Paleozoic Structural Deformation And Their Chronology Of Middle Segment Of Tian Shan

The east-west extending Tianshan orogenic belt in central Asia was formed mainly during Paleozoic by plate evolution. Located in remoted Northwest desert areas, Tianshan is not well studied on its structural deformation and geochronology. There are debutes on the evolutional process of Tianshan. One viewpoint is that plate subduction and collision have happened on the both side of central Tianshan strip during Paleozoic. Collision on the south side of central Tianshan is earlier than on the north side. Another viewpoint is that collision on the north side is earlier than on the south side. To resolve this problem, survey on structural deformation was conducted on crosssections in Ganggou-Bingdaban area. Geochronologic analysis was also done on mylonites and igneous rocks. Deformation characteristics on geometry and dynamics have been made clear and the ages of mylonites and igneous rocks attained. Recognitions of our research are:1. Central Tianshan northern margin fault has experienced two episodes of structural deformation in Early Pz and Late Pz which dextral strike-slip in Late Pz is remarkale.2. Lower Paleozoic strata outcroped in north section of central Tianshan strip and Lower Carboniferous overlaying basins located in south section of central Tianshan strip.3. Central Tianshan southern margin belt is the largest mylonitic belt and the most important and intact ophiolitic belt.4. Northern Tianshan Lower Paleozoic oceanic crust subducted south-ward and collisioned in Caledonian orogenic episodes (470-420Ma), accompanying with the openning of South Tianshan oceanic basin.5. Southern Tianshan oceanic crust subducted north-ward in early Hecynian orogenic episodes (390-360Ma).6. Southern Tianshan oceanic crust subducted north-ward and collisioned in middle Hecynian orogenic episodes (330-300Ma).7. Post-collision magmatic activities (290-270Ma) occured accompaning with dextral strike-slip deformation (270-250Ma) in late Hecynian orogenic episodes...