Contribution of the RSCM Geothermometry to Detect the Thermal Anomalies and Peak Temperatures Induced by Fluid Circulation in Metasediments

International audienceThe occurrence of deposits hosted by carbonaceous materials-rich metasediments is widespread. For this reason, we propose in this study to investigate the potential of the Raman Spectroscopy of Carbonaceous Material (RSCM) geothermometry to detect thermal anomalies in hydrothermal ore deposits environment. The chosen geological context is the Lucia subterrane in the Franciscan Complex (California, USA), which includes gold-bearing quartz veins (Underwood et al., 1995). Estimated Raman temperatures 1) confirmed the increase in the metamorphic grade towards the north already shown by Underwood et al. (1995), using classical methods like mineralogy and vitrinite reflectance and 2) exhibit anomalous values. These anomalies are probably due to the later hydrothermal event. This result suggests that RSCM could be used as a reliable tool to determine thermal anomalies caused by hot fluid-flow

Evaluation du degré de maturité de la matière organique par spectroscopie Raman: extension du géothermomètre RSCM vers la gamme 100-200°C.

National audienceLa connaissance de températures de formation des roches est un paramètre important pour la reconstitution et la modélisation de l'histoire de domaines et de processus géologiques. Parmi les nombreuses possibilités d'estimation des températures, le géothermomètre RSCM (Raman Spectroscopy of Carbonaceous Materials) apporte un critère relativement précis pour reconstituer l'évolution thermique d'un domaine géologique (histoire température-temps) à partir de l'étude des composés carbonés ubiquistes (e.g. Beyssac et al., 2002, Aoya et al., 2010, Lahfid et al., 2010). Cet outil fournit ainsi des contraintes pertinentes sur l'histoire thermique des formations géologiques. Cependant, il n'a été calibré que pour la gamme 200-640°C avec une précision absolue de +/- 50°C et une reproductibilité interne bien meilleure de l'ordre de 10-15°C. La présente étude vise à étendre l'applicabilité du géothermomètre RSCM vers des températures plus basses que celles investiguées précédemment. Il s'agit de la gamme 100-200°C. Une série d'échantillons a été sélectionné. Parmi les zones d'échantillonnage figurent des bassins de la chaîne pyrénéenne. Les pics de températures de ces échantillons ont été estimés par des méthodes conventionnelles parmi lesquelles figurent le pouvoir réflecteur de la vitrinite, les inclusions fluides et la cristallinité de l'illite. Un nouveau protocole de mesure, par microspectroscopie Raman, pour caractériser la structure des matériaux carbonés très désordonnés a été établi. Lors de l'analyse, plusieurs paramètres ont été ajustés tels que la puissance du laser, le nombre d'analyses par échantillon, le temps d'acquisition... Une série de spectres de référence ont été alors acquis. Ces spectres ont permis de réaliser dans un premier temps une calibration qualitative de la méthode RSCM pour la gamme 100-200°C. Afin de proposer une calibration quantitative, nous sommes entrain de définir une procédure fiable d'ajustement des spectres Raman afin de déterminer des paramètres Raman pertinents pour la quantification thermique des matériaux carbonés très désordonnés dont les pics thermiques correspondent à la gamme 100-200°C. Cette calibration pourra être appliquée pour reconstituer l'histoire thermique des bassins de marge passive profonde (cible actuelle pour l'industrie pétrolière)

Raman Spectroscopy of Carbonaceous Materials geothermometry: a reliable method to investigate thermal history of foreland basins.

