Growth of the upper crust in intra-oceanic island arcs by intrusion of basaltic magmas: the case of the Koloula Igneous Complex, Guadalcanal, Solomon Islands (SW Pacific)

Abstract The Pleistocene (2.2–1.5 Ma) Koloula Igneous Complex (KIC) on Guadalcanal in the Solomon island arc consists of a low-K calc-alkaline sequence ultramafic to felsic plutonic rocks. We present whole-rock major and trace element Sr–Nd-Pb isotope data, as well mineral compositions that record magmatic evolution complex. intrusive is grouped into two cycles, Cycle 1 2, comprising gabbroic or dioritic granodioritic data each cycle forms single fractional crystallisation trend. distinct radiogenic incompatible 2 intrusions imply slightly different mantle sources. KIC formed by shallow (0.1 GPa) mantle-derived Al-rich basaltic parental magmas (6–8 wt.% MgO) were deeper-level (0.7 fractionation olivine pyroxene from Mg-rich (~ 11 primary intra-oceanic arc. Olivine, clinopyroxene, plagioclase, amphibole, biotite, apatite, Fe–Ti oxides fractionated KIC’s high-Al form magmas. Liquid line descent trends calculated using mass balance calculations closely match observed data. crystallised at shallow, upper crustal depths ~ 2.0–3.0 km 20 km-thick crust. This complex typical other Cenozoic plutons Pacific arcs terms field relationships, petrology, chemistry geochemistry. Hornblende played significant role formation rocks these plutons, causing an enrichment SiO light rare earth elements. These represent fossil magma systems volcanoes; thus, crust probably generated migration centres.