COULD THE CHICXULUB METEORITE IMPACT 66 MY HAVE CAUSED BAJA BC TO SURGE NORTHWARDS?

The Chicxulub meteorite impact may have caused the accelerated plate motions along extensive detachment faults that led to unprecedented rapid northward movement of terranes along the western margin of North America. The Baja BC hypothesis posits that the crumpled, faulted and extensively sheared western margin of northwestern North America resulted from bringing diverse accreted terranes from latitudes near Baja, Mexico to British Columbia and even to the Yukon and Alaska. This movement would have been along a recent suture zone accommodating thousands of miles of movement between 90 my and 50 my ago, possibly mainly between 70 and 50 my. Evidence for this movement was based originally on paleomagnetism, but geologic and paleontologic evidence has also been accumulating and is consistent with tomotectonic imaging. The rate of (transpressive) dextral strike-slip movement along a Baja BC fault was 3 to 10 cm/year (or more), depending on when it began. Seismic waves generated by the Chicxulub impact and their reverberations may have accelerated it. The Chicxulub meteorite fell near the southern edge of an accreting double subduction zone’s newly formed suture extending northwards. Just to the northwest, a small plate fragment (the Orcas plate) was subducting northwestwards. The seismic waves from this impact location would have induced shattering, fracturing, shear zone acceleration, release of fluids and volatiles, and even localized melting along shear zones, including the Baja BC suture and Orcas plate trench. Analogous to surging glaciers responding to built-up stresses, the Baja BC terranes could have surged northwards in response to the impact’s effect on existing deformation and fault surfaces coupled with stresses due to North American and Orcas plate motions. Rapid sliding could be maintained as long as the release of fluids kept the effective friction low, with enhanced pore water pressure and metamorphism of the shear zone fabric accommodating the rapid motion. Rapid glacier flow mechanisms provide relevant comparisons for how such motion can be accommodated. The rapid northward movement of Baja BC would have continued as long as the Orcas plate pulled the terranes northwestwards while the North American plate moved southwestwards, effectively squeezing the suture zone fragments northwards.