The morphology and tectonics of the Mark area from Sea Beam and Sea MARC I observations (Mid-Atlantic Ridge 23° N)
The morphology and tectonics of the Mark area from Sea Beam and Sea MARC I observations (Mid-Atlantic Ridge 23° N)
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来自 Sea Beam 和 Sea MARC I 观测的 Mark 区域的形态和构造（大西洋中脊 23° N）
DOI：
10.1007/bf02424661
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发表时间：
1988
期刊：
影响因子：
--
通讯作者：
W. Ryan
中科院分区：
文献类型：
--
作者：
L. Kong;R. Detrick;P. J. Fox;L. Mayer;W. Ryan
高分辨率海束测深和 Sea MARC I 侧扫声纳数据已在 MARK 区域获得，该区域是凯恩断裂带以南大西洋中脊裂谷的 100 公里长部分。这些数据揭示了一个令人惊讶的复杂裂谷结构，该结构由两个不同的扩散单元组成，它们重叠形成一个小的零偏移变换或不一致区域。北部扩张单元由一个长 40-50 公里的岩浆强劲的活动山脊部分组成，从东部凯恩山脊转换交汇处向南延伸到北纬约 23°12′。该地区的裂谷以大型建筑火山脊为主，形成 200-500 米的地形，并与高温热液活动有关。南部扩张单元的特点是北北东走向的小型圆锥形火山带（高 50-200 m），这些火山建在相对古老、有裂隙且覆盖有沉积物的熔岩之上，在某些情况下火山本身也有裂隙和断层。该细胞似乎处于主要的伸展阶段，仅出现小的、孤立的喷发。这两个扩张单元在北纬 23°05′ 和北纬 23°17′ 之间的异常区域重叠，该异常区域缺乏发育良好的裂谷或新火山带，并且可能代表与东太平洋海隆发现的重叠扩张中心类似的缓慢扩张的山脊。尽管 MARK 地区十分复杂，但火山和构造活动似乎仅限于 10-17 公里宽的裂谷底部。沿着近垂直、小偏移正断层的块断层作用，伴随着少量的后倾（通常小于 5°），开始于山脊轴几公里内，并在地壳向上输送到裂谷壁时基本完成。中谷中形成的似乎是建筑火山脊的特征在裂谷山脉中基本上完好无损。陡坡面的大量流失和沟壑，以及埋藏低地势海底特征的沉积作用，是发生在裂谷之外的主要地质过程。本研究记录的马克裂谷和侧翼裂谷内的形态和结构异质性很大程度上是两个扩散细胞的产物，这两个扩散细胞独立于伸展构造运动和岩浆生产率的幕式变化之间的相互作用而演化。
High-resolution Sea Beam bathymetry and Sea MARC I side scan sonar data have been obtained in the MARK area, a 100-km-long portion of the Mid-Atlantic Ridge rift valley south of the Kane Fracture Zone. These data reveal a surprisingly complex rift valley structure that is composed of two distinct spreading cells which overlap to create a small, zero-offset transform or discordant zone. The northern spreading cell consists of a magmatically robust, active ridge segment 40–50 km in length that extends from the eastern Kane ridge-transform intersection south to about 23°12′ N. The rift valley in this area is dominated by a large constructional volcanic ridge that creates 200–500 m of relief and is associated with high-temperature hydrothermal activity. The southern spreading cell is characterized by a NNE-trending band of small (50–200 m high), conical volcanos that are built upon relatively old, fissured and sediment-covered lavas, and which in some cases are themselves fissured and faulted. This cell appears to be in a predominantly extensional phase with only small, isolated eruptions. These two spreading cells overlap in an anomalous zone between 23°05′ N and 23°17′ N that lacks a well-developed rift valley or neovolcanic zone, and may represent a slow-spreading ridge analogue to the overlapping spreading centers found at the East Pacific Rise. Despite the complexity of the MARK area, volcanic and tectonic activity appears to be confined to the 10–17 km wide rift valley floor. Block faulting along near-vertical, small-offset normal faults, accompanied by minor amounts of back-tilting (generally less than 5°), begins within a few km of the ridge axis and is largely completed by the time the crust is transported up into the rift valley walls. Features that appear to be constructional volcanic ridges formed in the median valley are preserved largely intact in the rift mountains. Mass-wasting and gullying of scarp faces, and sedimentation which buries low-relief seafloor features, are the major geological processes occurring outside of the rift valley. The morphological and structural heterogeneity within the MARK rift valley and in the flanking rift mountains documented in this study are largely the product of two spreading cells that evolve independently to the interplay between extensional tectonism and episodic variations in magma production rates.