Heterogeneous composition of garnets from gneisses in the shear zones (kola peninsula)

摘要

Composition and chemical zonality wereinvestigated for garnets from micaceous gneisses in a shear zonewith estimation of P-T conditiosn of their formation. The shearzone is located in the border between Kolsky and Belomorskymegablocks. Studied area is 100x450m in size. Wide variations ofthe Ca content in garnets have been revealed typical as for the areain the whole, so for separate outcrops, as well as for separatesamples. The maximum Ca bearing (up to 30-34% of grossular),and corresponding values of the metamorphism pressure (9.0-11.6kbar), has been detected in those places where intensive plasticdeformations had developed in blocks of rocks with the mostheterogeneous lithogeochemical composition. Garnets inhomogeneous gneisses, with weak appearance of plasticdeformations(i. e. formed under pressure 4.2—7.7 kbar), have thelower Ca content corresponding to 5—12% of grossular. Thus, itmay be concluded that the wide variability of Ca content isconnected with variations of the pressure caused in their turn byheterogeneous distrubution of stresses in the deep level shear zone.