Abstract
ABSTRACT: This paper approaches the record of SiO2-saturated potassic alkaline magmatism of Castanhal Quartz Monzonite, Mapuera Suite, and Ladeira da Vovó Quartz Syenite. These samples are located near the Northern border of the Amazon Basin. Such rocks show K2O + 2 > Na2O and K2O/Na2O < 2 values that confirm the potassic or shoshonitic character of these rocks. The Castanhal Quartz Monzonite contains less than 20% volume of quartz, which is also a characteristic of the shoshonitic or SiO2-satured potassic alkaline A-type magma signature observed on geochemical plots. Listric faults, representing the rifting phase of Amazon Basin formation, emplaced and reworked Ladeira da Vovó Quartz Syenite, which caused its granophyric texture, probably during the Tonian period. A group of 21 zircon crystals was extracted from a hornblende quartz monzonite and yields an average age of 1872 ± 6 Ma (MSWD = 2.4). However, an additional zircon crystal yielded a Trans-Amazonian age of 2062 ± 17 Ma. These potassic alkaline rocks of Orosirian (1872 Ma) age may correspond to a post-collisional setting. Dominantly negative εHft values and Hf TDM ages reveal a large contribution of a mafic crustal component from Mesoarchean to Neoarchean age (2.95 - 2.66 Ga), and a felsic crustal component from Neoarchean to later Siderian ages (2.51 - 2.34 Ga).
Highlights
There are still uncertainties about the origin and evolution of alkaline granitic magmas
Younger ages were obtained to Catrimâni Syenite (180 ± 5 Ma, Salas & Santos 1974; 100 Ma, Montalvão et al 1975), representing the youngest records of alkaline granitic rocks observed in the Uatumã-Anauá Domain (CPRM 2000)
The samples of hornblende quartz monzonite display seriated texture and interpenetrative contacts between quartz and plagioclases. These rocks present less than 20% wt. of quartz or SiO2-satured potassic alkaline A-type signatures
Summary
There are still uncertainties about the origin and evolution of alkaline granitic magmas. Systematic data on alkaline granitic magmatism into the Uatumã-Anauá Domain, Central-Northern Amazonian Craton (Fig. 1A and 1B), are restrict to Catrimâni and Água Boa regions, southeastern Roraima State (CPRM 2000). Younger ages were obtained to Catrimâni Syenite (180 ± 5 Ma, Salas & Santos 1974; 100 Ma, Montalvão et al 1975), representing the youngest records of alkaline granitic rocks observed in the Uatumã-Anauá Domain (CPRM 2000). Studied alkaline granitoids crop out along BR-174 federal road and Castanhal dirty road, and they are located right at the boundary between sedimentary sequences of the Amazon Basin and Água Branca granites (Terra Preta Granite) and Iricoumé volcanites, southernmost Uatumã-Anauá Domain, southwestern Presidente Figueiredo district, and northeastern Amazonas State (Fig. 1C; Valério et al 2009, 2012). This paper includes petrographic, whole-rock geochemical, in-situ U-Pb zircon geochronological and Hf isotope composition data upon the Castanhal Quartz Monzonite firstly, and field and petrographic features of the Ladeira da Vovó Quartz Syenite, secondly
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