The Geochemical and Zircon Trace Elements Characteristics of A‐type Granitoids in Boziguoer, Baicheng County, Xinjiang

Abstract

AbstractThe Boziguoer A‐type granitoids in Baicheng County, Xinjiang, belong to the northern margin of the Tarim platform as well as the neighboring EW‐oriented alkaline intrusive rocks. The rocks comprise an aegirine or arfvedsonite quartz alkali feldspar syenite, an aegirine or arfvedsonite alkali feldspar granite, and a biotite alkali feldspar syenite. The major rock‐forming minerals are albite, K‐feldspar, quartz, arfvedsonite, aegirine, and siderophyllite. The accessory minerals are mainly zircon, pyrochlore, thorite, fluorite, monazite, bastnaesite, xenotime, and astrophyllite. The chemical composition of the alkaline granitoids show that SiO2 varies from 64.55% to 72.29% with a mean value of 67.32%, Na2O+K2O is high (9.85%–11.87%) with a mean of 11.14%, K2O is 2.39%–5.47% (mean = 4.73%), the K2O/Na2O ratios are 0.31–0.96, Al2O3 ranges from 12.58% to 15.44%, and total FeOT is between 2.35% and 5.65%. CaO, MgO, MnO, and TiO2 are low. The REE content is high and the total SREE is (263–1219) ppm (mean = 776 ppm), showing LREE enrichment and HREE depletion with strong negative Eu anomalies. In addition, the chondrite‐normalized REE patterns of the alkaline granitoids belong to the “seagull” pattern of the right‐type. The Zr content is (113–1246) ppm (mean = 594 ppm), Zr+Nb+Ce+Y is between (478–2203) ppm with a mean of 1362 ppm. Furthermore, the alkaline granitoids have high HFSE (Ga, Nb, Ta, Zr, and Hf) content and low LILE (Ba, K, and Sr) content. The Nb/Ta ratio varies from 7.23 to 32.59 (mean = 16.59) and the Zr/Hf ratio is 16.69–58.04 (mean = 36.80). The zircons are depleted in LREE and enriched in HREE. The chondrite‐normalized REE patterns of the zircons are of the “seagull” pattern of the left‐inclined type with strong negative Eu anomaly and without a Ce anomaly. The Boziguoer A‐type granitoids share similar features with A1‐type granites. The average temperature of the granitic magma was estimated at 832–839°C. The Boziguoer A‐type granitoids show crust–mantle mixing and may have formed in an anorogenic intraplate tectonic setting under high‐temperature, anhydrous, and low oxygen fugacity conditions.