LAUSR

Abstract The geochemical compositions and zircon U-Pb ages of the Muhuguan and Mangling plutons of the North Qinling Terrane (NQT), China, provide insights into the basement rocks involved in magma genesis and the Mesozoic tectonic evolution of the NQT. Monzogranites from the two plutons are characterized by high SiO2 contents (69.3–77.0 wt%), low Mg numbers (0.21–0.38), enriched light rare-earth elements, Th, U, and Pb, depleted high-field-strength elements, and negative Eu anomalies. The source of the Mangling monzogranite is interpreted to have been deeper than that of the Muhuguan monzogranite, on the basis of its higher Sr/Y, (Dy/Yb)N, and (La/Yb)N ratios and lower SiO2 content. Sr-Nd isotopic compositions indicate similar but heterogeneous magma sources for the two granites: 87Sr/86Sri = 0.7070–0.7103 and eNd(t) = −7.0 to −15.0 for the Muhuguan granite, and 87Sr/86Sri = 0.7054–0.7083 and eNd(t) = −7.9 to −16.0 for the Mangling granite. The zircon U-Pb age results fall into two groups: (1) syn-magmatic zircons (153 to 140 Ma); and (2) inherited zircons that define five age clusters, namely Neoarchean-Paleoproterozoic (2633–2103 Ma), Paleoproterozoic to Mesoproterozoic (1988–1377 Ma), Neoproterozoic (975–605 Ma), Paleozoic (535–382 Ma), and Late Paleozoic – Early Mesozoic (329–187 Ma). These data are consistent with a derivation of the granites by mixing between melted underplated juvenile crust within the NQT and melts from basement rocks similar to those of the Xiong'er Group within the southern margin of the North China Craton (S-NCC). The involvement of S-NCC material is also supported by the unradiogenic whole-rock Pb isotopic composition of the Muhuguan and Mangling granites, which is similar to that of the S-NCC basement rocks. These results suggest that the widespread Late Jurassic to Early Cretaceous granitoid intrusions within the NQT were generated in an extensional geological setting associated with mantle upwelling. Melts were derived from underthrust S-NCC basement material and juvenile Neoproterozoic basaltic rocks.