Tectonic-Thermal Coupling Metallogenic Models of Tethys Himalaya Pb-Zn-Sb-Au Belt in Post-Collisional Stage

摘要

Crustal-scale extensions occurred in the Tibetan Plateau during the post-collision stage, and leucogranites, N-S and E-W faults and other tectonic-thermal events were developed in Tethys Himalaya, which formed a series of Pb-Zn-Sb-Au polymetallic deposits. The ore deposit may be distributed around the dome (with core of leucogranites), or along the N-S and E-W faults. Due to the lack of deep geophysical data, many different genesises of mineral deposit have been proposed by predecessors. This paper establishes the spatial relationship of deep tectonic-thermal events in the Tethys Himalaya Pb-Zn-Sb-Au belt by the N-S magnetotelluric (MT) profiles covering Cuonadong dome, the Southern Tibet Detachment System (STDS) and other tectonic-thermal events (length: 72 km, the basic point distance: 1 km): (a) a partial melting body was observed about 15 km below the Tethys Himalayan, which intruded in the form of leucogranites and formed domes; (b) the STDS and its secondary faults extended to deep the partial melting body. In combination of time relationship of tectonic-thermal events, a view has been presents that the Tethys Himalaya Pb-Zn-Sb-Au belt was formed in one tectonicthermal coupling metallogenic system in the post-collision stage. Two types of metallogenic models were formed based on whether the partial melting intruded or not: (a) the tectonicthermal coupling metallogenic model of leucogranites and the surrounding detachment faults of the dome (partial melting intruded in the form of leucogranites which driven ore-forming fluid to migrate in the surrounding detachment faults); (b) the tectonicthermal coupling metallogenic model of non-intruded partial melting and fault systems (under the extension stress, the N-S extension of Tibetan Plateau had formed the STDS and its secondary fault faults that extended to the partial melting body). This results in instantaneous low pressure, which decoupled the partial melting body and magmatic fluid and drove magmatic fluid and deep formation fluid to flow into fault system. Finally, the two fluids were mixed with atmospheric water to form ore. Also a hydrodinamical model for the long distance migration of ore-forming fluid along the fault systems within the Tethys Himalaya Pb-Zn-Sb-Au belt has been established. This study will provide a reference for subsequent geophysical prospecting in the belt.