10 research outputs found
PETROLOGIE ET GEOCHIMIE DES RHYOLITES D’AÏN SEDMA-COLLO (NE ALGERIEN) : ESSAI D’UN MODELE PETRO GENETIQUE
Le but de ce travail est de déterminer les caractéristiques et les variations pétrogéochimiques des rhyolites d’Aïn Sedma dans la région de Collo "NE algérien". Sur le plan géologique, ce complexe est constitué par quatre types de roches qui sont essentiellement représentées par des rhyolites, des granites, des microgranites et des microgranodiorites. Du point de vue pétrographique, les rhyolites montrent deux types de textures, une texture hyaline sphérolitique et l’autre microlitique porphyrique à tendance doléritique. Sa minéralogie, relativement constante, est composée principalement de quartz sphérolitique, plagioclase (andésine), orthose, biotite et rarement de muscovite, la chlorite et l’épidote apparaissent comme produits d’altération. Sur le plan géochimique, la rhyolite montre une forte proportion en SiO2, et une teneur en Na2O faible comparativement à celle de K2O. Elle appartient à la série calco alcaline hyper-potassique et montre un caractère peralumineux. La géochimie des traces et des terres rares représentées dans les diagrammes de discrimination géotectonique montrent que ces roches prennent naissances dans une croûte continentale pendant le stade de collision, à partir d’une source de magmas mafiques enrichis en LREE issues du manteau lithosphérique métasomatisé durant la subduction. Ces magmas ont ensuite évolué par cristallisation fractionnée et contamination crustale selon le modèle MASH (Melting-Assimilation-Storage-Homogeneization) en quarte phases pour former les roches filoniennes felsiques dans le secteur d’Aïn Sedma et au NW du Cap Bougaroun.MOTS CLES: Rhyolite, Aïn Sedma, NE Algérie, pétrographie, géochimie, pétrogenèse.ABSTRACTThe purpose of this work is to determine the characteristics and petrogeochemical changes for the rhyolites of Ain Sedma NE Algeria Collo. The study area is located at 11 kms northwest of the city of Collo. Geologically speaking this complex consists of four rock types: rhyolites, granites, microgranodiorite and microgranites. From petrography point of view, this rhyolite shows two types of texture, spherolitic hyaline texture and the other is microlitic porphyritic with dolerite trend. Its Mineralogy is relatively constant; it is mainly composed of spherulitic quartz, plagioclase (andesine), orthose, biotite and rarely muscovite, chlorite and epidote. geochemically this rhyolite shows a high proportion of SiO2, a low Na2O content compared to that of K2O and belongs to the hyper-potassium calc alkaline series and shows a peraluminous character. Trace geochemistry and rare earths combined with geotectonic discrimination diagrams show that these rocks originate in a continental crust during the collision stage, from a source of LREE enriched mafic magmas originating from the metasomatized lithospheric mantle during subduction , These magmas then evolved by fractional crystallization and crustal contamination according to the Melting-Assimilation-Storage-Homogeneization (MASH) model in the fourth phase to form the felsic vein rocks in the sector of Ain Sedma and NW of Cape Bougaroun
EVALUATION DES INDICES D’ALTERATION CHIMIQUE SUR UN PROFIL KAOLINISE CAS : TAMAZERT (NE ALGERIE)
