Gravedad en la estructura andina segmento 18°-42° S

Abstract

New data of the gravity potential field in Central Andes between latitudes 18°-42° S associated with existing geophysical and geological data allow to partially clarifying the crustal structure of the mountain range and its thickening. Structural evidences of the crust are known through seismic and gravimetric data, and geological projections. This structure and its composition change considerably from east to west, at the back-arc east area; Moho discontinuity is clearly recognized, however, measurements of the active seismic at the highlands and the western range are observed only with weak Moho presence. This does not occur in the data analysis of broadband seismology data, which indicates an
approximate discontinuity of 70 km. On the other hand, west from this structure along the coast, the oceanic Moho develops at an approximate depth of 40 km, which decreases from north to south according to the height and width of the
Andes structure.
The petrological properties of the rocks comprising the deep crust may change due to several processes that through the analysis show variations of the classic Moho discontinuity that not necessarily correspond to a crust-mantle petrological boundary. The tectonic shortening at the back-arc is the dominant process that contributes to the formation of the Central Andes root. Additionally at the forearc and arc, hydration of the mantle wedge produces, partially, a crust
thickening which is translated into a change in the regional gradient of the gravity potential field. This gradient is observed in east-west and north-south strike, which values in east-west strike vary between 2.9x10-⁵ ms-2 per kilometer
at Arica-Iquique area and 1.01x10-⁵ ms-2 gr/cm3 per kilometer at Valdivia-Puerto Montt area. This gradient is gradual in north-south strike. At the same time, Bouguer anomaly varies in the same proportion, with the highest variations
of 380x10-⁵ ms-2 in Antofagasta area and -50x10-⁵ ms-2 in Puerto Montt area.