Crustal control on the petrogenesis of adakite-like rocks

Abstract

Adakite-like rocks have attracted extensive interest as they record magmatic processes and mantle-crustal material recycling, and because they are associated with major porphyry Cu deposits. However, their petrogenesis is still under debate. In this study, we compiled ca. 7000 sets of whole-rock geochemical and Nd isotopic data of Phanerozoic adakite-like rocks worldwide from published literature, with the aim to characterize geochemically adakite-like rocks from subduction, collision, and post-collision settings. Statistical analysis highlights the different lanthanides + Y patterns from various types of juvenile and mature crust. Modelling of the statistically-processed data suggest that pure fractionation of amphibole and/or garnet cannot account for the lanthanides + Y patterns of adakite-like rocks, whereas partial melting of mafic protoliths is a possible mechanism. This study supports a adakite-like magma generation model by partial melting of the eclogitic lower crust. The melt was then mixed with depleted mantle-derived basaltic melt, and subsequently fractionated. Compared with the adakite-like magma formation from the juvenile crust, that from the mature crust is featured by higher degree of partial melting, greater depths and higher water content. Additionally, secular peaks of La/Yb value (which reflects the depth of magma source) of adakite-like rocks worldwide suggest that the period of magmatic activity in deep-level magma reservoirs could be used as the indicator of either the final stages of the Phanerozoic orogenesis, or craton activation by subduction.