Melchiorre M., Coltorti M., Grégoire Michel, Benoit M. (2015). Refertilization process in the Patagonian subcontinental lithospheric mantle of Estancia Sol de Mayo (Argentina). Tectonophysics, 650 (SI), p. 124-143. ISSN 0040-1951.
Titre du document
Refertilization process in the Patagonian subcontinental lithospheric mantle of Estancia Sol de Mayo (Argentina)
Melchiorre M., Coltorti M., Grégoire Michel, Benoit M.
Source
Tectonophysics, 2015,
650 (SI), p. 124-143 ISSN 0040-1951
Anhydrous mantle xenoliths equilibrated at 1003-1040 degrees C from Estancia Sol de Mayo (ESM, Central Patagonia, Argentina) and.entrained in post-plateau alkaline lavas belonging to Meseta Lago Buenos Aires have been investigated aiming at reconstructing the depletion and enrichment processes that affected this portion of the Patagonia lithospheric mantle. Xenoliths are characterized by a coarse-grained protogranular texture and are devoid of evident modal metasomatism. They show two texturally different clinopyroxenes: protogranular (cpx1) and texturally related to spinet (cpx2). Three different types of orthopyroxenes are also recognized: large protogranular crystals with exsolution lamellae (opxl); small clean and undeformed grains without exsolution lamellae (opx2) and small grains arranged in a vein (opx3). Major element composition of clinopyroxenes and orthopyroxenes highlights two different trends characterized by i) a high Al2O3 content at almost constant mg and ii) a slight increase in Al2O3 content with decreasing mg. Clinopyroxenes are enriched in LREE and are characterized by prominent to slightly negative Nb, Zr and Ti anomalies. No geochemical differences are observed between cpx1 and cpx2, while a discrimination can be observed between opxl and opx2 (LREE-depleted; prominent to slightly negative Ti and Zr anomalies) and opx3 (prominent positive Zr anomaly). Partial melting modeling using both major and trace elements, indicates a melting degree between similar to 5% and similar to 13% (up to similar to 23% according to major element modeling) for lherzolites and between similar to 20% and similar to 30% for harzburgites (down to similar to 5% according to trace element modeling). La/Yb and Al2O3, as well as Sr and Al2O3 negative correlations in clinopyroxenes point to a refertilization event affecting this lithospheric mantle. The agent was most probably a transitional alkaline/ subalkaline melt, as indicated by the presence of orthopyroxene in the vein and the similar geochemical features of ESM clinopyroxenes and those from Northern Patagonia pyroxenites which are derived from transitional alkaline/subalkaline lavas.
