Heat flow and deep temperatures in the Southeast Basin of France: Implications for local rheological...

Heat flow and deep temperatures in the Southeast Basin of France:Implications for local rheological contrasts

LAURENT GUILLOU-FROTTIER1, FRANCIS LUCAZEAU2, CYNTHIA GARIBALDI1,3, DAMIEN BONTE1,4

and RENAUD COUËFFE1

Keywords. – Heat flow, Temperature maps, Thermal modelling, Salt viscosity.

Abstract. – Triassic salt at 5-10 km depth may drive some of the recent tectonic features in southeastern France. We esti-mate the likely temperature range of the salt using two different approaches. The first of these, based on the extrapola-tion of deep temperatures obtained in oil exploration wells, predicts temperatures at a depth of 8 km to be in the rangeof 230-300oC. However, this prediction could be biased by a lack of deep measurements and problems related to lateralheat transfer caused by thermal conductivity contrasts. The second approach can overcome these problems by modellingthe actual heat transfer for appropriate basin geometry, including temperature-dependent thermal properties, and a man-tle heat flow of 35 mW.m-2. This latter value enables us to reproduce available temperature measurements and surfaceheat flow data. Here we evaluate the stationary temperature field along two sections constrained by seismic profiles, oneat a local scale across the Vistrenque graben and the other at a more regional scale across the Southeast Basin. Our find-ings suggest that the temperatures in the deepest parts of the evaporitic layer (11 km depth) can reach up to 398oC, butcan be as low as 150oC on the edge of the basin at the top of the salty layer. This temperature difference leads to impor-tant changes in salt viscosity. Results indicate that at a depth of 8 km, lateral viscosity contrasts within the evaporiticlayer may reach 40. Such rheological contrasts might favour and amplify local subsidence, as seems to have been thecase near the two Palaeogene half-grabens of Vistrenque and Valence, where deep hot zones are identified.

Flux de chaleur et températures profondes dans le bassin du Sud-Est de la France :conséquences sur les contrastes rhéologiques locaux

Mots-clés. – Flux de chaleur, Cartes de températures, Modèles thermiques, Viscosité du sel.

Résumé. – Le sel triasique à 5-10 km de profondeur peut guider la tectonique récente dans le Sud-Est de la France. Nousestimons ici, par le biais de deux approches différentes, le domaine des températures les plus probables dans cettecouche salifère. La première approche est basée sur l’extrapolation de températures profondes mesurées en forages pé-troliers, et prédit des valeurs entre 230 et 300 oC à 8 km de profondeur. Cependant, ces estimations peuvent être biaiséespar le faible nombre de températures profondes et par des problèmes reliés aux transferts latéraux de la chaleur, causéspar des contrastes de conductivité thermique. La deuxième approche qui permet de contourner ces problèmes consiste àmodéliser les transferts de chaleur dans un bassin dont la géométrie est connue, où les propriétés thermiques dépendentde la température, et où le flux de chaleur en provenance du manteau vaut 35 mW.m-2. Cette valeur permet de reproduireles données de températures profondes et de flux de chaleur. Le champ de température est calculé le long de deux cou-pes contraintes par des profils sismiques, l’une à l’échelle du graben de Vistrenque et l’autre à une plus grande échelleau-travers du bassin du Sud-Est. Nos résultats indiquent que les températures dans les zones les plus profondes de lacouche évaporitique (11 km de profondeur) peuvent atteindre 398 oC, mais qu’elles seraient aussi faibles que 170oC aubord du bassin, au sommet de la couche de sel. Ces différences de température se traduisent par des changements impor-tants de la viscosité du sel. Les résultats indiquent qu’à 8 km de profondeur, les contrastes de viscosité au sein de lacouche évaporitique peuvent atteindre 40. De tels contrastes rhéologiques pourraient favoriser et amplifier la subsidencelocale, comme cela semble avoir été le cas pour les deux hémi-grabens de Vistrenque et de Valence d’âge paléogène, oùdes zones chaudes profondes ont été identifiées.

INTRODUCTION

Large scale gravity extension has been proposed by severalauthors to explain the recent large-scale tectonic activity

in the Southeast Basin [Le Pichon et al., 2007; Rangin etal., 2007]. Triassic salt at significant depths (5-10 km)could play the role of the decoupling level [Vendeville,2007], as, according to heat-flow values, it could reach

Bull. Soc. géol. Fr., 2010, t. 181, no 6, pp. 531-546

Bull. Soc. géol. Fr., 2009, no 6

1. BRGM, Service des Ressources Minérales, 3, av. C. Guillemin, BP 36009, 45060 Orléans cedex 2, France. Tel: 02 38 64 47 91;Email: [email protected]. Dynamique des fluides géologiques, Institut de Physique du Globe de Paris, 1 rue Jussieu, 75238 Paris cedex 05, France3. Université de Nice, Laboratoire GéoAzur, 28 avenue Valrose, 06108 Nice cedex 2, France. Now at: Université du Maine, Bâtiment de géologie,Avenue Olivier Messiaen, 72085 Le Mans cedex 09, France4. Vrije Universiteit, Faculteit der Aard-en Levenswe tenschappen, subafdeling Tektoniek, de Boelelaan 1085, 1081 HV Amsterdam, The NetherlandsManuscrit déposé le 11 mai 2009; accepté après révision le 19 janvier 2009.

high temperatures in this area [Lucazeau and Vasseur,1989]. However, high surface heat flow values do not nec-essarily involve high temperatures at depth. It is thereforeimportant to know the temperature of salt in various placesof southeastern France, in order to correlate tectonic ob-servations with temperature variations. Unfortunately,most of the observations were made in shallower levels ofthe Southeast Basin, and temperature of salt has to be ex-trapolated.

In most cases, the estimation of temperature at depthcannot be done by simple linear extrapolation of the surfacegradient: physical properties (thermal conductivity, heat-production) vary with depth or temperature, and the upperparts of sedimentary basins are especially subject to suchlarge variations because of compaction processes. It istherefore necessary either to extrapolate temperature gra-dient obtained at greater depths or to model the actual heattransfers with appropriate geometry, physical properties andboundary conditions. We have used both of these ap-proaches in this paper in order to derive the temperature es-timates in the salt layer.

The temperature distribution in the Southeast Basin wasfirst studied in the 1980s for an inventory of geothermal re-sources [Gable, 1978; Haenel et al., 1980]. Most of the tem-peratures obtained were from bottom hole temperatures(BHT) made in oil exploration wells and a few of themwere recorded during production tests (DST). BHTs, whichare measured after the circulation of mud, need to be cor-rected but such information was not available at the timewhen these pioneer works were carried out. Thirty years on,the data set has been improved and reprocessed, includingcorrections and geostatistical analysis described in otherstudies [Bonté et al., 2010; Garibaldi et al., 2010]. Thisdata set has been used to estimate a new map of temperaturegradient at 5000 m that can be extrapolated to the depth ofTriassic salt.

This approach can be improved by using full modellingof the heat transfers rather than linear extrapolation from5000 m. This enables us to take into account both the actualgeometry of sedimentary layers as revealed by seismic pro-files, and the physical properties resulting from changes oflithology or temperatures. Finally, we are able to draw con-clusions on the consequence of temperatures variations inthe evaporitic layer for the rheology and tectonics of theSoutheast Basin. In particular, we have found that deep hottemperatures can be estimated below the two deepPalaeogene half-grabens of southeastern France, whichhave a similar tectonic history and comparable evaporiticcontent.

In addition to these geological results, our study mayalso provide valuable information concerning the use of saltcaverns for storage of liquid, gas and solid wastes. Indeed,lithological contrasts involving salty layers could lead tothermal and mechanical effects, which are not currentlywell known at this depth. For example, because salt forma-tions are impermeable, they are widely used to store largequantities of hydrocarbons; but the thermo-mechanical be-haviour of rock-salt remains poorly constrained and maylead to mechanical instabilities [Berest and Brouard, 2003;Chemia et al., 2009].

THERMAL REGIME AND SEDIMENTARY BASINS

It is generally understood that the thermal regime of theEarth’s crust is controlled by external thermal conditions atits boundaries, internal heat production, rock thermal prop-erties, transient solicitations, and possible advection of heatby crustal fluids [e.g., Jessop, 1990]. Based on the geologi-cal timescales investigated here (which vary from several totens of millions years), temperature at the Earth’s surfacecan be considered constant. On the opposite, there is no rea-son to assume that temperature at the base of the crust (i.e.,at Moho depth) is constant since the Moho discontinuity isseismically – and not thermally – defined. Whereas thefixed temperature condition at the surface is well known,the mantle heat input at the base of the crust may vary byseveral tens of mW.m-2 [Mareschal and Jaupart, 2004;Lucazeau et al., 2008]. Mantle heat flow value can be con-strained by surface heat flow measurements combined withgeological, gravity and seismic data [Guillou et al., 1994].Nonetheless, even if mantle heat flow is reasonably deter-mined, data on, or estimates regarding heat production ratesand the thermal conductivities of crustal rocks are neces-sary to build a realistic thermal model of the crust. More-over, the heterogeneous structure of the crust and associatedvariations in rock composition can result in significant con-trasts in thermal properties [e.g., Jaupart, 1983]. As a result,the measured surface heat flow data and even the inferredshallow temperature gradients are not sufficient to providereliable estimates of deep temperatures. Hopefully, usingreasonable estimations of thermal properties and preciseanalyses of the temperature measurements available, withina rather homogeneous geological entity, will enable us toconstrain deep thermal regime within a well constraineduncertainty.

Understanding of the thermal evolution of sedimentarybasins has benefited from the construction of large data-bases using well and seismic data provided by the petro-leum industry. In recent years, sedimentary basins haveturned out to represent new interesting targets for geother-mal projects [e.g., McKenna and Blackwell, 2004]. Indeed,hot shallow zones in sedimentary basins cannot only betriggered or maintained by transient evolution followingsubsidence [McKenzie, 1978], but also by the thermally in-sulating effect of sediment infill [Clauser and Huenges,1995]. The Southeast Basin of France in particular has al-ready been suggested as a potential reservoir of high tem-peratures at 5 km in depth [Haenel et al., 1980; Hurter andHaenel, 2002]. However, the deepest direct measurementsare rarely located below depths of 5 km, and shallower datamust therefore be extrapolated with caution. The publishedtemperature maps of southeastern France [Gable, 1978;Haenel et al., 1980] were actually constructed using a roughextrapolation of sometimes shallow and uncorrected tem-perature data. Additional seismic and well data – includingnew temperature measurements – are now available, and itis therefore possible to update these maps and estimate thegeothermal potential of the Southeast Basin [Garibaldiet al., 2010].

