Modulation of Deformation by Magmatic Tempo, Coast Mountains Batholith, British Columbia, Canada

The tectonomagmatic evolution of the southern Coast Mountains batholith, British Columbia reveals the relation of magmatic tempo, deformation, and relative plate motions which inform models for growth of continental crust and convergent plate dynamics. Magmatism in the southern batholith is episodic, derived primarily from the mantle, and reflects lower-plate dynamics (Cecil et al., 2018, https://doi.org/10.1029/2018gc007874, 2021, https://doi.org/10.1130/ges02361.1). New field, structural, geochronologic, and geobarometric results from the southern batholith document three episodes of deformation, each spatially and temporally coincident with a high magmatic flux event (HFE). Sinistral faulting (<117-103 Ma) and penetrative deformation (110-90 Ma) occurred only within two distinct areas affected by a HFE at 114-102 Ma. Following a magmatic lull, crustal shortening occurred after 90 Ma and before 72 Ma within the region affected by a second HFE (85-70 Ma). After 70 Ma and before 53 Ma, >100 km of dextral slip occurred on the Coast shear zone and minor shortening affected 64-62 Ma plutons, overlapping with the 64-61 Ma HFE. Thus, at the crustal level exposed in the southern batholith, the timing and location of deformation is linked to magmatic tempo and the style of deformation varies through time. These results suggest that magmatic HFE modulate the timing and location of deformation while relative plate motions during HFE influence the style of deformation. Periods of deformation in batholiths may thus record high-flux magmatic events and coeval plate motion but do not necessarily signal changes in plate motions. Plain Language Summary Understanding how continents grow and the dynamics of plate motions relies on knowing the geologic history of convergent margins. Here we present new data on the evolution of a Late Cretaceous-Paleogene convergent margin preserved in the southern Coast Mountains batholith in British Columbia. Magmatism in the southern batholith is episodic, derived primarily from the mantle, and reflects lower-plate dynamics (Cecil et al., 2018, https://doi.org/10.1029/2018gc007874, 2021, https://doi.org/10.1130/ges02361.1). Our new results show that the southern batholith experienced three episodes of deformation, each one coincident with one of three high-magmatic-flux events. This pattern suggests that the timing and location of deformation here is linked to magmatic tempo and the style of deformation varies independently. Thus, we conclude that magmatic patterns modulate the tempo and location of deformation and that relative plate motions during episodes of high-flux magmatism control the style of deformation. Periods of deformation in batholiths may thus record high-flux magmatic events and coeval plate motion but do not necessarily signal changes in plate motions.