發(fā)布時間：2018-03-23 08:22

  本文選題：天山　切入點：NEE向斷裂　出處：《國際地震動態(tài)》2017年09期 　論文類型：期刊論文

【摘要】：天山是遠離板塊邊界的陸內(nèi)造山帶,特點是構造變形復雜強烈,強震多發(fā)。天山南北向的變形速率約為20mm/a,約為印度板塊與歐亞板塊匯聚速率的一半左右,這一變形量是如何被天山吸收的,天山的構造變形又是如何進行的,其構造樣式如何?這些關鍵性問題目前仍存在較大的爭論。天山地區(qū)主要發(fā)育有3組構造帶,最顯著的是位于南北兩側山前與山體近乎平行的逆斷層—褶皺帶,同時,在山體內(nèi)部還發(fā)育有一系列NW向的右旋走滑斷裂和NEE向的左旋走滑斷裂,這些斷裂共同控制了天山的新生代構造變形。目前,對于天山山前的逆斷裂系統(tǒng)晚第四紀變形特征和滑動速率等方面研究非常豐富,對天山內(nèi)部NW向的右旋走滑斷裂晚第四紀活動特征也有一些定量數(shù)據(jù),而對NEE向斷裂晚第四紀以來的活動特征目前尚處空白狀態(tài)。本文以邁丹斷裂為切入點,通過對該斷裂晚第四紀以來的運動學特征、滑動速率和古地震活動特征等資料的詳細研究,獲得西南天山地區(qū)NEE向斷裂晚第四紀活動參數(shù),同時,通過收集和補充調查天山其他主要活動斷裂晚第四紀以來的運動特征,完善天山活動斷裂幾何學和運動學圖像;結合已有研究資料、地震活動特征和GPS數(shù)據(jù),研究天山內(nèi)部不同方向、不同運動性質的斷裂的活動特征,分析天山這些斷裂在天山的構造變形中發(fā)揮了怎樣的作用,在此基礎上進一步研究天山地區(qū)的構造變形樣式及其與地震的關系。本文得到的主要認識有:邁丹斷裂東段控制的阿合奇谷地內(nèi)發(fā)育有多級晚第四紀地貌面,利用光釋光、10Be暴露年齡以及14C等方法對玉山古溪兩岸的階地年齡進行了限定,并與氣候變化序列進行了比對,得到階地的廢棄形成發(fā)生在間冰期或者冰期—間冰期的轉換階段。玉山古溪T6階地(~20ka)之前,河流平均下切速率與邁丹斷裂的活動速率基本一致,表明晚更新世晚期之前,河流的下切與階地的形成主要受邁丹斷裂活動影響,是構造隆升導致的河流快速下切。~20ka之后河流的下切速率開始增大,至全新世中晚期,河流下切速率甚至達到~12mm/a,遠遠大于斷裂的活動速率,表明晚更新世末期以來,河流的下切與階地的形成主要受氣候因素驅動。全新世以來河流下切速率的快速增大,很可能是由于全新世期間氣候快速波動造成的。邁丹斷裂是一條全新世活動斷裂,該斷裂晚第四紀以來,以逆沖兼左旋走滑為主,通過精細測量被斷錯的晚第四紀地貌面和年代學測定,得到斷裂的逆沖滑動速率為(1.24±0.20)mm/a,左旋走滑速率為(1.74±0.61)mm/a。邁丹斷裂晚第四紀期間發(fā)生過多期斷錯地表的古地震事件,古地震平均復發(fā)間隔為3370~4265a,斷裂最新一次古地震事件發(fā)生在1.76ka之后。邁丹斷裂是柯坪推覆構造的根部斷裂,該斷裂晚第四紀以來發(fā)生過多次斷錯地表的強震事件。古地震研究表明,推覆體前緣的柯坪斷裂晚第四紀以來也發(fā)生過多期古地震事件,而且兩條構造上古地震事件的發(fā)生年代很接近,盡管我們并不能確定邁丹斷裂最新一次古地震事件是否與柯坪塔格斷裂上的是否為同一次事件,但這一現(xiàn)象反映該地區(qū)地震破裂存在兩種可能:(1)邁丹斷裂與柯坪塔格斷裂上最新一次古地震事件是同一次事件,這表明邁丹斷裂與柯坪塔格斷裂具有級聯(lián)破裂的特征;(2)邁丹斷裂上最新一次古地震事件與柯坪塔格斷裂上的不是同一期事件,分別單獨破裂,雖然兩條斷裂上的古地震事件不是同期破裂,但均發(fā)生在~1.7ka之后,時間間隔不長,表明柯坪推覆構造根部的邁丹斷裂和前緣的柯坪塔格斷裂之間可能存在相互的影響或關聯(lián),柯坪地區(qū)的強震活動具有叢集發(fā)生的特征。