DOCSLIB.ORG

Ocean Trench

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Ocean Trench R E S O U R C E L I B R A R Y E N C Y C L O P E D I C E N T RY Ocean trench Ocean trenches are long, narrow depressions on the seafloor. These chasms are the deepest parts of the ocean—and some of the deepest natural spots on Earth. G R A D E S 5 - 12+ S U B J E C T S Earth Science, Geology, Geography, Physical Geography C O N T E N T S 11 Images, 1 Video, 2 Links For the complete encyclopedic entry with media resources, visit: http://www.nationalgeographic.org/encyclopedia/ocean-trench/ Ocean trenches are long, narrow depressions on the seafloor. These chasms are the deepest parts of the ocean—and some of the deepest natural spots on Earth. Ocean trenches are found in every ocean basin on the planet, although the deepest ocean trenches ring the Pacific as part of the so-called “Ring of Fire” that also includes active volcanoes and earthquake zones. Ocean trenches are a result of tectonic activity, which describes the movement of the Earth’s lithosphere. In particular, ocean trenches are a feature of convergent plate boundaries, where two or more tectonic plates meet. At many convergent plate boundaries, dense lithosphere melts or slides beneath less-dense lithosphere in a process called subduction, creating a trench. Ocean trenches occupy the deepest layer of the ocean, the hadalpelagic zone. The intense pressure, lack of sunlight, and frigid temperatures of the hadalpelagic zone make ocean trenches some of the most unique habitats on Earth. How Ocean Trenches Form Subduction Zones When the leading edge of a dense tectonic plate meets the leading edge of a less-dense plate, the denser plate bends downward. This place where the denser plate subducts is called a subduction zone. Oceanic subduction zones almost always feature a small hill preceding the ocean trench itself. This hill, called the outer trench swell, marks the region where the subducting plate begins to buckle and fall beneath the more buoyant plate. Some ocean trenches are formed by subduction between a plate carrying continental crust and a plate carrying oceanic crust. Continental crust is always much more buoyant than oceanic crust, and oceanic crust will always subduct. Ocean trenches formed by this continental-oceanic boundary are asymmetrical. On a trench’s outer slope (the oceanic side), the slope is gentle as the plate gradually bends into the trench. On the inner slope (continental side), the trench walls are much more steep. The types of rocks found in these ocean trenches are also asymmetrical. The oceanic side is dominated by thick sedimentary rocks, while the continental side generally has a more igneous and metamorphic composition. Some of the most familiar ocean trenches are the result of this type of convergent plate boundary. The Peru-Chile Trench off the west coast of South America is formed by the oceanic crust of the Nazca plate subducting beneath the continental crust of the South American plate. The Ryukyu Trench, stretching out from southern Japan, is formed as the oceanic crust of the Philippine plate subducts beneath the continental crust of the Eurasian plate. More rarely, ocean trenches can be formed when two plates carrying oceanic crust meet. The Mariana Trench, in the South Pacific Ocean, is formed as the mighty Pacific plate subducts beneath the smaller, less-dense Philippine plate. In a subduction zone, some of the molten material—the former seafloor—can rise through volcanoes located near the trench. The volcanoes often build volcanic arcs—island mountain ranges that lie parallel to the trench. The Aleutian Trench is formed where the Pacific plate subducts beneath the North American plate in the Arctic region between the U.S. state of Alaska and the Russian region of Siberia. The Aleutian Islands form a volcanic arc that swings out from the Alaskan Peninsula and just north of the Aleutian Trench. Not all ocean trenches are in the Pacific, of course. The Puerto Rico Trench is a tectonically complex depression in part formed by the Lesser Antilles subduction zone. Here, the oceanic crust of the enormous North American plate (carrying the western Atlantic Ocean) is being subducted beneath the oceanic crust of the smaller Caribbean plate. Accretionary Wedges Accretionary wedges form at the bottom of ocean trenches created at some convergent plate boundaries. The rocks of an accretionary wedge are so deformed and fragmented they are known as melange—French for “mixture.” Accretionary wedges form as sediments from the dense, subducting tectonic plate are scraped off onto the less-dense plate. Sediments often found in accretionary wedges include basalts from the deep oceanic lithosphere, sedimentary rocks from the seafloor, and even traces of continental crust drawn into the wedge. The most common type of continental crust found in accretionary