Pub Date : 2015-07-01DOI: 10.2113/GSSGFBULL.186.4-5.207
M. Séranne, J. Lamarche, F. Agosta
During the past decade, the objective of the Task Force Sedimentary Basins of the International Lithosphere Program (ILP) has been the encouragement of the dialogue among researchers studying the basin fill and the whole lithospheric structure. The ILP 2013 annual meeting of the Task Force Sedimentary Basin held in Marseille (October 14–18th) was aimed at reviewing the current research on the possible links between deep and shallow processes in the Mediterranean region. More than a hundred scientists from academy and industry attended the conference, which involved a two day-long field trip to the Pyrenean and Alpine Forelands of Provence. Research areas represented at the 2013 ILP annual meeting included all disciplines pertaining to geology, geophysics …
{"title":"An introduction to Lithosphere dynamics of sedimentary basins – The Circum-Mediterranean basins and analogues","authors":"M. Séranne, J. Lamarche, F. Agosta","doi":"10.2113/GSSGFBULL.186.4-5.207","DOIUrl":"https://doi.org/10.2113/GSSGFBULL.186.4-5.207","url":null,"abstract":"During the past decade, the objective of the Task Force Sedimentary Basins of the International Lithosphere Program (ILP) has been the encouragement of the dialogue among researchers studying the basin fill and the whole lithospheric structure. The ILP 2013 annual meeting of the Task Force Sedimentary Basin held in Marseille (October 14–18th) was aimed at reviewing the current research on the possible links between deep and shallow processes in the Mediterranean region. More than a hundred scientists from academy and industry attended the conference, which involved a two day-long field trip to the Pyrenean and Alpine Forelands of Provence. Research areas represented at the 2013 ILP annual meeting included all disciplines pertaining to geology, geophysics …","PeriodicalId":55978,"journal":{"name":"Bulletin de la Societe Geologique de France","volume":"12 1","pages":"207-208"},"PeriodicalIF":0.0,"publicationDate":"2015-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80304134","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2015-07-01DOI: 10.2113/GSSGFBULL.186.4-5.243
F. Cavalcante, G. Prosser, F. Agosta, C. Belviso, Giuseppe Corrado
The Gorgoglione Formation represents the infill of a thrust-top basin, which records the tectonic evolution of the southern Apennines (Italy) since Upper Miocene times. The Upper Miocene basin was divided into two main sub-basins, showing both about NNW-SSW elongation. During ongoing contractional deformation, the Gorgoglione basin was incorporated into the allochthonous units of the Apennine fold-and-thrust belt, as outlined by the emplacement of thrust sheets of internal provenance (Sicilide Unit) and by the development of two main generations of tight to open folds. In this work, the modalities of deformation associated to the incorporation of the Gorgoglione Formation into the fold-and-thrust belt has been documented by means of mineralogical and structural analyses. Mineralogical data show that, in the northeastern sub-basin of the Gorgoglione Formation, the illite content and the order of illite/smectite mixed layer increase near the contact with the overlaying Sicilide Unit. These data are hence used to estimate the relative tectonic load produced by thrusting of the aforementioned tectonic unit. Structural data are consistent with tight, NNW-trending, meso-scale folds particularly frequent in the upper pelitic/arenaceous portion of the Gorgoglione Formation. Within these folded pelitic levels, a well-developed axial-plane foliation, and an ordered I/S (R1 and R3) with higher illite content, is documented. Instead, other folds developed far away from the Sicilide klippen show an incipient axial-plane foliation and a random I/S (R0) with lower illite amount is found in pelites. The data suggest that the eastern sub-basin of the Gorgoglione Formation underwent variable tectonic load, increasing from E to W, as well as deformation produced by thrusting of Sicilide sheet. The mineralogical data also indicate that illitization process is favoured for the high availability of potassium due to the dissolution of k-feldspar. High potassium availability affects the samples subjected to the highest diagenetic degree, characterized by kaolinite illitization process.
