Abstract
This study presents detailed petrology, major and trace element chemistry, Sr-Nd isotope, and in-situ zircon U-Pb dating and Hf-O isotopes on granites from the Qianlishan Complex of the Khondalite Belt in North China. Zircon SIMS U-Pb data indicate three episodes of Paleoproterozoic magmatism at ca. 2.06 Ga, 1.95 Ga and 1.92 Ga. Of those, the ca. 2.06 Ga hornblende monzogranites and fine-grained potassic granites display typical features of A-type granite, represented by metaluminous affinity, high FeOT/MgO ratios (3.29–5.63), and high Ga/Al and Zr + Nb + Ce + Y values with high zircon saturation temperatures (916–1000 °C). Moreover, they have positive zircon εHf values of +0.29 to +5.01 and homogenous δ18O values of 5.11–5.87 ‰, probably derived from the partial melting of calc-alkaline granitoids without addition of supracrustal rocks. The ca. 1.95 Ga garnet-bearing granites contain peraluminous minerals of garnet and muscovite and have high ASI index (>1.1) and δ18O values (7.14–9.18 ‰), indicating S-type granite. Their negative whole-rock εNd(t) values (−2.87 to −2.81) and zircon εHf(t) values (−4.06 to +1.29) suggest a source of ancient supracrustal rocks. The ca. 1.92 Ga coarse-grained potassic granites present metaluminous and magnesian signatures of I-type granite, including low A/CNK and FeOT/MgO ratios. Their negative εHf(t) values (−5.00 to −1.64) and homogenous δ18O values (5.20–6.00%) suggest that the original magma was derived primarily from enriched lower crust. The results, combined with regional geology and previous studies, establish a prolonged magmatic-metamorphic evolution of the Khondalite Belt from subduction to collision, involving ca. 2.3–2.0 Ga subduction-related arc magmatism, ca. 1.95 Ga syn-collisional high-pressure high-temperature crustal anatexis, and ca. 1.92 Ga post-collisional magmatism and synchronous ultrahigh temperature metamorphism.
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