SHRIMP Zircon U‐Pb Chronology and Geochemistry of the Henglingguan and Beiyu Granitoids in the Zhongtiao Mountains, Shanxi Province

Abstract

Abstract: Henglingguan and Beiyu metamorphic granitoids, distributed in the northwest of the Zhongtiaoshan Precambrian complex, comprise trondhjemites and calc‐alkaline monzogranites, displaying intrusive contacts with the Archean Zhaizi TTG gneisses. And the Beiyu metamorphic granitoids consist mainly of trondhjemites, distributed at the core of the Hujiayu anticline fold. New SHRIMP zircon U‐Pb dating data show that the weighted mean 207Pb/206Pb ages are 2435.9 Ma and 2477 Ma for the Henglingguan metamorphic calc‐alkaline monzogranites and Beiyu metamorphic trondhjemites, respectively, and reveal ∼2600 Ma inherited core in magmatic zircons. Whole‐rock geochemical data indicate that all the Henglingguan and Beiyu metamorphic trondhjemites and calcalkaline monzogranites belong to the metaluminous medium‐ and high‐potassium calc‐alkaline series. These rocks are characterized by relatively high total alkali contents (Na2O+K2O, up to 9.08%), depleted Nb, Ta, P and Ti, and right‐declined REE patterns with moderate to high LREEs/HREEs fractionation (the mean ratio of (La/Yb)n = 25). The Henglingguan and Beiyu metamorphic trondhjemites display negative Rb, Th and K anomalies in the multi‐element spider diagrams normalized by primitive mantle. Sm‐Nd isotopic data reveal that these granitoids have initial ∍Nd(t)=‐1.2 to +2.4 and Nd depleted mantle model ages of TMD= 2622 Ma‐2939 Ma. All these geochemical features indicate that these granitoids were formed in an continent‐marginal arc, and the trondhjemites mainly originated from partial melting of juvenile basaltic materials and, howbeit, the Henglingguan metamorphic calc‐alkaline monzogranites derived from recycling of materials in the ancient crust under a continent‐marginal arc. The granitic magma underwent contamination and fractional crystallization during their formation.