Multichannel seismic evidence for a subcrustal intrusive complex under Oahu and a model for Hawaiian volcanism
Multichannel seismic evidence for a subcrustal intrusive complex under Oahu and a model for Hawaiian volcanism
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欧胡岛地壳下侵入杂岩的多道地震证据和夏威夷火山活动模型
DOI：
10.1029/jb092ib13p13687
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发表时间：
1987
影响因子：
--
通讯作者：
T. Brocher
中科院分区：
文献类型：
--
作者：
U. Brink;T. Brocher
在宽孔径双船实验期间获得的多道地震反射和折射数据为夏威夷奥陶洛斯下复杂的壳幔（C-M）转换提供了证据。几个大口径的共同深度点线和三个扩大的扩展剖面表明，在火山脊下存在一个厚达3-6公里的C-M过渡带，该过渡带从奥陶洛斯中心向南北延伸100公里。这种异常的C-M转换可能代表了一个侵入上地幔和下地壳的深大杂岩，其侵入范围以奥陶系为中心，宽达200 km。在地壳底部附近存在如此大量的侵入体，意味着火山作用的表层表现只占夏威夷群岛深处产生的熔融量的一小部分。这一解释与先前预测上涌岩浆在莫霍面及以下圈闭和聚集的岩石学模型雅阁。我们已经建立了一个模型，这表明上涌岩浆和岩石圈弯曲应力场之间的相互作用可能会调制夏威夷火山的特征喷发历史。特别是，伴随着岛链周围的海洋地壳的弯曲的平面应力场的模型表明，在个别火山下的应力场随其相对于岛链尖端的位置而变化很大。当一座夏威夷大小的火山形成时，其下的偏压应力可能足以阻塞洋壳内涌上岩浆的通道，并终止喷发。进一步上涌的岩浆被模型预测为在地壳底部形成积水。当水平压应力沿着火山链的轴释放时，后断陷火山作用的恢复似乎发生在活盾状火山作用中心后面的恒定距离处。观测到的火山岩脉的方向与最大计算应力的方向一致。我们的模型意味着岩浆上升超过300公里宽的区域，海洋板块可能不会在岛屿下断裂。
Coincident multichannel seismic reflection and refraction data acquired during a wide-aperture two-ship experiment provide evidence for a complex crust-mantle (C-M) transition under Oahu, Hawaii. Several large-aperture common depth point lines and three expanding spread profiles suggest the existence of an anomalously thick (3–6 km) C-M transition zone underneath the volcanic ridge which extends for distances of 100 km to the north and south from the center of Oahu. The anomalous C-M transition may represent a plutonic complex which intruded into the upper mantle and the lower crust in a 200-km-wide area centered at Oahu. The existence of such a large volume of intrusions near the base of the crust implies that the surficial expression of volcanism constitutes only a small fraction of the amount of melt generated at depth under the Hawaiian Islands. This interpretation is in accord with previous petrological models which predict trapping and accumulation of upwelling magma at and below the Moho. We have constructed a model which suggests that the interaction between the upwelling magma and the lithospheric flexural stress field may modulate the characteristic eruption history of Hawaiian volcanoes. In particular, the model for the plane stress field which accompanies the flexure of the oceanic crust around island chains indicates that the stress field under individual volcanoes varies considerably with its position relative to the tip of the chain. As a Hawaiian-sized volcano develops, the magnitude of deviatoric compressive stresses under it is probably sufficient to block the conduits of the upwelling magma within the oceanic crust and to terminate eruptions. Further upwelling magma is predicted by the models to be ponded at the base of the crust. Resumption of posterosional volcanism seems to occur at a constant distance behind the center of active shield volcanism, as the horizontal compressive stresses along the axis of the chain are released. Observed orientations of dikes of this volcanic phase agree with the directions of the maximum calculated stresses. Our model implies that magma upwells over a 300-km-wide zone and that the oceanic plate may not be fractured under the islands.