GEOPHYSICAL AND GEOLOGIC EVIDENCE THAT AMERASIA BASIN, ARCTIC OCEAN WAS CREATED BY TWO PHASES OF ANTI-CLOCKWISE ROTATION

GRANTZ, Arthur, Palo Alto, CA 94303, [email protected] and HART, Patrick E., Menlo Park, CA 94025

Seismic reflection, gravity and aeromagnetic data indicate that the Amerasia Basin is the product of two phases of anti-clockwise rotation.  Phase 1 produced transitional crust by extensional thinning of continental crust and postulated crustal scale detachment on the Eskimo Lakes fault zone of the Canadian continental margin between ~195 Ma and ~131 Ma.  Phase 2 opening, by seafloor spreading, produced mid-ocean ridge basalt with northerly-trending symmetrical magnetic anomalies between ~131 and ~127.5 Ma. The symmetry of the proto-Amerasia Basin was disrupted by clockwise rotation of the Chukchi microplate into the basin from the post-phase 1 Eurasia margin prior to, or possibly penecontemporaneously with, phase 2 spreading.  Emplacement of the Alpha-Mendeleev Large Igneous Province (LIP) in the northern part of Amerasia Basin after rotation of the Chukchi microplate, but prior to deposition of capping middle-Campanian pelagites, created Canada Basin in the southern Amerasia Basin south of the LIP.

The western Amerasia Basin is filled with as much as 1.3 km of synrift sediment of westerly provenance deposited on extensionally faulted phase 1 transitional crust prior to and penecontemporaneously with the intrusion of the phase 2 oceanic crust.  Above the synrift beds are 6 to 7 km of sediment originating in the Mackenzie Delta to the southeast, where this sediment thickens to ~18 km. To the west these deposits onlap Northwind Escarpment, the east face of the Chukchi microplate.  Reconnaissance isopachs suggest that the volume of layer 1 in Canada Basin is roughly two and one half million cubic km.