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

该合同为在吉尔吉斯斯坦和中国西北部天山造山带西部开展主动地震反射项目以及后续被动地震和MT测量提供支持。天山是与印度-欧亚板块碰撞有关的大陆内厚皮挤压变形的一个壮观的例子，占这次碰撞变形的一半左右，并且它是活跃的。现有的研究结果表明，天山的南北边缘附近集中了形变，包括延伸至莫霍深度的高电阻率带在内的非均匀电阻率构造，以及与主要变形断层周围和造山带上累积的地质测量相关联的GPS变形测量。新工作的建立是为了允许在两种不同的容纳下地壳挤压变形的方法之间进行选择；一个是离散的断裂作用到最上层的地幔深处，另一个是下地壳的连续韧性增厚。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尺度断裂带，作为对第一个模型的验证。建议进行额外的被动地震工作，以测试向莫霍方向渗透的高t地幔上升流，这可能是刺激下地壳延展性和寻找上地幔界面的一种手段。MT工作的目的是重新处理和反演质量相当好的旧苏联时代MT数据，以提供与拟议地震线一致的覆盖范围，并收集塔里木盆地的其他地点，以改进采样并解决与塔里木-天山过渡相关的可能结构。＊＊＊

0309927RoeckerThis 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. ***