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得到了相当好的理解，这在很大程度上是因为广泛的社会兴趣（地震危险）和从石油勘探中获得的丰富的地下信息。然而，这些断层在深处发生了什么，人们知之甚少。解决这些问题的一种方法是地球物理成像，但由于晶体岩石中从低角度到高角度的结构成像问题，通常缺乏足够的物理性质变化，无法进行清晰的成像，因此这些研究既昂贵又模糊。解决这些问题的更高分辨率的技术是检查走滑剪切带的充分暴露的下倾剖面。这样的构造存在于阿拉斯加南部的Chugach山脉东部，本项目拟对该构造进行详细研究，以研究中下地壳深处走滑系统的三维结构。先前由国家科学基金会资助的PI和V.B. Sisson的研究已经记录了该系统上下部分的结构几何形状，但该系统的中地壳部分尚未被详细检查。根据最近的理论发展（如Teyssier等人，在出版中），PI的最初结论需要重新评估，因为陡峭剪切带穿过地壳柱的经典假设预测了与地壳柱不同的几何形状，在地壳柱中，上下地壳沿着广泛的分布流区分离。该项目将通过现场结构研究、运动学分析（有限和增量应变、剪切感测定以及通过生长纤维和石英LPO的发展获得的应变路径信息）来验证这些替代预测。

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).