{"title":"Post-depositional history of the Miocene Gorgoglione Formation (southern Apennines, Italy): inferences from mineralogical and structural analyses","authors":"F. Cavalcante, G. Prosser, F. Agosta, C. Belviso, Giuseppe Corrado","doi":"10.2113/GSSGFBULL.186.4-5.243","DOIUrl":"https://doi.org/10.2113/GSSGFBULL.186.4-5.243","url":null,"abstract":"The Gorgoglione Formation represents the infill of a thrust-top basin, which records the tectonic evolution of the southern Apennines (Italy) since Upper Miocene times. The Upper Miocene basin was divided into two main sub-basins, showing both about NNW-SSW elongation. During ongoing contractional deformation, the Gorgoglione basin was incorporated into the allochthonous units of the Apennine fold-and-thrust belt, as outlined by the emplacement of thrust sheets of internal provenance (Sicilide Unit) and by the development of two main generations of tight to open folds. In this work, the modalities of deformation associated to the incorporation of the Gorgoglione Formation into the fold-and-thrust belt has been documented by means of mineralogical and structural analyses. Mineralogical data show that, in the northeastern sub-basin of the Gorgoglione Formation, the illite content and the order of illite/smectite mixed layer increase near the contact with the overlaying Sicilide Unit. These data are hence used to estimate the relative tectonic load produced by thrusting of the aforementioned tectonic unit. Structural data are consistent with tight, NNW-trending, meso-scale folds particularly frequent in the upper pelitic/arenaceous portion of the Gorgoglione Formation. Within these folded pelitic levels, a well-developed axial-plane foliation, and an ordered I/S (R1 and R3) with higher illite content, is documented. Instead, other folds developed far away from the Sicilide klippen show an incipient axial-plane foliation and a random I/S (R0) with lower illite amount is found in pelites. The data suggest that the eastern sub-basin of the Gorgoglione Formation underwent variable tectonic load, increasing from E to W, as well as deformation produced by thrusting of Sicilide sheet. The mineralogical data also indicate that illitization process is favoured for the high availability of potassium due to the dissolution of k-feldspar. High potassium availability affects the samples subjected to the highest diagenetic degree, characterized by kaolinite illitization process.","PeriodicalId":55978,"journal":{"name":"Bulletin de la Societe Geologique de France","volume":"55 1","pages":"243-256"},"PeriodicalIF":0.0,"publicationDate":"2015-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85682219","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2015-07-01DOI: 10.2113/GSSGFBULL.186.4-5.353
Olivier Driussi, A. Briais, A. Maillard
Two major types of kinematic models have been proposed to explain the opening of the western Mediterranean basins (Liguro-Provencal and Algerian basins, and Valencia trough). In one type of models, all continental blocks bounding the basins drift to the southeast, driven by the rollback of the Tethys subduction slab. In the other type of models, the Alboran domain drifts to the southwest, implying a westward rollback of the broken subducting slab and a NE-SW opening of the Algerian basin. In most models, however, the structure of the Balearic promontory was not taken into account, despite its key location at the boundary of the three major basins. We used the interpretation of a large seismic database coupled to gravity and magnetic anomaly analyses to characterize the nature and structure of the South Balearic margin. The constraints brought by the new analyses allow us to suggest a new scenario for the opening of the Algerian basin. Seismic profiles show that the South Balearic margin is composed of four segments with different morphologies and crustal structures. Two segments, the Mazarron and the Emile Baudot escarpments, are characterized by steep scarps and sharp crustal thinning. Two other segments, the South Ibiza and South Menorca margins, have a smoother bathymetry and crustal thinning. We interpret the former in terms of transform margins, and the latter as divergent margins. The distribution of faults on the passive margin segments suggests that they have recorded at least two phases of deformation. A first phase of opening, probably in a NW-SE direction, affected the south Balearic margin, and possibly created some oceanic floor. The existence of the transform margin segments and the prominent NW-SE orientation of the magnetic lineations in the eastern Algerian basin suggest that most of this basin opened in a NE-SW direction, in different oceanic corridors. The two eastern corridors formed by the southwestward drift of the Kabylies. The western corridor, bounded by the transform segments of the South Balearic margin and the Algerian margin, results from the southwestward drift of the Alboran domain, as suggested by previous studies.
{"title":"Evidence for transform motion along the South Balearic margin and implications for the kinematics of opening of the Algerian basin","authors":"Olivier Driussi, A. Briais, A. Maillard","doi":"10.2113/GSSGFBULL.186.4-5.353","DOIUrl":"https://doi.org/10.2113/GSSGFBULL.186.4-5.353","url":null,"abstract":"Two major types of kinematic models have been proposed to explain the opening of the western Mediterranean basins (Liguro-Provencal and Algerian basins, and Valencia trough). In one type of models, all continental blocks bounding the basins drift to the southeast, driven by the rollback of the Tethys subduction slab. In the other type of models, the Alboran domain drifts to the southwest, implying a westward rollback of the broken subducting slab and a NE-SW opening of the Algerian basin. In most models, however, the structure of the Balearic promontory was not taken into account, despite its key location at the boundary of the three major basins. We used the interpretation of a large seismic database coupled to gravity and magnetic anomaly analyses to characterize the nature and structure of the South Balearic margin. The constraints brought by the new analyses allow us to suggest a new scenario for the opening of the Algerian basin. Seismic profiles show that the South Balearic margin is composed of four segments with different morphologies and crustal structures. Two segments, the Mazarron and the Emile Baudot escarpments, are characterized by steep scarps and sharp crustal thinning. Two other segments, the South Ibiza and South Menorca margins, have a smoother bathymetry and crustal thinning. We interpret the former in terms of transform margins, and the latter as divergent margins. The distribution