Bimodal magmatism of the Tucuma area, Carajas province: U-Pb geochronology, classification and processes

Author(s)

da Silva, Fernando Fernandes ; de Oliveira, Davis Carvalho ; Antonio, Paul Y. J. ; D'Agrella Filho, Manoel S. ; Lamarao, Claudio Nery

• Document type: Journal article
• Source: Journal of South American Earth Sciences; v. 72, p. 95-114, DEC 2016.
• Web of Science Citations: 6

Abstract

Geological mapping of the Tucuma area has enabled the identification of dike swarms intruded into an Archean basement. The disposition of these dikes is consistent with the well-defined NW-SE trending regional faults, and they can reach up to 20 km in length. They were divided into three main groups: (i) felsic dikes (70% of the dikes), composed exclusively of porphyritic rhyolite with euhedral phenocrysts of quartz and feldspars immersed in an aphyric felsite matrix; (ii) mafic dikes, with restricted occurrence, composed of basaltic andesite and subordinate basalt, with a mineralogical assembly consisting dominantly of plagioclase, clinopyroxene, orthopyroxene and olivine; and (iii) intermediate rocks, represented by andesite and dacite. Dacites are found in outcrops associated with felsic dikes, representing different degrees of hybridization or mixture of mafic and felsic magmas. This is evidenced by a large number of mafic enclaves in the felsic dikes and the frequent presence of embayment textures. SHRIMP U-Pb zircon dating of felsic dikes yielded an age of 1880.9 +/- 3.3 Ma. The felsic dikes are peraluminous to slightly metaluminous and akin to A2, ferroan and reduced granites. The intermediate and mafic dikes are metaluminous and belong to the tholeiitic series. Geochemical modeling showed that mafic rocks evolved by pyroxene and plagioclase crystallization, while K-feldspar and biotite are the fractionate phases in felsic magma. A simple binary mixture model was used to determine the origin of intermediate rocks. It indicated that mixing 60% of rhyolite and 40% basaltic andesite melts could have generated the dacitic composition, while the andesite liquid could be produced by mixing of 60% and 40% basaltic andesite and rhyolite melts, respectively. The mixing of basaltic and andesitic magmas probably occurred during ascent and storage in the crust, where andesite dikes are likely produced by a more homogeneous mixture at high depths in the continental crust (mixing), while dacite dikes can be generated in the upper crust at a lower temperature, providing a less efficient mixing process (mingling). The affinities observed between the felsic to intermediate rocks of the Rio Maria and Sao Felix do Xingu areas and the bimodal magmatism of the Tucuma area reinforce the hypothesis that in the Paleoproterozoic the Carajas province was affected by processes involving thermal perturbations in the upper mantle, mafic under plating, and associated crustal extension or transtension. The 1.88 Ga fissure-controlled A-type magmatism of the Tucuma area was emplaced similar to 1.0 to similar to 0.65 Ga after stabilization of the Archean crust. Its origin is not related to subduction processes but to the disruption of the supercontinent at the end of the Paleoproterozoic. (C) 2016 Elsevier Ltd. All rights reserved. (AU)

• FAPESP's process: 11/50887-6 - Paleomagnetism of proterozoic geological units from the Amazonian Craton, and its participation in the Columbia, Rodinia, and Gondwana supercontinents
• Grantee: Manoel Souza D'Agrella Filho
• Support Opportunities: Regular Research Grants