The Experts below are selected from a list of 258 Experts worldwide ranked by ideXlab platform
Liu Zhaoshu - One of the best experts on this subject based on the ideXlab platform.
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a crustal structure profile across the northern Continental Margin of the south china sea
Tectonophysics, 2001Co-Authors: Yan Pin, Liu ZhaoshuAbstract:An ocean bottom seismometer (OBS) geophysical experiment was carried out across the northern Continental Margin of the South China Sea. Two-dimension kinematic ray tracing was used to construct synthetic records and to define the geological model along the OBS profile. According to the calculation and interpretation of refracted P-wave phases. the crustal thickness decreases from 22 km (OBS-1) in littoral area to 8 km (OBS-15) in deep sea. The lower slope structured by volcanism changes sharply in Moho depth from 22 to 9 km. The volcanoes over the lower slope were markers of ocean-Continental transition zone. A high velocity layer (HVL) with an average thickness of 4 km was found in the base of the lower crust over the shelf and slope. The South China Sea was originated by the passive rifting of South China continent and seafloor spreading. However, geological and geophysical data collected in the northern Margin of the South China Sea show a small amount of magma intruded into or erupted onto the crust during pull-apart and breakup. Further analysis shows that the HVZ in the base of the thinned Continental crust was related to magmatism that occurred after the cessation of seafloor spreading of the South China Sea. Magmatism during the crustal extension and breakup is very weak. Therefore, the northern Continental Margin of the SCS is classified as non-volcanic passive Margin. The southern Margin of the South China Sea has a crust with a steady thickness of 18-24 km, which is different from the nor-them Margin of the South China Sea with a gradually thinned crust. They constitute an asymmetrically conjugated pair of passive Margins. (C) 2001 Elsevier Science B.V. All rights reserved.
Sunlin Chung - One of the best experts on this subject based on the ideXlab platform.
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magmatic switch on and switch off along the south china Continental Margin since the permian transition from an andean type to a western pacific type plate boundary
Tectonophysics, 2012Co-Authors: Sunlin ChungAbstract:Detrital zircon provenance data for the Tananao schist in eastern Taiwan is consistent with its protolith being deposited on the South China Continental Margin at around, or soon after, 150 Ma, rather than being of an exotic origin and much older as previously suggested. The absence of ca. 200 Ma zircons agrees with the presence of a magmatic gap in the region after the orogenic and magmatic front migrated to central South China, due to a flat-slab subduction. The characteristic lack of input from interior South China (i.e., the lack of 1100–750 Ma and 470–420 Ma populations), and the immature nature of some of the schist units, suggest that they were sourced from the nearby coastal regions. On the other hand, they exhibit a dominant 190–150 Ma magmatic zircon population, suggesting the presence of abundant magmatic rocks of that age along the coastal regions. This, along with our newly discovered ca. 180 Ma I-type granites from eastern Zhejiang and other ca. 190–180 Ma magmatic rocks recently reported from the coastal regions, led us to propose that a new Continental arc was initiated after ca. 190 Ma along the coastal region after a magmatic gap due to flat-slab subduction. This newly initiated arc likely persisted until ca. 90 Ma, and is represented by the I-type granitic rocks in eastern Taiwan. Slab roll-back likely caused the arc system to retreat towards the Pacific Ocean after 90 Ma, and ca. 60–17 Ma bimodal magmatism adjacent to the South China Sea signifies Continental Margin extension in the lead-up to, and during, the opening of the South China Sea. We thus argue that the Continental Margin of East Asia was transformed from an Andean-type plate Margin at 280–90 Ma, to the present-day Western Pacific-type plate Margin soon after 90 Ma.
Heiko Sahling - One of the best experts on this subject based on the ideXlab platform.
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gas emissions at the Continental Margin west of svalbard mapping sampling and quantification
Biogeosciences, 2014Co-Authors: Heiko Sahling, Miriam Romer, Thomas Pape, Benoit Berges, Dos Santos C Fereirra, Jan Boelmann, Patrizia Geprags, Michal Tomczyk, Nicolas Nowald, Werner DimmlerAbstract:We mapped, sampled, and quantified gas emissions at the Continental Margin west of Svalbard during R/V Heincke cruise He-387 in late summer 2012. Hydroacoustic mapping revealed that gas emissions were not limited to a zone just above 396 m water depth. Flares from this depth have gained significant attention in the scientific community in recent years because they may be caused by bottom-water warming-induced hydrate dissolution in the course of global warming and/or by recurring seasonal hydrate formation and decay. We found that gas emissions occurred widespread between about 80 and 415 m water depth, which indicates that hydrate dissolution might only be one of several triggers for active hydrocarbon seepage in that area. Gas emissions were remarkably intensive at the main ridge of the Forlandet moraine complex in 80 to 90 m water depths, and may be related to thawing permafrost. Focused seafloor investigations were performed with the remotely operated vehicle (ROV) "Cherokee". Geochemical analyses of gas bubbles sampled at about 240 m water depth as well as at the 396 m gas emission sites revealed that the vent gas is primarily composed of methane (> 99.70%) of microbial origin (average δ 13 C = −55.7‰ V-PDB). Estimates of the regional gas bubble flux from the seafloor to the water column in the area of possible hydrate decomposition were achieved by combining flare mapping using multibeam and single-beam echosounder data, bubble stream mapping using a ROV-mounted horizontally looking sonar, and quantification of individual bubble streams using ROV imagery and bubble counting. We estimated that about 53 × 10 6 mol methane were annually emitted at the two areas and allow for a large range of uncertainty due to our method (9 to 118 × 10 6 mol yr −1 ). First, these amounts show that gas emissions at the Continental Margin west of Svalbard were on the same order of magnitude as bubble emissions at other geological settings; second, they may be used to calibrate models predicting hydrate dissolution at present and in the future; and third, they may serve as a baseline (year 2012) estimate of the bubble flux that will potentially increase in the future due to ever-increasing global-warming-induced bottom water warming and hydrate dissociation.
