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，这些断层在深度上会发生什么，人们却知之甚少。解决这些问题的一种方法是地球物理成像，但这些研究费用昂贵，而且通常含糊不清，因为结晶岩石中从低角度到高角度的结构的成像问题往往缺乏足够的物理性质变化，无法进行清晰的成像。解决这些问题的一种更高分辨率的技术是检查暴露得很好的走滑剪切带下倾。这种结构存在于阿拉斯加南部的丘加奇山脉东部，该项目建议详细研究这种结构，以研究中、下地壳深度的走滑系统的三维结构。美国国家科学基金会之前由PI和V.B.Sisson资助的研究已经记录了该系统下部和上部的结构几何，但该系统的中地壳部分没有得到详细检查。根据最近的理论发展(例如，Teyssier等人，在出版中)，PI的最初结论需要重新评估，因为贯穿地壳柱的陡峭剪切带的经典假设预测了与地壳柱不同的几何结构，在地壳柱中，上地壳和下地壳沿着宽广的分布流动区域分离。该项目将通过现场结构研究、运动学分析(有限应变和增量应变、剪切传感测定以及通过生长纤维和石英LPO的开发获得的应变路径信息)的组合来检验这些备选预测。

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).