Filling the Eastern Himalayan Gap: Structural Architecture and Kinematics of the Himalayan Orogen in Bhutan

2400公里长的喜马拉雅褶皱和冲断带从巴基斯坦北部的南迦帕尔巴特地块延伸到西藏东部的南切巴尔瓦构造。只有少量的估计可以量化该褶皱和冲断带缩短的幅度和几何形状，而在该范围的东部地区则没有这样的估计，该地区的地貌、几何和岩性表现形式发生了根本性的变化。特别是下喜马拉雅系列（早-中元古代-古生代绿片岩相到未变质变质变质沉积岩的厚层序列）的缩短幅度、样式和时间等信息的缺乏，阻碍了对喜马拉雅造山带发育的认识。该项目的目标是确定在不丹王国暴露的下喜马拉雅系列的几何形状，缩短量和变形的运动学历史。为此，来自普林斯顿大学和不丹的一组科学家正在绘制从主要中央逆冲到主要锋面逆冲的小喜马拉雅序列。利用这些野外关系和碎屑锆石的新U-Pb年龄，建立了区域地层格架。结合新的热年代学和地质年代学年龄，依次恢复平衡的地壳尺度构造剖面，以阐明区域冷却模式和限制断层运动的时间。这些结果可以评估变形在空间和时间上是如何划分的，预测最小缩短估计，确定与平衡剖面和温度计兼容的最小横向和垂直侵蚀估计，并最终比较小喜马拉雅系列和大喜马拉雅系列之间变形和挖掘的时间和规模。喜马拉雅山脉是印度和亚洲之间持续碰撞的结果。在碰撞过程中，过去18亿年覆盖印度北部的沉积盖层与下面的基底分离。这种变形的沉积盖层，以及在其中发育的构造，记录了碰撞的变形历史。虽然它是世界上最著名的山脉之一，但只有少数估计量化了这种变形，而且没有对山带东部进行这样的估计。对不丹王国变形岩石的研究将为这一鲜为人知的山脉部分提供新的估计，与喜马拉雅山脉其他部分的估计相比，将有助于更好地了解碰撞山带的发展。该项目促进了不丹和美国科学家之间的科学合作，并通过培训不丹学生和提高对该国地质的了解来帮助不丹建设科学基础设施，这反过来对了解地震灾害和自然资源也很重要。

The 2,400 km long Himalayan fold and thrust belt extends from the Nanga Parbat massif in northern Pakistan to the Namche Barwa syntaxis in eastern Tibet. There are only a handful of estimates that quantify the magnitude and geometry of shortening along this fold and thrust belt with no such estimates in the eastern portion of the range, a region characterized by fundamental changes in the geomorphic, geometric, and lithologic expression of the belt. In particular, the lack of information on the magnitude, style, and timing of shortening in the Lower Himalayan Series, a thick succession of early to middle Proterozoic-Paleozoic greenschist facies to unmetamorphosed metasedimentary rocks within the belt, inhibits understanding of the development of the Himalayan orogenic belt. The goal of this project is to determine the geometry, amount of shortening, and kinematic history of deformation in the Lower Himalayan Series as exposed in the Kingdom of Bhutan. Toward this end, a team of scientists from Princeton University and Bhutan are mapping the Lesser Himalayan Sequence from the Main Central Thrust to the Main Frontal Thrust. These field relationships and new U-Pb ages of detrital zircons are used to develop a regional stratigraphic framework. Balanced crustal-scale structural cross-sections are restored sequentially when combined with new thermochronologic and geochronologic ages in order to elucidate regional cooling patterns and to constrain timing of fault motion. These results allow evaluation of how deformation is partitioned in space and time, prediction of minimum shortening estimates, determination of minimum lateral and vertical erosion estimates compatible with both the balanced section and thermochronometers, and in the end, comparison of the timing and magnitude of deformation and exhumation between the Lesser and Greater Himalayan Series.The Himalayan mountain range is a consequence of the ongoing collision between India and Asia. During collision, the sedimentary cover that had blanketed northern India for the last 1.8 billion years became detached from the underlying basement. This deformed sedimentary cover, and the structures that developed within it, record the deformation history of the collision. Although it is one of the world's most famous mountain ranges, only a handful of estimates quantify this deformation and there are no such estimates for the eastern portion of the mountain belt. This study of the deformed rocks in the Kingdom of Bhutan will provide new estimates for this poorly understood portion of the range and, when compared to estimates for other portions of the Himalayan Range, will lead to a better understanding of the development of collisional mountain belts. The project fosters scientific collaboration between scientists from Bhutan and the United States and helps to build scientific infrastructure in Bhutan by training of Bhutanese students and an improved knowledge of the geology of the country, which in turn is important for understanding earthquake hazards and natural resources.