Gravity, Transient Electro-Magnetic and Noise Seismic Exploration in the Puyuhuapi Geothermal Area, Southern Patagonia, Chile
Diego ARAVENA, Nicolas PEREZ-ESTAY, Mauricio MUÑOZ, Karin GARCIA, Pablo VALDENEGRO, Diego MORATA
[Universidad de Chile, Chile]
The Aysén region is located in Southern Patagonia, Chile (43°38′S to 49°16′S). It has optimum conditions for the formation of geothermal systems: magmatic processes, abundant rainfall and active faults systems (Negri et al., 2017 and references therein). The main structural feature in this region is the Liquiñe Ofqui Fault System (LOFS; Hervé 1976), composed by several NS to NNE major intra-arc dextral faults and many NE normal-dextral faults located in accommodation zones or faults-splay (Cembrano y Lara 2009). The LOFS is present between 39°S and 46°S latitude with several geothermal springs located along its borders. A good prospect for high-enthalpy production is the Puyuhuapi village. It is located in a N-S elongated basin, close to six hot-springs, nine minor eruptive centers and one of the major faults of the LOFS. Before a high-resolution geothermal prospection, it is necessary to precise some geological units to define geothermal targets. We took 81 gravity measurement and 13 horizontal vertical ratios of seismic noise (Nakamura, 1989) to understand the basin depth and possible density & impedance anomaly. Also, we measured 7 Transient Electro Magnetic (TEM) to constrain geological units and possible conductive bodies. We modeled the gravity anomaly and observed an asymmetric-basin with a depocenter in the western part. Nakamura methodology also indicate the same asymmetric-shape with some variations. Uncoupling of the results inferred from the Nakamura and gravimetric methods varies from 30 to 50 m for most data. The uncoupling could be related to: i) density contrast inside the basin, ii) S wave velocity variability within the basin and iii) an overestimation of the density contrast between the basins fill and basement (due to a fault damage zone). TEM results do not show major conductive bodies inside the soil-basin, at least in the first 100 m depth. The results of all the geophysical methods suggest that hot spring manifestations are punctual anomalies related with faults systems. We suggest that the Puyuhuapi basin is a transition zone between the major NNE trending faults. Thus, emplacement of the PVG and the occurrence of thermal springs may be related with normal NE faulting allowing fluids ascension. The existence of a geothermal reservoir is yet to be demonstrated.
|        Topic: Exploration||Paper Number: 11100|