Subduction initiation as recorded in the Izu-Bonin-Mariana forearc
Subduction initiation as recorded in the Izu-Bonin-Mariana forearc
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DOI：
10.1016/j.earscirev.2023.104573
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发表时间：
2023-10-03
影响因子：
12.1
通讯作者：
Christeson，Gail L.
中科院分区：
文献类型：
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作者：
Reagan，Mark K.;Pearce，Julian A.;Christeson，Gail L.
IODP探险352钻探了博宁弧外前缘的四个地点，详细记录了在约52.5 Ma太平洋板块俯冲开始后立即发生的一次短暂(1；2 Ma)海底扩张事件中的熔岩喷发和岩墙就位情况。这种扩张产生了长达120公里的大洋岩石圈，其结构类似于超俯冲带蛇绿岩。钻探了两组遗址：U1440和U1441遗址是最古老的，距离海沟最近，主要是回收的弧前玄武岩(FAB)；U1439和U1442遗址较年轻，距离海沟和回收的玻安岩较远。1440B孔和1439C孔都植根于岩脉复合体中，这证实了大部分钻探地壳可能是海底扩张的起源。地球化学证据表明，中生代海脊和盆地地体下方的地幔热柱变浅可能是太平洋板块开始俯冲到该地体下方的触发因素。印度大陆和亚洲大陆之间碰撞的时间和性质使得它也在触发这一事件中发挥了作用。在俯冲开始后，由于与板块回滚相关的伸展作用，海底开始扩张。进入这个新的伸展旋回的地幔由于熔融和与该热柱相关的古老的亏损地幔的并入而高度亏损。最初，板岩衍生的水溶液对地幔来源的贡献很小，然后经过减压熔融，产生了洋壳，其FAB成分类似于当今海底扩张环境中最不相容的元素贫化玄武岩。同样的，或者说是更新的山脊系统产生了低硅玻安岩(LSB)岩浆，一旦从俯冲的太平洋洋壳产生的水合熔体熔融了现在高度枯竭但仍然很热的地幔。高硅玻安岩(HSB)火山作用开始于约51.3 Ma，大约是海底扩张放缓和更集中的火山活动开始的时候，这是对相对于板块回滚的俯冲增加的响应。钻探区随后的历史标志是几公里的抬升和侵蚀，可能与其枯竭的地幔基础的蛇纹岩作用有关，随后延伸形成了小型沉积盆地。
IODP Expedition 352 drilled four sites in the Bonin outer forearc, providing a detailed record of lava eruption and dike emplacement during a short-lived (<2 Ma) seafloor spreading event that took place immediately after the initiation of Pacific Plate subduction at c. 52.5 Ma. This spreading produced up to 120 km of oceanic lithosphere with a structure analogous to that of a supra-subduction zone ophiolite. Two groups of sites were drilled: Sites U1440 and U1441 are oldest and nearest to the trench and principally recovered forearc basalt (FAB); Sites U1439 and U1442 are younger and farther from the trench and recovered boninites. Holes 1440B and 1439C are both rooted in dike complexes, confirming a likely seafloor spreading origin for most of the drilled crust. Geochemical evidence points to the shoaling of a mantle plume beneath a Mesozoic ridge and basin terrane as a likely trigger for the Pacific plate to begin to subduct beneath that terrane. The timing and nature of the collision between the Indian and Asian continents allows it also to have played a role in triggering this event. Seafloor spreading began due to extension related to slab rollback immediately following the start of subduction. Mantle entering this new extensional régime was highly depleted both by melting and by incorporation of ancient, depleted mantle associated with the plume. Initially, slab-derived aqueous fluids made negligible to small contributions to the mantle source, which then underwent decompression melting producing oceanic crust with a FAB composition that resembles the most incompatible element-depleted basalts in present-day seafloor spreading settings. The same, or a renewed, ridge system produced low-Si boninite (LSB) magmas once hydrous melts from the subducting Pacific oceanic crust fluxed the now highly depleted, but still hot, mantle. High-Si boninite (HSB) volcanism began at c. 51.3 Ma, about the time when seafloor spreading slowed and more focused volcanism began in response to increased subduction relative to slab rollback. The subsequent history of the drilled area was marked by several kilometers of uplift and erosion, perhaps related to serpentinization of its depleted mantle foundation, followed by extension to produce small sedimentary basins.