To check whether high temperatures are present at shal-low depths, it is possible to look at temperatures measuredat the bottom of oil exploration boreholes, both during andafter drilling. However, these bottom-hole temperature(BHT) measurements are generally performed within a few


532 GUILLOU-FROTTIER L.

hours of the end of cold mud circulation within the hole. Ifthese measurements are not corrected to account for thisdisturbance, the country rock temperature can be under-es-timated by several tens of oC. To avoid underestimation,empirical corrections are sometimes used when informationon log headers is unavailable [e.g., Husson et al., 2008a].But even when temporal data on BHT measurements are in-dicated, the appropriate correction is not easy to establish[Goutorbe et al., 2007] and several distinct temperaturemaps can be constructed. In addition, extrapolation methodsmay depend on depths of measurements and can thus pro-vide distinct temperature maps [e.g., Chopra and Holgate,2005]. While new temperature maps are presented in thisstudy, details on the adopted corrections and ongeostatistical data analysis are described elsewhere [seeGaribaldi et al., 2010].

Before presenting the new temperature maps of south-eastern France, it is useful to recall relationships betweensurface heat flow and deep temperatures. Indeed, high heatflow areas are often considered as primary targets for geo-thermal exploration, as if temperature profiles within thefirst kilometres were necessarily linear. Heat refraction ef-fects, which may be ubiquitous in sedimentary basins, arediscussed below with some possible applications to theSoutheast Basin. Finally, because mantle heat flow corre-sponds to the main unknown variable, it must be carefullyestimated since it strongly controls the temperature fieldwithin the entire crust. In this study, we use surface heatflow data, direct temperature measurements and well-stud-ied geological cross-sections alongside the thermal proper-ties of rocks, in order to infer the most probable mantle heatflow in the Southeast Basin area, and so deduce deep crustaltemperatures. Once we have determined the possible tem-perature range in the evaporitic layer of the Southeast Ba-sin, we will go on to discuss the consequences of ourfindings on the rheological properties of salt and onpossible associated gravity tectonics.

SURFACE HEAT FLOW AND DEEP TEMPERATURES

Heat conduction- 1D

Heat budget of the Earth can be estimated by measuringsurface heat flow density. This can be determined from acombined measurement of a stable temperature gradientand thermal conductivity of rock samples (Fourier’s law):

QT

z� ��

�

�(1)

Here, Q is the surface heat flow (W.m-2), � is thermal con-ductivity (W.m-1.K-1), T is temperature (K) and z is depth(m). In the simple case of a layered crust, where heat transferis steady-state, each rock layer i with a constant thermal con-ductivity �i is associated with a constant temperature gradi-ent such that their product gives the constant heat flow Q:

QT

z

T

z

T

zi

i

� ��

��

� � ��

��

� � � ��

��

��

�

��

�

��

�

�1

12

2

... (2)

In practice, we might easily encounter distinct rock typeswith different thermal conductivities, yielding differentlocal temperature gradients. It therefore follows that tem-perature does not necessarily increase in line with depth(fig. 1a).

In addition to Fourier’s law (equation 1), steady-statesurface heat flow may be separated in two components,namely the heat loss coming from the Earth’s mantle(Qm, W.m-2) and the heat production coming from crustallayers:

Q Q A Hm i ii

� � (3)

where Ai is the heat production rate (W.m-3) of a rock layer iof thickness Hi (m). Any variation in these two componentsleads to variation in surface heat flow. In other words, equa-tions (2) and (3) reveal that surface heat flow values maydepend on several independent variables such as heat inputfrom the mantle, changes in radiogenic element concentra-tion, and changes in crustal structure or thermal conductivi-ties. Figure 1b illustrates how such variable parameters canresult in significant surface heat flow changes.

Heat conduction- 2D

When two-dimensional crustal heterogeneities are consid-ered, such as the presence of high heat-producing granites[e.g., McLaren et al., 1999] or the proximity of low con-ducting rocks [e.g., Lee and Henyey, 1974], lateral heattransfer may lead to significant changes in either heat flowor temperature gradient. Salt structures may also lead toheat refraction effects because of the high thermal conduc-tivities of halite and anhydrite [e.g., Burrus and Foucher,1986]. Figures 1c and 1d show simple heat refraction ef-fects that lead either to important shifts of surface heatflow, but only small temperature changes (fig. 1c and fig.1d, left) or else to large disturbance of isotherms, but local-ised heat flow anomalies (fig. 1c, right). Figure 1d alsodemonstrates the way in which surface heat flow can beoverestimated if it is measured above the inclined sides ofmineralised bodies that contain highly conductive minerals[e.g. Mwenifumbo, 1993].

To summarise, the illustrations shown in figure 1 dem-onstrate that anomalous surface heat flow values are notnecessarily associated with hot temperatures at depth. Asimple localised thermal conductivity contrast can lead tostrong surface heat flow variations whereas underlying iso-therms are not significantly distorted (e.g. fig. 1d). In con-trast, at depths of several kilometres, temperaturedifferences of tens of degrees can exist between one siteand another, especially when anomalous bodies (thermalheterogeneities) are sufficiently wide (see large aspect ra-tio, in fig. 1c, right). Indeed, the buffering effect of thefixed temperature condition at the surface decreases withdepth, or, in other words, thermal disturbances from crustalheterogeneities develop more easily at depth, far away fromthe fixed temperature boundary condition imposed at thesurface.

Uncertainties

The difficulties encountered in studies of crustal thermal re-gimes lie in the scarcity of heat flow and deep temperaturedata. The construction of surface heat flow or temperaturemaps requires some interpolation, the quality of which canonly be quantified by geostatistical analysis [Lucazeau andVasseur, 1989; Bonté et al., 2010; Garibaldi et al., 2010].Any heat flow estimate from a single borehole that may belocated near a two-dimensional anomalous body may there-fore lead to significant interpolation error. In this respect, as


HEAT FLOW AND DEEP TEMPERATURES IN THE SOUTHEAST BASIN OF FRANCE 533

Vasseur [1982] emphasised, a heat flow map with manuallydrawn contours may be as valuable as an automatically gen-erated map. Theoretically, a geostatistical analysis of thedata enables us to quantify the uncertainties presented bythe automatically generated maps; but the unevendistribution of geothermal information may hamper the con-struction of precise temperature maps. Nevertheless, in well-studied areas such as sedimentary basins, hundreds of BHTmeasurements are generally available, and when they arecombined with available borehole temperature logs, the un-certainties of deep temperature estimates are reduced [e.g.,Förster, 2001]. It must be noted that at depths of severalkilometres, uncertainties may sometimes be as much as�10oC, suggesting that any deeper extrapolation may pro-duce less reliable results.

Thermal disturbances: long-term effects and fluid flow

Even if uncertainties in surface heat flow estimates are small,it should be kept in mind that measurements can show onlyan instantaneous picture of a possible long-term transientthermal evolution [e.g., Husson et al., 2008b]. Because of thelow thermal diffusivity of most rocks, large-scale tectonic

events (erosion, thrusting, sedimentation, etc.) may involvecooling or warming episodes that last from several tens tomore than one hundred million years. Here, such transient ef-fects that might however be of small amplitude [Lucazeauand Mailhé, 1986] are deliberately ignored. Similarly, it maybe useful to consider a spatially varying mantle heat flow be-neath the Southeast Basin since Hercynian areas would rep-resent thermally stable areas. Here, we have chosen a simplerapproach (no transient processes), which however includesthermal properties constrained by laboratory measurementsand by temperature-dependence laws.

Fluid circulation may also lead to perturbations in apurely conductive thermal regime. According to simple hy-drological models, the variation in surface heat flow result-ing from fluid circulation in one basin-scale aquifer can beas much as 5% from one edge of the basin to the other[Jessop, 1989]. In areas where rock is highly permeable,such as fault zones, and thus at a much finer scale, hydro-thermal convection may bring hot fluids at shallow depths[Fleming et al., 1998]. According to recent models that ac-count for a depth-dependent permeability, the induced ther-mal anomalies at a depth of a few kilometres could easily



FIG. 1. – Examples of heat refraction effects within the crust, leading to strong temperature differences at depth or strong surface heat flow variations.(a) example of a layered structure with a constant heat flow through all layers, consisting of insulating (porous) sediments, compacted sediments, conduc-ting salt, and “normal” basement. Dashed and dotted lines emphasise extreme temperature gradients that could be inferred from deep or shallow tempera-ture data; (b) synthesis of various mechanisms leading to surface heat flow variations; (c) examples of a thin vertical conducting body (left) creating asharp heat flow anomaly while leaving isotherms undisturbed; in contrast, a large insulating body (right) creates only localised heat flow increases butlarge-scale thermal perturbation; (d) surface heat flow variation created by an inclined conducting orebody.FIG. 1. – Exemples de refraction thermique au sein de la croûte, menant à des différences de température en profondeur ou à de fortes variations de flux dechaleur. (a) cas d’une structure crustale avec un flux de chaleur constant au travers de chacune des couches, celles-ci formant des sédiments isolants (po-reux), des sédiments compactés, du sel conducteur et un socle « normal ». Les lignes pointillées soulignent les gradients de température extrêmes qui peu-vent être déduits des données profondes ou des données de subsurface (b) synthèse de plusieurs mécanismes causant des variations de flux de chaleur;(c) exemples où un corps conducteur vertical et fin (à gauche) crée une anomalie brutale de flux de chaleur et ne perturbe pas les isothermes alors qu’uncorps large et isolant (à droite) provoque une large perturbation thermique mais uniquement des saut localisés du flux de chaleur; (d) variation du flux dechaleur en surface créé par un gisement conducteur incliné.

be as much as 10-20oC [Rühaak, 2009; Garibaldi et al.,2010]. Even if the thermal effects of hydrothermal convec-tion in permeable fault zones may be considered as steady-state disturbances, their thermal imprint should be negligi-ble at a distance of a few kilometres from the edges of thefault zone. Consequently, and because some several hun-dred BHT figures are available and regularly spaced in theSoutheast Basin, large-scale hydrological processes andpossible small-scale disturbances due to hydrothermal con-vection are not considered in the modelling part of thisstudy. Their possible involvement in the building of thermalanomalies is however accounted for in the discussion of theresults.

