Retrieving petrogenetic source, compositional diversity and tectono-magmatic scenario of Tethyan sediment-derived magmatic flare-up: A tale from petrochemical and multi-isotopic (Sr–Nd–B–Hf) systematics

The Earth's continental crust is predominantly composed of granitic rocks, yet the genesis of pure sediment-derived peraluminous granites (PGs) remains debated. This study investigates the Ordovician Mansehra granitic suite (ca. 476–483 Ma) from the northwestern Himalayas of Pakistan as an example of S-type granites, comparing them with global counterparts from Diancangshan-Ailaoshan (China), Tanggula-Damxung (Tibet), and Karamese (Turkey). Geochemical and isotopic data, including variable zircon εHf(t) values (−37.7 to + 12.6), enriched Sr isotope ratios ((⁸⁷Sr/⁸⁶Sr)i: 0.5678–0.7444), negative εNd(t) values (−13.4 to − 2.9), and a narrow δ¹¹B range (−15.4 ‰ to − 9.5 ‰), indicate that PGs formed through partial melting of heterogeneous, mature pelitic sources under shallow, low-pressure conditions in the lower–upper crust, with minimal mantle input. Heterogeneous Hf isotopic behavior reflects the disequilibrium melting of variable metasedimentary protoliths. Geochemical modeling highlights fluid-flux melting as the dominant process, except for the Tanggula granites, which exhibit characteristics of fluid-absent melting. Tectonically, the Mansehra PGs are interpreted as products of Proto-Tethyan oceanic subduction beneath northern Gondwana, formed through the disequilibrium melting of exhumed back-arc basin sediments. Slab break-off likely triggered asthenospheric upwelling, enhancing heat flux and driving anatexis and PG production. While global PGs represent different geodynamic evolutionary contexts, they predominantly display significant tectonic events rather than direct contributions to crustal growth. The Mansehra PGs, along with similar granites, record large-scale anatexis linked to collisional tectonics, providing critical insights into Earth's geodynamic evolution.