Geochemical constraints provided by the Freetown Layered Complex (Sierra Leone) on the origin of high-ti tholeiitic CAMP magmas

The Freetown Layered Complex (FLC) is a massive mafic layered intrusion cropping out along the coast of Sierra Leone. The present combined geochemical and geochronological (40Ar/39Ar on plagioclase: 201·7 ± 0·7 and 202·3 ± 2·3 Ma; U–Pb on baddeleyite: 198·794 ± 0·048/0·071/0·22 Ma) study of the comp...

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Published in:Journal of Petrology
Main Authors: Callegaro, S., Marzoli, A., Bertrand, H., Blichert-Toft, J., Reisberg, L., Cavazzini, G., Jourdan, Fred, Davies, J., Parisio, L., Bouchet, R., Paul, A., Schaltegger, U., Chiaradia, M.
Format: Article in Journal/Newspaper
Language:unknown
Published: Oxford University Press 2017
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Online Access:http://hdl.handle.net/20.500.11937/67922
https://doi.org/10.1093/petrology/egx073
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spelling ftcurtin:oai:espace.curtin.edu.au:20.500.11937/67922 2023-05-15T18:21:21+02:00 Geochemical constraints provided by the Freetown Layered Complex (Sierra Leone) on the origin of high-ti tholeiitic CAMP magmas Callegaro, S. Marzoli, A. Bertrand, H. Blichert-Toft, J. Reisberg, L. Cavazzini, G. Jourdan, Fred Davies, J. Parisio, L. Bouchet, R. Paul, A. Schaltegger, U. Chiaradia, M. 2017 restricted http://hdl.handle.net/20.500.11937/67922 https://doi.org/10.1093/petrology/egx073 unknown Oxford University Press http://hdl.handle.net/20.500.11937/67922 doi:10.1093/petrology/egx073 Journal Article 2017 ftcurtin https://doi.org/10.1093/petrology/egx073 2018-12-10T23:18:11Z The Freetown Layered Complex (FLC) is a massive mafic layered intrusion cropping out along the coast of Sierra Leone. The present combined geochemical and geochronological (40Ar/39Ar on plagioclase: 201·7 ± 0·7 and 202·3 ± 2·3 Ma; U–Pb on baddeleyite: 198·794 ± 0·048/0·071/0·22 Ma) study of the complex flags it as a high-Ti occurrence of the Central Atlantic Magmatic Province (CAMP). Sr–Nd–Pb–Os isotope data indicate that the FLC is unique with respect to previously studied CAMP occurrences, constituting a new isotopic end-member for this large igneous province (LIP). Notably, the contribution of ancient source(s) is required to explain its low 206Pb/204Pb and high 207Pb/204Pb. Although the internal isotopic variability of the FLC can be explained by modest assimilation (<10%) of lower crustal (granulitic) material, represented by a xenolith found within the complex itself, an atypical mantle source is required to account for its unusual Pb isotopic composition. We also present the first Hf isotopic data measured to date for CAMP rocks, which, in the case of the FLC, show a restricted range in 176Hf/177Hf, overlapping the ocean island basalt and mid-ocean ridge basalt fields on the terrestrial array, and can further be used to characterize the FLC isotopic end-member. We propose that the FLC formed by mixing of a predominantly asthenospheric parental magma with small volumes (1–3%) of geochemically highly enriched lamproitic melts derived from the sub-continental lithospheric mantle in a geodynamic context in which a Proterozoic mobile belt (Rokelide) bordered an Archean craton (Man). Within the CAMP, similar isotopic compositions, in particular low 206Pb/204Pb and high 207Pb/204Pb, are found only in regions that were once contiguous with Sierra Leone. A comparable involvement of enriched components stored within the cratonic lithosphere may be envisaged for the high-Ti magmatism in the CAMP and two other LIPs of the South Atlantic realm, Karoo and Paraná–Etendeka. These Gondwana magmatic provinces share with other mantle-derived magmas from the South Atlantic Ocean enriched isotopic signatures (DUPAL, LOMU, EMI) of much debated origin. The present mantle source model for the FLC, CAMP, and neighbouring LIPs suggests ancient enriched subcontinental lithospheric mantle as a plausible conveyor of such isotopic signatures in the South and Central Atlantic. Article in Journal/Newspaper South Atlantic Ocean Ocean Island Curtin University: espace Journal of Petrology 58 9 1811 1840
institution Open Polar
collection Curtin University: espace
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language unknown
