Abstract:
This paper is the result of geological survey engineering.
Objective Eastern Liuzhou is located in the eastern margin of Youjiang Basin. In recent years, a set of volcanic rock interlayer has been found in the Early Triassic Shipao Formation in the eastern Liuzhou for the first time, which provides an important basis for studying the tectonic evolution of the eastern margin of the Youjiang Basin.
Methods Taking the newly discovered volcanic rocks in Eastern Liuzhou as the research object, this paper investigates the formation age and magmatic source characteristics of the volcanic rocks in the eastern margin of the Youjiang Basin through LA-ICP-MS zircon U-Pb age and Hf isotope analysis.
Results The results show that the volcanic rocks are composed of tuff, tuff lava, and tuffaceous volcanic breccia, showing typical characteristics of volcanic rock. LA-ICP-MS zircon U-Pb age dating results show that the weighted mean ages of zircon in the two tuff samples are (244.0±1.9) Ma and (247.1±0.9) Ma respectively. The trace elements (U, Th, Hf, Nb) compositions of zircon show the characteristics of continental magma arcs-derived zircons. The zircon have εHf(t) values of -13.2--1.2, with second-stage model ages (TDMC) of 1.35-2.06 Ga, suggesting that their magma source is mainly crustal materials, with average crustal residual age of 1.7-2.06 Ga.
Conclusions The timing volcanic rock interlayer is basically consistent with the stratigraphic age of the Early Triassic Shipao Formation, and are the product of volcanic eruption during the late Early Triassic to the early Middle Triassic. The volcanic rocks were formed in volcanic arc-related, syn-collisional tectonic setting, which is the representative of the sedimentary environment of back-arc basin, and is related to the closure of the paleo-Tethys during the Indosinian period. This outcome provides new and crucial information for a better understanding the tectonic evolution of the paleo-Tethys.
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