Structural and petrochemical studies of chromite in the Vourinos ophiolite, N.W. Greece
Structural and petrochemical studies of chromite in the Vourinos ophiolite, N.W. Greece
Integrated field, petrographical and geochemical studies of chromite ores and their host tectonite peridotite have provided a basis for re-evaluation of the deformation of the Vourinos ophiolite. The Vourinos Mantle Sequence (MS) possesses a complex ductile tectonite fabric; increasingly heterogeneous, less ductile structures being superimposed on earlier fabrics. Deformation reflects long-lived (mainly simple) shear with components of northeastward thrusting and east-northeast trending dextral wrench motion. Earliest recognised fabrics occur throughout the MS but are more complex in dunite due to chromitite layering. Later ductile deformation nucleates preferentially in dunite bodies, forming shear zones between discrete harzburgite blocks of variable size. Peridotite textures confirm a variably strong deformation with syntectonic migration recrystallisation of olivine and Cr-spinel during simple shear. Olivine crystal slip systems indicate deformation dominantly > 1100oC with incipient lower temperature systems (≤800^oC) developing in reorientating grains. Lower temperature systems are pronounced in peridotites of highest strain rate. Derived strain rates of 10^-14 to 10^-16 s^-1 indicate plate tectonic rate deformation. Cr-spinel and orthopyroxene (OPx) chemistry support evidence of multiple melt extractions from the source mantle. Dunite represents segregated melt trapped and re-equilibrated with surrounding harzburgite. Deformation has not significantly altered ore or peridotite chemistry. Only in extremely deformed mylonite layers has OPx breakdown and Cr-spinel scavenging affected mineral chemistry. The Supra-Subduction Zone model is proposed as the most likely method of producing the observed chemical variation. An integrated model proposes at-ridge decoupling at plate tectonic rates in response to oblique closure. The resultant deformation is responsible for the dominant MS structures. Pre-existing chromium ore bodies are modified and upgraded mechanically by this deformation which is modelled for exploration purposes.
University of Southampton
1989
Moat, Thomas
(1989)
Structural and petrochemical studies of chromite in the Vourinos ophiolite, N.W. Greece.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
Integrated field, petrographical and geochemical studies of chromite ores and their host tectonite peridotite have provided a basis for re-evaluation of the deformation of the Vourinos ophiolite. The Vourinos Mantle Sequence (MS) possesses a complex ductile tectonite fabric; increasingly heterogeneous, less ductile structures being superimposed on earlier fabrics. Deformation reflects long-lived (mainly simple) shear with components of northeastward thrusting and east-northeast trending dextral wrench motion. Earliest recognised fabrics occur throughout the MS but are more complex in dunite due to chromitite layering. Later ductile deformation nucleates preferentially in dunite bodies, forming shear zones between discrete harzburgite blocks of variable size. Peridotite textures confirm a variably strong deformation with syntectonic migration recrystallisation of olivine and Cr-spinel during simple shear. Olivine crystal slip systems indicate deformation dominantly > 1100oC with incipient lower temperature systems (≤800^oC) developing in reorientating grains. Lower temperature systems are pronounced in peridotites of highest strain rate. Derived strain rates of 10^-14 to 10^-16 s^-1 indicate plate tectonic rate deformation. Cr-spinel and orthopyroxene (OPx) chemistry support evidence of multiple melt extractions from the source mantle. Dunite represents segregated melt trapped and re-equilibrated with surrounding harzburgite. Deformation has not significantly altered ore or peridotite chemistry. Only in extremely deformed mylonite layers has OPx breakdown and Cr-spinel scavenging affected mineral chemistry. The Supra-Subduction Zone model is proposed as the most likely method of producing the observed chemical variation. An integrated model proposes at-ridge decoupling at plate tectonic rates in response to oblique closure. The resultant deformation is responsible for the dominant MS structures. Pre-existing chromium ore bodies are modified and upgraded mechanically by this deformation which is modelled for exploration purposes.
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Published date: 1989
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Local EPrints ID: 461904
URI: http://eprints.soton.ac.uk/id/eprint/461904
PURE UUID: 1339368b-0b17-4f85-9155-cf44b7aabe0b
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Date deposited: 04 Jul 2022 18:58
Last modified: 04 Jul 2022 18:58
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Author:
Thomas Moat
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