Petrogenesis and Tectonic Significance of Shenxianshui Alkaline Granite in Gejiu, Yunnan Province, China

Abstract

AbstractThe Shenxianshui granites in the Gejiu western area were formed in the Late Cretaceous. Laser ablation inductively coupled plasma mass spectrometry indicates zircon U–Pb ages ranging from 85.97 ± 0.6 Ma to 90.67 ± 0.7 Ma. The intrusive rocks are peraluminous (A/CNK=1.03 to 1.33) and calc–alkaline, showing an affinity towards I–type granite. Large ion lithophilic elements are enriched in K and Rb, while high field strength elements are depleted. Moreover, light rare earth elements are significantly enriched, showing a slight negative Eu anomaly (Eu/Eu*=0.39 to 0.58). Shenxianshui granite has a relatively high initial Sr isotope ratio ((87Sr/86Sr)i = 0.7098∼0.7105), negative ɛNd(t) values (−7.99 to −7.44) and negative ɛHf(t) values(−8.37 to −2.58). Combined with previous studies, these characteristics suggest that the Shenxianshui alkaline granites were formed in a post–collision extensional environment. The basic granitic magma may have principally originated from the partial melting of the lower crust in the Mesoproterozoic era, and possibly contained mantle source materials. Shenxianshui alkaline granite was finally formed following the miscible magma and a high degree of crystal differentiation. The abundance of ore–forming elements indicates that Shenxianshui granite has the potential for mineralization of key metals and rare earth elements.