caa a22 4500 465791700 CHVBK 20180323112026.0 cr unu---uuuuu 170327e19901001xx s 000 0 eng 10.1007/BF00302493 doi (NATIONALLICENCE)springer-10.1007/BF00302493 Cooling kinetics of garnet websterites from the Freychinède orogenic lherzolite massif, French Pyrenees [Elektronische Daten] [Violaine Sautter, Jacques Fabriès] Clinopyroxene and orthopyroxene megacrysts with lamellar intergrowths of pyroxenes and garnet rarely survive in pyroxenite layers from the exposed spinel-lherzolite massifs because of the emplacement history into the crust. Such features are remarkably preserved in some thick bands (up to 1 m) from the Freychinède ultramafic body (Ariège, French Pyrenees). These bands display a symmetrical zoning from the edges to the centre due to the concurrent decrease of orthopyroxene/clinopyroxene and spinel/garnet modal ratios. Textural and chemical data suggest that the present pyroxenite parageneses resulted from subsolidus recrystallization of magmatic assemblages composed of Al-rich orthopyroxene and clinopyroxene with minor spinel. These primary assemblages were changed by subsolidus recrystallization connected with an isobaric cooling at upper-mantle depth (45-50 km) from solidus temperature (1250°C) down to steady equilibrium temperature (950° C). The primary Al-rich ortho-and clinopyroxenes behaved differently on cooling. In a first stage, orthopyroxene exsolved concomitant Al-rich clinopyroxene and garnet, whereas clinopyroxene exsolved only Al-rich orthopyroxene. The garnet exsolution in clinopyroxene host is delayed to lower temperatures. This multistage process could account for the contrasting shapes of diffusion gradients adjacent to exsolved garnet, which tend to be flat in host-orthopyroxene and steep in host-clinopyroxene. An independent thermal modelling, together with available Al-diffusion data in clinopyroxene, allows us to define a fast magmatic cooling followed by a two-stage subsolidus cooling (35° C/year-6 from 1250° C to 1050° C and 9° C/year-6 to 900° C). This matches the contrasted exsolution sequences observed in the pyroxene megacrysts. Springer-Verlag, 1990 Sautter Violaine Laboratoire de Géophysique et Géodynamique Interne, CNRS-URA 1369, Université Paris-Sud, 91405, ORSAY, France aut Fabriès Jacques Laboratoire de Minéralogie, CNRS-URA 736, Museum National d'Histoire Naturelle, 61 rue Buffon, 75005, Paris, France aut Contributions to Mineralogy and Petrology Springer-Verlag 105/5(1990-10-01), 533-549 0010-7999 105:5<533 1990 105 410 https://doi.org/10.1007/BF00302493 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/BF00302493 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Sautter Violaine Laboratoire de Géophysique et Géodynamique Interne, CNRS-URA 1369, Université Paris-Sud, 91405, ORSAY, France aut NATIONALLICENCE 700 1- Fabriès Jacques Laboratoire de Minéralogie, CNRS-URA 736, Museum National d'Histoire Naturelle, 61 rue Buffon, 75005, Paris, France aut NATIONALLICENCE 773 0- Contributions to Mineralogy and Petrology Springer-Verlag 105/5(1990-10-01), 533-549 0010-7999 105:5<533 1990 105 410 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer