Petrographic and geochemical characterization of the granitic rocks of the Araguainha impact crater, Brazil.
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2016
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Petrographic and geochemical data obtained on the Araguainha impact crater
(Goi as/Mato Grosso States, Brazil) indicate the existence of several molten products that
originated during impact-induced congruent melting of an alkali-granite exposed in the
inner part of the central uplift of the structure. Although previous studies have described
these melts to some extent, there is no detailed discussion on the petrographic and
geochemical variability in the granite and its impactogenic derivatives, and therefore, little is
known about the geochemical behavior and mobility of trace elements during its fusion in
the central part of the Araguainha crater. This paper demonstrates that the preserved
granitoid exposed in the core of the structure is a magnesium-rich granite, similar to
postcollisional, A-type granites, also found in terrains outside the Araguainha crater, in the
Bras ılia orogenic belt. The molten products are texturally distinct and different from the
original rock, but have very similar geochemical composition, making it difficult to separate
these lithotypes based on concentrations of major and minor elements. This also applies for
trace and rare earth elements (REE), thus indicating a high degree of homogenization
during impact-induced congruent melting under high pressure and postshock temperature
conditions. Petrographic observations, along with geochemical data, indicate that melting
occurs selectively, where some of the elements are transported with the melt.
Simultaneously, there is an effective dissolution of the rock (granite), which leads to
entrainment of the most resistant solid phases (intact or partially molten minerals) into the
melt. Minerals more resistant to melting, such as quartz and oxides, contribute substantially
to a chemical balance between the preserved granite and the fusion products generated
during the meteoritic impact.
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SILVA, D.; LANA, C. de C.; SOUZA FILHO, C. R. de. Petrographic and geochemical characterization of the granitic rocks of the Araguainha impact crater, Brazil. Meteoritics & Planetary Science, v. 51, n. 3, p. 443–467, 2016. Disponível em: <https://onlinelibrary.wiley.com/doi/full/10.1111/maps.12601>. Acesso em: 06 jul. 2017.