Ofioliti最新文献

{"title":"DIFFERENCES IN GAS VENTING FROM ULTRAMAFIC-HOSTED WARM SPRINGS: THE EXAMPLE OF OMAN AND VOLTRI OPHIOLITES","authors":"C. Boulart, V. Chavagnac, C. Monnin, A. Delacour, G. Ceuleneer, G. Hoareau","doi":"10.4454/OFIOLITI.V38I2.423","DOIUrl":"https://doi.org/10.4454/OFIOLITI.V38I2.423","url":null,"abstract":"Serpentinisation of mantle rocks, leading to natural venting of hydrogen and methane, has been reported to occur at the global scale, wherever fluids percolate in ultramafic formations. Here we compare gas composition from two on-land, low-temperature, and hyper-alkaline springs hosted on ultramafic rocks in the ophiolite massifs of the Sultanate of Oman and the Ligurian Alps (Voltri Group, Genoa region, Northern Italy). These two settings exhibit similar chemical and mineralogical features but show diverse styles of gas venting. Commonly to all hyper-alkaline springs, gases are characterised by relatively high N 2 , very low O 2 and CO 2 concentrations, and a strong enrichment in H 2 and CH 4 . The comparison between Oman and Liguria highlights a high variability of the H 2 /CH 4 ratios whereby the gas phase of the Oman Ophiolite is enriched in H 2 whereas being CH 4 enriched in the Voltri Ophiolite. These results combined with literature data define three groups that may reflect different stages of serpentinisation producing fluids from hydrogen-dominated to methane-dominated. The origin of these distinct groups might lie in the difference of the mineralogical composition of the rocks within which the fluids circulate, on the degree of alteration of the rocks and finally on the geological/metamorphic history of the ophiolite.","PeriodicalId":54690,"journal":{"name":"Ofioliti","volume":"58 1","pages":"142-156"},"PeriodicalIF":1.3,"publicationDate":"2013-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"70969389","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"PETROLOGICAL STUDY OF PLAGIOGRANITES IN THE NAIN OPHIOLITE (CENTRAL IRAN)","authors":"Zahra Rezaei, M. Noghreyan, M. Khalili","doi":"10.4454/OFIOLITI.V37I2.408","DOIUrl":"https://doi.org/10.4454/OFIOLITI.V37I2.408","url":null,"abstract":"The plagiogranites from the Nain ophiolite consist of plagioclase (albite to andesine), quartz, amphibole (mostly magnesio-hornblende), apatite, titanite and oxide phases. These rocks have low K 2 O, Sr and high Y contents, with low Sr/Y ratios; they are geochemically similar to volcanic arc granites. The chondrite normalized REE patterns of the selected samples are characterized by negative Eu anomalies. We propose that the Nain plagiogranites formed by fractional crystallization of a low-K tholeiitic magma in a supra-subduction setting.","PeriodicalId":54690,"journal":{"name":"Ofioliti","volume":"37 1","pages":"93-99"},"PeriodicalIF":1.3,"publicationDate":"2012-12-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"70968880","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"THE AYLI DAĞ OPHIOLITE SEQUENCE (CENTRAL-NORTHERN TURKEY): A FRAGMENT OF MIDDLE JURASSIC OCEANIC LITHOSPHERE WITHIN THE INTRA-PONTIDE SUTURE ZONE","authors":"M. C. Göncüoğlu, M. Marroni, Kaan Sayıt, U. K. Tekin, G. Ottria, L. Pandolfi, Alessandro Elero","doi":"10.4454/OFIOLITI.V37I2.407","DOIUrl":"https://doi.org/10.4454/OFIOLITI.V37I2.407","url":null,"abstract":"The Ayli Dag ophiolites occur as an independent tectonic unit within the Intra-Pontide suture zone, central-northern Turkey. They crop out, together withthe other units of the Intra-Pontide suture zone, at the top of the Late Cretaceous-Middle Paleocene foredeep sediments of the Sakarya Terrane. The Ayli Dagophiolites sequence include in its lower part a mantle sequence consisting of not less than 2-3 km-thick peridotites, topped by 500-600 m-thick layered gabbroswith alternating, dm- to m-thick layers of spinel-bearing dunites, melatroctolites, troctolites, ol-gabbros and leucogabbros. The gabbro sequence is overlainby a sheeted dyke complex, that shows a transition to 100-200 m-thick massive basaltic lava flows followed by 600-800 m-thick massive and pillow lavasand breccias alternating with ophiolite-bearing arenites and cherts.Geochemical evaluation of the mafic lavas and dykes reveals three distinct chemical groups that reflect melt generation within an intra-oceanic subductionsystem. Among these, the first