Abstract
Whole-rock geochemical and radiogenic data are combined with in situ trace and isotopic analyses of amphibole grains to characterize the source and the emplacement mechanisms of the magmas of the Sunda arc in the Batu Hijau district, Sumbawa, Indonesia. The low-K calc-alkaline magmatic suite in the area is characterized by a distinctively juvenile signature (143Nd/144Nd ~0.5130). Whole-rock trace element and Pb isotopic data (207Pb/204Pb ~15.603) suggest the involvement of a minimal (<0.1%) sediment component in arc petrogenesis. During the petrogenesis of the calc-alkaline plutons, the involvement of fluids that were not entirely derived from the dehydration of a subducting slab is reflected in the mineral chemistry of the primary hydrous magmatic amphiboles, which contain very low B and Li concentrations. We argue that the B- and Li-poor fluids implicated in the petrogenesis of the calc-alkaline melts were at least partially derived from dehydration of uprising asthenospheric mantle. The δD values of selected hydrous magmatic amphibole grains range between ca. −70‰ and 0‰, consistent with an original mantle-derived signature, which was subsequently modified due to a de-hydrogenation process. We put forward the hypothesis that in the Batu Hijau district an arc-transverse fault system facilitated the rise of asthenosphere-derived melts above a kink, or tear, in the subducting Indian Ocean Plate that underlies the Sunda arc. The melts ascended to upper-crustal levels and underwent fractionation while interacting with the arc crust or metasomatized lithospheric mantle wedge. As a result of this study, we emphasize the significance of crustal-scale faults as conduits that connect the mantle to upper-crustal levels in arc settings. The de-hydrogenation process that the tonalite plutons underwent in the Batu Hijau district may have been crucial to the genesis of associated Cu–Au porphyry mineralization and the development of the Pliocene Batu Hijau deposit. Consequently, we argue that deep structures may facilitate the efficient release of mineralizing fluids at high crustal-levels.
Published Version
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call