of faults on the passive margin segments suggests that they have recorded at least two phases of deformation. A first phase of opening, probably in a NW-SE direction, affected the south Balearic margin, and possibly created some oceanic floor. The existence of the transform margin segments and the prominent NW-SE orientation of the magnetic lineations in the eastern Algerian basin suggest that most of this basin opened in a NE-SW direction, in different oceanic corridors. The two eastern corridors formed by the southwestward drift of the Kabylies. The western corridor, bounded by the transform segments of the South Balearic margin and the Algerian margin, results from the southwestward drift of the Alboran domain, as suggested by previous studies.","PeriodicalId":55978,"journal":{"name":"Bulletin de la Societe Geologique de France","volume":"5 1","pages":"353-370"},"PeriodicalIF":0.0,"publicationDate":"2015-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84735210","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2015-07-01DOI: 10.2113/GSSGFBULL.186.4-5.371
E. Casciello, M. Fernández, J. Vergés, M. Cesarano, M. Torné
Since the early 70’s the majority of tectonic reconstructions of the western Mediterranean employ the Alboran domain notion as a migrating microcontinent or landmass mainly composed of Paleozoic-Triassic rocks affected by ‘Alpine’ HP-LT metamorphism. For nearly three decades, since the mid-80’s, the Alboran domain was considered as a fragment of the Alpine chain that moved westward, colliding into Iberia and North Africa to produce the Gibraltar arc and Betic-Rif chain. In 2012, a new hypothesis for the evolution of the western Mediterranean was presented in which the Betic-Rif orogenic chain originates from rollback of an initially SE-dipping subduction of the westernmost segments of the Ligurian-Tethys under the Africa margin. This interpretation considers the metamorphic ‘Alboran domain’ rocks as crustal successions of the hyper-extended African and Iberian continental margins, which have undergone a complete subduction-exhumation cycle above a NW- to W-retreating subduction. A key outcome of this hypothesis is that the Alboran domain is not a fragment of the Alpine chain but a consequence of rollback dynamics. In this contribution we try to elucidate the historical reasons behind the classical ‘Alpine’ interpretation of the Betic-Rif, by briefly describing key contributions, which appear linked in a logical sequence that traces the evolution of the Alboran domain concept since its original formulation by Andrieux and coauthors in 1971.
{"title":"The Alboran domain in the western Mediterranean evolution: the birth of a concept","authors":"E. Casciello, M. Fernández, J. Vergés, M. Cesarano, M. Torné","doi":"10.2113/GSSGFBULL.186.4-5.371","DOIUrl":"https://doi.org/10.2113/GSSGFBULL.186.4-5.371","url":null,"abstract":"Since the early 70’s the majority of tectonic reconstructions of the western Mediterranean employ the Alboran domain notion as a migrating microcontinent or landmass mainly composed of Paleozoic-Triassic rocks affected by ‘Alpine’ HP-LT metamorphism. For nearly three decades, since the mid-80’s, the Alboran domain was considered as a fragment of the Alpine chain that moved westward, colliding into Iberia and North Africa to produce the Gibraltar arc and Betic-Rif chain. In 2012, a new hypothesis for the evolution of the western Mediterranean was presented in which the Betic-Rif orogenic chain originates from rollback of an initially SE-dipping subduction of the westernmost segments of the Ligurian-Tethys under the Africa margin. This interpretation considers the metamorphic ‘Alboran domain’ rocks as crustal successions of the hyper-extended African and Iberian continental margins, which have undergone a complete subduction-exhumation cycle above a NW- to W-retreating subduction. A key outcome of this hypothesis is that the Alboran domain is not a fragment of the Alpine chain but a consequence of rollback dynamics.\u0000\u0000In this contribution we try to elucidate the historical reasons behind the classical ‘Alpine’ interpretation of the Betic-Rif, by briefly describing key contributions, which appear linked in a logical sequence that traces the evolution of the Alboran domain concept since its original formulation by Andrieux and coauthors in 1971.","PeriodicalId":55978,"journal":{"name":"Bulletin de la Societe Geologique de France","volume":"44 1","pages":"371-384"},"PeriodicalIF":0.0,"publicationDate":"2015-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79951910","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2015-07-01DOI: 10.2113/GSSGFBULL.186.4-5.331
A. Afilhado, M. Moulin, D. Aslanian, P. Schnurle, F. Klingelhoefer, H. Nouzé, M. Rabineau, E. Leroux, M. Beslier
Geophysical data acquired on the conjugate margins system of the Gulf of Lion and West Sardinia (GLWS) is unique in its ability to address fundamental questions about rifting (i.e. crustal thinning, the nature of the continent-ocean transition zone, the style of rifting and subsequent evolution, and the connection between deep and surface processes).While the Gulf of Lion (GoL) was the site of several deep seismic experiments, which occurred before the SARDINIA Experiment (ESP and ECORS Experiments in 1981 and 1988 respectively), the crustal structure of the West Sardinia margin remains unknown. This paper describes the first modeling of wide-angle and near-vertical reflection multi-channel seismic (MCS) profiles crossing the West Sardinia margin, in the Mediterranean Sea. The profiles were acquired, together with the exact conjugate of the profiles crossing the GoL, during the SARDINIA experiment in December 2006 with the French R/V L’Atalante.Forward wide-angle modeling of both data sets (wide-angle and multi-channel seismic) confirms that the margin is characterized by three distinct domains following the onshore unthinned, 26 km-thick continental crust : Domain V, where the crust thins from ~26 to 6 km in a width of about 75 km; Domain IV where the basement is characterized by high velocity gradients and lower crustal seismic velocities from 6.8 to 7.25 km/s, which are atypical for either crustal or upper mantle material, and Domain III composed of “atypical” oceanic crust.The structure observed on the West Sardinian margin presents a distribution of seismic velocities that is symmetrical with those observed on the Gulf of Lion’s side, except for the dimension of each domain and with respect to the initiation of seafloor spreading. This result does not support the hypothesis of simple shear mechanism operating along a lithospheric detachment during the formation of the Liguro-Provencal basin.
