Abstract:
The Southern Yenisey Range (Eastern Siberia) consists of the granulite-facies Kanskiy complex bordered by the lower-grade Yeniseyskiy and Yukseevskiy complexes. Samples of metapelite of the Kanskiy complex typically show characteristic garnet-forming reaction textures and near-isobaric cooling P-T paths. An important new result of this study concerns the difference in shape of the P-T paths from different parts of the Kanskiy granulite complex: metapelites collected similar to8 km from the boundary with the Yeniseyskiy complex followed a linear path with dP/dT approximate to 0.006 kbar/degreesC; metapelites collected similar to3 km from this boundary reveal a kinked P-T path with an interval of burial cooling (dP/dT approximate to -0.006 kbar/degreesC). The difference in the shape of the P-T paths is supported by the chemical zoning of garnet studied in the second group of samples. A mechanism of buoyant exhumation of granulite is suggested by comparison with the results of numerical modelling, which indicate that such a diversity of P-T paths may result from a transient disturbance of the thermal structure by rapid differential movement of material from different crustal levels. To arrive at a correct tectonic interpretation, the whole assemblage of interrelated P-T paths of metamorphic rocks collected from different localities within the same complex must be studied.
