THE DISCOVERY OF NEOPROTEROZOIC EXTENSIONAL STRUCTURES IN THE CENTRAL SICHUAN BLOCK, SICHUAN BASIN, SOUTH CHINA

The Central Sichuan Block (CSB) is the hardest block between the deep faults of Pujiang-Bazhong and Huaying Mountain in the central part of Sichuan Basin, which lies in the northwestern part of the upper Yangtze Craton of South China. The CSB has long been considered as the oldest and most stable core area of Yangtze Craton, with the uniform basement and high level of hardening. Here we present a detailed interpretation of deep structures in the CSB by integrating high-resolution seismic data (approx. 50,000 km²) with large-scale aeromagnetic data. Results show that eight Neoproterozoic extensional structures of different scales are nearly EW-, NEE-, and NW-trending in the CSB. Discovery of these extensional structures changes previous understanding of the CSB as a unified block. The extensional structures experienced one or two stages of extension in the longitudinal section, and filled with 3,000-5,000-m-thick weakly magnetic materials. Development of basal A-type granite in Weiyuan, Sichuan Basin and bimodal volcanic rocks of the Suxiong Formation, Western Sichuan confirms the CSB’s Neoproterozoic extensional tectonic setting. The newly discovered Neoproterozoic extensional structures are of great significance for source rock and favorable sedimentary facies distribution, reservoir development, and gas accumulation.