Late Mesoproterozoic passive continental margin in the northwestern Yangtze Block, South China: Insights from the Huodiya Group in the Hannan-Micangshan Massif

Whether the Yangtze Block was involved in the global late Mesoproterozoic orogeny remains contentious. The Mesoproterozoic Huodiya Group exposed in the Hannan-Micangshan Massif on the northwestern margin of the Yangtze Block could provide sufficient evidence to further clarify the regional tectonic affinity. However, quantitative insights into the depositional age, provenance and basin tectonic setting of the Huodiya Group still lack comprehensively constraining. This study presents a combined analysis of zircon U-Pb dating for meta-sedimentary rocks of the Shangliang Formation of the upper Huodiya Group and intruded gabbroic dykes. Intergraded dating results constrain the late Mesoproterozoic maximum depositional age at ca. 1050 Ma. Ca. 900 Ma formation age for the intruded gabbroic dyke, plus the minimum formation age of the overlying Xixiang Group at ca. 950 Ma, further suggests its deposition should be prior to ca. 950-900 Ma. Concordant detrital zircon ages define pronounced age clusters of ca. 2229-1741 and 2950-2388 Ma and few age populations of ca. 3232-3082 and 1069-1033 Ma, consistent with the tectonothermal events in proximal domains at the northwestern and northern Yangtze Block. Detrital zircon age distribution patterns and cumulative curves, coupled with the stable carbonate platform and shallow-marine facies sedimentation, suggest a passive continental margin setting for the Huodiya Group on the Yangtze Block margin at the late Mesoproterozoic. Comparative insights into the contemporaneous passive continental margin from north to southwest argue against the existence of a late Mesoproterozoic orogeny along the exterior periphery of the Yangtze Block. Systematic investigations on the Huodiya Group in the Hannan-Micangshan Massif indicate a late Mesoproterozoic depositional age and a nearby sediment supply for the basin. Comparative considerations reveal a passive continental margin setting on the northwestern periphery of the Yangtze Block during the late Mesoproterozoic. image