ABSTRACT

Compared to average Precambrian shield, the average Precambrian terrane in New Mexico contains more Si, K, Rb, U and REE and less Fe, Ti, Al, Mg, Ca, Cr, Ni, Co, Sr, Zr, and Ba. It also is characterized by a less fractionated light REE pattern, a larger negative Eu anomaly, larger Ba/Sr and Rb/Sr ratios, a smaller K/Rb ratio, and larger heat productivity. The lower crust in New Mexico is more depleted in K, Th, U, and related LIL elements than the crust beneath average Precambrian shield. Such depletion may be explained by transfer of LIL elements from deep to shallow crustal levels by rising granites that are produced by partial melting of the lower crust.