Emplacement processes of submarine volcaniclastic deposits (IODP Site C0011, Nankai Trough)
Emplacement processes of submarine volcaniclastic deposits (IODP Site C0011, Nankai Trough)
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海底火山碎屑沉积物的侵位过程（IODP Site C0011，南海海槽）
DOI：
10.1016/j.margeo.2013.06.017
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发表时间：
2013
期刊：
影响因子：
2.9
通讯作者：
Murray R.W.
中科院分区：
文献类型：
--
作者：
Schindlbeck J.C;Kutterolf S;Freundt A;Scudder R.P. Pickering K.T;Murray R.W.
在IODP NanTroSEIZE第322次考察期间，在四国盆地中部沉积物的中新世晚期（> 7.6 ~~ 9.1 Ma）上部的中度石化和生物扰动粉质粘土岩序列中，发现了四组凝灰质砂岩（TST 1、2、3a、3b）。为了评估凝灰质砂岩的侵位过程，我们研究了24个薄切片的模态和地球化学成分，揭示了每个层内系统的垂直变化。TST 1、2和3b为单床，而TST 3a至少由两个床组成，表明存在几个快速相继的沉积事件。这些层是密度分级的，因此，包括浮石火山砾在内的低密度火山碎屑在顶部富集，而致密的岩屑成分和矿物在底部富集。火山玻璃颗粒（浮石和碎片）是每个砂岩层的主要模态成分，在每个层中具有均匀的地球化学成分。此外，TST 1，2，和3A玻璃组合物完全重叠，但TST 3B玻璃有不同的组合物，是类似的矿物constituent.This独特的多阶段的方法，沉积学和地球化学方法的观察促进了详细的调查远火山衍生的，可能是海啸，浊积岩，以促进初级和次级诱导的质量流之间的区别。我们解释说，所有凝灰质砂岩的侵位浊流形成的主要爆发性火山喷发。然而，虽然TST 1，2，和3a浊流形成的大量火山碎屑流进入海洋爆发在日本大陆的火山，TST 3b是由浊流形成的浅海底或陆上火山喷发在伊豆小笠原弧与日本碰撞。这些关于远源浊积岩的结果鼓励人们在通过过去的事件进行灾害评估的范围内重新审视较老的海洋沉积物，特别是在靠近火山源的地区。
During IODP NanTroSEIZE Expedition 322, four packages of tuffaceous sandstones (TST 1, 2, 3a, 3b) were recovered within a moderately lithified and bioturbated silty claystone succession in the Late Miocene (> 7.6 to ~ 9.1 Ma) upper part of the middle Shikoku Basin deposits. To assess the emplacement processes of the tuffaceous sandstones we investigate modal and geochemical compositions of 24 thin sections that reveal systematic vertical changes within each bed. TST 1, 2 and 3b are single beds whereas TST 3a is composed of at least two beds suggesting several rapidly succeeding sedimentation events. The beds are density-graded such that low-density pyroclasts including pumice lapilli are enriched at the top whereas dense lithic components and minerals are enriched at the bottom.The volcanic glass particles (pumice and shards) that are the dominant modal constituents of each sandstone bed have homogeneous geochemical compositions in each bed. Moreover, TST 1, 2, and 3a glass compositions overlap completely but TST 3b glass has a different composition, as is analogously observed for the mineral compositions.This unique multistage approach of sedimentological and geochemical methods facilitated the detailed investigation of distal volcano-derived, probably tsunamogenic, turbidites in order to contribute to the distinction between primary and secondary induced mass flows. We interpret that all tuffaceous sandstones were emplaced by turbidity currents that were formed during major explosive volcanic eruptions. However, while TST 1, 2, and 3a turbidity currents formed by the entry into the ocean of voluminous pyroclastic flows erupted at a volcano on mainland Japan, TST 3b was emplaced by a turbidity current formed by a shallow submarine or subaerial volcanic eruption at the Izu–Bonin arc where it collided with Japan. These results regarding distal turbidites encourage the revisiting of older marine deposits in the scope of hazard evaluation through past events, especially in regions near to volcanic sources.
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