Mississippian assembly of the Nisutlin assemblage: evidence from primary contact relationships and Mississippian magmatism in the Teslin tectonic zone, part of the Yukon–Tanana terrane of south-central Yukon

Abstract

Metamorphosed and ductilely deformed sedimentary, plutonic, and volcanic rocks of the Nisutlin and Anvil assemblages make up the Yukon–Tanana terrane in the Teslin tectonic zone study area. The Nisutlin assemblage consists of siliceous schist–quartzite and graphitic phyllite that share a primary depositional contact, and Early Mississippian tonalite to quartz diorite that intrudes the siliceous schist–quartzite and possibly the graphitic phyllite. The Anvil assemblage includes metagabbro and mafic schist–greenstone that share an intrusive contact relationship. Tonalite to quartz diorite of the Nisutlin assemblage is characterized by minor zircon inheritance with an average Proterozoic age, εNd(350 Ma) values of −2.5 to −6.2, and Nd model ages of 1.50–1.79 Ga. These data suggest that the magmatic bodies have inherited a component of continentally derived material. Primary contact relationships and age data indicate that the Nisutlin assemblage had formed by Mississippian time, and regional correlations show that this assemblage makes up a large part of the Yukon–Tanana terrane of southern Yukon. Assembly of the Nisutlin assemblage by Mississippian time indicates that it did not form as a late Paleozoic and early Mesozoic subduction melange, and it suggests that its tectonic fabrics did not result from the progressive growth of a Permo-Triassic subduction complex. We suggest that the Nisutlin assemblage was part of a crustal block that lay outboard of North America in Mississippian time, and that it lay in the hanging-wall plate of a Permo-Triassic subduction zone as a relatively coherent assemblage, rather than forming within the zone as a subduction complex.

Mid- to late Paleozoic K-feldspar augen granitoids of the Yukon-Tanana terrane, Yukon, Canada: Implications for crustal growth and tectonic evolution of the northern Cordillera

“…9) that require signifi cant recycling of ancient, likely Proterozoic, upper-crustal material. These results are in accord with other augen granitoids and felsic rocks in the Yukon-Tanana terrane that have upper-crust-like trace-element characteristics (Dusel-Bacon and Aleinikoff, 1985;Dusel-Bacon et al, 2004;Piercey et al, 2006Piercey et al, , 2001, evolved Nd, Sr, and Pb isotopic attributes (Grant, 1997;Mortensen, 1992;Piercey et al, 2003a;Stevens et al, 1995), and inherited Proterozoic to Archean zircon (Mortensen, 1990(Mortensen, , 1992Murphy et al, 2006).…”

“…In the northern Cordillera, most of these granitoid studies have concentrated on the Mesozoic and Cenozoic intrusive rocks (e.g., Armstrong, 1988;Cui and Russell, 1995;Driver et al, 2000;Friedman et al, 1995;Ghosh and Lambert, 1995;Hart et al, 2004;Mair et al, 2006;Morris and Creaser, 2003), and only minor studies have been undertaken on Paleozoic plutonic rocks (e.g., Grant, 1997;Piercey et al, 2003a;Stevens et al, 1995). Paleozoic plutonic rocks, however, make up a signifi cant component of the Yukon-Tanana terrane and rocks of the pericratonic (or near-continent) terranes of the Cordillera and are key probes to the crustal evolution and crust-mantle interaction within these terranes.…”

“…Within the Yukon-Tanana terrane, there are two main granitoid plutonic groups: (1) the metaluminous, calc-alkalic, early Mississippian Simpson Range plutonic suite and equivalents (Grant, 1997;Mortensen, 1992;Piercey et al, 2003a;Stevens et al, 1995); and (2) Devonian to Permian augen granitoid suites (Dusel-Bacon and Aleinikoff, 1985;Mortensen, 1992;Piercey et al, 2003a). Previous studies on the Simpson Range plutonic suite have illustrated that they are largely the product of crust-mantle interaction within a magmatic arc system (Grant, 1997;Mortensen, 1992;Piercey et al, 2003a;Stevens et al, 1995).…”

“…Previous studies on the Simpson Range plutonic suite have illustrated that they are largely the product of crust-mantle interaction within a magmatic arc system (Grant, 1997;Mortensen, 1992;Piercey et al, 2003a;Stevens et al, 1995). In contrast, the knowledge base for the augen granitoids is much smaller (Dusel-Bacon and Aleinikoff, 1985;Dusel-Bacon and Aleinikoff, 1996;Piercey et al, 2003a).…”

Major and trace element compositions and Sr-Nd-Pb systematics of crystalline rocks from the Dawson Range, Yukon, Canada

“…Studies utilizing techniques such as geochemical (major, trace, and rare earth element) and isotopic (Nd, Sr, and Pb) analysis which can yield information regarding the origin and tectonic environment in which rock units are formed are absent for the Dawson Range. Hitherto, tectonic models for the origin of the Dawson Range area are based largely on the data from Devonian-Mississippian rocks of the southern Yukon and eastern Alaska (Mortensen 1992 and references therein; Stevens et al 1996;Creaser et al 1997;Grant 1997).This paper summarizes the geology and geochemical characteristics of the rock units (Devono-Mississippian Wolverine Creek Metamorphic Suite, mid-Cretaceous Dawson Range batholith, mid-Cretaceous Casino Plutonic Suite, and late Cretaceous plutons) from the Dawson Range in the ar-Can. …”