The missing half of the subduction factory: shipboard results from the Izu rear arc, IODP Expedition 350-猫眼课题宝

DOI：

10.1080/00206814.2017.1292469

发表时间：

2017-03

期刊：

International Geology Review

影响因子：

2.6

通讯作者：

中科院分区：

地球科学3区

文献类型：

作者：

C. Busby;Y. Tamura;P. Blum;G. Guérin;G. Andrews;A. Barker;J. Berger;E. Bongiolo;M. Bordiga;S. DeBari;J. Gill;C. Hamelin;Jihui Jia;E. John;A. Jonas;M. Jutzeler;M. Kars;Z. Kita;K. Konrad;S. Mahony;M. Martini;T. Miyazaki;R. Musgrave;D. B. Nascimento;A. Nichols;J. Ribeiro;Tomoki Sato;J. Schindlbeck;A. Schmitt;S. Straub;M. J. Mleneck-Vautravers;Alexandra Yang Yang-Alexandra-Yang-Yang-1592865429

摘要IODP第350次考察是第一次在伊豆-小笠原的后部进行钻探，尽管在弧轴到弧前区域已经钻探了几个地点;科学目的是通过钻探一个具有长期记录的深水火山岩剖面（地点U1437）来了解伊豆弧后的演化。伊豆后弧主要由一系列约100公里长、大致垂直于弧前的玄武质至英安质海山链构成。从这些疏浚样品的地球化学不同的弧前岩石，并进行钻探，以了解这种弧的不对称性。地点U1437位于两个弧后海山链之间一个约20公里宽的盆地内，距离弧前约90公里，钻探深度为海底以下1 804米，回收率极佳。我们预期钻探一个火山岩裙，但该剖面的泥质比预期的多（~60%），该剖面的剩余部分比根据其在伊豆弧内的位置预测的粒度细得多，一半由灰/凝灰岩组成，一半由细粒度的火山砾凝灰岩组成（碎屑6.4 cm）仅稀疏地散布在剖面的最低25%处，且仅遇到一个火成岩单元，即约1390 mbsf处的流纹岩泥晶侵入体。最低的生物地层基准面为867 mbsf（~6.5 Ma），最低的古地磁基准面为1300 mbsf（~9 Ma），流纹岩泥晶岩在~1390 mbsf测得的锆石U-Pb一致截距年龄为（13.6 + 1.6/−1.7）Ma。弧前和弧后的源有助于细粒（远端）火山碎屑岩的上部1320米，但粗粒（近端）火山碎屑岩在最低的25%的部分是地球化学相似的弧前，这表明弧不对称性是没有记录在岩石年龄超过13马。

ABSTRACT IODP Expedition 350 was the first to be drilled in the rear part of the Izu-Bonin, although several sites had been drilled in the arc axis to fore-arc region; the scientific objective was to understand the evolution of the Izu rear arc, by drilling a deep-water volcaniclastic section with a long temporal record (Site U1437). The Izu rear arc is dominated by a series of basaltic to dacitic seamount chains up to ~100-km long roughly perpendicular to the arc front. Dredge samples from these are geochemically distinct from arc front rocks, and drilling was undertaken to understand this arc asymmetry. Site U1437 lies in an ~20-km-wide basin between two rear arc seamount chains, ~90-km west of the arc front, and was drilled to 1804 m below the sea floor (mbsf) with excellent recovery. We expected to drill a volcaniclastic apron, but the section is much more mud-rich than expected (~60%), and the remaining fraction of the section is much finer-grained than predicted from its position within the Izu arc, composed half of ashes/tuffs, and half of lapilli tuffs of fine grain size (clasts 6.4 cm) are only sparsely scattered through the lowermost 25% of the section, and only one igneous unit was encountered, a rhyolite peperite intrusion at ~1390 mbsf. The lowest biostratigaphic datum is at 867 mbsf (~6.5 Ma), the lowest palaeomagnetic datum is at ~1300 mbsf (~9 Ma), and the rhyolite peperite at ~1390 mbsf has yielded a U–Pb zircon concordia intercept age of (13.6 + 1.6/−1.7) Ma. Both arc front and rear arc sources contributed to the fine-grained (distal) tephras of the upper 1320 m, but the coarse-grained (proximal) volcaniclastics in the lowest 25% of the section are geochemically similar to the arc front, suggesting arc asymmetry is not recorded in rocks older than ~13 Ma.

The missing half of the subduction factory: shipboard results from the Izu rear arc, IODP Expedition 350

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