Mantle control on magmatic flare-ups in the southern Coast Mountains batholith, British Columbia

Abstract The southern Coast Mountain batholith was episodically active from Jurassic to Eocene time and experienced four distinct high magmatic flux events during that period. Similar episodicity has been recognized in arcs worldwide, yet the mechanism(s) driving such punctuated behavior are debated. This study uses zircon Hf O isotopes, with whole-rock mineral geochemistry, track spatiotemporal changes Mountains melt sources evaluate models of flare-up crust formation Cordilleran arc systems. Zircon isotope analysis yielded consistently primitive values, all grains recording initial ?Hf between +6 +16. majority (97%) zircons analyzed ?18O values 4.2‰ 6.5‰, only five recorded up 8.3‰. These isotopic results interpreted reflect magmatism dominated by mantle melting periods across areas batholith, which argues against periodic input more melt-fertile crustal materials as driver episodic magmatism. They also indicate limited recycling is needed produce large volumes continental generated batholith. Although character intrusions relatively invariant through time, magmas emplaced flare-ups record higher Sr/Y La/Yb(N) lower Ti Yb concentrations, consistent thickened garnet present a fractionating phase. Flare-ups temporally associated when both widens advances inboard. We suggest landward shift into fertile lithospheric domains triggers voluminous accompanied and/or tectonic thickening. Overall, these demonstrate growth can be spatially complex without requiring variability contributions