The timing and cause of mountain building in central Asia

板块构造（地球表面由一些刚性碎片组成，这些碎片只在边缘附近的窄带中变形）作为地球表面海洋部分行为的准确描述已经被接受了近40年。与此同时，同样清楚的是，大陆板块的行为与大洋板块不同。大陆的变形并不局限于边缘的狭窄地带，而是在其内部蔓延数百公里。一个主要的例子是印度与亚洲的碰撞，这导致了从喜马拉雅山延伸到西伯利亚的山脉的形成，距离超过3000公里。大陆构造学研究的一个基本挑战是理解引起所观察到的变形的力--大陆变形的“动力学”研究。在我们研究造山运动的动力学之前，我们必须首先了解变形是如何演变成我们今天所看到的状态的。因此，对造山运动开始的时间及其空间演化提供精确的限制，是理解大陆变形力学的核心。印度和亚洲之间的碰撞开始于4500万年前，喜马拉雅山和青藏高原的变形在那之后不久就被记录下来了。已知碰撞带北方主要山脉的形成要比南方的年轻得多，但这些北方山脉形成和随后增长的现有制约因素太少，无法全面考察印度-欧亚大陆碰撞发展过程中每个阶段的地理范围，因此也无法全面考察其可能原因。我建议对哈萨克斯坦和蒙古西部的天山、准噶尔、阿拉套山和阿尔泰山进行勘察研究。这些山脉构成了印度大陆与亚洲大陆碰撞的最北端，目前对它们的发展知之甚少。裂变径迹和U-Th/He热年代学对构造演化的制约作用。这些技术记录了地球顶部1-3公里处岩石的冷却情况，将与A。卡特特别令人感兴趣的问题是，为什么中亚山脉的变形比喜马拉雅山脉和西藏的变形要晚得多。一个可能的解释是，变形带的宽度逐渐增加，山脉的起始年龄向北移动。其他主要的建议是，1000 - 1500万年前青藏高原的快速上升在亚洲大陆引入了导致造山运动向北推进的力量，或者亚洲太平洋边缘力量的变化导致了大陆内部变形的重组。通过揭示哈萨克斯坦和蒙古西部的造山历史，并对历史上每个阶段的时间进行严格的年龄限制，我将能够区分这些不同的情景，这些情景是造成我们今天看到的山脉分布的力量。我们选择关注哈萨克斯坦和蒙古西部的造山历史，因为：（1）人们对这一地区山脉的构造历史知之甚少，但对了解亚洲大陆变形的机制可能非常重要;（2）这些山脉很容易进入，我们通过2011年7月的勘察访问在哈萨克斯坦有过旅行经验，因此我们有信心在一个实地考察季节内成功完成所有采样工作;（3）我们对蒙古西部阿尔泰地区样品的初步测量表明，存在构造上有用的冷却信号。

Plate tectonics (the idea that the Earth's surface consists of a few rigid fragments that deform only in narrow bands round their edges) has been accepted for almost 40 years as an accurate description of the behaviour of the oceanic parts of the Earth's surface. At the same time, it has been equally clear that the continents do not behave like the oceanic plates. Deformation in continents is not restricted to narrow bands at their edges, but is spread many hundreds of kilometres through their interiors. A major example is the the collision of India with Asia, which has led to the formation of mountains stretching from the Himalaya to Siberia, over a distance of 3000 km. A fundamental challenge in the study of continental tectonics is to understand the forces that give rise to the observed deformation - the study of the 'dynamics' of continental deformation. Before we can investigate the dynamics of mountain-building we must first develop an understanding of how the deformation has evolved to the state in which we see it today. Providing precise constraints on the times of initiation of mountain-building, and on its spatial evolution, are thus central to understanding the mechanics of continental deformation. The collision between India and Asia began more than 45 Million years ago, and deformation within the Himalaya and Tibetan Plateau is recorded very soon after that time. The initiation of the major mountain ranges in the northern part of the collision zone is known to be much younger than in the south, but the existing constraints on initiation and subsequent growth in these northerly ranges are too few in number for the full geographic extent, and hence the likely cause, of each stage in the development of the evolving India-Eurasia collision to be examined. I propose a reconnaissance study of the Tien Shan, Dzungar Alatau and Altay mountains of Kazakhstan and western Mongolia. These ranges constitute some of the northernmost parts of the collision between the continents of India with Asia, and very little is known of their development at present. Constraints on the tectonic evolution will come from fission-track and U-Th/He thermochronometry. These techniques, which record the cooling of rocks through the top 1-3 km of the Earth undertaking, will be performed in collaboration with Dr. A. Carter. Of particular interest is the question as to why deformation in the mountain ranges of central Asia started much later than in the Himalaya and Tibet. One potential explanation is that the deformation zone is gradually increasing in width, with the initiation ages of mountain ranges younging to the north. Other leading suggestions are that a rapid rise of the Tibetan plateau 10-15 Million years ago introduced forces in the Asian continent that caused mountain-building to step northwards, or that changes in the forces at the Pacific margin of the Asia caused reorganization of deformation within the interior of the continent. By unravelling the history of mountain building in Kazakhstan and western Mongolia, and by placing firm age constraints on the timing of each stage in their history, I will be able to distinguish between these differing scenarios for the forces responsible for producing the distribution of mountains we see at the present day.We have chosen to focus on the history of mountain building in Kazakhstan and western Mongolia because: (1) The tectonic history of the mountain ranges in this area is poorly understood but is potentially very important for understanding the mechanics of continental deformation in Asia; (2) The mountains are easily accessible, and we have experience of travel in Kazakhstan through a reconnaissance visit in July 2011, such that we are confident that all sampling can be completed successfully in one field-season; (3) Our initial measurements from samples collected from the Altay of western Mongolia indicate that tectonically useful cooling signals are present.