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Exhumation of eclogitized continental basement during Variscan lithospheric delamination and gravitational collapse, Sudety Mountains, Poland

January 2, 1993

A Variscan,deep-crustal-level (eclogite-facies),continental basement massif in western Poland, the Snieznik complex, was tectonically exhumed. Crustal-penetrating mylonite zones record three main kinematic events: early top-to-the-north-directed thrusting, right-slip transpression-tension, and late top-to-the-south and -east normal faulting. Thrusting resulted in extreme crustal thickening and associated eclogite-facies metamorphism. Right-slip movements produced retrogressive crystal-plastic simple-shear zones. Normal faults flank Carboniferous to Early Permian terrigenous sedimentary basins, documenting tectonic and erosional denudation of the Snieznik complex during lithospheric extension. Sm/Nd isotopic dates previously reported for the in situ eclogite-facies metamorphic mineral assemblages are 341, 337, and 329 Ma (Brueckner et al., 1991). 40Ar/39Ar isotopic dates for metamorphic hornblende (338, 333, and 332 Ma), muscovite (329 and 329 Ma), and biotite (328 Ma) reflect times of cooling through the ∼500, 350, and 300 °C isotherms, respectively. These nearly concordant mineral dates document rapid cooling from ∼850 °C (eclogue-facies temperatures) to ∼300 °C. Rapid denudation of these deep-crustal rocks (∼19-22 kbar pressures, >70 km depth) is attributed to processes, similar to those of metamorphic-core complexes, that operated during lithospheric delamination and gravitational collapse. The sequence of late Paleozoic (Alleghanian) crustal thickening followed by right-slip transpression-tension followed by normal faulting recognized in the U.S. Appalachians implies that this tectonic pattern may exist throughout the Afleghanian-Variscan belt.

Publication Year 1993
Title Exhumation of eclogitized continental basement during Variscan lithospheric delamination and gravitational collapse, Sudety Mountains, Poland
DOI 10.1130/0091-7613(1993)021<1111:EOECBD>2.3.CO;2
Authors Mark G. Steltenpohl, Zbignew Cymerman, E.J. Krogh, Michael J. Kunk
Publication Type Article
Publication Subtype Journal Article
Series Title Geology
Index ID 70207645
Record Source USGS Publications Warehouse
USGS Organization Eastern Geology and Paleoclimate Science Center; Florence Bascom Geoscience Center