U-Pb geochronology, classification and evolutionary aspects of Granite Marajoara, Carajás Province

Abstract

The Marajoara granite (MjGr) is a stock intrusive in Mesoarchean granitoids of the Rio Maria domain, Carajás Province. It is formed by hololeucocratic rocks: equigranular (BMzE) and heterogranular (BMzH) monzogranite. Rapakivi texture and occurrences of porphyritic granite (EGp) and microgranular enclaves (EMg) are restricted to BMzH facies. Magnetic susceptibility (MS) values and the presence of magnetite show that the BMzH facies is akin to magnetite-seriesgranites, whereas the BMzE variety shows affinity with the ilmeniteones (low values of MS and opaque minerals). They are peraluminous and similar to the ferroan granites. These granitoids show affinities with oxidized (BMzH and EGp) and reduced (BMzE) A-type granites, and are related to the Jamon and Velho Guilherme suites, respectively. EMg hasan affinity with the magnesian granites and the calc-alkaline series, and EGp is originated from the interaction between EMg and BMzH liquids. Compositional gaps among the several varieties that constitute MjGr suggest that their magmas are not cogenetic. EMg represents basic magmatism from the enriched lithospheric mantle that would have been injected into the magma chamber during the underplating. The U-Pb zircon analyzes (SHRIMP) yield a crystallization age of 1885 ± 6 Ma. MjGr was emplaced inepizone in an extensional tectonic environment. The concentric zoning in MjGr and the reduced or no influence of the regional efforts suggest transport of the magma through dikes. Thus, MjGr’s construction results from the vertical rise of magmas through fractures and accommodation along the planes of the regional E-W foliation, followed by a change of vertical flow through a lateral scattering of the magma.