Zircon U-Pb age,petrogeochemical characteristics,and tectonic setting of trachyandesite in the Huoluotai area,northern segment of the Erguna Block
The origin of Late Mesozoic volcanic rocks in the NE Asia has become a research hotspot in recent years.Affected by the superposition of the Mongol-Okhotsk and Paleo-Pacific Ocean tectonic domains,the origin of volcanic rocks in the northern segment of the Erguna Block is more complicated.This paper investigates the petrogenesis and tectonic setting of the trachyandesite through zircon U-Pb dating and geochemical data from the trachyandesite in the Huoluotai area,northern segment of the Erguna Block.The zircon U-Pb dating gave a weighted mean age of 137.8±1.8 Ma,implying that the formation age of the Huoluotai trachyandesites was Early Cretaceous.The Huoluotai trachyandesites show distinctly fractionation of light and heavy rare-earth elements(LREE/HREE=15.83～16.71),and have weak Eu anomaly(δEu=0.84～0.88).Enriched in the large-ion lithophile elements(e.g.,Rb,Ba,and K)and depleted in high-field-strength elements(e.g.,Th,U,Ta,and Nb),they belong to the high-K calc-alkaline series.With high Sr(754.24×10-6～945.40×10-6)content and Sr/Y ratio(55.09～68.10),low Y(13.22×10-6～14.15×10-6)and Yb(0.97×10-6～1.02×10-6)contents,the Huoluotai trachyandesites belong to typical adakitic rocks derived from the partial melting of subducted oceanic plate,and their formation could be linked to the slab roll-back process of the Paleo-Pacific Ocean plate.
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