【作者】 李海兵；

【导师】 许志琴； 杨经绥；

【作者基本信息】 中国地质科学院 ， 构造地质学， 2001， 博士

【摘要】 本文通过对阿尔金断裂带中段出露的糜棱岩进行了详细的变形构造、变质岩石学、地球化学、同位素年代学及矿物包裹体的研究，提出了阿尔金断裂带的形成时代，并探讨了阿尔金断裂带最大累计走滑位移量，同时对走滑过程中伴随隆升作用进行了定量研究，以及活动走滑作用与逆冲作用的耦合关系及其与伸展作用的调节关系的研究，初步认识了走滑作用对高原北部隆升的贡献。阿尔金断裂带中段出露一套花岗质和角闪质糜棱岩及糜棱岩化岩石，经研究表明这套岩石是左行走滑剪切过程中同构造深熔作用的产物，是韧性转换挤压作用的结果。并在糜棱岩中首次发现剪切作用下形成的定向排列的长柱状深熔型锆石，这种锆石的晶体长轴方向与拉伸线理方向一致，代表走滑剪切过程中的构造应力方向。这一发现不仅说明能够利用定向锆石U-Pb同位素测年来确定构造年龄，而且为确定阿尔金断裂的形成时代奠定了基础。利用单颗粒锆石离子探针（SHRIMP）定年测得这种定向排列锆石的年龄为239—244Ma，另外，测得同样糜棱岩样品中定向生长的角闪石的⁴⁰Ar-³⁹Ar年龄为223—226Ma，表明了同构造深熔作用发生在印支期，说明阿尔金断裂带至少在印支期发生了强烈的走滑运动。在阿尔金断裂带东段北大窑-红柳峡地区出露一套来自于上地幔的橄榄玄武岩，在红柳峡地区其火山岩的K-Ar年龄为106—112Ma，而切割其火山岩的火山岩脉的⁴⁰Ar-³⁹Ar年龄为83Ma，在北大窑地区，发育在断裂带内的橄榄玄武岩的K-Ar年龄为99-105Ma，这套火山岩以熔岩层的形式被夹在白垩纪地层中，故时代为白垩纪，并且这套层状的火山岩已发生了同斜褶皱，同时，在阿尔金断裂带东侧、祁连山北缘，所伴随走滑过程形成的逆冲叠置岩片（J）中发现了大量的无根同逆冲构造的花岗岩浆活动，表明了阿尔金断裂带在走滑过程中，地壳加厚并产生了地壳熔融，由此可见，其83—112Ma火山岩的存在，是阿尔金断裂带再活动的证据。利用TM和SPOT卫星影像资料以及野外和室内的地貌学、构造地质学、岩石学及沉积学、年代学研究发现，在阿尔金断裂带中段发育一种特殊的长条状谷地地貌，其长宽比约大于50，谷地两侧的长边界由直线型具走滑分量的正断裂控制，谷地内分布新生代地层，阿尔金主断裂通过谷地，并在谷地内形成一系列走滑地貌。以谷地为中心两侧为反向的逆冲构造，使谷地两侧的由古老变质岩组成的地质体垂向挤出，构成长条形山体，这种特殊地貌我们称之为走滑断陷谷地（盆地）。这种巨型长条状走滑断陷谷地于上新世开始形成，全新世时期其地貌特征基本形成，它是阿尔金断裂带走滑变形过程中形成的特殊类型的地貌，是转换挤压作用和隆升作用的共同结果。这一认识的提出对认识谷地（盆地）、山脉之间的成因关系，以及早期古老地质体快速抬升的成因及山脉的形成具有重要意义。阿尔金断裂带走滑变形过程中伴随有强烈的隆升作用，其方式、规模各不相同。断裂带走滑过程中的隆升作用是以古老块体的抬升形式而表现。抬升形式总体以“逆冲构造+走滑构造”为主，根据构造组合特征划分为四种类型。党河南山是阿尔金断裂带走滑过程中形成的。阿尔金断裂带的肃北，阿克塞地区全新世以来的左行走滑速率为20-22mm／yr，伴随的隆升速率为5-11mm／yr。阿尔金断裂带走滑、逆冲、伸展之间可相互调节，肃北党河南山地区走滑速率从22.5mm／yr变为17mm／yr，部分能量转化为5mm／yr隆升速率造成山脉（党河南山）的形成和4mm／yr的伸展速率形成肃北盆地。在前人研究的基础上，通过变形构造几何学、岩石学以及区域构造对比研究，提出了在早古生代时期西昆仑和阿尔金南缘、柴北缘处于相同的构造背景之中，阿尔金榴辉岩带向西可能延至西昆仑，以及柴北缘蛇绿岩带向西与阿尔金南缘蛇绿岩带相连，再向西与西昆仑库地北蛇绿岩带相连，后被阿尔金断裂所切割。因此，得出了阿尔金断裂最大累计左行走滑位移量大约为900公里。阿尔金断裂带走滑过程中一部分能量转化为分支的逆冲断裂，逆冲作用使得前新生代地质体抬升成山。因此其走滑作用形成和控制了祁漫塔格山、党河南山、祁连山的崛起和分布，并控制了青藏高原北部生长、扩展的方向和调整、制约了盆—山耦合关系。对阿尔金断裂带形成时代研究的同时对活动走滑作用与逆冲作用的耦合关系研究及走滑作用对高原北部隆升的贡献研究，不仅对重塑阿尔金断裂带的演化历史具有重要意义，而且也为建立青藏高原的形成尤其是高原北部的隆升和扩展模型提供直接的基础资料。更多还原

【Abstract】 Through the detailed studies of deformed structure, metamorphic petrology, geochemistry, isotopicchronology and mineral inclusion on mylonites outcropped in the middle part of Altyn Tagh fault zone, theauthor gives the formation age of Altyn Tagh fault zone. The author also discusses its maximalaccumulated strike-slip displacement and carries out the quantitative research on the subsequent upliftingin the course of strike-slipping and that on the coupling relationship between the active strike-slipping andthe obduction as well as the coordinate relationship between the active strike-slipping and extending. Thusthe contribution of strike-slipping to the uplifting of North Qinghai-Tibet plateau is preliminarily pointedout in this paper.In the middle part of Altyn Tagh fault zone, there outcrops a set of granitic and hornblende mylonites,and mylonited rocks, which is shown to be products of syntectonic anatexis during the left-handed strike-slip shearing and to be results of ductile transformed