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.

中文翻译：

---

喜马拉雅前陆盆地和孟加拉扇沉积物中中新世物源的变化，特别参考碎屑石榴石化学

孟加拉扇中新世沉积物是在国际海洋发现计划远征 354 期间收集的，并使用岩相学和碎屑石榴石化学分析进行研究。还分析了由沉积在喜马拉雅前陆盆地的沉积物组成的中新世 Siwalik 群，以与孟加拉扇数据比较中新世期间的物源变化。我们的岩相分析显示，孟加拉扇和西瓦利克群的中新世沉积物主要由高喜马拉雅结晶 (HHC) 衍生的碎屑组成，如绿泥石、星形石、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因地层而异；大多数石榴石富含铁铝榴石，而缺乏锰铝榴石和镁铝榴石。然而，富含烟石的石榴石，被认为起源于 HHC 核心（麻粒岩相），发现于中新世下部至上部的沉积物中。HHC 衍生的碎屑石榴石的沉积开始于 Siwalik 群中中新世 (15 Ma) 和晚中新世 (10-9 Ma) 之前。相比之下，孟加拉扇数据表明，富含石榴石的石榴石出现在早中新世（17.3 Ma）和晚中新世（8.5-6.5 Ma）。我们得出结论，孟加拉扇沉积物记录了自早中新世以来出现在 Siwalik 沉积物中的 HHC 带的侵蚀。此外，我们发现在尼泊尔喜马拉雅前陆盆地和孟加拉扇中，HHC 衍生的输入从中新世晚期（12 Ma）到中中新世早期（10 Ma）减少。HHC衍生碎屑的消失可能是小喜马拉雅碎屑稀释的结果，