青藏高原西部喀喇昆仑断裂水平与垂直滑移速率和东南端位置的确定

The research we propose to embark upon within this proposal has two main focuses. We propose to improve to the next level, our understanding of one of the major active faults in Asia, the Karakorum fault (KF), located in western Tibet. Indeed, it has been the focus of many research groups recently, who attempted to determine its slip-rate at different timescales, with various techniques (GPS, InSAR, tectonic-geomorphology and long-term geologic) at different locations. However, despite the many recent results, the slip-rate along the KF remains debated (0-11 mm/yr), and whether it varies with time and/or location remains unknown. Chevalier et al. (2005a,b, 2006, 2011b, 2012) has devoted many efforts to suggest that the KF horizontal slip-rate seems to be spatially constant, maybe over its entire length. However, no studies yet attempted to quantify the normal slip component of the KF (which is dominant at places), nor to quantify the slip or activity along secondary branches (such as along the southern side of the Ayilari Range or the northern part of the Gar basin), nor focused of the location of its eastern terminus, which is highly debated. Is the KF going eastwards along the Yarlung Zangbo suture or south to the Pulan graben or both. We propose within this proposal to focus on three main studies about the KF: 1) to determine its normal slip-rate at various places along the fault, 2) to determine its horizontal and/or vertical slip-rate on the Holocene timescale to eventually compare the results with those determined with InSAR or GPS and discuss a possible slip-rate variation with time, and 3) investigate the activity along secondary branches such as the southern Ayilari Range and the northern part of the Gar basin, and more importantly, examine the Yarlung Zangbo into details to find evidence if the KF continues eastward of the Kailas or continues just southward into the Pulan graben.

青藏高原西北部的喀喇昆仑断裂是近年来众多研究关注的热点地区之一，曾通过多种技术手段（GPS、InSAR，构造地貌和地质学）在不同位置和不同时间尺度上进行过断裂滑移速率的研究，但至今有关沿喀喇昆仑断层的滑移速率仍存在争议。本项目拟通过野外考察及地貌位错测量，结合室内的宇宙成因核素测年工作，确认喀喇昆仑断裂是否存在短期（全新世以来）滑移速率、长期（第四纪以来）滑移速率和大地测量（近十年以来）滑移速率之间的差别，同时准确获得喀喇昆仑断裂包括水平运动和垂直运动在内的总的滑移速率，这对我们正确理解和认识喀喇昆仑断裂在的青藏高原现今变形中的作用具有重要意义。

本项目围绕青藏高原西部喀喇昆仑断裂展开研究，发表了一些新的结论，包括发表的四篇文章（分别发表在Gondwana Research, Geological Society of America Bulletin, Terra Nova and Earth and Planetary Science Letters期刊上）。具体内容如下：.1） 沿喀喇昆仑断裂中段晚第四纪以来右旋走滑速率大于3毫米/年，到南东段增加到8毫米/年。.2） 喀喇昆仑断裂在大于1000km、大于13-23Ma的时空范围下的走滑速率表明其协调了西喜马拉雅北东段的右旋走滑运动。.3） 在喀喇昆仑断裂的北西末端，公格尔山伸展断裂系统协调了由于帕米尔向北突出挤压作用造成的东西向的伸展。由于公格尔山伸展断裂系统是正断性质而喀喇昆仑断裂是走滑性质，有些人认为公格尔山伸展系统不是喀喇昆仑断裂的一部分。然而，我们找到了证据来证明公格尔山伸展断裂系统也具有右旋走滑的性质，例如，北西段木吉断裂的右旋走滑速率大于3-4mm/yr，南东段的塔合曼断层也有1mm/yr的右旋走滑。.4） 我们用什么是活动走滑断裂系统的基本定义，强调时间刻度的重要性来讨论断裂是否是活动的，证明了喀喇昆仑断裂和公格尔山伸展系统是同一断裂系统的两个部分。.5） 青藏高原西部另一个重要的活动断层是左旋走滑的龙木错-郭扎错断裂，这也是阿尔金主断裂的西段。研究显示龙木错-郭扎错断裂晚第四纪以来的走滑速率小于3毫米/年，这与大地测量和板块构造模型的研究结果相一致。.6） 龙木错-郭扎错断裂的走滑速率与喀喇喀什断裂的走滑速率（2mm/yr）相一致，但是这要比阿尔金断裂和喀喇昆仑断裂的走滑速率（分别是9mm/yr和8mm/yr）小，这说明有几毫米每年的伸展被阿什库勒地堑所吸收。附近很多近期的构造事件的证据显示其强烈的活动性，如1951年的火山喷发，2008和2014年的于田7.3级地震。.7） 龙木错-郭扎错断裂呈阶梯状的特征并且与阿尔金断裂运动方向相同，与周围的断裂比，有较小的走滑位错和走滑速率，这表明阿尔金断裂的这一段可能是最年轻的。.8） 龙木错-郭扎错左旋走滑断裂系统和此处两个主要断裂阿尔金断裂以及喀喇昆仑断裂共同形成一个三角结，控制着青藏高原向东的挤压作用。