The arc arises: The links between volcanic output, arc evolution and melt composition
The arc arises: The links between volcanic output, arc evolution and melt composition
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DOI：
10.1016/j.epsl.2016.12.027
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发表时间：
2017-03-01
影响因子：
5.3
通讯作者：
Li, He
中科院分区：
文献类型：
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作者：
Brandl, Philipp A.;Hamada, Morihisa;Li, He
俯冲起始是全球板块构造的关键过程。在伊豆-小博宁-马里亚纳 (IBM) 岛弧的海沟壁中已经确定了在俯冲起始和弧起始期间形成的单独岩性，但之前尚未描述过该过程的连续记录。在这里，我们展示了国际海洋发现计划第 351 次探险的结果，该探险在九州-帕劳海岭 (KPR) 以西的一个地点进行了钻探，这是一条代表原始 IBM 岛弧的死层火山链，在俯冲开始后大约 25 Ma 内活跃。 U1438 站点恢复了 150 m 的海洋火成岩基底和类似 1450 m 的上覆沉积物。这些沉积物的下部 1300 m 包括从不断演变的 KPR 弧前部脱落的火山碎屑重力流沉积物。我们从 U1438 遗址的沉积物中分离出了新鲜的岩浆矿物，并分析了 304 个玻璃（以前的熔体）包裹体，其主要成分是单斜辉石和斜长石。玻璃包裹体的成分保存了幼年岛弧的时间岩浆记录，与通过在 IBM 弧前钻探恢复的火山灰岩层确定的中新世中期到近期的主要活动相补充。玻璃包裹体记录了熔体成分在 11 Ma 的时间内逐渐转变为早期“钙碱”、高镁安山岩阶段到较年轻的拉斑岩阶段。高精度微量元素分析数据记录了深俯冲成分（例如，Th 与 Nb 的增加、轻稀土元素富集）和更肥沃的地幔源（反映在高场强元素丰度增加）的同时增加的影响。这种成分变化伴随着火山碎屑沉积物沉积速率的增加，反映了岩浆的产出和弧的成熟度。我们得出的结论是，只要地幔楔源没有大部分平流离开弧岩浆生成区域，或者角流的楔形补充速率不压倒岩浆提取速率，弧演化的“钙碱”阶段就可能持续下去。 (C) 2017 年作者。由 Elsevier B.V. 出版。这是一篇基于 CC BY 许可的开放获取文章。
Subduction initiation is a key process for global plate tectonics. Individual lithologies developed during subduction initiation and arc inception have been identified in the trench wall of the Izu-Bonin-Mariana (IBM) island arc but a continuous record of this process has not previously been described. Here, we present results from International Ocean Discovery Program Expedition 351 that drilled a single site west of the Kyushu-Palau Ridge (KPR), a chain of extinct stratovolcanoes that represents the proto-IBM island arc, active for similar to 25 Ma following subduction initiation. Site U1438 recovered 150 m of oceanic igneous basement and similar to 1450 m of overlying sediments. The lower 1300 m of these sediments comprise volcaniclastic gravity-flow deposits shed from the evolving KPR arc front. We separated fresh magmatic minerals from Site U1438 sediments, and analyzed 304 glass (formerly melt) inclusions, hosted by clinopyroxene and plagioclase.Compositions of glass inclusions preserve a temporal magmatic record of the juvenile island arc, complementary to the predominant mid-Miocene to recent activity determined from tephra layers recovered by drilling in the IBM forearc. The glass inclusions record the progressive transition of melt compositions dominated by an early 'calc-alkalic', high-Mg andesitic stage to a younger tholeiitic stage over a time period of 11 Ma. High-precision trace element analytical data record a simultaneously increasing influence of a deep subduction component (e.g., increase in Th vs. Nb, light rare earth element enrichment) and a more fertile mantle source (reflected in increased high field strength element abundances). This compositional change is accompanied by increased deposition rates of volcaniclastic sediments reflecting magmatic output and maturity of the arc. We conclude the 'calc-alkalic' stage of arc evolution may endure as long as mantle wedge sources are not mostly advected away from the zones of arc magma generation, or the rate of wedge replenishment by corner flow does not overwhelm the rate of magma extraction. (C) 2017 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license.