| Title | Gravity, Magnetics, and Seismic Reflection Studies at the Cerro Prieto Geothermal Field |
|---|---|
| Authors | Hector Luis Fonseca Lopez, Antonio Razo Montiel |
| Year | 1979 |
| Conference | DOE-CFE Symposium on Cerro Prieto |
| Keywords | |
| Abstract | Based on prior knowledge of regional geology determined from the interpretation of gravity and magnetic data, as well as information obtained from other studies, we have found that the seismic reflection method has provided the best results. This method has made the interpretation of basement and fault configuration more precise. It also seems to indicate that seismic dispersion and reflection attenuation zones in the area of the field may be related to areas of high metamorphism or high temperature. In order to increase our knowledge of the structural and geologic conditions affecting geothermal activity, a correlation of gravity, magnetic, and seismic reflection results obtained at Cerro Prieto has been made. Previous studies have already pointed to the connection between geothermal activity and active geologic structures. It was previously thought that in most cases these methods were only useful as a tool in determining geologic structure. At the present time, studies carried out in the Imperial Valley have demonstrated that some gravity anomalies, in addition to suggesting the shape and regional trends of the basement underlying the sedimentary series, show a high correlation with zones with high temperature gradients, as measured in wells. Probably through a secondary effect, these high temperatures may create metamorphic bodies with contrasting densities. A similar situation appears to exist at the Cerro Prieto geothermal field and in the whole of the Mexicali Valley. These metamorphic bodies seem also to interfere with the magnetic anomalies. This may be due to the hydrothermal alteration of minerals in the intrusive and encasing rocks, .and those of the sedimentary series, especially those minerals capable of producing magnetic anomalies. Del conoeimiento geologico regional previo, interpretado con gravimetrfa y magnetometrfa, en correlacion con la informacion disponible de otros trabajos, se ha observado que, de los metod os empleados, la sismica de reflexion es el que ha proporcionado los mejores resultados. Este metodo, que ha servido para afinar las interpretaciones del basamento y fa II as geologieas, tambien parece sugerir que algunas zonas de dispersion o atenuacion de los reflejos sismicos que se presentan en el campo pueden estar relacionados eon areas probablemente de gran metamorfismo o de altas temperaturas. Con el fin de amp liar el conocimiento de las condiciones geologieo-estructurales que gobiernan la actividad geotermiea se ha efectuado la correlacion de los diferentes metodos de gravimetria, magnetometria y sismica de reflexion realizados en el campo de Cerro Prieto. Estudios anteriores senalan la relacion de la actividad geotermica eon estructuras geologicas activas. Anteriormente se pensaba que en la mayoria de los casos, estos metodos tenian aplieacion solo como una herramienta para la determinacion de las estructuras geologicas. En la actualidad, estudios realizados en Imperial Valley demuestran que algunas anomalias gravimetricas, adem as de sugerir la forma y tendencia regional del basamentode la serie sedimentaria, presentan una estrecha relacion con areas de altos gradientes de temperatura medidos en pozos. Probablemente por algun efecto seeundario de estas altas temperaturas pueden originarse cuerpos metamorficos contrastantes en densidad. Situaciones similares parecen presentarse en el campo geotermico de Cerro Prieto y, en general, en el Valle de Mexicali. Dichos cuerpos metamorficos parecen interferir tambien sobre las anomalfas magneticas; esto puede ser por la alteracion hidrotermica de los minerales caracterfsticos de las roeas intrusivas y encajonantes o de la serie sedimentaria; especial mente de aquellos que son los que producen las anomal fas magneticas. |