jeanflop/post_ocr_correction2 huggingface dataset:
des âges compris entre 210 et 190 Ma. ([12], [13], [14]). L'intrusion se place ainsi vers la limite Trias-Lias [15]. Les mesures 40K-40Ar, effectuées sur le filon de Kemenez, ont donné des âges plus anciens, de: 243 + 12 Ma. [2]; 233 + 12 Ma. [14]. Les mesures réalisées par la même méthode sur le filon de Landivisiau ont fourni un âge isotopique moyen de 206,5 +10,5 Ma. (tableau II, éch. LC 85/126), qui indique, comme à Brenterc'h, une injection vers la limite Trias-Lias. Au total, les dolérites post-hercyniennes du Pays de Léon présentent les caractères suivants: (1) Grande homogénéité de composition chimique, indiquant la même source magmatique (affinité de tholeiite continentale); (2) Direction structurale semblable (N 130°E) suggérant le même régime tectonique; (3) Large extension latérale (plus de 60 km d'ouest en est dans l'état actuel des connaissances); (4) Intrusions possibles à deux périodes principales : durant le Trias et à la limite Trias-Lias. CONCLUSIONS. — Les résultats obtenus incitent à penser qu'à la fin des temps hercyniens, le Pays de Léon — et, d'une manière plus générale le Massif armoricain — a été le siège d'une activité magmatique plus importante qu'il n'était jusqu'ici soupçonné: (1) le magmatisme acide, souligné par des injections de microgranites, à dominantes potassique, est essentiellement d'âge permien; (2) le magmatisme lamprophyrique, potassique, peut être également rapporté à l'époque permienne; (3) le magmatisme doléritique tholeiitique, plus récent, se manifeste au Trias et vers la limite Trias-Lias. Au magmatisme de croûte continentale, encore lié à l'épilogue hercynien (microgranites et lamprophyres permiens) succède, au début du Secondaire, un magmatisme basaltique tholeiitique, à signification pré-atlantique. Note remise le 14 septembre 1988, acceptée le 9 novembre 1988. RÉFÉRENCES BIBLIOGRAPHIQUES [1] L. CHAURIS et coll., Bull. Soc. géol. minéral. Bretagne, C, 9, 1977, p. 5-17. [2] H. BELLON et coll, C.R. Acad. Sci. Paris, 301, série II, 1985, p. 297-302. [3] G. S. ODIN et N. H. GALE, C.R. Acad. Sci. Paris, 294, série II, 1982, p. 453-456. [4] L. CHAURIS et B. HALLEGOUET, Carte géol. à 1/50000, feuille Le Conquet (sous presse). [5] L. CHAURIS et B. HALLEGOUET, Carte
souligné par des injections de microgranites, à dominantes potassique, est essentiellement d'âge permien; (2) le magmatisme lamprophyrique, potassique, peut être également rapporté à l'époque permienne; (3) le magmatisme doléritique tholeiitique, plus récent, se manifeste au Trias et vers la limite Trias-Lias. Au magmatisme de croûte continentale, encore lié à l'épilogue hercynien (microgranites et lamprophyres permiens) succède, au début du Secondaire, un magmatisme basaltique tholeiitique, à signification pré-atlantique. Note remise le 14 septembre 1988, acceptée le 9 novembre 1988. RÉFÉRENCES BIBLIOGRAPHIQUES [1] L. CHAURIS et coll., Bull. Soc. géol. minéral. Bretagne, C, 9, 1977, p. 5-17. [2] H. BELLON et coll, C.R. Acad. Sci. Paris, 301, série II, 1985, p. 297-302. [3] G. S. ODIN et N. H. GALE, C.R. Acad. Sci. Paris, 294, série II, 1982, p. 453-456. [4] L. CHAURIS et B. HALLEGOUET, Carte géol. à 1/50000, feuille Le Conquet (sous presse). [5] L. CHAURIS et B. HALLEGOUET, Carte géol. à 1/50000, feuille Plouarzel (sous presse). [6] Y. GEORGET et coll., C.R. Acad. Sci. Paris, 302, série II, 1986, p. 237-242. [7] C. BARROIS, Carte géol. à 1/80000, feuille Plouguerneau, 1893. [8] C. BARROIS, Carte géol à 1 /80 000, feuille Lannion, 1909. [9] C. BARROIS, Carte géol. à 1/80000, feuille Quimper, 1891. [10] P. THONON et coll., T R.A.S.T., Lyon, 1979, p. 445. [11] A. FABRE et H. BELLON, 10e R.A.S.T., Bordeaux, 1984, p. 214. [12] C. J. D. A. ADAMS, Ph. D. Thesis, inédit, Oxford, 1967. [13] F. LEUTWEIN et coll., C.R. Acad. Sci. Paris, 275, série D, 1972, p. 1327-1330. [14] A. FABRE, Thèse, U.B.O., Brest, 1986, 156 p. [15] G. S. ODIN et W. S. KENNEDY, C.R. Acad. Sci. Paris, 294, série II, 1982, p. 383-386. H.B., L.C. et P.T. : Faculté des Sciences, G.I.S. Océanologie et Géodynamique, Département des Sciences de la Terre, U.B.O., 29287 Brest; B.H. : Laboratoire de Géographie de la Mer et des Littoraux, E.R. 27 du C.N.R.S., U.B.O., B.P. n° 814, 29285 Brest. C.R. Acad. Sci. Paris, t. 307, Série II, p. 2055-2060, 1988 2055 Géologie/Geo/ogy Premières descriptions pétrographiques de la série de pyroclastites du bassin sédimentaire mio-pliocène de l'oued
