Devonian Sedimentary Environments and Provenance of the Qinling Orogen: Constraints on Late Paleozoic Southward Accretionary Tectonics of the North China Craton

摘要

The Qinling orogen of central China occupies a key position in East Asia, and is of fundamental importance in unraveling its tectonic evolulion. Devonian sedimentary basins are located between the North Qinling arc and the Baishuijiang Devonian--Permian accretionary wedge. Paleocurrent indiclors and petrological and geochemical analyses show that turbiditic and coastal sandstones and pyroclasts developed in paleo-forearcs. Sedimentation of conglomerates and associated turbiditic and pyroclastic rocks evidently was related to the development of the North Qinling orogen rather than the South China craton. Gravels in the conglomerates were derived predominantly from the North Qinling and partly from its basement. Northward Devonian subduction and subsequent uplift caused successive forearc depocenters and associated facies belts to migrate southwards synchronously with sedimentation. Transpressive and transtensional faults segmented the basins into discrete half-graben sub-basins. Paleocurrent analysis adjacent to thrust faults demonstrates that thrust sheets crests were truncated by erosion and provided detritus for sub-basins. Shallow-marine and turbiditic depositional systems evolved in complex patterns to produce varied facies frameworks associated with complex subduction accretion. These facts, together with other geological and geochemical data, demonstrate that the North China craton grew southwards by arc-accretion processes from the end of the early Paleozoic to the beginning of the late Paleozoic, long before the integration of the North China and Yangtze cratons.