Tectonic setting of serpentinite exposures on the western median valley wall of the MARK area in the vicinity of Site 920
Tectonic setting of serpentinite exposures on the western median valley wall of the MARK area in the vicinity of Site 920
复制标题
Site 920 附近 MARK 地区西中谷壁蛇纹岩暴露的构造环境
DOI：
10.2973/odp.proc.sr.153.001.1997
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发表时间：
1997
影响因子：
3.9
通讯作者：
R. M. Lawrence
中科院分区：
文献类型：
--
作者：
J. Karson;R. M. Lawrence
地幔源蛇纹岩橄榄岩在MARK地区Kane Transform以南沿大西洋中脊的西中谷壁生长出一条宽约2公里、长约20公里的带。蛇纹岩从凯恩变换附近的大量辉长岩中向南延伸。该带沿与一个突出的新火山脊平行的一个明确的脊段的约一半长度延伸出来。它终止于南部的一个分段边界带，以一个测深凹陷为标志，其痕迹斜向向西北延伸到较古老的地壳中，在那里也疏浚了蛇纹岩。蛇纹岩被认为是由沿主要地壳拆离的岩石圈极端伸展暴露出来的，这表明基性深成岩在北部作为海洋核复合体出现。蛇纹岩中缓慢倾斜的变质组构和断裂面表明这两个相邻地区具有相似的构造历史。沿蛇纹石化橄榄岩带长度方向一致的高低温构造不支持底液隆升作为这些外来岩石暴露的机制。辉长岩-辉长岩侵入岩和上覆玄武岩熔岩表明，蛇纹岩是由上地幔物质的隆升和断裂暴露出来的，当上地幔物质在脊轴以下上升并横向扩散时，没有形成广泛的上覆岩浆地壳。这些类型的水合上地幔物质的暴露似乎是形成于岩浆预算低的缓慢扩张脊的洋壳的共同元素。
Mantle-derived serpentinized peridotites crop out in a belt approximately 2 km wide and 20 km long along the western median valley wall of the Mid-Atlantic Ridge just south of the Kane Transform in the MARK area. Serpentinites extend southward from extensive exposures of gabbroic rocks near the Kane Transform. The belt crops out along approximately half the length of a well-defined ridge segment parallel to a prominent neovolcanic ridge. It terminates in a segment boundary zone to the south marked by a bathymetric depression whose trace extends obliquely off axis northwestward into older crust where serpentinites have also been dredged. The serpentinites are considered to have been exposed by extreme lithospheric extension along a major crustal detachment, as suggested for mafic plutonic rocks that crop out as an oceanic core complex to the north. Gently dipping metamorphic fabrics and fault surfaces in the serpentinites suggest a similar structural history for these two adjacent areas. Consistently oriented high- and low-temperature fabrics along the length of the belt of serpentinized peridotites do not support diapiric uplift as a mechanism for the exposure of these exotic rocks. Gabbroic to diabasic intrusions and overlying basaltic lavas suggest that the serpentinites were exposed by uplift and faulting of upper mantle material that did not develop an extensive overlying magmatic crust as it rose beneath the ridge axis and spread laterally. These types of exposures of hydrated upper mantle material appear to be common elements of oceanic crust formed at slow-spreading ridges with low magma budgets.