1/80000, feuille Quimper, 1891. [10] P. THONON et coll., T R.A.S.T., Lyon, 1979, p. 445. [11] A. FABRE et H. BELLON, 10e R.A.S.T., Bordeaux, 1984, p. 214. [12] C. J. D. A. ADAMS, Ph. D. Thesis, inédit, Oxford, 1967. [13] F. LEUTWEIN et coll., C.R. Acad. Sci. Paris, 275, série D, 1972, p. 1327-1330. [14] A. FABRE, Thèse, U.B.O., Brest, 1986, 156 p. [15] G. S. ODIN et W. S. KENNEDY, C.R. Acad. Sci. Paris, 294, série II, 1982, p. 383-386. H.B., L.C. et P.T. : Faculté des Sciences, G.I.S. Océanologie et Géodynamique, Département des Sciences de la Terre, U.B.O., 29287 Brest; B.H. : Laboratoire de Géographie de la Mer et des Littoraux, E.R. 27 du C.N.R.S., U.B.O., B.P. n° 814, 29285 Brest. C.R. Acad. Sci. Paris, t. 307, Série II, p. 2055-2060, 1988 2055 Géologie/Geo/ogy Premières descriptions pétrographiques de la série de pyroclastites du bassin sédimentaire mio-pliocène de l'oued Zouara (Nefza, Tunisie septentrionale) Nejia LARIDHI OUAZAA Résumé — Les pyroclastites du bassin sédimentaire mio-pliocène de l'oued Zouara sont constituées par l'alternance de bancs de conglomérats polygéniques, de niveaux de chute de ponces et de cendres et des niveaux de tufs à diatomées. Dans la région de Nefza, une activité volcanique explosive, avec émission d'un magma acide riche en phase fluide, a été contemporaine de la sédimentation. First pétrographic descriptions of the pyroclastic deposits of the oued Zouara mio-pliocene sedimentary basin (Nefza, the northern part of Tunisia) Abstract — Pyroclastic deposits of Miocene-Pliocene sedimentary basin, are composed of alternative banks of polygenic conglomerates, pumice fall and volcanic ash levels, and tuff levels with diatoms. In this locality an explosive volcanic activity with emission of acid and magma rich in fluids was contemporaneous to sedimentation. Abridged English Version — The pyroclastic deposits of the Miocene-Pliocene sedimentary basin of Oued Zouara are interstratified in the series of Makta el Haddid. They look like a band in the SW-NE direction on the northern side of a Triassic diapir (Fig.). Such an occurrence of acid volcanic rocks in relation with the post-nappe Neogene in the Nefza basin has been mentioned by several authors ([1],
volcanique explosive, avec émission d'un magma acide riche en phase fluide, a été contemporaine de la sédimentation. First pétrographic descriptions of the pyroclastic deposits of the oued Zouara mio-pliocene sedimentary basin (Nefza, the northern part of Tunisia) Abstract — Pyroclastic deposits of Miocene-Pliocene sedimentary basin, are composed of alternative banks of polygenic conglomerates, pumice fall and volcanic ash levels, and tuff levels with diatoms. In this locality an explosive volcanic activity with emission of acid and magma rich in fluids was contemporaneous to sedimentation. Abridged English Version — The pyroclastic deposits of the Miocene-Pliocene sedimentary basin of Oued Zouara are interstratified in the series of Makta el Haddid. They look like a band in the SW-NE direction on the northern side of a Triassic diapir (Fig.). Such an occurrence of acid volcanic rocks in relation with the post-nappe Neogene in the Nefza basin has been mentioned by several authors ([1], [2]). DESCRIPTION. — The section under investigation is located on the left bank of Oued Sifane. The pyroclastites made up of heterogeneous materials have a stratified aspect. On their base, there is an outflow of altered rhyolite. On their summit, there is a sedimentary level made up of volcanic elements which gradually change into clay and lacustrine limestones. The polygenic conglomerates are made up of volcanic lava blocks of different size and composition. Therefore, we notice:— Rhyolitic lava blocks made up of plagioclase An45An28, sanidine Or79-Or74, biotite, cordierite, quartz and opaques. — Welded tuff blocks or ignimbrites (Photo 2): their mineral paragenesis comprises sanidine Or80-Or76, angular small fragments of quartz. The biotite is rare. — Silicified rhyolites with tourmaline (luxianite). The pumice fall and volcanic ash levels are clear and can be stratified locally. They include:— Pumice levels made up of pumice fragments linked together by a very fine volcanic ash cement (Photo 1). — Ash levels made up of more or less ovoid volcanic ash fragments in a matrix of finely pulverized glass (Photo 4). The tuffs are made up of pyroclastic debris of various size and order (bubble glass, Photo 8; indurated volcanic ash: dark scoria, Photo 7;
