TY - JOUR
T1 - Paleomagnetism and 40Ar/39Ar ages of mafic dikes from Salvador (Brazil)
T2 - New constraints on the São Francisco craton APW path between 1080 and 1010 Ma
AU - D'Agrella-Filho, Manoel S.
AU - Pacca, Igor I.G.
AU - Trindade, Ricardo I.F.
AU - Teixeira, Wilson
AU - Raposo, M. Irene B.
AU - Onstott, Tullis C.
N1 - Funding Information:
We would like to acknowledge referees. So, we thank E.M. Piccirillo, G. Bellieni, M.A. Tanner de Oliveira and C. Moraes Brito for assistance during sample collection. We appreciate the constructive reviews by J. Meert and S. Pisarevsky, and the editorial comments by A. Kröner. The 40 Ar/ 39 Ar geochronology was supported by NSF grant EAR-8805529 to T.C. Onstott and CNPq grant 522975/96-8 to W. Teixeira. The funding for the paleomagnetic research was provided by CNPq and FAPESP (grant 98/3621-4).
PY - 2004/6/30
Y1 - 2004/6/30
N2 - Paleomagnetic results from unmetamorphosed Mesoproterozoic mafic dikes of Salvador, northern São Francisco craton, yield either an easterly direction with high upward inclination (Dm=110.8°, Im=-79.3°, α95=8.4°, N=8, paleopole at 122.7°E, 6.4°N), or a westerly direction with high downward inclination (Dm=290.7°, Im=64.7°, α95=7.5°, N=7, paleopole at 282.6°E, 5.6°N). Additional paleomagnetic analyses on country rocks (granulites and amphibolitic dikes) yield paleomagnetic poles similar to those obtained in other metamorphic rocks from the São Francisco craton affected by the Transamazonian orogeny (2200-1900 Ma). Positive baked contact tests in two dikes, together with rock magnetic studies, supported by petrographic and radiometric analyses, indicate that the remanent directions isolated for the unmetamorphosed dikes are primary TRM's. 40Ar/39Ar step-heating analyses on biotite from a granulite sampled ∼90 cm away from the dike's contact yield an integrated age of 1021±8 Ma, whereas the plagioclase from the dike itself yields an integrated age of 1003±33 Ma, interpreted to be the time of the emplacement. Our data in conjunction with the available late Mesoproterozoic poles from the São Francisco craton allow to best constrain its APW path between 1080 and 1010 Ma.
AB - Paleomagnetic results from unmetamorphosed Mesoproterozoic mafic dikes of Salvador, northern São Francisco craton, yield either an easterly direction with high upward inclination (Dm=110.8°, Im=-79.3°, α95=8.4°, N=8, paleopole at 122.7°E, 6.4°N), or a westerly direction with high downward inclination (Dm=290.7°, Im=64.7°, α95=7.5°, N=7, paleopole at 282.6°E, 5.6°N). Additional paleomagnetic analyses on country rocks (granulites and amphibolitic dikes) yield paleomagnetic poles similar to those obtained in other metamorphic rocks from the São Francisco craton affected by the Transamazonian orogeny (2200-1900 Ma). Positive baked contact tests in two dikes, together with rock magnetic studies, supported by petrographic and radiometric analyses, indicate that the remanent directions isolated for the unmetamorphosed dikes are primary TRM's. 40Ar/39Ar step-heating analyses on biotite from a granulite sampled ∼90 cm away from the dike's contact yield an integrated age of 1021±8 Ma, whereas the plagioclase from the dike itself yields an integrated age of 1003±33 Ma, interpreted to be the time of the emplacement. Our data in conjunction with the available late Mesoproterozoic poles from the São Francisco craton allow to best constrain its APW path between 1080 and 1010 Ma.
KW - Ar/Ar geochronology
KW - Mafic dikes
KW - Mesoproterozoic
KW - Paleomagnetism
KW - Rodinia
KW - São Francisco craton
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U2 - 10.1016/j.precamres.2004.02.003
DO - 10.1016/j.precamres.2004.02.003
M3 - Article
AN - SCOPUS:2442659127
SN - 0301-9268
VL - 132
SP - 55
EP - 77
JO - Precambrian Research
JF - Precambrian Research
IS - 1-2
ER -