description The Freetown Layered Complex (FLC) is a massive mafic layered intrusion cropping out along the coast of Sierra Leone. The present combined geochemical and geochronological (40Ar/39Ar on plagioclase: 201·7 ± 0·7 and 202·3 ± 2·3 Ma; U–Pb on baddeleyite: 198·794 ± 0·048/0·071/0·22 Ma) study of the complex flags it as a high-Ti occurrence of the Central Atlantic Magmatic Province (CAMP). Sr–Nd–Pb–Os isotope data indicate that the FLC is unique with respect to previously studied CAMP occurrences, constituting a new isotopic end-member for this large igneous province (LIP). Notably, the contribution of ancient source(s) is required to explain its low 206Pb/204Pb and high 207Pb/204Pb. Although the internal isotopic variability of the FLC can be explained by modest assimilation (<10%) of lower crustal (granulitic) material, represented by a xenolith found within the complex itself, an atypical mantle source is required to account for its unusual Pb isotopic composition. We also present the first Hf isotopic data measured to date for CAMP rocks, which, in the case of the FLC, show a restricted range in 176Hf/177Hf, overlapping the ocean island basalt and mid-ocean ridge basalt fields on the terrestrial array, and can further be used to characterize the FLC isotopic end-member. We propose that the FLC formed by mixing of a predominantly asthenospheric parental magma with small volumes (1–3%) of geochemically highly enriched lamproitic melts derived from the sub-continental lithospheric mantle in a geodynamic context in which a Proterozoic mobile belt (Rokelide) bordered an Archean craton (Man). Within the CAMP, similar isotopic compositions, in particular low 206Pb/204Pb and high 207Pb/204Pb, are found only in regions that were once contiguous with Sierra Leone. A comparable involvement of enriched components stored within the cratonic lithosphere may be envisaged for the high-Ti magmatism in the CAMP and two other LIPs of the South Atlantic realm, Karoo and Paraná–Etendeka. These Gondwana magmatic provinces share with other mantle-derived magmas from the South Atlantic Ocean enriched isotopic signatures (DUPAL, LOMU, EMI) of much debated origin. The present mantle source model for the FLC, CAMP, and neighbouring LIPs suggests ancient enriched subcontinental lithospheric mantle as a plausible conveyor of such isotopic signatures in the South and Central Atlantic.
format Article in Journal/Newspaper
author Callegaro, S.
Marzoli, A.
Bertrand, H.
Blichert-Toft, J.
Reisberg, L.
Cavazzini, G.
Jourdan, Fred
Davies, J.
Parisio, L.
Bouchet, R.
Paul, A.
Schaltegger, U.
Chiaradia, M.
spellingShingle Callegaro, S.
Marzoli, A.
Bertrand, H.
Blichert-Toft, J.
Reisberg, L.
Cavazzini, G.
Jourdan, Fred
Davies, J.
Parisio, L.
Bouchet, R.
Paul, A.
Schaltegger, U.
Chiaradia, M.
Geochemical constraints provided by the Freetown Layered Complex (Sierra Leone) on the origin of high-ti tholeiitic CAMP magmas
author_facet Callegaro, S.
Marzoli, A.
Bertrand, H.
Blichert-Toft, J.
Reisberg, L.
Cavazzini, G.
Jourdan, Fred
Davies, J.
Parisio, L.
Bouchet, R.
Paul, A.
Schaltegger, U.
Chiaradia, M.
author_sort Callegaro, S.
title Geochemical constraints provided by the Freetown Layered Complex (Sierra Leone) on the origin of high-ti tholeiitic CAMP magmas
title_short Geochemical constraints provided by the Freetown Layered Complex (Sierra Leone) on the origin of high-ti tholeiitic CAMP magmas
title_full Geochemical constraints provided by the Freetown Layered Complex (Sierra Leone) on the origin of high-ti tholeiitic CAMP magmas
title_fullStr Geochemical constraints provided by the Freetown Layered Complex (Sierra Leone) on the origin of high-ti tholeiitic CAMP magmas
title_full_unstemmed Geochemical constraints provided by the Freetown Layered Complex (Sierra Leone) on the origin of high-ti tholeiitic CAMP magmas
title_sort geochemical constraints provided by the freetown layered complex (sierra leone) on the origin of high-ti tholeiitic camp magmas
publisher Oxford University Press
publishDate 2017
url http://hdl.handle.net/20.500.11937/67922
https://doi.org/10.1093/petrology/egx073
genre South Atlantic Ocean
Ocean Island
genre_facet South Atlantic Ocean
Ocean Island
op_relation http://hdl.handle.net/20.500.11937/67922
doi:10.1093/petrology/egx073
op_doi https://doi.org/10.1093/petrology/egx073
container_title Journal of Petrology
container_volume 58
container_issue 9
container_start_page 1811
op_container_end_page 1840
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