Zusammenfassung
Plate tectonics is expressed most simply in oceanic plates where a
thermal boundary layer or lithosphere 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.
Nutzer