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Título

METAMAFICS REMNANTS OF PALEOPROTEROZOIC OCEANIC CRUST IN THE SOUTHERN SÃO FRANCISCO CRATON: THE CLÁUDIO META-OPHIOLITE

Texto do resumo

Meta-ophiolites are important evidences of ancient oceanic crust, giving information about past tectonic and crustal evolution. Metamafics remnants of a Paleoproterozoic oceanic crust are preserved within the Southern São Francisco Craton, along the Cláudio Shear Zone (Brazil). They are associated with metaultramafic and metassedimentary rocks, suggesting a dismembered meta-ophiolite (Cláudio meta-ophiolite). Textural, mineralogical, and field relations allow to classify the metamafics protoliths as gabbros and basalts. Metagabbros preserve original igneous features (igneous pyroxene and magmatic layering) and mineral assemblages from very low- to medium-grade metamorphism (pumpellyite→chlorite→hornblende→clinozoisite→zoisite). Metabasalts are interleaved with high-grade metapelitic rocks and preserve the peak metamorphic assemblage: amphibole + plagioclase ± biotite (magmatic origin). The metamafic protoliths have a tholeiitic and sub-alkaline nature, with positive ƐNd (t) values (+3.2+5.6) indicating a magma source as a result of the partial melting of the upper mantle at shallow depth in the spinel-peridotite zone. Trace elements ratios and REE patterns suggest an E-MORB signature for both metagabbros and metabasalts, which are interpreted to be derived from by 25-35% and 10-15% partial melting of a spinel-peridotite mantle source, respectively. The metabasalts show crustal contamination, probably due to sediment basin interaction. The whole-rock Sm-Nd TDM age of 2354 Ma (mantle-separation age) and U-Pb age of 2050 Ma (peak metamorphism) from metamorphic zircons indicate a Paleoproterozoic evolution for the paleo-oceanic basin. The Cláudio meta-ophiolite is interpreted as a result of the paleo-ocean basin closure, initiated with a NW-dipping subduction and followed by continental collision between the Divinópolis and Campo Belo/Bonfim metamorphic complexes, contributing to the Columbia (Nuna) supercontinent formation. It is suggested that the dehydration of the subducted slab contributed with fluids for partial melting and migmatization of the Divinópolis complex (e.g. Kinawa migmatite in 2048-2032 Ma).

Palavras Chave

metamafics; meta-ophiolite; E-MORB; Paleoproterozoic; Southern São Francisco Craton.