wedges is volcanic material from islands on the overriding plate. Accretionary wedges are roughly shaped like a triangle with one angle pointing downward toward the trench. Because sediments are mostly scraped off from the subducting plate as it falls into the mantle, the youngest sediments are at the bottom of this triangle and the oldest are at the more flattened area above. This is the opposite of most rock formations, where geologists must dig deep to find older rocks. Active accretionary wedges, such as those located near the mouths of rivers or glaciers, can actually fill the ocean trench on which they form. (Rivers and glaciers transport and deposit tons of sediment into the ocean.) This accreted material can not only fill trenches, but rise above sea level to create islands that “hide” the ocean trenches beneath. The Caribbean island of Barbados, for example, sits atop the ocean trench created as the South American plate subducts beneath the Caribbean plate. Life in the Trenches Ocean trenches are some of the most hostile habitats on Earth. Pressure is more than 1,000 times that on the surface, and the water temperature is just above freezing. Perhaps most importantly, no sunlight penetrates the deepest ocean trenches, making photosynthesis impossible. Organisms that live in ocean trenches have evolved with unusual adaptations to thrive in these cold, dark canyons. Their behavior is a test of the so-called “visual interaction hypothesis,” which states that the greater an organism’s visibility, the more energy it must expend to catch prey or repel predators. In general, life in dark ocean trenches is isolated and slow-moving. Pressure Pressure at the bottom of the Challenger Deep, the deepest spot on Earth, is about 12,400 tons per square meter (8 tons per square inch). Large ocean animals, such as sharks and whales, cannot live at this crushing depth. Many organisms that thrive in these high-pressure environments lack gas-filled organs, such as lungs. These organisms, many related to sea stars or jellies, are made mostly of water and gelatinous material that cannot be crushed as easily as lungs or bones. Many of these creatures navigate the depths well enough to even make a vertical migration of more than 1,000 meters (3,281 feet) from the bottom of the trench—every day. Even the fish in deep trenches are gelatinous. Several species of bulb-headed snailfish, for example, dwell at the bottom of the Mariana Trench. The bodies of these fishes have been compared to tissue paper. Dark and Deep Shallower ocean trenches have less pressure, but may still fall outside the photic or sunlight zone, where light penetrates the water. Many fish species have adapted to life in these dark ocean trenches. Some use bioluminescence, meaning they produce their own “living light” in order to attract prey, find a mate, or repel a predator. Anglerfish, for instance, use a bioluminescent growth on the top of their heads (called an esca) to lure prey. The anglerfish then snaps up the little fish with its huge, toothy jaws. Food Webs Without photosynthesis, marine communities rely primarily on two unusual sources for nutrients. The first is “marine snow.” Marine snow is the continual fall of organic material from higher in the water column. Marine snow is mostly detritus, including excrement and the remains of dead organisms such as seaweed or fish. This nutrient-rich marine snow feeds such animals as sea cucumbers and vampire squid. Another source of nutrients for ocean-trench food webs comes not from photosynthesis, but from chemosynthesis. Chemosynthesis is the process in which producers in the ocean trench, such as bacteria, convert chemical compounds into organic nutrients. The chemical compounds used in chemosynthesis are methane or carbon dioxide ejected from hydrothermal vents and cold seeps, which spew these toxic, hot gases and fluids into the frigid ocean water. One common animal that relies on chemosynthetic bacteria for food is the giant tube worm. Exploring Trenches Ocean trenches remain one of the most elusive and little-known marine habitats. Until the 1950s, many oceanographers thought that these trenches were unchanging environments nearly devoid of life. Even today, most research on ocean trenches has relied on seafloor samples and photographic expeditions. That is slowly changing as explorers delve into the deep—literally. The Challenger Deep, at the bottom of the Mariana Trench, lies deep in the Pacific Ocean near the island of Guam. Only three people have visited the Challenger Deep, the deepest ocean trench in the world: a joint French-American crew (Jacques Piccard and Don Walsh) in 1960 and National Geographic Explorer-in-Residence James Cameron in 2012. (Two other unmanned expeditions have also explored the Challenger Deep.) Engineering submersibles to explore ocean trenches is presents a huge set of unique challenges.
