Dados da Submissão

Título

TRACING THE MAGMATIC AND POST-MAGMATIC EVOLUTION OF MANTLE SERPENTINITES FROM THE HOGGAR (ALGERIA).

Texto do resumo

The InTedeini serpentinites in the Hoggar shield (South Algeria) represent emplaced fragments of a mantle wedge that underline a major Neoproterozoic suture zone. This is supported by our recently published whole-rock major and trace element analyses, which showed that the main characteristics of the parent mantle peridotites are preserved, suggesting a highly depleted mantle protolith involved in a subduction zone. This includes intense dynamic melting episodes influenced by fluid influx and melt refertilization. By using mineral chemistry and isotopes, we seek to deepen our investigation of the magmatic and post-magmatic processes endured by these rocks through their evolution, such as serpentinization and carbonation. We found that the Platinum Group Element (PGE) compositions of the InTedeini serpentinites is marked by high Os and Ru concentrations, variable yet low Ir and Pt concentrations, while plotting in the field of anhydrous residual mantle peridotites. The 187Os/188Os ratios of these samples are lower than the primitive mantle value, and plot within the fresh mantle peridotites field. The obtained results point to the preservation of the PGE characteristics, corroborating the previous interpretation for intense melting of a depleted mantle source. The High Cr#, low to moderate Mg# and low Ti content of Cr-spinels, which reflect a mantle wedge origin for the InTedeini serpentinites precursor, decrease with the increase of Fe3+. This exchange leads to the formation of ferrichromite and magnetite rims around primary Cr-spinels cores and precipitation of magnetite in veinlets. This data attests to the alteration process of chromites and suggests possible oxidizing conditions. Ongoing C-O isotope analyses on these mantle wedge serpentinites will be essential in this study to clarify the source of carbon fluid that led to carbonate precipitation in these rocks. Overall, our current study, focused on the InTedeini serpentinites, contribute to our understanding of subduction-related geochemical processes and the evolution of ancient suture zones.

Palavras Chave

Serpentinite; Mantle; Spinel; PGE; Carbonation