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fluid seepage at the Continental Margin offshore costa rica and southern nicaragua
Geochemistry Geophysics Geosystems, 2008Co-Authors: Heiko Sahling, D G Masson, Cesar R Ranero, Veit Huhnerbach, Wilhelm Weinrebe, Ingo Klaucke, Dietmar BurkAbstract:A systematic search for methane-rich fluid seeps at the seafloor was conducted at the Pacific Continental Margin offshore southern Nicaragua and northern central Costa Rica, a convergent Margin characterized by subduction erosion. More than 100 fluid seeps were discovered using a combination of multibeam bathymetry, side-scan sonar imagery, TV-sled observations, and sampling. This corresponds, on average, to a seep site every 4 km along the Continental slope. In the northwestern part of the study area, subduction of oceanic crust formed at the East Pacific Rise is characterized by pervasive bending-induced faulting of the oceanic plate and a relatively uniform morphology of the overriding Continental Margin. Seepage at this part of the Margin typically occurs at approximately cone-shaped mounds 50 - 100 m high and up to 1 km wide at the base. Over 60 such mounds were identified on the 240 km long Margin segment. Some normal faults also host localized seepage. In contrast, in the southeast, the 220 km long Margin segment overriding the oceanic crust formed at the Cocos-Nazca Spreading Centre has a comparatively more irregular morphology caused mainly by the subduction of ridges and seamounts sitting on the oceanic plate. Over 40 seeps were located on this part of the Margin. This Margin segment with irregular morphology exhibits diverse seep structures. Seeps are related to landslide scars, seamount-subduction related fractures, mounds, and faults. Several backscatter anomalies in side-scan images are without apparent relief and are probably related to carbonate precipitation. Detected fluid seeps are not evenly distributed across the Margin but occur in a roughly Margin parallel band centered 28 ± 7 km landward of the trench. This distribution suggests that seeps are possibly fed to fluids rising from the plate boundary along deep-penetrating faults through the upper plate.
Giovanni Falco - One of the best experts on this subject based on the ideXlab platform.
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A newly discovered Pliocene volcanic field on the western Sardinia Continental Margin (western Mediterranean)
Geo-Marine Letters, 2016Co-Authors: Alessandro Conforti, Francesca Budillon, Renato Tonielli, Giovanni FalcoAbstract:A previously unknown submerged volcanic field offshore western Sardinia (western Mediterranean Sea), has been identified based on swath bathymetric data collected in 2009, 2010 and 2013, and high-resolution seismic profiles collected in 2011 and 2013. About 40 conical-shaped volcanic edifices (maximum width of about 1600 m and maximum height of about 180 m) and several lava outcrops (up to 1,200 m wide) were recognized at 20 to 150 m water depth over an area of 800 km^2. The volcanic edifices are mainly eruptive monogenic vents, mostly isolated with a rather distinct shape, or grouped to form a coalescent volcanic body in which single elements are often still recognizable. High-resolution seismics enabled identifying relationships between the volcanic bodies and Continental Margin successions. The edifices overlie a major erosional surface related to the Margin exposure following the Messinian salinity crisis, and are overlain by or interbedded with an early Pliocene marine unit. This seismo-stratigraphic pattern dates the volcanic activity to the early Pliocene, in agreement with the radiometric age of the Catalano island lavas (4.7 Ma) reported in earlier studies. The morphometry of the volcanic bodies suggests that cone erosion was higher at shallow water depths. Indeed, most of the shallow edifices are strongly eroded and flattened at 125 to 130 m water depth, plausibly explained by recurrent sub-aerial exposure during Pleistocene sea-level lowstands, whereas cones in deeper water are much better preserved. Volcanic vents and lava deposits, hereafter named the Catalano volcanic field (CVF), are emplaced along lineaments corresponding to the main directions of the normal fault system, which lowered the Sinis Basin and the western Sardinia Continental Margin. The CVF represents a volumetrically relevant phase of the late Miocene – Quaternary anorogenic volcanic cycle of Sardinia, which is related to the first stage of the extensional tectonics affecting the island since the late Miocene.
Yaolin Shi - One of the best experts on this subject based on the ideXlab platform.
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Lithospheric thermal isostasy of north Continental Margin of the South China Sea
Journal of Earth Science, 2009Co-Authors: Shi Chen, Jian Zhang, Yujun Sun, Yaolin ShiAbstract:Accompanied with rifting and detaching of the north Continental Margin of the South China Sea, the crust and the lithosphere become thinner away from the Continental Margin resulting from the tectonic activities, such as tensile deformation, thermal uplift, and cooling subsidence, etc.. Integrated with thermal, gravimetric, and isostatic analysis techniques, based on the seismic interpretation of the deep penetration seismic soundings across the northern Margin of the South China Sea, we reconstructed the lithospheric thermal structure and derived the variation of the crust boundary in the east and west parts of the seismic profile by using gravity anomaly data. We mainly studied the thermal isostasy problems using the bathymetry of the profiles and calculated the crust thinning effect due to the thermal variety in the rifting process. The results indicate that the thermal isostasy may reach 2.5 km, and the compositional variations in the lithospheric density and thickness may produce a variation of 4.0 km. Therefore, the compositional isostatic correction is very important to recover the relationship between surface heat flow and topography. Moreover, because of the high heat flow characteristic of the Continental Margin, building the model of lithospheric geotherm in this region is of great importan for studying the Cenozoic tectonic thermal evolution of the north passive Continental Margin of the South China Sea.