Isotopic (RbSr, UPb and SmNd) and trace element geochemistry of eclogites from the pan-African Belt: A case study of REE fractionation during high-grade metamorphism

Bernard-Griffiths, J.; Peucat, J.-J.; Ménot, René-Pierre

doi:10.1016/0024-4937(91)90019-h

Cited by 74 publications

(42 citation statements)

References 26 publications

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“…In the Dahomeyides two geochemical/geotectonic groups of mafic/ultramafic eclogites/granulites were defined (Affaton et al, 1980;Bernard-Griffiths et al, 1991;Castaing et al, 1994;Agbossoumondé et al, 2001Agbossoumondé et al, , 2004Caby, 2003;Attoh and Morgan, 2004;Duclaux et al, 2006). The first and rarer category comprises mainly eclogites with a clockwise metamorphic P-T evolution and geochemical signature of MORB.…”

Section: Discussionmentioning

confidence: 99%

Occurrence and geochemistry of metamafic rocks from the Forquilha Eclogite Zone, central Ceará (NE Brazil): geodynamic implications

2011

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In the northern region of the Borborema Province, a 30 km-long mafic/ultramafic belt of high pressure (HP) rocks called the Forquilha Eclogite Zone has been recently discovered in the Central Domain of Ceará State. The belt comprises three groups of rocks: (1) garnet amphibolites, (2) retrograded eclogites and (3) clinopyroxene-garnet amphibolites, all of them being hosted in garnet AE kyanite þ sillimanite schists and orthogneisses which are often migmatized. The geochemical analyses of 30 representative samples confirm differences among the three groups that were initially classified by petrography. The garnet amphibolites are the most depleted rocks, with relatively flat rare earth element (REE) PM pattern and (SPIDER) PM pattern with negative Rb, Th, Nb, Sr and Zr anomalies. It is the most fractionated group, ranging from picrobasalts to andesites. Fractional crystallization and mineral accumulation are indicated by Eu and Sr anomalies. The data show geochemical affinities with island-arc basalts. The retrograded eclogites display flat (REE) PM , but without Eu anomalies. Nb/La ratios are low and variable, as for slightly enriched MORB from ocean floor or intra-oceanic back-arc environments. However, a genetic link with the Group 1 rocks cannot be completely discarded. The clinopyroxene-garnet amphibolites are the most enriched group. (REE) PM and (SPIDER) PM patterns show many features of alkaline basalts. In the Nb/Yb versus Th/Yb diagram the data cluster near the E-MORB standard. Several geochemical aspects of these rocks fit well those from the HP/UHP Pan-African/Brasiliano Suture Zone in the Dahomeyides/Hoggar regions of West Africa. However, differences in their extent and lack of alignment preclude a direct correlation among these zones.

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Section: Discussionmentioning

confidence: 99%

Occurrence and geochemistry of metamafic rocks from the Forquilha Eclogite Zone, central Ceará (NE Brazil): geodynamic implications

2011

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“…600 Ma (Affaton et al 1991a;Attoh et al 1997). According to Affaton et al (1978), Caen-Vachette et al (1979), Bernard-Griffiths et al (1991) and Attoh et al (1997), the rocks of the Kara unit are Palaeoproterozoic in age (2064 90 Ma) and have been reworked during the Pan-African orogenesis (between 640 and 600 Ma ago).…”

Section: Geological Setting and Previous Geochronologymentioning

confidence: 95%

“…Henry and J.Y. Scanvic, unpublished data;MØnot 1977;Affaton et al 1978;Affaton 1990;Bernard-Griffiths et al 1991), the petrological, structural and geochronological characteristics of the Kabye Massif remain poorly known. The publication of the geological map of Kara at a scale of 1:200,000 (Affaton et al 1984), and the investigations of Sabi (1992), provided important insights to a better knowledge of this massif.…”

Section: Introductionmentioning

confidence: 99%

Pan-African granulite formation in the Kabye Massif of northern Togo (West Africa): Pb−Pb zircon ages

Affaton

Kröner²,

Seddoh

2000

International Journal of Earth Sciences

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Metamorphic zircons from seven granulite facies orthogneisses of tonalitic composition (enderbites), collected from four different nappes of the Kabye Massif in the Dahomeyide belt of northern Togo, were dated by the Pb±Pb evaporation method. They yielded consistent Neoproterozoic ages with a mean of 612.5 0.8 Ma, interpreted to reflect the peak of regional granulite facies metamorphism following Pan-African continental collision between the West African and Benin-Nigerian plates. These results support previous ages obtained by various chronometers on high-grade rocks from the same suture zone and from surrounding units in Togo, Benin and Ghana. They are also similar to zircon ages from granulites in the Mozambique belt of souteastern Africa. These Pan-African metamorphic ages reflect continental amalgamation resulting in the formation of the Gondwana supercontinent towards the end of the Neoproterozoic.

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“…Thus taken together high pressure metamorphism of the suture zone rocks occurred around 603-613 Ma and exhumation through the hornblende ages around 580-570 Ma (Attoh et al, 2007). U-Pb ages on zircon separates determined by Bernard-Grifiths et al (1991) from eclogite facies rocks from the suture zone in southern Togo had a discordant lower intercept of ~640 ± 53 Ma and Nd model ages (T DM ) of 1150 Ma (Bernard-Grifiths et al, 1991). Nd model age of 940 Ma was obtained by Attoh and Schmitz (1991) in the HP mafic granulites from the Shai Hills area in Ghana.…”

Section: Previous Geochronological Workmentioning

confidence: 93%

Petrological and Geochemical Characteristics of Mafic Granulites Associated with Alkaline Rocks in the Pan-African Dahomeyide Suture Zone, Southeastern Ghana

Nude¹,

Attoh²,

Shervais³

et al. 2012

Petrology - New Perspectives and Applications

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Isotopic (RbSr, UPb and SmNd) and trace element geochemistry of eclogites from the pan-African Belt: A case study of REE fractionation during high-grade metamorphism

Cited by 74 publications

References 26 publications

Occurrence and geochemistry of metamafic rocks from the Forquilha Eclogite Zone, central Ceará (NE Brazil): geodynamic implications

Occurrence and geochemistry of metamafic rocks from the Forquilha Eclogite Zone, central Ceará (NE Brazil): geodynamic implications

Pan-African granulite formation in the Kabye Massif of northern Togo (West Africa): Pb−Pb zircon ages

Petrological and Geochemical Characteristics of Mafic Granulites Associated with Alkaline Rocks in the Pan-African Dahomeyide Suture Zone, Southeastern Ghana

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