ZHANG Hai1, YU Yuan-shan1, WANG Xing-ming2, HE Hai2, XIAO Peng2, WANG Fu-ming2
(1. Chengdu Institute of Geology and MineralResources, Chengdu 610081, China;
2. No.405 Sichuan Bureau of Geological Exploration and Development of Mineral Resource, Dujiangyan 611830, China)
Abstract: Volcanic rocks from the western margin of the Lanping Basin are composed of andesite, andesitic volcanic breccia, amygdaloidal basalt and andesitic tuff. The weighted average age of LA-ICP-MS zircon U-Pb of andesite is (241.0 ± 3.7) Ma, indicating that the formation age of andesite is the middle Triassic epoch. The andesite and basalt in this suite of volcanic rocks share the same REE pattern, and both display right leaning, possessing a weak negative Eu anomaly (0.77－1.09) and an unobvious Ce anomaly (0.91－0.99), which indicates that the volcanic rocks originate from the same magmatic source. The volcanic rocks from this area fall into the category of calc-alkaline basalt series, enriched with LILE (e.g., Rb, Ba, Th, and U) and deficient in HFSE (e.g., Nb, Ta, Ti, and P), with high Al2O3 and low TiO2, presenting the features similar to those of island arc volcanic rocks. The volcanic rocks from this area are originated from the partial melting of the low grade of metasomatized lithospheric mantle source region; the protomagma has experienced the action of fractional crystallization dominated by orthopyroxene, and also experienced the hybridism of crust materials during the ascending process. Generally, the volcanic rocks display the characteristics of intraplate basalts and are in an extensional environment, with the geochemical information of subduction zones, which may be related to the slab break-off occurred during the eastward subduction of the Paleo-Tethyan major oceanic basin in the Sanjiang orogenic belt.
Keywords: volcanic rock; zircon; LA-ICP-MS U-Pb dating; western margin of the Lanping basin; Sanjiang orogenic belt
E-mail: zhanghai1980@sina.com
ACTA MINERALOGICA SINICA Vol. 37, No. 5, 2017, Page 596-607
