The Late Paleogene to Neogene Volcanic Arc in the Southern Central Andes (28°?37° S)

LITVAK V. D.; POMA, S.; JONES, R.; PAZ, L. F.; IANNELLI, S.; SPAGNUOLO, M.G.; KIRSTEIN L.A.; FOLGUERA, A.; RAMOS V. A.

The Evolution of the Chilean-Argentinean Andes

Springer International Publishing AG

Año: 2018; p. 503 - 536

Evolution of arc magmatism along the Southern Central Andes (~28°?37° S) is strongly controlled bychanges in the geometry of the downgoing slab (e.g., slab dip angle). This is particularly evident in thepresent-day Chilean-Pampean flat-slab and the late Miocene Payenia shallow subduction segments.Typical Andean-type volcanism was established from the late Oligocene to late Miocene in the high Andes(29°30″?30°30″S), with arc-related calc-alkaline volcanism having geochemical signatures that reflectchanges in the residual mineral assemblages related to increased crustal thickness (>50 km). The increasein crustal thickness resulted from increased compression along the Southern Central Andean margin due tothe subduction of the Juan Fernandez Ridge, and consequent shallowing of the downgoing slab in the lateMiocene. Associated with the decrease in the slab dip angle, the volcanic front migrated to the east. Furthersouth, magmas developed across the present-day Payenia back-arc region (35°?37° S) show an increase inslab-derived components in the middle Miocene to early Pliocene times, which also suggests a progressiveshallowing of the subducting slab at these latitudes. However, trace element ratios indicate a low-tointermediatepressure residual mineral assemblage and no significant increase in crustal thickness isapparent, unlike further north in the Chilean-Pampean flat-slab segment. Although flat-slab geometry stillprevails in this latter segment, re-steepening of the slab during early Pliocene times (~5?3 Ma) promotedan increase of arc and back-arc magmatism at these more southerly latitudes of the Southern CentralAndes. A dynamic link between slab geometry, geochemistry, and volcanic activity is therefore observedin the Southern Central Andes.