Abstract
This study presents new zircon ages and Sm-Nd whole-rock isotopic compositions for high-grade gneisses from the Udzungwa Mountain area in the central part of the Mozambique belt, Tanzania. The study area comprises a succession of layered granulite-facies para- and orthogneisses, mostly retrograded to amphibolite-facies. The original intrusive contacts became obscured or severely modified during non-coaxial ductile deformation, and extensive shearing occurred during retrogression. Structures reflecting the early deformational history were mostly obscured when the rocks were transported into the lower crust as documented by severe flattening. Only the fragmented gneisses in the eastern part of the area testify to a brittle regime. Structures in narrow low strain zones that predate the currently observed layering are preserved in rootless isoclinal folds and boudins. Magmatic and detrital zircons from tonalitic to felsic orthogneisses and a metapelite sample were dated using the U-Pb and Pb-Pb evaporation methods and SHRIMP II. Cathodoluminiscence images reveal ubiquitous xenocrystic cores, rimmed by clear, unzoned overgrowth due to high-grade metamorphism. Discordant U-Pb data therefore reflect core-rim relationships, and it was not always possible to obtain precise crystallisation ages. The analyses reveal Neoarchaean, Palaeoproterozoic and Neoproterozoic protolith ages. Nd isotopic systematics yielded strongly negative εNd(t)-values and Neoarchaean to Palaeoproterozoic model ages, even for gneisses emplaced in the Neoproterozoic. The trace element distribution suggests upper crustal derivation of the gneisses. Therefore, our study provides evidence that recycling of older crust played a major role during the evolution of the Kidatu area. Neoarchaean rocks are interpreted to represent fragments of the Tanzania craton. Our results, together with those of earlier workers, lead to the conclusion that the central part of the Mozambique belt mainly consists of ancient crustal remnants that were reworked during the Neoproterozoic Pan-African orogeny.
| Original language | English |
|---|---|
| Pages (from-to) | 139-155 |
| Number of pages | 17 |
| Journal | Journal of African Earth Sciences |
| Volume | 45 |
| Issue number | 2 |
| DOIs | |
| Publication status | Published - Jun 2006 |
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Archaean and Palaeoproterozoic gneisses reworked during a Neoproterozoic (Pan-African) high-grade event in the Mozambique belt of East Africa : Structural relationships and zircon ages from the Kidatu area, central Tanzania. / Vogt, M.; Kröner, A.; Poller, U.; Sommer, H.; Muhongo, S.; Wingate, M. T D.
In: Journal of African Earth Sciences, Vol. 45, No. 2, 06.2006, p. 139-155.Research output: Contribution to journal › Article
TY - JOUR
T1 - Archaean and Palaeoproterozoic gneisses reworked during a Neoproterozoic (Pan-African) high-grade event in the Mozambique belt of East Africa
T2 - Structural relationships and zircon ages from the Kidatu area, central Tanzania
AU - Vogt, M.
AU - Kröner, A.
AU - Poller, U.
AU - Sommer, H.
AU - Muhongo, S.
AU - Wingate, M. T D
PY - 2006/6
Y1 - 2006/6
N2 - This study presents new zircon ages and Sm-Nd whole-rock isotopic compositions for high-grade gneisses from the Udzungwa Mountain area in the central part of the Mozambique belt, Tanzania. The study area comprises a succession of layered granulite-facies para- and orthogneisses, mostly retrograded to amphibolite-facies. The original intrusive contacts became obscured or severely modified during non-coaxial ductile deformation, and extensive shearing occurred during retrogression. Structures reflecting the early deformational history were mostly obscured when the rocks were transported into the lower crust as documented by severe flattening. Only the fragmented gneisses in the eastern part of the area testify to a brittle regime. Structures in narrow low strain zones that predate the currently observed layering are preserved in rootless isoclinal folds and boudins. Magmatic and detrital zircons from tonalitic to felsic orthogneisses and a metapelite sample were dated using the U-Pb and Pb-Pb evaporation methods and SHRIMP II. Cathodoluminiscence images reveal ubiquitous xenocrystic cores, rimmed by clear, unzoned overgrowth due to high-grade metamorphism. Discordant U-Pb data therefore reflect core-rim relationships, and it was not always possible to obtain precise crystallisation ages. The analyses reveal Neoarchaean, Palaeoproterozoic and Neoproterozoic protolith ages. Nd isotopic systematics yielded strongly negative εNd(t)-values and Neoarchaean to Palaeoproterozoic model ages, even for gneisses emplaced in the Neoproterozoic. The trace element distribution suggests upper crustal derivation of the gneisses. Therefore, our study provides evidence that recycling of older crust played a major role during the evolution of the Kidatu area. Neoarchaean rocks are interpreted to represent fragments of the Tanzania craton. Our results, together with those of earlier workers, lead to the conclusion that the central part of the Mozambique belt mainly consists of ancient crustal remnants that were reworked during the Neoproterozoic Pan-African orogeny.
AB - This study presents new zircon ages and Sm-Nd whole-rock isotopic compositions for high-grade gneisses from the Udzungwa Mountain area in the central part of the Mozambique belt, Tanzania. The study area comprises a succession of layered granulite-facies para- and orthogneisses, mostly retrograded to amphibolite-facies. The original intrusive contacts became obscured or severely modified during non-coaxial ductile deformation, and extensive shearing occurred during retrogression. Structures reflecting the early deformational history were mostly obscured when the rocks were transported into the lower crust as documented by severe flattening. Only the fragmented gneisses in the eastern part of the area testify to a brittle regime. Structures in narrow low strain zones that predate the currently observed layering are preserved in rootless isoclinal folds and boudins. Magmatic and detrital zircons from tonalitic to felsic orthogneisses and a metapelite sample were dated using the U-Pb and Pb-Pb evaporation methods and SHRIMP II. Cathodoluminiscence images reveal ubiquitous xenocrystic cores, rimmed by clear, unzoned overgrowth due to high-grade metamorphism. Discordant U-Pb data therefore reflect core-rim relationships, and it was not always possible to obtain precise crystallisation ages. The analyses reveal Neoarchaean, Palaeoproterozoic and Neoproterozoic protolith ages. Nd isotopic systematics yielded strongly negative εNd(t)-values and Neoarchaean to Palaeoproterozoic model ages, even for gneisses emplaced in the Neoproterozoic. The trace element distribution suggests upper crustal derivation of the gneisses. Therefore, our study provides evidence that recycling of older crust played a major role during the evolution of the Kidatu area. Neoarchaean rocks are interpreted to represent fragments of the Tanzania craton. Our results, together with those of earlier workers, lead to the conclusion that the central part of the Mozambique belt mainly consists of ancient crustal remnants that were reworked during the Neoproterozoic Pan-African orogeny.
KW - Mozambique belt
KW - Palaeoproterozoic
KW - Reworking
KW - Structure
KW - Tanzania
KW - Zircon geochronology
UR - http://www.scopus.com/inward/record.url?scp=33646906213&partnerID=8YFLogxK
U2 - 10.1016/j.jafrearsci.2006.01.012
DO - 10.1016/j.jafrearsci.2006.01.012
M3 - Article
VL - 45
SP - 139
EP - 155
JO - Journal of African Earth Science
JF - Journal of African Earth Science
SN - 1464-343X
IS - 2
ER -