Mineralogical evidence for an ophiolite from the Outokumpu serpentinites in North Karelia, Finland

The serpentinites of the Outokumpu complex located in the early Proterozoic schist belt of North Karelia in Eastern Finland are investigated petrographically, mineralogically and chemically, with an emphasis on relict minerals, especially chrome spinel, and also olivine and orthopyroxene. The relict...

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Bibliographic Details
Published in:Bulletin of the Geological Society of Finland
Main Authors: J. Vuollo, T. Piirainen
Format: Article in Journal/Newspaper
Language:English
Published: Geological Society of Finland 1989
Subjects:
serpentinites
residual mantle peridotites
olivine cumulates
Alpine type ophiolite
Proterozoic
Outokumpu complex
Finland
Geology
QE1-996.5
karelia*
Online Access:https://doi.org/10.17741/bgsf/61.1.002
https://doaj.org/article/fc5edee21341478585c143d0be38042e
Description
Summary:The serpentinites of the Outokumpu complex located in the early Proterozoic schist belt of North Karelia in Eastern Finland are investigated petrographically, mineralogically and chemically, with an emphasis on relict minerals, especially chrome spinel, and also olivine and orthopyroxene. The relict minerals and textures provide evidence for an ophiolite of the Alpine type in the complex, and for the opinion that the serpentinites have originated from residual mantle peridotites and overlying olivine cumulates. The mantle peridotites, being serpentinized to chrysotile rocks, contain relicts of olivine (Fo91‒93), orthopyroxene (100*Mg/ (Mg + Fe) = 92‒94) and anhedral, euhedral or interstitial Cr-rich chrome spinel (Cr/(Cr +Al) 0.75‒0.98 and Mg/(Mg + Fe2+) 0.1‒0.4), while the cumulates have been serpentinized completely to antigorite rocks, being characterized by euhedral Al-rich chrome spinel (Cr/(Cr + AI) 0.65 and Mg/(Mg + Fe2+) 0.6).

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