The Temaguessine Fe-cordierite orbicular granite (Central Hoggar, Algeria):: U-PbSHRIMP age, petrology, origin and geodynamical consequences for the late Pan-African magmatism of the Tuareg shield

The Temaguessine high-level subcircular pluton is intrusive into the LATEA metacraton (Central Hoggar) Eburnian (2 Ga) basement and in the Pan-African (615 Ma) granitic batholiths along a major NW-SE oriented major shear zone. It is dated here (SHRIMP U-Pb on zircon) at 582 15 Ma. Composed of amphibole-biotite granite and biotite syenogranite, it comprises abundant enclaves: mafic maginatic enclaves, country-rock xenoliths and remarkable Fe-cordierite (#Fe = 0.87) orbicules. The orbicules have a core rich in cordierite (40%) and a leucocratic quartz-feldspar rim. They are interpreted as resulting from the incongruent melting of the ineta-wacke xenoliths collapsed into the magma: the breakdown of the biotite + quartz assemblage produced the cordierite and a quartz-feldspar minimum inelt that is expelled, forming the leucocratic rim. The orbicule generation occurred at T < 850 degrees and P < 0.3 GPa. The Fe-rich character of the cordierite resulted from the Fe-rich protolith (wacke with 4%,, Fe2O3 for 72% SiO2,). Strongly negative epsilon(Nd) (-9.6 to - 11.2), Nd T-DM model ages between 1.64 and 1.92 Ga, inherited zircons between 1.76 and 2.04 Ga and low to moderately high I-sr (0.704-0.710) indicate a Rb-depleted lower continental crust source for the Temguessine pluton; regional considerations impose however also the participation of asthenospheric material. The Ternaguessine pluton, together with other high-level subcircular pluton, is considered as marking the end of the Pan-African magma generation in the LATEA metacraton, resulting from the linear delamination along mega-shear zones, allowing asthenospheric uprise and melting of the lower continental crust. This implies that the younger Taourirt granitic province (535520 Ma) should be considered as a Cambrian intraplate anorogenic event and not as a very late Pan-African event. (c) 2007 Elsevier Ltd. All rights reserved.