QUATERNARY GEOLOGY AND FAULTING IN THE DAMXUNG-YANGBAJAIN BASIN, SOUTHERN TIBET
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摘要: 在当雄-羊八井盆地进行的详细地质填图工作表明,该盆地中堆积了上新世或早更新世以来多套不同成因的沉积物。其中最显著的是形成于约700~500kaB.P.、250~125kaB.P.和75~12kaB.P.等三个阶段的冰川和冰水沉积物,它们指示念青唐古拉山地区在中更新世以来曾有过三次冰期。对念青唐古拉山东南麓断裂带的研究表明,该断裂带包含了三条次级断层带,它们具有不断向盆地内部迁移和多期活动的特点,其中中更新世以来的几次重要活动分别发生在700~500kaB.P.、350~220 kaB.P.、140kaB.P.和70~50kaB.P.。断裂带错动中更新世以来地层所形成的断层崖高度随着地层时代的变新发生系统地减小,指示该断裂的垂直活动速率介于0.4mm/a~2mm/a之间,其中第四纪期间的长期的平均垂直活动速率为1.1±0.3mm/a,而全新世期间的垂直活动速率为1.4±0.6mm/a.Abstract: Detailed geological mapping conducted in the Damxung-Yangbajain basin shows that several sequences of deposits of different origins have been accumulated since the Pliocene or early Pleistocene,of which the most prominent are glacial and fluvioglacial deposits formed in the about 700~500,250~125 and 75~12 ka intervals,indicating that three glacial periods have occurred in the Nyainqêntanglha Mountains since the middle Pleistocene.Study of a fault zone at the southeastern piedmont of the Nyainqêntanglha Mountains indicates that this fault zone consists of three secondary fault zones,which have the features continuous migration toward the interior of the basin and repeated activities.The several important faultings since the middle Pleistocene occurred about 700~500,350~220,140 or so and 70~50 ka.The heights of fault scarps which have offset the sediments formed since the middle Pleistocene decrease with younging stratigraphic ages,suggesting that the rates of vertical movement of the fault change between 0.4 and 2 mm/a,of which the average rate of long-term vertical movement during the Quaternary is 1.1±0.3 mm/a,while that during the Holocene is 1.4±0.6 mm/a.
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