Evidence for Pliocene-Quaternary normal faulting in the hinterland of the Bhutan Himalaya
Evidence for Pliocene-Quaternary normal faulting in the hinterland of the Bhutan Himalaya
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DOI：
10.1130/l277.1
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发表时间：
2013-08-01
期刊：
影响因子：
2.4
通讯作者：
Whipple, K. X.
中科院分区：
文献类型：
--
作者：
Adams, B. A.;Hodges, K. V.;Whipple, K. X.
在喜马拉雅中部，过去的研究人员已经确定了一个独特的过渡，从南部的喜马拉雅山脉到北部的喜马拉雅山脉。局部地形起伏和山坡坡度，以及侵蚀和地表抬升速率，在向北过渡的过程中突然增加。在喜马拉雅东部，同样的地理变化也存在，但没有那么剧烈。我们在这里描述了一个以前没有记载的陡峭、北倾、脆性结构，它大致与不丹东部的这种地理转变相吻合——Lhuentse断层。低温(U-Th)/He磷灰石资料表明，鲁伦泽断裂自上新世以来一直处于活动状态，断裂带内邻距热液赤铁矿床的(U-Th)/He测年显示出第四纪滑动成分。虽然我们没有根据断层岩石的野外或岩石学分析确定断层运动学的确切证据，但(U-Th)/He磷灰石日期的中断模式表明正常意义上的位移，这与先前对喜马拉雅中部类似过渡的研究所期望的相反。我们认为Lhuentse断层的存在和活动证明了(1)喜马拉雅东部构造体制的近期演变，从一个几乎完全的南北缩短到一个在喜马拉雅变形前沿以北的地区，跨断层和正断层都越来越重要，或者(2)不丹中纬度地理过渡以南的一个活跃的复式构造体制。
In the central Himalaya, past researchers have identified a distinctive transition from the physiographic Lower Himalayan ranges in the south to the Higher Himalayan ranges in the north. Local relief and hillslope gradient, as well as erosion and surface uplift rates, increase abruptly across this transition to the north. In the eastern Himalaya, the same physiographic transition exists, but it is less dramatic. We describe here a previously undocumented steep, north-dipping, brittle structure that is roughly coincident with this physiographic transition in eastern Bhutan-the Lhuentse fault. Low-temperature (U-Th)/He apatite data suggest that the Lhuentse fault has been active since the Pliocene, and (U-Th)/He dates on offset hydrothermal hematite deposits from within the fault zone demonstrate a component of Quaternary slip. Although we identified no definitive evidence of fault kinematics based on field or petrographic analysis of the fault rocks, the disrupted pattern of (U-Th)/He apatite dates suggests normal-sense displacement, contrary to what was expected given previous studies of an analogous transition in the central Himalaya. We regard the existence and activity of the Lhuentse fault as evidence of (1) recent evolution in the tectonic regime of the eastern Himalaya from one of near-exclusive north-south shortening to one in which both transcurrent and normal faulting are increasingly important in the region north of the Himalayan deformation front, or (2) an active duplex south of the physiographic transition in the middle latitudes of Bhutan.