Morphology of the Explorer–Juan de Fuca slab edge in northern Cascadia: Imaging plate capture at a ridge-trench-transform triple junction

Evidence for trench-parallel mantle flow in the northern Cascade Arc from basalt geochemistry

“…Salal Glacier and Bridge River also coincide with the trace of the Nootka fault zone (Fig. 1a) that forms the boundary between the subducting Juan de Fuca plate and the nearly stagnant Explorer microplate (Audet et al, 2008;Riddihough, 1984). These characteristics are more consistent with generation of the northern GVB alkalic basalts by decompression melting of NE Pacific asthenosphere flowing into the Cascadia mantle wedge through a slab gap at the Nootka fault (Mullen and Weis, 2013).…”

“…Cousens, unpublished data, 2007) and subducting northern Cascadia sediment (Carpentier et al, 2014) (Fig. 4a).…”

“…There is currently no unambiguous means by which to distinguish subducting sediment input from crustal contamination. Northern Cascadia subducting sediment is terrigenous, derived from many of the same crustal rocks of western North America (Carpentier et al, 2014) that are potential contaminants for ascending magmas. Interaction with crustal rocks can therefore mimic many of the geochemical patterns considered 'diagnostic' of slab-derived contributions (Mullen and Weis, 2013).…”

Slab morphology in the Cascadia fore arc and its relation to episodic tremor and slip

“…Structural signals along line 2 show evidence of a well‐defined LVZ dipping gently NE along the entire profile that is most obvious in the reverberations P P [ t , b ] S and P S [ t , b ] S at ∼10–20 s. Oppositely polarized P [ t , b ] S signals indicate a shallowing of the LVZ signature that is mirrored by earlier arrivals of reverberated phases and has been interpreted as shearing due to slab stretching in this region [ Audet et al , 2008]. …”

Gas hydrate within the Winona Basin, offshore western Canada

“…Around 6 Ma the Explorer ridge broke away from the Juan de Fuca ridge and began migrating to the northwest; after 1.5 Ma the Revere-Dellwood fault was initiated and likewise propagated to the northwest. A sliver of plate is likely being subducted under Vancouver I. between the Nootka fault zone and Brooks peninsula, but subduction is not thought to occur north of this peninsula (Lewis et al, 1997;Kao et al, 2007;Audet et al, 2008). Various micro-plates have existed in the triple junction region during the rapid recent tectonic evolution; given the scrambled magnetic anomalies in the Explorer region (Botros and Johnson, 1988;Riddihough, 1977a,b;Wilson, 1988) and lack of dates in the sediments the history and configuration of these blocks are a matter of ongoing conjecture (Rohr and Furlong, 1995;Braunmiller and Nabelek, 2002;Ristau, 2004;Rohr and Tryon, 2010).…”