Chemical weathering indices are commonly used for characterizing weathering profiles developed on heterogeneous or homogeneous parent rock by incorporating bulk major element oxide chemistry into single metric of each sample. Chemical weathering indices evaluated in this study are: weathering index of Parker (WIP), the chemical index of alteration (CIA), chemical index of weathering (CIW), plagioclase index of alteration (PIA), Ruxton ratio (R). The main purpose of this study is to review the scope of chemical weathering affected different gneissic rocks especially in Tamazert area and test the ability of application of chemical weathering index for heterogeneous alteration profiles. Petrology and geochemistry of the major elements of rock and alteration product have been discussed in this work.Les indices d’altération chimique sont couramment utilisés pour caractériser les profils d’altération développés sur des roches mères hétérogènes ou homogènes. Parmi les indices d’altération évalués dans cette étude, l’indice de Parker (WIP), l’indice chimique d’altération (CIA), l’indice de météorisation chimique (CIW), l’indice d’altération des plagioclases (PIA), Ruxton ratio (R). L’objectif principal de cette étude est d'examiné l'étendue de l'altération chimique affectée les différentes roches surtout gneissiques dans la zone de Tamazert et de tester l’aptitude d’application des indices d’altération chimique pour des profils d’altération hétérogènes. La pétrographie et la géochimie des éléments majeurs de la roche mère et du produit d’altération ont été discuté dans ce travail
EVALUATION DES INDICES D'ALTERATION CHIMIQUE SUR UN PROFIL KAOLINISE CAS : TAMAZERT (NE ALGERIE) ASSESSMENT OF CHEMICAL WEATHERING INDICES IN KAOLINISED PROFIL CASE: TAMAZERT (NE ALGERIA)
peer reviewedLes indices d'altération chimique sont couramment utilisés pour caractériser les profils d'altération développés sur des roches mères hétérogènes ou homogènes. Parmi les indices d'altération évalués dans cette étude, l'indice de Parker (WIP), l'indice chimique d'altération (CIA), l'indice de météorisation chimique (CIW), l'indice d'altération des plagioclases (PIA), Ruxton ratio (R). L'objectif principal de cette étude est d'examiné l'étendue de l'altération chimique affectée les différentes roches surtout gneissiques dans la zone de Tamazert et de tester l'aptitude d'application des indices d'altération chimique pour des profils d'altération hétérogènes. La pétrographie et la géochimie des éléments majeurs de la roche mère et du produit d'altération ont été discuté dans ce travail
Mineralogy and Paragenesis Associations of Polymetallic Deposits (Pb-Zn-Cu-Ag) of Boudoukha and Sidi Kambar—NE Algeria
The Filfila (NE Algeria) topaz-bearing granites and their rare metal minerals : petrologic and metallogenic implications.
International audienc
Le complexe granitique Langhien du Filfila (nord-est constantinois, Algérie) : granites à cordiérite, granites à tourmaline et granites à métaux rares. Nouvelles données minéralogiques et géochimiques et conséquences pétrologiques.
The Central Hoggar Taourirt and albite-topaz post pan-African granites (Southern Algeria); their petrology, geochemistry and petrogenesis.
Detailed field, petrological and mineralogical studies of two 540-520 Ma post Pan-African granitoids from Central Hoggar, southern Algeria, show them to have two contrasting mineralogies. The topaz-albite (AT) granitoids are peraluminous rocks containing protolithionite and were probably derived from a volatile-rich magma. The Taourirt (T) granites are also peraluminous but are siderophyllitic biotite- and hornblende-bearing rocks formed from a volatile poorer melt compared with the AT granites but the aplopegmatitic stockscheiders are genetically related to these AT granites. The protolithionites are Li- and F-rich (Li2O = 1.86 ± 0.58 wt %; F 3.65 ± 1.19 wt %) Mg-poor (0.12 ± 0.12 wt %) and have many unoccupied octahedral sites (ΣVI = 4.76 ± 0.27 a.p.f.u.). The substitutions 2Fe2+ (2M2+) (Ti4+) ↔ AlIV+Li commonly found in biotites occurring in similar granitoids were insignificant during the crystallization of biotite in the Hoggar AT granites and stockscheiders. The siderophyllitic biotites are Fe-rich (FeO* = 26.57 ± 3.38), relatively rich in Li (Li2O = 0.36 ± 0.15 wt %) and F (1.11 ± 0.68 wt %), and have variable Mg contents (MgO = 1.89 ± 1.01 wt %). The substitutions 2Fe2+ (2Mg2+(Ti4+) ↔ AlVILi, and 2Al ↔ 3Fe2+ (3Mg2+) were important during the crystallization of biotite in these T granites. The T granites, which have steep REE patterns, (Ce/Yb)CN = 5.96 ± 3.14, were generated by fractionation of plagioclase + K-feldspar + biotite + magnetite (ilmenite) ± hornblende ± allanite but the AT granites exhibit flat REE patterns (Ce/Yb)CN = 0.76 ± 0.52, and have formed by fractionation of mainly plagioclase ± biotite ± K-feldspar ± monazite. Modelling of Rb, Ba, Sr, La, Ce, Sm, Eu, Yb, Lu, Y and (87Sr/86Sr) isotopic ratios indicates that the two granites do not represent simple segregated melts, they were not generated by combined wall rock assimilation-fractional crystallization processes of an evolving mantle-derived magma nor do they represent the evolved end-members of the magma from which the spatially associated 670-570 Ma early-late Pan-African granites were crystallized. The chemistry of these early-late orogenic granites could be explained by subduction related magmatism whereas the the post Pan-African granites melts produced in the lower crust from heterogeneous sources
Le complexe granitique Langhien du Filfila (nord-est constantinois, Algérie) : granites à cordiérite, granites à tourmaline et granites à métaux rares. Nouvelles données minéralogiques et géochimiques et conséquences pétrologiques.
The Central Hoggar Taourirt and albite-topaz post pan-African granites (Southern Algeria); their petrology, geochemistry and petrogenesis.
Detailed field, petrological and mineralogical studies of two 540-520 Ma post Pan-African granitoids from Central Hoggar, southern Algeria, show them to have two contrasting mineralogies. The topaz-albite (AT) granitoids are peraluminous rocks containing protolithionite and were probably derived from a volatile-rich magma. The Taourirt (T) granites are also peraluminous but are siderophyllitic biotite- and hornblende-bearing rocks formed from a volatile poorer melt compared with the AT granites but the aplopegmatitic stockscheiders are genetically related to these AT granites. The protolithionites are Li- and F-rich (Li2O = 1.86 ± 0.58 wt %; F 3.65 ± 1.19 wt %) Mg-poor (0.12 ± 0.12 wt %) and have many unoccupied octahedral sites (ΣVI = 4.76 ± 0.27 a.p.f.u.). The substitutions 2Fe2+ (2M2+) (Ti4+) ↔ AlIV+Li commonly found in biotites occurring in similar granitoids were insignificant during the crystallization of biotite in the Hoggar AT granites and stockscheiders. The siderophyllitic biotites are Fe-rich (FeO* = 26.57 ± 3.38), relatively rich in Li (Li2O = 0.36 ± 0.15 wt %) and F (1.11 ± 0.68 wt %), and have variable Mg contents (MgO = 1.89 ± 1.01 wt %). The substitutions 2Fe2+ (2Mg2+(Ti4+) ↔ AlVILi, and 2Al ↔ 3Fe2+ (3Mg2+) were important during the crystallization of biotite in these T granites. The T granites, which have steep REE patterns, (Ce/Yb)CN = 5.96 ± 3.14, were generated by fractionation of plagioclase + K-feldspar + biotite + magnetite (ilmenite) ± hornblende ± allanite but the AT granites exhibit flat REE patterns (Ce/Yb)CN = 0.76 ± 0.52, and have formed by fractionation of mainly plagioclase ± biotite ± K-feldspar ± monazite. Modelling of Rb, Ba, Sr, La, Ce, Sm, Eu, Yb, Lu, Y and (87Sr/86Sr) isotopic ratios indicates that the two granites do not represent simple segregated melts, they were not generated by combined wall rock assimilation-fractional crystallization processes of an evolving mantle-derived magma nor do they represent the evolved end-members of the magma from which the spatially associated 670-570 Ma early-late Pan-African granites were crystallized. The chemistry of these early-late orogenic granites could be explained by subduction related magmatism whereas the the post Pan-African granites melts produced in the lower crust from heterogeneous sources