喜马拉雅山脉新生代差异隆升的裂变径迹热年代学证据

裂变径迹年龄资料记录的雅鲁藏布江以南的喜马拉雅山脉的冷却年龄具有明显的时空差异性。在南北方向上,特提斯喜马拉雅的冷却年龄主要在8 Ma以前,局部为5.0~2.6 Ma,而高喜马拉雅的冷却年龄集中在5 Ma以后,大多数在3 Ma以来;在东西方向上体现在喜马拉雅东西构造结之间的高喜马拉雅带上,东喜马拉雅的不丹东部区域的裂变径迹热年代学数据揭示了8.0~3.0 Ma的冷却剥露的历史;东喜马拉雅的不丹西部区域为7.0~1.4 Ma;中喜马拉雅的尼泊尔地区为5.0~0.2 Ma;西喜马拉雅的印度西北部地区为3.0~1.0 Ma。最年轻的裂变径迹年龄显示出由中间向两侧增大,反映了地质晚近时期东西构造结间的高喜马拉雅山脉的剥露幅度由中间向两边减弱的趋势,揭示了以中喜马拉雅为隆升中心向两边拓展的趋势。综合有关裂变径迹年代学资料表明,喜马拉雅山脉的隆升主要发生在中新世以来,其表现为18~11 Ma、9 Ma以来的两个快速隆升期。喜马拉雅山脉隆升的动力体制可能由早期的挤压隆升—中新世的伸展隆升—上新世以来构造隆升为主,局部气候作用和构造作用耦合的山脉隆升机制。

Fission-track evidence of Cenozoic different uplift processes of Himalayan Mountains

Cooling ages of the Himalayan Mountains,south of Yarlung Zangbo River,recorded by fission-tracks show remarkably spatial and temporal differences.In the north-south direction,fission-track ages of Tethys Himalayan belt suggest that cooling occurred mainly before 8 Ma,partially between 5.0-2.6 Ma,but in the Higher Himalayan belt cooling mainly since 5 Ma,mostly since 3 Ma.In the east-west direction,spatial differences are embodied in the Higher Himalayan belt.Fission-track thermochronology showed that cooling and denudation occurred between 8.0-3.0 Ma in the Eastern Himalayas of central and eastern Bhutan,and cooling occurred between 7.0-1.4 Ma in western Bhutan.In the central Himalayas(Nepal) cooling occurred between 5.0-0.2 Ma,and cooling ages distribute between 3.0-1.0 Ma in the western Himalayas.The youngest fission track ages show an increasing trend from middle to both eastern and western sides,reflecting a denudation rate having become larger from centre towards the east and west of the Higher Himalayan belt between Eastern and Western Himalayan Syntaxes in the very recently geological time.A systematic investigation of published fission-track ages suggests that the denudation of the Himalayas occurred since the Miocene,exhibiting two uplifting stages: at 18-11 Ma and from 9 Ma onwards.The investigation also shows that the mechanism of the Himalayan uplift may have changed from an earlier compressional uplift to a later extensional uplift in the Miocene,caused by tectonic forces and coupled with the effects of local climate in the Late Miocene.