Multiple extractions of the Cretaceous silicic magma plumbing system beneath the Baiyunzhang-Lianhuashan Basins, eastern Guangdong, SE China

Abstract

The extensive magmatism along the southeastern coast of China during Late Cretaceous time formed a volcanic-intrusive complexes belt, on which many volcanic basins and calderas are located. A growing amount of research has been carried out to reveal the formation processes of the Cretaceous volcanic-intrusive complexes in SE China, especially the volcanic-plutonic complexes in Zhejiang and Fujian Provinces. However, volcanic-plutonic complexes in Guangdong Province have not received enough attention in the past relative to volcanic-plutonic complexes in Zhejiang and Fujian Provinces. Furthermore, it is difficult to identify the genetic connections and formation processes of different type of volcanic rock with its co-genetic intrusive rocks in volcanic basins or calderas with complex igneous rock types, but it also provides new insights into the volcanic plumbing system processes and magma reservoir differentiation. Therefore, we conducted detailed research on the volcanic-plutonic complexes in the Lianhuashan Basin and Baiyunzhang Basin in the Lianhuashan Fault Zone. The Lianhuashan volcanic-plutonic complex is comprised of ignimbrite, granite porphyry and rhyolite porphyry, while the Baiyunzhang volcanic-plutonic complex is comprised of ignimbrite, trachyte, rhyolite and quartz monzonite porphyry. The LA-ICP‒MS zircon U‒Pb dating results indicate that the crystallization of volcanic and intrusive rocks was contemporaneous within the error (143~138 Ma), and they had similar ranges of zircon Hf-O isotopes (εHf(t)= -2.8 to 8.9; δ18O=5.53 to 7.87 ‰) and whole-rock Nd isotopes (εNd(t)=-3.4 to -5.7). In addition, samples with high SiO2 contents (SiO2 ≥ 70 wt.%) exhibit high Rb/Sr ratios and depletions in Ba, Sr, P, Ti and Eu, while the samples with low SiO2 contents exhibit low Rb/Sr ratios and weak depletions in Ba, Sr, P, and Ti with insignificant negative Eu anomalies. Therefore, we suggest that the parent magmas of the Baiyunzhang-Lianhuashan Basins originated from the same deep-level magma reservoir, which underwent pulsatile magma extraction and formed two shallow-level magma reservoirs. The two shallow magma reservoirs each underwent different degrees of crystallization differentiation and crystal-melt separation, eventually forming ignimbrite, trachyte, rhyolite, granite porphyry and rhyolite porphyry through pulsed extraction. The remaining crystal mush consolidated in situ to form quartz monzonite porphyry intrusive rocks.