The fate of the Farallon slab beneath Patagonia and its links to Cenozoic intraplate magmatism, marine transgressions and topographic uplift

NAVARRETE, CÉSAR R.; GIANNI, GUIDO; MASSAFERRO, GABRIELA ISABEL; BUTLER, KRISTINA

EARTH-SCIENCE REVIEWS

ELSEVIER SCIENCE BV

Año: 2020 vol. 210

0012-8252

The arrival and subsequent stagnation of the Farallon/Nazca slab at the mantle transition zone below southernSouth America triggered seemingly unrelated large-scale geological processes in the second half of the Cenozoic.During this period, three poorly understood regional events have characterized the more recent geologicalhistory of Patagonia: i) the development of intense intraplate magmatism, ii) two large-scale marine transgressions,and iii) abnormally accelerated topographic uplift. We propose a geodynamic model that connects thesubducting slab mechanisms to these events based on seismic tomography, 2-D kinematic reconstructions, dynamicsubsidence models and a detailed literature review. According to our kinematic reconstruction, after thePaleocene-Eocene opening of the Aluk (Phoenix)/Farallon slab window, the Farallon oceanic slab arrived to themantle transition zone below Patagonia at ~36?32 Ma. This event caused the physical perturbation of thismantle layer, and dehydration melting of the uplifted portions by wadsleyite breakdown, triggering an intenseOligocene-middle Miocene intraplate magmatism significantly influenced by subduction-derived fluids.Simultaneously, due to increasing disturbance of the lower mantle during the Farallon slab penetration andstagnation in the mantle transition zone, a large subduction-induced mantle flow cell began to tilt the SouthAmerican plate. Tilting drove the two large marine transgressions which inundated much of the southernArgentina and Chile. Finally, in the latest Miocene-Pleistocene, Farallon-Nazca slab break-off induced the decompressionmelting of the sub-slab asthenosphere, generating the most recent magmatic episode in the northcentralPatagonia. This magmatism was partially contemporaneous with the Chile ridge (Nazca/Antarctic) slabwindow-related southern Patagonian igneous activity; and although both episodes show evidence of mantlemetasomatic inheritance, the north-central magmatism shows higher Th/La and 87Sr/86Sr ratios, and lower εNdvalues, suggesting possible contributions from the stagnant Farallon slab (wet plumes?). These modern magmaticepisodes can be directly linked to the Quaternary uplift of Patagonia by mantle upwelling.