which gradually change into clay and lacustrine limestones. The polygenic conglomerates are made up of volcanic lava blocks of different size and composition. Therefore, we notice:— Rhyolitic lava blocks made up of plagioclase An45An28, sanidine Or79-Or74, biotite, cordierite, quartz and opaques. — Welded tuff blocks or ignimbrites (Photo 2): their mineral paragenesis comprises sanidine Or80-Or76, angular small fragments of quartz. The biotite is rare. — Silicified rhyolites with tourmaline (luxianite). The pumice fall and volcanic ash levels are clear and can be stratified locally. They include:— Pumice levels made up of pumice fragments linked together by a very fine volcanic ash cement (Photo 1). — Ash levels made up of more or less ovoid volcanic ash fragments in a matrix of finely pulverized glass (Photo 4). The tuffs are made up of pyroclastic debris of various size and order (bubble glass, Photo 8; indurated volcanic ash: dark scoria, Photo 7; accretion-zoned lapilli, Photo 3 and welded tuff) and epiclastic materials originating from numidian sandstone. The whole series was deposited in an aqueous environment (presence of diatoms, Photos 5, 6). INTERPRETATION OF THE PYROCLASTIC DEPOSITS SETTING. — The pumice fall and the volcanic ash levels reveal volcanic activity of an explosive kind, in the form of pyroclastic materials which have settled in an aqueous environment as shown by the presence of diatoms. Quartz, alkali feldspar and plagioclase crystals constitute the dominant paragenesis of these rocks. Cordierite is the characteristic mineral of this hyperaluminous magma. For the first time, it has been demonstrated that volcano-sedimentary formations of Oued Zouara are pyroclastites which are the product of explosive volcanic activity, contemporaneous to sedimentation. I. INTRODUCTION. — The basin sedimentary of Oued Zouara is situated in the region of Nefza and forms part of a series of small basin sedimentaries installed at the Mio-Pliocene on the nappes of the Flysch Numidien. The terrains constituting the basin of Oued Zouara consist of three formations which are: the series sedimentary of Sidi Emmbarek, the series volcanic and sedimentary of Mokta el Hadid and the series sedimentary of Sidi el Berrak. The series of pyroclastites is interstratified
kind, in the form of pyroclastic materials which have settled in an aqueous environment as shown by the presence of diatoms. Quartz, alkali feldspar and plagioclase crystals constitute the dominant paragenesis of these rocks. Cordierite is the characteristic mineral of this hyperaluminous magma. For the first time, it has been demonstrated that volcano-sedimentary formations of Oued Zouara are pyroclastites which are the product of explosive volcanic activity, contemporaneous to sedimentation. I. INTRODUCTION. — The basin sedimentary of Oued Zouara is situated in the region of Nefza and forms part of a series of small basin sedimentaries installed at the Mio-Pliocene on the nappes of the Flysch Numidien. The terrains constituting the basin of Oued Zouara consist of three formations which are: the series sedimentary of Sidi Emmbarek, the series volcanic and sedimentary of Mokta el Hadid and the series sedimentary of Sidi el Berrak. The series of pyroclastites is interstratified within the series of Mokta el Hadid and appears as a band of direction SW-NE on the flank north of the diapir Triasique between the embouchure of Oued Zouara and the village of Ouled Gassen (fig.). The presence of these rocks volcanic acids in relation with the Neogene post-nappe within the basin of Nefza has been mentioned by several authors ([1], [2]). II. DESCRIPTION OF THE FACIES. — A section has been made at the level of the left bank of Oued Sifane. The pyroclastites have an aspect stratified and the beds almost vertical show that the material is heterogeneous. The series of pyroclastites is formed by the alternation of layers of variable thickness (a few centimeters up to a meter) of conglomerates polygenics, of levels of fall of pumice and ashes, of levels of ashes and of nuées ardentes; the series ends by a level sedimentary with volcanic elements which passes progressively to clays then to calcaires lacustres presenting numerous silicifications and levels with hematite and with goethite. At the base of the series of pyroclastites exists a flow of rhyolite fairly altered of color blanchâtre. 1. The conglomerate polygenique. — It is a conglomerate grossier formed of blocks
