Crustal magmatic anomalies fron the southern Payenia volcanic plateau, associated with the Nazca Plate tearing and plume head from gravimetric and magnetic data

FRANCISCO RUIZ; ANDRES FOLGUERA; ANA ASTORT; ANDRES ECHAURREN; HECTOR GARCÍA

Simposio; Primer Simposio de Tectónica Sudamericana; 2016

The Auca Mahuida volcanic shield is located on the southernmost part of the Payenia Volcanic Province on the retroarc of the Southern Central Andes. Its chemistry is interpreted from the fractionation of a contrasting magmatic source respect to the northern volcanic plateau, indicating mixed depleted and enriched mantle sources (Soager et al. 2015). After a ~15 My period of shallow subduction in the area (Kay 2006, Ramos & Folguera 2009), a sudden steepening of the Nazca plate during the last 4 Ma triggered a strong tearing located below the Auca Mahuida Plateau, evidenced by seismic tomographies (Pesicek et al. 2012). Later, Burd et al. (2015) described a complex plume head impacting at the southern Payenia plateau, feeding individual volcanic centers. The present study provides new-high resolution gravity and aerial-magnetic data that constitute undocumented information for the interpretation of the structure of the continental crust, subducted slab and upper mantle below the Auca Mahuida Plateau. A correlation between shallower resistivity isosurfaces (33?52 km depth) associated with the plume and the measured magnetic data depicts a ~150 km in diameter circular anomaly. According to gravity data, this high magnetic anomaly would correspond to a dense and cold body, which allows preliminarily interpreting this as an intrusive hosted in the middle crust. This intrusive body was probably originated from the upper mantle by an asthenospheric upwelling caused by the tearing. From deeper gravimetric components, applying a filter of upward continuation to the gravity field, the visualization of the tearing is better constrained. Additionally, using the EIGEN-6c4 model, Geoid data have been filtered in order to isolate deeper mass influences. This allows identifying a good correlation between the anomalous masses in the upper crust, a positive undulation due to anomalous masses in the upper mantle and the tearing visualized from the Bouguer deeper components. This work provides new data on the spatial relation between an asthenospheric anomaly, the tearing produced on the Nazca plate and a laccolith intruding the upper crust. Even though this laccolith is probably associated with the southern Payenia volcanic field, the dimensions goes from the Auca Mahuida volcano to the Pampa domain, far beyond the area of volcanism.