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Transcrustal magmatic systems in NE China: Insights from Early Cretaceous metaluminous–peraluminous–peralkaline rock associations in the southern Great Xing’an Range
Gondwana Research ( IF 7.2 ) Pub Date : 2024-09-19 , DOI: 10.1016/j.gr.2024.08.017 Li Tian, Jun Gou, Deyou Sun, Duo Zhang, Zhao Feng, Zhonghua He
Gondwana Research ( IF 7.2 ) Pub Date : 2024-09-19 , DOI: 10.1016/j.gr.2024.08.017 Li Tian, Jun Gou, Deyou Sun, Duo Zhang, Zhao Feng, Zhonghua He
The generation and evolution of crustal-scale magmatic systems are important in revealing the continental crust differentiation. In the Bayangeer-Aliwula area of Inner Mongolia, metaluminous–peraluminous–peralkaline rock assemblages provide a rare opportunity to evaluate Early Cretaceous magmatic systems. This study presents new geochemical data, including whole-rock and zircon geochemistry, zircon U–Pb dating, and Hf–O isotopic analysis of rocks formed between 132 and 121 Ma. The metaluminous rocks exhibit low SiO2 (55.35–65.65 wt%), low Rb/Sr (0.08–0.24) and (La/Yb)N (4.88–7.58) ratios, and positive εHf (t) values (+4.9 to +8.7). These features, along with enrichment in large-ion lithophile elements and depletion in Nb and Ta, suggest formation via partial melting of fluid-metasomatised lithospheric mantle. By contrast, peraluminous rocks have high SiO2 (69.37–80.58 wt%), a high differentiation index (DI = 88–95), and Fe-index (0.84–0.95), resembling highly fractionated I-type granites. They show high Rb/Sr (0.77–3.35) and (La/Yb)N (5.79–22.75) ratios, and positive εHf (t) values (+6.7 to +10.8), combined with the modelling results, indicating origin from partial melting of K-rich mafic lower crust followed by magma fractionation. Peralkaline rocks display typical ferroan A-type granite characteristics (Zr + Nb + Ce + Y = 906–4292 ppm; Fe-index = 0.96–0.99), with high SiO2 (74.02–77.50 wt%), high Rb/Sr (6.17–121.38), and (La/Yb)N ratios (2.19–17.72), and positive εHf (t) values (+3.1 to +9.6). Zircon geochemistry characteristics suggest that peralkaline and peraluminous felsic melts are different batches extracted from the same magma reservoir. Further analysis, including hyperbola diagrams and zircon oxygen isotope compositions, suggests peralkaline magma formation through the mixing of altered oceanic crust fluids and peraluminous melts after melt extraction. During Early Cretaceous, the transcrustal magmatic system provides a reasonable explanation for the petrogenesis of various contemporaneous rocks in the study area in southern Great Xing’an Range.
更新日期：2024-09-19
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