The Moho: Boundary above upper mantle peridotites or lower crustal eclogites? A global review and new interpretations for passive margins

Abstract

Abstract We have performed a global study of 2D crustal scale wide-angle profiles across passive margins, with regard to local elevations in the Moho which could possibly be interpreted as indicative of lower crustal eclogites. A total of 16 candidates have been found, mainly in the North Atlantic and around Australia. These cases make up c. 6% only of the total profile length studied, confirming the interpretation of the Moho generally representing the top of the mantle. The interpreted candidates for lower crustal eclogites indicate that there may be a link between eclogite bodies and continental suture zones in the Barents Sea, off mid-Norway, in the Newfoundland Appalachians and in the Yilgarn Craton, western Australia. It is also possible that there is a genetic link between the formation of Caledonian eclogites and the Jan Mayen Fracture Zone, which is the only major fracture zone in the North Atlantic. Several of the inferred lower crustal eclogite bodies are located close to lines of major changes in strain, such as coastlines and shelf edges, indicating that lower crustal eclogite bodies may be important in guiding the evolution of basin architecture. Interpreting the Moho beneath the Bedout High on the northwest shelf of Australia as the top of a body of lower crustal eclogites, may imply that the northern termination of the Lambert Shelf represents a paleo suture zone and that the western termination of the Broome Platform acted as a major transfer zone. The significant increase in crustal thickness implied by the eclogite model has important implications for estimates of stretching history, subsidence and hydrocarbon maturation modelling.