Structure of uppermost fast‐spread oceanic crust exposed at the Hess Deep Rift: Implications for subaxial processes at the East Pacific Rise
Structure of uppermost fast‐spread oceanic crust exposed at the Hess Deep Rift: Implications for subaxial processes at the East Pacific Rise
复制标题
赫斯深裂谷暴露的最上层快速扩张的洋壳结构：对东太平洋隆起次轴过程的影响
DOI：
--
复制
发表时间：
2002
期刊：
影响因子：
--
通讯作者：
A. Sutton
中科院分区：
文献类型：
--
作者：
J. Karson;E. Klein;S. Hurst;C. E. Lee;P. Rivizzigno;D. Curewitz;A. Morris;D. Miller;R. Varga;G. Christeson;B. Cushman;J. O’Neill;J. Brophy;K. Gillis;M. Stewart;A. Sutton
在赤道东太平洋海隆（EPR）快速扩张（135 mm/年，全速）时形成的最上层2 km的洋壳，沿着沿着赫斯裂谷的悬崖暴露了数十km。来自远程操作车辆（ARGO II）的大规模数字图像的马赛克和来自潜水器Alvin的直接观察记录了一定程度的地质复杂性和可变性，这些复杂性和可变性在大多数蛇绿岩研究或海底扩张的流行模型中并不明显。在玄武质火山岩和席状岩脉岩石单元中，记录了厚度和内部结构的剧烈变化。这些岩石单元的特征是广泛的断层，精细的断裂，以及几米到几十米宽的连贯地壳块体的旋转。最上面的玄武质熔岩基本上没有变形，总体上具有平缓倾斜的流动表面。然而，通过大部分玄武质熔岩单元，熔岩流接触倾向（20°-70 ° W）朝向EPR，并且通常在剖面中倾向向下增加。切割熔岩的岩脉和位于下方席状岩脉单元中的岩脉一般倾向（90°-40 ° E）远离EPR。较深层次的辉长岩几乎没有显示出上覆单元典型的强烈断裂的证据。我们解释这种上地壳结构的结果，在1-2公里的EPR，容纳玄武质熔岩单位增厚到10500米的亚轴沉降。熔岩和岩墙单元的厚度和空间相关结构的变化沿着裂谷陡崖表明岩浆供应的时间波动。这些结果表明，大量的脆性变形伴随着在赫斯深裂谷暴露的地壳部分的增生过程中的火山活动的消长。如果这种类型的结构是EPR产生的最上层洋壳的典型结构，那么这些过程可能在沿着快速扩张的洋中脊很常见。
The uppermost 2 km of the oceanic crust created at the fast spreading (135 mm yr−1, full rate) equatorial East Pacific Rise (EPR) is exposed for tens of kilometers along escarpments bounding the Hess Deep Rift. Mosaics of large‐scale digital images from the remotely operated vehicle (ROV) Argo II and direct observations from the submersible Alvin document a degree of geological complexity and variability that is not evident from most studies of ophiolites or prevailing models of seafloor spreading. Dramatic variations in the thickness and internal structure are documented in both the basaltic volcanic and sheeted dike rock units. These rock units are characterized by extensive faulting, fine‐scale fracturing, and rotations of coherent crustal blocks meters to tens of meters across. The uppermost basaltic lavas are essentially undeformed and have overall gently inclined flow surfaces. Through most of the basaltic lava unit, however, lava flow contacts dip (20°–70°W) toward the EPR and generally increase in dip downward in the section. Dikes cutting the lavas and in the underlying sheeted dike unit generally dip (90°–40°E) away from the EPR. Deeper level gabbroic rocks show little evidence of the intense fracturing typical of the overlying units. We interpret this upper crustal structure as the result of subaxial subsidence within 1–2 km of the EPR that accommodated the thickening of the basaltic lava unit to ∼500 m. Variations in the thickness of lava and dike units and spatially related structures along the rift escarpments suggest temporal fluctuations in magma supply. These results indicate that substantial brittle deformation accompanied waxing and waning volcanism during the accretion of the crustal section exposed at the Hess Deep Rift. If this type of structure is typical of uppermost oceanic crust generated at the EPR, these processes may be common along fast spreading mid‐ocean ridges.