Características estruturais, petrográficas e geoquímicas de enxame de diques máficos intrusivo em rochas metassedimentares do greenstone belt de Crixás, Goiás

Abstract

Diques e raros stocks máficos são comuns nos terrenos arqueanos de Goiás, onde ocorrem em enxames de 2.3-2.5 Ga nos complexos granito-gnáissicos (2.8 e 2.7 Ga) e nas seções estratigráficas inferiores de metakomatiitos e metabasaltos, mas eram desconhecidos nas unidades metassedimentares superiores dos greenstone belts. O detalhamento de seções de sondagem de área dos depósitos auríferos do greenstone belt de Crixás revelou que a intrusão destes diques ocorreu após os principais eventos de deformação e metamorfismo paleoproterozoicos da seção metassedimentar e sobre os quais dados de literatura indicam que zircão magmático dos mesmos possui a idade de 2170 ± 17 Ma. Dados petrográficos e geoquímicos registram tratar-se de diabásios com características composicionais de basaltos epicratônicos de alto-Ti semelhantes aos da Bacia do Paraná. A idade das intrusões se correlaciona com o curto intervalo de tempo (2,20 a 2,17 Ga) do Rhyaciano, durante o qual ocorreram sucessivos e localizados episódios de plumas mantélicas no Globo Terrestre.

The Paleoproterozoic Campinorte Arc: Tectonic evolution of a Central Brazil pre-Columbia orogeny

“…From bottom to top the greenstone belts sequence can be summarized as (a) basal metakomatiite; (b) metabasalts with local pillow structures and; (c) metasedimentary sequence with carbonaceous phyllite, metagraywacke, schist, metachert and gondites. Magmatism coeval with Paleoproterozoic basin formation is evidenced by 2.17 Ga mafic dikes cutting Crixás metagraywacke (Jost and Scandolara, 2010), ∼2.14 Ga metafelsic rock in the Pillar greenstone belt (Queiroz et al, 1999) and the ∼2.16 Ga Posselândia diorite east of the Hidrolina Complex (Jost et al, 1993). A provenance study of the Crixás and Guarinos greenstone belts upper metasedimentary rocks by Jost et al ( , 2012 provided a Paleoproterozoic sedimentation age of ∼2.15 Ga. Mixed mafic and felsic source contributions with Eu anomalies were determined by whole-rock geochemistry (Jost et al, 1996).…”

The Orogenic Crixás Gold Deposit, Goiás, Brazil: A Review and New Constraints on the Structural Control of Ore Bodies

“…2170 ± 17 Ma) that crosscut the ore intervals suggesting that deformation, metamorphism and mineralization occurred during approximately 30 Myr to 40 Myr within the Rhyacian. However, the ages of both mafic dike [50] and the possible hydrothermal zircons [42] are not accurate. They were obtained after calculating the regression line (upper intercept age) based on few results, and the former was also recently reconsidered as derived from possible xenocrysts [3].…”

First Detection of Methane within Chromitites of an Archean-Paleoproterozoic Greenstone Belt in Brazil

“…In the northern portion of the PGGB, [23] estimated that the metamorphic peak for the Cedrolina chromitites ( Figures 1B and 2) reached the low amphibolite facies (550-600 • C at 0.4-0.6 GPa), which was followed by retrometamorphism under greenschist facies conditions. Although the number of tectono-metamorphic events and their specific ages is not a consensus, four deformational stages have been suggested for the analogous Crixás Belt [31], two during the Paleoproterozoic (including the main event) and two in the Neoproterozoic.…”

“…Minerals 2019, 9, x FOR PEER REVIEW 4 of tectono-metamorphic events and their specific ages is not a consensus, four deformational stages have been suggested for the analogous Crixás Belt [31], two during the Paleoproterozoic (including the main event) and two in the Neoproterozoic.…”

“…The talc schist is composed mainly of talc (90%), chromite (<5%), hydrated Al-silicates (3%) and magnetite + Fe-hydroxide pseudomorphs after magnetite (2%) ( Figure 3B). tectono-metamorphic events and their specific ages is not a consensus, four deformational stages have been suggested for the analogous Crixás Belt [31], two during the Paleoproterozoic (including the main event) and two in the Neoproterozoic.…”