Detrital Mineral Thermochronology of the Indus Molasse, Northwestern Indian Himalaya

该项目将使用碎屑矿物热年代学来极大地提高我们对一个重要沉积序列的年龄范围、沉积历史和热演化的理解，该序列制约着欧亚大陆和印度之间大陆-大陆碰撞的时间。印度西北部印度河群的大陆沉积对碰撞事件的年龄提供了关键的制约。普遍接受的印度河磨拉石在鲁特斯-伊普里期开始沉积的说法并没有得到古生物或地质年代学数据的明确支持。除了大多数磨拉石必须比伊普拉斯石灰岩年轻这一事实外，在整个剖面的大部分时间里都没有识别出年龄诊断化石或火山层，而且印度河群(上渐新世介形类)唯一记录良好的化石组合的地层位置是有争议的。在这一重要序列中，对任何矿藏的年龄都没有明确的限制。这项工作的主要工具将是激光聚变40Ar/39Ar黑云母热年代学和激光加热和激光烧蚀(U-Th)/氦锆石热年代学。第一种方法利用了黑云母在印度河组砂岩中的广泛分布，以及该层序的沉积后变质作用处于足够低的温度，从而排除了40Ar/39Ar黑云母计时仪热重置的可能性。因此，每个样品中最年轻的碎屑黑云母提供了样品沉积年龄的上限。另一方面，(UTH)/He锆石计时仪的封闭温度范围足够低，应该被印度河群层序最高级别部分的沉积后变质作用重新设定。层序这些部分的锆石年龄将为层序所有部分的沉积年龄提供一个较低的边界，因为当时整个沉积盆地经历了浅成-安山期的变质作用。除了这些关于沉积年龄的重要括号，这项研究的结果将提供更好的洞察印度河群沉积物的来源，现代印度河水系可能的发育年龄，以及伴随着表层-风化变质作用的区域重要变形的时代。一名女研究生将把这项研究作为她的博士论文的主要重点。关于研究和教育基础设施，拟议的工作加强了亚利桑那州与印度和联合王国的外国研究机构之间的国际研究关系。

This project will use detrital mineral thermochronology to greatly improve our understanding of the age range, depositional history, and thermal evolution of an important sedimentary succession that constrains the timing of the continent-continent collision between Eurasia and India. Continental sediments of the Indus Group of northwest India provide a critical constraint on the age of the collisional event. The generally accepted beginning of deposition of the Indus molasse in Lutetian-Ypresian time is not explicitly supported by paleontological or geochronological data. Other than the fact that most of the molasse must be younger than Ypresian limestones, age-diagnostic fossils or volcanic horizons have not been identified throughout most of the section, and the stratigraphic position of the only well-documented fossil assemblage from the Indus Group (Upper Oligocene ostracods) is debatable. There are no firm constraints on the ages of any deposits in this important sequence. The principal tools of this work will be laser fusion 40Ar/39Ar biotite thermochronology and both laser heating and laser ablation (U-Th)/He zircon thermochronology. The first method capitalizes on the wide distribution of biotite in Indus Group sandstones and on the fact that post-depositional metamorphism of the sequence was at a low enough temperature to eliminate the possibility of thermal resetting of the 40Ar/39Ar biotite chronometer. Thus, the youngest detrital biotites in each sample provide an upper boundary of the sample's depositional age. The (UTh)/He zircon chronometer, on the other hand, has a closure temperature range low enough that it should have been reset by post-depositional metamorphism in the highest-grade portions of the Indus Group sequence. The zircon ages from these parts of the sequence will provide a lower boundary on depositional ages of all parts of the sequence, since the entire depositional basin experienced epizonal-anchizonal metamorphism at that time. In addition to these important brackets on the age of sedimentation, the results of this study will provide better insights into the provenance of Indus Group sediments, the likely developmental age of the modern Indus River drainage system, and the age of regionally important deformation that accompanied epizonal-anchizonal metamorphism.Broader ImpactsThe project will involve both graduate-level and undergraduate-level education through research participation. A female graduate student will make this research the principal focus of her Ph.D. dissertation. With regard to research and education infrastructure, the proposed work reinforces international research relationships among Arizona State and foreign research institutions in India and the United Kingdom.