Metamorphic History of the Archean Pikwitonei Granulite Domain and the Cross Lake Subprovince, Superior Province, Manitoba, Canada |
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| Authors: | MEZGER K; BOHLEN S R; HANSON G N |
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| Institution: | 1Department of Earth and Space Sciences, State University of New York Stony Brook, NY 11794
2 United States Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025 |
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| Abstract: | The Pikwitonei granulite domain and parts of the Cross Lakesubprovince, located along the northwestern margin of the ArcheanSuperior Province, expose an oblique cross-section through  20km of Archean continental crust. The area has been investigatedusing phase equilibrium and geochronological techniques to derivequantitative pressure-temperature-time paths as a function ofdepth in the crust. Ages from metamorphic minerals indicatethat metamorphism lasted at least from 2744 Ma to 259O Ma, butgrowth of garnet and zircon occurred only during short intervalsat 2744–2738, 2700–2687, 2660–2637, and 2629–2591Ma. Constraints from experimentally calibrated geobarometersand geothermometers and phase petrology indicate that ‘peak’conditions for the last metamorphism, at 2640 Ma, were 575?C/3kbat Utik Lake, 750?C/7kb at Cauchon Lake, 830?C/7?5–8 kbat Natawahunan Lake, and 9 kb close to the Thompson mobile belt. High-grade metamorphism was associated with intrusion and possiblyunderplating of magmas that had temperatures in excess of 1100?Cand contributed significant amounts of heat that promoted high-grademetamorphism. Mineral textures indicate that during progrademetamorphism, the terrane passed from the andalusite into thesillimanite stability field. After ‘peak’ metamorphismat 2640 Ma the terrane cooled nearly isobarically at a rateof 1–2?C/Ma. The observed characteristics of the amphiboliteto granulite terrane are consistent with a model where metamorphismoccurred in a continental magmatic arc setting with a magmaticarc superimposed on older continental crust. Following high-grademetamorphism, the time-integrated uplift rate was <70m/Ma.The crustal cross-section was exposed by late tectonic processesthat were unrelated to the high-grade metamorphism. |
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