PREVIOUS STUDIES ON THE THERMAL REGIMEOF THE SOUTHEAST BASIN

Mantle heat flow

Different time-dependent thermal processes have affectedthe area since the Oligocene (rifting of the lithosphere,probable lithospheric delamination, eastward drift of theCorsica-Sardinia block, etc.) [Seranne et al., 1995; Mascleet al., 1996; Mauffret and Gorini, 1996]. According toLucazeau and Mailhé [1986], a mantle heat flow anomalywould be present at the Corsica margins, but the SoutheastBasin and the adjacent Hercynian areas would have alreadyachieved thermal equilibrium. According to Burrus andFoucher [1986], an asymmetrical distribution of the mantleheat flow may explain the increasing trend of surface heatflow from the gulf of Lions to the Corsica-Sardinia block.In Hercynian areas adjacent to the Southeast Basin, the av-erage surface heat flow is 60 mW.m-2 and, according toLucazeau and Mailhé [1986], its crustal component (thesecond term in equation 3) would range from 35 to45 mW.m-2. It follows that the stable mantle heat flow valuebeneath the neighbouring Hercynian crust would be around20 � 5 mW.m-2. Since the average surface heat flow in theSoutheast Basin is 88 mW.m-2 (see following section), wemay expect either a local increase in mantle heat flow or asignificant more radiogenic basement beneath the basin.

In the adjacent Massif Central area, it has been sug-gested that the surface heat flow anomaly comes from therecent Cenozoic activity during which a mantle diapir mayhave brought an additional heat amount of 20-25 mW.m-2

[Lucazeau et al., 1984]. The length scale over which thesuggested mantle heat flow anomaly may occur is around150 km, a distance that corresponds to the characteristicscale of the Southeast Basin. A second hypothesis concern-ing the radiogenic component is more problematic. If thedifference between surface heat flows in the Hercyniancrust and in the Southeast Basin comes from the radiogeniccomponent, then it is necessary to explain the additional28 mW.m-2 within a 23 km thick basement [Tesauro et al.,2006] – a difference in composition yielding more than1.2 µW.m-3 on average. Even if differences in both lowercrusts exist, it seems difficult to avoid an increase in mantleheat flow beneath the Southeast Basin.

Surface heat flow maps

The first heat flow estimate in southeastern France wasmade by Hentinger and Jolivet [1970] at Manosque

(43o51’53” N and 05o45’36” E). At this site, a heat flowvalue of 101 mW.m-2 was obtained – a figure higher thanthe global average. Ten years later, fourteen heat flow val-ues were available in the “Rhône valley” area, yielding anaverage value of 110 mW.m-2 with a standard deviation of33 mW.m-2 [Vasseur and Nouri, 1980]. Contoured heat flowmaps then appeared for the whole country [Gable, 1978;Vasseur, 1982] and the last compilation was published byLucazeau and Vasseur [1989]. These authors includedneighbouring oceanic heat flow data in order to build a heatflow map of France and surrounding margins. In the“Southeastern France and adjacent Mediterranean” area, atotal of 106 heat flow data sets were compiled, amongwhich 67 were derived from oil exploration data. The aver-age of the 39 heat flow data sets estimated in shallow bore-holes at thermal equilibrium is 82 � 19 mW.m-2 whileestimates from oil exploration data gives 94 � 20 mW.m-2.Altogether, the mean heat flow in the Southeast Basin canbe estimated at 88 � 20 mW.m-2. When all heat flow datasets from France and its surrounding margins are accountedfor (479 heat flow estimates), the average value is87 � 22 mW/m2 (see table I in Lucazeau and Vasseur[1989]). In other words, the average heat flow value in theSoutheast Basin is similar to the average value of the wholecountry.

Figure 2 illustrates different heat flow maps in south-east France. As expected, different contouring procedureshave resulted from the distinct mapping techniques (size ofinterpolation windows, chosen variogram describing datadistribution, etc.). The account of marine heat flow dataalso plays a role in the contouring procedure. A map of un-certainties resulting from the krigging technique of Bonté etal. [2010] brings additional insights into how such differentcontours can be obtained (fig. 2, bottom right). It shouldalso be emphasised that contouring of heat flow values im-plicitly ignores the possibility that discontinuities exist –whereas by nature, heat flow, unlike temperature, can showa discontinuous pattern (see fig. 1c).

Temperature maps

The first temperature maps to show different depth levels inEurope were published by Haenel et al. [1980] in the “Atlasof subsurface temperatures in the European Community”.For France, data sets were originally compiled and cor-rected by Gable [1978]. At that time, the applied correctionof BHT measurements relied both on the few available DST(Drill Stem Test) measurements and on a statistical ap-proach, so that each depth was assigned a given correction(see Bonté et al. [2010] and Garibaldi et al. [2010]). Fig-ure 3 (left column) shows the temperature maps obtainedfor depths of 500 m, 2000 m and 5000 m depths, publishedby Haenel et al. [1980]. A few years later, an improved cor-rection applied to southeastern France data [Lucazeau et al.,1985] accounted for additional DST measurements and lo-cal averages of equilibrium values at given depths. The in-ferred temperature maps at depths of 500 m and 2000 m areshown in figure 3 (right column). Not only do significanttemperature differences appear, but it is clear that deep tem-perature patterns and heat flow patterns (fig. 2) are not wellcorrelated. In addition, the hottest area seems to movesouthwards from a depth of 500 m to a depth of 2000 m(from the north and east zones to the south central zone, as



shown by Lucazeau’s maps, fig. 3, right column). Thisthree-dimensional character of temperature anomalies in theSoutheast Basin has recently been proven elsewhere [Gari-baldi et al., 2010]. Due to the scarcity of deep temperaturedata, Lucazeau et al. [1985] did not construct any tempera-ture map for a depth of 5 km, and it is therefore importantto check the work completed by Haenel et al. [1980] thatsuggests a deep triangular hot zone (fig. 3, bottom left) overthe entire Southeast Basin. According to Lucazeau et al.[1985], the maps created by Haenel et al. [1980] probablyeither overestimate deep temperatures (see fig. 3, bottomright) or else overestimate the area where hot temperaturesare present.

NEW DATA AND DEEP TEMPERATURES

Oil exploration data, corrections and temperaturemaps

A previous heat flow map of France was drawn up in 1987,using all the temperature data that was then available (i.e.exploration data and classical measurements) and associ-ated thermal conductivity data. The recent new compilationof all BHT measurements available in France provides 977temperatures corrected for transient perturbations [Bonté etal., 2010; Garibaldi et al., 2010]. In the Southeast Basin, atotal of 192 oil exploration boreholes have provided 227corrected BHT data sets. Depending on the informationavailable in log headers, analytic or statistic correctionshave been applied. The “Instant Cylinder Source” correc-tion [Goutorbe et al., 2007] was applied to 25 data sets. Allother data was corrected with the AAPG method, whichalso accounts for local measurements such as DST data andpreviously corrected BHT data [Bonté et al., 2010; Gari-baldi et al., 2010].

Temperature maps at different depth levels have beenconstructed by a krigging procedure that is constrained by ageostatistical analysis. Because of the 3D repartition of thedata we used a 3D experimental variogram composed of a1D vertical variogram and a 2D horizontal variogram. Bothvariograms correspond to a linear combination between anugget effect (25oC2) and two Gaussian-type structures, re-sulting in a total sill of 187oC2. The horizontal range is23 km and the vertical range is 500 m. Figure 4 illustratestemperature distribution at depths of 2 and 5 km, and stan-dard deviation at 5 km depth. As mentioned earlier, it ispossible to see anomalous hot zones moving southward anddownwards, to greater depths. The highest corrected tem-perature reaches 194oC at 5 km depth. When a fixed surfacetemperature of 15oC is imposed, the average temperaturegradient in the entire basin is 30.6oC.km-1, but values of upto 36oC.km-1 have been obtained in the Drôme area (from46 corrected BHT data) and up to 42oC.km-1 in theVistrenque area (data from the Pierrefeu and Les Anglesboreholes – see below). However, low temperature gradi-ents are also inferred, such as between the depths of 1 and3 km in the Alès area: between these depths, temperatureincreases by only 30oC, while the temperature gradientrecovers and resumes the average below a depth of 3 km.

Temperatures at a depth of 5 km

At 5 km depth, our temperature map (fig. 4, middle) showsthat the average temperature can be estimated at ~170oC,with positive or negative anomalies reaching 25oC. Twocold and two hot anomalies are visible on land. Despite thefact that much less temperature data is available in the4000-6000 m layer (white dots), these anomalies are actu-ally determined using all the temperature data (black andwhite dots) from the 3D model [Garibaldi et al., 2010]. Thelowest temperature estimated at a depth of 5 km is 145oCwhile the highest temperature is likely to reach 194oC. Thesmoothing effect created by interpolation techniques can bequantified and the uncertainty on krigging procedure isavailable. Figure 4 (bottom) shows the standard deviation ofinterpolated temperatures at a depth of 5 km, and gives atypical uncertainty of ~10oC in well-constrained areas.



FIG. 2. – Distinct heat flow contours (mW/m2) in southeastern France, asrevealed by published and unpublished heat flow maps. Black dots corres-pond to the cities of Montpellier, Marseille, Carpentras, Gap, Valence andSaint-Flour. Scale and coordinates are indicated in the top figures. The re-cent heat flow map of Bonté et al. [2010] is shown in the bottom row, toge-ther with uncertainties of interpolated values (bottom). Encircled numbersrefer to the adjacent cross-sections where temperature field is modelled.FIG. 2. – Différents contours du flux de chaleur (en mW/m2) dans leSud-Est de la France, selon les cartes de flux de chaleur publiées. Lespoints noirs correspondent aux villes de Montpellier, Marseille, Carpen-tras, Gap et Saint-Flour. L’échelle et les coordonnées sont indiquées surles cartes du haut. La carte récente de Bonté et al. [2010] est montrée enbas à gauche avec les incertitudes sur les valeurs interpolées (en bas àdroite). Les chiffres encerclés se réfèrent aux coupes adjacentes au-traversdesquelles le champ de température est modélisé.