To investigate the thermal evolu-tion of foreland basins, many classical methods includ-ing clay mineralogy, vitrinite reflectance, fluid inclu-sions and illite cristalinity are used. These methods are probably not perfectly reliable taken individually, but provides a robust estimate when they give a coherent results. Raman Spectroscopy of Carbonaceous Materials (RSCM) could be an alternative method to constrain paleotempeartures of rocks. This method has been calibrated firstly in the range 330-640°C [1] then in the range 200-350° [2]. The aim of this study is to extend the applicability of this method towards palotemperatures lower than 200°C. For this purpose, we discuss a new fitting pro-cedure which would allow us to define a new Raman parameter R3. This parameter is different of RA1 [1] and R2 [2] used previously to characterize the thermal evolution of the Carbonaceous Materials. Raman spectra measured and treated are obtained by analysing samples from turbiditic deposits of differ-ent basins located in the western part of the South Pyrenean Zone. The thermal history of these samples, that underwent diagenesis, is well known using a vari-ous techniques. These methods are vitrinite reflec-tance, fluid inclusion thermometry, low-T thermochro-nology, index mineralogy and illite cristallinity. Although our results are preliminary, they suggest that the RSCM geothermometer could be a reliable method to constrain the thermal history of foreland basins. We are currently working on the acquisition of more data to determine temperatures of the basin that underwent diagenesis conditions during the Pyrenean activity. Referenc

Etude tectono-thermique d'un segment orogénique varisque à histoire géologique complexe : analyse structurale, géochronologique et thermique du massif des Jebilet, de l'extension à la compression

This thesis presents the reconstruction of the tectono-thermal history of the Paleozoic Jebilet massif (Morocco), from its pre-orogenic evolution at the Upper Devonian-Lower Carboniferous to its structuration during the variscan-alleghanian orogeny at the Upper Carboniferous-Lower Permian. To address this issue, this work is organized around two approaches: (1) one metrological applied to the Raman Spectroscopy of Carbonaceous Matterial (RSCM) and (2) the other integrating a structural and geochronological study and a thermicity analysis.The metrological approach allowed to validate the applicability of the RSCM geothermometer (1) in a context of polyphase metamorphism, (2) for carbonate rocks and skarns of Jebilet and (3) to propose a new parameter Raman RSA allowing to better specify temperatures above 500°C and extend the applicability of the method to maximum temperatures of up to 700°C.From the integrated approach, three tectono-thermal episodes were highlighted. The first episode D₀, corresponds to an extensive tectonic allowing the opening of the Jebilet basin at the Upper Devonian-Lower Carboniferous. This opening is accompanied by a HT thermal anomaly as shown by the important bimodal and granodioritic magmatic activity dated between 358 ± 7 Ma and 336 ± 4 Ma and the TRSCM higher than 500°C recorded by the rocks. During Upper Carboniferous, the compressive phase structuring the Jebilet massif begins with the emplacement of superficial nappes (D₁), followed by the variscan major phase (D2). Structural analysis showed a gradual evolution of D₂ deformation regime from coaxial compression to dextral transpression consistent with WNW-ESE to NW-SE horizontal shortening. D₂ is associated with two thermal events, the first is syn-tectonic with TRSCM between 300 and 400°C, and the second is syn- to post-tectonic with TRSCM between 600 and 660°C.This tectono-thermal context would be the expression of geodynamic processes involving from the Upper Devonian a delamination of the Rheic lithosphere by "slab break-off" or "slab roll-back" which would induce (1) the rise of hot asthenospheric current, and (2) the clockwise rotation of Gondwana and its gradual amalgamation with Laurussia structuring the variscan-alleghanian belt during the Upper Carboniferous-Lower Permian.Cette thèse présente la reconstruction de l’histoire tectono-thermique du massif varisque des Jebilet (Maroc) à fort potentiel minier, depuis son évolution pré-orogénique au Dévonien supérieur-Carbonifère inférieur jusqu’à sa structuration pendant l’orogénèse varisque-alléghanienne au Carbonifère supérieur-Permien inférieur. Pour répondre à cette problématique, ce travail s’organise autour de deux approches : (1) l’une métrologique appliquée à la géothermométrie Raman sur la matière carbonée (RSCM) et (2) l’autre intégrant une étude structurale, géochronologique et une analyse de la thermicité.L’approche métrologique a permis de valider l’applicabilité du géothermomètre RSCM (1) dans un contexte de métamorphisme polyphasé, (2) pour des roches carbonatées et des skarns des Jebilet et (3) de proposer un nouveau paramètre Raman RSA permettant de mieux préciser les températures supérieures à 500°C et d’étendre l’applicabilité de la méthode jusqu’à des températures maximales qui atteignent les 700°C.A partir de l’approche intégrée, trois épisodes tectono-thermiques ont été mis en évidence. Le premier épisode D₀ correspond à une tectonique extensive permettant l’ouverture du bassin des Jebilet au Dévonien supérieur-Carbonifère inférieur. Cette tectonique extensive est accompagnée par une anomalie thermique supérieure à 500°C déduites des mesures de géothermométrie RSCM (TRSCM) et par une importante activité magmatique bimodale et granodioritique datée dans ce travail entre 358 ± 7 et 336 ± 4 Ma. Au Carbonifère supérieur débute la phase compressive structurant le massif des Jebilet avec la mise en place de nappes superficielles au Namuro-Westphalien (D₁), suivie par la phase varisque majeure (D₂). L’analyse structurale a permis de montrer une évolution progressive du régime de déformation de D2 depuis une compression coaxiale à une transpression dextre compatible avec un raccourcissement horizontal WNW-ESE à NW-SE. D₂₁ est associée à deux événements thermiques, le premier syn-tectonique de moyenne température (300°<TRSCM<400°C), et le second syn- à post-tectonique de haute température (600°<TRSCM<660°C).Ce contexte tectono-thermique serait l’expression de processus géodynamiques impliquant à partir du Dévonien supérieur une délamination de la lithosphère rhéïque par « slab break-off » ou « slab roll-back » qui entrainerait (1) la remontée de courant asthénosphérique chaud, et (2) la rotation horaire de Gondwana et son amalgamation progressive avec Laurussia structurant au Carbonifère supérieur-Permien inférieur la chaine varisque-alléghanienne

