okhotsk bottom which rises 300-800 m above neighboring bottom. The surface of slopes is broken up by valleys, that are especially numerous near Derugin Deep slopes. The thickness of sediments at the top is up to 0,5 km increasing up to 2 km in lower parts of rise slopes. Academy of Sciences of USSR Rise is large block (100 x 200 miles) bounded by a system of faults. Within the northwestern part of this rise, horst-like fault blocks form the Peter Schmidt trough; to the south, this rise terminates abruptly by South-Okhotsk Basin. The surface of the basement covered by sediments (the thickness up to 1 - 1,5 km) is broken by numerous faults. Volcanic cones, several forming knolls, and some completely buried by sediments, occur sporadically at south-eastern flanks of Institute of Oceanology and Academy of Sciences of USSR Rises. It indicates the existence in central Sea of Okhotsk during Early Cenozoic and latest Cretaceous of a former volcanic ridge, that was noted by [Zhuravlev and Protas, 1981; Krasnyi, 1983]. The most vast deep-sea basins of Sea of Okhotsk bottom are South-Okhotsk, Derugin and TINRO [Gnibidenko, 1990]. South-Okhotsk Basin is most deep depression with greatest depth of 3374 m. Its bottom represents abyssal plain dipping to the south-west [Belousov and Udintsev, 1981]. The sedimentary cover of this basin is composed of flat-lying Cenozoic deposits [Kharakhinov et al., 1989]. Oligocene - Lower Miocene complex was deposited during the intensive submergence (up to 2,5 km). Middle-Upper Miocene complex is formed in deep-sea basin with uncompensated sedimentation. Pliocene-Quaternary complex composed of widespread turbidites. Sedimentary Cover of the Sea of Okhotsk Basin Sedimentary cover is widespread under the Sea of Okhotsk bottom and in neighboring areas. Compilation of seismic reflection profiles combined with geological mapping in onshore areas have delineated main features of the sediment stratigraphy, the sediment distribution, and structural fabric in the Sea of Okhotsk Basin [Zhuravlev, Antipov, 1993; Gnibidenko, 1990]. There is a considerable (up to 9 km) increase in sediment thickness of Cenozoic cover from the center of the Sea of Okhotsk bottom to its periphery. The thickness of individual seismic layers also changes in different parts of this bottom. The correlation of marine seismic and Cenozoic complexes within land is problematic and therefore there are different schemes of the seismic stratigraphy for sedimentary cover of the Sea of Okhotsk Basin. In this paper, we use the scheme by Zhuravlev and Antipov [1993]. Lower Cenozoic complex (Danian to Late Paleogene) is recognized better of all in TINRO and northern Okhotsk basins where it is studied by geological mapping, geophysical researches and core drilling in onshore area of Western Kamchatka. Marine seismic profiles demonstrate sharp change of this complex thickness that is primary controlled by topography of the bottom surface. In troughs with most full sequences, there are thickness of up to 6 km, but they are decreased at marine rises. The lower boundary of this complex very often is problematic. In Western Kamchatka, it includes thick (up to 4 km) terrigenous sequence of continental origin. This complex has very often folded-block structure. The age of this complex is based on the general correlation with onshore area but age of its lower parts is usually uncertain, especially for deep basins in south-western region. Middle Cenozoic complex (Late Paleogene to Late Miocene) is recognized over most of Sea of Okhotsk Basin. Its greatest thickness is fixed near Sakhalin, in TINRO Basin, and near outer shelf of Western Kamchatka. It is typical cover complex that is especially well presented in seismic profiles of South Okhotsk Deep. In central parts of Sea of Okhotsk, it fills numerous small grabens. In Western Kamchatka and Sakhalin areas, this complex consists of marine and continental mainly thin-coarse sediments (siliceous claystone, opoke, diatomite). In central and southern Sea of Okhotsk, especially near Kurile island arc, it includes large amount of volcaniclastic rocks. Upper Cenozoic complex (Late Miocene to Quaternary) is