在狮子湾和西撒丁岛(GLWS)的共轭边缘系统上获得的地球物理数据在解决裂谷作用的基本问题(即地壳变薄，大陆-海洋过渡带的性质，裂谷作用的风格和随后的演化，以及深层和表面过程之间的联系)方面具有独特的能力。虽然在撒丁岛实验(ESP和ECORS分别在1981年和1988年进行)之前，狮子湾(GoL)是几次深地震实验的地点，但西撒丁岛边缘的地壳结构仍然未知。本文首次对地中海西撒丁岛边缘的广角和近垂直反射多道地震剖面进行了建模。在2006年12月与法国R/V L 'Atalante进行的撒丁岛实验中，获得了这些剖面，以及穿越GoL的精确共轭剖面。两组数据的正演广角模拟(广角和多通道地震)证实，该边缘的特征是在陆上未变薄的26公里厚大陆地壳之后有三个不同的区域:V区，地壳变薄约26至6公里，宽度约75公里;ⅳ区基底以高速度梯度和6.8 ~ 7.25 km/s的下地壳地震速度为特征，对地壳和上地幔物质都是非典型;III区由“非典型”洋壳组成。在西撒丁岛边缘观测到的结构呈现出的地震速度分布与在狮子湾一侧观测到的地震速度分布是对称的，除了每个域的尺寸和海底扩张的开始。这一结果不支持利古罗-普罗旺斯盆地形成过程中沿岩石圈拆离作用的简单剪切机制假说。
{"title":"Deep crustal structure across a young passive margin from wide-angle and reflection seismic data (The SARDINIA Experiment) – II. Sardinia’s margin","authors":"A. Afilhado, M. Moulin, D. Aslanian, P. Schnurle, F. Klingelhoefer, H. Nouzé, M. Rabineau, E. Leroux, M. Beslier","doi":"10.2113/GSSGFBULL.186.4-5.331","DOIUrl":"https://doi.org/10.2113/GSSGFBULL.186.4-5.331","url":null,"abstract":"Geophysical data acquired on the conjugate margins system of the Gulf of Lion and West Sardinia (GLWS) is unique in its ability to address fundamental questions about rifting (i.e. crustal thinning, the nature of the continent-ocean transition zone, the style of rifting and subsequent evolution, and the connection between deep and surface processes).While the Gulf of Lion (GoL) was the site of several deep seismic experiments, which occurred before the SARDINIA Experiment (ESP and ECORS Experiments in 1981 and 1988 respectively), the crustal structure of the West Sardinia margin remains unknown. This paper describes the first modeling of wide-angle and near-vertical reflection multi-channel seismic (MCS) profiles crossing the West Sardinia margin, in the Mediterranean Sea. The profiles were acquired, together with the exact conjugate of the profiles crossing the GoL, during the SARDINIA experiment in December 2006 with the French R/V L’Atalante.Forward wide-angle modeling of both data sets (wide-angle and multi-channel seismic) confirms that the margin is characterized by three distinct domains following the onshore unthinned, 26 km-thick continental crust : Domain V, where the crust thins from ~26 to 6 km in a width of about 75 km; Domain IV where the basement is characterized by high velocity gradients and lower crustal seismic velocities from 6.8 to 7.25 km/s, which are atypical for either crustal or upper mantle material, and Domain III composed of “atypical” oceanic crust.The structure observed on the West Sardinian margin presents a distribution of seismic velocities that is symmetrical with those observed on the Gulf of Lion’s side, except for the dimension of each domain and with respect to the initiation of seafloor spreading. This result does not support the hypothesis of simple shear mechanism operating along a lithospheric detachment during the formation of the Liguro-Provencal basin.","PeriodicalId":55978,"journal":{"name":"Bulletin de la Societe Geologique de France","volume":"1 1","pages":"331-351"},"PeriodicalIF":0.0,"publicationDate":"2015-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89152969","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2015-03-01DOI: 10.2113/GSSGFBULL.186.2-3.117
D. Gapais, J. Brun, C. Gumiaux, F. Cagnard, G. Ruffet, C. L. C. D. Veslud
A synthesis of existing geological, structural and geophysical data shows that the south Armorican Hercynian belt was marked by syn-convergence crustal thinning and dextral wrenching that were in part coeval in late Carboniferous times. Our kinematic model is further supported by new structural data and 40Ar/39Ar ages on synkinematic leucogranites. Extension and strike-slip followed earlier crustal thickening and exhumation of high-pressure metamorphic units in late Devonian-early Carboniferous times. Crustal extension led to the development of core complexes cored by migmatites and crust-derived granite laccoliths. At this time, the South Armorican shear zone acted as a transfer zone separating the extending domain of South Brittany from the non-extending domain of Central Brittany submitted to dextral wrenching. The overall structural pattern and attached kinematics are compared with recent numerical models and illustrated by a 3D interpretative model that integrates geological and deep seismic reflection data (ARMOR 2 profile).
