کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
4717711 | 1638766 | 2007 | 10 صفحه PDF | دانلود رایگان |
عنوان انگلیسی مقاله ISI
Neoproterozoic anorogenic magmatism in the Southern Bahia Alkaline Province of NE Brazil: U-Pb and Pb-Pb ages of the blue sodalite syenites
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کلمات کلیدی
موضوعات مرتبط
مهندسی و علوم پایه
علوم زمین و سیارات
ژئوشیمی و پترولوژی
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چکیده انگلیسی
Blue sodalite syenite is a rare rock, and the Southern Bahia Alkaline Province (SBAP) is the only place in Brazil where economic deposits are found. This province forms part of the Archaean to Paleoproterozoic São Francisco craton, and contains a few batholiths, a large number of stocks and hundreds of dykes. Its southern part lies close to the tectonic contact between the craton and the Neoproterozoic Araçuaà mobile melt. Blue sodalite-bearing syenites are found in almost all the igneous bodies of the SBAP as dykes or pegmatitic masses hosted by nepheline syenite. Economically viable quantities for the production of dimension stones are found only in the Floresta Azul alkaline complex, the Itaju do Colônia and Rio Pardo stocks and the Itarantim batholith.U-Pb ages obtained for titanite from Itaju do Colônia (732 ± 8 Ma) and Rio Pardo (714 ± 8) and Pb-Pb evaporation ages of zircon from Floresta Azul (696 ± 3 Ma) and Itarantim (722 ± 5 Ma). The geochronology of the SBAP shows that the anorogenic alkaline magmatism persisted for at least 58 Ma, demonstrating an extensional tectonic environment in the southern part of the São Francisco craton at this time. The data show that the rift phase which preceded the formation of the Araçuaà orogen was active until at least 700 Ma. The reported ages are similar to those found for the nepheline syenite host bodies, which supports the conclusions of the previous petrologic study demonstrating that blue sodalite is formed during the crystallization of these bodies. Two different processes are involved. In the magmatic process, sodalite occurs as disseminated and interstitial crystals among alkali feldspar crystals, and is associated with calcite and cancrinite formed by destabilization of nepheline. In the metasomatic process, discontinuous bands of sodalite are in sharp contact with nepheline syenite pegmatite, and its crystal aggregates often contain relict textures of nepheline and albite been replaced by sodalite.
ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Lithos - Volume 97, Issues 1â2, August 2007, Pages 88-97
Journal: Lithos - Volume 97, Issues 1â2, August 2007, Pages 88-97
نویسندگان
Maria de Lourdes da Silva Rosa, Herbet Conceição, Moacir José Buenano Macambira, Marco Antonio Galarza, Mônica Pringsheim Cunha, Rita Cunha Leal Menezes, Moacyr Moura Marinho, BasÃlio Elesbão da Cruz Filho, Débora Correia Rios,