Hydrogeological system of erosional convergent margins and its influence on tectonics and interplate seismogenesis
Hydrogeological system of erosional convergent margins and its influence on tectonics and interplate seismogenesis
复制标题
DOI：
10.1029/2007gc001679
复制
发表时间：
2008-03
期刊：
影响因子：
3.7
通讯作者：
C. Ranero;I. Grevemeyer;H. Sahling;U. Barckhausen;C. Hensen;K. Wallmann;W. Weinrebe;P. Vannucchi;R. Huene;K. Mcintosh
中科院分区：
文献类型：
--
作者：
C. Ranero;I. Grevemeyer;H. Sahling;U. Barckhausen;C. Hensen;K. Wallmann;W. Weinrebe;P. Vannucchi;R. Huene;K. Mcintosh
在汇聚边缘，流体分布在大多数情况下与构造密切相关。这种关联在增生楔中已被广泛研究，但在地球上一半的汇聚边缘，构造侵蚀会磨蚀上覆板块，在这里，流体分布及其与构造的关系仍然是推测性的。在此，我们提出一个关于侵蚀性汇聚边缘水文系统的新概念模型。该模型主要基于来自尼加拉瓜和哥斯达黎加近海的中美洲海沟的新数据以及近期发表的观测结果，并且与来自其他侵蚀性边缘的观测结果一致。观测结果表明，侵蚀性边缘拥有此前未被识别的独特水文地质系统：沉积物孔隙中所含的大部分流体以及由早期脱水反应释放的流体，是通过破裂的上覆板块从板块边界排出，然后在海底沿斜坡渗出，而不是像在增生楔中所描述的那样沿着拆离面向变形前缘迁移。观测结果表明，板块边界断层带的相对流体丰度以及流体迁移影响长期构造以及从无震到发震行为的转变。板块边界上流体似乎更丰富的部分对应于长期构造侵蚀的位置，在那里上覆板块的构造减薄导致下沉和大陆斜坡的形成。这些观测结果之间的对应关系表明，构造侵蚀可能与超压流体向上覆板块的迁移有关。板块边界处超压流体的存在与在斜坡渗出处估计的最高流速是相符的。侵蚀性边缘板块边界从无震到发震行为的转变始于断层处流体量随深度减少的地方，这表明对板间地震存在控制作用。先前在增生板块边界描述的类似观测结果有力地表明，流体丰度对所有类型俯冲带的板间地震活动都有一级控制作用。我们假设，流体随深度的减少会增加颗粒间的接触，增加断层上的有效应力，并使断层带结构从一个较厚的断层带转变为一个更窄的局部滑动带。
Fluid distribution in convergent margins is by most accounts closely related to tectonics. This association has been widely studied at accretionary prisms, but at half of the Earth's convergent margins, tectonic erosion grinds down overriding plates, and here fluid distribution and its relation to tectonics remain speculative. Here we present a new conceptual model for the hydrological system of erosional convergent margins. The model is based largely on new data and recently published observations from along the Middle America Trench offshore Nicaragua and Costa Rica, and it is consistent with observations from other erosional margins. The observations indicate that erosional margins possess previously unrecognized distinct hydrogeological systems: Most fluid contained in the sediment pores and liberated by early dehydration reactions drains from the plate boundary through a fractured upper plate to seep at the seafloor across the slope, rather than migrating along the décollement toward the deformation front as described for accretionary prisms. The observations indicate that the relative fluid abundance across the plate‐boundary fault zone and fluid migration influence long‐term tectonics and the transition from aseismic to seismogenic behavior. The segment of the plate boundary where fluid appears to be more abundant corresponds to the locus of long‐term tectonic erosion, where tectonic thinning of the overriding plate causes subsidence and the formation of the continental slope. This correspondence between observations indicates that tectonic erosion is possibly linked to the migration of overpressured fluids into the overriding plate. The presence of overpressured fluids at the plate boundary is compatible with the highest flow rates estimated at slope seeps. The change from aseismic to seismogenic behavior along the plate boundary of the erosional margin begins where the amount of fluid at the fault declines with depth, indicating a control on interplate earthquakes. A previously described similar observation along accreting plate boundaries strongly indicates that fluid abundance exerts a first‐order control on interplate seismogenesis at all types of subduction zones. We hypothesize that fluid depletion with depth increases grain‐to‐grain contact, increasing effective stress on the fault, and modifies fault zone architecture from a thick fault zone to a narrower zone of localized slip.