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Inverted metamorphic zonation in a basement‐derived nappe sequence, eastern margin of the Bohemian Massif
Author(s) -
Štípská Pavla,
Schulmann Karel
Publication year - 1995
Publication title -
geological journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.721
H-Index - 54
eISSN - 1099-1034
pISSN - 0072-1050
DOI - 10.1002/gj.3350300315
Subject(s) - geology , nappe , metamorphism , massif , metamorphic rock , basement , granulite , geochemistry , petrology , seismology , geomorphology , facies , tectonics , civil engineering , structural basin , engineering
Inverted metamorphic zonation is developed in the basement‐derived nappe sequence at the eastern margin of the Bohemian Massif. Mineral reactions and geothermometry reveal an increase in temperature from 580–600°C to 650°C and an increase in pressure from 6 to 10 kbar from the bottom to the top of the nappe pile. Kinematic data and syntectonic crystallization of minerals indicate that the peak conditions were diachronously attained during a slow oblique underthrusting of the Brunovistulian basement. Geochronological data reveal about 20 Ma between granulite facies metamorphism of the upper plate and mineral cooling ages in lower plate, precluding perturbation of the geotherm by underthrusting. A model is suggested showing a progressive break‐up of the deepest part of the underthrust Brunovistulicum and subsequent migration of the intraplate to the base of the basement‐derived thrust sheet. The uplift of this unit led to its decompression while the rest of the basement was subject to continuous underthrusting. The inverted metamorphic zonation within a single unit is explained using a model of heterogeneous deformation of upward transported units and passive inversion of initially subhorizontal isograds.