| Title | GEOPHYSICAL IMAGING OF THE LIQUIÑE GEOTHERMAL SITE (39°S, CHILE) BY MEANS OF 3D GRAVITY INVERSION |
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| Authors | E. Daniel, A. Elena, C. Jorge G. F., A. Gloria, M. Eduardo, R. Tomás and P. Nicolás |
| Year | 2019 |
| Conference | New Zealand Geothermal Workshop |
| Keywords | Geothermal resources, Geophysical method, Bouguer gravity inversion, Liquiñe, Chile |
| Abstract | The Liquiñe geothermal site is characterized by an anomalous number of geothermal hot springs (with in-situ measured temperatures ranging between 35-75 °C), which are spatially related to the main NS lineaments of the Liquiñe-Ofqui Fault System (LOFS) and NW-SE Andean Transverse Faults (ATF). Country rocks are dominated by granitoids and scarce mylonitic gneisses. The lateral continuity of most of the mapped outcrops and structural elements are interrupted by dense vegetation and soil cover, which highlights the necessity to perform further geophysical campaigns aimed to constrain the structural control on thermal hot springs. In this work we present a gravimetric survey developed along the Liquiñe valley. NW-SE and N-S profiles, obtained in an area of ~36 km2, allowing us to define the subsurface morphology of the basement. To invert the Bouguer anomaly, we used the open source SimPEG software (https://simpeg.xyz/) to constrain a 3D density model within the extension of the gravimetric survey. Our results show two main Bouguer gravity anomalies were detected, the first one related to two main NS lineaments of the LOFS, which also correlates with the thermal spring manifestations within the Liquiñe village. This Bouguer anomaly is interpreted as the consequence of highly fractured rock zones, increasing permeability. The second major Bouguer gravity anomaly is related to a topographic relief, consistent with a recognized proximal ATF trace. An increase of the basin thickness from south to north, with a thickness of a ~10 m to a maximum of ~200 m, respectively. Furthermore, these observations are also supported with the 3D density model, for depths up to 300 m, which draws a picture of a complex three-dimensional structural system. |