【作者】 司家亮；

【导师】 万晓樵； 李海兵；

【作者基本信息】 中国地质大学（北京） ， 海洋地质， 2008， 博士

【摘要】 作为世界上最高、最厚、最新和体积最大的高原,青藏高原因其特殊位置而具全球性意义。近年来研究者已将目光转向高原北部,把研究探索板块碰撞远程效应作为主要目标。青藏高原北部边界由一系列断裂体系构成,包括祁连山北缘逆冲断裂系和西昆仑逆冲断裂系,是板块碰撞汇聚能量的重要调节器,由于靠近帕米尔西构造结这一显著变形域,西昆仑山抬升剥蚀过程的认识对于了解高原整体隆升无疑有着显著科学意义。在前人研究基础上,本文以西昆仑北缘和玛扎塔格新生代沉积为研究对象,通过实地剖面测量和考察、沉积物古地磁分析、构造地貌考察和卫片解译、碎屑锆石来源分析和地震资料解释等方法,分析高原西北缘新生代构造变形和沉积特征,反演构造隆升过程并探讨古环境演变,取得如下几点新认识。研究发现西昆仑山前不同地区新生代沉积具有相似的演化趋势,但磨拉石厚度自西向东总体减小,粗碎屑和深变质岩屑出现时间西部早于东部;沉积物古地磁参数测定显示新生代以来古流向发生大角度逆时针旋转,暗示了沉积源区的自西向东转换、块体的顺时针旋转或两者的共同作用;西昆仑山前水系在冲断带附近一致向东弯曲,河流阶地发育程度西部远高于东部,指示构造运动的向东扩展;玛扎塔格中新世砾岩最年轻锆石来自西昆仑西端和西南天山,随后出现东段组分。各种证据均表明新生代以来高原西北缘的构造隆升具有显著的脉动式不均一特征,一致表现为隆升启动时间和强度自西向东扩展的模式。根据玛扎塔格中新统的不对称褶皱和第四系变形特征,认为玛扎塔格断裂主逆冲方向自南向北,属西昆仑北缘冲断带的前锋断裂,柯克亚气田处于冲断带前缘背斜顶部,逆冲最前缘的位置可能还更进一步向北延伸。以古近纪石膏层为底界的浅部冲断使中新世地层褶皱变形,反向逆冲导致第四系变形,剖面顶部出现生长地层,说明逆冲活动时间可能为更新世晚期或全新世,表明西昆仑山前的北向逆冲一直延续至第四纪晚期,目前仍可能在持续进行。玛扎塔格剖面桔黄色弱固结砂岩层可能为风成沉积,区域对比认为其形成时代不迟于5.3Ma,暗示塔克拉玛干沙漠至少在中新世晚期已初具规模。西昆仑山前中新世以来的沉积物以隆升剥蚀物为主,夹有风成沉积物,反映了河流与沙漠互为进退的古环境演变过程,剧烈隆升期,急剧增大的高差形成发育的水系,沙漠被迫远离造山带向后收缩;构造运动间歇期剥蚀夷平使河流能量减弱,沙漠乘势向造山带扩张。与西昆仑山前相比,玛扎塔格地区这一时期粗粒碎屑沉积相对较少,风成沉积规模较大,可能是该地区构造隆升强度远远小于西昆仑山,水系欠发育,再加上靠近风沙源区,沙漠扩张强度较高所致。更多还原

【Abstract】 The Tibetan Plateau is the focus of international geoscientists. The long-distance effect of India-Eurasia collision on the northern plateau has been emphasized recently. The northern boundary of the Tibetan plateau, constituting of a series of faults including the Northern Qilian and the West Kunlun thrust system, is an important adjuster of ongoing plate convergence between India and Eurasia. Locating near the Pamir structural knot, the research on uplift and denudation of the West Kunlun is of fundamental significance for investigating uplift of the Tibetan plateau.Basing on previous research, Cenozoic sediments along the northern West Kunlun and in the Mazar Tag have been studied here on paleomagnetic feature, structural geomorphology, satellite image, detrital zircon provenance and seismic data. The deformation and sedimentary features were employed to discuss the tectonic uplift process and paleoenvironment change.The eastward spreading of Cenozoic tectonic activity can be supported by all following evidences: the molasse is thicker in the west than the east, volcanic and metamorphic rocks occur in the east firstly; anti-clockwise paleocurrent directions from Wuqia to Xiyu formation indicated by AMS; the identical eastward bend of various rivers, the anisomerous terraces developed from west to east and the west-to-east provenance transition of zircons in Miocene conglomerate collected from Mazar Tag.According to the features of fold in Miocene strata and deformation in quaternary lacustrine sediments, the faults in Mazar Tag are mainly northward thrust, as the front of the northern West Kunlun thrust. After developed the anticline where the Kekeya gas-field occur, the fault might further extend to the north. Defined by quaternary strata, the thrust in Mazar Tag was considered to be started in Pleistocene or Holocene, implying that the northward fault from the piedmont of West Kunlun Mountain continued to the late Quaternary period and might keep active presently. The orange incompact sandstone occurred in Miocene strata developed in Mazar Tag might be Aeolian and formed no late than 5.3Ma, suggesting the possible latest formation of the Taklimakan Desert. The pattern that fluvial sediments interlaid with Aeolian demonstrated the evolvement between river and desert. The reason why coarse sediments occurred in Mazar Tag is less than piedmont of West Kunlun is the closer to the desert.Then the conclusion can be summarized as follows: the growth of the Tibetan Plateau in different parts is not synchronous, as the western structural knot of the India-Eurasia collision, Pamir underwent intense tectonic movement. The frontal West Kunlun thrust made the mountain uplift firstly in the west segment and then spread to the east. Intense denudation accompanied with the rapid rise developed huge piedmont sediments; the rapidly uplifted height of the West Kunlun Mountain in late Cenozoic could have modified atmospheric circulation patterns, partially accounting for the arid climate in the Tarim Basin, and developed the aeolian interlaid with the fluvial sediments. The end of the frontal thrust from West Kunlun to Tarim Basin might have expanded to the hinterland and enhanced the ancient faults. In Mazar Tagh, the activity extended into the present and made the significant deformation in Quaternary lacustrine sediments.更多还原