The Paleoproterozoic Khondalite Belt, located in the northwestern segment of North China Craton (NCC), is characterized by widespread high-temperature/ultrahigh-temperature (UHT) granulite/gneiss and large-scale magmatic activity. The tectonic evolution is still controversial. Here, we report new geochronological, elemental, and Hf-O-Sr-Nd isotopic data for a Paleoproterozoic layered complex in the Jining terrane to constrain the tectonic evolution of the Khondalite Belt. In situ zircon U-Pb dating indicates that the Sanchakou gabbros were emplaced between ~1.94 Ga and ~1.82 Ga, which might be the heat source of UHT metamorphism. The elemental and Hf-O-Sr-Nd isotopic analysis shows that the formation of Sanchakou gabbros is consistent with the assimilation and fractional crystallization (AFC) process. The magma originates from the 10%~20% partial melting of the spinel + garnet lherzolite mantle. The Sanchakou gabbros are magmatic crystallization products mixed with crustal wallrocks in the magma chamber. We have established a tectonic evolution model involving asthenosphere upwelling after the amalgamation of the Ordos and Yinshan Blocks at ~1.95 Ga.
The Riduo intermediate-felsic volcanic rocks are located in the eastern Lhasa terrane in southern Tibet. Zircon U–Pb dating, geochemical and Sr–Nd–Hf isotope analyses were carried out to constrain the age, petrogenesis and magma source of the Riduo magma suite, including andesite, dacitic tuff, and quartz diorite. Zircon U–Pb dating yielded Early Miocene ages of 19.5 ± 0.5 Ma (andesite), 17.6 ± 0.3 Ma (dacitic tuff), and 15.6 ± 0.5 Ma (quartz diorite). Geochemically, this early Miocene suite is adakitic with high SiO2 (55.76–69.46 wt.%), Al2O3 (15.21–16.61 wt.%), Na2O (3.82–4.83 wt.%), Sr (427–1033 ppm), and Sr/Y (24.5–145), but low Y (< 17.8 ppm) and Yb (< 1.82 ppm). The rocks also have low to high K2O (0.44–3.82 wt.%). They are enriched in light rare earth elements (LREEs), large ion lithophile elements (LILEs, e.g. K, Rb, Th and U), but depleted in high-field strength elements (e.g. Nb, Ta) and heavy rare earth elements (HREEs), and have weakly negative to positive Eu anomalies. Isotope analyses reveal that most samples have high whole-rock initial 87Sr/86Sr ratios (0.705611–0.708807), low εNd(t) (−2.25 to −1.15), and positive zircon εHf (t) (+1.29 to +6.49). We suggest that the early Miocene magmas in the eastern Lhasa terrane were likely sourced from post-collisional partial melting of the juvenile lower crust with minor mantle input. The magmas may have been crustal-contaminated during their ascent to the upper crust along the N-S-trending Cona-Riduo rift.
The Riduo intermediate-felsic volcanic rocks are located in the eastern Lhasa terrane in southern Tibet. Zircon U–Pb dating, geochemical and Sr–Nd–Hf isotope analyses were carried out to constrain the age, petrogenesis and magma source of the Riduo magma suite, including andesite, dacitic tuff, and quartz diorite. Zircon U–Pb dating yielded Early Miocene ages of 19.5 ± 0.5 Ma (andesite), 17.6 ± 0.3 Ma (dacitic tuff), and 15.6 ± 0.5 Ma (quartz diorite). Geochemically, this early Miocene suite is adakitic with high SiO2 (55.76–69.46 wt.%), Al2O3 (15.21–16.61 wt.%), Na2O (3.82–4.83 wt.%), Sr (427–1033 ppm), and Sr/Y (24.5–145), but low Y (< 17.8 ppm) and Yb (< 1.82 ppm). The rocks also have low to high K2O (0.44–3.82 wt.%). They are enriched in light rare earth elements (LREEs), large ion lithophile elements (LILEs, e.g. K, Rb, Th and U), but depleted in high-field strength elements (e.g. Nb, Ta) and heavy rare earth elements (HREEs), and have weakly negative to positive Eu anomalies. Isotope analyses reveal that most samples have high whole-rock initial 87Sr/86Sr ratios (0.705611–0.708807), low εNd(t) (−2.25 to −1.15), and positive zircon εHf (t) (+1.29 to +6.49). We suggest that the early Miocene magmas in the eastern Lhasa terrane were likely sourced from post-collisional partial melting of the juvenile lower crust with minor mantle input. The magmas may have been crustal-contaminated during their ascent to the upper crust along the N-S-trending Cona-Riduo rift.
The Riduo intermediate-felsic volcanic rocks are located in the eastern Lhasa terrane in southern Tibet. Zircon U–Pb dating, geochemical and Sr–Nd–Hf isotope analyses were carried out to constrain the age, petrogenesis and magma source of the Riduo magma suite, including andesite, dacitic tuff, and quartz diorite. Zircon U–Pb dating yielded Early Miocene ages of 19.5 ± 0.5 Ma (andesite), 17.6 ± 0.3 Ma (dacitic tuff), and 15.6 ± 0.5 Ma (quartz diorite). Geochemically, this early Miocene suite is adakitic with high SiO2 (55.76–69.46 wt.%), Al2O3 (15.21–16.61 wt.%), Na2O (3.82–4.83 wt.%), Sr (427–1033 ppm), and Sr/Y (24.5–145), but low Y (< 17.8 ppm) and Yb (< 1.82 ppm). The rocks also have low to high K2O (0.44–3.82 wt.%). They are enriched in light rare earth elements (LREEs), large ion lithophile elements (LILEs, e.g. K, Rb, Th and U), but depleted in high-field strength elements (e.g. Nb, Ta) and heavy rare earth elements (HREEs), and have weakly negative to positive Eu anomalies. Isotope analyses reveal that most samples have high whole-rock initial 87Sr/86Sr ratios (0.705611–0.708807), low εNd(t) (−2.25 to −1.15), and positive zircon εHf (t) (+1.29 to +6.49). We suggest that the early Miocene magmas in the eastern Lhasa terrane were likely sourced from post-collisional partial melting of the juvenile lower crust with minor mantle input. The magmas may have been crustal-contaminated during their ascent to the upper crust along the N-S-trending Cona-Riduo rift.
The Shuangjianzishan super-large Ag-Pb-Zn deposit is situated in the southern Great Xing’an Range (SGXR), which is part of the eastern Central Asian Orogenic Belt (CAOB) and the northeastern Xing’an-Mongolia Orogenic Belt (XMOB). The host rock of this deposit is the Dashizhai Formation, characterized by a widely distributed, extremely thick slate in the Shuangjianzishan basin. Petrographically, the slate contains secondary minerals such as secondary quartz, biotite, sphalerite, pyrite, galena, and chalcopyrite, in addition to primary quartz, feldspar, and rock fragment. The whole-rock geochemical analysis indicates that the slate was deposited in an oxygen-deficient shale basin, influenced by calcium-rich volcanic ash and magmatic-hydrothermal fluids. The mineralogical characteristics of sulfide minerals and the in-situ sulfur isotopic composition of pyrites suggest that the sulfide minerals were likely formed before the primary metallogenic epoch, indicating pre-enrichment of metals. The color variation from black to green observed in the drilling core of the slate is attributed to differences in feldspar content, with the denser “black” slate marking the metallogenic horizon. Based on previous research, it is inferred that the slate is a product of the post-orogenic extensional tectonic setting of the XMOB in the Late Carboniferous, and it underwent alteration by epithermal magmatic-hydrothermal fluids during the Mesozoic metallogenic episode.
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