由断头河道确定阿尔金断层百万年尺度的滑动速率

The sinistral Altyn Tagh fault (ATF) transfers the contractional deformation northward, with the Indian plate indenting into the Eurasian continent. Therefore, slip rates of the ATF become key parameters to understand the buildup mechanics of the Himalaya-Tibet orogen and the extrusion of southeast and east Eurasia. Slip rates of the ATF from decade to 100,000-year scale have been constrained by analyzing offsets of geomorphic and geologic markers as well as satellite-based geodesy. These results are in almost consistent with each other. However, its “real-time” and average slip rates over millions of years are still not well known until now. We have found three beheaded channels in the north-northwest wall block of the ATF, the southeast Tarim. Their sedimentary characteristics are very similar to river-bed sediments of the modern Danghe River, and their ages get younger from west to east according to weathering degree of gravels of the beheaded channels beds and banks. Based on these facts observed, we put forward a kinematic model to interpret the formation process of the four beheaded channels. The channel of the long-lived Danghe river is offset gradually to form a kink-like segment along the ATF with accumulating of the ATF’s strike-slipping. With lengthening of the kink-like segment, a sudden flood event could result in abandoning of the downstream channel in the downhill direction to the ATF. The abandoned channel in the downhill is termed a beheaded channel. At the same time as abandoning, a new downstream channel in the downhill direction to the ATF, exactly juxtaposing with the upstream channel in the uphill, is worked out. While, the upstream channel in the uphill is still fixed due to north-northeast rafting of the south-southeast wall block of the ATF. This process has repeat by several times and several beheaded channels have been produced. These three beheaded channels have recorded the sinistral strike-slipping of the ATF over millions of years. Therefore, we propose to argument that the beheaded channels with the modern Danghe river share the same source region by analyzing characteristic parameters of the clasts in all the channels mentioned above, and composing KDE diagrams of detrital zircon ages populations of all the channels, to test our hypothesis kinematic model of the formation process of the beheaded channels. And we will date the formation and abandonment ages of all the beheaded channels and measure the slips recorded by them, and then calculate the “real-time” and average slip rates of the ATF, and then analyze the planar growth rate of the northern Tibetan plateau.

阿尔金断层的滑动速率是确定喜马拉雅-青藏高原造山带及欧亚大陆东南部变形机制的关键参数之一。构造地貌、古地震和天基大地测量约束了阿尔金断层十至十万年尺度的滑动速率，但更长时间尺度的“瞬时”和平均滑动速率尚待认识。我们在阿尔金断层北北西盘发现了三条河床沉积物与现代党河相似、自东而西逐条变老的断头河道。他们可能的形成过程是党河被阿尔金断层左行错折，随着错折量的增大，突发的洪水事件导致正对山区河道的下坡向形成了新河道，原有河道被废弃，而山区的河道持续保持稳定。这些废弃河道是数百万年尺度内阿尔金断层活动的连续地质记录。我们提出，构建各条断头河道和党河主干河床碎屑的特征参数、关键砾石的岩石学、碎屑锆石年龄谱，分析、论证各断头河道为党河在断层北侧的废弃古河道；测定断头河道的断距及其形成和废弃年龄，检验系列断头河道形成的运动学模型，约束阿尔金断层百万年尺度的滑动速率，进而分析高原向北的平面扩展速率。

阿尔金断层的左行走滑运动改造了党河河道。现代党河中游河床碎屑的岩石组分和碎屑锆石年龄谱与雁丹徒沟、沙山-山水沟和东沟-西土沟中基本一致，表明为他们是党河因阿尔金断层左行运动而废弃的中下游河道。他们分别记录了～49.5 km、～30.3 km和～19.2 km的滑动。风化强度表明他们的年龄在西而东变新。.阿尔金断层阿克赛挤压性转折段的活动造成阿克赛山的隆升。地震勘探揭示阿克赛山北麓山前为延伸至地表、向北前积的层序。这套前积层序的碎屑成分显示他们源于阿克赛山。因此，这套沉前积序记录了阿克赛挤压转折段的活动历史，其底界是阿克赛段开始活动的地质记录，暗示了阿尔金断层贯穿至该段的时间。.钻孔变形和钻具破坏显示2019年3月28日茫崖Mw 5.04级地震的同震破裂面积为45.30±10.24 km^2，最大同震滑动为400±13 mm，破裂面的倾角为～38.6°。由这些参数计算得到的地震矩为(1.81±0.47)×10^17 Nm，地震矩震级为Mw 5.47±0.16。石油地震勘探揭示这次地震的发震断层为向南西运动的英雄岭逆冲断层系统。这个断层系统的平均滑动速率为～0.2到～0.3 mm/yr。这个断层系统的面积和特征性的同震滑动表明其有产生Mw 7.65±0.03地震的潜力。.一条长～323.2 km、穿过西昆仑前陆的石油地震勘探剖面揭示了西昆仑造山带-塔西南前陆盆地系统的演化。～40 Ma到～30 Ma塔西南前陆盆地相对造山带的移动表明塔里木地块在向西昆仑的下冲过程中表现为粘弹性挠曲变形。～30 Ma以来，塔里木地块的下冲速率为～8.18 mm/y，包括~3.8–5.7 mm/yr的盆山系统缩短速率和西昆仑的侧向生长速率～4.4–2.5 mm/yr。前陆沉积层序的最底部表明西昆仑从～40 Ma开始隆升。前陆盆地的沉积速率在～11 Ma达到最大，并持续至今，表明西昆仑此时已达到了现在的有效高程。前陆沉积层序累积范围的突然增大表明塔里木地块的现代盆地地形自～25 Ma开始出现。.数值模拟显示，渐新世晚期，塔里木地块的南、北挠曲拗陷干涉形成盆地中部的挠曲隆起。～26 Ma以来，这个挠曲隆起向西昆仑移动了～52 km。塔里木地块披覆沉积层序的厚度从～26 Ma的230±30 m增加到现在的1910±200 m，这导致地块基准面抬升了356±80 m。