Basic tectonic framework and features of metallogenic series in Beishan area, Gansu Province

In Beishan area, the suture zone or ophiolite belt that represents the dividing of ocean-continent tectonic plate is nonexistent, and the main body is composed of East Tianshan and Tarim old land systems. Their collision boundary is generally located along Fangshankou-Heishan-Jianquanzi line; the area north of this line belongs to Dongtianshan old land system, and that south of this line is assigned to Tarim old land system. According to stratigraphic age, sedimentary formation, magmatism and crustal structure, the Dongtianshan old land system is divided into three second-grade tectonic units from north to south, i.e., Beishan island arc belt, Late Paleozoic back-arc rift zone and fault-uplift zone of central old land. They spatially make up an ocean-continent transitional framework of island arc-back-arc basin-foreland basement. The southern Tarim old land system experienced the evolution from the original continental nucleus to mature continental crust. Based on characteristics of crustal structure and tectonism, the authors also divided this old land system into three second-grade tectonic units from north to south, namely Early Paleozoic depression zone of Tarim old land margin, Hongliuyuan-Daqishan-Tiancang Paleozoic multicyclic rift zone and Tarim old land basement. Besides, the metallogenic series of different tectonic units are summarized in this paper.