The role of the central Andes gravity high in the control of the type and distribution of the back arc monogenetic basic volcanism cluster in the southern central andes

JOSÉ VIRAMONTE; BENJAMIN HEIT; WALTER BAEZ

Foz do Iguazu

Congreso; Meeting of the Americas 2010; 2010

AGU

The deep structural images obtained recently for the Southern Puna plateau at 25.50° S by Heit (2005) and Heit et al. (2007) from the REFUCA project, show a strong low-velocity anomaly that virtually "emanates" from depths near -200 km. This negative anomaly reaches the Moho discontinuity (-60km obtained with receiver function) as a single zone and then bifurcates into two branches; one located at the position of the CVZ and the other beneath the Galan Caldera on the eastern border of the plateau. Between these branches, gravity measurments by Goetze and Krause (2002) detected an important anomaly known as the ; one located at the position of the CVZ and the other beneath the Galan Caldera on the eastern border of the plateau. Between these branches, gravity measurments by Goetze and Krause (2002) detected an important anomaly known as the Central Andean Gravity High (CAGH) ,). Interpreted from isostatic residual values, the CAGH represents an elongated -NNW-SSE area that covers the city of Calama in Chile, the Atacama, Arizaro and Antofalla basins, ending in the Salar de Pipanaco depression in the southem Puna. This “belt” has a low Poisson number that suggests a rigid geotechnical behaviour. The distribution and type of the monogenetic basic back arc volcanism in the southern Central Andes is strongly controlled and influenciated by this structure. In effect, the OIB-like monogenetic cluster (Antofagasta de la Sierra-El Jote-Carachipampa) that represents the higher degrees of melting, ( Kay et al .,1994) is located in the central area of the “CAGH”, while the calcalkaline like monogenetic clusters ( Antofalla-Arizaro; Hombre Muerto- Pasto Ventura) that represent lower degrees of melting, are located at both sides of the gravity anomaly. If the CAGH represents a dense, refractory and brittle rock body, it is possible to suggest that: a) it might have a strong influence on the degree of melting concentration and distribution of magmas that have their origin at greater depths in this part of the Central Andes, b)The continental lithosphere in this area might be weakened by the presence of the CAGH, facilitating the ascent of mantle magmas that are able to reach the surface with very little contamination or assimilation. ,). Interpreted from isostatic residual values, the CAGH represents an elongated -NNW-SSE area that covers the city of Calama in Chile, the Atacama, Arizaro and Antofalla basins, ending in the Salar de Pipanaco depression in the southem Puna. This “belt” has a low Poisson number that suggests a rigid geotechnical behaviour. The distribution and type of the monogenetic basic back arc volcanism in the southern Central Andes is strongly controlled and influenciated by this structure. In effect, the OIB-like monogenetic cluster (Antofagasta de la Sierra-El Jote-Carachipampa) that represents the higher degrees of melting, ( Kay et al .,1994) is located in the central area of the “CAGH”, while the calcalkaline like monogenetic clusters ( Antofalla-Arizaro; Hombre Muerto- Pasto Ventura) that represent lower degrees of melting, are located at both sides of the gravity anomaly. If the CAGH represents a dense, refractory and brittle rock body, it is possible to suggest that: a) it might have a strong influence on the degree of melting concentration and distribution of magmas that have their origin at greater depths in this part of the Central Andes, b)The continental lithosphere in this area might be weakened by the presence of the CAGH, facilitating the ascent of mantle magmas that are able to reach the surface with very little contamination or assimilation.