{"title":"Extensional tectonics in the Hercynian Armorican belt (France). An overview","authors":"D. Gapais, J. Brun, C. Gumiaux, F. Cagnard, G. Ruffet, C. L. C. D. Veslud","doi":"10.2113/GSSGFBULL.186.2-3.117","DOIUrl":"https://doi.org/10.2113/GSSGFBULL.186.2-3.117","url":null,"abstract":"A synthesis of existing geological, structural and geophysical data shows that the south Armorican Hercynian belt was marked by syn-convergence crustal thinning and dextral wrenching that were in part coeval in late Carboniferous times. Our kinematic model is further supported by new structural data and 40Ar/39Ar ages on synkinematic leucogranites. Extension and strike-slip followed earlier crustal thickening and exhumation of high-pressure metamorphic units in late Devonian-early Carboniferous times. Crustal extension led to the development of core complexes cored by migmatites and crust-derived granite laccoliths. At this time, the South Armorican shear zone acted as a transfer zone separating the extending domain of South Brittany from the non-extending domain of Central Brittany submitted to dextral wrenching. The overall structural pattern and attached kinematics are compared with recent numerical models and illustrated by a 3D interpretative model that integrates geological and deep seismic reflection data (ARMOR 2 profile).","PeriodicalId":55978,"journal":{"name":"Bulletin de la Societe Geologique de France","volume":"33 1","pages":"117-129"},"PeriodicalIF":0.0,"publicationDate":"2015-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73383567","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2015-03-01DOI: 10.2113/GSSGFBULL.186.2-3.131
P. Hasalová, K. Schulmann, A. Tabaud, E. Oliot
During orogenic processes continental crust experiences significant partial melting. Repeated thermal pulses or fluctuation in fluid content can even cause multiple anatectic events that result in complex intrusion suits. In the Vosges mountains, France, two main generations of magmatic rocks are recorded. The first magmatic event occurred at ca. 340 Ma, and is represented by extensive K-Mg granitoids magmatism. The second magmatic event occurred at ca. 325 Ma and produced large quantity of felsic anatectic melts which further pervasively intruded and compositionally and texturally reworked previously formed granitoids. Detailed field and microstructural observations revealed continuous transitions from porphyritic granite with large euhedral Kfs and Pl phenocrysts (Type I granite) via intermediate granite (Type II) to fine-grained apparently isotropic granite (Type III) dominated by the neo-crystallized melt. The Type I granite preserves the original magmatic assemblage and has only incipient amount of the newly crystallized melt. The new melt-crystallized material forms narrow, fine-grained pathways along grain boundaries or cuts across pre-existing magmatic grains and forms an interlinked network. With increasing amount of the newly crystallized material the original magmatic grains are resorbed and show highly corroded shapes. The early formed feldspars grains have strong compositional zoning, with oscillatory zoned cores reflecting range of original magmatic compositions and rims showing later melt overgrowths. Original magmatic feldspars have different composition from the new phases crystallizing in the partially molten granite. We interpret the fine-grained microscopic corridors as melt pathways that were exploited by the new magma. We suggest that this melt pervasively migrated through the older granitoids resulting in mixture of inherited “xenocrysts” and of new melt-derived crystals. The interaction between the new melt and previously crystallized granitoids results in variety of granite textures and fabrics. These reflect different degrees of equilibration between the bulk rock and the passing melt. Finally, Type III granite carries mixed isotopic signature intermediate between the type I granite and the surrounding metasediments and granulites, suggesting mixing of the original granite with new later magma with source in these rocks.