widespread in the periphery of Sea of Okhotsk bottom but often absent in its central part and at tops of anticline structures. It is composed mainly of thin-coarse terrigenous marine deposits over most part of the bottom and of volcaniclastic deposits in its southern and eastern parts. In Northern Sakhalin and its inner shelf, it composed mainly of sands. The greatest thickness of this complex (up to 6 km) is fixed at Sakhalin slope of Derugin Deep. In other parts of Sea of Okhotsk bottom, its thickness usually does not prevail 2 km. The comparison of seismic sequences of Cenozoic cover in different tectonic units of Sea of Okhotsk bottom shows that a number of tectonic events took place in this region. In most cases, geophysical data provide supporting evidence for the long-time sedimentary hiatus between Cenozoic cover and underlying basement. An unconformity between the basement and Cenozoic cover is more clearly seen toward Sakhalin, Kamchatka, and Siberian coast, where it may be correlated with unconformity separating the Cenozoic sedimentary complex and folded basement [Gnibidenko, 1990]. It gives the evidence of active tectonic movements of Laramide phase [Zhuravlev and Antipov, 1993]. The Early Cenozoic time is characterized by the appearance of rifting structures. The structural unconformity between Upper and Middle Cenozoic seismic complexes shows the activity of tectonic movements in Late Miocene [Zhuravlev and Antipov, 1993]. The younger post-Pliocene structural movements may represent rejuvenation of movement along original lines of basement fabric, concomitant with the late Cenozoic rifting regime. Sea of Okhotsk Basement The conclusions about the composition and age of Sea of Okhotsk basement are based on tracing from land under the sedimentary cover of tectonic units of varying origin and age, on materials of dredging, and isotopic dating of dredged rocks. The outcrops of the Sea of Okhotsk basement are known in different parts of bottom [Figure 9]. Sedimentary, magmatic and metamorphic rocks [Table 1] were dredged from Kashevarov Arch, Academy of Sciences of USSR and Institute of Oceanology rises, lower part of South-Okhotsk Deep slopes [Geodekjan et al., 1976; Avchenko, 1987; Lelikov, 1992; VasilЎ¦ev et al., 1984; Gnibidenko, 1990; Belousov and Udintsev, 1981; Gnibidenko and Iljev, 1976;]. Sedimentary rocks consist of arcose and greywacke sandstone, argillite, siltstone, slate, minor limestone, and siliceous rocks. The rocks of Institute of Oceanology Rise and of the southern part of Okhotsk Arch were, probably, formed from mafic volcanics, also as fine-grained rocks of Kashevarov Rise. But, sandstone of Kashevarov Rise was formed from Na-granitoides and metamorphic rocks [Lelikov, 1992]. The presence of arcose sandstones within the Okhotsk Arch gives the evidence of the erosion of sialic complexes. The rocks dredged from north-eastern Okhotsk Arch contain Cenomanian-Turonian fauna. The another sedimentary complex from this tectonic unit is supposed to be of Mesozoic age [Lelikov, 1992]. In the northern Sea of Okhotsk, the most part of the bottom is covered by thick sediments, but basement rocks were dredged from Okhotsk Arch and Kashevarov Rise. The dredging from lower part of the south-eastern slope of Kashevarov Rise allowed to sample angular debrises of greenschist and ranging in size from pebbles to cobbles material including intermediate and siliceous tuff, andesite, quartz diorite, slate, siltstone, tuffaceous sandstone [Geodekjan et al., 1976]. From its south-western slope, it was recovered a great number of blocks of metamorphic (gneiss, granite-gneiss, amphibolite, minor quartz-biotite slate, and greenschist) and sedimentary (siliceous rocks, sandstone, siltstone, slate) rocks. Also, there are enough indurated sandstone, coal-bearing slates, and unindurated tuffaceous siltstone, argillite, and tuffaceous sandstone, as well as quartz diorite, granodiorite, granites, granite-porphyry, gabbro. To the east, from Kashevarov Rise it was recovered sedimentary rocks (clay, argillite, slate, siltstone, also as volcanic rocks (andesite, plagioandesite, dacite, rhyolite, minor basalt, andesitic