29 Petrology, Metamorphic (Posters)

Sunday, 9 October 2011
9:00 AM - 6:00 PM
Hall C

EARLY VARISCAN METAMORPHISM AND GARNET SPECIES IN THE GUILLERIES MASSIF, CATALAN COASTAL RANGES, NORTHEASTERN SPAIN

Paper number: 29-11
Program: Technical Sessions
Time: 9:00 AM – 6:00 PM

Authors

Abstract

The Guilleries Massif presents evidence of an early phase of the Variscan orogeny. This research explores the early stages of the Variscan through fieldwork, and documents relic mineral assemblages, fabrics, and P-T conditions. The focus includes the types of garnet found in the pelitic schists of the D’Osor Formation of the Guilleries as well as a comparison of the petrology of the D’Osor with the Susqueda diorite. In the Guilleries AND+CRD and BT+GRT+SIL in pelitic and semi-pelitic gneiss and schist likely preserve zones of regional metamorphism and folded S1 in garnet is truncated by a S2 crenulation cleavage. Marbles of Devonian age outline large recumbent isoclinal folds; all large structures and metamorphic zones are truncated by Neogene normal faults. AND+CRD grade rocks and S2 are truncated by the Susqueda diorite (crystallization age is 323 Ma.) In the aureole of the Susqueda diorite, contact metamorphism reached PYX+GRT+CRD grade. BT- and two-mica microgranites, ranging from meter-sized dikes and sills to mm-sized veins, trending northeast with crystallization ages of ca. 300 Ma, cross-cut all the country rocks of the massif.

Several types of garnet occur in specific petrologic settings. In pelitic schist, (a) small, idiomorphic garnets occur along the boundaries of quartz veins; (b) larger, subidiomorphic inclusion-filled garnets occur in the pelitic matrix as do (c) smaller, elongated garnet fragments. In massive, quartz-rich psammite, are (d) large, nodules of garnet. In the contact aureole of the Susqueda diorite and within the outer part of the diorite, (e) large, euhedral garnets occur. Composition maps of different types of garnet and dating monazite inclusions in them will clarify the interplay between low P/T regional metamorphism and fluid-dominated processes related to the intrusion of intermediate and felsic magmas. Ages of monazite included in (b)-type garnet provide a test of whether the Variscan orogeny included pre-Serpukhovian regional metamorphism.