How Do Intracontinental Faults Terminate? The Altyn Tagh Fault and Its Connection With a Possible S-Directed Backthrust System in Western Tibet as a Type Example

陆内断层如何终止？

• 批准号: 0310415
• 负责人: Eric Cowgill
• 金额: $ 22.81万
• 依托单位: University of California-Davis
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2003
• 资助国家: 美国
• 起止时间: 2003-06-01 至 2007-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0310415&HistoricalAwards=false
• 关键词: How; Do; Intracontinental; Faults; Terminate

There are currently two mutually exclusive views of continental deformation: either continents deform heterogeneously by breaking into microplates or they deform homogenously as continua. Distinguishing between these views centers on determining the extent to which intracontinental faults link to form microplate-boundary systems that remain active for tens to hundreds of millions of years. The Indo-Asian collision presents an excellent opportunity to understand the long-term evolution of fault linkages since it has been active throughout the Cenozoic and is cut by a number of major faults. The left-lateral Altyn Tagh fault is the largest of these structures, and has been active since the early stages of the collision. Understanding how this fault terminates is critical for determining if it has formed part of a long-lived microplate-boundary system. A field-based structural and thermochronologic study is testing the hypothesis that the western end of the Altyn Tagh fault linked with an early Cenozoic, south-directed backthrust belt. Field mapping and cooling histories derived from 40Ar/39Ar analyses of basement K-feldspars together indicate that three faults are key structures within this hypothesized south-directed backthrust belt. Whether the structural evolution of these three fault systems is consistent with predictions of the backthrust hypothesis, the following are are being determined for each fault system: 1) the geometry and history of motion, 2) the timing of deformation, 3) the total Cenozoic offset, and 4) how these faults link with the Altyn Tagh system. The study focuses on the Karakax, Yulung, and Loqzung systems. The Karakax fault is presently an active, north-dipping strike-slip fault but appears to have an earlier history of reverse/thrust motion. The Yulung fault system cuts Tertiary volcanics and may have uplifted a range of 6800 m peaks during south-directed thrusting. Within the Loqzung fault system, Cretaceous and Tertiary strata are locally deformed by south-directed structures. If the backthrust hypothesis is correct, the Altyn Tagh fault formed part of a microplate-boundary system that has existed since the earliest stages of the Indo-Asian collision. This result would support the microplate model for the Indo-Asian collision zone and contradict the idea that continental deformation is fundamentally homogeneous at long time scales.

目前有两种相互排斥的大陆变形观点：要么大陆变形不均匀，分裂成微板块，要么它们变形均匀连续。 区分这些观点的核心是确定陆内断层连接形成微板块边界系统的程度，这些微板块边界系统保持活跃了数千万到数亿年。 印度-亚洲碰撞提供了一个很好的机会，了解长期演变的断层联系，因为它一直活跃在整个新生代，并切断了一些主要的断层。 阿尔金左行断层是这些构造中最大的，自碰撞早期以来一直活动。 了解这种故障如何终止是至关重要的，以确定它是否已形成一个长期存在的微板边界系统的一部分。 一项基于野外的构造和热年代学研究正在检验阿尔金断层西端与新生代早期向南逆冲带相连的假设。 根据对基底钾长石的40 Ar/39 Ar分析得出的现场测绘和冷却历史表明，这三个断层是这一假设的南向逆冲带中的关键结构。 无论这三个断层系统的构造演化是否与逆冲推覆假说的预测相一致，对于每一个断层系统，以下是正在确定的：1）几何形状和运动历史，2）变形时间，3）总的新生代偏移，以及4）这些断层如何与阿尔金系统连接。 研究的重点是Karakax，裕隆和Loqzung系统。 Karakax断层目前是一个活跃的，北倾走滑断层，但似乎有一个早期的反向/逆冲运动的历史。 玉龙断裂系统切割第三纪火山岩，并可能在向南逆冲过程中抬升了6800米的山峰。 在洛宗断裂系统内，白垩系和第三系地层受到南向构造的局部变形。 如果逆冲推覆假说是正确的，那么阿尔金断层就形成了一个微板块边界系统的一部分，这个系统自印支-亚洲碰撞的最早阶段就存在了。 这一结果将支持印支-亚洲碰撞带的微板块模型，并与大陆变形在长时间尺度上基本均匀的观点相矛盾。