Cooling history of the Pacific lithosphere

Plate tectonics is expressed most simply in oceanic plates where a thermal boundary layer or blithosphereQ forms and thickens as the plate cools during its journey away from mid-ocean ridges. Numerous studies based dominantly on surface observables have established that the oceanic lithosphere, particularly across the Pacific, does not cool continuously as it ages. Based on a seismic model of the Pacific upper mantle inferred from a new compilation of seismic surface wave dispersion measurements, we show that, on average, the Pacific lithosphere has experienced a punctuated cooling history, cooling diffusively at ages until ~70 Ma and then reheating in the Central Pacific between ages of 70 and 100 Ma predominantly at depths between 70 and 150 km. At ages from 100 Ma to about 135 Ma, the processes of reheating are substantially weaker than in the Central Pacific. We show that thermal boundary layer instabilities (TBI) develop naturally as the plate cools and, with the right rheology, can explain the mean characteristics of the observed cooling history of the Pacific plate. D 2004 Elsevier B.V. All rights reserved.