{"title":"CORUNDUM-BEARING VEINS IN CHLORITITE FROM THE ETIROL-LEVAZ AUSTROALPINE CONTINENTAL SLICE (VALTOURNENCHE, AOSTA, ITALY)","authors":"R. Compagnoni, R. Cossio, D. Regis","doi":"10.4454/OFIOLITI.V46I2.542","DOIUrl":null,"url":null,"abstract":"The high-pressure (HP) continental Etirol-Levaz slice (ELS) is exposed on the right side of the Valtournenche (Aosta) at the contact between the overlying blueschist-facies Combin Zone and the underlying eclogite-facies Zermatt-Saas Zone. The ELS contains a layered metagabbro showing a complex evolution, which includes the pre-Alpine high-temperature (HT) recrystallization of the igneous mineralogies, and the polyphase Alpine metamorphism, initially at high-pressure (HP) quartz eclogite-facies, and greenschist-facies (GS) retrogression.In this paper, an unusual corundum-bearing ultramafic rocks associated with metagabbros are described. The studied sample is a Mg-chloritite with relict green spinel partly replaced by corundum, Mg-beltrandoite-2N3S (a new mineral of the hogbomite supergroup), Mg-chlorite and dolomite. The rock is crossed by mm- to cm-thick veins composed of coarse-grained corundum + Mg-chlorite + dolomite. P-T phase-diagram projections indicate that the corundum-bearing assemblages formed in the presence of a water-rich fluid (X(CO2) ≤ 0.04), during retrograde decompressional evolution. This stage follows the prograde HP-peak of the associated eclogites. The newly inferred prograde-to-retrograde P-T path suggests that the ELS and the underlying Zermatt-Saas Zone shared a common Alpine metamorphic evolution.The detailed study of the relict minerals preserved in the chloritite indicates its pre-Alpine protolith, a green spinel websterite, and its evolution, characterized by a high-T recrystallization of the original igneous asemblages. During the Alpine orogeny, the spinel websterite experienced metasomatic hydration that converted the original igneous rock into a chloritite.","PeriodicalId":1,"journal":{"name":"Accounts of Chemical Research","volume":null,"pages":null},"PeriodicalIF":16.4000,"publicationDate":"2021-07-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Accounts of Chemical Research","FirstCategoryId":"89","ListUrlMain":"https://doi.org/10.4454/OFIOLITI.V46I2.542","RegionNum":1,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"CHEMISTRY, MULTIDISCIPLINARY","Score":null,"Total":0}
引用次数: 0
Abstract
The high-pressure (HP) continental Etirol-Levaz slice (ELS) is exposed on the right side of the Valtournenche (Aosta) at the contact between the overlying blueschist-facies Combin Zone and the underlying eclogite-facies Zermatt-Saas Zone. The ELS contains a layered metagabbro showing a complex evolution, which includes the pre-Alpine high-temperature (HT) recrystallization of the igneous mineralogies, and the polyphase Alpine metamorphism, initially at high-pressure (HP) quartz eclogite-facies, and greenschist-facies (GS) retrogression.In this paper, an unusual corundum-bearing ultramafic rocks associated with metagabbros are described. The studied sample is a Mg-chloritite with relict green spinel partly replaced by corundum, Mg-beltrandoite-2N3S (a new mineral of the hogbomite supergroup), Mg-chlorite and dolomite. The rock is crossed by mm- to cm-thick veins composed of coarse-grained corundum + Mg-chlorite + dolomite. P-T phase-diagram projections indicate that the corundum-bearing assemblages formed in the presence of a water-rich fluid (X(CO2) ≤ 0.04), during retrograde decompressional evolution. This stage follows the prograde HP-peak of the associated eclogites. The newly inferred prograde-to-retrograde P-T path suggests that the ELS and the underlying Zermatt-Saas Zone shared a common Alpine metamorphic evolution.The detailed study of the relict minerals preserved in the chloritite indicates its pre-Alpine protolith, a green spinel websterite, and its evolution, characterized by a high-T recrystallization of the original igneous asemblages. During the Alpine orogeny, the spinel websterite experienced metasomatic hydration that converted the original igneous rock into a chloritite.
期刊介绍:
Accounts of Chemical Research presents short, concise and critical articles offering easy-to-read overviews of basic research and applications in all areas of chemistry and biochemistry. These short reviews focus on research from the author’s own laboratory and are designed to teach the reader about a research project. In addition, Accounts of Chemical Research publishes commentaries that give an informed opinion on a current research problem. Special Issues online are devoted to a single topic of unusual activity and significance.
Accounts of Chemical Research replaces the traditional article abstract with an article "Conspectus." These entries synopsize the research affording the reader a closer look at the content and significance of an article. Through this provision of a more detailed description of the article contents, the Conspectus enhances the article's discoverability by search engines and the exposure for the research.