FACIES CHARACTERIZATION AND VOLCANIC ARCHITECTURE IN ALEMANIA SUBBASIN.CRETACEOUS RIFT. NORTHWESTERN OF ARGENTINA

QUIROGA MIRTA; SALADO PAZ NATALIA ; ARONSIO MARCELO; BUSTOS EMILCE; VILLAGRAN AGUSTINA; BECCHIO RAUL ; ARENAS OLIVIA

Congreso; 14 Congreso de Mineralogía, Petrología Ignea y Metamorfica y Metalogenesis; 2023

In the northwestern of Argentina, the cretaceous rift is characterized by thick sedimentaryand volcanic successions that records the synrift (Pirgua Subgroup) and postrift (Balbuenaand Santa Bárbara Subgroups) episodes. The Pirgua subgroup comprises continental redbeds representing the maximum subsidence during the syn-rift stage development. Themain magmatism associated with this stage corresponds to “Las Conchas Basalt” (78-77Ma) and occurred in the upper part of the sedimentary sequence (Las CurtiembresFormation). We studied “Las Conchas Basalt” in Las Conchas canyon toward the southernportion of the Alemania subbasin. In this area we recognized different coherent volcanicand volcaniclastic units such as sheet lavas, aa lavas, pillow lavas, dykes, peperites,hyaloclastites, sediment-infill volcanic breccias, massive volcaniclastic breccias andpyroclastic surges. These units correspond to two main magmatism emplacement levels inthe actual topographic level: a) the subvolcanic level with dykes and diatremes (massivevolcaniclastic breccias and pyroclastic surges); and b) the volcanic/subarea level with lavaflows (aa, sheet and pillow lavas) associated to autoclastic (hyaloclastites and peperites)and sedimentary (sediment-infill volcanic breccia) breccias.