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The Relationship between Tectono-metamorphic Evolution and Argon Isotope Records in White Mica: Constraints from in situ 40Ar-39Ar Laser Analysis of the Variscan Basement of Sardinia |
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| Authors: | DI VINCENZO GIANFRANCO; CAROSI RODOLFO; PALMERI ROSARIA |
| Institution: | 1 ISTITUTO DI GEOSCIENZE E GEORISORSE–CNR, VIA MORUZZI 1, I-56124 PISA, ITALY 2 DIPARTIMENTO DI SCIENZE DELLA TERRA, UNIVERSITÀ DI PISA, VIA S. MARIA 53, I-56126 PISA, ITALY 3 MUSEO NAZIONALE DELL'ANTARTIDE, UNIVERSITÀ DI SIENA, VIA LATERINA 8, I-53100 SIENA, ITALY |
| Abstract: | The basement of Sardinia represents a nearly complete sectionof a segment of the Variscan belt that experienced a polyphasetectono-metamorphic evolution and Barrovian metamorphism. Thisbasement is well suited to investigate the relationship betweentectono-metamorphic evolution and argon isotope records in whitemica. Micaschists from the garnet zone (maximum T of up to 520–560°C)contain two texturally and chemically resolvable generationsof white mica: (1) deformed celadonite-rich flakes, defininga relict S1 foliation preserved within the main S2 foliationor enclosed in rotated albite porphyroblasts; (2) celadonite-poorwhite micas aligned along the main S2 foliation. The S1 foliationdeveloped earlier and at a deeper crustal level with respectto that at which the thermal peak was reached. From the staurolitezone (T of up to 590–625°C) to the sillimanite + K-feldsparzone, white mica is nearly uniform in composition (muscovite)and is predominantly aligned along the S2 foliation or is oflater crystallization. In situ 40Ar–39Ar laser analysesof white mica yielded ages of |
| Keywords: | : K– Ar systematics 40Ar– 39Ar laserprobe dating white mica Barrovian metamorphism Variscan belt |
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