Nadeau, Olivier; Stevenson, Ross et Jébrak, Michel
(2018).
« Interaction of mantle magmas and fluids with crustal fluids at the 1894 Ma Montviel alkaline-carbonatite complex, Canada: Insights from metasomatic and hydrothermal carbonates ».
Lithos, 296-29, pp. 563-579.
Fichier(s) associé(s) à ce document :
Résumé
Alkaline and carbonatite rocks are relatively rare but offer the opportunity to study the contribution of fluids in the genesis of mantle and crustal rocks because they are commonly affected by metasomatism. Carbonate minerals represent versatile archives of mantle and crustal magmatic-hydrothermal processes because they can have magmatic, metasomatic or hydrothermal origins and because they host the trace elements, stable and radiogenic isotopes required to unravel their petrogenesis. Previous studies have shown that the 1894 Ma Montviel alkaline carbonatite complex was emplaced through four injections of volatile-saturated, mantle magmas
which evolved through fractional crystallization, mixing of mantle and crustal fluids and metasomatism. Trace element analyses and δ 18 13 87 86
O, δ C, 143 Sr/144 Sr and Nd/ Nd isotope compositions of metasomatic and hydrothermal carbonates further support that each magma injection was accompanied by a volatile phase. Variations in trace element concentrations suggest that the carbonatite might have exsolved from a metasomatized mantle or hybrid silicate carbonatite magma, and that the fluid composition evolved towards higher REE and lower HFSE with increasing degree of segregation of the carbonatite magma and the silicate source. A strong correlation between the C-O-Sr isotopic systems show that mantle fluids mixed with crustal fluids, increasing the 87 86 Sr/ Sr from mantle to crustal values, and driving the C and O isotopic ratios towards respectively lighter and heavier values. The Sm/Nd isotopic system was weakly coupled with the other isotopic systems as depleted mantle fluids
mixed with crustal fluids and metasomatized the crystallizing magmas, thereby redistributing the REE and affecting their Sm/Nd ratios. The Nd isotopes suggest that the mixed mantle/crustal fluids redistributed the
rare earth elements, producing ultra-depleted (εNd = +10), normally depleted (εNd = +4) and slightly enriched (εNd = −2) isotopic compositions.
Altmetric
Altmetric
RECHERCHER
PARCOURIR
LIBRE ACCÈS
