Segment-scale variations in the crustal structure of 150-300 kyr old fast spreading oceanic crust (East Pacific Rise, 8°15′N-10°5′N) from wide-angle seismic refraction profiles
Segment-scale variations in the crustal structure of 150-300 kyr old fast spreading oceanic crust (East Pacific Rise, 8°15′N-10°5′N) from wide-angle seismic refraction profiles
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DOI：
10.1046/j.1365-246x.2003.01885.x
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发表时间：
2003-03-01
影响因子：
2.8
通讯作者：
Wilcock, WSD
中科院分区：
文献类型：
--
作者：
Canales, JP;Detrick, RS;Wilcock, WSD
本文同时反演了西凯罗斯断裂带和克利珀顿断裂带之间东太平洋海隆（EPR）上沿着15 - 30万年前地壳的二维厚度和速度结构的地震折射和广角莫霍面反射走时。我们的研究结果表明，脊分段和上地壳和中地壳地震速度之间有很强的相关性，段中心附近的速度较高，段两端附近的速度较低。低地壳速度在克利珀顿和Siqueiros FZ被解释为断裂造成的地壳脆性变形的变换域。9 ° 03 'N重叠扩张中心（OSC）向南传播时在太平洋板块上留下的残留重叠盆地，与上、中地壳速度负异常有关。这种异常与盆地内异常厚的喷出部分的存在以及盆地形成时旋转引起的构造蚀变、断裂和剪切一致。这个OSC在科科斯板块上留下的不协调带的特点是地壳速度中等偏低，这可能是因为OSC传播到老地壳时地壳破裂造成的。段中心附近较高的地壳速度可能反映了上地壳中较高的岩墙与喷出物的比例，以及地壳较低强度的构造蚀变，而不是段端部附近。最厚的地壳位于拉蒙海山之下（约9公里），并位于北纬9度03分的南纬偏轴迹线（7.3-7.8公里）以北的一个指向南方的V形带内。最薄的地壳（
We have simultaneously inverted seismic refraction and wide-angle Moho reflection traveltimes for the 2-D crustal thickness and velocity structure of 150-300 kyr old crust along the East Pacific Rise (EPR) between the Siqueiros and Clipperton fracture zones (FZs). Our results show a strong correlation between ridge segmentation and upper- and mid-crustal seismic velocities, with higher velocities near segment centres and lower velocities near segment ends. Low crustal velocities at the Clipperton and Siqueiros FZs are interpreted as fracturing resulting from brittle deformation of the crust in the transform domain. A relict overlap basin left on the Pacific Plate by the 9degrees03'N overlapping spreading centre (OSC) as it propagated southward is associated with a large (similar to1 km s(-1)), negative upper- and mid-crustal velocity anomaly. This anomaly is consistent with the presence of an unusually thick extrusive section within the basin and with tectonic alteration, fracturing and shearing arising from rotation of the basin as it was formed. The discordant zone left by this OSC on the Cocos Plate is characterized by moderately low crustal velocities, probably because of crustal fracturing as the OSC propagated into older crust. Higher crustal velocities near segment centres may reflect a higher ratio of dikes to extrusives in the upper crust, and lower-intensity tectonic alteration of the crust, than near segment ends.The mean crustal thickness along the EPR between the Siqueiros and Clipperton FZs is 6.7-6.8 km. The thickest crust is found beneath the Lamont seamounts (similar to9 km), and in a southward-pointing, V-shaped band located just north of the off-axis trace of the 9degrees03'N OSC (7.3-7.8 km). The thinnest crust (