Geochemistry, Chronology and Tectonic Implications of the Hadayang Schists in the Northern Great Xing’an Range, Northeast China

The Late Paleozoic tectonic evolution of the Xing&rsquo:an block in the eastern Central Asian orogenic belt has long been the subject of debate. In this paper, a comprehensive study of U-Pb zircon ages, Lu-Hf isotopes and whole-rock elemental analyses was carried out on Hadayang schists. Representative samples of the epidote-biotite-albite schist and biotite-albite schist yielded the weighted mean 206Pb/238U ages of 360 &plusmn: 2 Ma and 355 &plusmn: 3 Ma, respectively. This indicated the presence of Late Devonian&ndash:Early Carboniferous intermediate-basic rocks in the eastern Xing&rsquo:an block. The Hadayang schists exhibited a Na-rich, tholeiitic and calc-alkaline affinity in composition with low Mg# (35.2&ndash:53.0), Cr (23.7&ndash:86.5 ppm), Ni (21.1&ndash:40.0 ppm) and Co (12.1&ndash:30.6 ppm). They were characterized by enrichment of LILEs, depletion of HFSEs and highly positive zircon &epsilon:Hf(t) values (the average values were +8.93 and +9.29, respectively). The magma source of the Hadayang schists was a mantle that consisted of both spinel and garnet lherzolite, with a partial melting degree of 1%&ndash:5%, and it had undergone fractional crystallization of olivine, orthopyroxene and plagioclase. The Hadayang schists, together with other Late Devonian&ndash:Early Carboniferous intermediate-basic magmatic rocks in the eastern Xing&rsquo:an block, were formed in an intracontinental extension tectonic setting similar to that of the North American Basin and Range basalt. Moreover, Late Devonian&ndash:Early Carboniferous ophiolite under a similar tectonic background in the western Xing&rsquo:an block has been reported. We believe that the Xing&rsquo:an block would have been in the stage of intracontinental extension during the Late Devonian&ndash:Early Carboniferous.