Late Mesozoic metallogeny and intracontinental magmatism, southern Great Xing'an Range, northeastern China

Abstract

Mineral deposits are typically tied to plate margin processes, such as accretion or rifting. However, some major deposits occur in plate interiors, e.g., deposits in the southern Great Xing'an Range, lacking a clear association with the supercontinent cycle. Intrusive activity in the southern Great Xing'an Range peaked in late Mesozoic (i.e., 155–120Ma), simultaneously with large-scale mineralization in this area. In addition, the late Mesozoic granitoids show initial Nd and Hf isotopic signatures of depleted mantle, possibly newly underplated basaltic materials, with variable contamination from older crust, and with model ages younger than 1.0Ga. Fluid inclusion waters extracted from ore minerals (pyrite, galena, sphalerite, and chalcopyrite) associated with the late Mesozoic mineralization have elevated 3He/4He ratios, indicating a contribution of mantle-derived helium. Stable isotopes of fluid inclusion waters (hydrogen and oxygen) and of sulfide minerals (sulfur) confirm a magmatic source for these components. Lead isotope data of ore minerals indicate a significant mantle lead contribution from the newly underplated material. Thus, the southern Great Xing'an Range is best described as a typical, late Mesozoic, intracontinental metallogenic belt related to magmatism with a significant mantle contribution. The magmatism and mineralization took place in a setting of lithospheric extension and resulted because of the break-off of the southerly-dipping Mongol–Okhotsk oceanic slab at depth during closure of the Mongol–Okhotsk Ocean, which also restricted the westward movement of the Paleo-Pacific oceanic plate. This interplay between plate-tectonic events and mantle dynamics provides a good example of the evolution of magmatism and hydrothermal activity in intracontinental settings.