Mineral chemistry and crystallization conditions of the Bom Jardim de Goiás pluton Tocantins Province
DOI:
https://doi.org/10.11606/issn.2316-9095.v17-316Keywords:
Tocantins Province, Ediacaran, Tonalites, Geothermobarometry.Abstract
Post-collisional granite intrusions related to the Brasiliano cycle are widespread in the Goiás Magmatic Arc, central part of the Tocantins Province, Central Brazil. The Bom Jardim de Goiás pluton (PBJG) is one of these intrusions of Ediacaran age, which are intrusive into metasupracrustal rocks and orthogneisses of the Arenópolis Magmatic arc. According to petrographic descriptions, the PBJG rocks are classified as tonalite, granodiorite and quartz monzodiorite, with coarse-grained equigranular to fine- to medium-grained inequigranular texture. This paper presents mineral chemistry of amphibole, plagioclase, biotite and magnetite from the PBJG and an estimation of intensive parameters of crystallization. The amphibole of the PBJG is subhedral or anhedral, with chemical characteristics of the calcic-amphiboles edenite and Mg-hornblende. The plagioclase (andesine, An30-37) occurs as prismatic or lath-like grains, twinned on the albite law, with chemical zoning evidenced by alteration to sericite, epidote and carbonates toward the centre of the crystals. Biotite is brown, lamellar, and partially replaced by titanite, chlorite and epidote; it corresponds chemically to Mg-biotite. The magnetite is euhedral or anhedral, with quadratic or elongated sections and usually observed as inclusions within hornblende, clinopyroxene, biotite and titanite. The AlT content of hornblende indicates crystallization pressure of 2.1 to 4.0 kbar for the PBJG. These values are consistent with the presence of andalusite in the host rock. The amphibole-plagioclase geothermometer indicates temperatures between 692 and 791°C, that are relatively lower than those obtained from whole rock zircon saturation geothermometer (794 – 813°C), interpreted as closer to the liquidus temperature.
Downloads
Downloads
Published
Issue
Section
License
Authors who publish in this journal shall comply with the following terms:
- Authors keep their copyright and grant to Geologia USP: Série Científica the right of first publication, with the paper under the Creative Commons BY-NC-SA license (summary of the license: https://creativecommons.org/licenses/by-nc-sa/4.0 | full text of the license: https://creativecommons.org/licenses/by-nc-sa/4.0/legalcode) that allows the non-commercial sharing of the paper and granting the proper copyrights of the first publication in this journal.
- Authors are authorized to take additional contracts separately, for non-exclusive distribution of the version of the paper published in this journal (publish in institutional repository or as a book chapter), granting the proper copyrights of first publication in this journal.
- Authors are allowed and encouraged to publish and distribute their paper online (in institutional repositories or their personal page) at any point before or during the editorial process, since this can generate productive changes as well as increase the impact and citation of the published paper (See The effect of Open Access and downloads on citation impact).
