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AMS-07 Crustal evolution of the cratonic nuclei of South America

Sr-Nd isotopic and trace element characteristics of the Mesoproterozoic mafic intrusive rocks from Rondonia, sw Amazonian Craton

Vicente Girardi, Institute of Geosciences - USP (Brazil)
Wilson Teixeira, Institute of Geosciences - USP (Brazil)
Jorge Bettencourt, Institute of Geosciences - USP (Brazil)
Sandra Andrade, Institute of Geosciences - USP (Brazil)
M. S. Navarro, Institute of Geosciences - USP (Brazil)
Kei Sato, Institute of Geosciences - USP (Brazil)
 

Rocks of the Serra da Providncia Intrusive Suite are related to bimodal magmatism and are represented by A- type rapakivi granites, charnockites and mangerites genetically associated with diabase dikes, gabbros and amphibolites. Geochemical and isotopic data suggest that the original mafic melts derived from a depleted mantle source. Underplated mafic magma induced melting of a short-lived felsic crust, thus originating coeval felsic-mafic magmatism in accordance with a continental intraplate setting. The Colorado Complex comprises monzonite gneisses associated with amphibolite, gabbro and metadiabase dikes intercalated with schist, metaturbidite and BIF. The intrusive mafic-felsic bi-modal magmatism dates from 1337-1552 Ma. Mafic rocks and monzonite gneisses display juvenile signatures. Mafic samples are much less contaminated than the Serra da Previdncia and Nova Brasilndia ones. U/Pb zircon detrital ages of metaturbidites are 1.35 1.42 Ga, contemporaneous with sedimentation. The model here suggested relates the generation of the Colorado basaltic magma to the subduction of an oceanic slab into the peridotite wedge. According to this model the Colorado Complex began in an island arc setting. The Nova Brasilndia Sequence includes bimodal magmatism (970-1025 Ga) characterized by metadiabases, gabbros, metagabbros and amphibolites associated with granitic plutons intruding paragneisses, mica schists, and calc-silicate gneisses. The original tholeiitic magmas, derived from a depleted source, underwent crustal contamination by metasedimentary host rocks. Isotopic and geochemical data are in accordance the development of the Nova Brasilndia Sequence to an intracontinental rift setting.