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Pn wave velocity and anisotropy beneath Pamir and its adjacent regions

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Earthquake Science 2012年第5期25卷 485-493页

作者： Biao Feng Shunping Pei Key Laboratory of Continental Collision and Plateau Uplift Institute of Tibetan Plateau ResearchChinese Academy of Sciences University of Chinese Academy of Sciences

As the western end point of continental collision between the Indian and Eurasian plates, Pamir is an ideal place to research uplifting mechanisms in the Tibetan plateau. In this study, 141 644 Pn arrivals were used to obtain seismic wave velocities and anisotropy in the uppermost mantle beneath Pamir and its adjacent regions by performing tomographic inversion of Pn travel times. The data were selected from multiple databases, including ISC/EHB, the Annual Bulletin of Chinese Earthquakes, and regional bulletins of Xinjiang. The tomography results reveal significant features with high resolution and correlate well with geological structures. The main results are as follows：（1） The Pn wave velocities are particularly high in the old stable blocks such as Tarim basin, Indian plate and Tajik basin, while the low Pn velocities always lie in tectonically active regions like the western Tibetan plateau, Pamir, Tianshan and Hindu Kush. （2） Strong Pn anisotropy is found beneath the Indian-Eurasian collision zone; its direction is parallel to the collision are and nearly perpendicular to both the direction of maximum compression stress and relative crustal movement. The result is probably caused by the pure shear deformation in the uppermost mantle of the collision zone. （3） A geodynamic continent-continent collision model is proposed to show anisotropy and collision mechanisms between the Indian plate and the Tarim and Tajik basins.

关键词： Pn wave velocity tomography anisotropy Pamir

Focal depth estimates of earthquakes in the Himalayan-Tibetan region from teleseismic waveform modeling

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Earthquake Science 2012年第5期25卷 459-468页

作者： Ling Bai Jeroen Ritsema Junmeng Zhao Key Laboratory of Continental Collision and Plateau Uplift Institute of Tibetan Plateau ResearchChinese Academy of Sciences Department of Earth and Environmental Sciences University of Michigan

We estimate the focal depths and fault plane solutions of 46 moderate earthquakes in the Himalayan- Tibetan region by modeling the broadband waveforms of teleseismic P waves. The depths of 38 of these earth- quakes range between 0-40 km, with a peak at -5 km. One earthquake is located within the lower crust of the Indian shield. The remaining eight earthquakes occurred between depths of 80 -120 km and are all located in the Pamir-Hindu Kush and the Indo-Myanmar deep seismic zones. None of the earthquakes outside these deep seismic zones are located in the mantle. Global centroid moment tensor （CMT） solutions indicate that most earthquakes in northern Tibet and northern India had thrust-faulting mechanisms and that normal and strike-slip faulting earthquakes occurred primarily in central Tibet. These mechanisms are consistent with the predominantly NNW-SSE compression in the direction of current Himalayan-Tibetan continental collision.

关键词： continental collision zone Tibetan plateau focal depth strength of the continental lithosphere

Mio-Pleistocene minerals of core SG-1b in the Qaidam Basin(NE Tibetan plateau): implications for climate and uplift

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Mio-Pleistocene minerals of core SG-1b in the Qaidam Basin(N...

Focal depths and mechanisms of Tohoku-Oki aftershocks from teleseismic P wave modeling

2015中国地球科学联合学术年会

作者： Minghui Li Key Laboratory of Continental Collision and Plateau Uplift Institute of Tibetan Plateau Research CAS

Strong uplift of Tibetan plateau had great effect on sediments in Qaidam Basin since Late Miocene.However,we know little about the process of how the minerals response to the uplifting due to a sca

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Earthquake Science 2014年第1期27卷 1-13页

作者： Ling Bai Lorena Medina Luna Eric A.Hetland Jeroen Ritsema Key Laboratory of Continental Collision and Plateau Uplift Institute of Tibetan Plateau Research Chinese Academy of Sciences Department of Earth and Environmental Sciences University of Michigan

Aftershocks of the 2011 Tohoku-Oki great earthquake have a wide range of focal depths and fault plane mechanisms. We constrain the focal depths and focal mechanisms of 69 aftershocks with Mw 〉 5.4 by modeling the waveforms of teleseismic P and its trailing near-surface reflections pP and sP. We find that the ＂thrust events＂ are within 10 krn from the plate interface. The dip angles of these thrust events increase with depth from ~ 5~ to ~ 25~. The ＂non-thrust events＂ vary from 60 km above to 40 km below the plate interface. Normal and strike-slip events within the overriding plate point to redistribution of stress following the primary great earthquake; however, due to the spatially variable stress change in the Tohoku-Oki earthquake, an understanding of how the mainshock affected the stresses that led to the aftershocks requires accurate knowledge of the aftershock location.

