期刊
GONDWANA RESEARCH
卷 23, 期 3, 页码 865-879出版社
ELSEVIER SCIENCE BV
DOI: 10.1016/j.gr.2012.06.012
关键词
Ultrahigh-pressure metamorphism; Eclogite-garnet peridotite; Petrology; Geothermobarometry; Seve Nappe Complex; Scandinavian Caledonides
资金
- Slovak Scientific Grant Agency VEGA [2/0013/12]
- Slovak Research and Development Agency [APVV-0080-11]
- Knut & Alice Wallenberg Foundation
The first evidence for ultrahigh-pressure (UHP) metamorphism in the Seve Nappe Complex of the Scandinavian Caledonides is recorded by kyanite-bearing eclogite, found in a basic dyke within a garnet peridotite body exposed close to the lake Friningen in northern Jamtland (central Sweden). UHP metamorphic conditions of similar to 3 GPa and 800 degrees C, within the stability field of coesite, are constrained from geothermobarometry and calculated phase equilibria for the peak-pressure assemblage garnet + omphacite + kyanite + phengite. A prograde metamorphic evolution from a lower P-T (1.5-1.7 GPa and 700-750 degrees C) stage during subduction is inferred from inclusions of pargasitic amphibole, zoisite and kyanite in garnet cores. The post-UHP evolution is constrained from breakdown textures, such as exsolutions of kyanite and silica from the Ca-Eskola clinopyroxene. Near isothermal decompression of eclogite to lower crustal levels (similar to 0.8-1.0 GPa) led to formation of sapphirine, spinel, orthopyroxene and diopside at granulite facies conditions. Published age data suggest a Late Ordovician (460-445 Ma) age of the UHP metamorphism, interpreted to be related to subduction of Baltoscandian continental margin underneath an outboard terrane, possibly outermost Laurentia, during the final stages of closure of the Iapetus Ocean. The UHP rocks were emplaced from the hinterland collision zone during Scandian thrusting of the nappes onto the Baltoscandian foreland basin and platform. The record of P-T conditions and geochonological data from UHP rocks occurring within the allochthonous units of the Scandinavian Caledonides indicate that Ordovician UHP events may have affected much wider parts of the orogen than previously thought, involving deep subduction of the continental crust prior to final Scandian collision between Baltica and Laurentia. (C) 2012 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.
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