Abstract:

The monzonitic granites intruded into Devonian-Carboniferous Amunike formation in a long strip fashion in the Huashigou
area. According to the zircon U-Pb weighted mean age of 252.0 ± 2.1Ma determined using LA-ICP-MS, it was suggested that the rock
was formed in late Permian. Monzonitic granites contain rich SiO2 (69.8%~72.2%) and Al2O3 (14.2%~15.4%), and low TiO2, MgO
(0.28%~0.36%, 0.60%~0.77%, respectively), with A/CNK=1.08~1.14, rich alkali (Na2O+K2O = 6.57%~8.00%), relatively enriched Th,
K, Pb, depleted Nb, Ta, P and Ti, low content of Sr (201×10-6~248×10-6), high content of Y (19.4×10-6~24.0×10-6), enriched LREE, (La/
Yb)N=10.8~18.4, moderate anomaly negative Eu (δEu=0.55~0.68); whole-rock (87Sr/86Sr)I=0.7060~0.7061, εNd(t)=1.63~1.84, and εHf(t)=
8.79. The Nd and Hf model ages of whole-rock of monzonitic granites are 780~794 Ma and 694 Ma, respectively. Overall,
our study shows that the Huashigou monzonitic granites is the product of partial melting of Mid-Neoproterozoic basaltic lower crust by
the underplating heating of late Paleozoic basaltic magma under the tectonic setting of orogenic compression transforming into post
orogenic extension.

Key words: monzonitic granites, geochemistry, late Permian, tectonic setting, Huashigou, south Qilian Mountain