Collaborative Research: Helium-isotope Systematics Along Seismic Profiles in Tibet to Study Geometry of Indian and Tibetan Lithosphere

喜马拉雅-西藏是地球上印度和亚洲之间活跃的大陆-大陆碰撞的典型例子，但板块尺度的几何形状仍然存在争议。来自斯坦福大学和新墨西哥州大学的研究人员将对来自喜马拉雅山和西藏的温泉的流体进行采样和分析，以确定印度岩石圈的北方界限（以及亚洲岩石圈的南方界限），因此印度被迫（或俯冲）在亚洲之下的北方界限。这一努力将提高科学家绘制喜马拉雅山和西藏精确横截面的能力，使其比以前更深。对地球的新认识？美国最引人注目的山脉带和高原增强了公众对科学的兴趣，并提供了一个自然的机会，将地球科学纳入高中课程。为此，将制作一个关于该研究项目的新视频和旨在满足下一代科学标准的相关课程材料。关于印度地壳和地幔在西藏之下向北渗透一定距离的单一造山带剖面，人们没有达成一致意见。相反，越来越多的地震学观点支持从西到东，从地壳俯冲到岩石圈分层（俯冲回滚）到去块的巨大变化的模型。斯坦福大学帮助采集和解释了喜马拉雅/西藏多个地震断面的数据。从这些和其他已发表的配置文件的深反射和转换器的解释提供了可测试的模型，印度和西藏岩石圈的几何形状，因为它从西到东的西藏。对温泉中3 He/4 He比值的初步测量表明，在中国西藏（西藏和青海）的拉萨地块上存在显著的空间变化的地幔脱气作用。该研究小组将在西藏多达60个新地点的地热和碳酸流体以及相关的沉积物中进行采样，在两个野外季节中，沿着沿着几个断面，根据其可达性，地震数据的可用性和构造/地质背景进行选择。该团队将分析3 He/4 He，22 Ne，36 Ar，delta 13 C，delta 18 O，deltaD，87 Sr/86 Sr，主要和微量元素，以限制流体来源（地幔，地壳，大气，沉积，有机），了解流体混合和路径，并使用多组分化学地质测温法计算储层温度。 将重新分析地震数据，包括宽带地震和近垂直反射数据，以更好地了解取样流体的来源区域和输送途径。这些数据将制约印度板块地幔岩石圈和西藏初始熔融地幔的边界，并有助于确定西藏地幔缝合线。

Himalaya-Tibet is Earth's type example of active continent-continent collision, between India and Asia, yet the plate-scale geometry remains controversial. Researchers from Stanford University and the University of New Mexico will sample and analyze fluids from hot-springs, which are tracers of deeper structure, in the Himalaya and Tibet to locate the northern limit of the Indian lithosphere (and southern limit of the Asian lithosphere), hence the northern limit to which India has been forced (or underthrust) beneath Asia. This effort will improve scientists' ability to draw accurate cross-sections through the Himalaya and Tibet to greater depths than previously possible. This new understanding of Earth?s most dramatic mountain belt and plateau enhances public interest in science, and offers a natural opportunity to integrate earth science into high-school curricula. To this end, a new video about the research project and associated curricular materials designed to meet the Next Generation science Standards will be produced.The lithospheric geometry of continental collision remains controversial. There is no agreement on a single orogenic cross-section in which Indian crust and mantle penetrate a certain distance northwards beneath Tibet. Instead, growing seismological opinion supports models with large changes from west-to-east, from crustal underthrusting to lithospheric delamination (subduction roll-back) to de-blobbing. Stanford has helped acquire and interpret data from multiple seismic transects across Himalaya/Tibet. The interpretations of deep reflectors and converters from these and other published profiles provide testable models for the geometry of Indian and Tibetan lithospheres as it varies from west to east across Tibet. Pilot measurements of 3He/4He ratios in hot springs show significant, and spatially variable, mantle degassing across the Lhasa block in Chinese Tibet (Xizang and Qinghai). The research team will sample geothermal and carbonic fluids and associated travertines at up to 60 new locations in Tibet during two field seasons along several transects chosen for their accessibility, availability of seismic data, and tectonic/geologic setting. The team will analyze 3He/4He, 22Ne, 36Ar, delta13C, delta18O, deltaD, 87Sr/86Sr, major and trace elements to constrain fluid sources (mantle, crustal, atmospheric, sedimentary, organic), to understand fluid mixing and pathways, and to calculate reservoir temperatures using multi-component chemical geothermometry. Seismic data, both broadband teleseismic and near-vertical reflection data, will be re-analyzed to better understand the source regions and transport pathways of the sampled fluids. The data will constrain the boundary between Indian cratonic mantle lithosphere and Tibetan incipiently melting mantle and help define the mantle suture beneath Tibet.