Timiskaming volcanism in the Kirkland Lake area, Ontario, Canada
The petrography and chemistry of the Timiskaming volcanics of the Kirkland Lake area reveal three distinct yet intimately associated suites within a composite volcanic-sedimentary sequence. The initial phase of Timiskaming volcanism was characterized by calc-alkaline lavas, which are transitional be...
| Published in: | Canadian Journal of Earth Sciences |
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| Main Authors: | , |
| Format: | Article in Journal/Newspaper |
| Language: | English |
| Published: |
Canadian Science Publishing
1969
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| Subjects: | |
| Online Access: | http://dx.doi.org/10.1139/e69-012 http://www.nrcresearchpress.com/doi/pdf/10.1139/e69-012 |
| Summary: | The petrography and chemistry of the Timiskaming volcanics of the Kirkland Lake area reveal three distinct yet intimately associated suites within a composite volcanic-sedimentary sequence. The initial phase of Timiskaming volcanism was characterized by calc-alkaline lavas, which are transitional between the later alkaline volcanics of the Timiskaming and the underlying calcic Keewatin greenstones. Flows of alkalic mafic trachytes and a variety of leucitic lavas and pyroclastic rocks are the latest differentiates represented. This occurrence of leucitic volcanics is the first reported anywhere in the Precambrian. Deposition of sedimentary rocks and intrusions of syenite and mafic syenites were contemporaneous with the period of volcanism, but intrusions of feldspar porphyry were post-Timiskaming.The major mineral constituents are augite, biotite, plagioclase, leucite, and their alteration products. Potash feldspar and hornblende occur in subsidiary amounts, and magnetite and apatite are the common accessory minerals. The chemical composition of this volcanic sequence is marked by high alkalies, Al 2 O 3 , and low SiO 2 , P 2 O 5 , and TiO 2 . The calc-alkaline and alkaline lavas are rich in Na 2 O and poor in K 2 O and BaO, whereas the leucite lavas are high in K 2 O and BaO, and comparatively low in Na 2 O.The Kirkland Lake sequence is compared with similar exotic, but less altered, lavas of more recent age in order to clarify further the nature of Timiskaming volcanism. The alkalic association of the Kirkland Lake area is similar to those occurring at a late stage in the volcanic cycle of modern volcanic arcs and along orogenic belts marginal to major continental masses. |
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