Overview of Zhoukoudian rock mass

Zhoukoudian rock mass is a medium-sized rock mass with a nearly circular plane shape and an area of about 54 square kilometers. The rock mass and surrounding rock are in intrusive contact, and the Archean to Mesozoic surrounded the rock mass from the inside out and from the old to the new. The strata near the contact zone are Archaean old metamorphic rock series, which are Proterozoic, Cambrian, Ordovician, Carboniferous-Permian early and middle Jurassic in turn, and the newly invaded stratum is the Jiulongshan Formation in the middle Jurassic. It is a dome-shaped structure with rock mass as the core. The occurrence of rock mass and contact surface is steep and generally inclined to surrounding rock. It is a compound rock mass dominated by multi-stage magmatic emplacement.

Previous studies show that (Tan Yingjia, Ye,1987; Beijing Bureau of Geology and Mineral Resources, 199 1), Zhoukoudian rock mass is a concentric annular rock mass invaded in two phases, the first phase is synbiotic diorite and diorite, which are distributed in the outermost edge of the rock mass in a discontinuous chain; The granodiorite emplaced in the second stage (main stage) is located inside the rock mass and constitutes the main body of Zhoukoudian rock mass. The second stage of magmatic emplacement includes three pulsations, forming the so-called "marginal stage", "transitional stage" and "central stage" respectively. The short interval between the three intrusions leads to a gradual transition relationship between them, and the biotite belt appearing in some areas can be used as the symbol and dividing line of the three different pulse intervals (Figure 3. 1).