Multi-stage melt–rock interaction in the Mt. Maggiore Corsica, France ophiolitic peridotites: microstructural and geochemical evidenceReport as inadecuate




Multi-stage melt–rock interaction in the Mt. Maggiore Corsica, France ophiolitic peridotites: microstructural and geochemical evidence - Download this document for free, or read online. Document in PDF available to download.

Contributions to Mineralogy and Petrology

, Volume 156, Issue 4, pp 453–475

First Online: 07 April 2008Received: 29 November 2007Accepted: 10 March 2008

Abstract

Spinel and plagioclase peridotites from the Mt.Maggiore Corsica, France ophiolitic massif record a composite asthenosphere–lithosphere history of partial melting and subsequent multi-stage melt–rock interaction. Cpx-poor spinel lherzolites are consistent with mantle residues after low-degree fractional melting F = 5–10%. Opx + spinel symplectites at the rims of orthopyroxene porphyroclasts indicate post-melting lithospheric cooling T = 970–1,100°C; this was followed by formation of olivine embayments within pyroxene porphyroclasts by melt–rock interaction. Enrichment in modal olivine up to 85 wt% at constant bulk Mg values, and variable absolute REE contents at constant LREE-HREE indicate olivine precipitation and pyroxene dissolution during reactive porous melt flow. This stage occurred at spinel-facies depths, after incorporation of the peridotites in the thermal lithosphere. Plagioclase-enriched peridotites show melt impregnation microtextures, like opx + plag intergrowths replacing exsolved cpx porphyroclasts and interstitial gabbronoritic veinlets. This second melt–rock interaction stage caused systematic chemical changes in clinopyroxene e.g. Ti, REE, Zr, Y increase, related to the concomitant effects of local melt–rock interaction at decreasing melt mass, and crystallization of small <3% trapped melt fractions. LREE depletion in minerals of the gabbronoritic veinlets indicates that the impregnating melts were more depleted than normal MORB. Preserved microtextural evidence of previous melt–rock interaction in the impregnated peridotites suggests that they were progressively uplifted in response to lithosphere extension and thinning. Migrating melts were likely produced by mantle upwelling and melting related to extension; they were modified from olivine-saturated to opx-saturated compositions, and caused different styles of melt–rock interaction reactive spinel harzburgites, vs. impregnated plagioclase peridotites depending on the lithospheric depths at which interaction occurred.

KeywordsMelt–rock interaction Melt impregnation Reactive porous flow Mantle peridotites Alpine–Apennine ophiolites Communicated by J. Hoefs.

Electronic supplementary materialThe online version of this article doi:10.1007-s00410-008-0296-y contains supplementary material, which is available to authorized users.

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Author: Elisabetta Rampone - Giovanni B. Piccardo - Albrecht W. Hofmann

Source: https://link.springer.com/



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