Metamorphic and Tectonic Evolution of the Paleoproterozoic Thompson Nickel Belt, Manitoba
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2013-01-21
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Abstract
The Thompson Nickel Belt occurs along the northwestern margin of the Superior craton which was tectonically reworked during the Paleoproterozoic Trans-Hudson orogeny. This work represents the first comprehensive regional metamorphic study of the belt. Three nested metamorphic domains are present in the Thompson Nickel Belt which are elongate subparallel to the regional strike of the belt. The metamorphic domains consist of a central middle amphibolite-facies zone enclosed by an upper amphibolite-facies zone. The upper amphibolite-facies zone is flanked to the northwest and southeast by granulite-facies zones. The dominant phase of penetrative deformation was responsible for the development of regional isoclinal to recumbent folds accompanied by a regionally penetrative foliation. The analysis of microstructures suggests peak metamorphism was coincident with and possibly outlasted this penetrative event. Later generations of deformation resulted in tight, vertical to steeply incline folds commonly paralleled by shear zones with subvertical stretching lineations. Shear zones and fabrics generated by the later deformation events are commonly characterized by retrograde greenschist-facies mineral assemblages. The later generations of structures appear to exert a first order control on the present day distribution of metamorphic zones within the belt.
The regional metamorphism was characterized by relatively low pressures. Peak temperature and pressure conditions were estimated to be 550–620 °C and 3.0–5.0 kbar in the middle amphibolite-facies zone, 675–755 °C and 4.5–6.0 kbar in the upper amphibolite-facies zone, and 775–830 °C and 5.0–7.0 kbar in the granulite-facies zone. Closely spaced regional metamorphic isograds indicate locally steep geothermal gradients. Metamorphic pressure–temperature paths are interpreted to be broadly clockwise.
Collision between the Thompson Nickel Belt and the adjacent terranes of the Trans-Hudson Orogen was initiated ca. 1850 Ma. Progressive tectonic burial, accompanied by prograde metamorphism continued beyond ca. 1776 Ma. Peak metamorphic conditions were likely attained diachronously between the various metamorphic-facies zones; however, it appears to have been concurrent with, or outlasted, the dominant generation of penetrative deformation. Metamorphism was broadly synchronous with granitoid magmatism from ca. 1850 to 1750 Ma, which may have contributed to the low pressure–high temperature metamorphism characteristic of the TNB.
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Couëslan, C. G. (2013). Metamorphic and Tectonic Evolution of the Paleoproterozoic Thompson Nickel Belt, Manitoba (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/26888