CaracterizaÃÃo GeoquÃmica e IsotÃpica de MÃrmores do Terreno Rio Capibaribe na Zona Transversal da ProvÃncia Borborema - Nordeste do Brasil

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

The isotopic composition (δ13C, 87Sr/86Sr e Pb-Pb) of marbles from two localities (Surubim and Caruaru) of the Caroalina-Surubim Complex (Transversal Zone, Borborema Province, NE Brazil) was used to estimate the age of sedimentation and metamorphism of the protolithic carbonate sequence. These occurrences are part of one sedimentary succession deposited during the Meso- Neoproterozoic and metamorphosed at amphibolites fÃcies conditions. Intercalations of schists and pegmatite dikes are common in both occurrences and the Caruaru marbles also contains intercalations of paragneisses. The marbles are white to light gray-colored and composed by calcite, dolomite, tremolite, diopside, flogopite, quartz, graphite, titanite, plagioclase, chlorite, and biotite, among others. Whole-rock geochemical data show that the Caruaru marbles are dominantly calcic with CaO>40% and MgO<10% whereas those of Surubim are dolomitic with CaO<40% and MgO>12%. The silica content in both localities is <5%. Mineral and whole-rock chemistry of the Caruaru marbles suggest that the regional peak metamorphic temperature was close to 650ÂC. For the Surubim marbles, the estimated temperatures are slightly lower, within the middle-upper amphibolite facies conditions. δ13C values vary from -2,55 to +4,87âPDB and from -2,60 a +3,87âPDB in samples from the Caruaru and Surubim areas, respectively. The isotopic chemostratigraphy of C, O and Sr allows to conclude that: (a) the curves of temporal variation record primary fluctuations of the isotopic composition of C, O and Sr in the ocean water during the transition from the Meso- to the Neoproterozoic, possibly related to rifting and continental magmatic arcs during the Cariris Velhos event; (b) Sr87/Sr86 values are very homogeneous in the Caruaru marbles (0,70734 to 0,70785), but show a larger variation in the Surubim marbles (0,70634 to 0,70901). Analogy of these values with those from the literature suggests that both sequences have similar minimum and maximum deposition ages of 520 and 725Ma, respectively. In contrast, maximum deposition ages inferred from the δ13C values are higher 0.95-1.0Ga for Caruaru and 0,95Ga for Surubim). Similar time spans are found when the evolution curve for 87Sr/86Sr in rivers and oceans suggesting deposition around 0,70- 0,75Ga for the Caruaru marbles and 1 Ga for the Surubim marbles. These results also suggest that the study marbles were deposited during a period of sea-level rise during the Cariris Velhos event, with probable metamorphism at its final stages. 206Pb/204Pb ratios vary from 17,863 to 19,753 for the Caruaru marbles and from 17,744 to 19,222 for the Surubim marbles, defining metamorphic ages of 628 and 652Ma, respectively. In spite of the elevated errors, these data are compatible with a late neoproterozoic age of metamorphism. The chemical and physical characteristics of the studied marbles allow their classification as of good quality, due to their neutralizing power and relative total neutralizing power, indicating their use to the production of soils corrective and cement, important products for the economy of the state of Pernambuco

ASSUNTO(S)

geocronology (pb-pb) geocronologia (pb-pb) complexo caroalina - surubim provÃncia borborema rio capibaribe terrene caroalina-surubim metalogenia borborema province terreno rio capibaribe isotopic chemostratigraphic (c, o and sr) mÃrmores geociencias marbles quimioestratigrafia isotÃpica (c, o e sr)

ACESSO AO ARTIGO

Documentos Relacionados