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

IANNELLI, SOFÍA; LITVAK, VANESA D.; GIANNI, GUIDO; FERNÁNDEZ PAZ, LUCÍA; FOLGUERA, ANDRES

Quito

Simposio; 8° International Symposium on Andean Geodynamics; 2019

Instituto Geofísico EPN

Plate reconstructions show that the Farallon-Aluk mid-ocean ridge interacted with the Andean margin at 30°S by ~80 Ma and then moved southwards. This process influenced the margin producing contrasts in the magmatic evolution. At 35º30?S, the Late Cretaceous-Paleocene Los Ángeles Unit (67 Ma), developed with a tholeiitic to alkaline signature, and Sr-Nd isotopic trends similar to OIB magmatism. The coeval Plan de Los Yeuques Formation (34º30?S) and Naunauco Group(37-38ºS) show calc-alkaline signatures with arc-like trends. By Eocene times the Farallon-Aluk ridge reached the 42°S. Its influence is seen when comparing arc-like PVNM (37-38°) with the alkaline-like Pilcaniyeu Belt(40-42°S). The segmented configuration of this spreading ridge wouldhave favored the development of diachronic slab windows and the upwelling of more enriched mantle. This could explain the geochemical signatures and distribution of magmatism. A recent methodology combining plate reconstructions and seismic tomography supports the past existence of this process.