Exploring the orogenic nature of the Cariris Velhos event (ca. 1000-920 Ma) of the Borborema Province (NE Brazil)

The Cariris Velhos event (ca. 1000-920 Ma) is a significant marker in the early Neoproterozoic lithospheric record of the Borborema Province in NE Brazil. Despite its importance, the nature of this event remains unresolved having been linked to either continental rifting or accretionary-collisional orogeny. In this study, we support a compressive setting for the Cariris Velhos event based on compiled geochemical and isotopic data (Sm-Nd and Lu-Hf) from metagranitic rocks in the Alto Pajeu Terrane (central Borborema) and in the Pernambuco-Alagoas Super Terrane, as well as in the Riacho do Pontal and Sergipano fold belts (Southern Borborema). Geochemistry of these rocks share similarities with calcic to alkali-calcic and ferroan magmas, along with some Cordilleran magnesian members. They also correspond to meta-to peraluminous I- and S-type granitic rocks. Trace element distribution on spider diagrams reveals negative anomalies of HFSE (high field strength elements) such as Nb and Ta, which are typically associated with subduction-related settings. Additionally, chondrite normalized REE (rare-earth element) diagrams indicate mixing of both crustal and mantle material. Tectonic discriminant diagrams using elements with low mobility supports the hypothesis of a continental margin subduction-related setting. Calculated cNd and cHf values vary from negative to slightly positive, suggesting contributions from juvenile inputs and reworking of Meso-Paleoproterozoic crust, as indicated by the associated TDM model ages. Although the nature of the Cariris Velhos event requires further investigation, we suggest that, at least partially, it corresponded to an orogenic episode that might have occurred concurrently with continental break-up, similar to modern continental arc-retro arc foreland settings.