Structure Of La Primavera Caldera, Jalisco, Mexico, Deduced From Gravity Anomalies And Drilling Results

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Journal Article: Structure Of La Primavera Caldera, Jalisco, Mexico, Deduced From Gravity Anomalies And Drilling Results

Abstract
Previous studies of La Primavera caldera have mostly been based on surface geology and topography. Since 1980, many wells, exploring for geothermal energy, have reached depths of about 2 to 3 km at the center of the caldera. The results of the drillings, together with those of the gravity surveys, provide information about the subsurface structure of the caldera, and shed light on its formation. The drilling results and gravity anomalies at La Primavera caldera and San Marcos, located at about 40 km distance from the caldera, suggest that regional gravity anomalies can be interpreted in terms of depths of the granitic basements: the basement beneath La Primavera caldera is about 3 km deep and consists of roughly the same horizon as that beneath San Marcos. The drilling results within the caldera reveal that the depth of the caldera fills ranges from 0.3 to 1 km at the drilling sites. The andesite basement, about 1 km deep, remains approximately horizontal, and the granitic basement has a depth of about 3 km. The surface topographies, such as the postcaldera domes, scarcely disturb the subsurface strata. The local gravity anomalies show two lows within the caldera reflecting the configuration of caldera bottom, two funnel-shaped depressions, one of which corresponds to a vent of the Tala tuff deduced from geological observations. The mass deficiency within the caldera estimated from the gravity anomaly, satisfies the general relationship that the mass deficiency is proportional to the caldera diameter cubed. This means that caldera structure is three-dimensional: the larger the diameter, the deeper the funnel-shape. At present this argument may be limited to funnel-shaped calderas.

Authors 
I. Yokoyama and M. Mena








Published Journal 
Journal of Volcanology and Geothermal Research, 1991





DOI 
Not Provided
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Citation

I. Yokoyama,M. Mena. 1991. Structure Of La Primavera Caldera, Jalisco, Mexico, Deduced From Gravity Anomalies And Drilling Results. Journal of Volcanology and Geothermal Research. (!) .