the basin of Nefza has been mentioned by several authors ([1], [2]). II. DESCRIPTION OF THE FACIES. — A section has been made at the level of the left bank of Oued Sifane. The pyroclastites have an aspect stratified and the beds almost vertical show that the material is heterogeneous. The series of pyroclastites is formed by the alternation of layers of variable thickness (a few centimeters up to a meter) of conglomerates polygenics, of levels of fall of pumice and ashes, of levels of ashes and of nuées ardentes; the series ends by a level sedimentary with volcanic elements which passes progressively to clays then to calcaires lacustres presenting numerous silicifications and levels with hematite and with goethite. At the base of the series of pyroclastites exists a flow of rhyolite fairly altered of color blanchâtre. 1. The conglomerate polygenique. — It is a conglomerate grossier formed of blocks of volcanic rocks of various nature, at contours more or less rounded, of 1 to 15 cm in diameter. The size of these blocks exceeds sometimes the meter. Among these blocks, one distinguishes: (a) Of blocks of rhyodacitic lavas. — The rock is of color grey-greenish. Fissures of "retrait" (contraction thermique) linked to the cooling of the lava emitted have been observed on a great part of these blocks. It contains phénocristals of plagioclase, sanidine, biotite, cordierite, quartz and opaques, within a paste vitreous, perlitique, the glass is incolore and very fresh. The plagioclases are zoned and the composition general is that of an andesine An45An28. The compositions of the sanidines vary very little Or79-Or74. The presence of cordierite marks the character hyperaluminous of the lava. (b) Of blocks of tuf soudé or ignimbrite. — The rock is of color white greyish, at texture vitroclastique. It is formed by shards vitreuses allongées and welded (photo 2). The microcristals are not abundant. The plagioclase is absent, the sanidine is rare and its composition varies little Or80 to Or76; the biotite is very rare, it is under form of paillettes microscopiques; the quartz appears under form of small fragments angular coming from
thermique) linked to the cooling of the lava emitted have been observed on a great part of these blocks. It contains phénocristals of plagioclase, sanidine, biotite, cordierite, quartz and opaques, within a paste vitreous, perlitique, the glass is incolore and very fresh. The plagioclases are zoned and the composition general is that of an andesine An45An28. The compositions of the sanidines vary very little Or79-Or74. The presence of cordierite marks the character hyperaluminous of the lava. (b) Of blocks of tuf soudé or ignimbrite. — The rock is of color white greyish, at texture vitroclastique. It is formed by shards vitreuses allongées and welded (photo 2). The microcristals are not abundant. The plagioclase is absent, the sanidine is rare and its composition varies little Or80 to Or76; the biotite is very rare, it is under form of paillettes microscopiques; the quartz appears under form of small fragments angular coming from the fracturation of the crystals. (c) Of blocks of lavas with texture microgrenue: rhyolite silicifiée. — The rock is clear and fairly hard, the microphénocristals appear in the form of small lathes of plagioclase, feldspath alcalin subautomorphe with sometimes the macle of Carlsbad, of quartz; the mesostase is completely recrystallized under form of a mosaic of quartz; the tourmaline (luxianite) of origin vraisemblablement pneumatolytique exists in the form of automorphic crystals greenish-blue and at disposition radial. These blocks are linked by a matrix of volcanic glass very fine with debris of crystals of quartz and of feldspar. 2. The levels of falls of pumice and of ashes. — The levels are clear, generally whitish, lightly jaunâtre or greyish. Locally these levels can be stratified which gives to the rock an aspect of jaspe. (a) The levels of pumice. — They are constituted almost exclusively of fragments of pumice vacuolar of color greyish, of form ovoid or angular émoussée. These fragments come from the recent alluvions. Formation de pente, recouvrement divers, dunes récentes, dunes anciennes, Miocène supérieur, roches basiques, Miocène supérieur, rhyolites et pyroclastites, Miocène supérieur, conglomérats polygéniques, Miocène inférieur, « Numidien », Oligocène supérieur-« Numidien », Trias salifère, — Failles
