caa a22 4500 467890021 CHVBK 20180406152746.0 cr unu---uuuuu 170328e20060901xx s 000 0 eng 10.1007/s00710-006-0157-1 doi (NATIONALLICENCE)springer-10.1007/s00710-006-0157-1 Franciscan eclogite revisited: Reevaluation of the P - T evolution of tectonic blocks from Tiburon Peninsula, California, U.S.A [Elektronische Daten] [T. Tsujimori, K. Matsumoto, J. Wakabayashi, J. G. Liou] Summary: High-grade blocks in the Franciscan complex at Tiburon, California, record relatively low temperature eclogite-facies metamorphism and blueschist-facies overprinting. The eclogite-facies mineral assemblage contains prograde-zoned garnet + omphacite + epidote ± hornblende (katophoritic and barroisitic Ca-Na amphibole) ± glaucophane + phengite (∼3.5 Si p.f.u.) ± paragonite + rutile + quartz. The blueschist-facies mineral assemblage contains chlorite + titanite + glaucophane + epidote ± albite ± phengite (∼3.3 Si p.f.u.). Albite is not stable in the eclogite stage. New calculations based on garnet-omphacite-phengite thermobarometry and THERMOCALC average-P-T calculations yield peak eclogite-facies P-T conditions of P = 2.2-2.5 GPa and T = 550-620 °C; porphyroclastic omphacite with inclusions of garnet and paragonite yields an average-P-T of 1.8 ± 0.2 GPa at 490 ± 70 °C for the pre-peak stage. The inferred counterclockwise hairpin P-T trajectory suggests prograde eclogitization of a relatively "cold” subducting slab, and subsequent exhumation and blueschist-facies recrystallization by a decreasing geotherm. Although an epidote-garnet amphibolitic assemblage is ubiquitous in some blocks, P-T pseudosection analyses imply that the epidote-garnet amphibolitic assemblage is stable during prograde eclogite-facies metamorphism. Available geochronologic data combined with our new insight for the maximum pressure suggest an average exhumation rate of ∼5 km/Ma, as rapid as those of some ultrahigh pressure metamorphic terranes. Springer-Verlag, 2006 Tsujimori T. Department of Geological and Environmental Sciences, Stanford University, Stanford, California, U.S.A. aut Matsumoto K. Department of Geology and Mineralogy, Graduate School of Science, Kyoto University, Kyoto, Japan aut Wakabayashi J. Department of Earth and Environmental Sciences, California State University, Fresno, California, U.S.A. aut Liou J. G. Department of Geological and Environmental Sciences, Stanford University, Stanford, California, U.S.A. aut Mineralogy and Petrology Springer-Verlag 88/1-2(2006-09-01), 243-267 0930-0708 88:1-2<243 2006 88 710 https://doi.org/10.1007/s00710-006-0157-1 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/s00710-006-0157-1 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Tsujimori T. Department of Geological and Environmental Sciences, Stanford University, Stanford, California, U.S.A aut NATIONALLICENCE 700 1- Matsumoto K. Department of Geology and Mineralogy, Graduate School of Science, Kyoto University, Kyoto, Japan aut NATIONALLICENCE 700 1- Wakabayashi J. Department of Earth and Environmental Sciences, California State University, Fresno, California, U.S.A aut NATIONALLICENCE 700 1- Liou J. G. Department of Geological and Environmental Sciences, Stanford University, Stanford, California, U.S.A aut NATIONALLICENCE 773 0- Mineralogy and Petrology Springer-Verlag 88/1-2(2006-09-01), 243-267 0930-0708 88:1-2<243 2006 88 710 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer