An ANALYSIS OF FUPINGIAN METAMORPHISM IN THE TAIHANG MOUNTAINS, HEBEI PROVINCE

Fupingian metamorphism is a thermal event that took place in the Fuping- ian movement. The metamorphic age is about 2800 Ma. When the earliest continental nucleus of the North China platform was formed, the Fuping Group was its component part. The protoliths of the Fuping Group are represented by a formation of basic volcanic rocks-clastio rocks-magnesian carbonate rocks; the original tectonic environments are marked by an oceanic volcanic basin or voloanic island sea on the early event, exhibiting the nature of an embryonio miogeosyncline. Migmatization is intense and homogeneous. Folds are open domal composite anticlines. The Fuping Group belongs to the progressive metamorphic medium-pressure facies series. Granulite facies is marked by the appearance of Hy, a pressure of 7-10 kb and a temper ature of 750--850°; higher amphibolite facies is marked by the appearance of Di in metamorphic intermediate-basic rocks and Sil+Kf in metamorphic pelite. a pressure of greater than 5 kb and a temperature of 650-750℃; lower amphibolite facies is marked by the appearance of Ky+St in metamorphic pelite, Pl+Hb±Alm in metamorphic basic rocks and rare Di, a pressure of 4-10 kb and a temperature of 540-700℃. Analysing by use of the Schreinmakers method, the author has come to the conclusion that at a controlled temperature of 6-9 kb and with rising tempera- ture, the evolutionary sequence is as follows: Hb+Bi-Di+Bi-Hy+Di correspond to their metamorphic facies belt, with higher amphibplite facies predominating and there is a transitional belt between higher and lower amphibolite facies. Regional metametamorphism was controlled by its initial state: or various causes might lead to anatexis below 620℃, thus influencing the appearance or stability of high-temperature minerals. The Fuping Group may also be distin- guished from the Qianxi Group by its low heat flow value or a short duration of high temperature. Some minerals change with their optical properties of the facies zones. The classification of metamorphic facies has the features of empirical induction. The tectono-thermal events occurred synchronously or alternatively in succession or even overlapepd, showing no cyclic superimposition.