Age and genesis of dacite in Gujiaying Basin, southern Jiangxi Province, and its constraints on Early Paleozoic tectonic evolution

The Early Paleozoic tectonic property of the South China Plate has been a major dispute for a long time.The dacite intrusive in the Gujiaying Basin in southern Jiangxi was selected as a case to study its rock type, strata attribution, genesis and structural environment based on petrology, field-measured profile measurement, SHRIMP zircon U-Pb chronology, major trace elements and Sr-Nd-Pb-O isotopic analysis.The analysis results show that the volcanic rock is rich in silicon and potassium, low in sodium, and poor in magnesium, and belongs to the high-K calc-alkaline dacite.Its light and heavy REE show obvious fractionation(La/Yb=5.52~15.08), and it is rich in lithophile elements Rb, Th, K, loss of high field strength elements Ta, Nb, with obvious negative Eu anomalies, showing the characteristics of volcanic arc.SHRIMP zircon U-Pb dating yields 439.0±4.0 Ma, similar to that of Nanying dacite and andesite, suggesting products of magmatic activity from the Late Ordovician to the Early Silurian.The Gujiaying section is similar to the Qiaozishan standard section and the Zhongzhai standard section in the Nanjing Basin.It is a set of gray-white dacite, rhyolite, volcanic clastic rock, and shallow metamorphic rock series, which belongs to the Nanjing Formation.The negative ε_Nd(t) value(-6.5~-6.3), lower (⁸⁷Sr/⁸⁶Sr)_i value(0.70624~0.70704), younger T_DM2(1685~1703 Ma), and higher values(²⁰⁶Pb/²⁰⁴Pb)_i, (²⁰⁷Pb/²⁰⁴Pb)_i and (²⁰⁸Pb/²⁰⁴Pb)_i, indicating that the Gujiaying dacite was formed by partial melting of the Mesoproterozoic crustal material.It is inferred that the Gujiaying dacite was formed in an island-arc environment related to subduction, and ocean-continent subduction existed in southern Jiangxi-northern Guangdong during the Late Ordovician-Early Silurian period.