Detrital geochronology and geochemistry of Cretaceous-Early Miocene strata of Nepal: implications for timing and diachroneity of initial Himalayan orogenesis
Detrital geochronology and geochemistry of Cretaceous-Early Miocene strata of Nepal: implications for timing and diachroneity of initial Himalayan orogenesis
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DOI：
10.1016/j.epsl.2004.08.019
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发表时间：
2004-11-15
影响因子：
5.3
通讯作者：
Garzanti, E
中科院分区：
文献类型：
--
作者：
DeCelles, PG;Gehrels, GE;Garzanti, E
喜马拉雅造山带西部造山作用的开始在巴基斯坦北方和印度的同造山期地层记录中已有记载，时间为早始新世至中始新世（约52 Ma）。喜马拉雅造山带中部特提斯部分的始新世地层由浅海相碳酸盐岩组成，缺乏喜马拉雅造山作用初期的证据，因此留下了造山作用的开始沿沿着走向明显穿时的可能性。本文报道了白垩纪-古新世（？）尼泊尔中部小喜马拉雅带南部始新世和中新世下部地层。古新世（？）Amile组以锆石为主，U-Pb年龄为太古代-早元古代。寒武-奥陶纪和中-晚元古代锆石的突然涌入标志着向始新世Bhainskati组的过渡，并表明在新生喜马拉雅冲断带特提斯岩石的侵蚀开始。晚元古代锆石的比例增加的河流岩屑砂岩的下中新统杜姆里组的信号大喜马拉雅原岩的初始侵蚀。Nd同位素和微量元素数据支持U-Pb锆石年龄记录的去顶历史。尼泊尔始新世中期地层来自喜马拉雅冲断带，这一事实使喜马拉雅西北部和中部造山作用开始之间的最大时间间隔缩短到不超过2 My。(C)2004 Elsevier B. V.保留所有权利。
The onset of mountain building in the western part of the Himalayan orogenic belt has been documented in the synorogenic stratigraphic record of northern Pakistan and India as Early to Middle Eocene (similar to52 Ma). Eocene strata in the Tethyan portion of the central part of the Himalayan orogenic belt consist of shallow marine carbonate rocks that lack evidence for initial Himalayan orogenesis, thus leaving open the possibility that the onset of orogeny was significantly diachronous along strike. We report U-Pb ages of detrital zircons and Nd-isotopic and trace element data from associated mudrocks in Cretaceous-Paleocene(?), Eocene, and lower Miocene strata of the southern Lesser Himalayan zone of central Nepal. The Cretaceous-Paleocene(?) Amile Formation is dominated by zircons with Archean-Early Proterozoic U-Pb ages. An abrupt influx of Cambrian-Ordovician and Middle to Late Proterozoic zircons marks the transition into the Eocene Bhainskati Formation, and indicates the onset of erosion of Tethyan rocks in the nascent Himalayan thrust belt. An increased proportion of Late Proterozoic zircons in fluvial litharenites of the lower Miocene Dumri Formation signals initial erosion of Greater Himalayan protoliths. The Nd-isotopic and trace element data support the unroofing history documented by the U-Pb zircon ages. The fact that middle Eocene strata in Nepal were derived from the Himalayan thrust belt reduces the maximum time lag between the onset of orogenesis in the northwest and central Himalaya to no more than similar to2 My. (C) 2004 Elsevier B.V. All rights reserved.