Diorite enclaves and host granite of the early Miocene Gorontalo pluton in the North Sulawesi Arc, Indonesia: Implications for recycled oceanic crust and crust-mantle interaction

Abstract

• Granites from the Early Miocene Gorontalo pluton were derived from a juvenile crust. • Diorite enclaves originated from mixing of depleted mantle- and juvenile crust-derived magmas . • Sub-normal mantle δ 18 O values suggest the involvement of recycled altered oceanic crust . • Early Miocene crust-mantle interaction occurred in the North Sulawesi Arc. Zircon Hf-O isotopes, combined with whole-rock Sr-Nd-Pb isotopes, can provide unambiguous evidence for crustal recycling and crust-mantle interaction processes. The North Sulawesi Arc (Indonesian) was traditionally regarded as an intra-oceanic arc, and the diorite enclaves and host granites of the Gorontalo pluton provide excellent opportunities for evaluating these issues, based on our zircon U-Pb geochronological and Hf-O isotopic, and whole-rock geochemical analyses. This study firstly reports the zircon U-Pb ages of ∼20.1–22.4 Ma for the host granites and ∼19.5–20.4 Ma for the diorite enclaves. The host granites have high SiO 2 , and low 10000*Ga/Al, A/CNK and Rb/Sr, classified as unfractionated I-type granites. They are characterized by high εNd (t) (from +4.8 to +5.7), high zircon εHf (t) (from +11.1 to +16.4), sub-normal mantle zircon δ 18 O (4.6–5.4‰), moderate ( 206 Pb/ 204 Pb) i (18.29–18.45), and young two-stage Hf model ages (52–394 Ma), deriving from partial melting of a juvenile mafic crust. The diorite enclaves show typical magmatic textures and contain abundant acicular apatite and plagioclase megacrysts with an obvious rim-core texture. They also have high εNd (t) (from +4.8 to +5.1), high zircon εHf (t) (from +10.7 to +15.2), sub-normal mantle zircon δ 18 O (4.1–5.1‰) and moderate ( 206 Pb/ 204 Pb) i (18.3), interpreted as the products of mixing of magmas derived from a depleted mantle and a juvenile crust. The diorite enclaves have sub-normal mantle δ 18 O values, positive εNd (t) and zircon εHf (t) , suggesting recycled altered oceanic crust into depleted mantle prior to magma generation. The presence of the host granites and diorite enclaves provides robust evidence for early Miocene (or prior to early Miocene) crust-mantle interaction in the North Sulawesi Arc.