Geological and geochemical feature and formation cause of Pulang complex, Yunan Province. Geological Bulletin of China

Pulang complex can be divided into 3-stage intrusion based on contact relationship and lithologic features, namely quartz dioritic porphyrite, quartz monzonite-porphyry and grannitic diorite porphyry, it is indicated by the zircon U-Pb chronology resulte that these intrusion formed in indo-chinese epoch, between 221 and 206Ma. According to the geo-chemical feature, these rocks are high in Si and Al, low in alkali but relatively rich in Na, along with its development, it becomes richer in Si, alkali and K, lower in Al, Ca and Mg. Such LIL elements including Cs, Pb, K, Ba and Sr is apparently concentrated, while opposite for those inactive HFS elements including Y, Hf, Zr, Ti, Nb and Ta. Generally the rock displays negative Nb and positive Pb anomaly, which indicates that the magma originated from upper mantle or lower crust with crust substance involved in. Combines with Nd isotope test result, it is agreed that these multi-phase intrusions derived from comagmatic evolution and intrusion. With the help of tectonic background, porphyry rocks formed in volcanic arc structural environment of active continental margin, which can be regarded as the outcome of westwards subduction of oceanic crust along Ganzi-Litang trench.