group shows island-arc tholeiite (IAT)-like features, showing very-depleted characteristics (very high Zr/Nb, low Zr/Y and Nb/Y)ratios coupled with light rare-earth (LREE)-depleted chondrite-normalized patterns. The second group is more akin to back-arc basin basalts (BABB); it displaysnormal mid-ocean ridge basalt (N-MORB)-like high-field strength element (HFSE) distribution except for depletion in Nb, and flat REE patterns. The third groupis somewhat similar to the second one, displaying BABB-like characteristics, but it is more enriched in terms of absolute trace element abundances.The radiolarian cherts sampled from the top of the pillow lavas yielded less-diverse but characteristic radiolarian assemblages indicating the middleBathonian to early Callovian ages.The Ayli Dag Ophiolite is the first finding of back-arc type oceanic lithosphere in the Intra-Pontide suture zone. Together with previous data obtainedfrom basalts in the melange from the Intra-Pontide suture zone, this finding represents a proof that an intra-oceanic subduction within the Intra-Pontide oceanicbasin occurred in the Middle Jurassic time.","PeriodicalId":54690,"journal":{"name":"Ofioliti","volume":"37 1","pages":"77-92"},"PeriodicalIF":1.3,"publicationDate":"2012-12-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"70968764","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The structure of the hydrothermal root zone of the sheeted dikes in the fast-spread oceanic crust: A core-log integration study of ODP Hole 1256D, Eastern equatorial pacific.","authors":"M. Violay, P. Pezard, B. Ildefonse, B. Célérier, Agathe Deleau","doi":"10.4454/OFIOLITI.V37I1.402","DOIUrl":"https://doi.org/10.4454/OFIOLITI.V37I1.402","url":null,"abstract":"Ocean Drilling Program Hole 1256D reached for the first time the transition zone between the sheeted dike complex and the uppermost gabbros. The recovered crustal section offers a unique opportunity to study the deepest part of the hydrothermal system in present-day oceanic crust. We present a structural analysis of electrical borehole wall images. We identified, and measured the orientations of four categories of structures: major faults, minor fractures, possibly hydrothermal veins, and dikes. All structures tend to strike parallel to the paleo-ridge axis. Three major fault zones (meter thick) and dikes are steeply dipping (~ 75° on average) outward the ridge. Centimeter-thick moderately conductive planar features are interpreted as hydrothermal veins, are organized in arrays of consistent spacing, thickness, and orientation, and are dipping about 15-20° toward the ridge. This structural pattern is interpreted as an on-axis paleohydrothermal circulation system, with vertical, dike-parallel fractures, and sub-horizontal high-temperature hydrothermal veins at the base of the sheeted dike, which was subsequently rotated ~ 15° westward around a ridge-parallel, sub-horizontal axis. This rotation can be caused by upper-crustal block rotation along a listric normal fault, and/or subsidence at the ridge axis.","PeriodicalId":54690,"journal":{"name":"Ofioliti","volume":"37 1","pages":"1-11"},"PeriodicalIF":1.3,"publicationDate":"2012-06-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"70968894","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Genesis of vein-stockwork cryptocrystalline magnesite from the Dinaride ophiolites","authors":"I. Jurković, L. Palinkaš, V. Garašić, S. S. Palinkaš","doi":"10.4454/OFIOLITI.V37I1.403","DOIUrl":"https://doi.org/10.4454/OFIOLITI.V37I1.403","url":null,"abstract":"Vein and stock-work cryptocrystalline magnesite deposits, known also as Kraubath type, Gelmagnesite, and Khalilovo type, are widespread in the Tethyan ophiolites from the Alps to the Zagros mountains, including the Dinarides, but also in other ophiolite suites like California, etc. Thirteen samples from the magnesite deposits of the Dinaric and Vardar zone ophiolite belts were analyzed for C- and O-isotopes, major and trace elements, and REE. Genesis of cryptocrystalline magnesite has received two controversial interpretations, involving circulation of Mg-bearing ore fluids, “ per ascendum ” or “ per descendum ” mechanisms. Stable isotope data on C- and O-isotopes in magnesite deposits show significant positive correlation along the light-heavy isotope ratio from vein