Transported cataclasite, ophiolite and granodiorite in the Yukon: evidence of arc-continent collision

Abstract

Allochthonous Mesozoic and/or upper Paleozoic siliceous mylonite. sheared ophiolite and cataclastic granitic rocks are preserved in klippen above autochthonous, structurally imbricated Paleozoic and lower Mesozoic North American shelfstrata in central Yukon. The siliceous mylonite may be a trench melange the ophiolite oceanic forarc floor and the granitic rocks the roots of a northeast facing Early Mesozoic arc later accreted to North America. If so they imply that the arc system was partly thrust over the early Mesozoic North American margin. Northeast polarity of the arc suggests that it formed above southwestward subducting oceanic lithosphere and that the arc - continent suture marks a major closed ocean. This ocean may have spread in the Late Paleozoic and closed in the mid-Jurassic. Northeast abduction provides one continuous model for accreting the Early Mesozoic arc to North America for forming the [ore land [old and thrust belt, and for forming late-tectonic quartz monzonite plutons. It relates variations in the width o[ the [old belt to the degree of arc abduction. The duration and rates of the events are comparable to those in other mountain belts and subdue lion complexes

Geologic Setting of Eclogite-facies Assemblages in the St. Cyr Klippe, Yukon–Tanana Terrane, Yukon, Canada

“…1;Mortensen 1992;Nelson 1993;Nelson et al 2006;Colpron et al 2006a;Piercey et al, 2006Piercey et al, , 2012. This marginal basin was originally termed the Anvil Ocean by Tempelman-Kluit (1979).…”

“…Traditionally, the eclogite was assumed to have formed within the Slide Mountain terrane, a mid-to Late Paleozoic ocean basin that developed between the Yukon-Tanana arc and the western margin of North America (e.g. Tempelman-Kluit 1977, 1979Monger et al 1982;Colpron et al 2006aColpron et al , 2007. The St. Cyr area is the least known of four localities that preserve Permian eclogite in the Yukon-Tanana terrane (Figs.…”

“…1, 2, and 3;Erdmer 1992). Eclogite, garnet amphibolite, and low-grade mafic and ultramafic rocks in the St. Cyr klippe, previously mapped as part of a tectonic mélange, were considered to have formed within the Slide Mountain oceanic crust during subduction of the back-arc region (Tempelman-Kluit 1979;Erdmer 1992). However, Erdmer et al (1998) recognized that the Permian eclogite occurrences, including the St. Cyr localities, are hosted by quartzofeldspathic schist that seems to share a common metamorphic history.…”

“…5a). Several macroscopic, open to isoclinal folds with moderately to steeply plunging, northwest-trending fold axes were observed, parasitic to the larger-scale fold; however, the data are inconclusive as to whether they form part of a regional synform, like that mapped by Tempelman-Kluit (1979, 2012, thus we did not include a synform in our cross-section. Quartz and plagioclase stretching lineations plunge moderately to steeply in the down-dip direction of the foliation plane, parallel to the fold axes (Fig.…”

The Tooth of Time: The North American Cordillera from Tanya Atwater to Karin Sigloch

“…Conversely, why is there so little evidence of pre-Laramide (pre-125 Ma) tectonism and volcanism in the Rocky Mountains if a subduction zone existed on the continental margin at that time (Hildebrand 2009)? From time to time, iconoclastic scenarios have been invoked to account for these and other problems with the standard model. Some scenarios postulate that the Laramide orogeny resulted from west-dipping subduction and collision of a passive North American margin with a pre-assembled arc-bearing composite terrane (Moores 1970(Moores , 1998Tempelman-Kluit 1979;Mattauer et al 1983;Chamberlain and Lambert 1985;Lambert and Chamberlain 1988;Johnston 2001Johnston , 2008Johnston and Borel 2007;Hildebrand 2009Hildebrand , 2013. The two most recent iconoclasts, Stephen Johnston (University of Victoria) and Robert Hildebrand (University of California -Davis), arrived at nearly the same scenario independently, starting from different backgrounds and parts of the Cordillera.…”