%0 Journal Article
%9 ACL : Articles dans des revues avec comité de lecture répertoriées par l'AERES
%A Harvey, J.
%A Gannoun, A.
%A Burton, K.W.
%A Schiano, Pierre
%A Rogers, N.W.
%A Alard, O.
%T Unravelling the effects of melt depletion and secondary infiltration on mantle Re-Os isotopes beneath the French Massif Central
%D 2010
%L PAR00004542
%G ENG
%J Geochimica et Cosmochimica Acta
%@ 0016-7037
%K FRANCE
%M ISI:000273109700021
%N 1
%P 293-320
%R 10.1016/j.gca.2009.09.031
%U https://www.documentation.ird.fr/hor/PAR00004542
%> https://www.documentation.ird.fr/intranet/publi/2010/01/010049158.pdf
%V 74
%W Horizon (IRD)
%X Spinel lherzolite xenoliths from Mont Briancon, French Massif Central, retain evidence for multiple episodes of melt depletion and melt/fluid infiltration (metasomatism). Evidence for primary melt depletion is still preserved in the co-variation of bulk-rock major elements (MgO 38.7-46.1 wt.%; CaO 0.9-3.6 wt.%), and many samples yield unradiogenic bulk-rock Os isotope ratios (Os-187/Os-188 = 0.11541-0.12626). However, many individual xenoliths contain interstitial glasses and melt inclusions that are not in equilibrium with the major primary minerals. Incompatible trace element mass balance calculations demonstrate that metasomatic components comprise a significant proportion of the bulk-rock budget for these elements in some rocks, ranging to as much as 25%, of Nd and 40% of Sr Critically, for Re-Os geochronology, melt/fluid infiltration is accompanied by the mobilisation of Sulfide. Consequently, bulk-rock isotope measurements, whether using lithophile (e.g. Rb-Sr, Sm-Nd) or siderophile (Re-Os) based isotope systems, may only yield a perturbed and/or homogenised average of these multiple events. Osmium mass balance calculations demonstrate that bulk-rock Os in peridotite is dominated by contributions from two populations of sulfide grain: (i) interstitial, metasomatic Sulfide with low [Os] and radiogenic Os-187/Os-188, and (ii) primary sulfides with high [Os] and unradiogenic Os-187/Os-188, which have been preserved within host silicate grains and shielded from interaction with transient melts and fluid. The latter can account for >97% of bulk-rock Os and preserve geochronological information of the melt from which they originally precipitated as an immiscible liquid. The Re-depletion model ages of individual primary sulfide grains preserve evidence for melt depletion beneath the Massif Central from at least 1.8 Gyr ago despite the more recent metasomatic event(s).
%$ 064