Geophysical evidence of crustal-heterogeneity control of fault growth in the Neocomian Iguatu basin, NE Brazil
Geophysical evidence of crustal-heterogeneity control of fault growth in the Neocomian Iguatu basin, NE Brazil
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巴西东北部 Neocomian 伊瓜图盆地地壳非均质性控制断层生长的地球物理证据
DOI：
10.1016/j.jsames.2008.07.002
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发表时间：
2008
影响因子：
1.8
通讯作者：
R. Branco
中科院分区：
文献类型：
--
作者：
D. L. Castro;F. Bezerra;R. Branco
断层增长模型认为，裂缝的形成始于短断层段。这些部分的增长和他们的相互作用的知识是很重要的理解裂谷的几何形状和演变。在巴西东北部博尔博雷马省的北方，一个大陆规模的白垩纪伸展断层系统被观察到重新激活了韧性前寒武纪剪切带。断层形成小地堑，代表沉积盆地的裂谷阶段。我们集成了航空辐射和磁力数据与地面重力测量，以调查地壳的不均匀性对断层生长和这些地堑之一，伊瓜图盆地的伸展断层的发展的影响。以前的研究提出了地球物理数据，提供证据表明，伊瓜图盆地包含一个半地堑的几何形状。在我们的研究中，重力和航空地球物理数据表明，伊瓜图盆地的基底是由两个结构域组成的非均质结构框架的一部分，受到几个韧性剪切带的影响，并被一些花岗岩体侵入。重力模拟结果表明，该盆地由三个右旋雁列断裂段组成。它们形成了一个S形正断层系统，适应了前寒武纪剪切带从东西向大致南北向的强烈的90°弯曲。这些部分的增长导致了两个孤立的沉积中心的产生。重叠的故障段通过中继斜坡连接。释放断层几乎垂直或倾斜于三个主要的断层段形成边缘走向斜坡和地垒结构在两个沉积中心。3D重力建模结合了异质结构框架的干扰源的存在。模拟结果显示，最大沉积盖层厚度为1620 m，位于再活化剪切带的弯曲处。一个可能的花岗岩体的重力信号，在去除盆地填充沉积物的重力效应后，表明这种可能的侵入形成了一个大致平行于基底结构的地垒。最大位移量与断层长度的关系表明，半地堑形成时，断层段是独立形成的。但断层段之间由中继坡道连接，相互影响。我们解释的片段代表一个前链接，多段阶段的一个流产的裂谷系统。这种断层生长的模式也可能影响了该地区其他沉积盆地的裂谷阶段。
Models of fault growth propose that rift initiation starts with short fault segments. Knowledge of the growth of these segments and their interactions is important to understanding rift geometry and evolution. In the northern part of the Borborema Province, northeastern Brazil, a continental-scale, Cretaceous extensional system of faults has been observed to have reactivated ductile Precambrian shear zones. The faults form small grabens that represent the rift stage of the sedimentary basins. We integrated airborne radiometric and magnetic data with terrestrial gravity survey to investigate the influence of crustal heterogeneity on fault growth and the development of the extensional faults in one of these grabens, the Iguatu basin. Previous studies presented geophysical data, which provide evidence that the Iguatu basin contains a half-graben geometry. In our study, gravity and airborne geophysical data indicate that the basement of the Iguatu basin is part of a heterogeneous structural framework composed of two structural domains, is affected by several ductile shear zones and intruded by a few granite bodies. The gravity modeling reveals that this basin is composed of three right-bend en echelon fault segments. They form a sigmoid system of normal faults that accommodate the strong ∼90° bend of the Precambrian shear zones from E–W to roughly N–S. The growth of these segments led to the generation of two isolated depocenters. The overlapping fault segments link through relay ramps. Release faults that are nearly perpendicular or oblique to the three main fault segments form marginal strike ramps and horst structures in both depocenters. 3D-gravity modeling incorporates the presence of interfering sources of a heterogeneous structural framework. The modeling reveals a maximum sedimentary cover 1620m thick, which occurs at the bend of the reactivated shear zones. The gravity signature of a possible granite body, after removal of the gravity effect of the basin-filling deposits, indicates that this possible intrusion forms a horst oriented roughly parallel to the basement fabric. The relationship between maximum displacement and fault length indicates that the fault segments formed independently during the initiation of the half-graben. But the fault segments, linked by relay ramps, influence the development of one another. We interpret the segments to represent a pre-linkage, multisegmented stage of an aborted rift system. This pattern of fault growth may have also influenced the rift stage of other sedimentary basins in the region.