1. Zircon U-Pb age, trace element, and Hf isotopic constrains on the origin and evolution of the Emeishan Large Igneous Province
- Author
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Fu-Hao Xiong, Chen-Chen Yang, Min Deng, Hu Huang, Shijun Ni, Han-Ting Zhong, Mingcai Hou, and Peter A. Cawood
- Subjects
Basalt ,geography ,geography.geographical_feature_category ,010504 meteorology & atmospheric sciences ,Large igneous province ,Trace element ,Geochemistry ,Silicic ,Geology ,010502 geochemistry & geophysics ,01 natural sciences ,Volcanic rock ,13. Climate action ,Clastic rock ,Rhyolite ,0105 earth and related environmental sciences ,Zircon - Abstract
The late Permian to Early Triassic volcano-sedimentary succession associated with the Emeishan Large Igneous Province (LIP) is well preserved in the Binchuan area, Southwest China. This paper presents coupled zircon U-Pb age, trace element, and Hf isotope analyses from the succession, together with whole-rock geochemical compositions, to reveal the origin and evolution of volcanic rocks of the LIP. Zircons from the matrix and a rhyolite clast in the Lower Triassic conglomerate bed yield identical U-Pb ages of ca. 260 Ma and have geochemical affinities to those crystallized from within-plate magmas. These features, combined with the dominance of rhyolite clasts from this horizon, imply a source related to Emeishan silicic volcanic rocks. Zircons from silicic ignimbrite and rhyolite in the upper volcanic succession of the LIP display high eHf(t) values (+4.2 to +12.9), low Th/Nb and U/Yb ratios, and similar eNd(t) values (−0.17 to +0.47) to high-Ti basalts. These chemical and isotopic characteristics are consistent with the eroded silicic volcanic rocks, indicating that the late-stage silicic volcanic rocks were generated by fractionation of high-Ti basaltic magmas without significant crustal contamination. Although the late Permian zircons from the lower and upper low-Ti basalt successions all show arc-like geochemical characteristics with high Th/Nb and U/Yb ratios, the former has much lower eHf(t) values (−11.7 to −3.6) than the latter (+4.4 to +11.6), and the zircons from the upper low-Ti basalt succession show positive eHf(t) values similar to the studied rhyolites. Samples from the lower low-Ti basalt succession have relatively higher eNd(t) values (−2.66 to +3.38) than those from the upper low-Ti basalt succession (−4.48 to −0.82). These geochemical features indicate the early-stage low-Ti basalts may be mainly derived from a previously enriched subcontinental mantle lithosphere, whereas the late-stage low-Ti basalts may be generated from the increasing involvement of asthenospheric mantle source with crustal contamination.
- Published
- 2022