Sedimentation, metamorphism and uplift history of the La Ronge domain, Reindeer zone, Trans-Hudson orogen

• Main Author: Yang, Haiming
• Other Authors: Kyser, Thomas
• Format: Others
• Language: en
• Published: University of Saskatchewan 1999
• Online Access: http://library.usask.ca/theses/available/etd-10212004-002142

Metasedimentary rocks are found in the Central Metavolcanic, McLennan Lake and MacLean Lake belts of the Paleoproterozoic La Ronge domain, Reindeer zone, Trans-Hudson Orogen. Geological, geochemical and geochronological data indicate that there has been a shift in sediment sources from mixing of both local and distal sources for the metasedimentary rocks in the Central Metavolcanic belt and the MacLean Lake psammitic gneisses, to predominance of distal sources for the younger McLennan Lake meta-arkoses. Nappe emplacement occurred in the Reindeer zone when the McLennan Lake meta-arkoses were deposited at ca. 1830 Ma, which has facilitated transport of detritus from the uplifted terrains in the northwest to the McLennan Lake belt. This is different from the arc-trench tectonic regime that prevailed during the sedimentation of the older MacLean Lake psammitic gneisses. Two independent thrust systems may have existed during the closure of the Reindeer zone. Convergence was SW-directed between the southeastern parts of the zone and the Archean Saskachewan craton, whereas nappe emplacement was SE-directed in the La Ronge domain and terrains to the northwest. Interaction between the La Ronge domain and the lithotectonic elements in the southeast, such as the Saskachewan craton, and the Glennie and Kisseynew domains, was probably minimal prior to metamorphism. Rocks in the La Ronge domain were metamorphosed between 1820 and 1780 Ma. Peak metamorphic conditions were attained at the end of D1 deformation, during which the Central Metavolcanic belt was thrust onto the MacLean Lake belt along the McLennan Lake tectonic zone. Peak metamorphic conditions reached greenschist to middle amphibolite facies (480-630°C, 5.2-5.6 kbar) in the Central Metavolcanic belt, and upper amphibolite facies (600-740°C, 4.4-6.6 kbar) in the McLennan Lake and MacLean Lake belts. A relatively higher thermal gradient (40-50°C/km) existed in the latter two belts, which may have resulted from heat associated with lower crustal thinning and/or lithospheric delamination. 40Ar-39Ar and Sm-Nd geochronological data suggest that cooling and exhumation rates of the La Ronge domain were heterogeneous both spatially and temporally. A ca. 3°C/Ma cooling rate is calculated for the MacLean Lake belt for the time interval between 1810 and 1780 Ma, 5°C/Ma between 1780 and 1690 Ma, and <1°C/Ma thereafter. The McLennan Lake belt had been hot for a longer period of time than the MacLean Lake and Central Metavolcanic belts. 40Ar-39Ar data from the McLennan Lake tectonic zone suggest that the tectonic zone was active until as late as 1600 Ma. Arc-related volcanism, plutonism and associated sedimentation occurred at ca. 1880 Ma in the La Ronge domain. The arc-forearc-backarc tectonic regime was replaced by fluvial arkosic sedimentation and large-scale thrust emplacement at ca. 1830 Ma. The latter process resulted in the closure of the Reindeer ocean. Metamorphism took place at ca. 1820 to 1780 Ma and peak metamorphic conditions were reached at ca. 20 Ma after the deposition of the youngest sediments. Cooling and exhumation began at ca. 1780 Ma. Thus the evolutionary cycle of formation, thrusting, metamorphism and exhumation of the Paleoproterozoic juvenile rocks in the La Ronge domain took about 0.1 Ga (1.88-1.78 Ga).