The Maksyutov Complex: The first UHP terrane 40 years later
Published:January 01, 2007
Rachel Beane, Mary Leech, 2007. "The Maksyutov Complex: The first UHP terrane 40 years later", Convergent Margin Terranes and Associated Regions: A Tribute to W.G. Ernst, M. Cloos, W.D. Carlson, M.C. Gilbert, J.G. Liou, S.S. Sorensen
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Radial fractures around quartz inclusions in garnets from the Maksyutov Complex were first described nearly 20 years before coesite in crustal rocks was recognized elsewhere as evidence for ultrahigh-pressure (UHP) metamorphism and deep (>90 km) subduction. Twenty years later, evidence for microdiamond in garnet was described in the Maksyutov Complex. The intervening 40 years brought researchers from around the world to the south Ural Mountains of Russia to investigate the petrology, geochemistry, structure, and geochronology of the Maksyutov Complex. The well-studied Maksyutov Complex provides insights into the exhumation processes of UHP terranes.
The protolith of the UHP Kairakli unit of the Maksyutov Complex began as Cambrian rift-induced basalt intruded into Proterozoic metasedimentary rocks of the East European platform. The Kairakli unit was subducted eastward beneath the forming Magnitogorsk island arc and metamorphosed at 650 °C and 2.6–3.2 GPa at ca. 385 Ma. Synconvergent buoyant exhumation brought the Kairakli unit to lower-crustal depths, where shear zones juxtaposed it with the meta-ophiolite-bearing Karamola unit and an intervening sedimentary unit, the Yumaguzino quartzite, at ca. 360 Ma. By 315 Ma, all units were exhumed to 3–4 km depth.
Exhumation rates for the Maksyutov Complex of 5 mm/yr are much slower than the ∼25 mm/yr estimated for other UHP terranes. This calculated rate supports research that found fast exhumation rates are not the most efficient means to cool a UHP terrane so as to preserve coesite or microdiamond. Instead, the Maksyutov Complex, a thin slab (<10 km), probably was kept cool by continued subduction of cold crust during its buoyant exhumation.