New Fractal Evidence of Pacific Plate Subduction in the Late Mesozoic, Great Xing'an Range, Northeast China

Late Mesozoic granitoids are widespread in the Great Xing’an Range(GXR), which is part of a large igneous province in eastern China. The geodynamic setting of the Late Mesozoic granitoids is still debated, and there have been two dominant models proposed, subduction and thermal erosion. This study discusses the geodynamic mechanisms from a new perspective on ages of the granitoids and fractal dimensions of their shape. Our results show that granitoids become gradually older from South GXR to North GXR to Erguna Block(EB) in the Jurassic, and opposite in the Cretaceous. The fractal dimensions of the Perimeter-area model(DAP) exhibit the same features. The values of DAP are smaller from South GXR(0.673 1) to North GXR(0.628 0) to EB(0.607 9) in the Jurassic, and larger from South GXR(0.609 6) to North GXR(0.630 2) to EB(0.639 9) in the Cretaceous. This implies that the geometrical irregularities of the granitoids are shaped by subduction rather than thermal erosion. These spatial variations could be best explained by the subduction of the Pacific Plate and consequent granitoid magmatism in the Late Mesozoic, thus providing a new fractal evidence for Pacific Plate subduction mechanism and opening a new possibility method for studing plate movement.