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

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Mauricio Barcelos Haag , Carlos Augusto Sommer , Jairo Fransciso Savian , Alberto Tomás Caselli , Thiago Ribas Moncinhatto , Gelvam André Hartmann , Michael Ort , Wilbor Poletti , Ricardo Ivan Ferreira da Trindade 


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 microscopy. 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.



Earth Sciences, Geology, Geophysics and Seismology, Physical Sciences and Mathematics, Volcanology


Andes, Pyroclastic density current, Magnetic fabrics, Magnetic mineralogy, AMS, Non-welded ignimbrite, Caldera, Caviahue-Copahue, Flow direction


Published: 2021-05-14 14:13

Last Updated: 2021-12-17 06:21

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Comment #29 Mauricio Barcelos Haag @ 2021-05-19 02:42

Peer-reviewed version already available at: