Archean crustal evolution of the West African Craton; example of the Amsaga area (Reguibat Rise); U-Pb and Sm-Nd evidence for crustal growth and recycling

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doi: 10.1016/S0301-9268(98)00044-8
Authors:Potrel, A.; Peucat, J. J.; Fanning, C. M.
Author Affiliations:Primary:
CNRS, Géosciences Rennes, Rennes, France
Australian National University, Australia
Volume Title:Precambrian Research
Source:Precambrian Research, 90(3-4), p.107-117. Publisher: Elsevier, Amsterdam, International. ISSN: 0301-9268
Publication Date:1998
Note:In English. 20 refs.; illus., incl. 2 tables, geol. sketch maps
Summary:New geochronological data (U-Pb and Sm-Nd) are used to constrain the Archean crustal growth and evolution of the southwestern part of the Reguibat Rise (Amsaga area) in the West African craton. The results are summarized as follows. (1) U-Pb zircon data indicate an emplacement age of 2986±8 Ma for the magmatic protolith of a charnockitic pluton, in agreement with a whole-rock Sm-Nd isochron at 3012±142 Ma. Positive εNd(3.0) values ranging between 0.89 and 1.95 and agreement between Nd model ages (between 3.23 and 3.10 Ga) and U-Pb age indicate a juvenile origin for the magmatic protolith and imply a crustal growth event at ca 3.0 Ga. Seven rims of the charnockitic zircons yield discordant 207Pb/206Pb ages ranging from 2979±11 to 2737±11 Ma and are interpreted as resulting from growth during the granulitic event. (2) Whole-rock Sm-Nd data on migmatitic orthogneisses that form the central part of the area indicate an Archean age for their magmatic protolith (TDM ranging from 3.24 to 2.87 Ga) in agreement with a previous single zircon evaporation age of 2836±16 Ma (Potrel, 1994. Mémoire de Géosciences Rennes 56, 400). (3) Two late-tectonic, post-granulite plutons (both granite and gabbro) dated at ca 2.73 Ga mark the end of the granulitic event. The granite provides a U-Pb age of 2726±7 Ma and the gabbro a mineral Sm-Nd isochron age of 2706±54 Ma. The TDM ages ranging from 3.1 to 3.2 Ga indicate an origin by crustal reworking of the granite and negative εNd(2.7) value (-0.7) of the gabbro indicate crustal contamination during emplacement. These results, combined with previous work (Potrel et al., 1996. J. Geol. Soc., London, 153, 507-510), indicate that the Archean Reguibat Rise formed through a succession of crustal growth events from at least 3.50-3.45 Ga until 2.73 Ga. A major granulitic event took place at ca 2.73 Ga and was accompanied by emplacement of crustally derived magmas. Abstract Copyright (1998) Elsevier, B.V.
Sections:Age determination
Subjects:Absolute age; Archean; Continental crust; Crust; Dates; Emplacement; Gabbros; Genesis; Igneous rocks; Isochrons; Magmatism; Neoarchean; Nesosilicates; Orthosilicates; Plutonic rocks; Precambrian; Reworking; Silicates; Sm/Nd; U/Pb; Zircon; Zircon group; Africa; Mauritania; Reguibat Ridge; West Africa; West African Shield; Amsaga Mauritania
Coordinates:N201000 N211000 W0130000 W0134000
Abstract Numbers:99M/29
Record ID:1998042160
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands
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