Mantle flow through the Northern Cordilleran slab window revealed by volcanic geochemistry

Abstract

The Northern Cordilleran slab window formed beneath western Canada concurrently with the opening of the Californian slab window beneath the southwestern United States, beginning in Late Oligocene-Miocene time. A database of 3530 analyses from Miocene-Holocene volcanoes along a 3500-km-long transect, from the northern Cascade Arc to the Aleutian Arc, was used to investigate mantle conditions in the Northern Cordilleran slab window. Using geochemical ratios sensitive to tectonic affi nity, such as Nb/Zr, we show that typical volcanic arc compositions in the Cascade and Aleutian systems (derived from subduction-hydrated mantle) are separated by an extensive volcanic fi eld with intraplate compositions (derived from relatively anhydrous mantle). This chemically defi ned region of intraplate volcanism is spatially coincident with a geophysical model of the Northern Cordilleran slab window. We suggest that opening of the slab window triggered upwelling of anhydrous mantle and displacement of the hydrous mantle wedge, which had developed during extensive early Cenozoic arc and backarc volcanism in western Canada. High heat fl ow throughout the western Canadian Cordillera is broadly coincident with the fi eld of intraplate volcanism and is linked to slab window-induced mantle upwelling.

Asthenosphere–lithosphere interaction triggered by a slab window during ridge subduction: Trace element and Sr–Nd–Hf–Os isotopic evidence from Late Carboniferous tholeiites in the western Junggar area (NW China)

“…Adakites-high-Mg andesites are typically generated by partial melting of subducted slab edge or mafic arc basement. Alkaline and tholeiitic mafic magmas range from depleted MORB to enriched OIB type basalts and are derived from sub-arc lithospheric mantle, sub-slab and/or supra-slab asthenosphere, a subducted lithospheric mantle source, or some mixture of these sources (Cole and Stewart, 2009;Thorkelson et al, 2011). In the following sections, we consider these alternative mantle sources with specific reference to the Hatu tholeiites.…”

Chronostratigraphy of the Hottah terrane and Great Bear magmatic zone of Wopmay Orogen, Canada, and exploration of a terrane translation model

“…However, the evolving magmatic system is consistent with a rapidly rifting arc setting. Such an environment may result from a variety of subduction zone adjustments, including slab rollback, delamination, or flattening, or possibly the development of a pseudo-slab window from outboard ridge subduction (e.g., Dickinson 2002;Thorkelson et al 2011;Giba et al 2013). However, the suprasubduction zone geochemical signature of the rocks can also be attainted from a prior, rather than active, subduction-modified mantle (e.g., Bryan et al 2014).…”

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

“…Calc-alkaline volcanic rocks are attributed to subduction, and the small-volume of alkaline volcanic rocks is attributed to low-degree melting of asthenosphere and lithospheric mantle following mantle upwelling around the edge of the slab and through a slab-window (Thorkelson et al, 2011). A younger analog to the alkaline magmatism found in the Canadian (eastern) WA is the Neogene-Quaternary Northern Cordilleran volcanic province that ranges ~1200 km from central Yukon Territory to central British Columbia (Edwards and Russell, 1999;.…”

“…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.…”

“…Thorkelson et al (2011) enhances this model by including the influence a slab window, wherein the subsequent upwelling of mantle asthenosphere would induce melting. The changes in geochemistry seen in the St.…”