Cooling and exhumation history of the Fe-Ti-V oxide deposits in the Emeishan large igneous province, Southwest China

The mafic-ultramafic intrusions in the Emeishan large igneous province of Southwest China host giant Fe-Ti-V oxide deposits, and the Panzhihua−Xichang area (i.e., the Panxi area) is the largest Fe-Ti-V oxide ore district in the world. These intrusions primarily formed during the Permian and have been exhumed through a prolonged tectonic evolution. However, the cooling and exhumation history following their formation remains poorly constrained. This study systematically conducted apatite U-Pb dating and (U-Th)/He thermochronology on the Taihe, Baima, Hongge, and Panzhihua intrusions in the Panxi area. The U-Pb ages are 259.4 ± 1.8 Ma for Taihe, 259.5 ± 0.8 Ma for Baima, and 259.6 ± 0.8 Ma for Panzhihua. The apatite (U-Th)/He ages range from 23.7 ± 0.4 Ma to 9.6 ± 0.4 Ma in Taihe and decrease systematically with increasing stratigraphic depth, whereas the ages are 16.5 ± 0.3 Ma in Baima, 18.1 ± 0.3 Ma to 17.1 ± 0.3 Ma in Hongge, and 18.2 ± 0.4 Ma in Panzhihua. In conjunction with previously published zircon U-Pb ages, as well as feldspar and biotite Ar-Ar ages, this study reconstructs the cooling and exhumation history of these intrusions. These results show that after their formation, they rapidly cooled to an ambient crustal temperature (∼240 °C) at ca. 253 Ma at a rate of ∼100 °C/m.y. Subsequently, from ca. 253 Ma to ca. 24−17 Ma, these intrusions cooled down to 70 °C at a rate of ∼1 °C/m.y. From ca. 24−17 Ma to the present, the cooling rate increased to ∼1.5−2.9 °C/m.y., ultimately reaching surface temperatures. From the Late Permian to Eocene, the combined effects of the vertical movement of crustal rocks and the eastward movement of the Tibetan plateau uplift led to the slow uplift of the Panxi area, resulting in exhumation at a rate of ∼0.03 km/m.y. and a total rock exhumation of ∼6.9 km. From the late Eocene to the present, further compressional deformation of the Tibetan plateau resulted in an increase in the exhumation rate of these intrusions to ∼0.05−0.1 km/m.y., with a total exhumation of ∼1.6 km. The compressional deformation resulting from the eastward extrusion of the Tibetan plateau has resulted in more intense erosion of the strata, facilitating the exposure of the Fe-Ti-V oxide deposits within the central part of the Panxi area. Regions with less intense exhumation and exposure of Proterozoic and Paleozoic strata are likely to have greater potential for preserving ore deposits and are therefore recommended as key targets for future deep exploration of Fe-Ti-V oxide deposits.