Slab XRF analysis - The XRF analyses were run on a PANalytical Axios spectrometer using SuperQ software. Nb, Rb, Sr, Y, and Zr were measured using Super's 37mmRbSrYZr routine software program; other elements were measured with the IQ+37mmVac software program. The 37mmRbSrYZr routine uses specific pre-determined peak and background positions for which x-ray intensities are measured for 2-800 seconds (depending on the element). The intensity of the Rh Compton peak is used to estimate mass-absorption coefficients (MACs) for both unknowns and well-characterized natural standards. Peak intensities are computed and converted to concentrations using calibration curves employing at least 10 natural rock standards.