Detrital Record of the Eastern Himalaya, Assam and Bengal Basin

最近对喜马拉雅的研究表明，重要的地壳缩短、变质、隆起和侵蚀早在中新世中期和更年轻的记录之前就开始了，这些记录在siwalik和远孟加拉扇中得到了很好的记录。本项目拟通过在阿萨姆邦和孟加拉盆地暴露和钻探的新近地层分析晚始新世的碎屑年代学和矿物学，研究喜马拉雅东部低约束的造山和构造沉积的起始和随后的历史。这些地层代表了活动碎屑楔体中缺失的一环，而这些活动碎屑楔体曾被用来举例说明造山沉积和启发碰撞模型，但它们实际上尚未被用于研究造山和侵蚀过程的地层信息。本研究的目标包括：(1)确定喜马拉雅东部快速剥落的开始，并评估快速剥落的时间/和/或区域模式；(2)区分与孟加拉盆地连接的3个主要河流系统的沉积物输入；(3)评估主要流域沉积物源地的随时间变化。碎屑颗粒的冷却年龄将受到锆石裂变径迹分析的约束，并辅以来自前18 Ma地层中选定层位的钾长石的40AR/39Ar定年。碎屑组成将通过确定砂（石）模式来分析，特别是侧重于岩石碎片和重矿物种群，并辅以电气石、石榴石和角闪石的微探针分析。从恒河、雅鲁藏布江和梅克纳河（及相关）河流的现代泥沙开始，用实际的方法记录主要河流系统的沉积物输入，并通过新生代序列来评估喜马拉雅形成以来烃源岩的变化。这个项目的意义在于，在喜马拉雅山脉东部的前缘，大量未开发的地层记录可以在陆地上获得，它提供了重建造山作用和地表过程的机会，这些造山作用和地表过程是在数据之前从siwalik和远端孟加拉扇研究的地层，以及评估这个巨大的碎屑楔的新近纪部分沉积物组成的沿走向和下游变化。该项目的最终目标是提高对现代大陆碰撞中构造和地表过程的理解。拟议的地质年代学和成分分析，加上改进的地层控制和有关的正在进行的研究，将把现有的数据集扩展到整个喜马拉雅地区，为评价碰撞过程模型提供必要的基础事实。

9419086 Lundberg Recent work on the Himalaya suggest that significant crustal shortening, metamorphism, uplift and erosion began well before the mid-Miocene and younger record that has been well documented in the Siwaliks and distal Bengal fan. This project proposes to investigate the poorly-constrained initiation and ensuing history of orogenesis and tectonic sedimentation in the eastern Himalaya, by analyzing detrital geochronology and mineralogy of late Eocene through Recent strata exposed and drilled in Assam and the Bengal basin. These strata represent a missing link in an active clastic wedge that has been used to exemplify orogenic sedimentation and to inspire collisional models, yet they remain virtually unexploited for stratigraphic information on mountain-building and erosional processes. The objectives of this research include (1) determining the onset of rapid unroofing and evaluating temporal/and or regional patterns in rapid unroofing in the eastern Himalayas, (2) distinguishing sediment input from 3 major river systems that join in the Bengal basin, and (3) evaluating changes in sediment source terranes in the major drainages through time. Cooling ages of detrital grains will be constrained by fission-track analysis of zircon, complemented by 40AR/39Ar dating of potassium feldspar from selected horizons in pre-18 Ma strata. Detrital composition will be analyzed by determining sand (stone) modes, especially focusing on lithic fragments, and heavy-mineral populations, complemented by microprobe analyses of tourmalines, garnets, and amphiboles. Sediment input from the major river systems will be documented using an actualistic approach, beginning with modern sands from the Ganges, Brahmaputra, and Meghna (and related) rivers, and working back through Cenozoic sequences to assess changes in source rocks since inception of the Himalaya. The significance of this project lies in the largely unexploited stratigraphic record accessible onland in the eastern Himalayan foredee p, which provides the opportunity to reconstruct orogenesis and surface processes that pre-data strata studied from the Siwaliks and the distal Bengal fan, as well as to evaluate along-strike and downstream changes in sediment composition in the Neogene part of this immense clastic wedge. The ultimate objective of this project is to improve understanding of tectonic and surface processes in a well-constrained modern continental collision. The proposed geochronologic and compositional analyses, complemented by improved stratigraphic control and related ongoing studies, will extend existing data sets through the entire development of the Himalaya, providing ground truth necessary for evaluating models of collisional processes.