compression. The author for the first time discoversthe anateetic orientated long columnar zircon formed during shearing in mylonites, whose crystal long axisis accordant with the direction of stretching lineation, representing the orientation of structural stressduring strike-slip shearing. This discovery not only enables us to determine the structural age by U-Pbisotopic dating on orientated zircon, but also provides clue to determine the formation age of Altyn Taghfault zone. According to dating by single grained zircon ion microprobe （SHRIMP）, the age of theorientated zircon is 239 to 244Ma while the age of orientated hornblende by ⁴⁰Ar-³⁹Ar is 233 to 226Ma onthe same sample of mylonite. It indicates that the syntectonic anatex happened in Indo-Chinese epoch andthat a strong strike-slip movement ever took place in Altyn Tagh fault zone in the same epoch.In the area of Beidayao-Hongliuxia, the east part of Altyn Tagh fault zone, there outcrops a set ofdorgalite from upper mantle. In Hongliuxia, the age of volcanic rock by K-Ar is 106 to 112Ma while theage of the volcanic vein cutting the volcanic rock by ⁴⁰Ar-³⁹Ar is 83Ma. In Beidayao, the age of dorgalitegrown in the fault zone by K-Ar is 99 to 105Ma. This set of volcanic rocks in form of lava layer isintercalated in cretaceous strata, so the age is cretaceous. In this set of banded volcanic rocks, there existhomoclinal folds. In the eastern side of Altyn Tagh fault zone and the north of Qilian mountain, a largeamount of rootless syntectonic obducted magma is found within the obducted superimposed microlithonformed during the subsequent Strike-slipping. All indicate the crust increases in thickness and happens tomelt during the strike-slipping of Altyn Tagh fault zone, and then the existence of 83 to 112Ma volcanicrocks is the evidence for re-action of Altyn Tagh fault zone.According to TM & SPOT satellite data and outdoor & indoor studies on geomorphology, structuralgeology, petrology, sedimentology, chronology, it is found that there exists a special extended valley in themiddle part of Altyn Tagh fault zone. Its ratio of length and width is about more than 50 and the two sides’boundaries are controlled by the straightened normal fault with strike-slipping. Within the valley, theCenozoic strata are distributed. And Altyn Tagh fault zone passes through it and forms a series ofstrike-slip geomorphological terrace. Centered on the valley, the two sides are antithetic obducted faults,making the two sides’ geological blocks composed of old metamorphic rocks being squeezed vertically, constituting extended hills. We call this special geomorphological terrace strike-slip fault valley （basin）.This kind of macroscopic extended strike-slip fault valley began to form in Pliocene epoch and basicallycame into being in Holocene epoch, which is a special typed geomorphological terrace formed during thedeformation of strike-slipping in