basalt) and intrusive rocks (granites, minor granodiorite, and dolerite) [VasilЎ¦ev et al., 1984]. Large blocks of jasper, meta-andesite, and albitophyre were dredged from south-eastern slope of Okhotsk Arch to the east of Kashevarov Rise [VasilЎ¦ev, 1984]. The dredging of north-western and northern slopes of the Institute of Oceanology Rise allowed to sample large blocks and debrises composed of granodiorite, quartz granodiorite, rhyolite, schist, mica siliceous slate, phyllite, tuffaceous sandstone, and siltstone, minor biotite-hornblande gneiss [Geodekjan et al., 1976; Avchenko et al., 1987; Lelikov, 1992]. The dredging from south-western slope of this rise yielded diorite, granodiorite, granite, monthonite, also as pebbles of aplite, microdiorite, diabase, meta-andesite, meta-dacite, albitophyre, minor basalt, and andesite. The dredging of the northern slope of Academy of the Sciences Rise yielded pebbles and debrises composed of magmatic (quartz-diorite, dacite, andesite, siliceous and intermediate tuff, minor diabase, rhyolite, granodiorite, gabbro) and sedimentary (arcose sandstone and siltstone) rocks [Geodekjan et al., 1976; VasilЎ¦ev et al., 1984]. The central parts of the Academy of Sciences of USSR Rise, Institute of Oceanology Rise, and Kashevarov Rise are composed of weakly alternated intrusive rocks (diorite, granodiorite, granite, minor granosyenite, syenite, and gabbroides [Geodekjan et al., 1976; VasilЎ¦ev et al, 1984] and volcanic rocks (basalt, andesite, rhyolite, dacite, and trachydacite, minor lavo-breccias and siliceous tuff) [Gnibidenko, 1990; Lelikov, 1992]. Metamorphic rocks (amphibolites and different gneisses) were dredged from Institute of Oceanology Rise and Okhotsk Arch, also as rocks from Iona bank, metamorphosed in greenstone facies (phyllite, meta-effusive, slate). The major part of volcanic rocks is most probably of an island-arc origin. Chemical compositions of magmatic rocks of Institute of Oceanology and Academy of Sciences of USSR Rises have, mainly, calc-alkaline trends of differentiation similar to Upper Cretaceous volcanics of Eastern Kamchatka and Lesser Kurile Range [Geodekjan et al., 1976; Gnibidenko, 1990; Lelikov, 1992]. It is Cretaceous-Early Paleogene island-arc complex formed before Cenozoic cover formation. The basalt and dacite dredged from Academy of Sciences of USSR Rise yield K-Ar dates of 149-117 Ma [Gnibidenko,1990]. Lelikov [1992] reports the dates from 115 to 41,1 Ma for effusives; he divides intrusive rocks in two groups: Cretaceous, from 130 to 78 Ma, and Cretaceous-Paleogene, from 100 to 31 Ma. Gnibidenko [1990] notes the dates of 209 „b 4 Ma for the granodiorite from Institute of Oceanology Rise. The composition of the basement of South-Okhotsk Basin is poorly known. The dredging of western part of Kitami-Yamato Rise yielded debrises of a Tectonic Reconstructions Tectonic Reconstructions and Discussion. In previous sections, we have integrated modern geologic data on terranes of Kamchatka, Sakhalin and Sikhote-Alin to infer the geologic history of the Sea of Okhotsk region. The terrane analysis of above regions showes distinct paleotectonic connection between some terranes in the past. This connection is reconstructed for Sikhote-Alin and Hokkaido-Sakhalin systems of terranes, between Eastern composite terrane of Sakhalin and Central Kamchatka terranes, also as between terranes of Western Kamchatka and Siberia. It allowes to test tectonic model explaining the formation of the Sea of Okhotsk framework as a complex process of long-time discrete accretion and coastwise translation interrupted by episodes of rifting and destruction. The geological interpretation, presented here, fits well with the relative motion vectors computed by Engebretson et al., [1985]. The model in Figure 9 begins with Jurassic Period because the pre-Jurassic geology is too uncertain to permit a meaningful map reconstruction. In Early and Middle Jurassic, Mongol- Okhotsk paleoocean was between Siberia and Bureinsk-Khankaysky microcontinent. To the north, Uda-Murgal island arc existed at Siberian continental margin. In Late Jurassic, the closure of the Mongol-Okhotsk