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(Reference retrieved automatically from SciELO through information on FAPESP grant and its corresponding number as mentioned in the publication by the authors.)

Melanite-bearing nepheline syenite fragments and 40Ar/39Ar age of phlogopite megacrysts in conduit breccia from the Poços de Caldas Alkaline Massif (MG/SP), and implications

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Author(s):
Silvio Roberto Farias Vlach [1] ; Horstpeter Herberto Gustavo Jose Ulbrich [2] ; Mabel Norma Costas Ulbrich [3] ; Paulo Marcos Vasconcelos [4]
Total Authors: 4
Affiliation:
[1] São Paulo University. Institute of Geoscience. Department of Mineralogy and Geotectonics - Brasil
[2] São Paulo University. Institute of Geoscience. Department of Mineralogy and Geotectonics - Brasil
[3] São Paulo University. Institute of Geoscience. Department of Mineralogy and Geotectonics - Brasil
[4] University of Queensland. School of Earth Sciences - Austrália
Total Affiliations: 4
Document type: Journal article
Source: BRAZILIAN JOURNAL OF GEOLOGY; v. 48, n. 2, p. 391-402, 2018-06-00.
Abstract

ABSTRACT: The Poços de Caldas Alkaline Massif, located in southeast Brazil, is composed of tinguaites, as well as phonolites and nepheline syenites (NeS), together with assorted pyroclastic rocks. The latter constitute deposits within the Vale do Quartel, and show fragments of alkaline rocks (NeS, tinguaites), basaltic and ultramafic volcanics/subvolvanics, sandstones, and quartz-feldspathic rocks from the crystalline basement. NeS fragments with melanite, previously unknown, and cm-sized fragments of phlogopite megacrysts from related conduit breccia were chosen for detailed studies. The NeS fragments are medium- to coarse grained and contain K-feldspar (Or 95-83 ), secondary albite (Ab 97 ), altered nepheline, clinopyroxene (diopside, minor hedenbergite) and partially altered, zoned, idiomorphic melanite. These NeS fragments are typically metaluminous, and point to the existence of similar intrusions hidden at depth, an important input to the massif’s petrology. The phlogopite megacrysts are compositionally homogeneous, with high Ti, Mg and Al contents; Ba and F are minor components. Two phlogopite aliquots were dated and yielded identical 40 Ar/ 39 Ar plateau ages of 87.1(± 0.5) Ma and 86.6(± 0.5) Ma, which represent minimum and maximum values for phlogopite crystallization and breccia emplacement, respectively. Previously obtained ages for the Poços de Caldas rocks are concentrated in the 75-86 Ma range interval. (AU)

FAPESP's process: 12/06082-6 - The Paraná-Etendeka magmatic province in Brazil: temporal and petrologic relationships between the tholeiitic and alkaline magmatism and geodynamic implications
Grantee:Excelso Ruberti
Support Opportunities: Research Projects - Thematic Grants