Abstract The Nicobar Fan and Bengal fans can be considered as the eastern and western parts, respectively, of the largest submarine-fan system in the world. This study presents the integrated results of petrographic and provenance studies from the Nicobar Fan and evaluates these in the context of controls on sedimentation. Both fans were predominantly supplied by Himalaya-derived material from the main tectono-stratigraphic sequences as well as the Gangdese arc. A lack of volcanic material in the Nicobar Fan rules out sources from the Sumatra magmatic arc. Overall, the petrographic data shows a progressive decrease in sedimentary detritus and corresponding increase of higher-grade metamorphic detritus up-section. Changes in sediment provenance and exhumation rates in the Himalaya are seen to track changes in sediment accumulation rates. High sediment accumulation rates in the Bengal Fan occurred at ∼13.5–8.3 Ma, and in the Nicobar Fan from ∼9.5–5 Ma. Both fans show peak accumulation rates at 9.5–8.3 Ma (but with the Nicobar Fan being about twice as high), and both record a sharp drop from ∼5.5–5.2 Ma, that coincided with a change in river drainage associated with the Brahmaputra River diverting west of the uplifting Shillong Plateau. At ∼5 Ma, the Nicobar Fan was supplied by an eastern drainage route that finally closed at ∼2 Ma, when sediment accumulation rates in the Nicobar Fan significantly decreased. Sediment provenance record these changes in routing whereby Bengal Fan deposits include granitoid sources from the Namche Barwa massif in the eastern syntaxis that are not seen in the Nicobar Fan, likely due to a more localised eastern drainage that included material from the Indo-Burman wedge. Prior to ∼3 Ma, source exhumation rates were rapid and constant and the short lag-time rules out significant intermediate storage and mixing. In terms of climate versus tectonic controls, tectonically driven changes in the river network have had most influence on fan sedimentation.

中文翻译：

---

破译尼科巴和孟加拉潜艇迷之间的关系，印度洋

摘要 尼科巴扇和孟加拉扇分别是世界上最大的海底扇系统的东部和西部。本研究展示了尼科巴扇的岩相学和来源研究的综合结果，并在沉积控制的背景下对这些结果进行了评估。两扇扇主要由来自主要构造地层序列和冈底斯弧的喜马拉雅物质提供。尼科巴扇火山物质的缺乏排除了苏门答腊岩浆弧的来源。总体而言，岩相数据显示沉积碎屑逐渐减少，而更高等级的变质碎屑则相应增加。喜马拉雅山沉积物来源和折返率的变化被视为跟踪沉积物积累率的变化。孟加拉扇的高沉积物积累率发生在约 13.5-8.3 Ma，尼科巴扇发生在约 9.5-5 Ma。两个扇都在 9.5-8.3 Ma 处显示出峰值积累率（但尼科巴扇大约是其两倍），并且都记录了从 ~5.5-5.2 Ma 的急剧下降，这与与雅鲁藏布江相关的河流排水的变化一致在隆起的西隆高原向西转移。在约 5 Ma 时，尼科巴扇由东部排水路线供应，该路线最终在约 2 Ma 时关闭，当时尼科巴扇的沉积物积累速率显着下降。沉积物来源记录了这些路线的变化，因此孟加拉扇沉积物包括来自东部构造带的 Namche Barwa 地块的花岗岩来源，而在尼科巴扇中看不到，可能是由于更局部的东部排水系统，其中包括来自印缅楔子的物质。在~3 Ma 之前，源头折返率快速且恒定，且滞后时间短，排除了显着的中间存储和混合。在气候与构造控制方面，河网构造驱动的变化对扇沉积影响最大。