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

阿塔卡马断层带在安第斯山脉中部的前弧中可以追溯到近1000公里。 断裂带的北方终点位于智利伊基克以南，是一系列由走滑断层、逆冲断层和正断层所界定的复杂块体。 卫星雷达图像生成的数字地形显示，该地区是整个断层系统中构造活动最活跃的部分之一。 该地区覆盖了纳斯卡板块上的伊基克海脊正在向南美洲俯冲的一般区域，并与贝尼奥夫带的地震空区有很好的相关性，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生地。 我们正在使用Ar/Ar和铀系同位素方法测定这些年轻断层的年龄，并正在使用对暴露良好的断层的滑动方向的测量来研究它们的运动学。 这些现场数据正在结合起来，并在雷恩大学（法国）开发的地图视图块恢复程序进行分析，这将使我们能够量化该地区的应变和旋转。 然后，我们可以评估块体旋转与古地磁数据所激发的造山弯曲假说，以及研究所提出的弧平行压缩的起源。 最后，我们的野外工作和数字高程模型提供了一个有据可查的“之前”的图片，以比较“之后”的图片，以获得下一个大地震沿着这个板块边界，最大的地震记录的网站。 因此，最终我们将能够记录主要洋陆会聚系统的前弧在贝尼奥夫区地震活动期间如何变形。

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.