Hot and cold areas at 5 km depth

In the Camargue area (north-east of Montpellier, see shadedarea, fig. 2, top left), a number of oil exploration boreholeshave given high temperatures at a depth of 5 km, associatedwith a large temperature gradient. Below, we will describesome details of corrected BHT data coming from thePierrefeu and Les Angles boreholes, not only because they

belong to the “hottest boreholes” in the Provence area, butalso because significant variations in the temperature gradi-ent at Pierrefeu can be correlated with changes in thelithology.

At Pierrefeu, a constant temperature gradient of30oC.km-1 is estimated from the surface temperature and asingle corrected BHT data at a depth of 1740 m. Below1740 m, a salty layer (halite, anhydrite) of Oligocene ageextends down to a depth of 2550 m. Thermal conductivityof “rock salt” and halite may reach values of up to6.65 W.m-1.K-1 at 20oC [Yang, 1981] and up to4.80 W.m-1.K-1 at 400 K [Clauser, 2006]. Theoretically, aconstant heat flow through all layers implies that the tem-perature gradient must be decreased in a conducting rockunit (see equation 2). This is effectively observed across thesalty layer since changes in the geotherm slope are obtainedat both top and bottom boundaries (fig. 5a). The single mea-surement of thermal conductivity at this layer indicates ahigh value of 5.9 W.m-1.K-1 (measured at 20oC), thus con-firming the possible low temperature gradient within thesalty layer. Indeed, temperature gradient keeps a constantvalue of 24oC.km-1 until it changes to 40oC.km-1 at the baseof the salty layer, where shale and limestone are encoun-tered (2550 m). This high temperature gradient may be ex-plained by different causes, such as a high heat productionrate of basement rocks. It may also be due to the anisotropyof shale, resulting in a high thermal conductivity in the ho-rizontal direction and a low conductivity in the vertical di-rection, causing an increase in the vertical temperaturegradient.

If the thermal effect on thermal conductivity data wasaccounted for in figure 5a (red dots), then the apparent in-crease below 2550 m would disappear. Indeed, the valuesfor sedimentary rocks at temperatures between 100oC and200oC should be decreased by ~0.6 to 1.0 W.m-1.K-1 (seesection “Thermal properties”), and thermal conductivity ofthe salty layer may be lowered down to ~4.5 W.m-1.K-1 – avalue which is still 2-3 times higher than that of sedimen-tary rocks. Consequently, it appears that temperature-de-pendence of thermal conductivity does reinforce localcorrelations between the temperature profile and thermalconductivity values.

Figure 5b shows BHT and DST data from the Les An-gles borehole, 40 km from Pierrefeu. Corrected BHT dataand DST data at depths of 5 � 0.5 km confirm the probablevalue of 180-195oC at a depth of 5 km (e.g., two DST tem-perature data of 182oC and 193oC are recorded at 4987 mand 4990 m, respectively). The average temperature gradi-ent estimated at Les Angles between 3500 m and 5000 mequals 41.9oC.km-1, but, as demonstrated by gradient esti-mates in the Pierrefeu borehole, this large value may not bemaintained at greater depth since, for instance, basementrocks may have a higher thermal conductivity. Actually, ifthe temperature gradient at a depth of 5 km is estimatedfrom extrapolated or interpolated temperatures between 4and 5 km, then values ranging from 26 to 35oC.km-1 are ob-tained in the Camargue area (fig. 6a).

A second hot zone at 5 km depth is located southwest ofValence city (fig. 4). At 2 km depth, this hot anomaly ap-pears to extend in the north-east direction, within thePalaeogene Valence hemi-graben structure. The two deephot anomalies in the Southeast Basin could be related to



FIG. 3. – Temperature maps of Haenel et al. [1980] and Lucazeau et al.[1985] for the Southeast Basin. Black dots correspond to the same cities asin figure 2. At the bottom right are geotherms deduced from temperaturevalues east of Montpellier.FIG. 3. – Cartes des températures de Haenel et al. [1980] et Lucazeau et al.[1985] pour le bassin du Sud-Est. Les points noirs correspondent aux mê-mes villes que celles de la figure 2. En bas à droite sont reportés les géo-thermes déduits de ces cartes pour la région à l’est de Montpellier.

geological features of the Palaeogene Vistrenque and Va-lence hemi-grabens. Both of them exhibit a similar geologi-cal history and structure, such as: (i) the occurrence of aregional border fault; the Nîmes and the Cevennes faults,respectively, correspond to Hercynian structures removed

during Mesozoic and Palaeogene extensional events; (ii) anasymmetric geometry with larger depth on western side;(iii) the occurrence of Triassic salty levels which constitutemain decollement layer for Nîmes and Cévennes faults; (iv)a syn- and post-rift infill consisting of thick (2 to 3 km indepth) Tertiary sequences containing Oligocene evaporiticlayers. If positive anomalies (hot zones) are related to ther-mally insulating sediments, then it is unsurprising if we findanomalies with a somewhat larger size than the grabenscale.

Within the two cold areas of figure 4b, the lowest tem-perature gradients are 26 and 27oC.km-1 (fig. 6a). The low-est temperature gradient in the Southeast Basin (17oC.km-1)is located in the Drôme area, although temperature here ishigh. A value of 17oC.km-1 should thus be considered as theminimal temperature increase with depth in the entire basin.The reason behind such differences falls outside of thescope of this study, but we might suspect that thicknesses ofinsulating sediments or of conducting salty layers play amajor role in local temperature variations with depth.For example, the Pierrefeu geotherm clearly shows a10-15oC-cooling effect at 2.5 km depth due to the salty con-ducting layer (fig. 5a). Fluid circulation within permeablezones may also be invoked [e.g., Bächler et al., 2003]. Afuller discussion of such possible mechanisms can be foundin Garibaldi et al. [2010].

EXTRAPOLATION DOWN TO THE EVAPORITICLAYER

The geometry of the Triassic evaporitic layer beneath theSoutheast Basin is not well constrained, but seismiccross-sections help to suggest its probable depth and thick-ness variations [Benedicto et al., 1996]. The proportion ofevaporites within the Trias formation increases from about10% at the western edge of the basin to maybe 90% beneaththe basin centre, located around the city of Carpentras,~100 km north-east of Montpellier [M. Seranne, personalcommunication; Seguret et al., 1997]. Beneath theCamargue area, evaporites are located at approximately5-6 km in depth while the basement-Trias boundary deep-ens eastwards to more than 7-8 km beneath Carpentras. Thethickness of evaporites would be limited to 500 m beneaththe Camargue area while it seems likely to reach depths of2-3 km beneath the basin centre [M. Seranne, personal com-munication; Seguret et al., 1997]. Based on these estimatesof the Triassic salty layer geometry, a two-dimensional



FIG. 4. – New temperature maps in the Southeast Basin, as deduced from a krig-ging procedure based on a 3D geostatistical analysis (see text). The 3D thermalmodel is constrained by corrected BHT data. For any given map, white dots showBHT data located at � 1000 m from the related depth, while black dots show allboreholes with BHT data. A map depicting the standard deviation of estimated va-lues at a depth of 5 km depth is shown at the bottom.FIG. 4. – Nouvelles cartes des températures dans le bassin du Sud-Est obtenuesaprès une procédure de krigeage basée sur une analyse géostatistique en 3D. Lemodèle thermique 3D est contraint par l’ensemble des données BHT. Pour unecarte donnée, les points blancs montrent les données BHT situées à 1000 m dela profondeur considérée, alors que les points noirs montrent tous les forages pos-sédant des données BHT. La figure du bas montre la carte des écarts-types destempératures à 5 km de profondeur.

large-scale model is studied in section “Construction oftwo-dimensional models in the Camargue area”. Rough val-ues are, however, inferred from the deepest temperaturesand temperature gradients estimates.

Because similar hot temperatures are inferred at a depthof 5 km depth beneath the Camargue area and beneathCarpentras (fig. 4b), both regions are studied below. Signif-icant temperature differences may be obtained within theTriassic evaporites, which are thin and shallow beneathCamargue, and thick and deep beneath Carpentras.

Rough estimates

The simplest way to infer deep temperatures from availablemeasurements is a linear extrapolation of the deepest esti-mated temperature gradients. This method implicitly ig-nores the role of lithological contrasts, such as the presenceof a conductive salty layer, and should thus be consideredas a first order approximation. However, it must be notedthat thermal conductivity contrasts are decreased at hightemperatures, so that a linear extrapolation from deepest es-timates should not be strongly biased. According to the av-erage values estimated in the preceding section,temperatures of 200oC and 320oC would be reached atdepths of 6 km and 10 km, respectively. When lateral varia-tions are accounted for, significant temperature differencesare expected at these depths: for example in the Drômearea, a low temperature gradient would be present at a depthof 5 km (fig. 6a), while the Vistrenque graben area is char-acterised by a high temperature gradient at the same depth(fig. 5 and 6a). Considering both temperatures and tempera-ture gradient values at a depth of 5 km (fig. 6a and 6b), tem-peratures up to 300oC at a depth of 8 km are likely (fig. 6c).This hot zone, which corresponds to the Vistrenque grabenarea, is surrounded on the western and eastern sides by tem-peratures which are up to 70oC lower. Similarly, by usingdeep temperatures and deep temperature gradients aroundthe Valence city, we can predict another hot zone (295oC) at8 km depth (fig. 6b).

In order to better constrain deep temperatures, we havedeveloped below a two-dimensional approach, where tem-perature estimates result from numerical simulations of heattransfer within the basin, and where thermal properties andgeological data are accounted for. A first model focuses onthe Vistrenque graben and is dedicated to the reproductionof temperature data from the Pierrefeu borehole. With thismodel, possible mantle heat flow values and bulk heat pro-duction of the basement have been deduced. A secondmodel, at a larger scale, and with the inferred mantle heatflow value, accounts for possible depth and thickness varia-tions within the evaporitic layer, in order to bracket deeptemperatures.

