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Reply to Comment on "U-Pb baddeleyite ages and geochemistry of dolerite dykes in the Bas-Draa inlier of the Anti-Atlas of Morocco: Newly identified 1380 Ma event in the West African Craton" by Andre Michard and Dominique Gasquet

Söderlund, Ulf LU ; Ibanez-Mejia, Mauricio ; El Bahat, Abdelhakim ; Ernst, Richard E. ; Ikenne, Moha ; Soulaimani, Abderrahmane ; Youbi, Nasrrddine ; Cousens, Brian ; El Janati, M'hamed and Hafid, Ahmid (2013) In Lithos 174. p.101-108
Abstract
Baddeleyite (ZrO2) is today recognized as the key mineral for dating the emplacement of mantle-derived igneous rocks, primarily gabbro and dolerite dykes and sills. The comment by Michard and Gasquet calls for a discussion on the significance of baddeleyite U-Pb TIMS dates of two dykes in the Bas-Draa inlier, dated at 1381 +/- 8 and 1384 +/- 6 Ma, presented in El Bahat et al. (2013-in this issue). They suggest that the U-Pb systematics were "seriously perturbed in the Bas-Draa region" with the main argument being a lack of age matches between the ca. 1385 Ma dykes in Bas-Draa and the 2040, 1650 and 885 Ma dykes in adjacent inliers to the east. To infer an older age for these dykes, as suggested by Michard and Gasquet, and explain the ca.... (More)
Baddeleyite (ZrO2) is today recognized as the key mineral for dating the emplacement of mantle-derived igneous rocks, primarily gabbro and dolerite dykes and sills. The comment by Michard and Gasquet calls for a discussion on the significance of baddeleyite U-Pb TIMS dates of two dykes in the Bas-Draa inlier, dated at 1381 +/- 8 and 1384 +/- 6 Ma, presented in El Bahat et al. (2013-in this issue). They suggest that the U-Pb systematics were "seriously perturbed in the Bas-Draa region" with the main argument being a lack of age matches between the ca. 1385 Ma dykes in Bas-Draa and the 2040, 1650 and 885 Ma dykes in adjacent inliers to the east. To infer an older age for these dykes, as suggested by Michard and Gasquet, and explain the ca. 1385 Ma TIMS results would require two separate events of perturbation, in the Mesoproterozoic and a subsequent Variscan event. However, such an alternative is improbable from basic theoretical reasoning using U-Pb isotopic systematics and our current understanding of the behaviour of baddeleyite in metamorphic systems. In addition, we present new LA-ICPMS U-Pb age data of baddeleyite from one of the dated dykes from Bas-Draa. The new LA-ICPMS U-Pb age of 1416 +/- 7 Ma is slightly but significantly older than our TIMS 1384 +/- 6 Ma upper intercept age, nevertheless confirming this dyke could not correspond to any of the other mafic intrusions dated in the inliers to the east. The IA-ICPMS result also contributes to a deeper understanding on the effects of secondary processes in baddeleyite in general, and suggests a modified methodological approach for samples with complex geological histories. (C) 2013 Elsevier B.V. All rights reserved. (Less)
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author
; ; ; ; ; ; ; ; and
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Baddeleyite, U-Pb, Concordia diagram, Discordance, TIMS, LA-ICPMS
in
Lithos
volume
174
pages
101 - 108
publisher
Elsevier
external identifiers
  • wos:000321680400009
  • scopus:84878971708
ISSN
0024-4937
DOI
10.1016/j.lithos.2013.04.003
language
English
LU publication?
yes
id
db600df3-72a6-4d6e-abf4-2701f4bb2481 (old id 3975598)
date added to LUP
2016-04-01 10:11:40
date last changed
2022-03-19 18:18:28
@misc{db600df3-72a6-4d6e-abf4-2701f4bb2481,
  abstract     = {{Baddeleyite (ZrO2) is today recognized as the key mineral for dating the emplacement of mantle-derived igneous rocks, primarily gabbro and dolerite dykes and sills. The comment by Michard and Gasquet calls for a discussion on the significance of baddeleyite U-Pb TIMS dates of two dykes in the Bas-Draa inlier, dated at 1381 +/- 8 and 1384 +/- 6 Ma, presented in El Bahat et al. (2013-in this issue). They suggest that the U-Pb systematics were "seriously perturbed in the Bas-Draa region" with the main argument being a lack of age matches between the ca. 1385 Ma dykes in Bas-Draa and the 2040, 1650 and 885 Ma dykes in adjacent inliers to the east. To infer an older age for these dykes, as suggested by Michard and Gasquet, and explain the ca. 1385 Ma TIMS results would require two separate events of perturbation, in the Mesoproterozoic and a subsequent Variscan event. However, such an alternative is improbable from basic theoretical reasoning using U-Pb isotopic systematics and our current understanding of the behaviour of baddeleyite in metamorphic systems. In addition, we present new LA-ICPMS U-Pb age data of baddeleyite from one of the dated dykes from Bas-Draa. The new LA-ICPMS U-Pb age of 1416 +/- 7 Ma is slightly but significantly older than our TIMS 1384 +/- 6 Ma upper intercept age, nevertheless confirming this dyke could not correspond to any of the other mafic intrusions dated in the inliers to the east. The IA-ICPMS result also contributes to a deeper understanding on the effects of secondary processes in baddeleyite in general, and suggests a modified methodological approach for samples with complex geological histories. (C) 2013 Elsevier B.V. All rights reserved.}},
  author       = {{Söderlund, Ulf and Ibanez-Mejia, Mauricio and El Bahat, Abdelhakim and Ernst, Richard E. and Ikenne, Moha and Soulaimani, Abderrahmane and Youbi, Nasrrddine and Cousens, Brian and El Janati, M'hamed and Hafid, Ahmid}},
  issn         = {{0024-4937}},
  keywords     = {{Baddeleyite; U-Pb; Concordia diagram; Discordance; TIMS; LA-ICPMS}},
  language     = {{eng}},
  pages        = {{101--108}},
  publisher    = {{Elsevier}},
  series       = {{Lithos}},
  title        = {{Reply to Comment on "U-Pb baddeleyite ages and geochemistry of dolerite dykes in the Bas-Draa inlier of the Anti-Atlas of Morocco: Newly identified 1380 Ma event in the West African Craton" by Andre Michard and Dominique Gasquet}},
  url          = {{http://dx.doi.org/10.1016/j.lithos.2013.04.003}},
  doi          = {{10.1016/j.lithos.2013.04.003}},
  volume       = {{174}},
  year         = {{2013}},
}