Geochronology and metamorphic <i>P</i> - <i>T</i> - <i>X</i> evolution of the Eburnean granulite-facies metapelites of Tidjenouine (Central Hoggar, Algeria): witness of the LATEA metacratonic evolution

Geological Society Special Publication - Tập 297 Số 1 - Trang 111-146 - 2008
Abderrahmane Bendaoud1, Khadidja Ouzegane1, Gaston Godard2, Jean-Paul Liégeois3, Jean-Robert Kiénast4, Olivier Bruguier5, Amar Drareni1
1Faculté des Sciences de la Terre, de la Géographie et de l'Aménagement du Territoire, USTHB, BP 32, Dar el Beida 16111, Alger,Algérie (e-mail: )
2Equipe Géobiosphère actuelle et primitive, CNRS IPGP, Université Paris 7-Denis Diderot, 4 place Jussieu, case 89, Paris Cedex 05, France
3Isotope Geology, Africa Museum, B-3080 Tervuren, Belgium
4Laboratoire de Géosciences Marines, UFR des Sciences Physiques de la Terre, Université Paris 7-Denis Diderot, UMR 7097, 4 place Jussieu, Tour 14, 5ième Etage Paris Cedex 05, France
5ISTEEM-CNRS, cc 056, Université de Montpellier II, Place Eugène Bataillon, F-34095 Montpellier, France

Tóm tắt

Abstract Central Hoggar, within the Tuareg shield to the east of the West African craton, is known for its complexity owing to the interplay of the Eburnean and Pan-African orogenies. The Tidjenouine area in the Laouni terrane belongs to the LATEA metacraton and displays spectacular examples of granulite-facies migmatitic metapelites. Here, we present a detailed petrological study coupled with in situ U–Pb zircon dating by laser-ablation inductively coupled plasma mass spectrometry (ICP-MS) that allows us to constrain the relative role of the Eburnean and Pan-African orogenies and hence to constrain how the LATEA Eburnean microcontinent has been partly destabilized during the Pan-African orogeny; that is, its metacratonic evolution. These metapelites have recorded different metamorphic stages. A clockwise P–T evolution is demonstrated on the basis of textural relationships, modelling in KFMASH and FMASH systems and thermobarometry. The prograde evolution implies several melting reactions involving the breakdown of biotite and gedrite. Peak metamorphic P–T conditions of 860±50 °C and 7–8 kbar (M 1 ) were followed by a decrease of pressure to 4.3±1 kbar and of temperature to around 700 °C, associated with the development of migmatites (M 2 ). After cooling, a third thermal phase at c . 650 °C and 3–4 kbar (M 3 ) occurred. U–Pb zircon laser ablation ICP-MS analysis allows us to date the protolith of the migmatites at 2151±8 Ma, the granulite-facies and migmatitic metamorphisms (M 1 –M 2 ) at 2062±39 Ma and the medium-grade metamorphic assemblage (M 3 ) at 614±11 Ma. This last event is coeval with the emplacement of large Pan-African granitic batholiths. These data show that the main metamorphic events are Eburnean in age. The Pan-African orogeny, in contrast, is associated mainly with medium-grade metamorphism but also mega-shear zones and granitic batholiths, characterized by a high temperature gradient. This can be considered as typical of a metacratonic evolution.

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Geological Society Special Publication

Tập 297 Số 1

111-146

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