Protoliths and petrogenesis of Archean gneisses from the Kenora area, English River Subprovince, northwest Ontario
Identifieur interne : 004072 ( Main/Exploration ); précédent : 004071; suivant : 004073Protoliths and petrogenesis of Archean gneisses from the Kenora area, English River Subprovince, northwest Ontario
Auteurs : Charles F. Gower [Canada] ; Dalim K. Paul [Inde] ; James H. Crocket [Canada]Source :
- Precambrian Research [ 0301-9268 ] ; 1981.
Abstract
Archean gneissic rocks in the Kenora area can be divided into three groups: 1.(1) remnants of a dominantly mafic supracrustal sequence;2.(2) biotite tonalite gneisses;3.(3) granitic pegmatoid gneisses.From field, petrographic and compositional data, the biotite tonalite gneisses are interpreted as plutonic rocks derived by partial melting of the supracrustal sequence. The granitic pegmatoid gneisses are considered to be the product of fractional crystallization of the tonalitic magma. Attempts were made to reconstruct this scheme by computer-assisted trace element modelling using REEs.With the source rock constrained to one having a bulk composition similar to that of the fine-grained amphibolites within the supracrustal sequence (comparable to Archean tholeiite elsewhere), the most satisfactory source rock was found to be a two-pyroxene garnet granulite (quartz 5%, plagioclase 25–35%, clinopyroxene 30–40%, orthopyroxene 15–25%, garnet 5–15%). This, when 10% melted under equilibrium, non-modal conditions, will yield a model melt with a REE pattern similar to that observed in the tonalites. Quartz eclogite, granulite without garnet, and amphibolite are not acceptable source rocks under the modelling conditions used. The mineralogy of the optimum model source rock is similar to that expected in a quartz tholeiite melting between 45 and 50 km depth.The granitic pegmatoid gneisses have very low REE content, especially LREEs, and their patterns defied conventional modelling. They may result from REE loss in residual fluids or the end result, after precipitation of REE-rich phases, such as allanite.
Url:
DOI: 10.1016/0301-9268(82)90026-2
Affiliations:
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Gower</name><affiliation wicri:level="1"><country xml:lang="fr">Canada</country><wicri:regionArea>Department of Mines and Energy, Newfoundland and Labrador, P.O. Box 4750, St. John's</wicri:regionArea><wicri:noRegion>St. John's</wicri:noRegion></affiliation></author><author><name sortKey="Paul, Dalim K" sort="Paul, Dalim K" uniqKey="Paul D" first="Dalim K." last="Paul">Dalim K. Paul</name><affiliation wicri:level="1"><country xml:lang="fr">Inde</country><wicri:regionArea>Geochronology Division, Geological Survey of India, 29, J.L. Nehru Road</wicri:regionArea><wicri:noRegion>J.L. Nehru Road</wicri:noRegion></affiliation></author><author><name sortKey="Crocket, James H" sort="Crocket, James H" uniqKey="Crocket J" first="James H." last="Crocket">James H. Crocket</name><affiliation wicri:level="1"><country xml:lang="fr">Canada</country><wicri:regionArea>Department of Geology, McMaster University, Hamilton</wicri:regionArea><wicri:noRegion>Hamilton</wicri:noRegion></affiliation></author></analytic><monogr></monogr><series><title level="j">Precambrian Research</title><title level="j" type="abbrev">PRECAM</title><idno type="ISSN">0301-9268</idno><imprint><publisher>ELSEVIER</publisher><date type="published" when="1981">1981</date><biblScope unit="volume">17</biblScope><biblScope unit="issue">3–4</biblScope><biblScope unit="page" from="245">245</biblScope><biblScope unit="page" to="248">248</biblScope></imprint><idno type="ISSN">0301-9268</idno></series><idno type="istex">A69428074ACAAD71A898ADDE91351F93D9C1B3C0</idno><idno type="DOI">10.1016/0301-9268(82)90026-2</idno><idno type="PII">0301-9268(82)90026-2</idno></biblStruct></sourceDesc><seriesStmt><idno type="ISSN">0301-9268</idno></seriesStmt></fileDesc><profileDesc><textClass></textClass><langUsage><language ident="en">en</language></langUsage></profileDesc></teiHeader><front><div type="abstract" xml:lang="en">Archean gneissic rocks in the Kenora area can be divided into three groups: 1.(1) remnants of a dominantly mafic supracrustal sequence;2.(2) biotite tonalite gneisses;3.(3) granitic pegmatoid gneisses.From field, petrographic and compositional data, the biotite tonalite gneisses are interpreted as plutonic rocks derived by partial melting of the supracrustal sequence. The granitic pegmatoid gneisses are considered to be the product of fractional crystallization of the tonalitic magma. Attempts were made to reconstruct this scheme by computer-assisted trace element modelling using REEs.With the source rock constrained to one having a bulk composition similar to that of the fine-grained amphibolites within the supracrustal sequence (comparable to Archean tholeiite elsewhere), the most satisfactory source rock was found to be a two-pyroxene garnet granulite (quartz 5%, plagioclase 25–35%, clinopyroxene 30–40%, orthopyroxene 15–25%, garnet 5–15%). This, when 10% melted under equilibrium, non-modal conditions, will yield a model melt with a REE pattern similar to that observed in the tonalites. Quartz eclogite, granulite without garnet, and amphibolite are not acceptable source rocks under the modelling conditions used. The mineralogy of the optimum model source rock is similar to that expected in a quartz tholeiite melting between 45 and 50 km depth.The granitic pegmatoid gneisses have very low REE content, especially LREEs, and their patterns defied conventional modelling. They may result from REE loss in residual fluids or the end result, after precipitation of REE-rich phases, such as allanite.</div></front></TEI><affiliations><list><country><li>Canada</li><li>Inde</li></country></list><tree><country name="Canada"><noRegion><name sortKey="Gower, Charles F" sort="Gower, Charles F" uniqKey="Gower C" first="Charles F." last="Gower">Charles F. Gower</name></noRegion><name sortKey="Crocket, James H" sort="Crocket, James H" uniqKey="Crocket J" first="James H." last="Crocket">James H. Crocket</name></country><country name="Inde"><noRegion><name sortKey="Paul, Dalim K" sort="Paul, Dalim K" uniqKey="Paul D" first="Dalim K." last="Paul">Dalim K. 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