Carbon contents of the magnetite-series and ilmenite-series granitoids in Japan.

Abstract

Representative magnetite-series (n=75) and ilmenite-series (n=143) granitoids, and metamorphic rocks (n=11) from the Ryoke Belt, Sanyo Belt, Sanin Belt, Hidaka Belt, Outer Zone of Southwest Japan and Green Tuff Belt, were analyzed for total and noncarbonate carbon contents by combustion and infrared absorption photometry. Noncarbonate carbon contents of the ilmenite-series granitoids (58 and 61 ppm in the average for granodiorite and monzogranite, respectively) are slightly higher than those of the magnetite-series granitoids (39 and 35 ppm), especially of the sodic type (13 ppm for tonalite). Some ilmenite-series granitoids have noncarbonate carbon contents as high as 200-300 ppm at few places. In the carbonate vs noncarbonate carbon contents diagram, common ilmenite-series granitoids have values between those of the sodic granitoids and metamorphic rocks indicating that the ilmenite-series granitoids were formed by mixing of both the igneous and sedimentary source materials. A rather ambiguous separation of the magnetite series from the ilmenite series in these contents may also be due to remobilization of carbon after the granitoids solidified.