Petrogenesis and geological significance of Late Mesoproterozoic gabbro in the western Yangtze Block: Constrains from zircon U-Pb-Hf isotopes and whole-rock geochemistry

This study presents systematic analysis of zircon U-Pb-Hf isotopes, whole-rock major and trace elements, and Sr-Nd isotopes of the Jinchuan gabbros, aiming to explore its petrogenesis and geological significance. The Jinchuan gabbros has Zircon U-Pb age of 1 041.1±1.1 Ma, it has moderate SiO₂ (50.26% to 51.16%), CaO (6.59% to 7.64 %), K₂O (1.22% to 1.96%) contents, with high Al₂O₃ (16.38% to 17.15%) and TiO₂ (2.61% to 2.80%) contents, belonging to low-K tholeiite rocks. These gabbros were enriched in light rare earth elements and large ionic lithophile elements (e.g., Ba, Sr), as well as depleted in heavy rare earth elements and high field strength elements (e.g., Nb, Ta, Th), with weak Eu anomalies (δEu = 0.99 to 1.11).They have negative εNd(t) values (-3.61 to -2.75) and positive zircon εHf(t) (+1.62 to +7.58) contents. These geochemical features indicate the Jinchuan gabbros were originated from the enriched mantle source that metasomatized by middle Mesoproterozoic subduction fluids preserved in the lithosphere mantle. Combined with the coeval A-type granites and intra-plate basaltic magmatism, the Jinchuan gabbros formed in an intracontinental rift environment under a passive continental margin, representing the magmatic response of the Rodinia supercontinent under local extensional tectonic mechanism during the late Mesoproterozoic.