The late exhumation history of the ultrahigh‐pressure Maksyutov Complex, south Ural Mountains, from new apatite fission track data

Abstract

Apatite fission track samples were collected from the ultrahigh‐pressure (UHP) Maksyutov Complex, south Ural Mountains, in the foot wall of the Main Uralian fault (MUF) to constrain the low‐temperature cooling history and to establish the late stage exhumation rate for the complex. Fission track samples were taken along a 70‐km north‐south transect and a 5‐km east‐west traverse through the Maksyutov Complex, with two samples from the hanging wall of the MUF. Apparent age and track length modeling results indicate that the Maksyutov Complex was exhumed and cooled to 110°C en masse in the Early Permian (300 ± 25 Ma). The east‐west transect shows that no significant interunit movement occurred in the Maksyutov Complex after ∼315 Ma; on the basis of higher‐temperature thermochronometers, the entire Maksyutov Complex must have been assembled between 335 and 315 Ma. Modeling for the north‐south transect indicates that exhumation occurred contemporaneously in the north and south regions of the complex with cooling to 110°C between 375 and 315 Ma, coinciding with the onset of the Uralian orogeny. Comparison of modeling for Maksyutov samples and an Ordovician metasediment from the hanging wall of the MUF indicates that late movement on the MUF was minor and that the footwall and hanging wall had a similar cooling history after the late Carboniferous (∼300 Ma). Exhumation rates range from 0.3 to 1.5 mm yr¹ between a high‐pressure metamorphic event at 375 and 315 Ma using current heat flow data. Our calculated exhumation rate for the Maksyutov Complex is consistent with the complex being a UHP terrane, even though coesite and diamond are not preserved.