Parallele entre la géochimie des schistes paléozoiques et celle des formations granitiques dans le Massif du Lys-Caillaouas (Pyrénées centrales)

The granitic “Lys-Caillaouas” Massive outcrops on 50 km² in the paleozoic series of the axial zone, situated in the North West of the Maladetta. It is known for its apparent stratified formations, emphasized by pelitic (Northern and French part of the Massive) and calcareous (Southern and Spanish part) enclaves. Its “emplacement” by syncinematic intrusion of a “granite magma” was formerly postulated with reference to the then wide-spread theory of magmas and “magmatical phases” of orogeneses. However care had not been taken to examine if this scheme would take into account the particular features of this Massive as they appear through a detailed study. Starting from entirely different points of view, the authors do not think it permissible, as a method of thinking, to consider a priori the granite as extraneous to the formations in which it crops out. For this reason, starting with the mainly structural observations of M.Clin (1959), which were completed by recent mapping done by a geological group of Nancy, they have undertaken in the “Lys-Caillaouas” massive and in its vicinity, a comparative geochemical study of the paleozoic basement of the axial zone and of the igneous formations therein enclosed. These different igneous facies, from porphyroblastic granites to quartz diorite, countain enclaves, some of them mainly pelitic and others calcareous. Besides these facies are arranged in sequences and in folded structures well related to those of the paleozoic host formation. These two facts clearly show:

• -the sedimentary origin of the most apparent differenciations of the igneous complex.
• -the “keeping in place“ of sedimentary horizons during the granitization which is an observed fact and not a hypothesis as is the case with the “emplacement” of granites.