Geochronology, Elements And Hf Isotope Geochemical Characteristics Of The Paleozoic Granites In Honghuaerji Area, Northeast Of Great Xing’an Range

Study area is located at Northeast of Great Xing’an Range, its tectonic position is located at Xing’an terrane in the eastern segment of the Inner Mongolia-Da Hinggan Mountains orogenic belt. According to the zircon U-Pb ages, elements geochemistry and the Hf isotope data of the Paleozoic granites, we determine their emplacement timing, analysis their petrological and geochemical characteristics, and discuss their magma sources, petrogenesis and tectonic setting. The results will be significant in discussing the regional tectonic evolution in Great Xing’an Range.We choose two Paleozoic granite samples for zircon LA-ICP-MS U–Pb dating. The zircons of these samples all display oscillatory zoning structures and have high values of Th/U, which implies a magmatic origin. This indicates that the dated ages could represent the emplacement timing of the granites. According to these dating results, Paleozoic granites can be divided into two phase, that is alkali-feldspar granite of Early Carboniferous(348.9 ± 2.1 Ma)and monzonitic granite of Late Carboniferous(310.5 ± 1.3 Ma).The major elements of the alkali-feldspar granite of Early Carboniferous are characterized by high SiO2, K2 O, TFeO and low Al2O3, CaO, MgO; the REE are characterized by the typical sea-gull lines with obvious negative Eu; the trace elements are characterized by enrich of LILE such as Rb, Th, U, K and deplete of Ba, Sr, P, Ti. The zircons saturation temperatures of these granites are very high, and the samples fall into the fields of A-type granitoids in the discrimination diagrams, which shows the same characteristics with A-type granites. The elements of the monzonitic granite of Late Carboniferous are characterized by high SiO2, Na2 O and low P2O5, with SiO2 content and P2O5 content presenting an inverse relationship; Most samples have ACNK values of not more than 1.1 except two. The zircons saturation temperatures of these granites are lower than temperatures of A-type granites(850℃), and the samples fall into the fields of the fractionated I-type granitoids in the discrimination diagrams, which shows the same characteristics with I-type granites. Combining with the positive εHf(t) values and two-stage model ages, it is considered that the primary magma of Paleozoic granites were derived from partial melting of crustal rocks.Combining with discrimination diagrams and regional tectonic environment, it is considered that it is related to the system of collision and merging of Xing’an terrane and Songnen terrane.