Load more

Recommended publications
  • Cambridge University Press 978-1-108-44568-9 — Active Faults of the World Robert Yeats Index More Information
    Cambridge University Press 978-1-108-44568-9 — Active Faults of the World Robert Yeats Index More Information Index Abancay Deflection, 201, 204–206, 223 Allmendinger, R. W., 206 Abant, Turkey, earthquake of 1957 Ms 7.0, 286 allochthonous terranes, 26 Abdrakhmatov, K. Y., 381, 383 Alpine fault, New Zealand, 482, 486, 489–490, 493 Abercrombie, R. E., 461, 464 Alps, 245, 249 Abers, G. A., 475–477 Alquist-Priolo Act, California, 75 Abidin, H. Z., 464 Altay Range, 384–387 Abiz, Iran, fault, 318 Alteriis, G., 251 Acambay graben, Mexico, 182 Altiplano Plateau, 190, 191, 200, 204, 205, 222 Acambay, Mexico, earthquake of 1912 Ms 6.7, 181 Altunel, E., 305, 322 Accra, Ghana, earthquake of 1939 M 6.4, 235 Altyn Tagh fault, 336, 355, 358, 360, 362, 364–366, accreted terrane, 3 378 Acocella, V., 234 Alvarado, P., 210, 214 active fault front, 408 Álvarez-Marrón, J. M., 219 Adamek, S., 170 Amaziahu, Dead Sea, fault, 297 Adams, J., 52, 66, 71–73, 87, 494 Ambraseys, N. N., 226, 229–231, 234, 259, 264, 275, Adria, 249, 250 277, 286, 288–290, 292, 296, 300, 301, 311, 321, Afar Triangle and triple junction, 226, 227, 231–233, 328, 334, 339, 341, 352, 353 237 Ammon, C. J., 464 Afghan (Helmand) block, 318 Amuri, New Zealand, earthquake of 1888 Mw 7–7.3, 486 Agadir, Morocco, earthquake of 1960 Ms 5.9, 243 Amurian Plate, 389, 399 Age of Enlightenment, 239 Anatolia Plate, 263, 268, 292, 293 Agua Blanca fault, Baja California, 107 Ancash, Peru, earthquake of 1946 M 6.3 to 6.9, 201 Aguilera, J., vii, 79, 138, 189 Ancón fault, Venezuela, 166 Airy, G.
    [Show full text]
  • Geologists Suggest Horseshoe Abyssal Plain May Be Start of a Subduction Zone 8 May 2019, by Bob Yirka
    Geologists suggest Horseshoe Abyssal Plain may be start of a subduction zone 8 May 2019, by Bob Yirka against one another. Over by the Iberian Peninsula, the opposite appears to be happening—the African and Eurasian plates are pulling apart as the former creeps east toward the Americas. Duarte noted that back in 2012, other researchers conducting seismic wave tests found what appeared to be a dense mass of unknown material beneath the epicenter of the 1969 quake. Some in the field suggested it could be the start of a subduction zone. Then, last year, another team conducted high-resolution imaging of the area and also found evidence of the mass, confirming that it truly existed. Other research has shown that the area just above the mass experiences routine tiny earthquakes. Duarte suggests the evidence to date indicates that the bottom of the plate is peeling away. This could happen, he explained, due to serpentinization in which water percolates through plate fractures and reacts with material beneath the surface, resulting A composite image of the Western hemisphere of the in the formation of soft green minerals. The soft Earth. Credit: NASA mineral layer, he suggests, is peeling away. And if that is the case, then it is likely the area is in the process of creating a subduction zone. He reports that he and his team members built models of their A team of geologists led by João Duarte gave a ideas and that they confirmed what he suspected. presentation at this past month's European The earthquakes were the result of the process of Geosciences Union meeting that included a birthing a new subduction zone.
    [Show full text]
  • Coastal and Marine Ecological Classification Standard (2012)
    FGDC-STD-018-2012 Coastal and Marine Ecological Classification Standard Marine and Coastal Spatial Data Subcommittee Federal Geographic Data Committee June, 2012 Federal Geographic Data Committee FGDC-STD-018-2012 Coastal and Marine Ecological Classification Standard, June 2012 ______________________________________________________________________________________ CONTENTS PAGE 1. Introduction ..................................................................................................................... 1 1.1 Objectives ................................................................................................................ 1 1.2 Need ......................................................................................................................... 2 1.3 Scope ........................................................................................................................ 2 1.4 Application ............................................................................................................... 3 1.5 Relationship to Previous FGDC Standards .............................................................. 4 1.6 Development Procedures ......................................................................................... 5 1.7 Guiding Principles ................................................................................................... 7 1.7.1 Build a Scientifically Sound Ecological Classification .................................... 7 1.7.2 Meet the Needs of a Wide Range of Users ......................................................
    [Show full text]
  • I I 71-15,061 CAMERON, Christopher Paul, 1940- PALEOMAGNETISM of SHEMYA and ADAK ISLANDS, ALEUTIAN ISLANDS, ALASKA. University O
    Paleomagnetism Of Shemya And Adak Islands, Aleutian Islands, Alaska Item Type Thesis Authors Cameron, Christopher Paul Download date 23/09/2021 14:56:00 Link to Item http://hdl.handle.net/11122/9194 I I 71-15,061 CAMERON, Christopher Paul, 1940- PALEOMAGNETISM OF SHEMYA AND ADAK ISLANDS, ALEUTIAN ISLANDS, ALASKA. University of Alaska, Ph.D., 1970 Geology University Microfilms, A XEROX Company, Ann Arbor, Michigan tutc nTCCTDTATTOM MAC HTTM MTPROFIT.MFD F.VAPTT.Y AS RF.OF.TVF.D Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. PALE01IAGNETISM OF SHEMYA AMD ADAK ISLAUDS, ALEUTIAN ISLANDS, ALASKA A DISSERTATION Presented to the Faculty of the University of Alaska in Partial Fulfillment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY by Christopher P/" Cameron B. S. College, Alaska May, 1970 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. PALEOilAGNETISM OF SHEMYA AND ADAK ISLANDS, ALEUTIAN ISLANDS, ALASKA APPROVED: f t l ‘y l .V" ■i. n ■ ■< < ; N w 1 T *W -C ltc-JL It / _ _ ____ /vx... , ~ ~ 7 YdSV Chairman APPPvOVED: dai£ 3 / 3 0 / 7 0 Dean of the College of Earth Sciences and Mineral Industry Vice President for Research and Advanced Study Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ABSTRACT Paleomagnetic results are presented for Tertiary and Quaternary volcanic rocks from Shemya and Adak Islands, Aleutian Islands, Alaska. The specimens were collected and measured using standard paleomagnetic methods. Alternating field demagnetization techniques were applied to test the stability of the remanence and to remove unwanted secondary components of magnetization.
    [Show full text]
  • 3.16 Oceanic Plateaus A.C.Kerr Cardiffuniversity,Wales,UK
    3.16 Oceanic Plateaus A.C.Kerr CardiffUniversity,Wales,UK 3.16.1 INTRODUCTION 537 3.16.2 FORMATION OF OCEANIC PLATEAUS 539 3.16.3 PRESERVATIONOFOCEANIC PLATEAUS 540 3.16.4GEOCHEMISTRY OF CRETACEOUSOCEANICPLATEAUS 540 3.16.4.1 GeneralChemicalCharacteristics 540 3.16.4.2 MantlePlumeSource Regions ofOceanic Plateaus 541 3.16.4.3 Caribbean–ColombianOceanic Plateau(, 90 Ma) 544 3.16.4.4OntongJavaPlateau(, 122 and , 90 Ma) 548 3.16.5THE INFLUENCE OF CONTINENTALCRUST ON OCEANIC PLATEAUS 549 3.16.5.1 The NorthAtlantic Igneous Province ( , 60 Ma to Present Day) 549 3.16.5.2 The KerguelenIgneous Province ( , 133 Ma to Present Day) 550 3.16.6 IDENTIFICATION OF OCEANIC PLATEAUS IN THE GEOLOGICAL RECORD 551 3.16.6.1 Diagnostic FeaturesofOceanic Plateaus 552 3.16.6.2 Mafic Triassic Accreted Terranesinthe NorthAmericanCordillera 553 3.16.6.3 Carboniferous to CretaceousAccreted Oceanic Plateaus inJapan 554 3.16.7 PRECAMBRIAN OCEANICPLATEAUS 556 3.16.8ENVIRONMENTAL IMPACT OF OCEANICPLATEAU FORMATION557 3.16.8.1 Cenomanian–TuronianBoundary (CTB)Extinction Event 558 3.16.8.2 LinksbetweenCTB Oceanic PlateauVolcanism andEnvironmentalPerturbation 558 3.16.9 CONCLUDING STATEMENTS 560 REFERENCES 561 3.16.1 INTRODUCTION knowledge ofthe oceanbasins hasimproved over the last 25years,many moreoceanic plateaus Although the existence oflarge continentalflood havebeenidentified (Figure1).Coffinand basalt provinceshasbeenknownfor some Eldholm (1992) introduced the term “large igneous considerabletime, e.g.,Holmes(1918),the provinces” (LIPs) asageneric term encompassing recognition thatsimilarfloodbasalt provinces oceanic plateaus,continentalfloodbasalt alsoexist belowthe oceans isrelatively recent. In provinces,andthoseprovinceswhich form at the early 1970s increasingamounts ofevidence the continent–oceanboundary (volcanic rifted fromseismic reflection andrefraction studies margins).
