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在新赫布里底群岛迈沃岛上的沙瓦拉组(晚渐新世—早中新世)下部的地质剖面中,可辨认出八种岩相。这八种岩起代表一个主要由重力流机制形成的、向西延伸的深海扇。的深海扇海底上还存在有非钙质的红色粉砂岩和少量绿色粉砂岩(这说明沉积作用超越了碳酸盐的补偿深度,即4250米以下)以及极少量的薄层大气降尘。前人的研究认为,现在的迈沃岛地区曾是中中新世时发生过裂谷作用的地区。然而,晚更新统—早中新统地层沉积的巨大深度表明,那次裂谷作用应发生在晚渐新世之前。由于在迈沃岛以南的彭特科斯特岛上发现了年龄为35—28百万年的渐新世蛇绿岩套,证明裂谷作用应发生得更早。蛇绿岩可能形成在弧间环境中。作者对新赫布里底群岛渐新世弧系的重建是对现代马里亚纳弧系的一次模拟。弧间的裂谷作用停止于早中新世。在中—晚中新世时,俯冲带可能已向要转移到迈沃—彭特科斯特扩张轴。
Eight lithofacies are discernible in the lower part of the Chavala Formation (Late Oligocene-Early Miocene) on the island of Mauvoo, New Hebrides. These eight rocks represent a deep-sea fan extending westward, mainly formed by the mechanism of gravity flow. Of the calcareous red siltstone and a small amount of green siltstone on the sea floor of the deep sea fan (indicating that sedimentation is beyond the depth of carbonate compensation ie 4250 m below sea level) and a very small amount of thin-layer atmospheric dustfall. According to previous studies, the area of Mauwoo Island was once a rift area during the Middle Miocene. However, the tremendous depth of Late Pleistocene-Early Miocene sediments suggests that that rifting should occur before the late Oligocene. The discovery of an Oligocene ophiolite suite 35 to 28 million years old on the island of Pencott, south of Mauwoo Island, demonstrates that rifting should occur earlier. Ophiolite may form in the arc environment. The author’s reconstruction of the Oligocene arc system in the New Hebrides is a simulation of the modern Mariana arc. The rifting between arcs ceased in the early Miocene. During the Mid-Late Miocene, the subduction zone may have been moving to the Maewoo-Penteost expansion axis.