Depositional age and genesis of the host strata of the Shuangjianzishan Ag–Pb–Zn deposit: Implications for the Late Carboniferous magmatic–hydrothermal activities and tectonic evolution of the eastern central Asia orogenic belt

The Shuangjianzishan Ag–Pb–Zn deposit is hosted by an over 2030-m-thick succession of Late Carboniferous slate-dominated deep-water sediments. Three tuff layers interbedded with slates yield zircon U–Pb ages of 314.4 ± 2.5 Ma, 315.9 ± 3.6 Ma, and 317.9 ± 2.3 Ma. Using Monte-Carlo simulations, we constrain the maximum time span between the bottom tuff and the top tuff to no longer than 6.9 Myr at a 2σ (95.3%) confidence level. On the basis of this time span, the long-term accumulation rate of the Shuangjianzishan slates is 294 m/Myr. This accumulation rate is faster than any subduction-related accumulation rates by at least 30%; it is similar to that of fine deposits in a rift setting. The variably low δ¹⁸O of the zircons from the interbedded tuffs also suggest that a high-temperature hydrothermal alteration occurred during the generation of the low δ¹⁸O parental magma. Magmatic–hydrothermal events related to a rifting event are the most likely mechanism that caused the low δ¹⁸O signature. The chemical compositions of the slates suggest that their source rocks were very immature, probably similar to contemporary intermediate to acidic volcanic rocks. On the basis of down-well logging data, the dipping angle data are plotted with the stratigraphic depth of each stratum. The stable dipping angle of the slates also supports a sedimentation processes in an active rifting environment.