Distribution, nature, and origin of Neogene-Quaternary magmatism in the northern Cordilleran volcanic province, Canada

Abstract

The northern Cordilleran volcanic province encompasses a broad area of Neogene to Quaternary volcanism in northwestern British Columbia, the Yukon Territory, and adjacent eastern Alaska. Volcanic rocks of the northern Cordilleran volcanic province range in age from 20 Ma to ca. 200 yr B.P. and are dominantly alkali olivine basalt and hawaiite. A variety of more strongly alkaline rock types not commonly found in the North American Cordillera are locally abundant in the northern Cordilleran volcanic province. These include nephelinite, basanite, and peralkaline phonolite, trachyte, and comendite. The most MgO-rich nephelinites, basanites, and alkaline basalts from throughout the northern Cordilleran volcanic province show trace element abundances and isotopic compositions that are consistent with an asthenospheric source region similar to that for average oceanic island basalt and for post-5 Ma alkaline basalts from the Basin and Range. Our petrologic observations help constrain the origin of northern Cordilleran volcanic province magmatism as well as lithosphere changes between the four major basement terranes that underlie the province. Results from phase equilibria calculations and the spatial distributions of volcanic rock types and magmatic inclusions are more consistent with the existence of thicker lithosphere beneath Stikinia, which underlies the southern part of the northern Cordilleran volcanic province, than beneath the Cache Creek and Yukon-Tanana terranes, which underlie the northern part of the northern Cordilleran volcanic province. Our results support a model for initiation of northern Cordilleran volcanic province magmatism due to incipient rifting of the northern Cordillera, driven by changes in relative plate motion between the Pacific and North American plates ca. 15-10 Ma.

Pyroclastic passage zones in glaciovolcanic sequences

“…1) and records the dynamic interplay between changes in the intensity of the effusive phase of eruption and changes in lake levels. Hence, Kima'Kho is a subglacial volcano that preserves passage-zone geometries in both explosive and effusive sequences 20,22,24 . The evidence for, and implications of, a passage zone within a pyroclastic succession are developed below.…”

“…In glaciovolcanic settings, the elevation of the passage-zone surface unequivocally records the height and depth of the paleo-englacial lake at a specific point in time and space [16][17][18] . This elevation fixes the minimum thickness of the enclosing ice sheet and has been used as a paleoclimate proxy by constraining glaciations in both southern and northern hemispheres, including Antarctica 5,8,16 , Iceland 7,19 and British Columbia 1,[20][21][22][23] . However, previous workers have only identified glaciovolcanic passage zones 16,17,22 within effusive volcanic sequences where the passage zone separates subaqueous lavafed delta lithofacies from overlying subaerial lavas.…”

Basanite glaciovolcanism at Llangorse mountain, northern British Columbia, Canada

“…8; e.g., Mathews 1951Mathews , 1952. This association of volcanic eruption with glaciation is typical of the NCVP, where there is abundant evidence of synglacial and subglacial volcanism reflecting the coincidence of Pliocene to Pleistocene glaciers with volcanism (Edwards and Russell 2000). For example, the Tuya-Teslin volcanic district contains numerous subglacial volcanic edifices, including the type locality for tuyas (Mathews 1947;.…”

“…The Northern Cordilleran Volcanic Province (NCVP) comprises Miocene to Holocene volcanic rocks distributed across northwestern British Columbia, the Yukon Territory, and eastern Alaska (Edwards and Russell 2000). The NCVP is dominated by small, mafic alkaline centres that represent single eruptive events or cycles, although longlived, chemically evolved volcanic centres do occur (e.g., Mount Edziza, Hoodoo Mountain, Level Mountain).…”

Initiation of the Wrangell Arc: A Record of Tectonic Changes in an Arc-Transform Junction Revealed by New Geochemistry and Geochronology of the ~29–18 Ma Sonya Creek Volcanic Field, Alaska

“…Changes in relative plate motions between the Pacific and North American plates ca. 10 Ma allowed asthenosphere to upwell through a slab-window, causing extensional stresses and decompression melting of OIB-like mantle to produce alkaline magmatism (Edwards and Russell, 2000;Thorkelson et al, 2011). Specific volcanic geochemistry depends on the local asthenosphere and lithospheric mantle, but changes in plate motion drove magmatism 100's of km's inboard of the continental margin.…”