The Late Paleozoic geodynamic environment of Qiongheba arc, eastern Junggar: Evidence form spatial and temporal distribution patterns of dark dykes in Hersai pluton
Feng Qianwen1,2, Zhou Kefa1,2, Wang Jinlin1,2
1. Xinjiang Institute of Ecology and Geography, Xinjinag Research Center for Mineral Resources, Chinese Academy of Sciences, Ürümqi 830011;
2. Xinjiang Key Laboratory of Mineral Resources and Digital Geology, Ürümqi 830011
The eastern Junggar, located among the Altai, eastern Tianshan and Junggar Basin, is the key area to understand the tectonic evolution of the central Asian orogenic belt(also called North Asian orogenic region). Previous studies mostly focused on rock associations and geochemical characteristics of the eastern Junggar, but the structural deformations, specially the deformations in middle-small scale, were rarely involved. This study initially find that there are large amount of dark-colored mafic dykes emplaced in eastern Junggar, they were formed by mafic magma from the deep intruding into the earlier formed fractures in the host rocks. Dykes can provide both temporal and spatial constrains on the mechanism of structural fractures. In Hersai pluton, a granite pluton of Qiongheba arc in eastern Junggar, 874 segments of dark dykes are distinguished by high-resolution remote sensing interpretation and previous regional survey. The Hersai pluton was formed in Early Devonian and dykes were formed in Late Carboniferous to Early Permian. The majority of their strikes are NWW-SEE and minority strikes are NE-SW and NW-SE. Macroscopic deformations of the dykes reveal that the NWW-SEE trending dyke-fractures are extensional caused by NWW-SEE compression, the NE-SW dyke-fractures are compressional-dextral, and the NW-SE dyke-fractures are extensional-sinistral. Combined these dyke-fractures with different trending into consideration, they were caused by NWW-SEE regional compression. This study reveals that during the Late Devonian to the Early Carboniferous, Hersai pluton was compressed by NWW-SEE maximum principal stress and different groups of fractures were formed, which may be caused by intercontinental collision after termination of ocean basin. The occurrence of mafic dykes in the Late Carboniferous to the Early Permian may be caused by so-called post-collisional extensions.
. The Late Paleozoic geodynamic environment of Qiongheba arc, eastern Junggar: Evidence form spatial and temporal distribution patterns of dark dykes in Hersai pluton[J]. Chinese Journal of Geology, 2015, 50(4): 1068-1082.