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

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. [ABSTRACT FROM AUTHOR]