Large volume submarine ignimbrites in the Shikoku Basin: An example for explosive volcanism in the Western Pacific during the Late Miocene
Large volume submarine ignimbrites in the Shikoku Basin: An example for explosive volcanism in the Western Pacific during the Late Miocene
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DOI：
10.1002/2014gc005263
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发表时间：
2014-05
期刊：
影响因子：
3.7
通讯作者：
S. Kutterolf;J. Schindlbeck;R. Scudder;R. Murray;K. Pickering;A. Freundt;S. Labanieh;K. Heydolph;S. Saito;H. Naruse;M. Underwood;Huaichun Wu
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作者：
S. Kutterolf;J. Schindlbeck;R. Scudder;R. Murray;K. Pickering;A. Freundt;S. Labanieh;K. Heydolph;S. Saito;H. Naruse;M. Underwood;Huaichun Wu
IODP第322次考察期间，在南海地区四国盆地（C 0011 B站）发现了晚中新世（7.6 ~ 19.1Ma）凝灰质和火山碎屑砂岩。该层段由生物扰动粉质粘土岩组成，包括4个1-7 m厚的凝灰质砂岩（TST）夹层，含57-82%（体积）火山碎屑。我们使用的主要和微量元素玻璃成分，以及放射性同位素组成，表明凝灰质砂岩床来自单一的喷发事件，大多数（TST 1，2，3A）来自不同的喷发从一个类似的源区，我们已经确定是日本大陆，350公里远。特别是，诊断微量元素比率（例如，Th/La、Sm/La、Rb/Hf、Th/Nb和U/Th）和同位素数据表明，大陆地壳下的地幔来源有显著贡献，这与日本大陆来源最一致，可能排除了伊豆-小笠原岛弧和弧后作为较年轻TST层的源区。然而，在最古老的砂岩层（TST 3b，单元IIb）上测量的一些化学数据显示出与伊豆-小笠原成分的亲和力或可以明确地归因于该成分。虽然我们不能完全排除所有TST层都来自未知和外来的伊豆-小笠原的可能性，但收集到的证据与TST 1至3a的古本州弧的起源最一致。因此，我们认为伊豆-小笠原弧和本州古弧之间的前碰撞带是喷发产物最有可能进入海洋的区域，同时也与附近（约200 km）可能的中新世源区（位于古NE-本州弧）的凝灰质砂岩有关。估计分布面积的凝灰质砂岩在中新世之间的源区和350公里远的远征322，使用水深的限制，我们计算出的砂岩层之间的最小喷发岩浆体积为101和17 km 3（致密岩石当量（DRE））。我们的结论是，在晚中新世期间，在古本州弧和伊豆-小笠原弧的碰撞带附近发生了几次大规模的喷发，并以米厚的片状火山碎屑沉积物覆盖了整个菲律宾海板块，这些火山碎屑沉积物现在在南海俯冲带中俯冲。
During IODP Expedition 322, an interval of Late Miocene (7.6 to ∼9.1 Ma) tuffaceous and volcaniclastic sandstones was discovered in the Shikoku Basin (Site C0011B), Nankai region. This interval consists of bioturbated silty claystone including four 1–7 m thick interbeds of tuffaceous sandstones (TST) containing 57–82% (by volume) pyroclasts. We use major and trace element glass compositions, as well as radiogenic isotope compositions, to show that the tuffaceous sandstones beds derived from single eruptive events, and that the majority (TST 1, 2, 3a) came from different eruptions from a similar source region, which we have identified to be the Japanese mainland, 350 km away. In particular, diagnostic trace element ratios (e.g., Th/La, Sm/La, Rb/Hf, Th/Nb, and U/Th) and isotopic data indicate a marked contribution from a mantle source beneath continental crust, which is most consistent with a Japanese mainland source and likely excludes the Izu‐Bonin island arc and back arc as a source region for the younger TST beds. Nevertheless, some of the chemical data measured on the oldest sandstone bed (TST 3b, Unit IIb) show affinity to or can clearly be attributed to an Izu‐Bonin composition. While we cannot completely exclude the possibility that all TST beds derived from unknown and exotic Izu‐Bonin source(s), the collected lines of evidence are most consistent with an origin from the paleo‐Honshu arc for TST 1 through 3a. We therefore suggest the former collision zone between the Izu‐Bonin arc and Honshu paleo‐arc as the most likely region where the eruptive products entered the ocean, also concurrent with nearby (∼200 km) possible Miocene source areas for the tuffaceous sandstones at the paleo‐NE‐Honshu arc. Estimating the distribution area of the tuffaceous sandstones in the Miocene between this source region and the ∼350 km distant Expedition 322, using bathymetric constraints, we calculate that the sandstone beds represent minimum erupted magma volumes between ∼1 and 17 km3 (Dense Rock Equivalent (DRE)). We conclude that several large volume eruptions occurred during the Late Miocene time next to the collision zone of paleo‐Honshu and Izu‐Bonin arc and covered the entire Philippine Sea plate with meter thick, sheet‐like pyroclastic deposits that are now subducted in the Nankai subduction zone.