Collaborative Research: Structure of the Crust and Upper Mantle Beneath the Tibetan Plateau Interior (INDEPTH III)

合作研究：青藏高原内部地壳和上地幔的结构（INDEPTH III）

• 批准号: 9614616
• 负责人: James Ni
• 金额: --
• 依托单位: New Mexico State University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1997
• 资助国家: 美国
• 起止时间: 1997-09-01 至 2007-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9614616&HistoricalAwards=false
• 关键词: Collaborative; Research; Structure; Crust; Upper

9614616 Ni This project is the third phase of Project INDEPTH (INternational DEep Profiling of Tibet and the Himalaya), a collaborateve, multinational, multidisciplinary program to investigate the lithosphere beneath the Himalaya/Tibet Plateau collision zone. Support is provided by NSF (Continental Dynamics Program), the Chinese National Natural Science Foundation, the Chinese Ministry of Geology and the DeutschesForschungs Gemneinshaft (Germany). Project INDEPTH has completed two field Programs in southern Tibet aimed at elucidating the structure of the lithosphere beneath this key region. The first, undertaken in 1992, was a feasibility study of deep reflection profiling on the high Tibetan Plateau that had the additional scientific goal of tracking the top of the Indian plate underthrusting the Himalaya (INDEPTH I). The second, undertaken in 1993-94, was a much more substantial program involving the acquisition of complementary CMP reflection, wide- angle reflection, broadband earthquake, magnetotelluric, and surface geological data along a transect (including INDEPTH I) extending approximately 300 km north of the crest of the Himalaya (INDEPTH II). The combined INDEPTH I-II results yeild a refined and exciting new view of the lithosphere beneath southern Tibet. They support some previous hypotheses while necessarily contradicting others. Among other things, the INDEPTH data imply that: 1)Indian continental crust does not extend as a coherent unit in the footwall of the India-Asia decollement for a significan distance north of the Tsangpo suture (and may not extend that far); 2) in contrast, Indian mantle lithosphere in contact with the overlying crust apparently does extend at least 150 km north of the suture; 3) the Tsangpo suture is not currently a lithosphere-penetrating structure, but rather is cut off in the mikkle crust by a younger feature, and finally, perhaps of greatest global significance; 4) the new data strongly imply the existence of a widespread mid- crustal partial melt layer beneath southern Tibet. Taken together the data lead to a model for the current behavior of the southern Tibetan Plateau lithosphere wherein the Indian continental crust underthrusting the southern margin of the Plateau partially melts in the vicinity of the North Himalayan domes, thereby contributing to a partially molten effectively fluid, mid-crustal layer that underlies the Plateau to the north. These results have important implications for how the Himalaya/Tibetan Plateau as a whole has evolved, and for our concepts of lithosphere formation and modification during continent-continent collisions in general. The purpose of INDEPTH III is to address three fundamental, interrelated issues about the nature and evolution of the lithosphere beneath the region. These are: 1) What is the magnitude and mechanism(s) of accommodation of Neogene/Quaternary deformation within the Tibetan Plateau? 2)Is there an areally extensive mid-crustal partial melt layer within the Tibetan crust that has exerted a primary control on the Neogene/Quaternary structural evolution and present morphology of the Plateau? and 3) What is the nature and cause of the reported first-order south to north change in the character of the mantle lithosphere beneath the Plateau? The program includes magnetotelluric profiling and broadband earthquake recording to assess the bulk electrical resistivity and velocity structure of the crust and upper mantle beneath the region. These data will provide primary information on the presence or absence of seismically attenuating crustal melt within the interior of the Plateau, and characterize the south-to- north upper mantle transition beneath the region. These efforts will be augmented by a modest controlled-source "test", and a modest field geology program aimed at delineating the geometry of upper crustal structure, the distribution of Neogene/Quaternary shortening, and the existence of a mid-crustal bright-s pot horizon which, if present, may indicate a mid-crustal partial melt zone. ***

9614616 Ni 该项目是 INDEPTH 项目（西藏和喜马拉雅国际深度剖析）的第三阶段，这是一个合作、跨国、多学科项目，旨在调查喜马拉雅/青藏高原碰撞带下方的岩石圈。 NSF（大陆动力学计划）、中国国家自然科学基金委员会、中国地质部和 DeutschesForschungs Gemneinshaft（德国）提供支持。 INDEPTH 项目已在西藏南部完成了两项实地计划，旨在阐明这一关键地区下方的岩石圈结构。 第一个项目于 1992 年进行，是对青藏高原高地深度反射剖面进行可行性研究，其额外的科学目标是跟踪冲向喜马拉雅山的印度板块顶部 (INDEPTH I)。 第二个项目于 1993-94 年进行，是一个更为实质性的项目，涉及沿着向北延伸约 300 公里的横断面（包括 INDEPTH I）采集互补的 CMP 反射、广角反射、宽带地震、大地电磁和地表地质数据。喜马拉雅山的顶峰（INDEPTH II）。 INDEPTH I-II 的综合结果为西藏南部下方的岩石圈提供了一个精致且令人兴奋的新视图。 他们支持之前的一些假设，同时必然与其他假设相矛盾。 除其他外，INDEPTH 数据表明： 1）印度大陆地壳在印度-亚洲滑脱下盘中并没有作为一个连贯单元延伸至雅鲁藏布江缝合线以北相当大的距离（并且可能不会延伸那么远）； 2) 相比之下，与上覆地壳接触的印度地幔岩石圈显然确实向缝合线以北延伸了至少 150 公里； 3）目前，雅鲁藏布江缝合带并不是一个贯穿岩石圈的结构，而是在米克勒地壳中被一个较年轻的特征所切断，最后，也许具有最大的全球意义； 4）新数据强烈暗示藏南下方存在广泛的中地壳部分熔融层。 综合这些数据，得出了青藏高原南部岩石圈当前行为的模型，其中，俯冲青藏高原南缘的印度大陆地壳在北喜马拉雅山穹顶附近部分熔融，从而形成了部分熔融的有效流体，位于北部高原下方的中地壳层。 这些结果对于喜马拉雅山/青藏高原作为一个整体如何演化以及我们在大陆与大陆碰撞期间岩石圈形成和改变的概念具有重要意义。 INDEPTH III 的目的是解决有关该区域下方岩石圈的性质和演化的三个基本的、相互关联的问题。 它们是： 1) 青藏高原内新近纪/第四纪变形的调节幅度和机制是什么？ 2）青藏高原地壳内是否存在面积广泛的中地壳部分熔融层，对青藏高原新近纪/第四纪构造演化和现今形态起主要控制作用？ 3）所报告的高原下方地幔岩石圈特征从南到北的一级变化的性质和原因是什么？ 该计划包括大地电磁剖面和宽带地震记录，以评估该区域下方地壳和上地幔的体电阻率和速度结构。 这些数据将提供有关高原内部是否存在地震衰减地壳熔化的主要信息，并描述该地区下方从南到北的上地幔过渡特征。 这些努力将通过适度的受控源“测试”和适度的现场地质学计划来增强，该计划旨在描绘上地壳结构的几何形状、新近纪/第四纪缩短的分布以及中地壳亮带的存在。锅层位，如果存在，可能表明中地壳部分熔融带。 ***