Construction of two-dimensional models in theCamargue area

Figure 7 illustrates the two-dimensional models for (a) theVistrenque half-graben, and (b) for the entire crust whereevaporites show varying depths and thicknesses. In this lat-ter case, two cross-sections are considered: the first one isseismically constrained and the second one shows anotherpossible geometry. Thermal boundary conditions are shownin figure 7c. Heat production rates and thermal conductivityvalues are detailed in the following sections. In the first

model, the most probable values for heat production ratesand thermal conductivity values of sedimentary units areconsidered. Two unknown parameters, namely the heat pro-duction rate of the basement and the mantle heat flow value,are systematically varied. However, the mantle heat input isconsidered as the main unknown value since previous esti-mates on crustal heat production in the area have been pub-lished [Lucazeau and Mailhé, 1986]. Results from this firstmodel, namely the most probable values for heat productionrate of the basement and the mantle heat flow value, arethen inserted in the second model to infer possible deeptemperatures within the evaporitic layer.

Thermal modelling consists of solving heat transferequation within a conductive steady-state thermal regime intwo dimensions (no heat transfer by advection). To do this,the finite-element commercial code Comsol Multiphysics™is used. Mesh consists of more than 100,000 triangular ele-ments for the first model in which sedimentary units are de-tailed, and around 10,000 triangular elements for the secondsimpler models. At the surface, a constant surface tempera-ture of 15oC is applied, while no heat transfer occurs on lat-eral sides. At the bottom of the crust, mantle heat flow is



FIG. 5. – Corrected BHT data (circles) for two boreholes east of Montpel-lier (Pierrefeu and Les Angles). Large temperature gradients are estimatedat depth, and a slight decrease in temperature gradient is observed withinthe salty layer crossed by the Pierrefeu borehole. Thermal conductivity va-lues (full dots on top figure) were measured at room temperature, and aredifficult to use since porosity values are unknown and possible anisotropyis not considered (see text).FIG. 5. – Données BHT corrigées (cercles) pour deux forages à l’est deMontpellier (Pierrefeu et Les Angles). De forts gradients de températuresont estimés en profondeur, et une légère diminution du gradient est ob-servée au sein de la couche salée traversée par le forage de Pierrefeu. Lesconductivités thermiques (points sur la figure du haut) ont été mesurées àtempérature ambiante, et sont difficile à utiliser puisque les valeurs de po-rosité sont inconnues et que la possible anisotropie n’est pas considérée(voir texte).

assumed to remain constant and uniform beneath the entirecrustal portion. In the first model, the geological cross-sec-tion of Benedicto et al. [1996] is adopted (fig. 7a), with

distinction between sedimentary formations. In the secondmodels (fig. 7b), we focus on the varying thickness of theTriassic evaporitic layer. The first cross-section includes asoutheastern deepening of the basin down to a depth of9 km (bottom of the evaporitic layer), as suggested bySeranne et al. [2007]. The second cross-section accountsfor the maximum depth of the basin, estimated at 11 km be-neath the city of Carpentras. The adopted thermalproperties for sedimentary formations are detailed below.

Thermal properties

Heat production

When gamma-ray logs from exploration boreholes areavailable, then heat production rates can be easily estimatedwith an acceptable error of less than 10% [Bücker andRybach, 1996]. In this study, we only had access to logheaders, where BHT data are mentioned. We have thereforeused data from literature on heat production rates ofsedimentary rocks.

A number of studies related to the thermal evolution ofsedimentary basins have published laboratory measure-ments of heat production rates in sedimentary rocks[McKenna and Sharp, 1998; Norden and Förster, 2006].Models of petroleum systems [e.g., McBride et al., 1998]also used heat production values for recent to Jurassic for-mations from various studies. Recent to Oligocene forma-tions in the Gulf of Mexico basin have an average heatproduction rate dependent on lithology that ranges from 0.9to 1.7 µW.m-3 [McKenna and Sharp, 1998]. For the sameages, a model by McBride et al. [1998] uses values between1.3 and 2.2 µW.m-3, while Norden and Förster [2006] mea-sured heat production rates between 1.0 and 1.3 µW.m-3.For Cretaceous to Jurassic formations, these studies indi-cate values ranging from 0.6 to 1.4 µW.m-3, 0.1 to2.2 µW.m-3, and 0.6 to 1.5 µW.m-3, respectively. Triassicformations of the Northeast German basin have an averageheat production rate of 1.0 µW.m-3 [Norden and Förster,2006]. In other words, recent to Oligocene formations canreasonably be assigned a value of 1.3 µW.m-3 while a lowervalue of 1.0 µW.m-3 can be assigned to Cretaceous, Jurassicand Triassic formations.

In order to keep previous estimates of bulk heat produc-tion of the Gulf of Lion basin [Lucazeau and Mailhé, 1986],heat production rate of basement rocks below the Southeastbasin has been chosen so that the total amount of heat flow



FIG. 6. – (Top) map and values of temperature gradient at a depth of 5 km, esti-mated from extrapolated data at depths of 4-5 km. (Bottom) probable tempera-ture differences at 8 km in depth, as inferred from temperature (middle) andtemperature gradient maps (top) at 5 km depth. The red star corresponds to thelocation of the Pierrefeu borehole within the Vistrenque graben. Contouredareas correspond to anomalous zones as revealed by temperature map of tempe-rature at 5 km depth.FIG. 6. – (En haut) : carte du gradient de température à 5 km de profondeur, es-timée à partir des données extrapolées à 4 et 5 km. (En bas) : différence pro-bable des températures à 8 km de profondeur déduite des cartes destempératures (milieu) et des gradients de température à 5 km de profondeur (enhaut). L’étoile rouge correspond à la position du forage de Pierrefeu dans legraben de Vistrenque. Les zones contourées correspondent aux anomalies révé-lées par la carte des températures à 5 km de profondeur.

due to crustal heat production (second term in equation 3)equals 45 mW.m-2. When 1.3 µW.m-3 is assigned to recentto Oligocene sediments (a 5 km-thick sequence), a 28 km-thick crust involves 1.6 µW.m-3 in basement rocks (23 kmthick), thus providing 45 mW.m-2 for the crustal componentof the surface heat flow.

Thermal conductivity

In order to create a more realistic model, the tempera-ture-dependence of thermal conductivity of rocks can beimplemented in the numerical procedure. Thermal conduc-tivity measurements of halite at temperatures up to 400oCwere reported by Birch and Clark [1940], and those for“rock salt” were measured from 0.4 to 1000 K and reported

by Yang [1981]. These data show that halite and rock saltgradually lose their conductivity as temperature increases(fig. 8). Sedimentary rocks are also known to show a de-crease of thermal conductivity with temperature increase.From 0 to 300oC, there is a reduction by nearly a factor oftwo: from about 2.2-4.1 to 1.3-2.3 W.m-1.K-1, and from6.0-7.0 to 2.5-3.1 W.m-1.K-1 for halite and rock salt (fig. 8).The decreasing effect of temperature on thermal conductiv-ity is also present in basement (or crystalline) rocks, but ismuch less important (from about 2.5 to 1.8 W.m-1.K-1). Dif-ferent empirical relations for temperature-dependence ofthermal conductivity have been suggested [Sass et al.,1992; Seipold, 1998; Vosteen and Schellschmidt, 2003].For crystalline rocks of the eastern Alpine crust, the generallaw suggested by Vosteen and Schellschmidt [2003] can beadjusted by a degree 3 polynomial expression. The follow-ing relation is valid below 400oC, where heat transfer byradiation is not significant:

�cry T T T T( ) . .� � � � � � �� 2507 0 0036 210 4106 2 9 3 (4)

where T is temperature in oC. Similarly, these authors sug-gested a general law for sedimentary formations, which canbe expressed (up to 400oC) by a degree 2 polynomialexpression:

� �sed sedT T T( ) ( ) .� � � � ��0 0 0064 710 6 2 (5)

As demonstrated by errors bars in diagrams by Vosteen andSchellschmidt [2003] (see fig. 8) and indicated by Clauserand Huenges [1995] in their work on porosity, the startingvalue �sed ( )0 may differ from one type of sediment to theother. Even if many tens of thermal conductivity measure-ments of rocks from the Southeast Basin were performeddecades ago, both porosity values and lithological informa-tion remain unknown or else are too scarce to enable an ac-curate estimate of �sed ( )0 for each formation. In addition, itis somewhat dangerous to use thermal conductivity mea-surements from deep samples since they were actually mea-sured at room temperature. Consequently, starting values of�i ( )0 , where i represents one lithology, are here adjusted ina reasonable range in order to fit lithological informationand temperature data from the Pierrefeu borehole.

For rock salt and halite, temperature dependence is toostrong, meaning that a simple inverse law, such as the onegiven by Vosteen and Schellschmidt [2003] for sedimentaryunits, cannot be applied. However, a polynomial fit can beapplied to numerical values listed in Clauser [2006] andranging from 0 to 400oC:�halite T T T T( ) . . ?� � � � � � � � �� 6101 0 024 7 10 5 105 8 3 (6)

�rock salt T T T T( ) . . ?� � � � � � � � �� 7134 0 023 4 10 3 105 8 3 (7)

The following steady-state model incorporates thesetemperature-dependence conductivity laws for sedimentaryunits and crystalline rocks (expressed in equations 4 to 7).

Results

The four main temperature data sets (15oC at the surface,64oC at 1740 m, 85oC at 2550 m and 180-190oC at 5000 m)have been reproduced with thermal parameters listed in ta-ble I and temperature-dependence laws previously de-scribed. The salty layer is assigned a lower thermalconductivity value at 0oC than that presented in equation (6)or (7) because it was not possible to reproduce the slight



FIG. 7. – Models of simplified crustal structures for (a) the Vistrenque gra-ben, northeast of Montpellier, after Benedicto et al. [1996], and (b) twonorthwest – southeast cross sections, the first one being constrained byseismic data [Seranne et al., 2007] and the second one crossing the deepestpart of the basin (see location of cross-sections in figure 2, top left). Ther-mal conditions applied to thermal modelling are indicated in (c). Note thatthe varying amount of evaporites within the Trias formation is consideredin the second models.FIG. 7. – Modèles des structures crustales simplifiées pour (a) le graben deVistrenque, au nord-est de Montpellier, d’après Benedicto et al. [1996], etpour (b) une structure crustale ouest-est incluant une géométrie variée dela couche évaporitique (voir position des cuopes en figure 2). Les condi-tions thermiques utilisées pour la modélisation sont indiquées en (c). Lavariation de la quantité d’évaporites au sein du Trias est prise en comptedans le deuxième modèle.

change in temperature gradient crossing this layer using athermal conductivity contrast that was too high (fig. 5a).This may be interpreted by the presence of both sedimentsand salt in the layer, involving a higher conductivity thanthat of sediments but lower than that of pure salt rock. Simi-larly, it is assumed than the Triassic evaporites do not corre-spond to 100% of halite, and a value of 5.0 is assigned tothe 0oC value in equation (6).

