Lithostratigraphy of the Grao Para Group, Serra dos Carajas, Brazil

Conference · Tue Jan 01 04:00:00 EST 1985 · Geol. Soc. Am., Abstr. Programs; (United States)

OSTI ID:6596780

Gibbs, A K; Wirth, K R

The Grao para Group (GPG) is the low-grade metavolcanic portion of the largest metasupracrustal fold belt of the eastern Guapore Shield. It hosts the enormous Serra dos Carajas banded iron formations and was considered to be Early Proterozoic in age. Roughly 4-6 km of metavolcanic rocks underlie 300-400 m thick BIF, and more mafic volcanics overlie them. Subalkaline basalts, basaltic andesites and shoshonites predominate. The basalts and andesites have higher K/sub 2/O (1.5-3.0%) than is typical of Archean greenstone belts, and have LREE-enriched patterns. Spilitic alteration, yielding extreme K/Na ratios, is only locally apparent. The chemical compositions of the volcanics, their bimodal character, and isotopic signatures are consistent with their eruption through continental or transitional crust. The surrounding region contains rocks that may comprise an older, more typical Archean greenstone-granite gneiss terrane. Stratigraphic relations with the overlying sandstones, conglomerates, shales, cherts and carbonates require further work. In areal extent and apparent supracontinental setting, the Carajas iron deposits are like Lake Superior and Hamersley deposits; in age and direct association with volcanic rocks they are like Algoma-type sequences. The GPG has analogies with some Proterozoic belts in SW USA, and with younger continental rift deposits. It is also similar to some of the youngest shoshonite-bearing sequences in the Superior Province, but other Archean examples are rare.

• Research Organization: Cornell Univ., Ithaca, NY (USA)
• OSTI ID: 6596780
• Report Number(s): CONF-8510489-
• Conference Information: Journal Name: Geol. Soc. Am., Abstr. Programs; (United States) Journal Volume: 17
• Country of Publication: United States
• Language: English

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AGE ESTIMATION
BRAZIL
CHEMICAL COMPOSITION
CHEMISTRY
DEVELOPING COUNTRIES
GEOCHEMISTRY
GEOLOGIC FORMATIONS
GEOLOGIC HISTORY
GEOLOGY
IGNEOUS ROCKS
LATIN AMERICA
LITHOLOGY
METAMORPHIC ROCKS
PETROLOGY
ROCKS
SOUTH AMERICA
STRATIGRAPHY
VOLCANIC ROCKS