Abstract:
Objective The high−silica rhyolites (usually SiO2>75%) display unique geochemical characteristics and mineral assemblages, often associated with rare−metal mineralization, and are important parts of the upper continental crust. The petrogenesis study of high−silica rhyolites has great significance to understanding the reworking and evolution process of the continental crust.
Methods In this paper, a suite of high−silica rhyolites was found in Jarud Banner, southern Great Xing'an Range. We conducted petrological analysis, zircon U−Pb dating, and whole−rock geochemical studies on the high−silica rhyolites.
Results The obtained LA−ICP−MS zircon U−Pb age is 156.1±0.9 Ma, indicating that the high−silica rhyolites formed in Late Jurassic. The chemical analyses show that the high−silica rhyolites are characterized by rich in SiO2, high K2O, low Al2O3, TFeO, MgO, TiO2, Na2O, relatively rich in light rare earth elements (LREEs) and large ion lithophile elements (LILEs, e.g. Rb, K, Th, U), depletion in high field strength elements (HFSEs, such as Nb, Ta, P, Ti) and Ba, Sr, and varying degrees of Eu negative anomalies.
Conclusions All these geochemical characteristics suggest that the high−silica rhyolite magma in Jarud Banner has undergone intense fractional crystallization of minerals such as K−feldspar, plagioclase, biotite, monazite, and allanite, characterized by high fractionated rhyolite and generated in the shallow crust under the extensional tectonic setting. This suite of high−silica rhyolites offers new clues and directions for targeting rare metal deposits associated with high fractionated magmas in the southern Great Xing'an Range.
下载: