Geologia USP. Série Científica (Aug 2011)
Geochemistry and Petrogenesis of Metabasites from the Votuverava Group (Apiaí Terrane, Southern Ribeira Belt): Evidence of a Calymmian Back-arc Basin Frederico
Abstract
The Votuverava Group (ca. 1500 - 1400 Ma), which is part of the Apiaí Terrane, a segment of the Southern RibeiraBelt, is composed of distal turbidites with signifi cant basic magmatism represented by concordant lenses of metabasite.Twenty metabasite samples were investigated using geochemical analyses (major and trace elements). Three groups (G1,G2, G3) were identifi ed based on Ti/V ratios, rare earth element patterns and MORB-normalized multi-element diagrams.All samples have tholeiitic signatures. The G1 group has a volcanic arc signature, with Ti/V ratios of 15 - 20, enrichmentof large ion lithophile elements (LILE) and depletion in high fi eld strength elements (HFSE) relative to the MORB. Thetrace element pattern indicates an important contribution of the subduction component. The G2 group has a MORBtypecomposition, with Ti/V ratios of 22 - 28. Nevertheless, the trace element behavior indicates a small contributionof the subduction component. The G3 group has an enriched MORB signature, with Ti/V ratio of approximately 40 andenrichment of LILE and HFSE. The variability of the TiO2/Yb and Nb/Yb ratios suggests that the G1 and G2 rocks were generated by shallow melting (N-MORB and E-MORB mantle sources, respectively). The G3 rocks are enriched in Ti and Nb, suggesting interaction between MORB and plume mantle sources. The coexistence of volcanic arc basalt and mid-ocean ridge basalt compositions, the overall geochemical patterns, and the sedimentary environment of the Votuverava Group are consistent with a backarc basin environment.
