Effects of Paleogene faults on the reconstruction of the metamorphic history of the northwestern Thor-Odin culmination of the Monashee complex, southeastern British Columbia

Abstract

Differences in U-Pb metamorphic monazite ages in the northwestern Thor-Odin culmination of the Monashee complex, southern Canadian Cordillera, are explained in the context of the NNW-trending subvertical transcurrent Paleogene Victor Creek fault. Similar faults are present throughout the Canadian Cordillera. We demonstrate their potential importance in the interpretation of the history of Cordilleran deformation and metamorphism. A pervasive transposition foliation (S T) is present throughout the Thor-Odin culmination as a result of Cordilleran and possibly earlier deformation. A pre-S T (or early S T) foliation is preserved as aligned inclusion trails in porphyroblasts such as garnet and kyanite. Monazite U-(Th-)Pb isotope dilution-thermal ionization and secondary ion microprobe mass spectrometry (ID-TIMS, SIMS) ages are used to relate monazite growth to pre-and syn-S T fabrics and associated metamorphism. The ages of both pre-and syn-S T fabrics, and the gap between pre-and syn-S T ages decrease toward the east, in an apparently continuous manner. While monazite west of the Victor Creek fault is latest Cretaceous to earliest Eocene in age, monazite east of the Victor Creek fault is exclusively Eocene. Correlation of rock types across the faults is difficult because the same rock units are repeated many times on either side. However, distinctly different retained ages of metamorphism, and previously recognized differences in structures and detrital zircon signatures across the fault indicate 5-60 km offset along the fault. Similar trends occur across other faults along the western Monashee complex, and faults here and elsewhere in the Canadian Cordillera may have similar geological significance.

Metamorphic evolution and SIMS U-Pb geochronology of the Qingshigou area, Dunhuang block, NW China: Tectonic implications of the southernmost Central Asian orogenic belt

“…Determination of the metamorphic P-T conditions of these rocks and more importantly, linking the absolute timing of metamorphism to the P-T paths are key factors in understanding their tectonic evolution (Harley, 1989;Grujic et al, 2011;Zhao et al, 2010). Deciphering metamorphic textures and pressure-temperature-time (P-T-t) history enables us to better understand the dynamic factors producing the corresponding P-T conditions, the duration of these conditions, and the subsequent exhumation process (e.g., Harley, 1989;O'Brien and Rötzler, 2003;Ambrose et al, 2015;Kuiper et al, 2015;Likhanov et al, 2015).…”

Characterizing the Southwestern Extent of the Norumbega Fault System, a Mid-Paleozoic Crustal-Scale Strike-Slip Fault System in the New England Appalachians

“…The metamorphic grade in the MB increases westward from lower-greenschist facies to amphibolite facies (Lyons et al, 1997;Robinson, 1981;Wintsch et al, 1992;Watts et al, 2000). The MB underwent multiple folding events beginning with several generations of m-to km-scale, east-verging isoclinal folds, followed by local north-trending horizontal recumbent chevron folds (Robinson, 1978(Robinson, ,1981Goldstein, 1994;Kopera and Walsh, 2014;Kuiper et al, 2014;Charnock, 2015). Metamorphism of the MB has been interpreted as primarily a result of the Alleghanian orogeny (Goldstein, 1994;Attenoukon, 2009).…”

“…Potential NFS-related faults to the southeast A number of major faults has been recognized in eastern MA and eastern CT including the Clinton-Newbury, Bloody Bluff, Flint Hill-Silver Lake-Wekepeke, and Honey Hill-Lake Char faults (Figure 1.1; Goldstein and Hepburn, 1999;Bothner and Hussey, 1999). The Clinton-Newbury fault (CNF) along the northwestern boundary of the Nashoba terrane dips moderately to steeply to the NW and shows sinistral shear that has been overprinted by normal shear (Goldstein, 1994;Dougherty and Kuiper, 2013;Kuiper et al, 2014;He, 2017). It brings greenschist facies metasedimentary rocks of the Merrimack belt into contact with highly metamorphosed and deformed upper amphibolite facies rocks of the Nashoba terrane.…”

Deconstructing the Infrastructure: A Complex History of Diachronous Metamorphism and Progressive Deformation during the Late Cretaceous to Eocene in the Thor-Odin–Pinnacles Area of Southeastern British Columbia

“…Based on currently available data and the interpretations presented in this study, the Thor-Odin dome does not seem to be a good candidate for developing through the double dome model of Rey et al (2011) because there is currently no good estimate for where the steep dividing shear zone would be. The dominant steep features in the Thor-Odin area are N-S striking, steep to near-vertical brittle faults (some dextral strike-slip, some normal) that post-date and dismember metamorphic sequences (Kruse and Williams 2007;Kuiper et al 2015) and largely reflect extension after peak metamorphism and subsequent exhumation.…”