西南天山北东东走向断裂的晚第四纪活动特征及在天山构造变形中的作用

发布时间：2018-03-23 08:22

  本文选题：天山　切入点：NEE向断裂　出处：《国际地震动态》2017年09期 　论文类型：期刊论文

【摘要】：天山是远离板块边界的陆内造山带,特点是构造变形复杂强烈,强震多发。天山南北向的变形速率约为20mm/a,约为印度板块与欧亚板块汇聚速率的一半左右,这一变形量是如何被天山吸收的,天山的构造变形又是如何进行的,其构造样式如何?这些关键性问题目前仍存在较大的争论。天山地区主要发育有3组构造带,最显著的是位于南北两侧山前与山体近乎平行的逆断层—褶皱带,同时,在山体内部还发育有一系列NW向的右旋走滑断裂和NEE向的左旋走滑断裂,这些断裂共同控制了天山的新生代构造变形。目前,对于天山山前的逆断裂系统晚第四纪变形特征和滑动速率等方面研究非常丰富,对天山内部NW向的右旋走滑断裂晚第四纪活动特征也有一些定量数据,而对NEE向断裂晚第四纪以来的活动特征目前尚处空白状态。本文以迈丹断裂为切入点,通过对该断裂晚第四纪以来的运动学特征、滑动速率和古地震活动特征等资料的详细研究,获得西南天山地区NEE向断裂晚第四纪活动参数,同时,通过收集和补充调查天山其他主要活动断裂晚第四纪以来的运动特征,完善天山活动断裂几何学和运动学图像;结合已有研究资料、地震活动特征和GPS数据,研究天山内部不同方向、不同运动性质的断裂的活动特征,分析天山这些断裂在天山的构造变形中发挥了怎样的作用,在此基础上进一步研究天山地区的构造变形样式及其与地震的关系。本文得到的主要认识有:迈丹断裂东段控制的阿合奇谷地内发育有多级晚第四纪地貌面,利用光释光、10Be暴露年龄以及14C等方法对玉山古溪两岸的阶地年龄进行了限定,并与气候变化序列进行了比对,得到阶地的废弃形成发生在间冰期或者冰期—间冰期的转换阶段。玉山古溪T6阶地(~20ka)之前,河流平均下切速率与迈丹断裂的活动速率基本一致,表明晚更新世晚期之前,河流的下切与阶地的形成主要受迈丹断裂活动影响,是构造隆升导致的河流快速下切。~20ka之后河流的下切速率开始增大,至全新世中晚期,河流下切速率甚至达到~12mm/a,远远大于断裂的活动速率,表明晚更新世末期以来,河流的下切与阶地的形成主要受气候因素驱动。全新世以来河流下切速率的快速增大,很可能是由于全新世期间气候快速波动造成的。迈丹断裂是一条全新世活动断裂,该断裂晚第四纪以来,以逆冲兼左旋走滑为主,通过精细测量被断错的晚第四纪地貌面和年代学测定,得到断裂的逆冲滑动速率为(1.24±0.20)mm/a,左旋走滑速率为(1.74±0.61)mm/a。迈丹断裂晚第四纪期间发生过多期断错地表的古地震事件,古地震平均复发间隔为3370~4265a,断裂最新一次古地震事件发生在1.76ka之后。迈丹断裂是柯坪推覆构造的根部断裂,该断裂晚第四纪以来发生过多次断错地表的强震事件。古地震研究表明,推覆体前缘的柯坪断裂晚第四纪以来也发生过多期古地震事件,而且两条构造上古地震事件的发生年代很接近,尽管我们并不能确定迈丹断裂最新一次古地震事件是否与柯坪塔格断裂上的是否为同一次事件,但这一现象反映该地区地震破裂存在两种可能:(1)迈丹断裂与柯坪塔格断裂上最新一次古地震事件是同一次事件,这表明迈丹断裂与柯坪塔格断裂具有级联破裂的特征;(2)迈丹断裂上最新一次古地震事件与柯坪塔格断裂上的不是同一期事件,分别单独破裂,虽然两条断裂上的古地震事件不是同期破裂,但均发生在~1.7ka之后,时间间隔不长,表明柯坪推覆构造根部的迈丹断裂和前缘的柯坪塔格断裂之间可能存在相互的影响或关联,柯坪地区的强震活动具有丛集发生的特征。迈丹断裂晚第四纪活动的发现,表明西南天山柯坪推覆构造与天山其他地区的推覆构造变形模式不同,推覆体最前缘的柯坪断裂活动强烈,而根部断裂晚第四纪以来也有很强的活动,断裂的新活动并没有完全迁移到推覆体前缘的新生构造带上,这可能是一种无序或反序的构造变形模式。西南天山地区的左旋走滑运动主要发生在推覆体根部的迈丹断裂上,推覆体前缘的逆断裂—背斜以逆冲运动为主,没有明显的走滑运动。GPS资料表明,普昌断裂以西的地区,应变没有完全闭锁集中在根部的迈丹断裂上,一部分应变通过滑脱面传递到前缘的逆断裂-背斜带上;在柯坪推覆构造的东部地区,从根部的迈丹断裂至前缘的柯坪塔格断裂可能是一个孕震体系,震间的形变主要在推覆体根部的构造上闭锁,前缘构造基本没有明显变形,这可能是柯坪推覆构造东西两侧中小地震活动存在明显差异的主要原因。西南天山还发育有两条NEE走向的断裂,通过变形地貌测量与年代学测定得到那拉提断裂晚第四纪以来以左旋逆冲运动为主,断裂逆冲速率~2.1 mm/a,左旋走滑速率为~2.5mm/a;克敏断裂也是一条左旋走滑断裂,断裂的左旋走滑速率为~1.5mm/a。西南天山3条NEE向的断裂带吸收了~6mm/a的左旋走滑运动,与塔里木斜向俯冲造成的左旋走滑运动量基本一致,这表明塔里木斜向俯冲造成的左旋走滑运动在西南天山地区基本被分解吸收。西南天山地区吸收了塔里木向天山俯冲汇聚绝大部分的压缩速率和左旋剪切运动,挤压缩短在山体内部和山前的新生褶皱带上均有分配,左旋剪切则主要发生在天山内部高角度的边界断裂上,整个西南天山构成了一个大型的花状构造。在天山南北两侧,构造变形以逆断层为代表的地壳缩短和增厚为特征,而天山内部则为一个大型的剪切带,同时还具有明显的逆冲运动。天山地区主要存在两组走滑断裂,一是NEE向的左旋走滑构造,另一组是NW-NWW向的右旋走滑断裂,这两组断裂主要发育在天山内部,但这些断裂共同调节了山体内部的走滑剪切运动,山体内部高角度的走滑逆冲断裂与山前低倾角的逆冲断裂系共同组成了天山构造变形图像。天山地区的压缩变形主要分布在天山南北两侧的山前地区,而天山内部的活动断裂则具有明显的走滑分量,在剖面上,整个天山形成了一个大型的花状构造。尽管天山整体的构造变形为西强东弱,不同地区变形强度和幅度差异较大,但是天山南北和东西两侧的构造变形样式还是基本对称的。受塔里木块体向北的挤压作用,西南天山地区总体走向为NEE向,南天山东段整体则呈NWW走向,与塔里木与南天山的分界断裂在形态上构成一个"三角形"向北楔入。整个西南天山内部是一个大型的左旋剪切带,南天山东段整体为右旋走滑性质,塔里木和南天山之间的边界断裂以逆冲运动为主。在天山北部受到刚性准噶尔地块阻挡的作用下,北天山西段构造线整体NW-NWW向,而90°E以东的北天山地区构造线整体为NEE走向,与近东西走向的准噶尔与北天山的分界断裂在形态上构成一个倒"三角形"向南楔入。北天山西段右旋走滑性质的博—阿断裂和喀什河断裂所围限的楔形块体整体向西运动,北天山东段NEE向的左旋走滑断裂构成了倒"三角楔"的东边界,准噶尔与北天山的分界逆冲断裂带是"三角楔"的底界。在近南北向的挤压应力下,天山的构造变形整体以压缩变形为主,山体内部发育的一系列走滑构造带表明,天山在东西方向上还存在一定的侧向挤出,这些走滑断裂调节了天山不同地区压缩量的差异。地质数据和GPS资料均证实,天山地区逆冲运动量要明显大于走滑分量,山体内部走滑断裂所控制的块体虽然存在向东西两侧的侧向挤出,但与南北向最大达~18mm/a的压缩速率相比,变形速率不高,侧向挤出幅度有限。
