Collaborative Research: Resolving Conflicting Thermobarometry and Stratigraphy in the Tethyan Himalaya: is Non-lithostatic Pressure During Orogenesis Preserved at Crustal Scales?

造山带中出露的变质岩记录了造山过程中地壳的埋藏和加热。通常认为，由折返岩石记录的变质压力反映了它们的埋藏深度。这种压力又被用来重建山脉带的演化，并完善我们对基本板块构造过程的认识。然而，最近的研究表明，一些岩石记录的压力并不能反映它们的真实埋藏深度（即，“非岩石静力压力”），从而潜在地使我们对造山运动的理解复杂化。印度西北部的特提斯喜马拉雅山是一个独特的位置，以测试有争议的概念，非岩石静力学压力，因为以前的结构，沉积学和古生物学的意见，有关埋藏深度的冲突与记录的变质压力。通过综合实地和实验室研究，将对特提斯喜马拉雅地区的非岩石静压力的保存进行测试，以揭示几何、温度和压力的关系，并评估喜马拉雅造山带记录的非岩石静压力条件的可行性。该项目通过以下方式为国家利益服务：（1）通过测试和挑战地球科学中的“岩石静压力”范式，在科学方面取得根本性进展;（2）培训STEM领域的研究生和本科生;（3）支持三名早期职业教师建立具有全球竞争力的研究计划;（4）与研究人员和机构开展国际合作;以及（5）开发一个公众可访问的实地考察指南，该指南将探索印度西北部喜马拉雅山的地质，并侧重于科学解释如何随着新的观察而演变。变质岩记录的压力是否准确地反映了埋藏深度，或者是否可以代表非岩石静力学压力条件--所谓的构造超压--是有争议的。数值模型和理论表明，非岩石静压力条件是可能的，甚至可能在几个构造环境，但这种现象的直接，明确的观察是罕见的。研究小组在西喜马拉雅确定了一个独特的研究地点，数十年来对特提斯地层剖面的沉积学调查与基底地层的变质压力估计不一致，这意味着埋藏约28公里。现有的运动学模型，从实地研究不建议这样的埋深的部分，因此，压力估计和palmographic重建之间的差异，需要更系统的调查。我们假设，从基底特提斯地层的变质压力反映非岩石静力学压力条件下，在区域尺度（10公里）。这将通过一个系统的研究计划进行测试，包括地质测绘，定量显微结构分析，变质热压力和岩石年代学，碎屑锆石地质年代学和低温热年代学。地质记录中是否保存有非岩石静压力，以及保存的长度尺度，一直是地学界确定的构造学领域的重要研究目标。区域规模的非岩石静力学压力的经验支持，需要在变质岩石学和构造的范式转变，理解断裂带，造山带和板块规模的动力学的演变具有深远的意义。如果研究发现不需要非岩石静压力来解释特提斯喜马拉雅西部的地质差异，这项研究仍然会提供重要的地质关系，以评估和推进喜马拉雅构造模型。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Metamorphic rocks exposed in mountain belts record crustal burial and heating during mountain building. The metamorphic pressures recorded by exhumed rocks are commonly assumed to reflect their burial depth. Such pressures are in turn used to reconstruct the evolution of mountain belts and refine our knowledge of fundamental plate-tectonic processes. However, recent studies suggest that some rocks record pressures that do not reflect their true burial depths (i.e., “non-lithostatic pressure”), thus potentially complicating our understanding of mountain building events. The Tethyan Himalaya in northwestern India is a unique location to test the controversial concept of non-lithostatic pressure because previous structural, sedimentological, and paleontological observations regarding burial depths conflict with recorded metamorphic pressures. The preservation of non-lithostatic pressure in the Tethyan Himalaya will be tested via an integrated field and laboratory study to reveal the geometric, temperature, and pressure relationships and assess the viability of non-lithostatic pressure conditions recorded in the Himalayan orogen. This project serves national interests by: (1) making fundamental advances in science through testing and challenging the “lithostatic pressure” paradigm in the Earth Sciences; (2) training graduate and undergraduate students in STEM; (3) supporting three early-career faculty to establish globally competitive research programs; (4) international collaboration with researchers and institutions; and (5) development of a publicly accessible field-trip guide that will explore the geology of the Himalaya of northwestern India and focus on how scientific interpretations evolve with new observations. Whether pressures recorded by metamorphic rocks accurately reflect burial depths or can represent non-lithostatic pressure conditions—so called tectonic overpressure—is controversial. Numerical models and theory suggest that non-lithostatic pressure conditions are possible, and even likely in several tectonic settings, but direct, unambiguous observations of this phenomenon are rare. The research team has identified a unique study site in the western Himalaya where decades of sedimentological investigations of the Tethyan stratigraphic section are inconsistent with metamorphic pressure estimates from basal strata that imply ~28+ km burial. Existing kinematic models from field studies do not suggest such burial depths of the section, and thus the discrepancy between pressure estimates and palinspastic reconstructions requires more systematic investigation. We hypothesize that metamorphic pressures from the basal Tethyan strata reflect non-lithostatic pressure conditions at the regional scale (10’s of km). This will be tested via a systematic research plan involving geologic mapping, quantitative microstructural analysis, metamorphic thermobarometry and petrochronology, detrital zircon geochronology, and low-temperature thermochronology. Whether or not non-lithostatic pressure is preserved in the geological record, and the length-scales over which it is preserved, has been identified by the geoscience community as an important research goal in the field of tectonics. Empirical support of regional-scale, non-lithostatic pressures would require a paradigm shift in metamorphic petrology and tectonics, with profound implications for understanding the evolution of fault zones, orogens, and plate-scale dynamics. If the research finds that non-lithostatic pressure is not required to explain the geological discrepancies in the western Tethyan Himalaya, this study will still provide important geologic relationships to evaluate and advance models of Himalayan tectonics.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.