关键词： Tohoku-Oki aftershocks Focal depths Focal mechanisms Coseismic stress change

Geochemical Characteristics of Volcanic Rocks from ODP Site 794,Yamato Basin:Implications for Deep Mantle Processes of the Japan Sea

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Acta Geologica Sinica(English Edition) 2015年第4期89卷 1189-1212页

作者： CHEN Shuangshuang LIU Jiaqi GUO Zhengfu CHEN Shengsheng SUN Chunqing key laboratory of Cenozoic Geology and Environment Institute of Geology and GeophysicsChinese Academy of Sciences University of Chinese Academy of Sciences Key Laboratory of Continental Collision and Plateau Uplift Institute of Tibet Plateau ResearchChinese Academy of Sciences

Deep mantle processes and the dynamic mechanism of magmatism in the Japan Sea Basin are important processes that have not been studied in detail. In this paper, systematic evaluation of basalt samples from the ocean drilling program Site 794 in the Japan Sea was performed, which included petrography, whole-rock major- and trace-element analysis, Sr-Nd-Pb isotopic composition, and electron microprobe analysis of plagioclase and clinopyroxene. These basalts belong to the tholeiitic series with porphyritic texture and massive Ca-rich plagioclase, clinopyroxene, and minor olivine phenocrysts. The basalts are characterized as flat rare earth elements and high-field-strength elements with remarkably low ratios of （La/Yb）N （0.75-2.51）, significant positive anomalies of Ba, Sr, and Rb and no Eu anomaly （dEn = 0.99-1.36）. The samples showed relatively high 87Sr/86Sr （0.70425- 0.70522）, 207pb/204pb （15.511-15.610）, and 208pb/204pb （38.064-38.557） values and a low 143Nd/144Nd ratio （0.51271-0.51295）. The basalts from Site 794 can be divided into upper, middle, and lower volcanic rocks （UVR, MVR, and LVR） on the basis of their stratigraphic level. The MVR was geochemically derived from the depleted mantle, whereas the UVR and LVR originated from a nondepleted and relatively enriched mantle source with contributions from subducted Pacific plate fluid and sediments. Use of geothermobarometers indicates that the crystallization pressure for the UVR and LVR （6.25-11.19 kbar） was significantly higher than that of the MVR （3.48-5.84 kbar）. The UVR and LVR may have been derived from the low-degree （5%-10%） partial melting of spinel lherzolite, while the MVR originated from a shallower mantle source with a high degree （10%-20%） of partial melting. In addition, the geochemical characteristics of the samples are consistent with a younger age （13-17 Ma） and the depleted composition of the MVR and an older age （17-23 Ma） and slightly enriched composition of the UVR and LVR. Therefore, temporal changes in the mantle source from old and e

关键词： Basalt deep mantle process geothermobarometer Yamato Basin

Differential surface uplift: Cenozoic paleoelevation history of the Tibetan plateau

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Science China Earth Sciences 2016年第11期59卷 2105-2120页

作者： LIU XiaoHui XU Qiang DING Lin Key Laboratory of Continental Collision and Plateau Uplift Institute of Tibetan Plateau Research Chinese Academy of Sciences Center for Excellence in Tibetan plateau Earth Science Chinese Academy of Sciences College of Resources and Environment University of Chinese Academy of Sciences

The surface uplift history of the Tibetan plateau has provided a key boundary criterion for various geological, climatic,and environmental events since the Cenozoic. The paleoelevation history of the plateau is organically associated with interactions amongst deep geodynamics, earth surface processes, and climate change. Understanding of plateau uplift history has been advanced by the development of a number of paleoaltimetries and their application to studies of the Tibetan plateau: the paleogeomorphic scenario for the Early Eocene Tibetan plateau is thought to include two high mountains, the ca. 4500 m Gangdese Mountains to the south, and the ca. 5000 m Qiangtang Center Watershed Mountains to the north. Between these ranges, a low-elevation basin(ca. 2500 m) is thought to have been present. The Himalayas in the southern Tibetan plateau was close to sea level at this time,while the Hoh Xil Basin in the north reached an elevation of no more than 1500 m. Thus, the so-called "Roof of the World" Tibetan plateau formed subsequent to the Miocene. Nevertheless,, the uplift histories of the different terranes that comprise this plateau currently remain unclear, which constrains the uplift history reconstruction of the entire Tibetan plateau. Additional paleoelevation data from different areas, obtained using multi-paleoaltimeters, is required to resolve the forms and processes of Tibetan plateau uplift and extension.

