Miocene provenance change in Himalayan foreland basin and Bengal Fan sediments, with special reference to detrital garnet chemistry
Miocene provenance change in Himalayan foreland basin and Bengal Fan sediments, with special reference to detrital garnet chemistry
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DOI：
10.1111/iar.12408
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发表时间：
2021-01
期刊：
影响因子：
1.5
通讯作者：
Kohki Yoshida;T. Nakajima;Yukihide Matsumoto;A. Osaki;L. Rai;J. Cruz;H. Sakai
中科院分区：
文献类型：
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作者：
Kohki Yoshida;T. Nakajima;Yukihide Matsumoto;A. Osaki;L. Rai;J. Cruz;H. Sakai
孟加拉扇中新世沉积物是在国际大洋发现计划354期间采集的，并使用岩石学和碎屑石榴石化学分析进行了研究。分析了喜马拉雅前陆盆地沉积的中新世Siwalik群，并与孟加拉扇资料对比分析了中新世的物源变化。岩相学分析表明，孟加拉扇群和斯瓦利克群中新世沉积物主要由喜马拉雅晚期结晶(HHC)形成的碎屑组成，如绿泥石、十字石、硅线石和/或蓝晶石，它们出现在副矿物中。碎屑石榴石的化学成分在地层中各不相同；大部分石榴石富含铁铝榴石，而辉石和辉绿石含量较低。但在下、上中新世沉积中发现了富含镁铝榴石的石榴石，认为它来自HHC核(麻粒岩相)。Siwalik群中HHC碎屑石榴石的沉积始于中中新世以前(15 Ma)，晚中新世以前(10~9 Ma)。相反，孟加拉扇资料表明，富镁石榴石出现在早中新世(17.3 Ma)和晚中新世(8.5~6.5 Ma)。我们认为，孟加拉扇沉积记录了早中新世以来Siwalik沉积中出现的HHC带的侵蚀。此外，我们发现尼泊尔喜马拉雅前陆盆地和孟加拉扇中中新世晚期(12 Ma)至中中新世早期(10 Ma)HHC来源的输入都是减少的。HHC来源碎屑的消失可能是小喜马拉雅碎屑稀释的结果，这表明由变质和未变质沉积岩组成的小喜马拉雅带被抬升。
Bengal Fan Miocene sediments were collected during International Ocean Discovery Program Expedition 354 and investigated using petrographic and detrital garnet chemistry analyses. The Miocene Siwalik Group, which is composed of sediments deposited in the Himalayan foreland basin, was also analyzed for comparison with the Bengal Fan data for the provenance change during the Miocene. Our petrographic analyses revealed that the Miocene sediments of the Bengal Fan and Siwalik Group consist predominantly of Higher Himalayan Crystalline (HHC)‐derived detritus such as chloritoid, staurolite, sillimanite, and/or kyanite, which appear among the accessory minerals. The chemistry of the detrital garnet varies across the stratigraphy; most of the garnet is rich in almandine and poor in spessartine and pyrope. However, pyrope‐rich garnet, which is considered to originate from the HHC core (granulite facies), was found in the lower to upper Miocene deposits. The deposition of HHC‐derived detrital garnet began before the Middle Miocene (15 Ma) and before the Late Miocene (10–9 Ma) in the Siwalik Group. The Bengal Fan data, by contrast, indicated that pyrope‐rich garnet appeared in the Early Miocene (17.3 Ma) and Late Miocene (8.5–6.5 Ma). We conclude that the Bengal Fan sediments record the erosion of the HHC zone since the Early Miocene that appears in the Siwalik sediments. Furthermore, we found that the HHC‐derived inputs decreased from the late Middle Miocene (12 Ma) to the early Middle Miocene (10 Ma) in both the Nepal Himalaya foreland basin and the Bengal Fan. The disappearance of the HHC‐derived detritus is probably the result of dilution by Lesser Himalayan detritus, which suggests that the Lesser Himalayan zone, which is composed of metamorphosed and unmetamorphosed sedimentary rocks, was uplifted.