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IGNEOOUS-LECTURE 4 - Coggle Diagram

- - - - Proportion involved estimated by mass-balanced calculations based on average composition of cont crust, depleted mantle, primitive mantle and rate at which crust has formed
        
        50% mantle involved in cont crust formation,
        but could be lower at 25%
        
        Spinel-perovskite transition is endothermic: resists
        mantle convection. Separate upper/lower mantle means
        that cont crust formed from upper mantle only:
        consistent with mass-balance calculations
        
        Separate convection explains mantle array. Lower mantle's composition close to primitive mantle. Mantle plumes pass through depleted mantle and mix: explains composition of MORB and OIB
        
        Tomography shows that subducting slab penetrates 660km discontinuity: lower mantle has ocean crust sediments