The fine upper crustal structure below the Qin-Hang and Wuyishan metallogenic belts revealed by double beamforming ambient noise tomography

The South China region, as one of the significant Wu-Sn polymetallic metallogenic provinces in the world, is the most representative area in Mesozoic mineralization in eastern China. However, there are some differences in type and origin of the mineral deposits among the major metallogenic belts in this province. To better understand the regional metallogenic setting and determine the factors controlling the metallogenic differences, using the seismic ambient noise data recorded by "Wanzai-Yongchun" joint active- and passive-sourced seismic experiment, we performed the double beamforming ambient noise tomography and resolved the S-wave velocity model beneath the survey profile. Combined the available results, we draw the following conclusions: (1) The upper crustal S-wave model maps the known faults with different types and depth extent based on different seismic velocity features. The Jiangshan-Shaoxing Fault in the Qin-Hang belt, with the nature of reverse thrust, dipping north-west and running through the crust, had controlled the porphyry magma system in Mesozoic. The strike-slip faults in the Wuyishan belt, almost running through the upper crust with a dip angle, as well as with the neighboring listric faults, have controlled the occurrence and development of the strike slip pull apart basins and volcano graben basins. (2) There are strong lateral S-wave velocity variations across the survey profile, and the bulk S-wave velocity in the Wuyishan belt is slightly higher than that of the Qin-Hang belt, reflecting that the upper crustal compositional structure in the Qin-Hang belt is mainly crust-source granites and acid volcanic rocks, whereas the Wuyishan belt is composed of huge thick Proterozoic metamorphic volcanic-sedimentary rocks. (3) Comprehensive analysis confirms that the differences in middle-lower crustal compositional structure are the essential factors contributing the different types and origin of the mineral deposits between the Qin-Hang and Wuyishan metallogenic belts. Although the shallow bulk S-wave velocity in the Wuyishan belt is slightly higher than that of the Qin-Hang belt, the high-velocity anomalies exist significantly in the lower crust in the Qin-Hang belt, which implies that its lower crust possesses more mafic components ; the lower crust of the Wuyishan belt exhibits a relatively low seismic velocity, which reflects the nature of paleo-felsic ancient crust.