邁丹斷裂晚第四紀活動的發(fā)現(xiàn),表明西南天山柯坪推覆構造與天山其他地區(qū)的推覆構造變形模式不同,推覆體最前緣的柯坪斷裂活動強烈,而根部斷裂晚第四紀以來也有很強的活動,斷裂的新活動并沒有完全遷移到推覆體前緣的新生構造帶上,這可能是一種無序或反序的構造變形模式。西南天山地區(qū)的左旋走滑運動主要發(fā)生在推覆體根部的邁丹斷裂上,推覆體前緣的逆斷裂—背斜以逆沖運動為主,沒有明顯的走滑運動。GPS資料表明,普昌斷裂以西的地區(qū),應變沒有完全閉鎖集中在根部的邁丹斷裂上,一部分應變通過滑脫面?zhèn)鬟f到前緣的逆斷裂-背斜帶上;在柯坪推覆構造的東部地區(qū),從根部的邁丹斷裂至前緣的柯坪塔格斷裂可能是一個孕震體系,震間的形變主要在推覆體根部的構造上閉鎖,前緣構造基本沒有明顯變形,這可能是柯坪推覆構造東西兩側中小地震活動存在明顯差異的主要原因。西南天山還發(fā)育有兩條NEE走向的斷裂,通過變形地貌測量與年代學測定得到那拉提斷裂晚第四紀以來以左旋逆沖運動為主,斷裂逆沖速率~2.1 mm/a,左旋走滑速率為~2.5mm/a;克敏斷裂也是一條左旋走滑斷裂,斷裂的左旋走滑速率為~1.5mm/a。西南天山3條NEE向的斷裂帶吸收了~6mm/a的左旋走滑運動,與塔里木斜向俯沖造成的左旋走滑運動量基本一致,這表明塔里木斜向俯沖造成的左旋走滑運動在西南天山地區(qū)基本被分解吸收。西南天山地區(qū)吸收了塔里木向天山俯沖匯聚絕大部分的壓縮速率和左旋剪切運動,擠壓縮短在山體內(nèi)部和山前的新生褶皺帶上均有分配,左旋剪切則主要發(fā)生在天山內(nèi)部高角度的邊界斷裂上,整個西南天山構成了一個大型的花狀構造。在天山南北兩側,構造變形以逆斷層為代表的地殼縮短和增厚為特征,而天山內(nèi)部則為一個大型的剪切帶,同時還具有明顯的逆沖運動。天山地區(qū)主要存在兩組走滑斷裂,一是NEE向的左旋走滑構造,另一組是NW-NWW向的右旋走滑斷裂,這兩組斷裂主要發(fā)育在天山內(nèi)部,但這些斷裂共同調節(jié)了山體內(nèi)部的走滑剪切運動,山體內(nèi)部高角度的走滑逆沖斷裂與山前低傾角的逆沖斷裂系共同組成了天山構造變形圖像。天山地區(qū)的壓縮變形主要分布在天山南北兩側的山前地區(qū),而天山內(nèi)部的活動斷裂則具有明顯的走滑分量,在剖面上,整個天山形成了一個大型的花狀構造。盡管天山整體的構造變形為西強東弱,不同地區(qū)變形強度和幅度差異較大,但是天山南北和東西兩側的構造變形樣式還是基本對稱的。受塔里木塊體向北的擠壓作用,西南天山地區(qū)總體走向為NEE向,南天山東段整體則呈NWW走向,與塔里木與南天山的分界斷裂在形態(tài)上構成一個"三角形"向北楔入。整個西南天山內(nèi)部是一個大型的左旋剪切帶,南天山東段整體為右旋走滑性質,塔里木和南天山之間的邊界斷裂以逆沖運動為主。在天山北部受到剛性準噶爾地塊阻擋的作用下,北天山西段構造線整體NW-NWW向,而90°E以東的北天山地區(qū)構造線整體為NEE走向,與近東西走向的準噶爾與北天山的分界斷裂在形態(tài)上構成一個倒"三角形"向南楔入。北天山西段右旋走滑性質的博—阿斷裂和喀什河斷裂所圍限的楔形塊體整體向西運動,北天山東段NEE向的左旋走滑斷裂構成了倒"三角楔"的東邊界,準噶爾與北天山的分界逆沖斷裂帶是"三角楔"的底界。在近南北向的擠壓應力下,天山的構造變形整體以壓縮變形為主,山體內(nèi)部發(fā)育的一系列走滑構造帶表明,天山在東西方向上還存在一定的側向擠出,這些走滑斷裂調節(jié)了天山不同地區(qū)壓縮量的差異。地質數(shù)據(jù)和GPS資料均證實,天山地區(qū)逆沖運動量要明顯大于走滑分量,山體內(nèi)部走滑斷裂所控制的塊體雖然存在向東西兩側的側向擠出,但與南北向最大達~18mm/a的壓縮速率相比,變形速率不高,側向擠出幅度有限。
[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EE鍚戠殑鏂甯﹀惛鏀朵簡~6mm/a鐨勫乏鏃嬭蛋婊戣繍鍔，

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