Tectono-thermal study of a variscan orogenic segment with a complex geological history : structural, geochronological and thermal analysis of the Jebilet massif, from extension to compression

Cette thèse présente la reconstruction de l’histoire tectono-thermique du massif varisque des Jebilet (Maroc) à fort potentiel minier, depuis son évolution pré-orogénique au Dévonien supérieur-Carbonifère inférieur jusqu’à sa structuration pendant l’orogénèse varisque-alléghanienne au Carbonifère supérieur-Permien inférieur. Pour répondre à cette problématique, ce travail s’organise autour de deux approches : (1) l’une métrologique appliquée à la géothermométrie Raman sur la matière carbonée (RSCM) et (2) l’autre intégrant une étude structurale, géochronologique et une analyse de la thermicité.L’approche métrologique a permis de valider l’applicabilité du géothermomètre RSCM (1) dans un contexte de métamorphisme polyphasé, (2) pour des roches carbonatées et des skarns des Jebilet et (3) de proposer un nouveau paramètre Raman RSA permettant de mieux préciser les températures supérieures à 500°C et d’étendre l’applicabilité de la méthode jusqu’à des températures maximales qui atteignent les 700°C.A partir de l’approche intégrée, trois épisodes tectono-thermiques ont été mis en évidence. Le premier épisode D₀ correspond à une tectonique extensive permettant l’ouverture du bassin des Jebilet au Dévonien supérieur-Carbonifère inférieur. Cette tectonique extensive est accompagnée par une anomalie thermique supérieure à 500°C déduites des mesures de géothermométrie RSCM (TRSCM) et par une importante activité magmatique bimodale et granodioritique datée dans ce travail entre 358 ± 7 et 336 ± 4 Ma. Au Carbonifère supérieur débute la phase compressive structurant le massif des Jebilet avec la mise en place de nappes superficielles au Namuro-Westphalien (D₁), suivie par la phase varisque majeure (D₂). L’analyse structurale a permis de montrer une évolution progressive du régime de déformation de D2 depuis une compression coaxiale à une transpression dextre compatible avec un raccourcissement horizontal WNW-ESE à NW-SE. D₂₁ est associée à deux événements thermiques, le premier syn-tectonique de moyenne température (300°<TRSCM<400°C), et le second syn- à post-tectonique de haute température (600°<TRSCM<660°C).Ce contexte tectono-thermique serait l’expression de processus géodynamiques impliquant à partir du Dévonien supérieur une délamination de la lithosphère rhéïque par « slab break-off » ou « slab roll-back » qui entrainerait (1) la remontée de courant asthénosphérique chaud, et (2) la rotation horaire de Gondwana et son amalgamation progressive avec Laurussia structurant au Carbonifère supérieur-Permien inférieur la chaine varisque-alléghanienne.This thesis presents the reconstruction of the tectono-thermal history of the Paleozoic Jebilet massif (Morocco), from its pre-orogenic evolution at the Upper Devonian-Lower Carboniferous to its structuration during the variscan-alleghanian orogeny at the Upper Carboniferous-Lower Permian. To address this issue, this work is organized around two approaches: (1) one metrological applied to the Raman Spectroscopy of Carbonaceous Matterial (RSCM) and (2) the other integrating a structural and geochronological study and a thermicity analysis.The metrological approach allowed to validate the applicability of the RSCM geothermometer (1) in a context of polyphase metamorphism, (2) for carbonate rocks and skarns of Jebilet and (3) to propose a new parameter Raman RSA allowing to better specify temperatures above 500°C and extend the applicability of the method to maximum temperatures of up to 700°C.From the integrated approach, three tectono-thermal episodes were highlighted. The first episode D₀, corresponds to an extensive tectonic allowing the opening of the Jebilet basin at the Upper Devonian-Lower Carboniferous. This opening is accompanied by a HT thermal