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

暴露于山带的变质岩记录了造山过程中的地壳埋藏和加热作用。被挖掘出的岩石所记录的变质压力通常被认为反映了它们的埋藏深度。这样的压力反过来被用来重建山带的演化，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其真实的埋藏深度（即“非静岩压力”），从而可能使我们对造山事件的理解复杂化。印度西北部的特提斯喜马拉雅地区是检验有争议的非静岩压力概念的独特地点，因为之前关于埋藏深度的构造、沉积学和古生物学观察与记录的变质压力相冲突。将通过综合现场和实验室研究来测试特提斯喜马拉雅地区非静岩压力的保存情况，以揭示几何、温度和压力关系，并评估喜马拉雅造山带记录的非静岩压力条件的可行性。该项目符合国家利益：(1)通过测试和挑战地球科学中的“静岩压力”范式，在科学上取得根本性进展；(2)培养研究生和本科生的STEM技能；(3)支持3名早期职业教师建立具有全球竞争力的研究项目；(4)与研究人员和机构的国际合作；(5)开发一份可公开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脉的地质，并重点关注科学解释如何随着新的观察而发展。变质岩记录的压力是否能准确反映埋藏深度，或者是否能代表非静岩压力条件——即所谓的构造超压——是有争议的。数值模型和理论表明，非静岩压力条件是可能的，甚至在一些构造环境中也是可能的，但对这种现象的直接、明确的观测很少。研究小组在喜马拉雅西部确定了一个独特的研究地点，在那里对特提斯地层剖面进行了数十年的沉积学调查，结果与基底地层的变质压力估计不一致，这意味着~28+ km的埋藏。现有的野外研究的运动学模型并没有显示出该剖面的埋藏深度，因此压力估算和复原之间的差异需要更系统的调查。我们假设来自特提斯基底地层的变质压力反映了区域尺度（10公里）的非静岩压力条件。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、变质热气压测量和岩石年代学、碎屑锆石年代学和低温热年代学。非静岩压力是否被保存在地质记录中，以及它被保存的长度尺度，已经被地球科学界确定为构造学领域的一个重要研究目标。区域尺度、非静岩压力的经验支持需要变质岩石学和构造学的范式转变，这对理解断裂带、造山带和板块尺度动力学的演化具有深远的意义。如果研究发现不需要非静岩压力来解释特提斯喜马拉雅西部的地质差异，该研究仍将为喜马拉雅构造模型的评价和发展提供重要的地质关系。该奖项反映了美国国家科学基金会的法定使命，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.