[Abstract]:Tianshan is far away from the plate boundary intracontinental orogenic belt, tectonic deformation characteristics are complex and strong, strong earthquake. The rate of deformation to the north and south of the Tianshan Mountains is about 20mm/a, about half of the India plate and the Eurasian plate convergence rate, the amount of deformation is to be absorbed by the Tianshan mountains, tectonic deformation and how the day the structural style? These key problems still exist great controversy. The main development of Tianshan area has 3 tectonic belts, most notably in the north and south sides of the Piedmont and mountain near parallel thrust - fold belt, at the same time, in the mountain also has a series of internal development NW to dextral strike slip fault and the NEE trending sinistral strike slip fault, the fault controlled the Tianshan Cenozoic tectonic deformation. At present, the inverse system of Late Quaternary fault slip rate and deformation characteristics of such research is very abundant in front of Tianshan Rich, on the inner Tianshan Mountains NW trending dextral strike slip characteristics of Late Quaternary active faults also have some quantitative data, and on the characteristics of faults since Late Quaternary NEE is still blank. This paper takes the Maidan fault as the starting point, based on the characteristics of the movement since the late Quaternary fault slip rate, detailed study and the characteristics of seismic activity data, Southwest Tianshan area NEE parameters to late Quaternary fault activity at the same time, the motion characteristics of the late Quaternary collection and other supplementary investigations of major active faults since the Tianshan, Tianshan perfect activity fracture geometry and kinematics of the image; combining with the existing research data, the characteristics of seismic activity and GPS data of inner Tianshan Mountains in different directions, different nature of the motion characteristics of the fault activities, analysis of these faults in Tianshan played what role in the tectonic deformation of Tianshan Mountains, on the basis of Further study on tectonic deformation style of Tianshan area and its relation with the earthquake. The main ideas are: the eastern section of the Akeqi Valley Maidan fault control developed in multistage late Quaternary geomorphic surfaces, using OSL, 10Be exposure age and 14C methods on Yushan ancient river terraces on both sides of the age were limited, and compared with climate change sequence, are abandoned terraces formation occurred in interglacial glacial and interglacial periods or conversion phase. Yushan ancient river terraces of T6 (~20ka), the average river incision rate and the rate of movement of the Maidan fault are basically the same, before that late Pleistocene, river incision formation and the main terrace affected by the Maidan fault activity, is caused by rapid uplift of river cut.~20ka river incision rate began to increase, and in the late Holocene, river incision rate even Up to ~12mm/a, far greater than the fault activity rate, indicates that since the late Pleistocene, river incision formation and terraces is mainly influenced by climate factors driving. A rapid increase in the Holocene river incision rate, probably due to rapid climate fluctuations during the Holocene. Maidan fault is a Holocene Active fault. The fault since late Quaternary, the thrust and strike slip, through the late Quaternary landforms fine measurements are fault plane and dating, get thrust slip rate for fracture (1.24 + 0.20) mm/a, sinistral