Tectonic Processes and the History of the Mariana Arc: A Synthesis of the Results of Deep Sea Drilli
Tectonic Processes and the History of the Mariana Arc: A Synthesis of the Results of Deep Sea Drilli
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DOI：
10.2973/dsdp.proc.60.154.1982
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发表时间：
1982-03
期刊：
影响因子：
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通讯作者：
D. Hussong;S. Uyeda
中科院分区：
文献类型：
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作者：
D. Hussong;S. Uyeda
DSDP Leg 60 在北纬 18° 的东西向断面上钻探了 10 个地点，横跨马里亚纳弧系统的构造活动海沟、火山弧和伸展弧后盆地。对这些岩心的分析，加上在钻探准备过程中收集的大量地质和地球物理信息，构成了目前在两个海洋岩石圈板块汇聚区域中可用的最完整的数据集。在马里亚纳弧（菲律宾板块）上没有发现太平洋板块沉积物或地壳岩石的明显增生。现已从距火山弧几十公里的海沟坡折处对弧火成岩基底进行了采样，其年龄为早渐新世或始新世，经地球化学鉴定为弧起源。显然，仅产生净沉降的张性变形（表示为高角度断层）和垂直运动发生在海沟两侧，并且随着接近海沟轴线而增加。在海沟、海沟内壁和弧前东部的大部分地区仅观察到稀疏的沉积物。总的来说，这些特征表明，尽管过去可能发生过一些增生时期，但北纬 18° 的马里亚纳弧前部受到俯冲板块的整体构造侵蚀。自始新世以来，弧火山活动可能一直持续，但最初的弧后盆地裂谷发生在弧火山处或附近，产生剧烈的沉降，随后在深水中喷发，火山物质的横向输送有限。明显的弧前火山出现在海沟轴附近，俯冲海洋板块仅 15 至 30 公里深。如果这些特征是火山和原地的，那么它们的岩浆源必须来自俯冲带的更深处（需要大量的岩浆横向输送）或来自海洋板块，或者它们必须是曾经位于更深的俯冲板片上方的较古老的特征。北纬 18° 马里亚纳海槽的弧后扩张显然始于晚中新世弧火山活动轴以东的裂谷，大致对称，并以小于 2.15 厘米/年的半速率持续至今。因此，目前的马里亚纳岛弧火山是建立在薄地壳之上的，该地壳在地理学上是弧后盆地的一部分，并且要么是拉伸、变薄和下沉的弧地壳，要么是在弧后扩张中心生成的。弧后扩张具有脊/转换/脊几何形状、地震分布、地壳结构、地貌和 MORB 型岩石，这些岩石都模仿成熟、大型深海扩张中心，但又存在微妙且一致的不同。然而，马里亚纳海槽可能与其他不太知名的地区类似，这些地区相对较厚的岛弧或大陆地壳最初正在裂谷。日本、马里亚纳群岛、墨西哥和危地马拉海域IPOD活动边缘钻探的结果表明，俯冲和板块运动几何形状、弧后扩张、岩浆类型、垂直构造以及弧前增生与构造侵蚀的发生之间可能存在系统关系。
DSDP Leg 60 drilled 10 sites on an east-west transect at 18°N across the tectonically active trench, volcanic arc, and extensional back-arc basin on the Mariana arc system. The analysis of these cores, augmented by considerable geological and geophysical information collected in preparation for the drilling, comprises the most complete data set presently available in a zone of convergence of two ocean lithospheric plates. No significant accretion of Pacific plate sediment or crustal rocks is found on the overriding Mariana arc (Philippine plate). The arc igneous basement, which has now been sampled from the trench slope break to within a few tens of kilometers from the volcanic arc, is of early Oligocene or Eocene age and is geochemically identified as being of arc origin. Apparently exclusively tensional deformation (expressed as high-angle faulting) and vertical movement producing net subsidence occur on both sides of the trench and increase with proximity to the trench axis. Only sparse sediments are observed in the trench, on the inner trench wall, and on much of the eastern part of the fore-arc. Collectively, these features suggest that, although some periods of accretion may have occurred in the past, the Mariana fore-arc at 18°N is subject to overall tectonic erosion by the subducting plate. Arc volcanism has probably been continuous since the Eocene, but initial back-arc basin rifting has occurred at or near the arc volcanoes, producing drastic subsidence and subsequent eruption in deep water with limited lateral transport of volcanic material. Apparent fore-arc volcanoes occur close to the trench axis where the subducting ocean plate is only 15 to 30 km deep. If these features are volcanic and autochthonous, their magma source must be either from deeper in the subduction zone (requiring considerable lateral transport of the magma) or in the oceanic plate—or they must be older features that were once above a much deeper subducting slab. Back-arc spreading in the Mariana Trough at 18°N apparently began with rifting somewhat east of the axis of arc volcanism in the latest Miocene, is approximately symmetric, and has continued at a half-rate of less than 2.15 cm/y, to present. The present Mariana arc volcanoes are thus built over thin crust that is physiographically part of the back arc basin and is either stretched, thinned, and subsided arc crust or was generated at the back-arc spreading center. Backarc spreading has ridge/transform/ridge geometry, earthquake distribution, crustal structure, geomorphology, and MORB-type rocks that all mimic—yet are subtly and consistently different from—mature, large, deep ocean spreading centers. The Mariana Trough may, however, be similar to other less well-known regions where the relatively thick island arc or continental crust is initially rifting. The results of IPOD active margin drilling off Japan, the Marianas, Mexico, and Guatemala suggest that there may be systematic relationships between subduction and plate motion geometry, back-arc spreading, magma types, vertical tectonics, and the occurrence of fore-arc accretion versus tectonic erosion.