to stock-work and sedimentary type ore bodies. The thirteen new samples confirmed the same regularity, as a rule for cryptocrystalline magnesite. It should be stressed that there are some exceptions, marked by different isotope patterns, represented by deposits located close to the products of the Tertiary volcanic activity. This paper brings arguments both in favor and against the two genetic models, supported by the new geochemical data. The authors favour, however, the per descendum model, stating generation beneath the lateritic weathering crusts, which covered a wide area of the obducted ophiolites, subjected to warm, humid tropical climate in the Early Cretaceous. The laterite crusts acted as a chromatographic column separating immobile elements from mobilized magnesia in solution, which percolating down through a fracture system, deposited magnesite as a result of increased pH. The self refining of ore forming fluids produced almost monomineralic magnesite veins, with or without selvages. The fractionation of light C- and O-isotopes in magnesite needs isotopic light CO 2 , commonly interpreted as a derivate of deep seated decarboxylation of organic rich sediments. However, this behaviour of light C- and O-isotopes on a regional scale can be convincingly explained also by closed/semiclosed fractionation between atmospheric CO 2 and magnesite in the descending fluid, controlled by the Rayleigh equation.","PeriodicalId":54690,"journal":{"name":"Ofioliti","volume":"37 1","pages":"13-26"},"PeriodicalIF":1.3,"publicationDate":"2012-06-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"70968940","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"CHROMITITES OF THE URALS (PART 1): OVERVIEWOF CHROMITE MINERAL CHEMISTRY AND GEO-TECTONIC SETTING","authors":"G. Garuti, Evgeny V. Evgeny, O. Thalhammer, F. Zaccarini","doi":"10.4454/OFIOLITI.V37I1.404","DOIUrl":"https://doi.org/10.4454/OFIOLITI.V37I1.404","url":null,"abstract":"Published and unpublished compositions of chromite in 333 chromitite samples from 14 ultramafic complexes of the Urals are overviewed. The chromitites occur in the mantle unit and/or the supra-Moho cumulate sequence of ophiolite complexes, as well as in Alaskan-type intrusions. They vary in size from giant ore deposits associated with ophiolites (e.g., Kempirsai, Ray-Iz, Voykar-Syninsky) to sub-economic mineralization in the Alaskan-type complexes (e.g., Svetly Bor, Kachkanar). Mantle-hosted chromitites occur either as discordant, podiform, high-Cr ore bodies and sub-concordant elongated lenses of high-Al chromite. In the supra-Moho sequences of ophiolites, chromitite is mainly of the high-Al variety, and occurs as concordant layers alternated with peridotite and pyroxenite cumulates. In the Alaskan-type intrusions of the Urals, chromitite occurs as centimeter to meter-size pods and lenses having syngenetic or epigenetic relationship with the host dunite. Calculated melt compositions in equilibrium with chromite and comparison of chromite composition with those from various volcanic suites, and chromitites from different plutonic complexes, allow division of the Urals chromitites into four different compositional groups, corresponding to different geodynamic environments of formation: 1) The high-Al, low-Ti suite (Al 2 O 3 > 20 wt%, Cr# 20 wt%, Cr# 0.70, Al 2 O 3 0.70, Al 2 O 3 < 20 wt%, TiO 2 = 0.38-1.30 wt%, Fe 3+ # = 0.20-1.29, δ logf(O 2 ) = +0.9 ÷ +5.9) is represented by chromitites from the Urals Alaskan-type intrusions and the East-Khabarny complex. They have crystallized from Fe-rich magma (av. FeO/MgO = 1.35) under oxygen- fugacity conditions well above the FMQ buffer. The melt is characterized by high-Ti, high-K, calc-alkaline composition, having many geochemical characteristics in common with ankaramites. It was generated by partial melting of a fluid-metasomatized mantle source, in a subduction-influenced arc setting. However, the close similarity with the zoned complexes emplaced in the Russian-Far-East craton suggests that formation of Alaskan-type melts may be not restricted to SSZ, island arc settings.","PeriodicalId":54690,"journal":{"name":"Ofioliti","volume":"37 1","pages":"27-53"},"PeriodicalIF":1.3,"publicationDate":"2012-06-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"70968957","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"ECLOGITE-FACIES