anomaly as shown by the important bimodal and granodioritic magmatic activity dated between 358 ± 7 Ma and 336 ± 4 Ma and the TRSCM higher than 500°C recorded by the rocks. During Upper Carboniferous, the compressive phase structuring the Jebilet massif begins with the emplacement of superficial nappes (D₁), followed by the variscan major phase (D2). Structural analysis showed a gradual evolution of D₂ deformation regime from coaxial compression to dextral transpression consistent with WNW-ESE to NW-SE horizontal shortening. D₂ is associated with two thermal events, the first is syn-tectonic with TRSCM between 300 and 400°C, and the second is syn- to post-tectonic with TRSCM between 600 and 660°C.This tectono-thermal context would be the expression of geodynamic processes involving from the Upper Devonian a delamination of the Rheic lithosphere by "slab break-off" or "slab roll-back" which would induce (1) the rise of hot asthenospheric current, and (2) the clockwise rotation of Gondwana and its gradual amalgamation with Laurussia structuring the variscan-alleghanian belt during the Upper Carboniferous-Lower Permian

The contribution of the RSCM geothermometry to detect the thermal anomalies in metasediments, induced by hidden intrusions and fluid circulation

International audienceThe study of the maturity of CM provides a relatively precise tool to estimate the thermal evolution of rocks and therefore to provide relevant constraints on the burial/exhumation history of geological formations. Both the CM structure and chemistry give information about the degree of transformation during the geological history that involves carbonization during advanced diagenesis, low-grade metamorphism and graphitization under more intense metamorphism. The characterization of the CM structure by Raman Spectroscopy can be used to estimate temperature maxima. Consequently, a new geothermometer has been developed, namely the Raman Spectroscopy of Carbonaceous Material (RSCM). This tool measures the structural evolution of the organic matter that is present in rocks. A version of the RSCM, proposed to accurately measure temperatures ranging from 330° to 650°C, was first developed by Beyssac et al (2002). Its application range was later expanded to lower temperatures between 200° and 350°C by Lahfid et al (2010).The objective of this study is to show the accuracy of the of the RSCM geothermometer to 1) delimit the metamorphic area due to hidden intrusions and 2) to elucidate the thermal anomalies induced by fluid-flow.For these purposes, we respectively have chosen the Guemassa massif (morocco), which includes the Hajjar Zn-Pb-Cu mine and the Lucia subterrane in the Franciscan Complex (California, USA), which includes gold-bearing quartz veins.In the Guemassa massif, our peak temperature estimated show values superior to 500°C. These temperatures differ from the ones obtained by other classical methods, which are not higher than 450°C. Nevertheless, fluid inclusion homogenization temperatures of 450°C represent minimum trapping temperature conditions, since the fluids were trapped above boiling conditions. Also, 450°C represents minimum thermic condition for the biotite isograd (Hibti, 2001). Higher Raman temperatures obtained in this work confirm the hypothesis of a late heat flow related to a deep granitic intrusion (Hibti, 2001, Watanabe, 2002). This intrusion could be closer to the Hajjar deposit which would explain the higher Raman temperature around the mineralization.The use of the RSCM geothermometry in the Lucia subterrane, reveals anomalous values of maximum temperature, recorded in Los Burros area (gold district). These anomalous values seem to be caused by a hydrothermal overprint in the Los Burros district.These results suggest that RSCM could be used as a reliable tool to geothermometer to determine the thermal effect of hidden intrusions and fluid circulations in metasediments