Altyn Tagh fault zone and joint result of transpression and uplifting. Thisis of great importance to understand the genetic relations of the valley （basin） and mountain range, and theorigin of early old geological blocks’ quick uplifting and the formation of the mountain range.Altyn Tagh fault zone ever happened to strongly uplift subsequently during its strike-slip deformation,but its way and scale are different. The uplifting during the fault zone’s strike-slipping is taken on as theuplifting of the old geological blocks. The uplifting pattern generally focuses on "obducted fault + strike-slip fault". According to the characteristics of structure pattern, the uplifting pattern can be divided intofour types. Mount Danghenan is formed during the strike-slipping of Altyn Tagh fault zone.In Subei and Akesai in Altyn Tagh fault zone, the rate of the left-handed strike-slipping is 20 to22mm/yr since Holocene epoch and the subsequent uplifting rate is 5 to 11mm/yr. In Altyn Tagh fault zone,the strike-slipping, obduction and stretching can be coordinated. In Mount Danghenan of Subei, the rate ofstrike-slipping changes from 22.5mm/yr to 17mm/yr, part of which is transformed to be uplifting rate5mm/yr forming the range （Mount Danghenan） and to be stretching rate 3mm/yr forming Subei basin.On the basis of predecessors’ research, through the comparative studies on deformed structuralgeometry, petrology and regional structure, the author thinks that West Kunlun, South Altyn and NorthQaidam are situated in the same structural background in Early Paleozoic era. Altyn eclogitic zonepossibly extends west to West Kunlun. And North Qaidam ophiolitic zone in the west is connected withSouth Altyn ophiolitic zone and towards west continually being attached to Kudlibei ophiolitic zone ofWest Kunlun which is cut by Altyn Tagh fault afterwards. Therefore, it comes that the maximalaccumulated left-handed strike-slip displacement of Altyn Tagh fault is about 900km.During the strike-slipping of Altyn Tagh fault zone, part of energy is transformed to that of obductedfault which made the pre-Cenozoic geological bodies uplift to form hills. Hence the strike-slipping formsand controls the distribution of Mounts Qimantage, Danghenan, Qilian, and also controls the growth andextension direction of North Qinghai-Tibet plateau, coordinating and constraining the coupling relations ofbasin and hill.Research on the formation age of Altyn Tagh fault zone together with the coupling relations of activestrike-slipping and obduction as well as the contribution of the strike-slipping to the uplifting of NorthQinghai-Tibet plateau is not only of great importance to reconstruct the evolutionary history of Altyn Taghfault zone, but also provides first-hand basic data on establishing the formation pattern of Qinghai-Tibetplateau, especially establishing the uplifting & extension model for North Qinghai-Tibet plateau.更多还原