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Título

ARE THERE TRACES OF A NEOPROTEROZOIC OPHIOLITE IN THE WESTERN HOGGAR (ALGERIA)?

Texto do resumo

Structural, petrological and geophysical data indicate the existence of an accretionary wedge in the InTedeini domain, Western Hoggar shield. This is evidenced by the coexistence of mantle and crustal rocks including metagabbros, metabasalts, metasedimentary formations, as well as mantle serpentinites that mark a major Neoproterozoic suture zone. Our focus lies on the petro-geochemistry of poorly studied mafic rocks from InTedeini, with the aim to infer their origin and geodynamic setting. These rocks can be subdivided in two distinct geochemical types: Type-1 is subalkaline (Nb/Y <0.1) with low Th, Nb and Ta contents and LaN/YbN ratios <1, resembling those of Normal-type mid-Ocean Ridge basalts (N-MORB). Whereas the Type-2 rocks display slight enrichment in Th, Ta, Nb (Nb/Y: 0.12 - 0.4), and LaN/YbN ratios: 1.5 - 6.1, resembling the chemistry of Enriched-type (E-) MORB. Such geochemical enrichment from N-MORB to E-MORB composition suggests mixing of melts derived likely from a depleted and fertile mantle sources at the spreading center. This is supported by the preliminary Rb-Sr and Sm-Nd isotopic analyses, which indicate a derivation from a mantle origin without continental crust contamination. Based on our results, we propose that these mid-ocean ridge type mafic rocks represent remnants of the Neoproterozoic oceanic crust generated during the magmatic seafloor spreading of the Goiás-Pharusian ocean, subsequently stacked in a collisional accretionary wedge following the ocean closure (~631Ma). The occurrence of this ensemble together with the exhumed mantle wedge fragments likely indicate the preservation of a suture zone, which bears a dismembered subduction-related ophiolite suite in the Hoggar shield, and more broadly, in West Gondwana.

Palavras Chave

mafic; ophiolite; Neoproterozoic; suture