Relation Between Metamorphic Zoning and Graphitizing Degree in Sambagawa Metamorphic Belt

根据泥质和砂质片岩的矿物组合特征，将关东山桑巴川变质地体划分为三个带。这些区域从低到高依次为1区、2区和3区。带状边界是非常复杂的，往往难以精确追踪。泥质岩和砂质岩的石墨化度是变质温度的函数，石墨化度与石榴子石对的Mg-Fe分配系数之间存在良好的正相关关系。因此，建立了以下分区分类的基础。1区; G. D. <27，第2带;石榴石+石榴石，G. D. 28-35和3带;石榴子石+黑云母和石榴子石+黑云母; D. 36岁以上。2区的一些薄透镜状岩体在1区区域内夹层，1区和3区岩石的薄透镜状岩体在2区夹层，2区的薄透镜状岩体在3区夹层。该区域的带状结构被解释为许多透镜的堆叠，每个透镜具有特定的组合和G。D.此外，在与区域3邻接的区域2透镜中，G. D.不增加他们的边界，但减少。与四国中部三钵川地体的岩石学资料相比，发现有显著差异：1）两地区泥质片岩中石榴石的出现温度大致相同（G. D.另一方面，黑云母的形成温度明显较低（G. D.约36）比四国（G. D.石榴石带的温度宽度关东比四国窄。这表明前者的变质压力也低于后者。

The Sambagawa metamorphic terrain of Kanto Mountains is classified into three zones on the basis of mineral assemblages of pelitic and psammitic schists. The zones are, from lower to higher grade, Zone 1, Zone 2 and Zone 3. The zonal boundaries are highly complicated and often difficult to trace precisely. The graphitizing degree measured on pelitic and psammitic rocks is a function of metamorphic temperature, and a good positive correlation is observed between the degree and the Mg-Fe partition coefficient in garnet-chlorite pair of the same rock. Therefore, the basis of zonal classification has been established as follows. Zone 1 ; chlorite, G. D. <27, Zone 2 ; chlorite+garnet, G. D. 28-35, and Zone 3 ; chlorite+garnet+biotite and chlorite+biotite, G. D. >36. A few thin lenticular masses of Zone 2 are interlayered in the Zone 1 area, those of Zone 1 and Zone 3 rocks in Zone 2, and those of Zone 2 in Zone 3. The zonal structure of the area is interpreted to be stacks of a number of lenses, each of which has a particular assemblage and G. D. Furthermore, in a Zone 2 lens contiguous to Zone 3, G. D. does not increases towards their boundary but decreases. Therefore, that boundary is not a thermal isograd of metamorphic crystallization.As compared with the petrological data obtained in the central Shikoku Sambagawa terrain, remarkable differences have been found. 1) The appearance temperature of garnet in pelitic schists are roughly the same in both areas (G. D. about 28), 2) on the other hand, the temperature of biotite formation is distinctly lower (G. D. about 36) in Kanto Mountains than in Shikoku (G. D. about 50), and 3) the temperature width of the garnet zone is narrower in Kanto than in Shikoku. It is suggested that the metamorphic pressure also is lower in the former than in the latter areas.