Cap rock efficiency of geothermal systems in fold-and-thrust belts: Evidence from paleo-thermal and structural analyses in Rosario de La Frontera geothermal area (NW Argentina)

Abstract

Cap rock characterization of geothermal systems is often neglected despite fracturing\ud may reduce its efficiency and favours fluid migration. We investigated the siliciclastic cap\ud rock of Rosario de La Frontera geothermal system (NW Argentina) in order to assess its\ud quality as a function of fracture patterns and related thermal alteration.\ud Paleothermal investigations (XRD on fine-grained fraction of sediments, organic matter\ud optical analysis and fluid inclusions on veins) and 1D thermal modelling allowed us to\ud distinguish the thermal fingerprint associated to sedimentary burial from that related to fluid\ud migration.\ud The geothermal system is hosted in a Neogene N-S anticline dissected by high angle\ud NNW- and ENE-striking faults. Its cap rock can be grouped into two quality categories:\ud ● rocks acting as good insulators, deformed by NNW–SSE and E–W shear\ud fractures, NNE-SSW gypsum- and N-S-striking calcite-filled veins that\ud developed during the initial stage of anticline growth. Maximum paleotemperatures\ud (<60 °C) were experienced during deposition to folding phases.\ud ● rocks acting as bad insulators, deformed by NNW-SSE fault planes and NNWand\ud WNW-striking sets of fractures associated to late transpressive\ud kinematics. Maximum paleo-temperatures higher than about 115 °C are linked to\ud fluid migration from the reservoir to surface (with a reservoir top at maximum depths\ud of 2.5 km) along fault damage zones. This multi-method approach turned out to be particularly useful to trace the main\ud pathways of hot fluids and can be applied in blind geothermal systems where either\ud subsurface data are scarce or surface thermal anomalies are lacking

Development of an Intrawedge Tectonic Mélange by Out‐of‐Sequence Thrusting, Buttressing, and Intraformational Rheological Contrast, Mt. Massico Ridge, Apennines, Italy

“…However, mixed layers I-S from samples located in the upper portion of the clastic sedimentary succession display levels of thermal maturity higher than those recorded by the thermal maturity curve (black line in Figure 13b). In these samples, we observed the coexistence of mixed layers C-S and lowexpandable I-S, which suggest strong fluid-rock interaction and hot fluid circulation (e.g., Maffucci et al, 2016).…”

Clay mineral associations in the clay cap from the Cerro Pabellón blind geothermal system, Andean Cordillera, Northern Chile

“…The cap-rock, the heat source, the reservoir and recharge areas are the main four elements in hydrothermal convective geothermal systems. To be effective, a cap-rock should be impermeable enough to maintain the reservoir temperature and the pressure and enthalpy of the system through time (Todesco & Giordano, 2010; Maffucci et al ., 2016; Sánchez-Alfaro et al ., 2016). In volcanic and volcaniclastic systems, the development of large, thick cap rocks is favoured by intense argillic alteration which leads to the formation of the clay cap.…”

Precambrian faulting episodes and insights into the tectonothermal history of north Australia: microstructural evidence and K–Ar, &lt;sup&gt;40&lt;/sup&gt;Ar–&lt;sup&gt;39&lt;/sup&gt;Ar, and Rb–Sr dating of syntectonic illite from the intracratonic Millungera Basin

“…van der Pluijm et al, 2001;Duvall et al, 2011). However, assuming that 2M 1 illite is systematically of detrital origin can be misleading since the formation of authigenic 2M 1 illite in diagenetic to hydrothermal conditions is also reported in the literature (e.g, Lonker and Gerald, 1990;Clauer and Liewig, 2013), and brittle faulting can produce authigenic 2M 1 illite particularly in areas of elevated geothermal gradients or deeper parts of exhumed faults (Zwingmann et al, 2010;Viola et al, 2013;Mancktelow et al, 2015). While successful isotopic dating of brittle faulting within a single fault core was reported previously (Viola et al, 2013), the present study integrating fault rocks from different depths and locations is a new and challenging approach to help us better understand illite crystallization in gouges during relatively low-temperature brittle fault reactivation episodes in complex Precambrian tectonic settings.…”