Rifting in SW China: structural and sedimentary investigation of the initial crustal response to emplacement of the Permian Emeishan LIP

Detailed structural, volcanic, and sedimentary investigations of the crustal response to the emplacement of the Middle–Late Permian Emeishan large igneous province show that a rifting system developed prior to the main stage of flood basalt eruptions, in the form of sedimentary breccias, clastic sedimentary deposits and mafic hydromagmatic units. Detrital zircon grains from sandstones yield ~750–800 Ma LA-ICP-MS 206 Pb/ 238 U age clusters, showing that material was sourced from the Yangtze crystalline basement. Gabbros and pegmatites intruded along the normal faults of the rift system yield zircon ages of 264–260 Ma, and thus constrain the timing of rifting. N–S-trending rift zones developed along the western flank of the Pan-Xi palaeo-uplift, with NE–SW- and NNE–SSW-trending rifts on the eastern side and along the western and eastern margins of the Yangtze Block. The rifting progressed in pulses, with an initial phase of normal faulting followed by rapid deposition of breccias. Later there was lower-energy deposition of sandstone, with accompanying rhyolitic eruptions. This was followed by low-energy sedimentation of mudstones and dolomites, with accompanying hydromagmatic deposits. Rift system formation was constrained by a combination of far- and near-field tectonic stresses due to plate motions and lithospheric interaction with initial Emeishan volcanism.