CONTINENTAL CONSEQUENCES OF MAGMATIC INTRAPLATING OF SEDIMENTS LURKING IN THE DEEP

Recent attempts to constrain the bulk composition of the deep crust via seismic receiver function analysis and geochemical modeling support one prevailing view that lower continental crust is predominantly mafic. However, several observations from granulite terranes and limited xenolith data support the hypothesis that significant volumes of lower continental crust involve felsic material originally deposited at the surface. This contradiction is reconciled using field relationships in one of Earth’s largest lower crustal granulite terranes combined with phase equilibria modeling to demonstrate that intraplating of mafic magmas into felsic metasedimentary gneisses produces deep crustal seismic observables at cratonic and Cordilleran Moho conditions. Magmatic intraplating and partial melting of supracrustal rocks lurking in the deep enhances differentiation of continental crust and produces significant variability in composition, structure, and lower crustal seismic velocity. This heterogeneity is largely masked by the low spatial resolution of seismic observations and leads to underestimation of the volume of felsic lower continental crust. The presence of voluminous supracrustal rocks lurking in the deep continental crust implies that weathering, erosion, and recycling of the uppermost crust into the lower crust are critical processes for redistributing crustal heat production and refining the composition of the continents.