Thor-Odin dome: Constraints on Paleocene-Eocene anatexis and deformation, leucogranite generation and the tectonic evolution of the southern Omineca belt, Canadian Cordillera

Thor-Odin dome is one of two structural culminations of the Monashee complex, located in the southeastern Omineca belt of the Canadian Cordillera. The dome comprises a supracrustal cover sequence and >1.8 Ga North American basement rocks that experienced polydeformation, high-grade metamorphism and anatexis during the Late Cretaceous - Eocene stage of the Cordilleran orogen. Pervasive Paleocene - Eocene deformation transposed and overprinted Precambrian relationships and structures.; Basement ortho- and paragneiss contain ubiquitous stromatic leucosome as well as discrete phenocrystic and pegmatitic vein-type leucosome, which are all interpreted to have formed as a result of in situ melting in the Paleocene-Eocene. The stromatic leucosome is infolded with the country rock (F2) and contains a weak foliation. The phenocrystic and pegmatitic vein-type leucosome crosscut the stromatic leucosome, as well as the transposition foliation (S2). SHRIMP 206Pb/ 238U zircon ages range from ca. 56 to 52 Ma, interpreted as the timing of leucosome crystallization. Evidence for in situ anatexis includes: igneous textures, field relations, major and trace element chemistry, Nd isotope chemistry and zircon morphology. The onset of anatexis, at ca. 56 Ma, was a result of regional prograde metamorphism and was, at least in part, coincident with the formation of the penetrative (S2) transposition foliation and large recumbent (F2) tight to isoclinal folds. Pervasive anatexis continued during F3 and F4 folding.; The timing of metamorphism in Thor-Odin basement gneiss was constrained by U-Pb SHRIMP analyses of monazite from cordierite-gedrite rocks and interlayered quartzite. Monazite grains have 206Pb/238U ages ranging from ca. 56 to 52 Ma. Monazite grew and/or were recrystallized during high-grade metamorphism and anatexis. Intergration of events with published geothermobarometry results indicate that peak metamorphism of 8-10 kbar and 800 °C in the basement gneiss culminated by ca. 56 Ma with the onset of anatexis, and the rocks underwent subsequent isothermal decompression, to < 5 kbar, which ended ca. 52 Ma.; Anatexis in the basement gneiss of Thor-Odin was synchronous with the emplacement at higher structural levels of the 62-52 Ma peraluminous, S-type Ladybird leucogranite suite. Leucosome from Thor-Odin dome and the leucogranites have similar major and trace element chemistry, classifying as peraluminous, S-type granites. In addition, they have overlapping isotopic signatures with epsilonNdL values of -5.0 to -17.2 for the leucogranites and -9.5 to -23.6 for the leucosome samples.