Development of fault and vein networks in a carbonate sequence near Hayl al-Shaz, Oman Mountains
Development of fault and vein networks in a carbonate sequence near Hayl al-Shaz, Oman Mountains
复制标题
阿曼山脉Hayl al-Shaz 附近碳酸盐岩层序中断层和脉络的发育
作者：
S. Virgo;M. Arndt;Zoé Sobisch;J. Urai
我们对阿曼山脉中部 Jabal Shams 南翼的倾斜坡度进行了高分辨率结构研究。该研究的目标是：（1）测试对该地区结构要素现有的基于卫星的解释； （二）编制准确的地质图； (3) 收集广泛的断层和层理面、断层断距、矿脉和节理的结构数据集。这些数据与阿曼山脉和地下的现有构造演化模型进行了比较，并用于评估这些结构作为阿曼地下碳酸盐岩储层断层和裂缝系统类比的适用性。被深河谷切切的干净岩石完全暴露，可以详细绘制白垩纪卡马群第 3 段的复杂断层、矿脉和节理系统。为了制图目的，该成员被分为八个单元，垂直地层长度约为 100 m。该地图几乎完全基于直接实地观察。它包括在许多位置测量断层断距以及构建剖面，其精确度在几米之内。对现有基于卫星的结构要素解释的地面实况表明，可以使用遥感数据以高置信度绘制断层图。断层范围为次震级，断层深度只有几分米。然而，现有的对骨水泥骨折的解释被证明是不正确的：其中大多数是沿着重新激活的静脉形成的开放性骨折。
研究区最突出的构造是一组共轭的 ESE 走向断层，断距可分辨为几厘米到数百米。这些断层包含成束的粗粒方解石脉，在重新活化过程中可能会角砾化。我们将这些断层解释为共轭正斜断层组，在 Al Jabal al-Akhdar 背斜折叠期间与层理一起旋转。方解石矿脉有多代，偏移较小，与层理成大角度，有时呈阶梯状。对高角度层理处的纹理之间清晰的套印关系的分析与 Holland 等人的解释一致。 （2009a）；然而，我们将矿脉走向逆时针旋转解释为在正常断层之前开始并在正常断层之后结束。研究区的正断层晚于层理平行剪切脉。因此，这些断层是在塞梅尔河和哈瓦西纳河就位后形成的。此前，它们被解释为与阿曼北部和阿拉伯联合酋长国地下的区域正向斜滑断层具有相同的年龄，该断层是在 Filbrandt 等人提出的坎帕尼亚 Fiqa 地层早期沉积期间演化的。 （2006）。我们将它们解释为与 Fournier 等人的第一阶段扩展同时期。 （2006）。这些断层的重新激活和新矿脉的演化伴随着 Al Jabal al-Akhdar 背斜的折叠，以及通过先前存在的微矿脉的重新激活而最终隆起和节理。因此，研究区域的断层与地下断层的运动学和年龄相当。然而，它们形成的深度和流体压力要大得多，因此直接使用这些结构作为阿曼地下储层断层和裂缝系统的类比应谨慎进行。
We present a high-resolution structural study on the dip slope of the southern flank of Jabal Shams in the central Oman Mountains. The objectives of the study were: (1) to test existing satellite-based interpretations of structural elements in the area; (2) prepare an accurate geological map; and (3) collect an extensive structural dataset of fault and bedding planes, fault throws, veins and joints. These data are compared with existing models of tectonic evolution in the Oman Mountains and the subsurface, and used to assess the applicability of these structures as analogs for fault and fracture systems in subsurface carbonate reservoirs in Oman. The complete exposure of clean rock incised by deep wadis allowed detailed mapping of the complex fault, vein and joint system hosted by Member 3 of the Cretaceous Kahmah Group. The member was divided into eight units for mapping purposes, in about 100 m of vertical stratigraphy. The map was almost exclusively based on direct field observations. It includes measurement of fault throw in many locations and the construction of profiles, which are accurate to within a few meters. Ground-truthing of existing satellite-based interpretations of structural elements showed that faults can be mapped with high confidence using remote-sensing data. The faults range into the subseismic scale with throws as little as a few decimeters. However, the existing interpretation of lineaments as cemented fractures was shown to be incorrect: the majority of these are open fractures formed along reactivated veins.
The most prominent structure in the study area is a conjugate set of ESE-striking faults with throws resolvable from several centimeters to hundreds of meters. These faults contain bundles of coarse-grained calcite veins, which may be brecciated during reactivation. We interpret these faults to be a conjugate normal- to oblique fault set, which was rotated together with bedding during the folding of the Al Jabal al-Akhdar anticline. There are many generations of calcite veins with minor offset and at high-angle-to-bedding, sometimes in en-echelon sets. Analysis of clear overprinting relationships between veins at high-angle-to-bedding is consistent with the interpretations of Holland et al. (2009a); however we interpret the anticlockwise rotation of vein strike orientation to start before and end after the normal faulting. The normal faults post-date the bedding-parallel shear veins in the study area. Thus these faults formed after the emplacement of the Semail and Hawasina Nappes. They were previously interpreted to be of the same age as the regional normal- to oblique-slip faults in the subsurface of northern Oman and the United Arab Emirates, which evolved during the early deposition of the Campanian Fiqa Formation as proposed by Filbrandt et al. (2006). We interpret them also to be coeval with the Phase I extension of Fournier et al. (2006). The reactivation of these faults and the evolution of new veins was followed by folding of the Al Jabal al-Akhdar anticline and final uplift and jointing by reactivation of pre-existing microveins. Thus the faults in the study area are of comparable kinematics and age as those in the subsurface. However they formed at much greater depth and fluid pressures, so that direct use of these structures as analogs for fault and fracture systems in subsurface reservoirs in Oman should be undertaken with care.