Figures 9a and 9b show the computed temperature pro-files at Pierrefeu, with a varying mantle heat flow. A mantleheat flow value of 35 mW.m-2 enables us to reproduce tem-perature data from the Pierrefeu borehole (black circles infigure 9a). This is not the case for mantle heat flow valueslower than 30 or greater than 40 mW.m-2. Figure 9c illus-trates the two-dimensional thermal field around the basinwith a mantle heat flow value of 35 mW.m-2. Figure 9dshows surface heat flow variations computed for mantleheat flow values ranging from 30 to 40 mW.m-2. The mostprobable value of 35 mW.m-2 would imply a Moho tempera-ture of ~820oC, and a surface heat flow of 80-82 mW.m-2

outside the deep graben. Computed surface heat flow valuesare therefore in accordance with measured surface heat flowvariations shown in figure 2, since computed values rangefrom 73 and 90 mW.m-2. With this model, temperatures at10 km depth beneath Pierrefeu may reach 350-400oC.

In order to test the effect of a varying depth and thick-ness of the Triassic evaporitic layer, the second models,shown in figure 10, account for slightly simpler thermalproperties than those listed in table I. Temperature-depend-ence laws of equations (4) and (7) are assigned to basementrocks and to the evaporitic layer, respectively. Tempera-ture-dependence law of equation (5) is assigned to sedi-ments with a 0oC value of 2.5 W.m-1.K-1. A mantle heatflow value of 35 mW.m-2 is used for both models. Figure10c and 10d illustrate the 2D thermal field (white iso-therms) together with the temperature-dependent thermalconductivity distribution (colour scale). Temperatures alongthe upper and lower boundaries of the evaporitic layer areshown, with a maximum value of 398oC reached at a depthof 11 km depth below the deepest part of the basin. Even inthe first case where deepest evaporites only reach 9 km, avalue of 384oC is computed. However, it must be noted thatif the 0oC value of equation (5) (i.e. �sed ( )0 ) is set to3.0 W.m-1.K-1, then the temperature gradient within the sed-iments is decreased, and the highest temperature is loweredto 310oC at a depth of 11 km. Another important result isthe presence of a large horizontal temperature differencewithin a few tens of kilometres (fig. 10, bottom). In this cal-culation, the varying amount of salt within evaporites is ac-counted for, but it turns out that at temperatures exceeding200oC, the decrease of thermal conductivity is more impor-tant than the slight increase due to halite enrichment of thelayer. To summarise, temperatures within the thick and deepevaporitic layer may show large variations (e.g. from 150 to398oC, top and bottom boundaries, respectively), with amaximum temperature probably greater than 310oC.

CONSEQUENCES FOR RHEOLOGICALCONTRASTS

The rheology of “dry” salt is described by a dislocationcreep law, in which temperature, stress, strain rate and grainsize play a role. In particular, for small strain rates, vanKeken et al. [1993] showed that for a given grain size, saltviscosity would decrease by an order of magnitude between20 and 160oC. For a small grain size of 0.5 cm, salt viscos-ity at small strain rates does not exceed 1017 Pa.s, while itmay reach 1020 Pa.s for a grain size of 3 cm. However,“wet” salt (the dry-wet threshold value being considered as0.05 wt.%) can be considered as a Newtonian fluid whose



FIG. 8. – Temperature-dependence of thermal conductivity for rock salt, ha-lite, sedimentary rocks and crystalline rocks (see text for references and de-tails).FIG. 8. – Conductivité thermique de la roche sale, de l’halite, des rochessédimentaires et cristallines en fonction de la température (voir texte pourles références et les détails).

TABLE I. – Thermal parameters used in the 2D numerical models dedicated(i) to the reproduction of the Pierrefeu borehole temperature data (fig. 7a)and (ii) to estimates of deep temperatures in the evaporitic layer (fig. 7b).Temperature-dependence laws for thermal conductivity are detailed in thetext.Tabl. I. – Paramètres thermiques utilisés dans les modèles numériques 2Ddestinés (i) à la reproduction des données de température du forage dePierrefeu (fig. 7a) et (ii) aux estimations des températures profondes de lacouche évaporitique (fig. 7b). Les lois de dépendance en température pourla conductivité thermique sont détaillées dans le texte.

rheology is described by a diffusion creep law [Weijermarset al., 1993]. In this case, the effective viscosity of wet saltis temperature-dependent, but is independent of stress orstrain rate [Weijermars et al., 1993].

At a depth of 1 km depth, Weijemars et al. [1993] useda viscosity value of 1017 Pa.s and a value some 10 timeslower at 140oC [for experimental data up to 200oC, seeCarter et al., 1993]. The value of 1017 Pa.s also correspondsto salt viscosity value used in preliminary models of saltdiapirism by Poliakov et al. [1996]. According to a recentstudy, values of 1018 to 1019 Pa.s would represent a thresh-old value below which internal deformation of salt may oc-cur [Chemia et al., 2009]. In the Southeast Basin, Triassicevaporites would be at temperatures much higher than170oC, and their effective viscosity is thus lower than 1016

Pa.s, but grain size and the amount of water must be knownbefore a reliable estimate can be given. Thermal contrastshigher than 70oC at 8 km depth should induce lateral varia-tion in salt viscosity, which may induce mechanical distur-bances. When the effects of temperature-dependence on saltviscosity are accounted for [e.g., van Keken et al., 1993],we get a decrease in viscosity by a factor of 10 from 20oCto 140oC. By applying the similar Arrhenius law at a tem-perature of 300oC, a factor of 40 is obtained (see ibid,equation 7 describing salt viscosity associated with pressuresolution creep).

Within these hot zones, we might suggest that the viscos-ity of the evaporites is so low that any vertical subsidenceevent would occur preferentially through this low-viscositypart of the evaporitic layer. Such a scenario should, however,be supported by additional geological evidence and physicalanalyses. In particular, it may be interesting to model crustalextension and sedimentation events with adequatethermo-mechanical properties of salt and sediments. As

emphasised by Tuncay and Ortoleva [2004], basin modellingstudies and problems related to salt tectonic regimes shouldbe solved simultaneously for thermal and mechanical re-gimes because salt rheology is temperature-dependent.

It is nevertheless interesting to note that a spatial correla-tion seems to exist between deep hot zones and the locationof deep half-grabens (Vistrenque and Valence). Small-scaleevaporitic basins and grabens could actually reveal deep hotzones, where underlying evaporites would have had less vis-cous resistance, thus implying enhanced local subsidence(see also the “falling diapirs” of Vendeville and Jackson[1992]). In this sense, formation of small-scale extensionalstructures (for example, the Vistrenque and Valence half-grabens) could have been favoured and amplified by lateralviscosity contrasts due to temperature differences in the un-derlying evaporitic layer. Indeed, mechanical interactions be-tween salt and sediments have already been identified toexplain the geometry of sedimentary systems [Dos Reis etal., 2005]. Such scenarios should, however, be confirmed bythermo-mechanical modelling of transient evolution account-ing for sedimentation episodes and subsidence events. Fur-thermore, the results of such modelling, if focused onpresent-day salt-sediments interactions at a few kilometres indepth, should help policymakers to decide on the possiblerisks of storing liquid, gas and solid waste in salt caverns.

DISCUSSION AND CONCLUSION

The possibility that the upper crust of the Southeast Basinhas undergone gravity tectonics by sliding over an evaporiticlayer has been partly approached in this paper. Study of suchlarge-scale processes, however, needs a complete assessmentof large-scale tectonic forces as well as the knowledge ofthree-dimensional geometry of the evaporitic layer. One



FIG. 9. – Results from 2D thermal modelling of heat transfer within and around the Vistrenque graben. (a) computed temperature profiles at Pierrefeu loca-tion for a varying mantle heat flow Qm; (b) crustal geotherms for the same varying Qm values; (c) 2D thermal field where Qm =35 mW.m-2; (d) surface heatflow variation above and around the Vistrenque graben for a varying mantle heat flow.FIG. 9. – Résultats de la modélisation autour du graben de Vistrenque. (a) Profils thermiques calculés à Pierrefeu pour un flux mantellique Qm variable ;(b) géotherme sur toute la croûte pour les mêmes variations de Qm ; (c) champ thermique avec Qm =35 mW/m2 ; (d) variation du flux de chaleur en surfaceau-dessus et autour du graben de Vistrenque pour un flux mantellique variable.

fundamental question deals with the behaviour of salt in theductile regime under specific pressures and temperatures.While the three-dimensional geometry of the evaporitic layeris not well known, the three-dimensional thermal field is nowbetter constrained since several cold and warm zones havebeen determined. One result of our findings is that salt vis-cosity at depth of 5-11 km is clearly sufficiently low to per-mit horizontal ductile flow, but lateral viscosity contrastsmay also favour local subsidence. In addition, it should benoted that present-day crustal velocities in the Southeast

Basin are not significant since the maximum value recordedat Montpellier does not exceed 0.7 � 0.6 mm/yr, in compari-son with the Central Europe reference frame [Nocquet andCalais, 2003]. In the case of a much higher horizontal veloc-ity, it might be possible to assign an important role tolarge-scale horizontal tectonic events, but for small horizon-tal motions, localised subsidence might be favoured. How-ever, details on the scale of gravity tectonic events deserve amuch more rigorous analysis, accounting for geometric prop-erties of the evaporitic layer (thickness and slope) and of theoverburden [for reviews and examples, see Hudec and Jack-son, 2007 and Cartwright and Jackson, 2008].

