Unraveling the tectonic tapestry of granitic rocks: Petrogenetic insights from Triassic silicic plutonic and volcanic magmatism in the northern Tibetan Plateau

Abstract The petrogenetic typology of granites and their volcanic equivalents is crucial for understanding petrogenesis, but their magma sources and tectonic settings remain controversial. To clarify the relationship between granite typology and magma sources as well as geodynamic settings, an integrated study was conducted on the Keri silicic volcanic and plutonic rocks in the East Kunlun orogenic belt, northern Tibetan Plateau. Field geology and geochronology reveal that the ca. 208 Ma rhyolitic volcanic rocks directly overlie the ca. 228 Ma syenogranite pluton, which indicates that the East Kunlun orogenic belt underwent rapid uplift between 228 Ma and 208 Ma. The syenogranites show high silica and strongly peraluminous compositions (SiO2 = 76.45–78.96 wt%, A/CNK = 1.08–1.23), and enrichment in light rare earth elements [(La/Yb)N = 4.53–12.37] with negative Eu anomalies (Eu/Eu* = 0.08–0.56), similar to highly fractionated S-type granites. They exhibit enriched Sr-Nd-Hf isotopes [87Sr/86Sr = 0.7071–0.7089, εNd(t) = −5.73 to −6.83, εHf(t) = −8.33 to −1.45], which suggests an origin from the partial melting of Mesoproterozoic metagreywacke. Conversely, the rhyolitic volcanic rocks display A1-type granite affinities [i.e., 10,000*Ga/Al = 3.34–4.88; (Zr + Nb + Ce + Y) = 440–853 ppm; Y/Nb = 0.21–0.76] and weakly enriched or depleted Sr-Nd isotopes [87Sr/86Sr = 0.7066–0.7073, εNd(t) = −2.41 to −2.92; εHf(t) = 0.17–3.17], with high Nb-Ta contents (average of Nb = 94.74 ppm; Ta = 6.38 ppm). Petrogenetic and geochemical modeling indicate that these A1-type rhyolitic volcanic rocks were derived from Nb- and Ta-enriched oceanic-island basalt–like basaltic magmas that underwent extensive differentiation with minor crustal contamination. This study not only reveals a tectonic transition in the East Kunlun orogenic belt from syn-collisional compression to postcollisional extension during 228–208 Ma, but also demonstrates that the genetic types of granitic rocks are primarily controlled by their magma sources and magmatic evolution rather than tectonic settings. While a single granite rock may not precisely constrain the tectonic setting, the assemblage of diverse granite types with unique contact relationships holds significant tectonic implications.