Fluid–rock interaction and deformation in ultramafic mélange: Studies using the isocon method

Abstract

Fluid–rock interaction and deformation in ultramafic melange were studied using the isocon method. In ultramafic melange in the Nishisonogi metamorphic rocks, pelitic-schist blocks have albitized rims. The isocon analysis indicates losses of H₂O and C, decoupling of LILE from HFSE and REE, and solid-volume change of about -20 % during albitization. The decrease in solid volume could reduce pore-fluid pressure and promote influx of fluid and deformation of rocks. Similarly, jadeitite blocks have albitite rinds. The isocon analysis indicates gains of K₂O, H₂O, Sr and Ba, losses of SiO₂, Na₂O and Fe₂O₃, and solid-volume change of about +10 % during albitization. The albitite rinds could protect the jadeitite cores from retrogression, because the increase in solid volume reduces permeability.