paleo-ocean occurred due to the collision of Bureinsk-Khankaysky microcontinent to Siberia that result in formation of vast landmass in the western part of this region [Khanchuk, 1993]. Pra-Pacific ocean was situated to the east and to the south off above new formed continent. The fragments of this oceanic basin are represented by most ancient oceanic assemblages of Sakhalin - interbedded chert, radiolarite, limestone, volcanics, and volcaniclastic rocks of Paleozoic and Triassic - Early Cretaceous age in Western, Central-Sakhalinsky, Langeriysky, Susunaysky, Nabilsky, and (as a numerous blocks) in the Anivsky, Gomonsky and East-Schmidtovsky terranes [Rikhter,1986]. The chert sequences in these terranes are specified by the absence of terrigenous material; stability conditions of deep-sea sedimentation during a long temporary interval; the low rate of sedimentation (400-500 m. for 130-140 Ma) comparable with that at modern abyssal plate; specific character of fossils (radiolarians, less often conodontes and fragments of siliceous sponges); the manganese mineralization. They are interpreted as parts of Paleozoic-Mesozoic sedimentary cover of abyssal parts of the oceanic plate. Langeriysky and Susunaysky terranes as well as Gomonsky, Anivsky and East-Shmidtovsky terranes include volcanic formations (fragments of oceanic volcanic rises). Gomonsky and Anivsky terranes comprise also interbedded carbonatous and volcanic rocks containing shallow-water fauna. On the north, the Paleozoic and Mesozoic oceanic formations are exposed in terranes of Koryak accretionary system. In the very beginning of Neocomian, the Kula plate was being subducted beneath Siberian margin and to the north along the Koryak and Beringian margins [Scholl et al., 1987; Scholl and Stevenson, 1989]. The chain of active volcanoes (Uda - Murgal belt) traced to the northeast to Koryak margin (Figure 10b). The Omgon-Kvakhonsky island arc existed in the northeastern part of the region from Late Jurassic through Hauterivian time. The metamorphism and granitization took place in deep parts of this island arc. It is possible that a back-arc basin or minor plate was bounded by Omgon-Kvakhonsky island arc to the east and Murgal volcanic belt (island arc of Andyan type) to the west. The similarity between fragments of Omgon-Kvakhonsky island arc exposed in Omgon terrane and in the basement of the West Kamchatkan terrane and complexes of the same age in southern Koryak accretionary system [Bondarenko and Sokolkov, 1990] allowes to suppose that Omgon-Kvakhonsky island arc was a part of system of island arcs existed near Eurasia. In Sikhote-Alin, the lateral variety of tectonic units consisted (from the west to the east) of Bureinsk-Khankaysky continent, Sikhote-Alin shallow-water basin and oceanic plate. In the end of Early Cretaceous (Barremian-Aptian), Siberian continent have enlarged after intensive folding and microplate collisions. Kvakhonskaya island arc (Figure 11a) was disrupted and its nothern continuation was accreted onto continental margin. The general thickening of the crust and metamorphism in the northeastern part of the region took place 127 - 116 Ma ago, that is supported by mentioned above isotopic data on age of metamorphic rocks in the Sredinny terrane of Kamchatka. Later, it was a basement of deep-sea terrigenous sediments formed near continental slope of Siberia. The small Stenovaya island arc and back-arc basin appeared somewhere to the northeast. Sikhote-Alin accretionary system have been formed during docking onto Bureinsk-Khankaysky margin of Gorinsky, Nizhne-Amursk, Samarkinsky, Hungarian and Zhuravlevsky terranes. Kemsky island arc existed to the east. It is likely, that this accretion episode occurred during the oblique subduction of oceanic Kula plate, because all terranes in Sikhote-Alin accretionary prism are displaced by left-lateral strike-sleep faults acted from Late Triassic to Recent time [Parfenov, 1984; Khanchuk, 1993]. In Middle Cretaceous, Okhotsk-Chukotsk volcanic belt, similar to recent Andean margin of South America, originated in the location of the Mesozoic Uda-Murgal island arc [Parfenov, 1984]. In Albian- Cenomanian