Geodynamic evolution in the post-collisional stage of the East Kunlun Orogenic Belt: constraints from the Late Triassic intermediate–felsic igneous rocks

Abstract

AbstractThe Late Triassic igneous rocks associated with post-collision are widely distributed in the East Kunlun Orogenic Belt (EKOB), but their specific dynamic mechanism and evolutional process are still controversial. To address these key issues, we investigated the geochronology and geochemistry of intermediate–felsic igneous rocks from the EKOB, including trachyandesite, rhyolite, porphyritic monzogranite, syenogranite, granite porphyry and crystalline tuff. Zircon U–Pb isotopes of these rocks indicate that they were formed between 231.1 and 215.8 Ma (i.e. Late Triassic). These igneous rocks have moderate to high SiO2 (60.29–79.56 wt%) and low mantle compatible element contents (e.g. Co: 0.37–12.62 ppm; Ni: 1.55–15.59 ppm), suggesting that continental crustal-derived material played an important role in their formation. Porphyritic monzogranite (231.1 Ma), syenogranite (228.1 Ma), trachyandesite (227.4 Ma) and rhyolite (215.8 Ma) have Nb/U (1.41–4.71) and Ce/Pb (1.48–6.19) ratios like that of the crust, with εHf(t) values (–1.31 to 2.26) and old two-stage model (TDM2) ages of 1340–1119 Ma, suggesting that they originated from the partial melting of a Mesoproterozoic crust with minor mantle material involved in their source. Crystalline tuff (224.6 Ma) and granite porphyry (222.3 Ma) have Nb/U (1.93–3.81) and Ce/Pb (0.30–3.18) ratios, negative εHf(t) values (–7.04 to −5.12) and old TDM2 ages (1703–1581 Ma) closer to those of crust, suggesting that they were derived from the partial melting of a Paleo–Mesoproterozoic continental crust without addition of mantle material. Based on our new data and published data, the Late Triassic igneous rocks from the EKOB can be divided into three stages, 236–227, 226–218 and 216–208 Ma, corresponding to slab break-off, lithospheric mantle delamination and thickened lower crust delamination, respectively.KEY POINTSThe intermediate–felsic igneous rocks from the East Kunlun Orogenic Belt are dated from 231.1 to 215.8 Ma (i.e. Late Triassic).These igneous rocks were derived from the partial melting of ancient continental crust.The Late Triassic igneous rocks from the East Kunlun Orogenic Belt can be divided into three stages, including slab break-off, lithospheric mantle delamination and thickened lower crust delamination.Keywords: East Kunlun Orogenic BeltLate Triassicpost-collisional magmatismgeodynamic evolutionintermediate–felsic igneous rocksslab break-offdelamination Data availability statementThe authors confirm that the data supporting the findings of this study are available within the article and the Supplemental data.Disclosure statementNo potential conflict of interest was reported by the author(s).Additional informationFundingThis research was funded by the Key Research Program of the National Natural Science Foundation of China (92062217), the Kunlun Talents High-end Innovative and Entrepreneurial Talents Project of Qinghai Province ([2022] No. 32), the Science and Technology Project of Qinghai Province (2019-ZJ-7009) and the Kunlun Talents High-end Innovative and Entrepreneurial Talents Project of Qinghai Province ([2021] No. 16).