The continental margin off Oregon from seismic investigations
The continental margin off Oregon from seismic investigations
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地震调查显示的俄勒冈州外大陆边缘
DOI：
10.1016/s0040-1951(00)00190-6
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发表时间：
2000
期刊：
影响因子：
2.9
通讯作者：
D. Klaeschen
中科院分区：
文献类型：
--
作者：
M. Gerdom;A. Tréhu;E. Flueh;D. Klaeschen
1996年4月和5月，在德国考察船索内号上对俄勒冈州和华盛顿外的卡斯卡迪亚大陆边缘进行了一次地球物理研究，这是地球物理研究所、美国地质勘探局和美国海洋科学委员会之间的一项合作实验。本研究的对象是俄勒冈州中部近海，实验涉及使用海底地震仪（OBS）和水听器（OBH）以及陆地记录仪沿沿着三个横跨大陆边缘的剖面收集广角折射和反射数据。二维模型的旅行时间提供了一个详细的速度结构下，这些配置文件。胡安·德富卡板块的俯冲洋壳可以从海沟追溯到海岸线向陆地方向约10公里的位置。在海岸线上，莫霍面的深度为30公里。板块的倾角从海沟向西的1.5°变化到增生杂岩以下的约6.5°，再向东到海岸以下的约16°。形成锡莱茨海脊西缘的后挡板，是一个大约50 Ma前增生到北美的海洋高原，通过观测得到了很好的定义。它位于变形锋以东约60km处，向海倾斜40°。在其向海的边缘，锡莱茨海盆的底部似乎与俯冲洋壳接触，这意味着沉积物不太可能俯冲到更深的地方。该接触带以东的上洋壳比西部薄。在超过18公里的深度，海洋地壳的顶部是在几个陆地记录和一个海底仪器的数据中观察到的临界前反射的起源。这些反射很可能是由变质相变从洋壳释放出来的流体引起的。
In April and May 1996, a geophysical study of the Cascadia continental margin off Oregon and Washington was carried out aboard the German RV Sonne as a cooperative experiment between GEOMAR, the USGS and COAS. Offshore central Oregon, which is the subject of this study, the experiment involved the collection of wide-angle refraction and reflection data along three profiles across the continental margin using ocean-bottom seismometers (OBS) and hydrophones (OBH) as well as land recorders. Two-dimensional modelling of the travel times provides a detailed velocity structure beneath these profiles. The subducting oceanic crust of the Juan de Fuca plate can be traced from the trench to its position some 10km landward of the coastline. At the coastline, the Moho has a depth of 30km. The dip of the plate changes from 1.5° westward of the trench to about 6.5° below the accretionary complex and to about 16° further eastward below the coast. The backstop forming western edge of the Siletz terrane, an oceanic plateau that was accreted to North America about 50Ma ago, is well defined by the observations. It is located about 60km to the east of the deformation front and has a seaward dip of 40°. At its seaward edge, the base of the Siletz terrane seems to be in contact with the subducting oceanic crust implying that sediments are unlikely to be subducted to greater depths. The upper oceanic crust is thinner to the east of this contact than to the west. At depths greater than 18km, the top of the oceanic crust is the origin of pre-critical reflections observable in several land recordings and in the data of one ocean bottom instrument. These reflections are most likely caused by fluids that are released from the oceanic crust by metamorphic facies transition.