Аннотация:We have determined the character of the metamorphic evolution of the Maksyutov eclogiteglaucophane
shist complex in the Southern Urals, the periodicity of its formation and the specific
thermodynamic parameters of mineral formation at each stage of metamorphism based on a detailed
microprobe study of the composition and zoning of coexisting minerals (garnet and pyroxene). Middle -
Late Paleozoic Maxyutovsky eclogite- glaucophane-shist complex is known as a subduction complex of
high (HP) - ultrahigh (UHP) pressures. The characteristic phases of ultrahigh (UHP) pressure (coesite
pseudomorphs after quartz, graphite cuboids after diamond, microdiamond inclusions) have been described
previously in [1-5]. New analytical data on the composition of garnet and clinopyroxene confirm the highpressure
origin of eclogitic rocks, which were found in the lower part of the complex in the form of
numerous lenses, boudins and interlayers among glaucophane and feldspar-micaceous schists.
Thermobarometric calculations of the metamorphism parameters of eclogite associations were
performed on the basis of a microprobe study of the composition and zoning of coexisting phases in the Grt
+ Cpx ± Pl + Qz paragenesis using the Grt-Cpx geothermometer by Powell [6] and the improved Pl-Cpx-
Qz geobarometer by Perchuk [7]. Garnet in the eclogites of the Maksyutovsky complex is almost always
zoned, has a direct, reverse and inversion zoning, while the clinopyroxene composition varies
insignificantly (XJd ~ 22-40 mol %). The composition of the plagioclase corresponds to albite, which
indicates its later formation. Therefore, the compositions of coexisting phases in Pl-containing eclogites
correspond to the parameters of the final, relatively low-temperature stages of the complex evolution. The
trends of temperature and pressure variations during the crystallization of zoned garnet grains (from the
center to the edge) in equilibrium with clinopyroxene were studied in samples having different weathering
degree: from central and outer parts of large boudins, from eclogite layers in the Grt-Cpx-Gln-Mu-Qz
matrix, in large porphyroblastic garnet and in small newly formed crystals from the rock matrix. Garnet
grains with a direct and reverse zoning, which are often found in one sample and demonstrate the conjugate
progressive and regressive Р-Т trends which indicate individual stages of the complex development. Based
on the obtained data, at least four episodes of metamorphic transformations of the Maksyutov complex are
defined. The age data of the individual stages [3, 4, 8] considered together with the metamorphism
parameters form a common P-T-t trend of the complex formation, which determines the position of the
metamorphic field gradient during its exhumation.
