The Cleft revealed: Geologic, magnetic, and morphologic evidence for construction of upper oceanic crust along the southern Juan de Fuca Ridge
The Cleft revealed: Geologic, magnetic, and morphologic evidence for construction of upper oceanic crust along the southern Juan de Fuca Ridge
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裂缝揭示了：沿胡安德富卡海岭南部形成上洋壳的地质、磁性和形态学证据
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发表时间：
2006
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通讯作者：
N. Maher
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作者：
D. Stakes;M. Perfit;M. Tivey;D. Caress;T. Ramirez;N. Maher
使用高分辨率测绘系统、遥控潜水器（REO）观测、安装在卫星上的磁力计以及对回收熔岩的地球化学分析，对胡安·德富卡海脊南部裂缝段（JdFR）的地质和结构进行了研究。使用多波束（EM 300）的测深制图结合现场观测，重点关注近轴和侧翼区域，提供了JdFR南端0至400 ka上地壳的详细图像。在包括16次潜水的三次航行中，共收集了53个岩心和276个精确定位的岩石或玻璃样品。我们在这些潜水过程中对海底的观察表明，许多构成和/或覆盖轴向谷侧翼突出山脊的无断层和广泛的熔岩流源自形成于高度构造区的山脊平行断层和裂缝，这些断层和裂缝形成了轴向谷的壁。这些近轴和侧翼喷发的地球化学演化和异质性与地壳岩浆房或岩浆带较冷的远缘内的起源一致。相比之下，最近的轴向喷发更原始（较高的MgO），化学均匀的裂片，片，和大量的流动，产生一个独特的磁高的轴向山谷。我们认为，离轴观察到的同构造盖层火山岩是从近轴和侧翼裂缝喷发的，并产生了一个加厚的喷出层，如磁力和地震数据所示。这个模型表明，许多熔岩，包括高架山脊，界定轴向山谷的裂缝段喷发期间的岩浆周期的崩溃，而不是在强大的阶段，建立了一个新的岩浆周期。
The geology and structure of the Cleft Segment of the Southern Juan de Fuca Ridge (JdFR) have been examined using high‐resolution mapping systems, observations by remotely operated vehicle (ROV), ROV‐mounted magnetometer, and the geochemical analysis of recovered lavas. Bathymetric mapping using multibeam (EM300) coupled with in situ observations that focused on near‐axis and flank regions provides a detailed picture of 0 to 400 ka upper crust created at the southern terminus of the JdFR. A total of 53 rock cores and 276 precisely located rock or glass samples were collected during three cruises that included sixteen ROV dives. Our observations of the seafloor during these dives suggest that many of the unfaulted and extensive lava flows that comprise and/or cap the prominent ridges that flank the axial valley emanate from ridge parallel faults and fissures that formed in the highly tectonized zone that forms the walls of the axial valley. The geochemically evolved and heterogeneous nature of these near‐axis and flank eruptions is consistent with an origin within the cooler distal edges of a crustal magma chamber or mush zone. In contrast, the most recent axial eruptions are more primitive (higher MgO), chemically homogeneous lobate, sheet, and massive flows that generate a distinct magnetic high over the axial valley. We suggest that the syntectonic capping volcanics observed off‐axis were erupted from near‐axis and flank fissures and created a thickened extrusive layer as suggested by the magnetic and seismic data. This model suggests that many of the lavas that comprise the elevated ridges that bound the axial valley of the Cleft Segment were erupted during the collapse of a magmatic cycle not during the robust phase that established a new magmatic cycle.