Méthodes d'analyse sur site et en temps réel pour la caractérisation multi-échelle chimique et minéralogique

International audienceAfin d’accélérer la caractérisation chimique et minéralogique des matières premières minérales au cours de leurs cycles de vie (exploration, extraction, transformation/procédé, recyclage/valorisation, stockage), les industriels sont à la recherche de solutions analytiques innovantes capables de réaliser des mesures sur site en temps réel pour répondre à leurs besoins.Récemment, la miniaturisation des composants analytiques associée à l'amélioration des équipements analytiques et l’utilisation de logiciels de traitement plus puissants et sophistiqués offre de nouvelles perspectives analytiques rapides et précises pour obtenir des informations chimiques et minéralogiques directement sur site en temps réel.Le projet européen collaboratif SOLSA a permis le développement de ce type de solution analytique qui reposent sur la combinaison d’analyses acquises par différents capteurs permettant de collecter en temps réel et directement sur site de grande quantité de données (morphologique, minéralogique, chimique) dont le traitement automatisé dans un référentiel de données unifiées via l’utilisation d’un logiciel décisionnel est une réelle avancée. Développé et testé pour opérer dans le domaine des mines et carrières dans un premier temps, la modularité de ce concept le rend utilisable dès qu’il est question de manipulation et de tri de matériaux, de suivi de production, de contrôle qualité ou encore pour améliorer les connaissances d’un process

Post-Metamorphic Thermal Anomaly across the Nacimiento Block, Central California: a Hydrothermal Overprint?

International audienceThe thermal history of the Nacimiento block located within the Franciscan Complex (California, USA) has been previously proposed based on both vitrinite reflectance (Rm) and illite cristallinity methods (Underwood et al., 1995). These authors suggest that the Nacimiento block is locally perturbed by a thermal anomaly (up to 300ºC), probably caused by post-metamorphic hydrothermal activity linked to the emplacement of an Au-deposit: the Los Burros Gold deposit. Although both thermal anomaly and deposit seem spatially correlated, their relationship is still poorly constrained. Detailed geological and structural mapping within the Los Burros Mining District (LBMD) coupled with a thermal study was conducted to better understand processes responsible for the anomalous temperatures recorded near the deposit. The regional maximum temperature reached by metasediments from the Nacimiento block have been first investigated using the Raman Spectroscopy of Carbonaceous Materials (RSCM) method. In addition, through careful fluid-inclusion and stable isotopes (O and C) studies on the deposit, the temperature and the potential source of the fluid responsible for the Los Burros Au-deposit emplacement were investigated. RSCM technique confirms the presence of a thermal anomaly in the range 260-320ºC near LBMD. However, our structural and petrographic results suggest that the thermal anomaly is not correlated to a post-metamorphic hydrothermal overprint but rather to a late, transpressive deformation uplifting buried metamorphic rocks

Post-Metamorphic Thermal Anomaly across the Nacimiento Block, Central California: a Hydrothermal Overprint?

