Petrology and U/Pb geochronology of the Telohat migmatites,Aleksod, Central Hoggar,Algeria |
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Authors: | Pierre Barbey Jean-Michel Bertrand Serge Angoua Danielle Dautel |
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Institution: | (1) Laboratoire de Pétrologie, Université de Nancy I, B.P.239, F-54506 Vandoeuvre-lès-Nancy cedex, France;(2) Centre de Recherches Pétrographiques et Géochimiques, B.P.20, F-54501 Vandoeuvre-lès-Nancy cedex, France |
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Abstract: | The Aleksod region is composed of metasedimentary rocks and large areas of biotite and hornblende-bearing migmatites. Anatexis
associated with the main deformation stages, occurred under high pressure and temperature conditions estimated at 13±2 Kbar
and 750±50° C. The bulk mineralogical composition of the Telohat migmatites shows that their protolith was granodioritic.
Internal structures of zircons and U-Pb data suggest a polyphased evolution, with a 2131±12 Ma age for the protolith and a
609±17 Ma age for the Pan-African tectono-metamorphic evolution, thus precluding any Kibaran event in the Aleksod area. Leucosomes
are richer in Sr and display lower Rb, Zr, Nb, Y, Th, U and REE contents than melanosomes wherein accessory phases are stored.
Eu contents are also lower in the leucosomes but in lesser proportion than the other rare earth's, leading to a significant
positive anomaly. Petrogenetic modelling accounting for accessory mineral phases clearly shows that the trace element contents
of leucosomes and melanosomes follow a distribution law consistent neither with equilibrium nor fractional melting. Their
trace element patterns are best explained by the model of disequilibrium melting, with mixing of a few residual phases. The
present results and previous Sr isotopic data as well raise the question of disequilibrium melting in anatexis of crustal
material
CRPG Contribution no 782 |
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