SEA-FLOOR HYDROTHERMALLY-ALTERED ROCKS: CALCULATED PHASE EQUILIBRIA FOR AN EXAMPLE FROM THEWESTERN ALPS AT SERVETTE","authors":"G. Rebay, R. Powell","doi":"10.4454/OFIOLITI.V37I1.405","DOIUrl":"https://doi.org/10.4454/OFIOLITI.V37I1.405","url":null,"abstract":"In the St. Marcel Valley at Servette in the Western Alps metabasic rocks crop out that were variably altered in a sea-floor hydrothermal system. Successively, they were metamorphosed to eclogite facies. This was used as an opportunity to explore the range of eclogite-facies mineral assemblages that can develop in such altered rocks. The continuum is represented qualitatively by a series of rock-types: eclogite, glaucophanite, talc schist and chlorite schist, with increasing alteration, supposed to all have involved eclogite-facies mineral assemblages. Later, they were variably retrogressed under greenschist-facies conditions. The eclogite-facies mineral assemblages developed from the broad alteration trend represented by the four rock-types have been forward-modelled in terms of three composition vectors. P-T pseudo-sections for the compositions used to represent the rock-types suggest that a P-T of about 22 kbar and 600°C is consistent for the conditions of formation of the rock-types. T-X pseudo-sections along the composition vectors are used to represent the alteration continuum showing the way the mineral assemblages are affected by the degree of alteration.","PeriodicalId":54690,"journal":{"name":"Ofioliti","volume":"37 1","pages":"55-63"},"PeriodicalIF":1.3,"publicationDate":"2012-06-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"70968614","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"P-T CONSTRAINTS FROM PHYLLOSILICATES OF THE LIGURIDE COMPLEX OF THE POLLINO AREA (SOUTHERN APENNINES, ITALY): GEOLOGICAL INFERENCES","authors":"F. Cavalcante, C. Belviso, Salvatore Laurita, G. Prosser","doi":"10.4454/OFIOLITI.V37I2.406","DOIUrl":"https://doi.org/10.4454/OFIOLITI.V37I2.406","url":null,"abstract":"In this paper a mineralogical study of pelite and metapelite samples collected in the Pollino area (Southern Apennines, Basilicata, Italy) was performed byX-ray diffraction (XRD), with the aim to define in detail the thermobaric conditions of the ophiolite-bearing Liguride Complex during subduction. The twomain tectonic units of the Liguride Complex, namely the metamorphic Frido Unit and the non-metamorphic North Calabria Unit, have been sampled in thisstudy. Results indicate that in the Pollino area the metamorphic grade show an overall decrease from the SW to the NE. The Frido Unit it is characterized byHP/LT metamorphism. The highest values of temperature (280-330°C) and pressure (11-13 kbar) were detected in the southern sector of the area. The intermediatevalues (T = 250±30°C and P = 8-10 kbar) were observed in the central sector, whereas lowest values (T = 180±20°C and P = 7±0.5 kbar) were registeredin the northern sector. These thermobaric conditions and the inferred geothermal gradient (≈ 8°C/km) are in accordance with the lawsonite-blueschistmineral assemblage shown in associated metabasite and with the presence of aragonite in the carbonate levels. Data obtained from pelites of the North-CalabriaUnit indicate high diagenetic thermobaric conditions with temperatures of 110-150°C and pressures of 2-3 kbar. More in detail, temperature values of130-150°C and of 110-140°C are obtained in the Crete Nere and the Saraceno Formations, respectively. These moderate variations in the diagenetic grademight be influenced by differences in the bulk rock composition. The wide range of temperature and pressure conditions documented within the LigurideComplex indicates that samples have been collected in different thrust sheets characterized by variable metamorphic overprint. Systematic variations in thermobaricconditions are particularly evident within the metamorphic Frido Unit, which is probably made up of some thrust sheets and/or slices derived fromdifferent portions of the accretionary wedge.","PeriodicalId":54690,"journal":{"name":"Ofioliti","volume":"37 1","pages":"65-75"},"PeriodicalIF":1.3,"publicationDate":"2012-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"70968713","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"THE GEOLOGY OF THE ZLATIBOR-MALJEN AREA (WESTERN