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

出露在山带中的变质岩记录了造山过程中地壳的埋藏和加热。由折返岩石记录的变质压力通常被认为反映了它们的埋藏深度。这些压力反过来被用来重建山脉带的演化，并提炼我们对基本板块构造过程的知识。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“非止石压力”)，因此可能会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山脉是检验非静岩压力这一有争议概念的独特地点，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。特提斯喜马拉雅地区非静压压力的保存将通过综合野外和实验室研究来测试，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压条件的可行性。该项目通过以下方式服务于国家利益：(1)通过测试和挑战地球科学中的“静岩压”范式，在科学方面取得根本性进展；(2)培训STEM方面的研究生和本科生；(3)支持三名职业早期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)编制一份可公开查阅的实地考察指南，该指南将探索印度西北部喜马拉雅山脉的地质情况，并侧重于科学解释如何随着新的观测而演变。变质岩记录的压力是否准确地反映了埋藏深度，或者是否能够代表非静岩压力条件--即所谓的构造超压--存在争议。数值模型和理论表明，非静岩压力条件是可能的，甚至在几个构造环境中也是可能的，但对这种现象的直接、明确的观察是罕见的。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，数十年的特提斯地层剖面的沉积学调查与基准层的变质压力估计不一致，这意味着大约28公里的埋藏。现有的野外研究的运动学模型并没有表明该剖面的埋藏深度，因此，压力估计和古迹重建之间的差异需要更系统的研究。我们推测，基底特提斯地层的变质压力反映了区域尺度(10‘S千米)的非静岩压力条件。这将通过一项系统的研究计划进行验证，该计划涉及地质填图、定量微结构分析、变质温压测量和岩石年代学、碎屑锆石年代学和低温热年代学。地质记录中是否保存了非静岩压力及其保存的长度尺度，已被地学界确定为构造学领域的一个重要研究目标。区域规模的非岩石静压力的经验支持将需要变质岩石学和构造学的范式转变，这将对理解断裂带、造山带和板块尺度动力学的演化产生深远的影响。如果研究发现非静压不需要解释西特提斯喜马拉雅地区的地质差异，这项研究仍然将为评估和推进喜马拉雅构造模型提供重要的地质关系。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.