Triassic to Middle Jurassic geodynamic evolution of southwestern Gondwana in Patagonia: From a large flat-slab to a plume suction in a roll-back subduction setting

NAVARRETE CESAR; GIANNI G; ENCINAS A; MARQUEZ M; KAMERBEEK M; VALLE M; FOLGUERA A

EARTH-SCIENCE REVIEWS

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2019

0012-8252

A novel geodynamic evolution model of the southwestern region of Gondwana from the late Triassic to themiddle Jurassic period is proposed in this contribution, based on new data collected in the Patagonian regionand an exhaustive bibliographic review. New geochemical data of La Leona Fm. (Deseado Massif) and a newzircon U/Pb age (207.6+4.1/−2.3 Ma), added to a compilation of previous geochronological and geochemicaldata, allow confirming the existence of an Upper Triassic magmatic arc in central Patagonia, with typicaladakitic features. This volcanic arc developed about ~1000?1100 km away from the hypothetical paleo-trench(at its most distal portion) in and intraplate position. New geological mapping carried out in the surroundingareas of these arc-related products allowed recognizing an important and previously underestimated late Triassiccontractional episode that affected the south-central Patagonian region, which can be correlated with multipleevents of deformation in southwestern Gondwana as far as in the Cape and Sierra de la Ventana fold belts. Afterthis contractional episode, the Jurassic Chon Aike Silicic Large Igneous Province (SLIP - Deseado Massif andNorth Patagonian Massif) outbursts from a crustal source linked to a mantle thermal anomaly, as new geochemicaldata and previous data indicate.New and previous structural, geochemical, and geochronological data allow us to propose the existence of alate Triassic-earliest early Jurassic flat-slab episode (~227?190? Ma), here referred to as the South Gondwanianflat-slab, comparable in size with the largest present and previously documented flat-slab configurations onEarth. This event would have been responsible for the inland arc migration, from a western position on theAntarctic Peninsula to central Patagonia (Central Patagonian Batholith), as well as the widespread contractionalpulse registered in southwestern Gondwana. The existence of this late Triassic shallow subduction episode isreinforced by a combination of P-wave seismic tomographic data and a recent plate kinematic reconstructionthat reveal an anomalous inland location for the subducted slab, presently at the base of the lower mantle. InLower Jurassic times, a slab-detachment episode developed simultaneously with the impingement and southwestwarddisplacement of the Karoo mantle plume, would have favored the destabilization of the flat-subductionconfiguration. A re-establishment of the subduction in southwestern Gondwana, associated with the LowerJurassic magmatic arc retraction (Subcordilleran Patagonian Batholith), occurred under extensional conditionsmost likely associated with slab rollback and a southwestward asthenospheric return flow. This upper mantleflow may have exerted a suction effect on the Karoo mantle plume towards Patagonia, expanding its lifespanwith a continuous southwestward rejuvenation of the synextensional SLIP Chon Aike´s magmatism.