The circulation of fluids through oceanic crust on ridge flanks is intimately tied to the evolution of mid-ocean ridges. Ridge flanks are areas far from the influence of mid-ocean ridges, comprising over 50% of global ocean basins and could hold up to 2% of the world's seawater within porous crust (Johnson, et al. 2003). Basement fluids, residing within ridge flanks, are formed from seawater that is entrained into oceanic crust and is isolated from vertical mixing with the overlying ocean by lower permeability sediment. This fluid is driven through the basement of ridge flanks by thermal pressure gradients. Previous hydrological research on the eastern flanks of the Juan de Fuca Ridge provides evidence for fluid flow within the upper basement crust that becomes increasingly isolated from seawater with increasing distance from the ridge axis. Close to the ridge, dissolved inorganic radiocarbon (DIC) ages show a systematic increase with distance from the ridge axis. We present the first DIC 14C ages of hydrothermal fluids from Baby Bare seamount, 100 km from the axis, as well as new data from ODP Hole 1026B (3.5 My crustal age) and ages from diffuse hydrothermal vents of the Endeavour ridge axis. Crustal fluids from 1026B and Baby Bare have ages of 11 kyr and 9.5-10 kyr, respectively, when corrected for the age of background seawater. These fluids are 2-3 times older than previously reported for fluids from 1026B. The offset in age for the two sites is in agreement with evidence for ridge-parallel crustal fluid flow, from South to North, as inferred during earlier studies. The difference in ages estimated from our samples and those collected during ODP Leg 168 might result from drilling-induced contamination via entrainment of non-basement seawater at the time of prior sampling.
See more of Poster Session I
See more of The 10th International Conference on Accelerator Mass Spectrometry (September 5-10, 2005)