Geochemical, Sr-Nd-Pb, and Zircon Hf-O Isotopic Compositions of Eocene-Oligocene Shoshonitic and Potassic Adakite-like Felsic Intrusions in Western Yunnan, SW China: Petrogenesis and Tectonic Implications

Abstract

Coeval potassic adakite-like and shoshonitic felsic intrusions in the western Yunnan province of SW China are spatially and temporally associated with Eocene^Oligocene shoshonitic mafic volcanic rocks. The shoshonitic syenite and quartz monzonite intrusions are characterized by high K 2 O contents (49^68 wt %) and K 2 O/Na 2 O ratios (11^17), high Y (17^348 ppm) and Yb (150^316 ppm) contents, nearly flat heavy rare earth element (HREE) patterns and moderate Eu anomalies (Eu/Eu* 065^078). The potassic adakite-like granite and quartz monzonite intrusions are characterized by enrichment in light rare earth elements (LREE), depletion in HREE and fractionated HREE patterns, high Sr (328^1423 ppm), Sr/Y (38^243) and La/Yb (23^62), and low Y