HR: 1340h
AN: V23B-1431    [Abstracts]
TI: Using Thermal Subsidence Of The Seafloor To Validate The Geologic Timescale To 80 Ma
AU: * Carlson, R L
EM: carlson@geo.tamu.edu
AF: Department og Geology & Geophysics, Texas A&M University, College Station, TX 77843- 3115, United States
AU: Willson, S
AF: Department og Geology & Geophysics, Texas A&M University, College Station, TX 77843- 3115, United States
AB: Age calibration of the geologic timescale is based largely on cyclostratigraphy and radiometric ages, but validation (as opposed to calibration) of the timescale is difficult because most time dependent geologic processes that might serve as clocks are frought with ambiguities and uncertainties. An exception is the well- understood thermal-isostatic subsidence of the sea floor after it forms at mid-ocean ridges. To a very good approximation, depth is a linear function of the square root of sea floor age for ages less than about 80 Ma. Known sea floor depths and ages have been widely used to study global and regional subsidence, but if the model parameters (thermal diffusivity, mantle temperature, mantle density, and lithosphere density) can be independently determined, the subsidence model can be used to estimate the age of oceanic basement from its depth t = sqrt\{(d - dr)/S)\} where d is depth, dr is the depth of the mid-ocean ridge crest, and S is the rate of subsidence. We have used reported depths and ages from a suite of 41 sites where normal oceanic basement was penetrated by drilling during the Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP) to test this approach. Basement ages were estimated from magnetic lineations using the geomagnetic reversal timescale and/or from the biostratigraphic age of the oldest sediment overlying basement. The correlation between observed and predicted depths is 0.97, with an RMS difference of 8 Ma. Much of the misfit is from the ten oldest sites; the misfit for 31 sites with basement ages less than 55 Ma is 4 Ma. We conclude that this approach can be used to validate the geologic timescale. The next steps in this study are to update the basement ages based on the most recent calibrations, and to include the temperature dependence of the thermal diffusivity in the subsidence model.
DE: 1032 Mid-oceanic ridge processes (3614, 8416)
DE: 3036 Ocean drilling
DE: 9699 General or miscellaneous
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting