Abstract:
This paper is the result of geological survey engineering.
Objective The Kaladawan area is located within the area defined by the NE-striking Altun strike-slip fault to the north and EWstriking northern Altun fault. The cumulated gabbro is exposed to the north Altun Fault 4 km to the south, basic marine volcanic rocks such as occipital basalt occur in both north and south. As the main component rock type of oceanic crust, the study of cumulate gabbro will further reveal the evolution characteristics of early Paleozoic Altun oceanic crust.
Methods In this paper, petrology, mineralogy, geochemistry and zircon SHRIMP U-Pb dating of cumulate gabbro in the Kaladawan area have been studied.
Results The study shows that the cumulate gabbro in Kaladawan can be divided into two types: pegmatite and coarse-grained, and has the characteristics of gradual transition. The geochemistry features include low K2O content (average is 0.44%), flat REE partition curves (the average LREE/HREE value is 2.54), positive Eu anomalies (the average δEu value is 1.05), and negative Nb and Ta anomalies (the average Nb and Ta content is 2.31×10-6 and 0.16×10-6, respectively), which indicates that it occurs in the tectonic environment of the back-arc basin. The zircon SHRIMP U-Pb age of 514-516 Ma is very close to that of the adjacent intermediate-basic volcanic rocks of 517 Ma, indicating that the cumulate gabbro was formed in late Cambrian of the early Paleozoic.
Conclusions The results show that there was an obvious oceanic crust spreading during the late Cambrian in the Kaladawan area. This result, together with island arc intermediate-acid volcanic rocks 478-485 Ma and co-collisional intermediate-acid intrusive rocks 477-488 Ma, constitutes a complete sequence of regional tectonic evolution, and an evolutionary history of the early Paleozoic oceanic crust spreading and plate subduction to continental collision in the North Altun region is further determined.
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