Petrogenesis of the Huashanguan A-type granite complex and its implications for the early evolution of the Yangtze Block

Abstract An integrated study of petrography, zircon U-Pb ages, Hf-O isotope compositions, as well as whole rock geochemistry was carried out for a Paleoproterozoic granite complex in the northern Yangtze Block, to investigate its petrogenesis and geological significances. Petrographically, the Huashanguan complex is a granite complex comprised of monzogranite in the marginal facies and K-feldspar granite in the central facies. U-Pb dating of magmatic zircons from the monzogranite and K-feldspar granite yielded ages of 1816 ± 50 Ma and 1843 ± 9 Ma respectively. The more precise age of 1843 ± 9 Ma is suggested to represent the formation age of the Huashanguan complex. The granites have uniform negative zircon e Hf (t) values of −20.2 to −15.8, with corresponding T DM2 ages of ca. 3.6–3.5 Ga. The δ 18 O values average at 6.80 ± 0.09‰. These indicate that the granites were generated by partly melting of Archean rocks, implying the widespread of Archean basement in the Yangtze Block. The monzogranites display low FeO T and MgO contents and evolved trace element features, suggesting their formation by more fractional crystallization from similar parent magma of the K-feldspar granites. The occurrence of the Huashanguan granite complex indicates that the Yangtze Block has experienced a tectonic transition from tectonic convergence to extension at ca. 1.85 Ga, possibly due to the collapse of the ca. 2.0 Ga orogeny.