A new member of the Kurosegawa tectonic zone was found in serpentinite near Kochi City, SW Japan. These rocks are high-P, low-T schists derived from basalt and chert. Three metamorphic events can be deciphered in the high-P schists, based upon the texture and mineral paragenesis: first, low-P metamorphism at intermediate to high grade; second, high-P, low-T metamorphism of the jadeite-glaucophane facies; and the third, retrograde crystallization of the second stage high-P schists within the stability field of lawsonite + pumpellyite + glaucophane. Further, analcite formed, replacing jadeite. The second and third stages of metamorphism can be distinguished on pyroxene mineralogy: jadeite + quartz were stable in the second, but albite + quartz + aegirine-jadeite were stable in the third. Not all the high-P, low- T schists suffered low-P metamorphism before they were metamorphosed by the high-P stage; some basaltic rocks changed directly to high- P, low-T schists. Two muscovites in the schists gave K/Ar ages of 208-240 m.y., and a relic igneous biotite, partly replaced by chlorite, gave 225 m.y. These values differ not only from those of the Sanbagawa schists, but also from the other members of the Kurosegawa zone. (Following abstracts)M.Ak.
|Number of pages||11|
|Journal||Journal of the Japanese Association of Mineralogists, Petrologists & Economic Geologists|
|Publication status||Published - Jan 1 1978|
ASJC Scopus subject areas
- Environmental Science(all)
- Earth and Planetary Sciences(all)