    [Show full text]
  • Contrasting Volcano Spacing Along SW Japan Arc Caused by Difference
    www.nature.com/scientificreports OPEN Contrasting volcano spacing along SW Japan arc caused by diference in age of subducting lithosphere Yoshiyuki Tatsumi1,2*, Nobuaki Suenaga3, Shoichi Yoshioka2,3, Katsuya Kaneko 1,2 & Takumi Matsumoto4 The SW Japan arc built by subduction of the Philippine Sea (PHS) plate exhibits uneven distribution of volcanoes: thirteen Quaternary composite volcanoes form in the western half of this arc, Kyushu Island, while only two in the eastern half, Chugoku district. Reconstruction of the PHS plate back to 14 Ma, together with examinations based on thermal structure models constrained by high- density heat fow data and a petrological model for dehydration reactions suggest that fuids are discharged actively at depths of 90–100 km in the hydrous layer at the top of the old (> 50 Ma), hence, cold lithosphere sinking beneath Kyushu Island. In contrast, the young (15–25 Ma) oceanic crust downgoing beneath Chugoku district releases fuids largely at shallower depths, i.e. beneath the non- volcanic forearc, to cause characteristic tectonic tremors and low-frequency earthquakes (LFEs) and be the source of specifc brine springs. Much larger amounts of fuids supplied to the magma source region in the western SW Japan arc could build more densely-distributed volcanoes. Subduction zone volcanoes tend to exhibit regular spacing along a volcanic arc, although the spacing of volcanoes within individual arcs is ofen variable from arc to arc1, 2. A broad positive correlation between the linear density of active volcanoes and the rate of plate convergence suggests that the faster subduction contributes to greater melt production in the mantle wedge3–5.
    [Show full text]
  • Mantle Flow Through the Northern Cordilleran Slab Window Revealed by Volcanic Geochemistry
    Downloaded from geology.gsapubs.org on February 23, 2011 Mantle fl ow through the Northern Cordilleran slab window revealed by volcanic geochemistry Derek J. Thorkelson*, Julianne K. Madsen, and Christa L. Sluggett Department of Earth Sciences, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada ABSTRACT 180°W 135°W 90°W 45°W 0° The Northern Cordilleran slab window formed beneath west- ern Canada concurrently with the opening of the Californian slab N 60°N window beneath the southwestern United States, beginning in Late North Oligocene–Miocene time. A database of 3530 analyses from Miocene– American Holocene volcanoes along a 3500-km-long transect, from the north- Juan Vancouver Northern de ern Cascade Arc to the Aleutian Arc, was used to investigate mantle Cordilleran Fuca conditions in the Northern Cordilleran slab window. Using geochemi- Caribbean 30°N Californian Mexico Eurasian cal ratios sensitive to tectonic affi nity, such as Nb/Zr, we show that City and typical volcanic arc compositions in the Cascade and Aleutian sys- Central African American Cocos tems (derived from subduction-hydrated mantle) are separated by an Pacific 0° extensive volcanic fi eld with intraplate compositions (derived from La Paz relatively anhydrous mantle). This chemically defi ned region of intra- South Nazca American plate volcanism is spatially coincident with a geophysical model of 30°S the Northern Cordilleran slab window. We suggest that opening of Santiago the slab window triggered upwelling of anhydrous mantle and dis- Patagonian placement of the hydrous mantle wedge, which had developed during extensive early Cenozoic arc and backarc volcanism in western Can- Scotia Antarctic Antarctic 60°S ada.