{"title":"Microstructural evidences for mineralogical inheritance in partially molten rocks: example from the Vosges Mts","authors":"P. Hasalová, K. Schulmann, A. Tabaud, E. Oliot","doi":"10.2113/GSSGFBULL.186.2-3.131","DOIUrl":"https://doi.org/10.2113/GSSGFBULL.186.2-3.131","url":null,"abstract":"During orogenic processes continental crust experiences significant partial melting. Repeated thermal pulses or fluctuation in fluid content can even cause multiple anatectic events that result in complex intrusion suits. In the Vosges mountains, France, two main generations of magmatic rocks are recorded. The first magmatic event occurred at ca. 340 Ma, and is represented by extensive K-Mg granitoids magmatism. The second magmatic event occurred at ca. 325 Ma and produced large quantity of felsic anatectic melts which further pervasively intruded and compositionally and texturally reworked previously formed granitoids. Detailed field and microstructural observations revealed continuous transitions from porphyritic granite with large euhedral Kfs and Pl phenocrysts (Type I granite) via intermediate granite (Type II) to fine-grained apparently isotropic granite (Type III) dominated by the neo-crystallized melt. The Type I granite preserves the original magmatic assemblage and has only incipient amount of the newly crystallized melt. The new melt-crystallized material forms narrow, fine-grained pathways along grain boundaries or cuts across pre-existing magmatic grains and forms an interlinked network. With increasing amount of the newly crystallized material the original magmatic grains are resorbed and show highly corroded shapes. The early formed feldspars grains have strong compositional zoning, with oscillatory zoned cores reflecting range of original magmatic compositions and rims showing later melt overgrowths. Original magmatic feldspars have different composition from the new phases crystallizing in the partially molten granite. We interpret the fine-grained microscopic corridors as melt pathways that were exploited by the new magma. We suggest that this melt pervasively migrated through the older granitoids resulting in mixture of inherited “xenocrysts” and of new melt-derived crystals. The interaction between the new melt and previously crystallized granitoids results in variety of granite textures and fabrics. These reflect different degrees of equilibration between the bulk rock and the passing melt. Finally, Type III granite carries mixed isotopic signature intermediate between the type I granite and the surrounding metasediments and granulites, suggesting mixing of the original granite with new later magma with source in these rocks.","PeriodicalId":55978,"journal":{"name":"Bulletin de la Societe Geologique de France","volume":"20 1","pages":"131-143"},"PeriodicalIF":0.0,"publicationDate":"2015-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81603213","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2015-03-01DOI: 10.2113/GSSGFBULL.186.2-3.63
R. Augier, Flavien Choulet, M. Faure, Paul Turrillot
By drastically reducing the bulk strength of crustal materials, partial-melting is one of the main parameter controlling the rheological behaviour of the continental crust. With more than ca. 50% of the outcropping surface characterised by migmatites and granites, the coastal South Armorican domain, offers an opportunity to study deep-orogenic processes and more particularly, to understand the role of partial-melting for the late-evolution of the Variscan belt. To date, time-constraints are scarce hindering the understanding of this crucial stage in the Variscan belt evolution. This paper provides 29 new U-Th/Pb chemical ages on monazite collected over five sampling areas consisting in migmatite domes and late regional classic plutons. Based on structural, textural and chemical criteria, three main U-Th/Pb age-groups are distinguished. The first group, settled at ca. 335–330 Ma concerns samples of restites and core-domains of the monazite crystals for most of the granite massifs. Its significance is ascribed to inherited crystallisation ages probably recording the crossing of prograde monazite forming reactions (i.e. metamorphic isograds) during increasing P-T conditions in an overall nappe-stacking context. The second group that clusters at ca. 325–320 Ma corresponds to newly formed monazite grains that crystallised from juvenile silicate melts. Ages of this group are interpreted as crystallisation ages of leucosomes after a major partial-melting event that affected the whole domain. The last ca. 320 Ma group corresponds to rim-domains of monazite crystals. It is interpreted as the emplacement age of most of the large-scale granite massifs and therefore fixes the end of the partial-melting event.The inception and drastic generalisation of partial-melting at peak-P conditions therefore coincides with a major change in the tectonic regime recorded at regional-scale. In the lights of these results, this implies that (1) either continuous stacking of continental crustal units, rich in radiogenic elements, led to an increase of temperature within the orogenic wedge provoking partial-melting, the resulting drop in the crustal strength inducing collapse and lateral expansion of the belt, or (2) a drastic change of the boundary conditions has induced hot asthenospheric upwelling which in turn led to coeval extension and partial-melting. At a more local scale, strain benefited of the low-strength of the magmatic bodies prior to complete crystallisation promoting intense strain localisation within the South Armorican domain large-scale laccoliths often referred to as synkinematic plutons.