Another important consequence of temperature maps il-lustrated in this study deals with possible hydrothermal pro-cesses within permeable zones. Some of the identified thermalanomalies may partly result from hydrothermal convection infaulted zones, as it has been suggested in the Landau area(Rhine graben) [Bächler et al., 2003], in the western Molassebasin, Germany [Rühaak, 2009], and in the Ashanti belt,Ghana [Harcouët-Menou et al., 2009]. According to thesestudies, lateral temperature differences reaching 15oC in a per-meable zone can be explained by convective processes [seealso Fleming et al., 1998]. The sign inversion of thermalanomalies within the Cevennes fault area (negative anomaliesat 2000 m switched to positive anomalies at 5000 m depth)can also be explained by superimposed convective cells in-duced by the depth-dependence character of permeability[Ingebritsen and Manning, 1999]. Details on these convectiveprocesses can be found in Garibaldi et al. [2010].

Several independent mechanisms can contribute to theformation of large amplitude thermal anomalies at depth. Ifconvective circulation of hydrothermal fluids can explain lo-cal temperature differences of � 15oC at a given depth, addi-tional processes are still needed to reach differences as largeas 50oC, as inferred from corrected BHT data at a depth of5 km. Clearly, the insulating character of sediments [Clauserand Huenges, 1995], lithological contrasts and possible sharpvariations in mantle heat flow can induce such thermal ef-fects. It should be noted that models of figure 9 were per-formed with a constant mantle heat flow value.

The Southeast Basin where sediment thickness can lo-cally exceed 10 km, is underlain by an evaporitic layer ofwhich the thermal effect (high thermal conductivity) canalso play a role. Even if the thermal conductivities of rocksapproach 1.5-3.0 W/m/K at temperatures of 300oC, (fig. 8),rock salt and halite are still 1.5-2 times as conductive asother rocks, implying that deep hot temperatures of the in-termediate crust can be easily conducted vertically througha thick and thermally conducting evaporitic layer.

The relatively small-scale and heterogeneous structureof thermal maps illustrated in figures 4 and 6 does not allowus to invoke large-scale mechanisms (e.g., mantle pro-cesses) as the main sources of the identified thermal anoma-lies. However, geological systems of the upper crust (largepermeable faulted zones, thick sedimentary units, evaporiticlayer with a varying thickness, hemi-grabens) may be com-bined to induce complex spatial distribution of theunderground thermal regime.

Acknowledgements. – This study was partly supported by a BRGM-InstitutCarnot grant. The English has been proofread by Rosie Marshall. We thankLaurent Husson and an anonymous reviewer for their constructive andthoughtful comments. This is BRGM publication 06342.



FIG. 10. – Results from thermal modelling of heat transfer around a varyinggeometry of the evaporitic layer, as outlined by two cross-sections. a) loca-tion of the two cross-sections; b) the first cross-section is adapted from Sé-ranne et al. [2007] and is constrained by seismic data; the second onecrosses the deepest part of the basin, estimated at 11 km depth; c) case ofthe first cross-section : temperature field (white isotherms), thermalconductivity (colour scale) and temperature profiles along the top and bot-tom boundaries of the evaporitic layer; d) same as c) for the secondcross-section.FIG. 10. – Résultats tirés de la modélisation des transferts de chaleur au-tour d’une couche évaporitique de géométrie variable, comme le montreles deux coupes. a) position des deux coupes ; b) la première coupe,adaptée de Séranne et al. [2007], est contrainte par des données sismi-ques; la deuxième coupe croise la partie la plus profonde du bassin, es-timée à 11 km ; c) cas de la première coupe : champ de température(isothermes en blanc), conductivité thermique (en couleur) et profils detempérature le long des limites inférieure et supérieure de la couche évapo-ritique ; d) identique à c) mais pour la deuxième coupe.

References

BÄCHLER D., KOHL T. & RYBACH L. (2003). – Impact of graben-parallelfaults on hydrothermal convection – Rhine graben case study. –Phys. Chem.. Earth, 28, 431-441.

BENEDICTO A., LABAUME P., SÉGURET M. & SERANNE M. (1996). –Low-angle crustal ramp and basin geometry in the Gulf of Lionpassive margin: Oligocene-Aquitanian Vistrenque graben, SEFrance. – Tectonics, 15, 1192-1212.

BEREST P. & BROUARD B. (2003). – Safety of salt caverns used for under-ground storage – blow out, mechanical instability, seepage, ca-vern abandonment. – Oil Gas Sci. Technol. – Revue de l’InstitutFrançais du Pétrole, 58, 361-384.

BIRCH F. & CLARK H. (1940). – The thermal conductivity of rocks and itsdependence, upon temperature and composition, Part I. – Am. J.Sci., 238, 529-558.

BÜCKER C. & RYBACH L. (1996). – A simple method to determine heat pro-duction from gamma-ray logs. – Mar. Petrol. Geol., 13, 373-375.

BONTÉ D., GUILLOU-FROTTIER L., GARIBALDI C., BOURGINE B., LOPEZ S.,BOUCHOT V. & LUCAZEAU F. (2010). – Subsurface temperaturemaps in French sedimentary basins: new data compilation andinterpolation. – SGF meeting “Hydrothermalisme en milieucontinental”, Le Bourget-du-lac – Aix-les-Bains, 23-24 october2008. In: D. GASQUET, J.-Y. JOSNIN & Y. LAGABRIELLE, Eds, Hy-drothermalisme en domaine continental. – Bull. Soc. géol. Fr.,181, 4, 377-380.

BONTÉ D., GUILLOU-FROTTIER L., LUCAZEAU F., LOPEZ S. & BOUCHOT V. –New heat flow map of France. – BRGM report, in prep., 2010.

BURRUS J. & FOUCHER J.-P. (1986). – Contribution to the thermal regime ofthe provençal basin based on flumed heat flow surveys and pre-vious investigations. – Tectonophysics, 128, 303-354.

CARTER N.L., HORSEMAN S.T., RUSSEL J.E. & HANDIN J. (1993). – Rheolo-gy of salt. – J. Struct. Geol., 15, 1257-1271.

CARTWRIGHT J.A. & JACKSON M.P.A. (2008). – Initiation of gravitationalcollapse of an evaporitic basin margin: the Messinian salinegiant, Levant basin, eastern Mediterranean. – Geol. Soc. Amer.Bull., 120, 399-413.

CHEMIA Z., SCHMELING H. & KOYI H. (2009). – The effect of the salt visco-sity on future evolution of the Gorleben salt diapir, Germany. –Tectonophysics, 473, 446-456.

CHOPRA P. & HOLGATE F. (2005). – A GIS analysis of temperature in theAustralian crust. – Proc. World Geothermal Congress, 24-29April 2005, Antalya, Turkey,

CLAUSER C. (2006). – Geothermal energy. In: K. HEINLOTH, Ed., Lan-dolt-Börnstein, Group VIII: Advanced materials and technolo-gies, Vol. 3: Energy Technologies, Subvol. C: RenewableEnergies. – Springer Verlag, Heidelberg-Berlin, 493-604.

CLAUSER C. & HUENGES E. (1995). – Thermal conductivity of rocks and mi-nerals. In: T.J. AHRENS, Ed., Rock physics and phase relations: ahandbook of physical constants, vol 3. – AGU, WashingtonD.C., AGU Ref. Shelf, 105-126.

DOR REIS A.T., GORINI C. & MAUFFRET A. (2005). – Implications of salt-se-diment interactions on the architecture of the Gulf of Lionsdeep-water sedimentary systems – western Mediterranean Sea. –Mar. Petrol. Geol., 22, 713-746.

FLEMING C.G., COUPLES G.D. & HASZELDINE R.S. (1998). – Thermal effectsof fluid flow in steep fault zones. – Geol. Soc. London, Spec.Pub., 147, 217-229.

FÖRSTER A. (2001). – Analysis of borehole temperature data in the Nor-theast German basin: continuous logs versus bottom-hole tempe-ratures. – Petrol. Geosc., 7, 241-254.

GABLE R. (1978). – Acquisition et rassemblement de données géothermi-ques disponibles en France. – BRGM Report 78 SGN 284 GTH,60p.

GARIBALDI C., GUILLOU-FROTTIER L., LARDEAUX J.-M., BONTÉ D., LOPEZ

S., BOUCHOT V. & LEDRU P. (2010). – Relationship between ther-mal anomalies, geological structures and fluid flow: new evi-dence in application to the Provence basin (southeast France). –SGF meeting “Hydrothermalisme en milieu continental”,Le-Bourget-du-Lac – Aix-les-bains, 23-24 october 2008. In: D.GASQUET, J.-Y. JOSNIN & Y. LAGABRIELLE, Eds, Hydrotherma-lisme en domaine continental. – Bull. Soc. géol. Fr., 181, 4,363-376.

GOUTORBE B., LUCAZEAU F. & BONNEVILLE A. (2007). – Comparison of se-veral BHT correction methods: a case study of an Australiandata set. – Geophys. J. Int., 170, 913-922,

GUILLOU L., MARESCHAL J.-C., JAUPART C., GARIÉPY C., BIENFAIT G. &LAPOINTE R. (1994). – Heat flow, gravity and structure of theAbitibi belt, Superior Province, Canada: implications for mantleheat flow. – Earth Planet. Sci. Lett., 122, 103-123.

HAENEL R., LEGRAND R., BALLING N., SAXOV S., BRAM K., GABLE R., MEU-

NIER J., FANELLI M., ROSSI A., SALOMONE M., TAFFI L., PRINS S.,BURLEY A.J., EDMUNDS W.M., OXBURG E. R., RICHARDSON S. W.& WHEILDON J. (1980). – Atlas of subsurface temperatures in theEuropean Community. – The Commission of the European Com-munities, Directorate-General Scientific and Technical Informa-tion, EUR 6578 EN, Brussels-Luxemburg.

HARCOUËT-MENOU V., GUILLOU-FROTTIER L., BONNEVILLE A., ADLER P.-M.& MOURZENKO V. (2009). – Hydrothermal convection in andaround mineralized fault zones: insights from two and three-di-mensional numerical modeling applied to the Ashanti belt, Gha-na. – Geofluids, 9, 116-137.

HENTINGER R. & JOLIVET J. (1970). – Nouvelles déterminations du fluxgéothermique en France. – Tectonophysics, 10, 127-146.

HUDEC M.R. & JACKSON M.P.A. (2007). – Terra infirma: understanding salttectonics. – Earth Sci. Rev., 82, 1-28.