关键词： Paleoelevation 微分表面高举新生代西藏的高原

Topsoil C/N ratios in the Qilian Mountains area: implications for the use of subaqueous sediment C/N ratios in paleo-environmental reconstructions to indicate organic sources

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Topsoil C/N ratios in the Qilian Mountains area: implication...

Seismic detection of the X-discontinuity beneath the Ryukyu subduction zone from the SdP conversion phase

2015中国地球科学联合学术年会

作者： Yan Zhao Fuli Wu Xiaomin Fang Yibo Yang Key Laboratory of Continental Collision and Plateau Uplift Institute of Tibetan Plateau Research CAS

Sediment carbon/nitrogen(C/N)ratios can play an important role in reconstructing lacustrine and coastal paleo-environments,because significantly different C/N ratios result from aquatic phytoplankt

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Earth and Planetary Physics 2018年第3期2卷 208-219页

作者： QingHui Cui WenLan Li GuoHui Li MaiNing Ma XiaoYu Guan YuanZe Zhou key laboratory of Computational Geodynamics Chinese Academy of Sciences College of Earth and Planetary Sciences University of Chinese Academy of Sciences Key Laboratory of Continental Collision and Plateau Uplift Institute of Tibetan Plateau ResearchChinese Academy of Sciences

The X-discontinuity,which appears at the depth of approximately 300 km,is an important seismic interface with positive velocity contrasts in the upper mantle.Detecting its presence and topography can be useful to understand phase transformations of relevant mantle minerals under the high-temperature and high-pressure circumstance of the Earth's interior.In this study,we detect the X-discontinuity beneath the Ryukyu subduction zone using five intermediate-depth events recorded by the dense Alaska Regional Network(AK).The X-discontinuity is successfully revealed from the robust slant stacking of the secondary down-going and converting Sd P phases.From the depth distribution of conversion points,we find that the X-discontinuity's depth ranges between 269 km and 313 km,with an average depth of 295 km.All the conversion points are located beneath the down-dipping side of the Philippine Sea slab.From energy comparisons in vespagrams for observed and synthetic seismograms,the strong converted energy is more likely from a thin high-velocity layer,and the S-wave velocity jumps across the X-discontinuity are up to 5% to 8% with an average of 6.0%.According to previous petrological and seismological studies,the X-discontinuity we detected can be interpreted as the phase transformation of coesite to stishovite in eclogitic materials within the oceanic crust.

关键词： Ryukyu subduction zone X-discontinuity coesite-stishovite transformation dense network SdP conversion phase

Paleoaltimetry reconstructions of the Tibetan plateau:progress and contradictions

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National Science Review 2015年第4期2卷 417-437页

作者： Tao Deng Lin Ding key laboratory of Vertebrate Evolution and Human Origins Institute of Vertebrate Paleontology and PaleoanthropologyChinese Academy of Sciences CAS Center for Excellence in Tibetan plateau Earth Sciences Key Laboratory of Continental Collision and Plateau Uplift Institute of Tibetan Plateau ResearchChinese Academy of Sciences

Over the last two decades, many quantitative paleoaltimetry reconstructions of the Tibetan plateau have been published, but they are still preliminary and controversial, although several approaches have been combined paleontology and geochemistry, including vertebrate, plant, and pollen fossils as well as oxygen,carbon, and hydrogen isotopes. he Tibetan plateau is the youngest and highest plateau on Earth, and its paleoaltimetry reconstructions are crucial to interpret its geodynamic evolution and to understand the climatic changes in Asia. Uplit histories of the Tibetan plateau based on diferent proxies difer considerably, and two viewpoints are pointedly opposing on the paleoaltimetry estimations of the Tibetan plateau. One viewpoint is that the Tibetan plateau did not strongly uplit to reach its modern elevation until the Late Miocene, but another one, mainly based on stable isotopes, argues that the Tibetan plateau formed early during the Indo-Asian collision and reached its modern elevation in the Paleogene or by the Middle Miocene. With either a geochemical or paleontological approach, the present is used as the key to the past.However, there are great diiculties because modern processes of isotopic fractionation and species for creature distribution are not easily precisely determined. In addition, the climatic and environmental backgrounds of past geological times have massive diferences from the present, and associated adjustments are inluenced by many human factors. In the future work, the applications of multidisciplinary comprehensive methods and cross-checks of their results will be productive, and we look forward to achieving more reliable estimates for paleoelevations of the Tibetan plateau.

关键词： Tibetan plateau Cenozoic paleoelevation paleontology stable isotope