1. Initial splitting and proliferation of Mesoproterozoic continental nuclei
On the one hand, this period represents the beginning of crustal rock series deposition in the ancient land system, on the other hand, it reveals the difference of proliferation or growth mode between the north and south landmasses. Specifically, the early (Great Wall Age) old land cracking mainly occurred in Tarim old land system, represented by the volcanic rift event of Qianzi sub-group. At this time, the ancient land system in the East Tianshan Mountains is dominated by a set of stable continental margin clastic rocks (ancient caves and wells). In the middle period (Jixian period), the Tarnum ancient land system basically lacked the proliferation process of crustal rock series in this period, but replaced it with a wider intermediate-acid magma intrusion event, which made the continental crust in a vertical proliferation or growth process and developed into a mature continental crust or more cratonization; On the other hand, the East Tianshan paleoland system on the north side increases the bedding of the upper crust or supracrustal rock series, and has a set of stable carbonate platform deposits. Of course, there is also weak volcanism, which has become an important provenance basis of sedimentary metamorphic iron ore (Hongshan type) in this area. Late stage (Qingbaikou stage): The situation is completely opposite. The east Tianshan paleoland system is basically missing, and it is in the process of land uplift, erosion and thinning, while the accumulation of the southern Tarim paleoland system mainly occurs in the northern continental margin rift zone, characterized by stable carbonate platform facies accumulation.
The early Paleozoic continental rift and intracontinental magmatic accretion continental rift events are mainly represented by the early Paleozoic east-west rift system and some northwest rift systems in the central paleo-uplift belt of the East Tianshan paleo-system, which are the main periods of large-scale cracking events of this paleo-system. According to the bimodal volcanic rock or igneous rock structure combination, it should belong to a crust-mantle magma proliferation process under the extension mechanism, and the age can be from CAMBRIAN to SILURIAN.
The continental margin accretion event, represented by the Beishan island arc on the northern margin of the East Tianshan ancient land system, is an island arc volcanic sedimentary accretion event that occurred when the Asian ocean subducted to the continental margin. The age can be from Ordovician to Devonian, which is equivalent to the geological event process product of ocean-land collision from the middle stage of ancient Asian ocean development to the extinction stage.
However, the continental crust accretion process of Tarim paleoland system, besides the accumulation of foreland rift basins characterized by the deposition of ice rafts and black rock series in the northern margin, is mainly manifested by the intermediate-acid intrusion of the paleoland system and the important geological events of the development of more mature continental crust. The time limit can extend from Sinian to Devonian.
Comparing the continental crust proliferation or growth patterns of the two ancient land systems in this period, it is found that the eastern Tianshan ancient land system in the north is based on rift and volcanism, while the Tarim ancient land in the south is based on the proliferation and intermediate-acid magmatism of the northern rift basin.
2. Uplift and orogeny of continental rift and magma floor in late Paleozoic.
It is mainly represented by Carboniferous-Permian rift events on the north and south sides of the central ancient land fault ridge belt in Beishan. However, due to the different affiliation and structural position of ancient land system, there are obvious differences in nature and types. Among them, the rift events of the ancient land system in the East Tianshan Mountains mainly developed with the extension of the Baishan back-arc basin. Tarim Paleocontinental Rift is located in the south of Hongliuyuan-Daqishan Line, which is marked by Carboniferous-Permian alternating volcanic deposits and a large number of intermediate-acid and basic ultrabasic rock intrusions, showing a continental rift proliferation model.
Magmatic underplating, uplifting and orogenic proliferation events are limited to the central paleocontinental fault uplift zone of the East Tianshan paleocontinental system, mainly due to the lack of stratigraphic deposits of the corresponding era, and the basic ultrabasic rocks and intermediate-acidic bimodal magmatic intrusion events are the ways of uplifting and orogenic proliferation.
It should be said that by the end of the late Paleozoic, the structural pattern of the whole Beishan area had basically been finalized. In addition to the integration of two ancient land systems into Eurasia, an island arc or a mature continental margin arc-back arc basin-foreland basement-continental rift structural system or continental crust proliferation or growth process has been formed as a whole from north to south, and its dynamic mechanism can be fully included in Eurasia dynamics.
3. Mesozoic-Cenozoic intracontinental evolution and large-scale strike-slip
According to the analysis of sinistral strike-slip characteristics of Mesozoic and Cenozoic continental extensional basins and fault systems, the intracontinental evolution at this stage is mainly controlled by fault superposition and strike-slip in northeast and northwest directions. Among them, the NE-trending structure can basically correspond to the NE-trending fault system and strike-slip construction in Altun Mountain, while the NW-trending structure should be a reflection of the superposition or composite relationship under the same stress field boundary conditions after the integration of Alashan and Qilian westward structures into Eurasia. Of course, it also includes the superimposed influence of Tianshan-Yinshan east-west structural system and Jurassic potash granite intrusion.