Geochemistry and geochronology of the Imbicuí Complex, Western Dom Feliciano Belt, Brazil: Tonian adakite-like subduction-related rocks

Abstract

Dioritic-tonalitic-trondhjemitic metamorphic rocks represent the Imbicuí Complex in Western Dom Feliciano Belt, São Gabriel Terrane, Lavras do Sul region, Brazil. This complex presents rocks with an adakite-like signature showing high Sr contents (573.5–1337 ppm), Sr/Y ratio higher than 64.08, low Y content (< 33.7 ppm), (La/Yb)N > 10, and YbN < 16 being classified as Type 1, high silica and high-Al2O3 adakites. The adakites present a low-K calc-alkaline affinity, with a U–Pb LA-ICP-MS in zircon crystallization age of 828 ± 8 Ma, the product of an eclogitic melting source. Subordinate, metagabbroic rocks occur with tholeiitic affinity, presenting a U–Pb LA-ICP-MS in zircon crystallization age of 845 ± 5 Ma. The adakitic rocks showed εNd(828) (+ 8.2 to + 7.5), model ages Nd-TDM of 0.8 and 0.9 Ga, similar to the age of crystallization, suggesting that these magmas represent juvenile rocks generated in an orogenic environment mixed with reworked rocks (ratios 206Pb/204Pb and 207Pb/204Pb, 17.70 to 18.40 and 15.49 and 15.55) during an oceanic slab melting associated to the closure of Charrua Ocean throughout Tonian in the Western Dom Feliciano Belt.