Spatial and temporal trends in exhumation of the Eastern Himalaya and syntaxis as determined from a multitechnique detrital thermochronological study of the Bengal Fan
Spatial and temporal trends in exhumation of the Eastern Himalaya and syntaxis as determined from a multitechnique detrital thermochronological study of the Bengal Fan
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DOI：
10.1130/b35031.1
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发表时间：
2019-03
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通讯作者：
Y. Najman;Chris Mark;D. Barfod;A. Carter;R. Parrish;D. Chew;L. Gemignani
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作者：
Y. Najman;Chris Mark;D. Barfod;A. Carter;R. Parrish;D. Chew;L. Gemignani
孟加拉扇提供了喜马拉雅东部和中部新近纪发掘的记录。本文首次对国际海洋发现计划（IODP）第354次远征期间收集的孟加拉扇中部沉积物样品进行了碎屑热年代学研究（磷灰石和金红石U-Pb，云母Ar-Ar，锆石裂变径迹）。金红石和锆石裂变径迹热时计数据显示，滞后时间在5.59 ~ 3.47 Ma之间发生了变化。最古老的样品（滞后时间为6 m.y）的沉积年龄为5.59-4.50 Ma，然后锆石和金红石种群呈现静态峰值，直到bbbb12 Ma。从5.59-4.50 Ma到bb0 - 12 Ma，这段时间最容易被解释为记录了大喜马拉雅地区的被动侵蚀。然而，单粒的滞后时间小于4毫秒，但具有较高的分析不确定性，记录在这个间隔。对于年龄超过10 Ma的沉积物，这些颗粒来自大喜马拉雅地区，直到大约14 Ma才被迅速挖掘出来。在小于10 Ma的沉积物中，这些颗粒可能代表了地块南部合成反形的缓慢但仍然快速的挖掘。从14.5 Ma到研究剖面底部的17 Ma，再次记录了<1 Ma的滞后时间，反映了大喜马拉雅地区的快速挖掘时期。云母40Ar/39Ar和磷灰石U-Pb数据对合成物的挖掘不敏感：我们将此归因于合成物岩性中白色云母的缺乏，以及普通Pb的高水平，导致U-Pb年龄分别具有不可接受的高不确定性。
The Bengal Fan provides a Neogene record of Eastern and Central Himalaya exhumation. We provide the first detrital thermochronological study (apatite and rutile U-Pb, mica Ar-Ar, zircon fission track) of sediment samples collected during International Ocean Discovery Program (IODP) Expedition 354 to the mid–Bengal Fan. Our data from rutile and zircon fission-track thermochronometry show a shift in lag times over the interval 5.59–3.47 Ma. The oldest sample with a lag time of 6 m.y.) has a depositional age of 5.59–4.50 Ma, and the zircon and rutile populations then show a static peak until >12 Ma. This interval, from 5.59–4.50 Ma to >12 Ma, is most easily interpreted as recording passive erosion of the Greater Himalaya. However, single grains with lag times of <4 m.y., but with high analytical uncertainty, are recorded over this interval. For sediments older than 10 Ma, these grains were derived from the Greater Himalaya, which was exhuming rapidly until ca. 14 Ma. In sediments younger than 10 Ma, these grains could represent slower, yet still rapid, exhumation of the syntaxial antiform to the south of the massif. Lag times <1 m.y. are again recorded from 14.5 Ma to the base of the studied section at 17 Ma, reflecting a period of Greater Himalayan rapid exhumation. Mica 40Ar/39Ar and apatite U-Pb data are not sensitive to syntaxial exhumation: We ascribe this to the paucity of white mica in syntaxial lithologies, and to high levels of common Pb, resulting in U-Pb ages associated with unacceptably high uncertainties, respectively.