AMS and rock magnetism in the Caviahue-Copahue Volcanic Complex (Southern Andes): Emission center, flow dynamics, and implications to the emplacement of non-welded PDCs

Fil: Haag, Mauricio Barcelos. Instituto de Geociências, Universidade Federal do Rio Grande do Sul. Brasil. Fil: Sommer, Carlos Augusto. Instituto de Geociências, Universidade Federal do Rio Grande do Sul. Brasil. Fil: Savian, Jairo Fransciso. Instituto de Geociências, Universidade Federal do Rio Grande do Sul. Brasil. Fil: Caselli, Alberto. Universidad Nacional de Río Negro. Laboratorio de Estudio y Seguimiento de Volcanes Activos. Argentina. Fil: Moncinhatto, Thiago Ribas. Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo. Brasil. Fil: Hartmannd, Gelvam André. Instituto de Geociências, Universidade Estadual de Campinas. Brasil. Fil: Ort, Michael. School of Earth and Sustainability. Estados Unidos. Fil: Poletti, Wilbor. Instituto de Ciência e Tecnologia, Universidade Federal dos Vales do Jequitinhonha e Mucuri. Brasil Fil: Ferreira da Trindade, Ricardo Ivan. Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo. Brasil. Pyroclastic deposits can cover significant areas and register major geological events. Despite their importance, understanding depositional dynamics of pyroclastic density currents (PDCs) and linking explosive deposits to their emission centers is still a challenge, especially in the case of non-welded, massive ignimbrites. Located in the Southern Andes, the Caviahue Copahue Volcanic Complex (CCVC) comprises one of the most active volcanic centers in the Andean Belt. This volcanic complex hosts massive ignimbrites with both source emplacement poorly constrained, currently grouped in the Riscos Bayos Ignimbrites (RBI). In this contribution, we perform a full magnetic characterization and anisotropy of magnetic susceptibility (AMS) study on the massive RBI of the CCVC. The magnetic characterization was performed using magnetic experiments including isothermal remanet magnetization, thermomagnetic curves, hysteresis loops, first-order reversal curves, and scanning electron mi croscopy. Magnetic experiments indicate primary, multi-domain, high Curie temperature titanomagnetites as the AMS carriers. Ellipsoids are predominately oblate, with a low degree of anisotropy and east-southeastward imbrication. This fabric arrangement is consistent with PDC sedimentary fabrics deposited under laminar flow conditions. Despite RBI massive structure AMS data reveals changes in transport capacity of the PDC and particle organization. These changes are marked by increasing AMS dispersion and decreasing degree of anisotropy up-section within flow units. Directional statistics of AMS data implies the Las Mellizas Caldera as the emission center of RBI. The reconstructed flow path also suggests the PDC overrun of the Caviahue Caldera topographic rim. This study highlights the application of AMS to the identification of emission centers of explosive deposits, featuring its application to massive ignimbrites.