Collaborative Research: Discrete vs Continuous Continental Deformation and the Role of the Lower Crust in the Tien Shan

该奖项为主动地震反射计划提供支持，并在天山造山带西部、吉尔吉斯斯坦和中国西北部进行被动地震和大地电磁测量。天山是与印度-欧亚碰撞有关的陆内厚皮挤压变形的壮观例子，约占这次碰撞变形的一半，而且它是活跃的。已有的结果表明，天山北缘和南缘附近的变形集中，包括延伸到莫霍面深处的高电阻率带的不均匀电阻率结构，以及GPS形变测量，这些测量结果与主要变形断裂周围的地质测量结果相关联，并在造山带上累积。这项新工作的建立是为了允许在两种不同的方式之间进行选择，以适应下地壳的挤压变形；一种是通过离散的断层作用到达最上部的地幔深度，另一种是通过在下地壳持续的韧性增厚。这项工作的一个基石是密集的CMP反射剖面，以寻找可追溯到上地幔的地壳规模断裂带，作为对第一个模型的验证。建议进行额外的被动地震工作，以测试向莫霍面渗透的较高温度的地幔隆起，这可能是一种刺激下地壳韧性和寻找上地幔界面的手段。MT工作的目的是重新处理和反演据声称具有良好质量的较旧的苏联时代MT数据，以提供与拟议的地震线一致的覆盖范围，并将更多的站点收集到塔里木盆地，以改进采样和解决与塔里木-天山过渡有关的可能构造。***

0310116KnappThis award provides support for an active seismic reflection program, and follow up passive seismic and MT surveying in the western Tien Shan orogen, Kyrgystan and NW China. The Tien Shan is a spectacular example of intracontinental thick-skinned compressional deformation associated with the India-Eurasia collision, taking up about half of this collision's deformation, and it is active. Existing results show a concentration of deformation near the northern and southern margins of the Tien Shan, inhomogeneous resistivity structure including high resistivity zones extending to Moho depths, and GPS deformation measurements which correlate with geological measurements estimated around the major deforming faults and cumulative over the orogen. The new work is set up to allow a choice between two distinct means of accommodating the compressional deformation in the lower crust; one by discrete faulting to uppermost mantle depths, and the other by continuous ductile thickening in the lower crust. A cornerstone of the effort is a dense CMP reflection profile to search for crustal scale fault zones traceable to the upper mantle as a verification of the first model. Additional passive seismic work is advocated to test for higher-T mantle upwellings penetrating toward the Moho presumably as a means of stimulating lower crustal ductility and to search for upper mantle interfaces. MT work is aimed at reprocessing and inverting older Soviet-era MT data stated to be of fair-good quality to provide coincident coverage with the proposed seismic line, and to collect additional sites into the Tarim Basin to improve sampling and resolve possible structures associated with the Tarim-Tien Shan transition. ***