Geochronological and Geochemical study of Palaeoproterozoic gneissic granites and clinopyroxenite xenoliths from NW Fujian, SE China: Implications for the crustal evolution of the Cathaysia Block

摘要: Abstract U–Pb zircon dating of gneissic granite samples in northwestern Fujian Province, Southeast China, gave Neoarchean to Palaeoproterozoic ages (2.6–1.9 Ga) for the rounded cores and upper intercept (1851 ± 21 Ma, 1857 ± 29 Ma, respectively) zoned rims that have oscillatory growth zoning yield e Hf ( t ) values between −8.8 +3.7 T DM model 2.1 2.6 Ga. These granites are peraluminous (A/CNK = 0.94–1.28), characterized by high SiO 2 (68–72 wt.%), Al O 3 (14–15 wt.%) low CaO, MgO, FeO , TiO P 5 contents. They also possess relatively REE contents moderate LREE/HREE fractionation display pronounced negative anomalies Nb, Ta, Sr, Ti. All these features indicate precursor magmas were likely formed partial melting sedimentary rocks. Clinopyroxenite xenoliths with gneissosity structures found they Ni Cr, but CaO/Al (4.1–5.3), /TiO ratios (8.7–9.5) HREE depletion. similar typical Al-depleted type komatiites. Their geochemical characteristics, such as (Gd/Yb) N HREE, Y, Zr suggest mantle source residual garnet. The Ta Ti a strong arc-related affinity. Our results recently published data granitic mafic basement rocks this region, reveal 1.85 Ga was an important period evolution Cathaysia Block, possibly related Columbia supercontinent assembly. Large amount magma emplaced, probably result old materials.