JURASSIC TO RECENT TECTONIC EVOLUTION OF NORTH AMERICA: A preliminary model using GPlates software Martha Henderson Mitch Mihalynuk Karin Sigloch Stephen Johnston Grace Shephard

Angayucham Mezcalera -Mantle tomography looks at the seismic structure of the mantle. -Key: Recognize high velocity domains (cold dense oceanic lithosphere forming slabs) –Slabs can be traced from deep within the mantle to active subduction zones world wide Karin’s 3D Model -high resolution thanks to high density USArray and cutting edge seismic processing techniques -major vertical slab walls produced by stationary subduction zones. Most important for this model are Mezcalera and Angayucham -1800km depthmagenta, blue is almost at surface, 200km intervals Image is taken as if sitting in center of earth looking up at walls—isosurface (equal velocity) which contains faster than average mantle Take away: 1. extent and shape of massive chevron formed by Mezcalera and Angayucham slabs is 10,000km long 2. vertical slabs = stationary subduction zone; therefore stationary arc above 3. calibrate the rate at which the slab sink and you can back calculate age range of the arc forming above it. This has been done ~10mm/a (Sigloch and Mihalynuk, 2013, Nature)

Superterrane I Superterrane II Superterrane I -early Jurassic arc (similar to the Aleutian arc) Superterrane II -170-present all of Insular (constructed on older substrate)

NOTES on limitations of the model: 1. Terranes fixed in size no deformation 2. Unlikely that extent of terranes shown today are representative of their arc origins (deformed along margin) 3. This model utilizes the full palemag offsets  creates some space problems MAJOR GEOLOGIC EPOCHS 1. New North American margin created by mid Jurassic- by loosely accreted Intermontane terranes +US relatives 2. Westward subduction beneath Early Jurassic to Late Jurassic intraoceanic archipelago (terminating diachronously into Eocene). 3. Subduction reversal established oceanward of intraoceanic archipelago by ~125Ma 3. Alaska forms by buckling the northern Mesozoic intraoceanic arc terranes in the Late Cretaceous/early Tertiary between northward translating Insular + western Intermontane superterranes and Siberian backstop (Siberia not shown).