SERBIA): A GEOTRAVERSE ACROSS THE OPHIOLITES OF THE DINARIC-HELLENIC COLLISIONAL BELT","authors":"M. Chiari, N. Djerić, Francesca Garfagnoli, H. Hrvatović, M. Krstič, N. Levi, Alessandro Malasoma, M. Marroni, F. Menna, G. Nirta, L. Pandolfi, G. Principi, E. Saccani, U. Stojadinovic","doi":"10.4454/OFIOLITI.V36.I2.3","DOIUrl":"https://doi.org/10.4454/OFIOLITI.V36.I2.3","url":null,"abstract":"In this paper, we describe the stratigraphic and structural features of the tectonic units cropping out along the Zlatibor-Maljen geotraverse, located in western Serbia at the boundary with Bosnia-Herzegovina, and we present also a 1:100,000 scale geological map. The study area corresponds to a SSW-NNE geotraverse, where the main oceanic and continental tectonic units of the Dinaric-Hellenic belt are well exposed. Along this geotraverse, the tectonic pile includes at the top the units derived from the European Plate, here represented only by the Ljig Unit, that was thrust over the oceanic units, cropping out in two distinct massifs, the Zlatibor and Maljen ones. In both massifs the oceanic units consist of a sub-ophiolite melange overthrust by an ophiolite unit represented exclusively by mantle peridotites with the metamorphic sole at their base. In turn the oceanic units are overthrust the Adria-derived units, here represented by the East Bosnian-Durmitor and Drina-Ivanjica Units, respectively located westward and eastward of the Zlatibor Massif. The geological data and the tectonic reconstruction suggest that the ophiolites of the two s may have originated in the same composite oceanic basin that experienced oceanic opening, intra-oceanic subduction, development of supra-subduction oceanic basins and finally closure, in a time span ranging from Middle Triassic to Late Jurassic. The stratigraphic and structural dataset presented in this paper allows some insights about the geodynamic history of the northern area of the Dinaric-Hellenic belt, as well as a comparison with the reconstructions proposed for the southernmost area by other authors.","PeriodicalId":54690,"journal":{"name":"Ofioliti","volume":"36 1","pages":"139-166"},"PeriodicalIF":1.3,"publicationDate":"2011-12-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"70968742","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"TWO MESOZOIC OCEANIC PHASES RECORDED IN THE BASIC AND METABASIC ROCKS OF THE NAIN AND ASHIN-ZAVAR OPHIOLITIC MÉLANGES (ISFAHAN PROVINCE, CENTRAL IRAN","authors":"N. Shirdashtzadeh, G. Torabi, S. Arai","doi":"10.4454/OFIOLITI.V36.I2.5","DOIUrl":"https://doi.org/10.4454/OFIOLITI.V36.I2.5","url":null,"abstract":"The Mesozoic ophiolitic melanges of Nain and Ashin-Zavar are located in the western part of the Central-East Iranian microcontinent (CEIM), along the major faults of Nain-Baft and Dorouneh. They contain two different groups of highly metamorphosed rocks (amphibolitic rocks, schists, marbles and quartzites) formed through metamorphism of oceanic basaltic and sedimentary units, and also some less metamorphosed rocks (sheeted dikes, pillow lavas, limestones and radiolarian cherts), that were tectonically melanged. These features show that they formed in two distinct phases. Geochemical data point to an island arc tholeiitic affinity for the amphibolitic rocks, and to a MORB nature for the pillow lavas and sheeted dikes that are related to a back-arc basin. Accordingly, oceanic crust extensional processes should have been active during two phases: a- In Early Jurassic, the Nain and Ashin-Zavar oceanic crust segments started spreading and producing diabasic dikes and pillow lavas, covered by pelagic sediments, then they suffered a high-grade metamorphism during the closure of this oceanic sector around the Middle Jurassic. b- During Early-Late Cretaceous to Paleocene, oceanic spreading produced sheeted dikes, massive basalts, and basaltic pillow lavas thoroughout the Austrian orogenic phase. There is no evidence of high-grade metamorphism as amphibolitic rocks. Radiolarian cherts and Globotruncana limestones of Late Cretaceous age cover the basaltic rocks.","PeriodicalId":54690,"journal":{"name":"Ofioliti","volume":"36 1","pages":"191-205"},"PeriodicalIF":1.3,"publicationDate":"2011-12-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"70968849","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}