TECTONIC DEFORMATION OF ACTIVE FAULT-RELATED FOLD BELTS IN THE NORTH PIEDMONT OF THE CENTRAL TIANSHAN MOUNTAINS,NW CHINA
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摘要: 天山中段北麓发育有3排受逆断裂控制的背斜带,对这些构造带的研究有助于认识天山及其前陆盆地晚新生代构造变形的机理。基于地层变形分析,并结合前人的研究成果,从整体上探讨了这3排构造带的变形时间与基本模式。分析表明,天山北麓第Ⅰ排构造带的托斯台背斜自中新世褶皱作用明显; 第Ⅱ排构造带吐谷鲁背斜于约6.0Ma开始生长,伴随发育同构造沉积即生长地层; 第Ⅲ排构造带独山子背斜发育时间应晚于约2.6Ma。这一变形时间序列揭示天山北麓3排逆断裂-褶皱带的构造变形具有向前陆盆地逐步扩展的特征,并伴随产生幅度不等的地壳缩短。天山北麓约8~15km的地壳缩短总量表明,晚新生代以来构造驱动沿约130km宽的山麓带是相对均一的。Abstract: In the north piedmont of the Tianshan Mountains,there are three sub-parallel reverse fault-controlled fold belts. They are products of Late Cenozoic tectonic deformation. In fold belt I,the Tuositai anticline is a typical structure we studied. It has risen since the Miocene,although it sprouted in the Late Mesozoic. In fold belt II,we studied the Tugulu anticline. It began deforming in about.6.0Ma,accompanied with syntectonic deposition. and then experienced two times of obvious deformation,respectively in 5.2Ma and 3.5Ma. In fold belt Ⅲ,the Dushanzi anticline was studied. It should began deforming after about 2.6Ma because Neogene-Pleistocene strata were folded. That the Middle Pleistocene strata unconformably overlie the Lower Pleistocene Xiyu conglomerate indicates that its significant deformation should be in Early to Middle Pleistocene. The deformation sequence of these Late Cenozoic anticlines shows that tectonic deformation has progressively migrated northward. At the same time,a significant crustal shortening occurred in the north piedmont of the Tianshan Mountains. It was estimated that the total magnitude of shortening there should range from 8km to 15km.
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