西藏吉隆地区高喜马拉雅新近纪冷却剥露——来自裂变径迹年龄的证据  

Neogene exhumation of the Greater Himalaya Slab in Gyirong area,Tibet,constrained by fission track geochronology

作　　者：李明[1,2] 王岸[1,2] 刘超[3] 王国灿[1,2] 李涛[4] Garver John I 

机构地区：[1]中国地质大学地质过程与矿产资源国家重点实验室,湖北武汉430074 [2]中国地质大学地球科学学院,湖北武汉430074 [3]辽宁省国土资源厅,辽宁沈阳110032 [4]安徽省地质矿产勘查局313地质队,安徽六安237010 [5]Geologic Department,Union College

出　　处：《地质通报》2013年第1期86-92,共7页Geological Bulletin of China

基　　金：中国地质调查局项目<青藏高原新近纪隆升过程与地质事件群研究>(编号:1212011121261);<青藏高原新生代地质过程与第四纪环境演变综合研究>(编号:1212010733802);国家自然科学基金项目<中新世以来高喜马拉雅岩石剥露与地表气候-构造响应研究>(批准号:40902060);国家创新研究群体科学基金(编号:40921062)

摘　　要：裂变径迹年代学测试表明,吉隆地区高喜马拉雅约30km的南北剖面上锆石裂变径迹年龄介于13～2.4Ma之间,磷灰石裂变径迹年龄介于1.9～0.6Ma之间;在空间上,裂变径迹年龄与高程及纬度都具有正相关关系。综合区域热年代学资料,裂变径迹年代学数据揭示出研究区高喜马拉雅经历了3个阶段的冷却剥露过程:①中新世中期至约13Ma,藏南拆离系(STDS)大规模伸展拆离作用引发的高喜马拉雅岩石区域性的构造剥露;②中新世晚期伴随STDS韧性变形的结束,缓慢冷却剥露阶段;③上新世前后,5.8～2.7Ma以来,快速并不断加速的冷却剥露作用。综合对比研究区构造地貌特征及热年代学空间格局,提出上新世以来高喜马拉雅快速并加速的剥露作用,是由流域以河流切蚀为代表的地表作用过程驱动。Constituting the material majority and high topography of the Himalaya, the Greater Himalayan Slab （GHS） occurs as the best scientific media for revealing the deformation, surface uplift and topographic evolution of the Himalayan Orogenic Belt. This pa- per focuses on the field of the Gyirong area in central Himalaya and relies on fission track （FT） thermochronology in revealing the cooling and exhumation and further related tectonic and topographic information of the GHS. Fission track thermochronology yields zircon FT ages between 13 and 2.4Ma and apatite FT ages between 1.9 and 0.6Ma across a 30km north-south GHS section. Spatially,the FT ages show positive correlation with both elevation and latitude position. In combination with regional thermochronologies, these FT ages suggest three episodes of coohng and exhumation of the GHS. ① Middle Miocene, to -13Ma, regional syntectonic rock cooling by large scale extension of the Southern Tibet Detachment System （STDS）; ② Late Miocene slowed cooling by the ceasing of ductile extension of the STDS; ③ approximately since Phocene, from -5.8-2.7Ma, rapid and accelerated coohng. Combined with tec- tonic landform analysis of the Gyirong drainage, the FT thermochronological spatial pattern suggests that the Pliocene rapid cooling was driven by surface processes donfinated by river incision. The regional transition from tectonic to climatic exhumation of the Himalaya may probably imply that the Himalaya had accomplished a significant elevation before Late Miocene, and further drove a significant change in local and even global chmate, which in turn established the base for chmate exhumation of the Himalaya since Phocene.

关 键 词：喜马拉雅 裂变径迹 吉隆 西藏 

分 类 号：P534.61[天文地球—古生物学与地层学]