time, the Kula plate underwent tectonic compression near Eurasia and Kemsky island arc was accreted onto Sikhote-Alin margin. The local blueschist facies metamorphism of metaophiolite and volcanic and sedimentary rocks of ocean crust took place 96-90 Ma ago in fault zone (Figure 11b). In Late Cretaceous (Coniacian), the Kronotsk-Shipunsky island arc was generated somewhere to the south. Rock assemblages, and geochemistry affinities of volcanic rocks presented in Kronotsk-Shipunsky terrane in Kamchatka are similar to those of the Tonga-Kermadec island arc [Khubunaya, 1987]. Paleomagnetic data on Upper Cretaceous rocks of the Kronotsk-Shipunsky terrane are absent while the paleolatitude from Paleogene rocks is 41o „b 6oN [Bazhenov et al., 1992]. In Campanian - Maastrichtian time, the new island arc was generated in the northwest Pacific, extending from approximately 32o-55oN paleolatitude (Figure 12a). The fragments of this island arc are exposed in modern framework of Sea of Okhotsk region as Western Schmidtovsky and Kotikovsky terranes of Sakhalin (western segment of arc), as Ozernovsk-Valaginsky terrane of Kamchatka (eastern segment of this arc) and, likely, in the central part of Sea of Okhotsk (Institute of Oceanology and Academy of Sciences of USSR Rises). Rymniksky-Irunei back-arc basin or a minor plate must have existed between this island arc to the east and Eurasia margin to the west. In the northern part of this basin, deep-sea terrigenous sediments deposited on complex basement with accretionary framework (Central-Kamchatkan and Ganalsky composite metamorphic terranes). To the south, this basin is characterized mainly tuff-siliceous sedimentation because Irunei terrane in Central Kamchatka almost does not contain terrigenous sediments. There are geologic constraints in this region on tectonic reconstructions for Campanian-Maastrichtian time. The reconstruction of the positions in the past of volcanic and sedimentary complexes of Campanian-Maastrichtian age from tectonic sheets of Kamchatka and Southern Koryak revealed the existence of vast transition zone of Western Pacific type. It is possible to find all complexes from shallow-water terrigenous assemblages (typical to Koryak continental slope) to deep-sea tuff-siliceous ones (Irunei back-arc basin) and to island arc volcanics (Ozernovsko-Valaginsky island arc). The general shortening of above transitional zone during attachment of this island arc onto Koryak margin composes not less than 1500-2500 km. It supports the model 2 of Geist et al., [1994] which postulates that ancient island arcs were generated in the periphery but not in the center of Pacific ocean and, later, were accreted onto continent margins and then were displaced along these margins by large-scale coastwise translation processes. Paleomagnetic data provide important information on the originating latitude (40-430 N) of the Ozernovsko-Valaginsky segment of this island arc [Kovalenko, 1990; 1992; Savostin, Heiphetz, 1988]. Maastrichtian to Danian rocks of this arc (Karaginsky Island and Olyutorsky region) formed at 40o-45o N paleolatitude. In contrast, late Eocene rocks from the Olyutorsky region yield a paleolatitude of 61o, which is approximately its current latitude. These results confirm the conclusion that docking of the Ozernovsko-Valaginsky segment of this island arc finished to Late Eocene time. Since the end of Cretaceous-very beginning Paleogene, after 85 Ma, the Kula plate was subducted along the ancient Beringian margin while the Pacific plate was subducted along the Eurasian margin [Engebretson et al., 1985]. This configuration remained somewhat the same up to 43 Ma when the Kula-Pacific spreading center died, although major shifts in the Euler poles occurred between 43-85 Ma [Engebretson et al., 1985]. Counterclockwise rotation of Kula-Pacific spreading between 55-56 Ma has been demonstrated by Lonsdale (1988) and thus, Kula plate motion during the Eocene is subject to some uncertainty. After 43 Ma, the Pacific plate was moving to the west-northwest subnormal to Eurasian margin with several shifts in the Euler poles up to the present time. The tectonic framework of