High Mg# and Nb/Ta ratios, and Cr and Ni contents of the Xichahe adakitic tonalitie indicate that the parental magma mixed with a mantle melt. In conjunction with high Ba (877.13-1963.52 ppm) and Sr (820.76-1252.75 ppm), low Y (10.58-18.30 ppm) and HREE, e.g., Yb = 0.79-1.51 ppm), trace elements, and REE patterns suggest that the tonalite magma protolith was most likely a feldsparpoor, garnet ± amphibole-rich eclogite assemblage.
Chondrite-normalized rare-earth element patterns of the tonalite are characterized by high (La/Yb)N ratios and concave-upward shapes of HREE, and without a significant Eu anomaly (δEu = 0.65-1.10). With the exception of higher Mg# (52.94-67.59) values, the tonalite has compositional similarities to high-silica adakites from suprasubduction-zone tectonic settings. The Xichahe tonalite emplaced into the Proterozoic Foping metamorphic complex, south Qinling Mountains, central China, has been dated at 213.6 ± 2.2 Ma using the LA-ICP MS zircon U-Pb method, indicating that it is post-orogenic (≤242 ± 21 Ma).
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