Deep‐penetrating MCS images of the South Gabon Basin: implications for rift tectonics and post‐breakup salt remobilization
Deep‐penetrating MCS images of the South Gabon Basin: implications for rift tectonics and post‐breakup salt remobilization
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南加蓬盆地的深层 MCS 图像：对裂谷构造和裂解后盐再活化的影响
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发表时间：
1996
期刊：
影响因子：
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通讯作者：
J. A. Austin
中科院分区：
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作者：
J. Meyers;B. Rosendahl;J. A. Austin
摘要 沿加蓬南缘部分地区的裂谷边缘结构通过四个深穿透、多道地震反射（MCS）剖面进行解释。确定了一系列综合断层地壳块，它们被非洲和南美洲白垩纪裂谷期间形成的主要向海倾斜的断层带分开。拉伸应变比为 ≅ 1.5。这些断层要么横断整个地壳部分，要么被可能代表分离的中地壳反射的不连续区域所中断。
外部声学基底高点位于大陆坡的海边。在地震几何、相关的正磁异常和自由空气重力增加的综合基础上，这些外部高点被解释为标志着从裂谷大陆地壳到“原洋地壳”的断层过渡，可能由镁铁质火山岩和可能的衰减大陆地壳块的碎片组成。阿普第盐的外缘位于大陆架边缘西南 165 公里处。这些盐形成了覆盖在外部高点上的 1.5 公里厚的地平线，并且它可能是当地的，这表明盐是与原洋地壳同时沉积的。
裂谷后边缘沉降过程中大陆裂谷块之间的差异沉降和倾斜导致了上覆阿普第盐的交感阶地斜坡几何形状。盐台形成于地壳块顶部上方，盐往往垂直上升，形成枕状和底辟。连接阶地的坡道往往形成于面向大海的断层带之上；那里的盐流既有横向的，也有纵向的，沿着生长断层的下盘形成了三角形的底辟。大多数生长断层仅存在于盐基底内，但也有少数继续进入所解释的同裂谷序列中。
Abstract Rifted margin architecture along part of the southern Gabonese margin is interpreted from four deep-penetration, multichannel seismic reflection (MCS) profiles. A series of synthetically faulted crustal blocks are identified, separated by dominantly seaward-dipping fault zones formed during Cretaceous rifting between Africa and South America. Extensional strain ratios are ≅ 1.5. These faults appear either to transect the entire crustal section or are interrupted by discontinuous zones of midcrustal reflections which may represent detachments.
Outer acoustic basement highs are situated just seaward of the continental slope. On the combined basis of seismic geometry, an associated positive magnetic anomaly and an increase in free-air gravity, these outer highs are interpreted to mark faulted transitions from rifted continental crust to ‘proto-oceanic crust’, presumably composed of mafic volcanic rocks and possibly slivers of attenuated continental crustal blocks. The outer edge of Aptian salt lies °165 km south-west of the edge of the continental shelf. The salt forms an° 1.5-km-thick horizon overlying the outer highs, and it may be autochthonous there, suggesting salt was deposited contemporaneously with emplacement of proto-oceanic crust.
Differential subsidence and tilting between continental rift-blocks during post-rift margin subsidence has resulted in a sympathetic terrace-ramp geometry in overlying Aptian salt. Salt terraces form above tops of crustal blocks, where salt tends to rise vertically, creating pillows and diapirs. Ramps connecting terraces tend to form above seaward-facing fault zones; salt flowage there has been both lateral and vertical, creating triangular diapirs along the footwalls of growth faults. Most of these growth-faults sole within the salt base, but a few continue into the interpreted synrift succession.