ROLE OF STRUCTURAL CONTROL IN DEFINING THE GEOTHERMAL SYSTEM(S) IN SOUTH-CENTRAL CHILE

Two distinct domains of the geothermal systems, viz. structural (or non-volcanic) and volcanic have been identified in the south-central Chile, based on the chemical signatures of the thermal discharges and structural analysis of the lineaments. These two domains are distinct in their ways of heating up of meteoric water, which is the feeder to these geothermal systems. The geothermal system(s) of the volcanic domain are closely associated with the volcanic centers. The process of heating is through deeper circulation of meteoric water in the case of the geothermal system(s) of the structural (non-volcanic) domain. In the case of the geothermal system(s) of volcanic domain, the heating of meteoric water is through absorption of heat and condensation of steam and gases by meteoric water during lateral circulation. These discharges do not exhibit the typical signatures of steam heated waters, which are subdued by near surface processes.

The relation between the geothermal systems and fracture density (FD) is quite evident from the structural analysis. FD correlates very well with the surface geothermal manifestations, as well as with the recharge areas of these geothermal systems. An increase in the (secondary) permeability in the uppermost 200-300 m in the areas of relatively high FD values, considered in the conceptual model, is consistent with the lithology, structure and stratigraphy of the area. Although the lineaments scatter in a wide range, the absence of lineaments between N60°E and N100°E is noticeable, and is consistent with displacement and stress data (Lavenu and Cembrano, 1999; Cembrano et al., 2007; Lara and Cembrano, 2009) of the Liquiñe-Ofqui Fault Zone. This indicates that such lineaments, which represent fractures and faults, are the result of recent deformation, causing secondary permeability that facilitates the subsurface flow particularly in NW-SE and N-S directions.

References:

Cembrano, J., A. Lavenu, G. Yañez (coordinators), R. Riquelme, M. Garcia, G. González, G. Herail, 2007. In: T. Moreno, W. Gibbons (Eds), The Geology of Chile, The Geological Society, London, 147–178.

Cembrano, J., E. Schermer, A. Lavenu, A. Sanhueza, 2000. Tectonophysics 319: 129–149.

Cembrano, J., L. Lara, 2009. Tectonophysics 471: 96–113.

Lavenu, A., J. Cembrano, 1999. Journal of Structural Geology 21: 1669–1691.