under form of a mosaic of quartz; the tourmaline (luxianite) of origin vraisemblablement pneumatolytique exists in the form of automorphic crystals greenish-blue and at disposition radial. These blocks are linked by a matrix of volcanic glass very fine with debris of crystals of quartz and of feldspar. 2. The levels of falls of pumice and of ashes. — The levels are clear, generally whitish, lightly jaunâtre or greyish. Locally these levels can be stratified which gives to the rock an aspect of jaspe. (a) The levels of pumice. — They are constituted almost exclusively of fragments of pumice vacuolar of color greyish, of form ovoid or angular émoussée. These fragments come from the recent alluvions. Formation de pente, recouvrement divers, dunes récentes, dunes anciennes, Miocène supérieur, roches basiques, Miocène supérieur, rhyolites et pyroclastites, Miocène supérieur, conglomérats polygéniques, Miocène inférieur, « Numidien », Oligocène supérieur-« Numidien », Trias salifère, — Failles observées, — Failles supposées, Contacts anormaux des unités allochtones, Pendage normal, Pendage inverse. Extract of Neijra geological map, H. Rouvier 1/50,000 showing the localization of the pyroclastites series. Photo 3. — Lapilli d'accrétion zoné. Photo 3. — Accretion zoned lapilli. Photo 4. — Texture vitroclastique de débris de cendre volcanique. Photo 4. — Vitroclastic texture. Photos 5 et 6. — Diatomées pennées dans une matrice de verre volcanique. Photos 5 and 6. — Pennate diatoms. Photo 7. — Scories sombres dans une matrice de verre volcanique riche en débris de cristaux de quartz et feldspath. Photo 1. — Dark scories. Photo 8. — Débris de ponce, de cendre volcanique dans une matrice de verre volcanique très fin. Photo 8. — Débris of pumice and volcanic ash. C. R. Acad. Sci. Paris, t. 307, Série II, p. 2055-2060, 1988 Les fragments de ponces sont liés entre eux par un ciment de verre volcanique très fin, blanchâtre ou très légèrement coloré en brun. Ce verre est constitué par des échardes vitreuses tordues et coalescentes (photo 1). Les minéraux présents sont de rares fragments de quartz et de feldspath craquelés à faciès anguleux. (b) Les niveaux de cendres. — Ces niveaux sont blanchâtres
Photo 4. — Vitroclastic texture. Photos 5 et 6. — Diatomées pennées dans une matrice de verre volcanique. Photos 5 and 6. — Pennate diatoms. Photo 7. — Scories sombres dans une matrice de verre volcanique riche en débris de cristaux de quartz et feldspath. Photo 1. — Dark scories. Photo 8. — Débris de ponce, de cendre volcanique dans une matrice de verre volcanique très fin. Photo 8. — Débris of pumice and volcanic ash. C. R. Acad. Sci. Paris, t. 307, Série II, p. 2055-2060, 1988 Les fragments de ponces sont liés entre eux par un ciment de verre volcanique très fin, blanchâtre ou très légèrement coloré en brun. Ce verre est constitué par des échardes vitreuses tordues et coalescentes (photo 1). Les minéraux présents sont de rares fragments de quartz et de feldspath craquelés à faciès anguleux. (b) Les niveaux de cendres. — Ces niveaux sont blanchâtres ou beige clair et souvent friables. Ils sont formés par des fragments plus ou moins ovoïdes de cendre volcanique dans un ciment de verre finement pulvérisé. Cette roche est formée presque exclusivement d'échardes d'origine vitroclastique, très fines et coalescentes (photo 4); les phases cristallines présentes sont de très fins débris de quartz volcanique et de feldspath aux arêtes vives. 3. Les tufs. — Ils sont constitués par un assemblage de débris pyroclastiques de taille et de nature variées et de matériel épiclastique provenant des grès numidiens. Les éléments pyroclastiques sont des débris de : — verre bulleux à vacuoles arrondies, elliptiques ou étirées; le verre est frais et limpide (photo 8); — lave à texture hyaline perlitique dont le verre est très frais; — cendres volcaniques indurées; — scories sombres, les cavités sont de forme et de taille irrégulières, les cloisons sont épaisses (photo 7); — lapillis d'accrétion présentant un zonage (photo 3); — tufs soudés ou ignimbrite à texture vitroclastique formés d'échardes vitreuses. La matrice est formée par des cendres volcaniques très fines, certains niveaux sont enrichis en débris de cristaux de quartz (volcaniques et détritiques) et de feldspath limpide aux contours irréguliers et craquelés. Ce niveau est un