ESTIMATION OF FORMATION TEMPERATURES OF FAULT ZONES

Muscovite-quartz schist is observed in many places of the Ekou granite in the Wutai Moutainarea, Shansi Porovinece, Near the muscovite quartz schist in muscovitized granite, the formationtemperature of pericline twinning of plagioclase is 415-466℃. At locality 502-3, the periclinetwin in muscovite quartz schist gives a formation temperature of 402℃. The formation tempera-ture of pericline twinning of plagioclase from muscovite-plagioclase gneiss and muscovite ganuli-tite in Shizui, Wutai Mountain area, Shansi Province, is 475-481℃. These data indicate thatmuscovite quartz schist and its surrounding rocks have derformation temperatures of 400-500℃.The metamorphic temperature of muscovite granite at Vassalboro, South-central Maine, USA, isestmated at 425±25℃ by Ferry.Based on an estimation of the deformation temperature of granitd gneiss at both sides of bi-otite schist originating from amphibolite the formation temperature is 519-521℃. A deformationtemperature of 512℃ has been got in biotite schist derived from amphibolite not far from it nearShizui. These data are very close and it can be assumed that the formation temperature of thisfauIt zone is 517±5℃. The biotite schist was formed at 450-540℃, inferred from hornblende-plagiochase and plagioclase geothermornetry. The metamorphic temperature in the fault zone of ultramafic rocks cannot be measured acco-rately. Until now it is evident that chlorite schist derived from ultramafic rockis not stable athigh amphibolite grade, but exists at low amphibolite grade or even lower temperature. Close tothis fault zone in biotite gneiss 4 deformation temperatures were measured to be 525-545℃. Itcan be concluded that the tectonic deformation temperature of chlorite schist is also 525-545℃.Nodular gneiss is a tectonite formed at the contact of gneiss and granite, which had a defor-mation tmeperature of 534℃. Nodular gneiss consists of chorite, plagiclase and quartz, which isconsistent with greenschist facies metamorphism. The study of four kinds of fault zones indicates that the formation temperature of fault zonescan be determined directly through estirnation of the deformation temperature of plagioclase, Cor-relation of deformation temperature and metamorphic temperature shows that they are similar butthe deformation temperature gives a narrow range, which suggests that deformation and metanor-phism in these fault zones are coeval.