Constraining erosion during arc-arc collision from turbidite sands in the Nankai

增生杂岩中的沉积岩潜在地记录了俯冲带在很长一段地质时期内的演化。增生型活动大陆边缘既是陆壳向地幔的主要下沉部位，也是陆壳形成的场所。因此，了解这些大陆边的形成过程，对于限制大陆地壳的形成和维持至关重要。洋弧向大陆边的加积是大陆地壳形成的一个关键阶段，但这些事件的证据往往模糊不清。在这个项目中，我们将确定是什么过程控制沉积物的流量到一个沟系统，从而可能从类似的沉积物在较老的复杂去卷积。特别是，我们将研究的影响，弧弧碰撞的侵蚀的一个活跃的边缘系统。我们选择研究日本西南部的南海海槽，因为它是典型的剖面增生大陆边缘，不仅来自本州的中生代增生杂岩，而且来自伊豆-小笠原弧与日本大陆碰撞形成的山脉。我们进一步测试是否这种碰撞或气候变化在中更新世过渡~0.9 Ma的主要控制日本的侵蚀。我们将应用矿物学和热年代学方法的沉积物恢复IODP远征316，尼科尔森航行作为船上的科学家。这些样品的年代为上新世-新近纪（2.0- 0.5Ma），是南海边缘的增生砂。我们还建议描述从钻探地点向岸上排出伊豆碰撞区和四万多增生综合体的现代河流沉积物的特征。使用对比构造/岩浆的历史的Shimanto复杂相比，伊豆碰撞区，我们将限制其相对影响的沉积物生产和流量的沟槽。目前的模型预测伊豆-小笠原弧在大约1 Ma左右与日本相撞。我们将通过分析过去2.0-0.5 Ma的15个砂层来测试这一点，以确定该事件的材料诊断何时首次到达南开海槽。我们将使用经过验证的重矿物分析，这些分析可以识别出已知可诊断碰撞区的特定颗粒。单粒辉石和角闪石颗粒的主要元素分析将限制随着时间的推移，在原产地的变化，使我们能够在100千公里内的侵蚀模式的变化。此外，锆石颗粒的LA-ICP-MS U-Pb测年将用于进一步限制源区的变化，因为伊豆-小笠原碰撞带提供的锆石年龄小于40 Ma，与岛满岛带的中生代年龄形成对比。来自磷灰石和锆石裂变径迹分析（AFT和ZFT）的热年代学数据，结合生物地层学数据，将提供的沉积物源区的折返的时间和速度的限制，允许重建的演变过程中的弧与日本大陆的碰撞景观。这样做，我们将更好地了解如何弧增生的进展，从而如何亚洲大陆地壳已建成在漫长的地质时期。

Sedimentary rocks in accretionary complexes potentially record the evolution of subduction zones over long periods of geological time. Accretionary active continental margins are both major sinks of continental crust back into the mantle and locations for continental crustal formation. As a result understanding the processes that construct these margins is essential to constraining how the continental crust is built and maintained. Accretion of oceanic arcs to continental margins is a key stage in the building of continental crust, yet evidence for these events is often obscure. In this project we will determine what processes control the flux of sediment to a trench system and thus what might be deconvolved from similar deposits in older complexes. In particular, we will examine the impact that arc-arc collision has had on the erosion of an active margin system. We choose to study the Nankai Trough of SW Japan because it is the type-section accretionary continental margin and derives sediment, not only from Mesozoic accretionary complexes in Honshu, but also from the mountains formed by the collision of the Izu-Bonin Arc with the Japanese mainland. We further test whether this collision or the climate changes during the Mid-Pleistocene transition ~0.9 Ma are the primary controls on erosion of Japan. We will apply mineralogy and thermochronology methods to sediments recovered by IODP Expedition 316, on which Nicholson sailed as a shipboard scientist. The samples are dated as Pliocene-Recent (2.0-0.5 Ma) and are accretionary sands of the Nankai margin. We also propose to characterize modern river sediments draining both the Izu collision zone and the Shimanto Accretionary Complex, immediately onshore from the drill sites. Using the contrasting tectonic/magmatic histories of the Shimanto Complex compared to the Izu collision zone we will constrain their relative influences on sediment production and flux to the trench. Present models predict that the Izu-Bonin Arc collided with Japan around 1 Ma. We shall test this by analyzing 15 sands spanning the last 2.0-0.5 Ma in order to determine when material diagnostic of that event first reaches the Nankai Trough. We will use proven heavy mineral analyses that can identify specific grains known to be diagnostic of the collision zone. Single grain major element analysis of pyroxene and amphibole grains will constrain changes in provenance through time, allowing us to date changes in erosion patterns within 100 ky. In addition, LA-ICP-MS U-Pb dating of zircon grains will be used to further constrain changes in source area, because the Izu-Bonin collision zone supplies zircons younger than 40 Ma, contrasting with Mesozoic ages in those derived from the Shimanto Belt. Thermochronological data derived from apatite and zircon fission track analysis (AFT and ZFT), combined with biostratigraphic data, will provide constraints on the timing and rate of exhumation of the sediment source areas, allowing reconstructions of the evolution of the landscape during the collision of the arc with the Japanese mainland. In doing so we will better understand how the arc accretion progresses and thus how the continental crust of Asia has been constructed over long periods of geological time.