    [Show full text]
  • Constraints on the Moho in Japan and Kamchatka
    Tectonophysics 609 (2013) 184–201 Contents lists available at ScienceDirect Tectonophysics journal homepage: www.elsevier.com/locate/tecto Review Article Constraints on the Moho in Japan and Kamchatka Takaya Iwasaki a, Vadim Levin b,⁎, Alex Nikulin b, Takashi Iidaka a a Earthquake Research Institute, University of Tokyo, Japan b Rutgers University, NJ, USA article info abstract Article history: This review collects and systematizes in one place a variety of results which offer constraints on the depth Received 1 July 2012 and the nature of the Moho beneath the Kamchatka peninsula and the islands of Japan. We also include stud- Received in revised form 12 November 2012 ies of the Izu–Bonin volcanic arc. All results have already been published separately in a variety of venues, and Accepted 22 November 2012 the primary goal of the present review is to describe them in the same language and in comparable terms. Available online 3 December 2012 For both regions we include studies using artificial and natural seismic sources, such as refraction and reflec- tion profiling, detection and interpretation of converted-mode body waves (receiver functions), surface wave Keywords: Kamchatka dispersion studies (in Kamchatka) and tomographic imaging (in Japan). The amount of work done in Japan is Japan significantly larger than in Kamchatka, and resulting constraints on the properties of the crust and the upper- Crustal structure most mantle are more detailed. Upper-mantle structure Japan and Kamchatka display a number of similarities in their crustal structure, most notably the average Moho crustal thickness in excess of 30 km (typical of continental regions), and the generally gradational nature of the crust–mantle transition where volcanic arcs are presently active.
    [Show full text]
  • Geometrical Effects of a Subducted Seamount on Stopping Megathrust
    GEOPHYSICAL RESEARCH LETTERS, VOL. 40, 1–6, doi:10.1002/grl.50509, 2013 Geometrical effects of a subducted seamount on stopping megathrust ruptures Hongfeng Yang,1,2 Yajing Liu,1,3 and Jian Lin1 Received 6 March 2013; revised 18 April 2013; accepted 25 April 2013. [1] We have numerically simulated dynamic ruptures along rich sediments into seismogenic zone [Bangs et al., 2006]. a “slip-weakening” megathrust fault with a subducted The presence of entrained fluid-rich sediments in the vicinity seamount of realistic geometry, demonstrating that of a subducted seamount would reduce effective normal seamounts can act as a barrier to earthquake ruptures. Such stress and lubricate the thrust interface, leading to little barrier effect is calculated to be stronger for increased elastic strain accumulation and thus inhibiting coseismic seamount normal stress relative to the ambient level, for ruptures [Mochizuki et al., 2008; Singh et al., 2011]. Further- larger seamount height-to-width ratio, and for shorter more, it was proposed that seamount subduction may create seamount-to-nucleation distance. As the seamount height a complex fracture network in the overriding plate, making it increases from 0 to 40% of its basal width, the required unfavorable for the generation of large earthquakes [Wang increase in the effective normal stress on the seamount to and Bilek, 2011]. Thus, the specific mechanisms for stop ruptures drops by as much as ~20%. We further subducted seamounts to stop coseismic ruptures could be demonstrate that when a seamount is subducted adjacent to complex and remain open for debate. the earthquake nucleation zone, coseismic ruptures can be [3] Previous numerical studies have modeled a subducted stopped even if the seamount has a lower effective normal seamount as a patch under elevated effective normal stress stress than the ambient level.
    [Show full text]
  • Subducting Oceanic High Causes Compressional Faulting In
    Available online at www.sciencedirect.com Tectonophysics 466 (2009) 255–267 www.elsevier.com/locate/tecto Subducting oceanic high causes compressional faulting in southernmost Ryukyu forearc as revealed by hypocentral determinations of earthquakes and reflection/refraction seismic data ⁎ Yvonne Font a, , Serge Lallemand b a Géosciences Azur, UMR IRD–CNRS–UPMC–UNSA 6526, 06235 Villefranche-sur-Mer, France b Géosciences Montpellier, UMR CNRS–UM2 5243, CC.60, UM2, place E. Bataillon, 34095 Montpellier, France Available online 22 November 2007 Abstract Absolute earthquake hypocenter locations have been determined in the area offshore eastern Taiwan, at the Southernmost Ryukyu subduction zone. Location process is run within a 3D velocity model by combining the Taiwanese and neighboring Japanese networks and using the 3D MAXI technique. The study focuses on the most active seismic cluster in the Taiwan region that occurs in the forearc domain offshore eastern Taiwan. Earthquakes distribute mainly along 2 active planes. The first one aligns along the subduction interface and the second one, shallower affects the overriding margin. Focal mechanisms within the shallow group indicate that nodal planes are either compatible with high-angle back- thrusts or low-angle thrusts. The active seismic deformation exclusively indicates reverse faulting revealing that the forearc basement undergoes trench-perpendicular strong compression. By integrating the seismological image into the regional context, we favor the hypothesis in which the dense seismicity occurring offshore marks the activity of en-échelon high-angle reverse faults accommodating the uplift of a broken piece of Ryukyu Arc basement, called Hoping Basement Rise. The uplift is inferred to be caused by the subduction of an oceanic relief, either exotic block, seamount or oceanic crust sliver.