{"title":"A turning-point in the evolution of the Variscan orogen: the ca. 325 Ma regional partial-melting event of the coastal South Armorican domain (South Brittany and Vendée, France)","authors":"R. Augier, Flavien Choulet, M. Faure, Paul Turrillot","doi":"10.2113/GSSGFBULL.186.2-3.63","DOIUrl":"https://doi.org/10.2113/GSSGFBULL.186.2-3.63","url":null,"abstract":"By drastically reducing the bulk strength of crustal materials, partial-melting is one of the main parameter controlling the rheological behaviour of the continental crust. With more than ca. 50% of the outcropping surface characterised by migmatites and granites, the coastal South Armorican domain, offers an opportunity to study deep-orogenic processes and more particularly, to understand the role of partial-melting for the late-evolution of the Variscan belt. To date, time-constraints are scarce hindering the understanding of this crucial stage in the Variscan belt evolution. This paper provides 29 new U-Th/Pb chemical ages on monazite collected over five sampling areas consisting in migmatite domes and late regional classic plutons. Based on structural, textural and chemical criteria, three main U-Th/Pb age-groups are distinguished. The first group, settled at ca. 335–330 Ma concerns samples of restites and core-domains of the monazite crystals for most of the granite massifs. Its significance is ascribed to inherited crystallisation ages probably recording the crossing of prograde monazite forming reactions (i.e. metamorphic isograds) during increasing P-T conditions in an overall nappe-stacking context. The second group that clusters at ca. 325–320 Ma corresponds to newly formed monazite grains that crystallised from juvenile silicate melts. Ages of this group are interpreted as crystallisation ages of leucosomes after a major partial-melting event that affected the whole domain. The last ca. 320 Ma group corresponds to rim-domains of monazite crystals. It is interpreted as the emplacement age of most of the large-scale granite massifs and therefore fixes the end of the partial-melting event.The inception and drastic generalisation of partial-melting at peak-P conditions therefore coincides with a major change in the tectonic regime recorded at regional-scale. In the lights of these results, this implies that (1) either continuous stacking of continental crustal units, rich in radiogenic elements, led to an increase of temperature within the orogenic wedge provoking partial-melting, the resulting drop in the crustal strength inducing collapse and lateral expansion of the belt, or (2) a drastic change of the boundary conditions has induced hot asthenospheric upwelling which in turn led to coeval extension and partial-melting. At a more local scale, strain benefited of the low-strength of the magmatic bodies prior to complete crystallisation promoting intense strain localisation within the South Armorican domain large-scale laccoliths often referred to as synkinematic plutons.","PeriodicalId":55978,"journal":{"name":"Bulletin de la Societe Geologique de France","volume":"36 1","pages":"63-91"},"PeriodicalIF":0.0,"publicationDate":"2015-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73830508","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2015-03-01DOI: 10.2113/GSSGFBULL.186.2-3.59
J. Lardeaux, P. Barbey
Publication of this special volume of the Bulletin de la Societe geologique de France, dedicated to the evolution of the southern segment of the European Variscan chain, is an opportunity for the French community of Geosciences to pay a friendly honoring tribute to Philippe Rossi, a tireless promoter of geology within the important institution that is the Bureau de Recherches Geologiques et Minieres (BRGM). After his secondary studies at the Lycee J.B. Corot in Savigny-sur-Orge, Philippe Rossi discovered geology at the Universite Paris-Sud (Orsay), where he defended in 1975 a Doctorat thesis entitled: “ Geologie et gitologie du Cerro San Cristobal Logrosan, Caceres, Espagne”. In the wake of his thesis, Philippe joined the BRGM where he went, from the 1980s, to play a prominent role as both a geologist specialist of the Variscan chain in Europe, and a key player of the evolution and accomplishment of the French mapping program (Programme de la Carte Geologique de la France). First of all, Philippe is recognized in our community as a researcher enthusiast about the petrologic and geodynamic evolution of the European Variscan chain. In 1986, he defended a Doctorat d’Etat thesis at the Universite P. Sabatier (Toulouse) entitled: “ Organisation et genese d’un grand batholite orogenique : le batholite calco-alcalin de la Corse ”. In parallel, Philippe has led the cartographic synthesis of Corsica at 1/250 000 published in 1980, and was involved in the survey of 7 geological maps at 1/50 000 in Corsica, to be published between 1984 and 2012. In 2009, he and his colleagues published a remarkable synthesis of the Corso-Sardinian segment of the Variscan chain, updated in 2014 with regard to the place of Corsica in the Variscan “puzzle”. This work conducted in collaboration with A. Cocherie within the BRGM, but also with many French and …
《法国地质学会公报》(Bulletin de la Societe geologique de France)这一专刊的出版，致力于欧洲Variscan链南段的演变，是法国地球科学界向菲利普·罗西(Philippe Rossi)表示友好敬意的机会，他是法国地质调查局(Bureau de Recherches Geologiques et Minieres，简称BRGM)这个重要机构中孜孜不倦的地质学推动者。菲利普·罗西在奥尔格河萨维尼的中学J.B.柯罗中学完成中学学业后，在巴黎第一大学(奥赛)发现了地质学，并于1975年在那里为他的博士论文辩护，题目是:“西班牙卡塞雷斯圣克里斯托瓦尔洛格罗桑的地质学”。在他的论文之后，菲利普加入了BRGM，从20世纪80年代开始，他作为欧洲Variscan链的地质学家专家和法国测绘计划(Programme de la Carte Geologique de la France)的发展和完成发挥了重要作用。首先，菲利普在我们的社区中被公认为是欧洲Variscan链的岩石学和地球动力学演化的研究爱好者。1986年，他在P. Sabatier大学(图卢兹)为一篇博士论文辩护，题目是:“大岩浆岩造山构造的组织:le batholite calco- calcalin de la Corse”。同时，菲利普还领导了1980年出版的科西嘉1/25万的地图合成，并参与了将于1984年至2012年出版的科西嘉1/5万地质图的调查。2009年，他和他的同事发表了一篇关于瓦里斯坎链的科西嘉-撒丁岛部分的非凡合成，并于2014年更新了科西嘉在瓦里斯坎“谜题”中的位置。这项工作是与BRGM内的A. Cocherie合作进行的，也与许多法国和…
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Pub Date : 2015-03-01DOI: 10.2113/GSSGFBULL.186.2-3.93
P. Barbey, A. Villaros, C. Marignac, J. Montel
