Incredible India: High Resolution Proterozoic Paleogeography through integrated studies of mafic dykes

在漫长的地球历史中，大陆地壳的运动导致了更大的大陆的周期性组合，这些大陆被称为超级大陆。最近的超级大陆盘古大陆大约在3亿年前合并，而更古老的超级大陆被假设形成于大约6亿年前（Pannotia）， 10亿年前（Rodinia）和18亿年前（Columbia/Nuna）。超大陆与地球历史上一些重要的发展有着一致的关系，包括经济矿床的形成（哥伦比亚）、严重的气候波动（罗迪尼亚）和现代动物门的进化（潘诺提亚）。由于现代大陆拥有古代地壳的分散残留物，确定超大陆组合的时间需要整个地球的古地磁和地质年代学知识。印度半岛是五块古代大陆地壳的融合，这五块大陆地壳分别是Aravalli、Bundelkhand、Singhbhum、Dharwar和Bastar克拉通。本文的研究重点是通过对火成岩磁性方向的研究，确定5个克拉通地块的古地理组合。这个多元化的研究团队，包括本科生、研究生和外国合作者，目标是在Dharwar、Bundelkhand和Singhbhum克拉通的三个关键地区。在这次调查中收集的古地磁数据被纳入全球古地理模型，这是理解更大规模问题的关键，例如：所有大陆何时组合成更大的超大陆？地球磁场是如何随时间变化的？古代的气候条件是什么？它们如何帮助我们了解未来的气候？这项研究的重要社会影响包括：培训研究生和本科生学习一门重要的STEM学科，开展教育外展活动，与一所两年制社区学院合作，在以非裔美国人和西班牙裔美国人为主的中学开展K-12课堂外展活动，以及为来自代表性不足群体的大学STEM学生提供指导。该项目还涉及与印度科学家的国际科学合作。研究人员概述了一系列旨在澄清印度半岛地质历史和解释全球构造意义的目标。在这个建议中进行的工作正在产生1)细化导致印度组装的事件顺序，2)也阐明了印度在拟议的哥伦比亚/努纳和罗迪尼亚超级大陆中的位置。在对全球构造模型的回顾中，指出印度半岛在整个元古代被视为一个统一的地块，但现有的古地磁和地质年代学资料并不支持这一结论。此外，来自印度中部构造带的构造和年代学数据表明，直到~1100-900 Ma才实现统一。将来自印度的强大的古地磁记录与来自世界各地的结果进行比较，将确定元古代板块构造的速度和模式，有助于回答现代构造何时开始的问题。在回顾罗迪尼亚和哥伦比亚的“传统”模型时，很明显，超级大陆的中心结构似乎没有什么变化。如果罗迪尼亚构造只代表了哥伦比亚/努纳的微小变化，这可能反映了现代（显生宙）板块构造的一些潜在差异，或者可能是整个地质时期板块组织规则的基本模式。这些数据使研究人员能够评估印度克拉通的潜在“近邻”，如华北、东南极洲、澳大利亚、波罗的海、非洲部分地区和马达加斯加。这些贡献为研究古代地球气候梯度、磁场的行为和强度、真正的极移记录以及在以前相邻的克拉通中可能拥有重要成矿矿床的大型火成岩省的确定增添了重要的组成部分。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。

The motion of continental crust over long periods of Earth history results in the periodic assembly of larger landmasses referred to as supercontinents. The most recent supercontinent, Pangea, coalesced about 300 million years ago, whereas older supercontinents are hypothesized to have formed around 600 million years ago (Pannotia), 1000 million years ago (Rodinia), and 1800 million years ago (Columbia/Nuna). Supercontinents have a coincident relationship to some important developments in Earth history including the formation of economic mineral deposits (Columbia), severe climatic fluctuations (Rodinia) and the evolution of modern animal phyla (Pannotia). Because modern continents hold the dispersed remnants of ancient crust, determining the timing of supercontinent assembly requires paleomagnetic and geochronologic knowledge of the entire globe. Peninsular India is a fusion of five ancient pieces of continental crust known as the Aravalli, Bundelkhand, Singhbhum, Dharwar, and Bastar cratons. The research in this proposal is focused on determining the paleogeographic assembly of the five cratonic pieces by an investigation into the magnetic directions in igneous rocks. The diverse research team, including undergraduate students, graduate students and foreign collaborators, targets three key regions in the Dharwar, Bundelkhand and Singhbhum cratons. The paleomagnetic data being gathered in this investigation is incorporated into global paleogeographic models that are key to understanding larger scale questions such as: When were all continents assembled into larger supercontinents?, How has the Earth's magnetic field changed through time?, and What were ancient climatic conditions and how might they help us understand future climates?. Important societal impacts from this study include the training of graduate and undergraduate students in an important STEM discipline, educational outreach activities and collaboration with a 2-year community college, K-12 classroom outreach including predominantly African-American and Hispanic middle schools, and efforts that involve mentorship of university STEM students from underrepresented groups. The project also involves international scientific collaboration with scientists from India.The investigators outline a series of goals aimed to clarify the geological history of Peninsular India and interpret global tectonic implications. The work conducted in this proposal is generating that 1) refine the sequence of events that led to India's assembly, and 2) also elucidate India's place in the proposed supercontinents of Columbia/Nuna and Rodinia. In a review of global tectonic models, it is noted that Peninsular India is treated as a unified block during the entire Proterozoic, but available paleomagnetic and geochronologic data do not support such a conclusion. Additionally, structural and geochronological data from the Central Indian Tectonic Zone suggest that unity was not achieved until ~1100-900 Ma. Comparing a robust paleomagnetic record from India with results from around the globe will establish the tempo and mode of plate tectonics in the Proterozoic, helping answer the question of when modern style tectonics began. In reviewing "traditional" models of Rodinia and Columbia, it is apparent that the central structure of the supercontinents appears to show little change. If the Rodinia configuration represents only a slight variation on Columbia/Nuna, this might reflect some underlying difference from modern-style (Phanerozoic) plate tectonics, or perhaps fundamental mode of plate organization regularity throughout geologic time. These data allow the researchers to evaluate potential "nearest neighbors" to the Indian cratons such as North China, East Antarctica, Australia, Baltica, and parts of Africa and Madagascar. The contributions add an important component to studies of ancient climatic gradients across the Earth, behavior and strength of the magnetic field, the record of true polar wander, and the identification of large igneous provinces in formerly adjacent cratons that may host important metallogenic ore deposits.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.