Forearc Deformation in the Central Andes: The Northern Terminus of the Atacama Fault Zone

阿塔卡马断裂带可以在中央安第斯山脉的弧前追踪到近1000公里。断裂带的北端位于智利伊基克以南，由走滑、逆冲和正断层包围的一系列复杂地块组成。卫星雷达图像生成的数字地形图表明，该地区是整个断裂系统中构造最活跃的部分之一。该地区位于纳斯卡板块上的伊基克海脊正被俯冲到南美洲地下的总体区域之上，并与贝尼奥夫带的地震空隙密切相关，许多地震学家认为，贝尼奥夫带将是该板块边界上下一次大地震的发源地。我们正在使用Ar/Ar和铀系同位素方法测定这些年轻断裂的年龄，并通过测量暴露良好的断裂上的滑动方向来研究它们的运动学。这些现场数据正在法国雷恩大学开发的地图视图块恢复程序中进行组合和分析，这将使我们能够量化该地区的应变和旋转。然后，我们可以评估由古地磁数据激发的块体旋转与造山斜弯曲假说，以及调查所提出的弧形平行挤压的起源。最后，我们的野外工作和数字高程模型提供了一张记录良好的“之前”图片，以与沿着该板块边界获得的下一次大地震后的“之后”图片进行比较，该板块边界是有记录以来最大地震的地点。因此，我们最终将能够记录主要海洋大陆会聚系统的前弧在贝尼奥夫带地震活动期间是如何变形的。

Allmendinger0087431The Atacama fault zone can be traced for nearly 1000 km in the forearc of the Central Andes. The northern terminus of the fault zone occurs just south of Iquique, Chile, in a series of complex blocks bounded by strike-slip, thrust, and normal faults. Digital topography produced from satellite radar imagery shows that this area is one of the most tectonically active parts of the entire fault system. The area overlies the general region where the Iquique ridge on the Nazca plate is being subducted beneath South America, and correlates well with a seismic gap in the Benioff zone that many seismologists believe will be the site of the next major earthquake on this plate boundary. We are dating these young faults using Ar/Ar and Uranium series isotopic methods, and are also studying their kinematics using measurements of slip directions on the well-exposed faults. These field data are being combined and analyzed in a map view block restoration program developed at the Universite de Rennes (France), which will allow us to quantify the strain and rotation in the region. Then, we can evaluate block rotation versus oroclinal bending hypotheses spurred by paleomagnetic data, as well as investigate the origin of proposed arc parallel compression. Finally, our fieldwork and digital elevation model provides a well-documented "before" picture to compare to the "after" picture to be obtained following the next great earthquake along this plate boundary, site of the largest earthquake on record. Thus, eventually we will be able to document how the forearc of a major ocean continent convergence system deforms during Benioff zone seismicity.