An Unusually Warm Upper‐Crust in the Late Paleozoic North China Continental Arc: Implications for the Thermal Modification of the Giant Bayan Obo REE Deposit

Abstract

The thermal state of the continental crust plays an important role in the understanding of the geophysical, geological, and geochemical evolution of continental magmatic arcs (Rothstein & Manning, 2003). The thermal state of the continental crust controls not only rheology and deformation which are sensitive to temperature, but also overprints of early formed ore deposits in mid-to upper-crustal levels. Modern continental arcs, such as the central Andes arc, have large crustal thicknesses of 50-80 km (Beck et al., 1996;McGlashan et al., 2008) and are therefore characterized by low average geothermal gradients (ca. 15°C/km) by using a crustal thickness of 60 km and Moho temperature of 900°C (Cao et al., 2019). However, the mid-to upper-crust may have high geothermal gradients of 30-50°C/km as a result of heat transfer due to magma migration in continental arcs (Cao et al., 2019;Rothstein & Manning, 2003). Numerical modeling results show that geothermal gradients in the upper-crust in continental arcs are high but decrease significantly in the lower crust below the level at which magmas pond (Rothstein & Manning, 2003). Extremely high geothermal gradients >60°C/km have been reported in the upper-crust of some low-pressure/high-temperature metamorphic belts including magmatic arcs, regions of

The application of THz-TDS in the characterization of Bayan Obo magnetite ore composition

“…This area has the world's largest light rare earth deposit and the second largest niobium (Nb) deposit, as well as a large iron ore deposit. The ore-forming process of the Bayan Obo mining area is very complex, and it has the characteristics of high element and mineral composition, low grade, fine particle size of useful minerals, and diverse types of ores, which brings great difficulties to the exploration, recovery, and utilization of resources 19 – 21 .…”