Late Triassic to Jurassic Tectonic Evolution of the Northern Sichuan Foreland Basin, South China Craton

Abstract

The Northern Sichuan Foreland Basin, which is located in the northwest of South China Craton (SCC), was formed by the intracontinental thrusting between the Qinling Orogenic Belt (QOB) and SCC. The Upper Triassic to Jurassic sedimentary successions within this foreland basin, contain crucial information for revealing the intracontinental deformation sequence between the QOB and the SCC. In this study, based on a systematic dataset, including the palaeocurrent orientation, sandstone modal composition, and detrital zircons U–Pb age data, we attempt to reveal the tectonic processes during the Late Triassic to Jurassic interval. The palaeocurrent orientations, which is primarily directed in the southward and northwestward directions, indicate that the sediments were sourced from the north and southeast. The sandstone clastic components reveal multiple sources, including the magmatic arc and continental crust. Detrital zircons from six samples yield six major U–Pb age groups, including 2650–2350, 2050–1720, 1000–620, 520–380, 350–210, and 205–160 Ma. The Upper Triassic sediments contain a relatively high density of 2490, 1860, 810, 440, and 230 Ma, which are mostly consistent with the QOB, northern SCC and Jiangnan Suture Zone provenances. The majority age population of 2050–1750 Ma observed within the Xujiahe Formation, is considered to be primarily sourced from northern SCC, suggesting the uplift and erosion of the northern SCC, probably imply extreme shortening between the QOB and SCC. The Baitianba and Xintiangou formations, which contain lesser 2050–1720 Ma aged zircons, indicate a period of lacustrine expansion and tectonic quiescence after the shortening. The Middle Jurassic Shaximiao Formation, and the Upper Jurassic Suining and Penglaizhen formations, involve a major age population of 2050–1720 Ma that were sourced from northern SCC, indicate another phase of uplifting of the northern SCC related to a second stage of extreme intracontinental shortening and deformation between the SCC and the QOB. In summary, the above results indicate that, an initial phase of extensive shortening between the QOB and the SCC during the Late Triassic, was followed by a period of tectonic quiescence during the Early Jurassic, and another phase of extreme intracontinental shortening between the QOB and SCC during the Middle to Late Jurassic.