A multiphase plate tectonic history of the southeast continental margin of Oman
A multiphase plate tectonic history of the southeast continental margin of Oman
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阿曼东南大陆边缘的多期板块构造历史
DOI：
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发表时间：
1990
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影响因子：
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通讯作者：
W. Prell
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文献类型：
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作者：
G. Mountain;W. Prell
西印度洋主要盆地形成于晚侏罗世印度-马达加斯加-南极洲与非洲-阿拉伯分离时期。从北到南分别是欧文盆地、北索马里盆地、西索马里盆地和莫桑比克盆地。中生代磁异常证实后两个地区的构造没有发生变化；相比之下，欧文盆地和北索马里盆地的异常尚未被发现，留下了一个或两个被随后的扩散事件叠加的可能性。尽管如此，许多研究人员选择假设欧文盆地内的基底是侏罗纪至早白垩世海洋地壳的原始碎片，而阿曼东南部自印度裂谷以来一直是被动边缘。1986年罗伯特·d·康拉德号上获得的海洋地球物理数据提供了新的信息，表明必须形成一个更复杂的区域板块历史。在欧文盆地收集的地震反射剖面揭示了与侏罗纪时代不一致的构造。首先，欧文盆地基底比侏罗纪以来热沉降预测的浅1 km以上。其次，通过对欧文海岭上的DSDP 224测点进行地震追踪，可以估计欧文盆地沉积物的年龄。这两种方法都证明欧文盆地的年龄不超过晚白垩纪。阿曼东南边缘18°N附近的地震剖面显示出复杂的变形特征，与简单的被动边缘历史不相容。在大陆斜坡下绘制了以基底断裂为界的厚沉积盆地。抵消达到非常接近海底，这表明它们在最近的过去一直很活跃。我们在Ra 's Madrakah西南75公里处，以及在那里和Masirah岛暴露的蛇绿岩走向处，获得了许多地下室的交叉点。这一特征的磁、地震和构造特征都与它是同一片海洋地壳的沿走向的隐伏延伸相一致。为了使这些观测结果与有关西北印度洋开放历史的既定事实相一致，我们提出以下设想。首先，侏罗纪时期印度-马达加斯加-南极洲与非洲-阿拉伯分离，形成了原始欧文盆地。然而，随着晚白垩世印度与马达加斯加的分离，新的扩张脊沿阿曼东南边缘偏移，而不是像许多人认为的那样在欧文脊偏移。在这一构造发展阶段，原欧文盆地地壳被带向东北，最终与亚洲碰撞和俯冲。结果形成了一个与晚白垩世欧文盆地相邻的走滑阿曼边缘。目前在阿曼东南海岸发现的蛇绿岩是晚白垩世欧文盆地地壳的碎片，可能是沿该板块边界的转压运动的结果。这种安排一直持续到新近纪又有一个传播中心打开了亚丁湾。后一种板块几何形状的重组导致了欧文盆地的主要压应力，导致了欧文脊的抬升（很容易通过与DSDP站点224相关的剖面中的地层关系看到），以及阿曼边缘晚白垩世断层的重新激活。我们预计，通过比较阿曼东南部晚白垩世后的构造活动和我们的海洋地震和钻井数据，可以验证这一多阶段历史。
Abstract The major basins of the western Indian Ocean formed during the Late Jurassic separation of India-Madagascar-Antarctica from Africa-Arabia. From north to south these are the Owen, North Somali, West Somali, and Mozambique Basins. Mesozoic magnetic anomalies confirm that these latter two regions have remained tectonically unchanged; by contrast, anomalies have yet to be identified in the Owen and North Somali Basins, leaving open the possibility that one or both have been overprinted by subsequent spreading events. Nonetheless, many researchers have chosen to assume that the basement within the Owen Basin is an unaltered fragment of Jurassic to Early Cretaceous oceanic crust, and that SE Oman has been a passive margin since its rifting from India. Marine geophysical data acquired aboard R/V Robert D. Conrad during 1986 provides new information that suggests a more complex regional plate history must be developed. Seismic reflection profiles collected across the Owen Basin reveal structure that is not consistent with a Jurassic age. First, we observe that basement in the Owen Basin is more than 1 km shallower than should be expected from thermal subsidence since Jurassic time. Second, the age of sediments in the Owen Basin can be estimated by tracing them seismically to DSDP Site 224 on the Owen Ridge. Both of these procedures argue for the Owen Basin being no older than Late Cretaceous. Seismic profiles along the SE Oman Margin near 18°N show complex deformational features that are incompatible with a simple passive margin history. A thick sedimentary basin bounded by basement-involved faults was mapped beneath the continental slope. Offsets reach to very near the seafloor, suggesting they have been active in the recent past. We acquired numerous crossings of a basement feature 75 km SW of Ra’s Madrakah and along the strike of ophiolites exposed there and at Masirah Island. The magnetic, seismic, and structural characteristics of this feature are all consistent with its being a buried, along-strike extension of this same slice of oceanic crust. To reconcile these observations with well-established facts concerning the opening history of the NW Indian Ocean, we propose the following scenario. First, a proto-Owen Basin formed in Jurassic time when India-Madagascar-Antarctica separated from Africa-Arabia. However, following the Late Cretaceous separation of India from Madagascar, the new spreading ridge was offset along the SE Oman margin, not at the Owen Ridge as is assumed by many. During this stage of tectonic development, the proto-Owen Basin crust was carried northeastward towards eventual collision and subduction with Asia. The result was a strike-slip Oman margin adjacent to a Late Cretaceous Owen Basin. Ophiolites now found along the SE coast of Oman are fragments of this Late Cretaceous Owen Basin crust, and were probably emplaced as a result of transpressional motion along this plate boundary. This arrangement persisted until yet another spreading centre opened the Gulf of Aden in Neogene time. The latter reorganization of plate geometries led to major compressive stresses across the Owen Basin that resulted in elevation of the Owen Ridge (readily seen by way of stratal relationships in profiles tied to DSDP Site 224), and reactivation of Late Cretaceous faults along the Oman Margin. We anticipate that verification of this multiple-phase history will emerge from future comparisons between post-Late Cretaceous tectonism within SE Oman and our marine seismic and drilling data.