The West European Variscan chain is a remarkable illustration of how partial melting marks out the geodynamic evolution of mountain belt through time. Here, we focus on the Late Carboniferous melting events reported in the southeastern French Massif Central (Velay dome), with emphasis on the modes of partial melting, relationships between partial melting and magma emplacement, transition between the melting episodes and related P-T-t path. Following nappe stacking events under medium pressure/temperature conditions (M1 and M2 events), three melting events are identified in the southern envelope of the Velay dome.A first melting episode (M3 event) occurred within the biotite stability field at 325–315 Ma (T ≈ 720°C and P = 0.5–0.6 GPa). It led to the complete disappearance of muscovite and to the formation of migmatites consisting of biotite ± sillimanite melanosome and of granitic/tonalitic leucosomes depending on protolith composition. It is interpreted as the result of internal heating mainly linked to decay of heat producing elements accumulated in a thickened crust. It resulted in the formation of a partially molten middle crust with decoupling between the lower and upper crust, late-collisional extension and crustal thinning.The second episode of melting (M4 event) occurred at ca. 304 Ma (T 800°C and P 0.4 GPa), synchronously with emplacement of the Velay granites and growth of the dome. It led to the breakdown of biotite and growth of cordierite (locally garnet or tourmaline), with formation of diatexites and heterogeneous granites. This high-T event synchronous with crustal extension is considered to result from intrusion of hot mantle-derived and lower crustal magmas triggering catastrophic melting in the middle crust. This event ends with local retrograde hydrous melting within the stability field of biotite close to the solidus in response to local input of water during temperature drop in the late stage of emplacement of the Velay dome.The last evidence of melting in this area (M5 event) corresponds to emplacement of late granites generated under conditions estimated at ≈850°C and 0.4–0.6 GPa. They may have been generated from melting of specific lithologies triggered by injection of mafic magmas. These granites emplaced in a partly cooled crust (medium-grade conditions). The emplacement age of these granites is not well constrained (305–295 Ma) though they clearly post-date the Velay granites.The melting episodes in the Velay area and generation of granites appear to correspond to the conjunction between (i) the effects of collision-related crust thickening and (ii) those related to slab break off and asthenospheric mantle decompression melting. The driving process is mainly the internal radiogenic heat in a first stage, relayed by the propagation of a thermal anomaly initially located in the lower crust (M3 event), but which subsequently rose to the middle and upper crustal levels through magma transfer (M4 event). Overall, the Velay
{"title":"Multiphase melting, magma emplacement and P-T-time path in late-collisional context: the Velay example (Massif Central, France)","authors":"P. Barbey, A. Villaros, C. Marignac, J. Montel","doi":"10.2113/GSSGFBULL.186.2-3.93","DOIUrl":"https://doi.org/10.2113/GSSGFBULL.186.2-3.93","url":null,"abstract":"The West European Variscan chain is a remarkable illustration of how partial melting marks out the geodynamic evolution of mountain belt through time. Here, we focus on the Late Carboniferous melting events reported in the southeastern French Massif Central (Velay dome), with emphasis on the modes of partial melting, relationships between partial melting and magma emplacement, transition between the melting episodes and related P-T-t path. Following nappe stacking events under medium pressure/temperature conditions (M1 and M2 events), three melting events are identified in the southern envelope of the Velay dome.A first melting episode (M3 event) occurred within the biotite stability field at 325–315 Ma (T ≈ 720°C and P = 0.5–0.6 GPa). It led to the complete disappearance of muscovite and to the formation of migmatites consisting of biotite ± sillimanite melanosome and of granitic/tonalitic leucosomes depending on protolith composition. It is interpreted as the result of internal heating mainly linked to decay of heat producing elements accumulated in a thickened crust. It resulted in the formation of a partially molten middle crust with decoupling between the lower and upper crust, late-collisional extension and crustal thinning.The second episode of melting (M4 event) occurred at ca. 304 Ma (T 800°C and P 0.4 GPa), synchronously with emplacement of the Velay granites and growth of the dome. It led to the breakdown of biotite and growth of cordierite (locally garnet or tourmaline), with formation of diatexites and heterogeneous granites. This high-T event synchronous with crustal extension is considered to result from intrusion of hot mantle-derived and lower crustal magmas triggering catastrophic melting in the middle crust. This event ends with local retrograde hydrous melting within the stability field of biotite close to the solidus in response to local input of water during temperature drop in the late stage of emplacement of the Velay dome.The last evidence of melting in this area (M5 event) corresponds to emplacement of late granites generated under conditions estimated at ≈850°C and 0.4–0.6 GPa. They may have been generated from melting of specific lithologies triggered by injection of mafic magmas. These granites emplaced in a partly cooled crust (medium-grade conditions). The emplacement age of these granites is not well constrained (305–295 Ma) though they clearly post-date the Velay granites.The melting episodes in the Velay area and generation of granites appear to correspond to the conjunction between (i) the effects of collision-related crust thickening and (ii) those related to slab break off and asthenospheric mantle decompression melting. The driving process is mainly the internal radiogenic heat in a first stage, relayed by the propagation of a thermal anomaly initially located in the lower crust (M3 event), but which subsequently rose to the middle and upper crustal levels through magma transfer (M4 event). Overall, the Velay","PeriodicalId":55978,"journal":{"name":"Bulletin de la Societe Geologique de France","volume":"9 1","pages":"93-116"},"PeriodicalIF":0.0,"publicationDate":"2015-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90439788","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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