The passage of the Farallon-Aluk spreading ridge along the Andean margin

Abstract

Plate reconstructions show that the Farallon-Aluk mid-ocean ridge interacted with the Andean marginat 30°S by ~80 Ma and then moved southwards. This process influenced the marginproducing contrasts in the magmatic evolution. At 35º30?S, the Late Cretaceous-Paleocene LosAngeles Unit (67 Ma; Fennell et al., in press), developed with a tholeiitic to alkalinesignature, and Sr-Nd isotopic trends similar to OIB magmatism (Iannelli et al., 2018). The coevalPlan de Los Yeuques Formation (34º30?S, Muñoz et al., 2018) and Naunauco Group (37-38ºS,Zamora Valcarce et al., 2006) show calc-alkaline signatures with arc-like trends. By Eocenetimes the Farallon-Aluk ridge reached the 42°S. Its influence is seen when comparing arc-likePVNM (37-38°S; Llambías and Rapela 1989) with the alkaline-like Pilcaniyeu Belt (40-42°S;Aragón et al. 2011). The segmented configuration of this spreading ridge would have favored thedevelopment of diachronic slab windows and the upwelling of more enriched mantle. This couldexplain the geochemical signatures and distribution of magmatism. A recent methodologycombining plate reconstructions and seismic tomography supports the past existence of thisprocess.