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 degrees C). Moreover, they have positive zircon epsilon Hf values of +0.29 to +5.01 and homogenous delta O-18 values of 5.11-5.87 parts per thousand, probably derived from the partial melting of talc-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 delta O-18 values (7.14-9.18 parts per thousand), indicating S-type granite. Their negative whole-rock epsilon Nd(t) values (-2.87 to -2.81) and zircon epsilon Hf(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 epsilon Hf(t) values (-5.00 to -1.64) and homogenous delta O-18 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 syncollisional high-pressure high-temperature crustal anatexis, and ca. 1.92 Ga post-collisional magmatism and synchronous ultrahigh temperature metamorphism.
NSTL
Elsevier