隠岐島後の泥質ミグマタイトに含まれる流体包有物の研究

その他

Thisstudy examined composition offluid inclusionsin leucocratic and melanocratic pads of pelitic migmatites from oki-Dogo to understand fluid activity throughout p-T history of high-T/10W-p metamorphic terrane. Calculated fluid density and isochores range from o.73 to o.84 g/cm3 and from 450 to 540゜c at 3 kbar, respectively, for H20, and from o.71 to o.87 g/cm3 and from 540 t0860゜c for c02 indusions. The temperature range for the C02 indusions is almost consistent with previously estimated peak and retrogade conditions; 750~820゜c at 1.5~4 kbar for peak and 580~630゜c at 29~3.9 kbar for retrograde conditions. The range for the H20 inclusions
is, however, significanuy lower than the retrograde condition. our results therefore suggest that co.-bearing auid was dominant during peak to retrograde metamorphism, while H.0-rich fluid infiltrated at the last stage of metamorphism.
Graphite is the most probable source of co. because the co. inclusion becomes dominant with increasing modal abundance of graphite in migmatites. origin of H20 is not clearly understood, but probably associated with an uplifting of metamorphic terrane providing H.0-bearing hydrothermal auid from middle crust. The Iater H20 infiltration brought about hydration of garnet and biotite to chlorite and muscovite, which marks the end of thermal events of oki metamorphic rocks.