Composition of deep crust imaged by USArray

The deployment of Earthscope/USArray has helped produce high resolution seismic models of the crust and uppermost mantle. In this work, we push one step forward, further using the seismic observables to study the crustal composition of the contnental US. The silica content (SiO 2 ) of the crust is an important but enigmatic issue: it helps to understand the chemical and dynamic evolution of the crust-mantle system as well as the formation mechanism of the continent, but its quantification is still under debate due to no direct access to the deep crust. Here we show that by applying a sequential H-κ stacking method to the rigorously quality-controlled receiver functions, reliable Vp/Vs ratios of the crystalline crust can be measured from the seismograms recorded by USArray. Combining together with high-resolution shear velocities, a 1-D SiO 2 wt% model at each station in USArray can be deduced based on petrological database. From the SiO 2 wt% mapped at more than 1400 stations, horizontal, vertical and secular patterns are found in the contienntal US: 1)Western US is more felsic than Central-Eastern US on average. Different crustal types shows different SiO 2 wt% distributions. 2) From top to bottom of the crystalline crust, the average SiO 2 decreases. Mid-Lower crust has similar SiO 2 wt% distribution to xenoliths rather than high grade metamorphic terrains. 3)There is no change in SiO 2 wt% between Archean-Proterozoic boundary as suggested in some previous studies. The results reveal that crustal composition is strongly affected by Phanerozoic tectonism and provides insights of the nature of the deep crust, allowing a better assessment of global crustal composition.