2006/09/25 by S. Saito, Satoshi Saito, M. Arima +2 · 1 citation
Earth and Planetary Sciences · #Geological and Geochemical Analysis #High-pressure geophysics and materials #earthquake and tectonic studies
paper · doi:10.1093/petrology/egl055
The Miocene Tokuwa pluton of ‘I-type ’ granitoid affinity was emplaced discordantly into a Cretaceous to Paleogene accretion-ary complex and induced a contact aureole in which various thermally metamorphosed rocks were developed, including hornfels, metatexite, diatexite and cordierite-bearing tonalite (Crd-tonalite) of ‘S-type ’ granite affinity. The thermally metamorphosed rocks show low-pressure reaction textures culminating in partial melting. Peak PTconditions of 3 kbar at 7808C are estimated on the basis of the TWQ thermobarometer for the garnet-bearing rocks. The rocks in the contact aureole exhibit a gradual transition from hornfels, through metatexite and diatexite to Crd-tonalite. The Sr-isotopic composition at the time of Tokuwa pluton emplace-ment at 12 Ma decreases systematically from metatexite (0710007112) through diatexite (0707807094) to Crd-tonalite (0706707068); this trend is interpreted in terms of mixing between theTokuwa magma and the aureole migmatites. The field relationships, geochemical data, and isotopic data collectively suggest that the emplacement of theTokuwa pluton triggered partial melting of the surrounding metasedimentary rocks. Subsequent hybridization of theTokuwa magma with the metatexite in variable proportions produced the Crd-tonalite and diatexite.The hybridiza-tion was caused by invasion of the Tokuwa magma into the migmatite zone, accompanied by gravitational collapse of the previously crystallized wall of the magma chamber. The data presented demonstrate that even a relatively low-temperature, shallow, ‘I-type ’ granitoid pluton can induce contact anatexis and hybrid ‘S-type’granitoid formation at the intrusive contact. KEY WORDS: contact metamorphism; hybridization; magmahost-rock interaction; migmatite; ‘S-type’granitoid