slip rate is (1.74 + 0.61) mm/a. Maidan fault in Late Quaternary during ancient multi phase fault surface seismic events, the average recurrence interval of ancient earthquakes is 3370~4265a, breaking the latest paleoseismic events occurred after 1.76ka. Maidan fault is the root fracture of Kalpin nappe structure, the fault in the late section The four century have occurred since the events of fault surface. Many ancient seismic studies show that the front edge of the nappe Keping fault since Late Quaternary period also occurred in many ancient seismic events, and in the two ancient tectonic earthquake events is very close, although we can not determine whether the Maidan fault of the latest ancient earthquake the event and whether the kalpintag fault on the same event, but this phenomenon reflects the earthquake rupture area there are two possibilities: (1) the Maidan fault and kalpintag fault on the latest Paleaoearthquake events is the same event, which indicates that the characteristics of cascade rupture fracture and fracture of kalpintag Maidan; (2) on the Maidan fault of the latest ancient seismic event and kalpintag fault is not on the same stage, separately although ancient earthquake rupture, rupture fracture is not on the two over the same period, but occurred in ~1. After 7ka, the interval is not long, there may exist mutual influence or association between kalpintag fault show that the Kalpin thrust tectonic root Maidan fault and the leading edge, strong earthquake activity in Keping area has the features of cluster occurred. Late Quaternary activity of the Maidan fault that nappe tectonic deformation pattern show Kalpin thrust system in Southwest Tianshan and the other the different regions to push the Kalpin fracture nappe activities as the front of the strong, and the root fracture since the late Quaternary have very strong activity, new active faults and without new structure completely migrated to nappe front, it is possible to construct a deformation model of disordered or reverse order. Southwest Tianshan area of sinistral strike slip movement occurred mainly in the Maidan fault nappe root, reverse fault - anticline thrust nappe front to thrust movement, no obvious slip.GPS Data show that the Puchang west of the fault area, the strain did not fully concentrated in the roots of the Maidan fault block, a part of the strain transfer to the front of the reverse fault anticline belt through the detachment surface; in Kalpin nappe structure in the eastern region, from the roots to the front of the Maidan fault Ke Ping Qiulitage fault may be a the seismogenic system, mainly in the interseismic deformation tectonic nappe atresia roots, frontal structure basically no obvious deformation, this may be the main reason of Kalpin nappe structure on both sides of the earthquake are obviously different. Also there are two development in Southwest Tianshan Mountains NEE trending fracture, deformation and geochronology by topography measurement was obtained Nalati fault since Late Quaternary to sinistral thrust movement, fault thrust rate ~2.1 mm/a, sinistral slip rate is ~2.5mm/a; the fracture is a sensitive sinistral strike slip fault fault, l 璧版粦閫熺巼涓簙1.5mm/a.瑗垮崡澶╁北3鏉�NEE鍚戠殑鏂�瑁傚甫鍚告敹浜唦6mm/a鐨勫乏鏃嬭蛋婊戣繍鍔，

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