STRUCTURAL AND COMPOSITIONAL HETEROGENEITY OF THE CONTINENTAL LITHOSPHERE FROM GEOPHYSICAL DATA

The continental lithospheric mantle (CLM) is as heterogeneous as the continental crust. Significant regional variations in continental geotherms, upper mantle seismic velocities, and mantle gravity anomalies are well correlated with tectono-thermal ages of the lithosphere. A joint analysis of thermal, gravity, and seismic tomography data indicates strong lateral and vertical compositional variations in the CLM. (1) Global-scale lateral compositional variations in densities and seismic velocities in the Archean-Paleoproterozoic lithospheric mantle are in the overall agreement with xenolith data and are related to mantle depletion and processes of lithosphere formation. (2) The bases of the TBL (thermal thickness of the continental lithosphere) and the LAB (the lithosphere-asthenosphere boundary as constrained by the tomography models) may extend significantly deeper than the base of the geophysically determined chemical boundary layer (CBL). (3) The magnitude of compositional variations derived from geophysical data is significantly stronger than indicated by petrologic data. It suggests that cratonic xenoliths maybe non-representative of the "intact" cratonic mantle and sample CLM modified by post-formation melt-metasomatism. Lateral and vertical variations in the magnitude of compositional density and seismic velocity anomalies, that exist within the individual cratons, reflect the processes of the spatial-temporal evolution of the continental lithosphere, including its growth, metasomatic reworking, recycling, and selective preservation. This conclusion is illustrated by global and regional examples from different continents.