Detrital Record of the Eastern Himalaya, Assam and Bengal Basin

9419086伦德伯格最近对喜马拉雅山脉的研究表明，重大的地壳缩短、变质、抬升和侵蚀早在中新世中期和更年轻的记录之前就开始了，这在西瓦利克和远孟加拉扇中得到了很好的记录。该项目建议通过分析阿萨姆邦和孟加拉盆地最近暴露和钻探的地层中晚始新世的碎屑年代学和矿物学，来研究喜马拉雅东部造山和构造沉积的不受约束的启动和随后的历史。这些地层是活动碎屑楔中缺失的一环，已被用来例证造山沉积和激发碰撞模型，但它们实际上仍然没有被开发，以获得关于造山和侵蚀过程的地层信息。这项研究的目标包括：(1)确定喜马拉雅东部快速剥离的开始时间和评估快速剥离的时间和/或区域模式；(2)区分汇入孟加拉盆地的3个主要水系的泥沙输入；以及(3)评估主要流域泥沙来源地体随时间的变化。碎屑颗粒的冷却年龄将受到锆石裂变径迹分析的限制，并辅之以18 Ma前地层选定层位的钾长石40Ar/39Ar测年。碎屑成分将通过确定砂(石)模式来分析，特别是侧重于岩屑和重矿物群体，并辅之以电气石、石榴石和角闪石的微探针分析。主要河流系统的沉积物输入将以实际的方法记录下来，从恒河、雅鲁藏布江和梅格纳(及相关)河流的现代砂体开始，通过新生代层序来评估自喜马拉雅山脉开始以来源岩的变化。该项目的意义在于，在喜马拉雅东部前缘的陆地上可获得大量未开发的地层记录，这为重建Siwaliks和孟加拉远端扇所研究的造山作用和地表过程以及评估这一巨大碎屑楔体的新近纪部分沉积成分的沿走向和下游变化提供了机会。该项目的最终目标是提高对现代大陆碰撞中构造和表面过程的理解。拟议的地质年代学和成分分析，辅之以改进的地层控制和正在进行的相关研究，将把现有的数据集扩展到喜马拉雅山脉的整个发展过程，为评估碰撞过程模型提供必要的基本事实。

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.