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This study is predominantly about the differences in shale pore structure and the controlling factors of shale gas content between Lower Silurian and Lower Cambrian from the upper Yangtze plate, which are of great significance to the occurrence mechanism of shale gas. The field emission scanning electron microscopy combined with Particles (Pores) and Cracks Analysis System software, CO2/N2 adsorption and the high-pressure mercury injection porosimetry, and methane adsorption were used to investigate characteristics of overall shale pore structure and organic matter pore, heterogeneity and gas content of the Lower Paleozoic in southern Sichuan Basin and northern Guizhou province from the upper Yangtze plate. Results show that porosity and the development of organic matter pores of the Lower Silurian are better than that of the Lower Cambrian, and there are four main types of pore, including interparticle pore, intraparticle pore, organic matter pore and micro-fracture. The micropores of the Lower Cambrian shale provide major pore volume and specific surface areas. In the Lower Silurian shale, there are mesopores besides micropores. Fractal dimensions representing pore structure complexity and heterogeneity gradually increase with the increase in pore volume and specific surface areas. There is a significant positive linear relationship between total organic carbon content and micropores volume and specific surface areas of the Lower Paleozoic shale, and the correlation of the Lower Silurian is more obvious than that of the Lower Cambrian. The plane porosity of organic matter increases with the increase in total organic carbon when it is less than 5%. The plane porosity of organic matter pores is positively correlated with clay minerals content and negatively correlated with brittle minerals content. The adsorption gas content of Lower Silurian and Lower Cambrian shale are 1.51–3.86 m3/t (average, 2.31 m3/t) and 0.35–2.38 m3/t (average, 1.36 m3/t). Total organic carbon, clay minerals and porosity are the main controlling factors for the differences in shale gas content between Lower Cambrian and Lower Silurian from the upper Yangtze plate. Probability entropy and organic matter plane porosity of the Lower Silurian are higher than those of Lower Cambrian shale, but form factor and roundness is smaller.

The U-Pb and Lu-Hf isotopic research of detrital zircons was carried out in southern modern rivers of the South Tianshan (STS) orogenic belt to understand the accretionary processes and crustal evolution in this region. Detrital zircons from river sands yield two dominant age populations at 460-390 Ma and 310-260 Ma with several Precambrian age groups. Such age patterns imply that the significant magmatic events occurred during the Palaeozoic in the STS. Comparative studies on U-Pb age of the detrital zircons from northern and southern river sands in the STS belt provide constraints on the tectonic evolution of the STS belt and its surrounding blocks. Abundant 500-460 Ma detrital zircons in northern river sands probably reflect a bidirectional subduction of the Palaeozoic Central Tianshan Ocean under the Yili Block and the Central Tianshan Block. The 460-390 Ma zircon population in both northern and southern river sands likely implies a bidirectional subduction of the South Tianshan Ocean. A lack of the 380-320 Ma zircon grains in the southern river sands may indicates the northward subduction of the South Tianshan Ocean. A final collision between the Tarim Craton and the southwestern Central Asian Orogenic Belt possibly took place in the Late Carboniferous; the 310-260 Ma zircon population in both northern and southern river sands suggests syn-and post-collisional magmatism. Based on the Hf isotopic signatures in the detrital zircon and magmatic zircons, we propose new constraints on the Palaeozoic crustal evolution of the STS. The continent formation in the STS belt was characterised by reworking of the ancient crust in a compressional environment during the Ordovician (ca. 460-440 Ma). Abundant significant juvenile materials progressively added to the crust through time in an extensional tectonic regime since Late Ordovician to Devonian (ca. 440-390 Ma). The crustal formation is mainly dominated by reworking of the Precambrian basement rocks with limited contribution of juvenile components input into magma formation during Late Carboniferous to Early Permian (ca. 310-260 Ma).