博格达山北麓的活动缩短作用

Crustal shortening is primary deformation in convergent plate boundaries. Quantitatively elucidating this type of structures is still challenging for structural geologists, however. Ongoing crustal shortening due to the India-Tibet collision is distributed within the Himalayan-Tibetan orogen and Central Asia. The Tianshan range due to the India-Tibet collision, in Central Asia, is one of the highest and most rapidly deforming intracontinental rejuvenation mountain belts with many EW-trending shortening structures on its both piedmonts. We are planning to take active tectonics in the northern front of the Bogda range, the northern branch of the eastern Tianshan range, as examples to deeply understand the shortening process in central Asia. In the northern front of the Bogda range, there are three active crustal shortening structures including the Fukang thrust fault (the FKF), the Santai and the Gumudi anticlines. To elucidate quantitatively their shortening, we shall measure geometric and kinematic parameters of the FKF, the Santai and Gumudi anticlines at natural and man-made outcrops and identify well-preserved deformed geomorphic markers in field trips; measure uplifting and folding of deformed geomorphic markers covering causative structures with DGPS instruments and to collect cosmogenic nuclides samples from these geomorphic markers for dating; interpret petroleum seismic data crossing these structures to construct mathematical relationships between deformation of geologic and geomorphic markers and amounts of horizontal shortening; and trench and/or modify naturally well-exposed sections to measure deformation of late Quaternary sedimentary horizons covering causative structures and collect OSL and/or 14C samples from these horizons for dating. Based on works mentioned above, the total shortening and shortening rate crossing the northern front of the Bogda range can be calculated, and its allocation on the three structures can be retrieved. This study will be valuable for evaluating earthquake hazards of the cities of Urumqi, Fukang and Jiamsar located in the northern piedmont of the Bogda range.

地壳缩短是聚敛板块边界带的基本变形，定量认识缩短构造的几何学和运动学是一项挑战性的工作。进行中的印度板块向北的运动引起的板内缩短主要分布在喜马拉雅-青藏造山带及中亚。天山是印藏碰撞引起的晚新生代板内再生造山带，为中亚最活跃的板内缩短构造。我们选择天山东段北支博格达山北麓的活动构造（包括阜康断层、三台背斜和古牧地背斜）认识该地区的缩短作用。为定量描述这些构造记录的晚新生代缩短作用，我们计划通过野外地质调查，识别并测量他们的活动造成的地貌面的隆升和褶皱；利用油气勘探资料精细解析他们的深部几何结构，构建上盘的褶皱和隆升与水平缩短之间的定量运动学关系；开挖探槽或修整天然剖面，识别和测量晚第四纪沉积层的变形；选用恰当的测年技术精确约束变形地貌面和沉积层的年龄；依据前述结果，计算或模拟计算博格达山北麓各关联活动构造的缩短量和缩短速率。该工作可为乌鲁木齐、阜康和吉木萨尔的地震安全性评估提供活动构造依据。