Contribution to petrogenesis of the Paleoproterozoic Basaltic Magmatism from the Araí continental rift, central Brazil
Journal of South American Earth Sciences(2021)
摘要
The Paleoproterozoic Araí continental rift, Central Brazil, hosts metabasaltic lava flows interbedded with a thick transgressive metasedimentary sequence at the basal portion of the Araí Group (Arraias Formation). The lava flows have basalt to basaltic andesite compositions, subalkaline, tholeiitic and within-plate geochemical signatures. These rocks still have low to moderate REEs content, negative Ta, Ti, Nb anomalies, higher La/Nb (2.69–5.06) and lower La/Ba (0.03–0.23) ratios, suggesting some degree of contamination. Isotopic geology data presented in this paper revealed zircon U–Pb crystallization age of 1783 ± 17 Ma, with a significant frequency of inherited zircon from Rhyacian (2221 ± 14 Ma), negative εNd (t) = −4.46 to −6.58, Nd TDM model age from 2.49 to 2.72 Ga and 87Sr/86Sr(i) = 0.702400–0.708293. The εNd(t) vs Nb/La and εNd(t) vs 87Sr/86Sr diagrams suggest low to moderate contamination rate, linked to interactions of the plume-derived magmas with the subcontinental lithospheric mantle and the Archean-Paleoproterozoic continental old-crust, during to ascent and intrusion episodes, respectively. These new data are nicely correlated with the available isotopic data (U–Pb, Sm–Nd, Sr–Sr) on the acid volcanic and A-type granites from the basal portion of the Araí rift, indicating an important bimodal magmatic event, with volcano-plutonic characteristics, occurred during the continental syn-rift stage.
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关键词
Araí Group,Continental rift,Tocantins Province,Brasília Belt,Basaltic magmatism,Geochemical,Geochronology
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