    [Show full text]
  • The Next Generation of Ocean Exploration. Kelly Walsh Repeats Father’S Historic Dive, 60 Years Later, on Father’S Day Weekend
    From father to son; the next generation of ocean exploration. Kelly Walsh repeats father’s historic dive, 60 years later, on Father’s Day weekend DSSV Pressure Drop. Challenger Deep, Mariana Trench 200miles SW of Guam. June 20th, 2020 – Kelly Walsh, 52, today completed a historic dive to approximately 10,925m in the Challenger Deep. The dive location was the Western Pool, the same area that was visited by Kelly’s father, Captain Don Walsh, USN (Ret), PhD, who was the pilot of the bathyscaph ‘Trieste’ during the first dive to the Challenger Deep in 1960. Mr. Walsh’s 12- hour dive, coordinated by EYOS Expeditions, was undertaken aboard the deep-sea vehicle Triton 36000/2 ‘Limiting Factor” piloted by the owner of the vehicle Victor Vescovo, a Dallas, Texas based businessman and explorer. The expedition to the Challenger Deep is a joint venture by Caladan Oceanic, Triton Submarines and EYOS Expeditions. Mr. Vescovo and his team made headlines last year by completing a circumnavigation of the globe that enabled Mr. Vescovo to become the first person to dive to the deepest point of each of the worlds five oceans. The dives by father and son connect a circle of exploration history that spans 60 years. “It was a hugely emotional journey for me,” said Kelly Walsh aboard DSSV Pressure Drop, the expedition’s mothership. “I have been immersed in the story of Dad’s dive since I was born-- people find it fascinating. It has taken 60 years but thanks to EYOS Expeditions and Victor Vescovo we have now taken this quantum leap forward in our ability to explore the deep ocean.
    [Show full text]
  • Latitude Volcanoes Dubious Case for Slab Melting in the Northern
    Dubious case for slab melting in the Northern volcanic zone of the Andes: Comment and Reply COMMENT Moreover, the SiO2 range of “putative slab melts” is assumed to represent the silica content of primary magmas produced in front of the E. Bourdon Carnegie Ridge. Such an assumption should be valid only if all magmas Department of Geology, Royal Holloway, University of London, represent true primary melts. However, fractional crystallization is an effi - Egham, Surrey TW20 0EX, UK cient process able to strongly modify silica content of magmas (including P. Samaniego in the Northern volcanic zone). Consequently, silica defi nitely appears to Departamento de Geofísica, Escuela Politecnica Nacional, be an inappropriate geochemical feature to distinguish slab melts. AP 17-01-2759, Quito, Ecuador Garrison and Davidson (2003) also argue that the lack of unequivocal M. Monzier, C. Robin, J.-P. Eissen geochemical variation along the arc excludes slab melting. However, data re- IRD, UR 031, Laboratoire Magmas et Volcans, Universite Blaise cently presented (Monzier et al., 2003) show systematic geochemical varia- Pascal, 5 rue Kessler, 63038 Clermont-Ferrand, France tion along the arc, all showing a negative or positive peak between 0.5°N and H. Martin 1°S. Among those, Y and La/Yb display clear minimums and maximums, UMR 6524, Laboratoire Magmas et Volcans, Universite Blaise Pascal, respectively, precisely where the Carnegie Ridge is subducting (Fig. 1). Such 5 rue Kessler, 63038 Clermont-Ferrand, France behavior refl ects the intervention of slab melts in the petrogenesis of the magmas, directly related to the subduction of the Carnegie Ridge. Recently, Garrison and Davidson (2003) questioned the possibility We agree with the Garrison and Davidson (2003) conclusion that that the adakites of the Northern volcanic zone of the Andes were gener- the magma geochemical signature characterizes the source and not any ated by slab melting.
    [Show full text]