Geothermal anomalies in the Valles‐Penedes Graben Master Fault: Convection through the Horst as a possible mechanism

Abstract

Four different mechanisms (frictional heating, magmatic intrusion, free convection, and forced convection) have been tested as possible causes to explain the localized and relatively high geothermal anomalies found along master faults of graben structures. Forced convection is the only mechanism found to be generally able to generate the anomalies. The Vall•s-Pened•s basin (NE Spain) is used to illustrate the results of the different mechanisms. In general, it is concluded that forced convection will generate geothermal anomalies when several conditions are met: water circulation has to be deep and slow in its descent; deep reaching faults must exist to allow a rapid ascension of water; and some sort of sealing along the ascending conduit has to prevent mixing with cold water. The hydraulic model of the Vall•s-Pened•s graben rules out a possible circulation through the sediments filling the basin, and therefore a circulation model through the adjacent horst is proposed. This model is supported by isotopic data. Such a model is not restricted to horst and graben structures but can be used to explain anomalies found in compressive geological settings. 1986]. THE VALL•2S-PENEDf!!S GRABEN Geological Setting The Vall•s-Pened•s graben (Figure 1) is an extensional structure that may be related to the European Cenozoic Rift System which transects western Europe in a roughly NS direction [Julivert et al., 1974]. The northeastern part of Iberia was under compression during most of the Paleogene with ENE-WSW and NW-SE fault reactivation.An extensional episode caused basin formation starting at the beginning of the Neogene (Figure 1). The Vall•s-Pened•s graben is filled with arkosic and clay sediments of Neogene age. The NW shoulder of the graben, formed by the Montseny Massif, is mainly late Hercynian granitoids and Paleozoic sedimentary rocks. The SE shoulder is mainly late Hercynian plutonic rocks and Mesozoic sediments. Depth to the basement is about 3000 m and 1000 m at the NW and SE margins, respectively (Figures 2a and 2b). Hydrological and Thermal DataThe study area is delimited by four natural groundwater divides: The Montseny Massif to the north, the Mogent and 4887 E. Banda and M. Fernhndez, Institut Jaume Almera, CSIC, Marff i Franqu6s s/n,

Recent Basal Melting of a Mid‐Latitude Glacier on Mars

“…We highlight that the rift setting of the newly identified candidate esker in Tempe Terra is similar to the graben in which the Phlegra Montes candidate VFF‐linked esker is located (Figure c) (Gallagher & Balme, ). Terrestrial graben/rifts are commonly associated with elevated geothermal heat flux (e.g., Fernàndez & Banda, ; Jordan et al, ). Additionally, strong glacier flow convergence in these steep‐sided troughs could drive significant viscous strain heating of glacial ice.…”

Thermal effects of linked lithospheric and upper crustal–scale processes: Insights from numerical modeling of the Cenozoic Central Catalan Coastal Ranges (NE Spain)

“…This mechanism has been invoked by Fernàndez and Banda [1989, 1990] to explain the present‐day local geothermal anomalies reported along some of the main extensional faults and in the axial region of the Valencia Through. They proposed a model of topography‐driven flow (forced convection) in which meteoric waters percolate through the elevated footwall areas to deep levels and come back to the surface following fault planes (e.g., NE segment of the Vallès‐Penedès Fault [ Fernàndez and Banda , 1990]). This hypothesis has been successfully verified by numerical modeling studies implicitly incorporating heat transport and fluid flow equations, yielding variations in temperatures of several tens of degrees at shallow depths (up to 3 km) due to groundwater flow, and has been applied to several locations in the CCR [ Fernàndez et al , 1990b, 1998; Carmona et al , 2000; Bitzer et al , 2001].…”

“…Heat convection by groundwater flow [e.g., Swanberg , 1983; Bodri , 1994; Bodri and Rybach , 1998] can have a strong effect on the geothermal gradient, and is shown to be able to cause a difference of a factor 2 in geothermal gradients between recharge and discharge areas [ Person et al , 1995]. This mechanism has been invoked by Fernàndez and Banda [1989, 1990] to explain the present‐day local geothermal anomalies reported along some of the main extensional faults and in the axial region of the Valencia Through. They proposed a model of topography‐driven flow (forced convection) in which meteoric waters percolate through the elevated footwall areas to deep levels and come back to the surface following fault planes (e.g., NE segment of the Vallès‐Penedès Fault [ Fernàndez and Banda , 1990]).…”

“…Gray box is temperature interval constrained by the AFT thermochronometers (i.e., the partial annealing zone, PAZ). percolate through the elevated footwall areas to deep levels and come back to the surface following fault planes (e.g., NE segment of the Vallès-Penedès Fault [Fernàndez and Banda, 1990]). This hypothesis has been successfully verified by numerical modeling studies implicitly incorporating heat transport and fluid flow equations, yielding variations in temperatures of several tens of degrees at shallow depths (up to 3 km) due to groundwater flow, and has been applied to several locations in the CCR [Fernàndez et al, 1990b[Fernàndez et al, , 1998Carmona et al, 2000;Bitzer et al, 2001].…”

One‐dimensional models of groundwater flow, sediment thermal history and petroleum generation within continental rift basins

“…1 A). Such conditions are typical of many continental rifts such as the Rhine Graben (Clauser, 1989;Person & Garven, 1989, 1992, the Uinta Basin (Willet & Chapman, 1989), the Basin and Range (Hulen et a[., 1994), the Dead Sea Rift (bsar, 1985) and the Valles-Pendes Graben (Fernandez & Banda, 1990). Many of these rifts also contain significant accumulations of organic matter and petroleum (Harding, 1984).…”