HURTER S. & HAENEL R., Eds (2002). – Atlas of geothermal resources inEurope. – Office for official publications of the European Com-munities, EUR 17811, Luxemburg.

HUSSON L., HENRY P. & LE PICHON X. (2008a). – Thermal regime of theNW shelf of the Gulf of Mexico – Part A: thermal and pressurefields. – Bull. Soc. géol. Fr., 179, 129-137.

HUSSON L., LE PICHON X., HENRY P., FLOTTE N. & RANGIN C. (2008b). –Thermal regime of the NW shelf of the Gulf of Mexico – Part B:heat flow. – Bull. Soc. géol. Fr., 179, 139-145.

INGEBRITSEN S.E. & MANNING C.E. (1999). – Geological implications of apermeability-depth curve for the continental crust. – Geology,27, 1107-1110.

JAUPART C. (1983). – Horizontal heat transfer due to radioactivity contrasts:causes and consequences of the linear heat flow relation. – Geo-phys. J. Roy. Astron. Soc., 75, 411-435.

JESSOP A.M. (1989). – Hydrological distortion of heat flow in sedimentarybasins. – Tectonophysics, 164, 211-218.

JESSOP A.M. (1990). – Thermal geophysics. – Elsevier, Amsterdam, 306p.,LEE T.C. & HENYEY T.L. (1974). – Heat flow refraction along dissimilar

media. – Geophys. J. Roy. Astron. Soc., 39, 319-333.LE PICHON X., RANGIN C., LOGET N., LIN J.-Y., HAMON Y. & FLOTTÉ N.

(2007). – Un bassin mésozoïque déstabilisé par la distensionoligocène. – SGF meeting “Tectonique récente de la Provence :rôle des couches ductiles”, Aix-en-provence, 14-15 juin 2007

LE PICHON X., RANGIN C., HAMON Y., LOGET N., LIN J. Y., ANDRÉANI L. &FLOTTÉ N. (2010). – Geodynamics of the France Southeast Ba-sin. In: X. LE PICHON and C. RANGIN, Eds, Geodynamics of theFrance Southeast Basin: Importance of gravity tectonics. – Bull.Soc. géol. Fr., 181, 6, 471-501.

LUCAZEAU F. & MAILHÉ D. (1986). – Heat flow, heat production and fissiontrack data from the Hercynian basement around the Provençalbasin (western Mediterranean). – Tectonophysics, 128, 335-356.

LUCAZEAU F. & VASSEUR G. (1989). – Heat flow density data from Franceand surrounding margins. – Tectonophysics, 164, 251-258.

LUCAZEAU F., VASSEUR G. & BAYER R. (1984). – Interpretation of heat flowdata in the French Massif Central – Tectonophysics, 103,99-119.

LUCAZEAU F., VASSEUR G., FOUCHER J.-P. & MONGELLI F. (1985). – In: D.A. GALSON and S. MUELLER, Eds, Second workshop on the Euro-pean Geotraverse Project Eur. Sci. Found., Amsterdam, Nether-lands, Venice, Italy, pp. 59-63,.

LUCAZEAU F., LEROY S., BONNEVILLE A., GOUTORBE B., ROLANDONE F.,D’ACREMONT E., WATREMEZ L., DÜSÜNUR D., TUCHAIS P.,HUCHON P. & BELLAHSEN N. (2008). – Persistent thermal activityat the eastern Gulf of Aden after continental break-up. – NatureGeosc., 1, 854-858.



MARESCHAL J.-C. & JAUPART C. (2004). – Variations of surface heat flowand lithospheric thermal structure beneath the North Americancraton. – Earth Planet. Sci. Lett., 223, 65-77.

MASCLE A., VIALLY R., DEVILLE E., BIJU-DUVAL B. & ROY J.P. (1996). –The petroleum evaluation of a tectonically complex area: thewestern margin of the Southeast Basin (France). – Mar. petrol.Geol., 13, 941-961.

MAUFFRET A. & GORINI C. (1996). – Structural style and geodynamic evo-lution of Camargue and Western Provencal basin, southeasternFrance – Tectonics, 15, 356-375.

MCBRIDE B.C., WEIMER P. & ROWAN M.G. (1998). – The effect of alloch-thonous salt on the petroleum systems of northern Green Canyonand Ewing Bank (offshore Louisiana), northern Gulf of Mexico.– AAPG Bull., 82-5B, 1083-1112.

MCLAREN S., SANDIFORD M. & HAND M. (1999). – High radiogenicheat-producing granites and metamorphism – an example fromthe western Mount Isa inlier, Australia. – Geology, 27, 679-682.

MCKENNA T.E. & SHARP J.M. (1998). – Radiogenic heat production in sedi-mentary rocks of the Gulf of Mexico basin, South Texas. –AAPG Bull., 82, 484-496.

MCKENNA J.R. & BLACKWELL D.D. (2004). – Numerical modelling of tran-sient Basin and Range extensional geothermal systems. – Geo-thermics, 33, 457-476.

MCKENZIE D. (1978). – Some remarks on the development of sedimentarybasins. – Earth Planet. Sci. Lett., 40, 25-32.

MWENIFUMBO C.J. (1993). – Temperature logging in mineral exploration. –J. Applied Geophysics, 30, 297-313.

NOCQUET J.-M. & CALAIS E. (2003). – Crustal velocity field of western Eu-rope from permanent GPS array solutions, 1996-2001. – Geo-phys. J. Int., 154, 72-88.

NORDEN B. & FÖRSTER A. (2006). – Thermal conductivity and radiogenicheat production of sedimentary and magmatic rocks in the Nor-theast German basin. – AAPG Bull., 90, 939-962.

POLIAKOV A.N.B., PODLADCHIKOV Y.Y., DAWSON E.C. & TALBOT C.J.(1996). – Salt diapirism with simultaneous brittle faulting andviscous flow. – Geol. Soc. London, Spec. Pub., 100, 291-302.

RANGIN C., LE PICHON X., CHAMOT-ROOKE N., HAMON Y., LOGET N. & LIN

J.-Y. (2007). – Extension triasique à oligocène en Provenceimagée par la sismique et la géologie de terrain. – SGF meeting“Tectonique récente de la Provence: rôle des couches ductiles”,Aix-en-Provence, 14-15 juin 2007

RANGIN C., LE PICHON X., LOGET N. & HAMON Y. (2010). – Gravity tecto-nics in the SE basin (Provence, France) imaged with seismicdata. In: X. LE PICHON and C. RANGIN, Eds, Geodynamics of theFrance Southeast Basin: Importance of gravity tectonics. – Bull.Soc. géol. Fr., 181, 6, 503-530.

RÜHAAK W. (2009). – Multidimensional modelling of the thermal and flowregime in the western part of the molasse Basin, southern Ger-many. – PhD. Thesis, Aachen University, 99p.

SASS J.H., LACHENCRUCH A.H. & MOSES T.H. (1992). – Heat flow from ascientific research well at Cajon Pass, California. – J. Geophys.Res., 77, 6966-6983.

SEGURET M., BENEDICTO A. & SERANNE M. (1997). – Structure profonde dela région du Gard rhodanien – apport du retraitement et de laréinterprétation de données sismiques régionales. In: JournéesScientifiques Gard, Bagnols/Cèze, vol. Atlas des Posters,ANDRA-CNRS, Ed., 31-32.

SEIPOLD U. (1998). – Temperature-dependence of thermal transport proper-ties of crystalline rocks – a general law. – Tectonophysics,291,161-171.

SERANNE M., BENEDICTO A., LABAUME P., TRUFFERT C. & PASCAL G.(1995). – Structural style and evolution of the Gulf of Lion Oli-go-Miocene rifting: role of the Pyrenean orogeny. – Mar. Petrol.Geol., 12, 809-820.

SERANNE M., BENEDICTO A., SANCHIS E., LABAUME P. & SEGURET M.(2007). – Rifting Oligocène en Languedoc : un modèle d’exten-sion de couverture. – SGF meeting “Tectonique récente de laProvence : rôle des couches ductiles”, Aix-en-Provence, 14-15juin 2007.

TESAURO M., KABAN M. & CLOETINGH S. (2006). – A new lithospheric mo-del as input for the European strength map. – Engine workshop,“Defining, exploring, imaging and assessing reservoirs for po-tential heat exchange”, Potsdam, Germany, 6-8 November 2006.

TUNCAY K. & ORTOLEVA P. (2004). – Quantitative basin modeling: pre-sent-state and future developments towards predictability. –Geofluids, 4, 23-39.

VAN KEKEN P.E., SPIERS C.J., VAN DEN BERG A.P. & MUYZERT E.J. (1993). –The effective viscosity of rocksalt: implementation of steady-state creep laws in numerical models of salt diapirism. – Tecto-nophysics, 225, 457-476.

VASSEUR G. (1982). – Synthèse des résultats de flux géothermique enFrance. – Ann. Géophys., 38, 189-201.

VASSEUR G. & NOURI Y. (1980). – Trend of heat flow in France: relationwith deep structures. – Tectonophysics, 65, 209-223.

VENDEVILLE B. (2007). – Déstabilisation des couches salifères sous un bas-sin ou une marge; surcharge sédimentaire, glissement et étale-ment gravitaires. – SGF meeting “Tectonique récente de laProvence: rôle des couches ductiles”, Aix-en-provence, 14-15juin 2007.

VENDEVILLE B.C. & JACKSON M.P.A. (1992). – The fall of diapirs duringthin-skinned extension. – Mar. Petrol. Geol., 9, 354-371.

VOSTEEN A. & SCHELLSCHMIDT R. (2003). – Influence of temperature onthermal conductivity, thermal capacity and thermal diffusivityfor different types of rocks. – Phys. Chem. Earth, 28, 499-509.

WEIJERMARS R., JACKSON M.P.A. & VENDEVILLE B. (1993). – Rheologicaland tectonic modeling of salt provinves – Tectonophysics, 217,143-174.

YANG J.M. (1981). – In: L.H. GEVANTMAN, Ed., Physical properties data forrock salt. – Monograph 167, National Bureau of Standards, Was-hington, D.C., 205-221.



Heat flow and deep temperatures in the Southeast Basin of France: Implications for local rheological...

Documents

Transcript of Heat flow and deep temperatures in the Southeast Basin of France: Implications for local rheological...