Estudo geoquímico e isotópico (U-Pb/Lu-Hf) de novas ocorrências de granitos tipo-A no Domínio Carajás.

Abstract

The Carajás Mineral Province was the setting of an extensive magmatic event, marked by anorogenic granitic intrusions and associated dykes. Geological mapping methods carried out in the central portion of the Canaã dos Carajás Domain allowed the individualization of two new anorogenic granitic stocks. These granites occur as isotropic, semicircular shaped stocks, which occur as intrusions in Archean granitic rocks of the Vila União and Cruzadão granite suites. And are classified as monzogranites and divided into biotite-monzogranite equigranular facies (BMzE) and biotite monzogranite porphyritic (BMzP) facies, where biotite is the main ferromagnesian mineral and are often associated with fluorite, in addition to allanite, zircon, apatite and epidote. They are meta- to peraluminous, with a high content of HSFE iron-related with a reduced to moderately oxidized character. When compared to others type-A granites of the Carajás Mineral Province, these granites display significant contrasts with the Jamon and Velho Guilherme suites and are similar to those observed in the Serra dos Carajás suite and, consequently, the Gogó da Onça Granite. Geochronological data of U-Pb in zircon revealed that crystallization age of these granites is ~1893 ± 13 Ma, and associated with isotopic data of Lu-Hf indicate crustal sources for these rocks, with strongly negative ƐHf values ranging from -14 at -17°C and TDM between 3.38 Ga to 3.57 Ga. Based on this informations, the geochemical modeling imply that these granites were generated from partial melting of tonalitic granites of similar composition to the Arco Verde Tonalite or Caracol Tonalite from the Rio Maria Domain. Such results are suitablewith the hypothesis that these granites were generated from a fusion of Archean granitoids and placed in a shallow crust between 1.88 and 1.86 Ga.