Pacific microplate and the Pangea supercontinent in the Early to Middle Jurassic

New biostratigraphic data based on radiolarians recovered from deep within the oceanic crustal section of Ocean Drilling Program Hole 801C in the west ern Pacific, along with existing radiometric information, date this oceanic crust as late Bajocian-early Bathonian (170-165 Ma). The overlying basal s ediments at Hole 801C are essentially identical in age (middle Bathonian, 1 64-162 Ma) to the basal sediments at Deep Sea Drilling Program Hole 534A in the central Atlantic. We estimate the time of formation of the Pacific pla te as 175-170 Ma and the time of initial separation of the Pangea supercont inent in the central Atlantic as 190-180 Ma. We also identify a time of ext ensive subduction-zone magmatism (175-159 Ma) at the eastern and western ed ges of Pangea. We suggest that the initial plate separation of Pangea incre ased subduction rates at its outer margins and altered the plate boundaries in the Pacific superocean, leading to formation of the Pacific plate.