In-situ, integrated U-Pb, Hf and O isotopic study of igneous, metamorphic and detrital zircons. Implications to crustal evolution and geodynamics

Zircon data from South Karakoram gneiss dome provide evidence for Proterozoic inherited cores (1.8-1.9 Ga and 2.3-.2.5 Ga) surrounded by migmatitic overgrowth with ages ranging from ∼6 to ∼20Ma. Oxygen isotopic data of Neogene migmatite and inherited core is similar and indistinguishable ranging from 7.5 to 9.5 ‰. However, Neogene overgrowth is significantly less evolved than the inherited core in terms of Hf composition. This implies that the Hf composition of the migmatitic zircons is not controlled exclusively by the dissolution of the inherited cores and that contamination by external melts is likely. Isotopic data from the Baltoro plutonic unit in south Karakoram at the junction of India-Asian collision zone suggested that post collision magmatism in this region has more complex petrogenetic history than previously thought and is better explained by the involvement of at least three sources (1) Karakoram gneisses, (2) Cretaceous calc-alkaline Karakoram crust and (3) Asian lithospheric metasomatised mantle. However, direct contribution from juvenile pristine mantle is less likely as observed oxygen and hafnium isotopic data do not support juvenile sources. Based on plate configuration, Hf-O isotopic data and absence of the post 35 Ma magmatism in Kohistan-Ladakh arc, we suggest that the role of arc related component in generating the Miocene Baltoro plutonic unit is less likely during a possible breaking of subducted Indian continental lithosphere. The U-Pb and Hf isotopic data of REE-enriched alluvial deposits from west coast of Red Sea suggested that the detrital zircons are juvenile (mantle derived) and Neoproterozoic in age. Northern fan is sourced either from NE-ward or immediate westward granitoid gneisses. While alluvial fan in south close to Egypt-Sudan border is sourced from northern highlands of Sudan or from magmatic rocks in southern Egypt desert. No involvement of pre-Neoproterozoic evolved continental crust was identified