Crustal Structure of Strike-slip Fault Systems from a down-plunge section in the eastern Chugach Mountains, Alaska

走滑系统的近地表断层模式现在已经相当好地理解了，这在很大程度上是因为广泛的社会利益（地震危险）和从石油勘探中获得的大量地下信息。然而，人们对这些断层在深处会发生什么却知之甚少。解决这些问题的一种方法是地球物理成像，但这些研究是昂贵的，通常是模糊的，因为成像问题的结构范围从低到高的角度在结晶岩石，往往缺乏足够的变化，在物理性质的清晰成像。解决这些问题的一个更高分辨率的技术是检查走滑剪切带的暴露良好的下倾。这种结构存在于阿拉斯加南部的楚加奇山脉东部，本项目建议详细研究这种结构，以研究地壳中下层走滑系统的三维结构。以前NSF资助的研究由PI和V. B。Sisson已经记录了该系统上部和下部的结构几何形状，但尚未详细研究该系统的中地壳部分。根据最近的理论发展（例如，Teyssier等人，（出版中）PI的初步结论需要重新评估，因为陡峭剪切带穿透地壳柱的经典假设预测的几何形状与地壳柱不同，在地壳柱中，上地壳和下地壳沿着广泛的分布流动区分离。该项目将通过结合现场结构研究、运动学分析（有限应变和增量应变、剪切方向测定以及通过生长纤维和石英LPO开发的应变路径信息）来测试这些替代预测。

Near-surface fault patterns of strike-slip systems are now reasonably well understood, inlarge part because of extensive societal interest (seismic hazard) and a wealth ofsubsurface information obtained from petroleum exploration. What happens to thesefaults at depth, however, is poorly understood. One approach to resolve these questionsis geophysical imaging, but these studies are expensive and typically ambiguous becauseof imaging problems of structures ranging from low to high angle in crystalline rocks thatoften lack sufficient variation in physical properties for clear imaging. A much higherresolution technique to resolve these issues is to examine well-exposed down-plungesections of strike-slip shear zones. Such a structure exists in eastern Chugach Mountainsof southern Alaska, and this project proposes to examine this structure in detail toinvestigate the three-dimensional architecture of strike-slip systems at mid to lowercrustal depths. Previous NSF funded research by the PI and V.B. Sisson has documentedthe structural geometry of the lower and upper portions of the system, but a mid-crustalportion of the system has not been examined in detail. In light of recent theoreticaldevelopments (e.g. Teyssier et al., in press) the PI's initial conclusions require re-evaluation because the classic hypothesis of steep shear zones penetrating through the crustal column predicts a different geometry than a crustal column in which the upper and lower crust are detached along a broad zone of distributed flow. This project will test these alternative predictions through a combination of field structural studies, kinematic analyses (finite and incremental strain, shear-sense determination, and strain path information through growth fibers and development of quartz LPO's).