Sakhalin turned into the collage of different terranes and the main framework of this island was formed in the end of Cretaceous-very beginning Paleogene. The collision boundary between Anivo-Central-Sakhalinsky and Eastern terranes in Sakhalin is marked by greenschist facies metamorphic rocks with age 71-58 Ma (Langeriysky terrane). In the northern part of the region, the collision of the Ozernovsk-Valaginsky island arc with Eurasia prior to northward transport provides an explanation for cessation of island arc volcanism in latest Cretaceous-early Paleocene time. Moreover, the cessation of Ozernovsk-Valaginsky island arc volcanism is coeval with the cessation of Okhotsk-Chukotka volcanism along the eastern Siberia margin [Belyi, 1994]. This collision leaded to the beginning of the closure of Irunei back-arc basin and to tectonic superposition of back-arc and island-arc complexes (West-Kamchatka, Iruney, Ozernovsko-Valaginsky terranes) in the northern part of Sea of Okhotsk region. This event is not dated in Central Kamchatka, but it is fixed in Oluytorsky region of Koryak highlands with the similar geology [Mitrofanov, 1977; Kazimirov et al., 1987]. Prior to the formation of the Aleutian Arc at about 55 Ma, the Kula and possibly Pacific plates were being subducted beneath Kamchatka. Formation of the Aleutian Arc is proposed to have been caused by the buckling of the fast-moving Kula plate at southern Alaskan margin [Scholl and Stevenson, 1989], possibly triggered by the accretion of the Ozernovsko-Valaginsky island-arc in the Olyutorsky region [Worral, 1991]. During the early history of the Aleutian Arc, the western terminus of the arc did not extend west past Shirshov Ridge and therefore, Pacific or Kula plate subduction continued during Paleogene time along the length of the Kamchatka and southern Koryak margin. The open corridor must have existed between Kamchatka and western terminus of the Aleutian arc according to the hypothesis about coastwise translation of Ozernovsko-Valaginsky island arc. The history of Pacific and Kula plates best supports accretion of the Ozernovsk-Valaginsky paleo - island arc during latest Cretaceous - early Paleocene and northward translation ending at 43-50 Ma. In Cenozoic, after accretion in the end of Cretaceous-very beginning of Paleogene, large-scale rifting processes appeared in whole region. They raised high amplitude block and rifting movements within the Sea of Okhotsk bottom and created main features of its modern tectonic framework. Raznitsin [1982] supposes that the formation of Derugin Deep continued in western part of the region as a result of this rifting process. Later, lower complex of sedimentary cover filled grabens in the bottom. The volcanic activity of Ozernovsko-Valaginsky island arc died out and newly formed Vetlovsky oceanic basin begun to be formed to the east (Figure 9). It is possible, that it was connected with general change of Pacific plate movements resulted in a change of general compression to rifting in this region. The Euler pole change at 43 Ma for the Pacific plate resulted in a change from oblique convergence to sub-normal convergence along the Kamchatka margin [Engebretson et al., 1985] and is probably responsible for the widespread Eocene deformation episode and cessation of northward terrane motion. The time span when most of the coastwise translation took place was between the end of the formation of the Ozernovsk-Valaginsky island arc (latest Cretaceous) and 43 Ma. Structures in the Olyutorsky region indicate that the Koryak mountains provided a buttress to margin-parallel motion (ending 50 Ma), although southward along the eastern Kamchatka margin, coastwise translation may have continued until late Eocene time. The very intensive tectonic compression in Middle Eocene led to final closing of the Iruney basin also as to closure of Vetlovsky marginal basin with formation of Vetlovsky collision suture, that was overlapped later (Oligocene to Miocene) by clastic deposits of the Tyushevsk Cenozoic Basin. The attachment of Kronotsko-Shipunsky arc fragments and Kamchatka Cape terrane to Kamchatka also apparently had occurred to middle