2004 Denver Annual Meeting (November 7–10, 2004)

Paper No. 4
Presentation Time: 2:15 PM


GAINA, Carmen and MUELLER, Ralph Dietmar, School of Geosciences, Univ of Sydney, Edgeworth David Bldg., F05, Sydney, 2006, Australia, carmen@geosci.usyd.edu.au

Understanding the interplay between oceanic crustal production, mid-ocean ridge volumes, mantle convection, long-term sea level changes and fluctuations in the carbon dioxide levels is one of the first-order goals of Earth science. In order to investigate how the oceanic crustal production varied through time we created complete digital paleo-seafloor age grids for the last 130 million years. A combination of methods and datasets were used to map and reconstruct preserved and subducted oceanic regions. A wealth of geophysical datasets (seismic profiles, magnetic anomalies and gravity anomaly derived from satellite altimetry) were used to derive the age of oceanic crust, spreading rates, geometry and fabric of the seafloor. A compilation of geological data from published studies (type and ages of dredged rocks, evidence of subduction related magmatism and metamorphism, ophiolites) in conjunction with published results from ODP and DSDP cruises were employed to constrain and groundtruth our models. The tectonic history of various oceanic areas has been revisited using both quantitative and qualitative methods. The new results have been integrated in a global tectonic model and newly constructed isochrons were used to update the present day oceanic agegrid. Paleo-oceans are modelled by creating “synthetic plates” whose locations and geometry is established on the basis of preserved M-sequence magnetic lineations, paleogeography, regional geological data and the rules of plate tectonics. This method has been used to reconstruct subducted Neo-Tehys ocean and the Izanagi/Kula, Farallon and Phoenix plates. A number of seafloor spreading ridge relocations has been taken into account, some of them documenting Cretaceous Normal Superchron (CNS) oceanic crustal accretion, and therefore adding more constraints on the evaluation of seafloor spreading rates during the CNS. The relative plate motion models used to derive isochrons were linked to an absolute plate model based on moving hotspots to reconstruct isochrons in a desired framework, in order to produce gridded paleo-age maps of the ocean floor. Our preliminary results show that the mean spreading rate decreased from a value of approximately 145 mm/yr in the Barremian to 85 mm/yr in the Maastrichtian. In the last 75 million years the spreading rate remained almost constant.