Temporal and Petrogenetic Constraints on Volcanic Accretionary Processes at 9-10 Degrees North East Pacific Rise

摘要

Major and trace element, and Sr, Nd, Hf, Pb, and 238U-230Th-226Ra isotope compositions were measured in mid-ocean ridge basalts (MORB) from 9 deg -10 deg N along the East Pacific Rise (EPR) to determine eruption ages and to place temporal constraints on volcanic and magmatic processes. At 9 deg 30'N EPR, 238U-230Th-226Ra compositions indicate enriched MORB (E-MORB) collected off-axis erupted >8 ka and that E-MORB magmatism is interspersed with normal MORB magmatism. Lava ages are consistent with eruption from the axial summit trough (AST) and flow down the ridge flanks, which is in contrast to previous studies that suggested E-MORB erupted from off-axis vents. At 9 deg 50'N EPR, seven discrete eruptive units are distinguished out to approximately 0.8-2 km on either side of the AST by high precision 238U, 232Th, and 226Ra sample concentrations. Model ages indicate the neo-volcanic zone is.