Late Palaeozoic igneous rocks of the Great Xing'an Range, NE China: the Tayuan example

The Tayuan plutons located at the boundary of the Erguna and Xing'an blocks expose a coexisting mafic-felsic association that is made of monzogranite and gabbro-monzodiorite as well as subordinate quartz monzonite. LA-ICP-MS U-Pb zircon dating revealed a synchronous emplacement of the monzogranite (314-317 Ma), gabbro (308-315 Ma), and quartz monzonite (310 +/- 3 Ma). The majority of these intrusions are characterized by an enrichment in light rare earth elements relative to heavy rare earth elements and a depletion of high strength field elements (e.g. Nb, Ta, Ti). Zircons from the gabbro and monzogranite have epsilon(Hf)(t) values of 1.1-9.6 and -3.0-3.3, respectively. Geochemical data show that the gabbro-monzodiorite may have been generated by the melting of a fluid-metasomatized lithospheric mantle, while the monzogranite may have been formed by a partial melting of the Mesoproterozoic crust. The quartz monzonite has similar whole-rock geochemical and Hf isotopic compositions to those of the gabbros and could have been produced from the same mantle source as that from which the gabbros were extracted. The Tayuan plutonic rocks have high contents of K2O and total alkalis and show a northwestward polarity like that of the continental margin plutonic rocks along the Hegenshan-Heihe suture zone. Combined with data from published studies, our data indicate that the Tayuan intrusive rocks were generated by the northwestward subduction of the Hegenshan-Heihe Oceanic plate.