Eocene. Coastwise translation appears to be the most likely mechanism for the bringing the Kronotsko-Shipunsky island arc terrane from 40oN-55oN to its present position. Most of the coastwise translation took place 43-66 Ma ago. A considerable overall increase in the crystal thickness and thus augmentation of the continental block took place in this time. The intensive metamorphism occurred in the lower part of the crust during of the tectonic superposition of different sequences, that is demonstrated in Khavivensky metamorphic terrane of Kamchatka. Coastwise translation of Ozernovsko-Valaginsky island arc until Middle Eocene requires that strike-slip faults must have been present along the Kamchatka peninsula during Paleogene time. Moreover, these faults would have to be inboard to transport the Late Cretaceous rock exposed in the eastern ranges of Kamchatka. The great amount of coastwise translation at speeds similar to Pacific or Kula plate speed during Paleogene also suggests that a transform, rather than subduction, boundary separated the continental and oceanic pla Tethys Ocean the age of ocean floor Terrane A terrane in geology is a fragment of crustal material formed on, or broken off from, one tectonic plate and accreted — "sutured" — to crust lying on another plate. The crustal block or fragment preserves its own distinctive geologic history, which is different from that of the surrounding areas (hence the term "exotic" terrane). The suture zone between a terrane and the crust it attaches to is usually identifiable as a fault. Overview A terrane is not necessarily an independent microplate in origin, since it may not contain the full thickness of the lithosphere. It a piece of crust which has been transported laterally, usually as part of a larger plate, and is relatively buoyant due to thickness or low density. When the plate of which it was a part subducted under another plate, the terrane failed to subduct, detached from its transporting plate, and accreted onto he overriding plate. Therefore, the terrane transfered from one plate to the other. Typically, accreting terranes are portions of continental crust which have rifted off another continental mass and been transported surrounded by oceanic crust, or old island arcs formed at some distant subduction zone. The concept of "terranes" developed from studies in the 1970s of the complicated Pacific Cordilleran ("backbone") orogenic margin of North America, a complex and diverse geological potpourri that was difficult to explain until the new science of plate tectonics illuminated the ability of crustal fragments to "drift" thousands of miles from their origin and fetch up, crumpled, against an exotic shore. Such terranes were dubbed "accreted terranes" by geologists. :"It was soon determined that these exotic crustal slices had in fact originated as "suspect terranes" in regions at some considerable remove, frequently thousands of kilometers, from the orogenic belt where they had eventually ended up. It followed that the present orogenic belt was itself an accretionary collage, composed of numerous terranes derived from around the circum-Pacific region and now sutured together along major faults. These concepts were soon applied to other, older orogenic belts, e.g. the Appalachian belt of North America.... Support for the new hypothesis came not only from structural and lithological studies, but also from studies of faunal biodiversity and palaeomagnetism." (Carney "et al.") When terranes are composed of repeated accretionary events, and hence are composed of subunits with distinct history and structure, they may be called superterranes. [ [http://www.geop.ubc.ca/Lithoprobe/transect/terrane.html University of British Columbia website: Terranes] ] see also * Geology of Victoria * Avalonia * Chilenia * Smartville Block * Sonomia Terrane * Narryer Gneiss Terrane * Salinian Block * Wrangellia Terrane * Yakutat Block Notes External links http://dic.academic.ru/dic.nsf/enwiki/633379 • [http://www.geop.ubc.ca/Lithoprobe/transect/terrane.html Terrane: a definition] * [http://www.glassearth.com/terranepages/terranes.htm New techniques for modelling terranes in