Origin of C type adakite magmas in the NE Xing'an block, NE China and tectonic implication

摘要

In this paper,we report new whole-rock geochemical and zircon U-Pb data for monzogranites in the NE Xing'an block.These data constrained the petrogenesis of C type (high Sr/Y) adakitic rocks and showed the spatial extent of the influence of the Mongol-Okhostsk ocean tectonic regime and the collision between the Jiamusi Massif and Songliao Terrane.New zircon laser-ablation inductivity coupled plasma mass spectrometry (LA-ICP-MS) U-Pb data indicated that the monzogranites in the studied area were emplaced in the Early Jurassic (～ 180 Ma).These rocks were characterized by unusally high SiO2 (≥67.49),and Sr (461-759 ppm),but strikingly low Y (4.63-8.06 ppm) and HREE (∑HREE =3.83-6.49 ppm,Yb =0.5-0.77 ppm)contents,with therefore high Sr/Y (67.2-119) and (La/Yb)N (29.7-41.5) ratios,showing the geochemical characteristics of C type adakitic granite.The data displayed negligible Eu anomalies (Eu/Eu*=0.77-1.08),LREE-enriched and pronounced negative Nb and Ta anomalies.The C-type adakites in the studied area were most likely derived from the partial melting of a thickened lower continental curst.The magma source is most likely dominated by amphibolites and garnet amphibolites.In combination with previously-reported data from igneous rocks from the Mesozoic in NE China,we conclude that the Xing'an block was influenced by the Mongol-Okhotsk subduction tectonic system,and experiences compressive settings from the amalgamation of the Jiamusi block in the east of the CAOB.