International audienceThe thermal history of the Nacimiento block located within the Franciscan Complex (California, USA) has been previously proposed based on both vitrinite reflectance (Rm) and illite cristallinity methods (Underwood et al., 1995). These authors suggest that the Nacimiento block is locally perturbed by a thermal anomaly (up to 300ºC), probably caused by post-metamorphic hydrothermal activity linked to the emplacement of an Au-deposit: the Los Burros Gold deposit. Although both thermal anomaly and deposit seem spatially correlated, their relationship is still poorly constrained. Detailed geological and structural mapping within the Los Burros Mining District (LBMD) coupled with a thermal study was conducted to better understand processes responsible for the anomalous temperatures recorded near the deposit. The regional maximum temperature reached by metasediments from the Nacimiento block have been first investigated using the Raman Spectroscopy of Carbonaceous Materials (RSCM) method. In addition, through careful fluid-inclusion and stable isotopes (O and C) studies on the deposit, the temperature and the potential source of the fluid responsible for the Los Burros Au-deposit emplacement were investigated. RSCM technique confirms the presence of a thermal anomaly in the range 260-320ºC near LBMD. However, our structural and petrographic results suggest that the thermal anomaly is not correlated to a post-metamorphic hydrothermal overprint but rather to a late, transpressive deformation uplifting buried metamorphic rocks

Can we apply the RSCM geothermometry approach to study the thermal history of a complex tectono-metamorphic context: the Jebilet massif (Variscan Belt, Morocco)?

International audienceUnderstanding the thermal evolution of rocks is a key parameter to reconstruct basins or mountain belts history for industrial purposes. Varied geothermometers such as mineralogy, isotopes or illite crystallinity are commonly used to estimate paleotemperatures. However, these methods are not easy to use in all metamorphic contexts. An alternative approach is based physico-chemical transformation of organic material originally present in the rock. During geological time, the organic material undergoes two distinctive processes: (1) the carbonization during diagenesis and catagenesis and (2) the graphitization during metamorphism. Raman microspectroscopy is a suitable technique to study and measure these transformations. Beyssac et al. (2002) established a correlation between the temperature and a Raman parameter of the CM called R2. This parameter R2 varies between 0 and 0.7 and shows a correlation with the peak temperature of the metamorphism in the range 330-640°C. The RSCM geothermometer has an absolute precision of ± 50°C due to uncertainties on petrological data used for the calibration. The RSCM calibration established by Beyssac et al. (2002) was extended towards low temperatures in the range of 200-330°C with an absolute precision of ± 25°C (Lahfid et al., 2010). Until now, the reliability of the RSCM method has never been demonstrated for contexts with superposition of regional and contact metamorphism, such as many Variscan contexts. The present study aims at testing the applicability of the RSCM method to these polyphased metamorphism terrains and at investigating the cumulative molecular transformations of carbonaceous materials related to metamorphic superposition. To address the above issues, samples were collected in the Variscan Jebilet massif of the Moroccan Meseta. Mineralogical, thermobarometric and RSCM methods have been used in this study to determine the peak T recorded by the analysed rocks. The results obtained for greenschist facies metapelitic rocks show a good agreement between the mineralogical assemblage Chlorite–Phengite–Felspar–Quartz and theRaman temperatures ranging from 330 to 394 ± 50°C. In the metapelitic rocks that underwent higher metamorphism grades (hornfels/amphibolite facies), four dominant mineral assemblages were observed: (1) Chlorite–Biotite, (2) Cordierite–Biotite, (3) Andalusite–Garnet–Bt, (4) Andalusite–Cordierite–Biotite. The corresponding Raman temperatures vary respectively between 474 ± 50°C and 628 ± 50°C. The pseudo-sections generated for samples from the hornfels/amphibolite facies confirmed the peak temperatures measured by the RSCM method. Our results do not support clear evidence of potential molecular cumulative effect on CM triggered by overprinted metamorphism. Therefore, the RSCM method is suitable to investigate the peak temperature within a polymetamorphic context