three dimensions] * [http://www.antarctica.ac.uk/Key_Topics/Geological_Evolution/terrane_analysis/ West Antarctica terrane analysis] * [http://imnh.isu.edu/digitalatlas/geo/accreted/attext/atmain.htm Examples of accreted terrane in Idaho] * [http://www.alaskageography.com/essays/geologic_history.htm Alaskan Terranes] Terrane definition Gabrielse et al. (1991, DNAG G-2) define a "terrane" as an area possessing unique tectonic assemblages (lithostratigraphic units representing a specific depositional or volcanic setting responding to a tectonic event), which differs from adjacent terranes and is bounded by faults. The term "terrane" does not have any genetic significance nor does it imply an origin far removed from adjacent terranes or its present position relative to the craton. Terranes are only defined by their internal assemblage composition. The “terrane” definition can be extended further. An "accreted terrane" refers to a terrane that has become attached to a continental margin in the later stage of its tectonic history. Several terranes can become amalgamated by overlap assemblages or "stitched together" by intrusions and form superterranes" before final accretion to a continent. "Subterranes" are divisions of terranes in which a certain affinity exists, but not necessarily a stratigraphic continuity. "Pericratonic terranes" are situated between accreted terranes and ancestral continental margin. They may have stratigraphic affinities to the continental margin or represent metamorphosed sediments that were deposited at or near the continent. This definition has led some authors to criticize the terrane concept as being too vague and general, claiming it only confuses discussion and is neither an improvement over older terminology, which uses more descriptive terms like "sliver", "block" or "fragment", nor a new concept (Sengцr & Dewey 1991 in Dewey et al. "Allochtonous terranes"). As well the term "terrane" (or "terrain") has already been used in geographic and stratigraphic connotation. A good example within the North American Cordillera is the debate around the Yukon-Tanana and the Nisling terrane definition (Mortensen, Tectonics 11, 1992). However, despite this criticism, the terrane concept is the accepted terminology used in modern discussion of the Canadian Cordillera. geosyncline, how it connected with terranes? Геосинклиналь складкообразования земной коры ГЕОСИНКЛИНАЛЬ ГЕОСИНКЛИНАЛЬ (от гео... и синклиналь) (геосинклинальный пояс) - длинный (десятки и сотни километров) относительно узкий и глубокий прогиб земной коры, возникающий на дне морского бассейна, обычно ограниченный разломами и заполненный мощными толщами осадочных и вулканических пород. В результате длительных и интенсивных тектонических деформаций превращается в сложную складчатую структуру - часть горного сооружения. Геосинклинали расположены обычно или в зоне перехода от океана к континенту, или между континентами. Рассматриваются как области превращения океанической земной коры в континентальную. Пример современного аналога геосинклиналя - островные дуги (вместе с глубоководными желобами) окраинных и внутренних морей. В этом смысле геосинклиналь - синоним геосинклинального пояса. all about geology Accretion (geology) Accretion is a process by which material is added to a tectonic plate. This material may be sediment, volcanic arcs, seamounts or other igneous features. When two tectonic plates collide, one of the plates may slide under the other. This process is called subduction. The plate which is being subducted (the plate going under), is floating on the asthenosphere and is pushed up and against the other plate. Sediment on the ocean floor will often be scraped by the subducted plate. This scraping causes the sediment to come off the subducted plate and form a mass of material called the "accretionary wedge", which attaches itself to the subducting plate (the top plate). Volcanic island arcs or seamounts may collide with the continent, and as they are of relatively light material (i.e. low density) they will often not be subducted, but are thrust into the side of the continent, thereby adding to it. Accretion Accretion Theory |
