Site 1224, at the Hawaii-2 observatory in the northeastern Pacific Ocean (Fig. F1), is situated west of isochron 20 (45 Ma) and was formed between the Pacific and Farallon plates at a fast half-rate of ~71 mm/yr (Atwater, 1989; Cande and Kent, 1992).
In the northeastern Pacific Ocean, Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP) operations have recovered igneous basement at few sites. Only three DSDP and ODP holes penetrated >100 m into igneous basement—DSDP Leg 65 Hole 483B; ODP Leg 203 Hole 1243A, and ODP Leg 200 Hole 1224F—although several other sites have penetrated <100 m of igneous basement (Shipboard Scientific Party, 2003a, 2003b) (Fig. F1, Table T1). Therefore, studies of igneous basement at Site 1224 are critical to constrain the temporal and geographical variation of mid-ocean volcanism at the East Pacific Rise.