Provenance of the Late Permian Xuanwei Formation in the Upper Yangtze Block: Constraints from the Sedimentary Record and Tectonic Implications

Xuanwei Formation is composed of mudstone,siltstone,and sandstone,with local conglomerate.However,its provenance and tectonic setting have been scarcely studied.In this paper,we use sedimentology,electron probe microanalysis(EPMA),and detrital zircon dating to investigate its source area and depositional tectonic setting.The facies assemblages indicate that it formed in alluvial fan and fluvial river sedimentary environments.The strata thicknesses and facies distribution indicate that the sediment supply was from the west.The results of EPMA show that chromian spinels within the sediments are characterized by high Cr#and varying Mg#.Discrimination plots suggest that these spinels were sourced from large igneous province(LIP)magmatic rocks.The laser ablation inductively coupled plasma mass spectrometry(LA-ICP-MS)U–Pb chronology of detrital zircons suggests that the sediments were derived from intermediate–acid igneous rocks dating back to 251–260?Ma.We could,therefore,conclude that the provenance of the Xuanwei Formation is from Emeishan basalt and synchronous felsic igneous rocks,which is consistent with the composition of the detrital framework.The detrital zircon dates also suggest that felsic magmatism occurred during the Late Permian,not after the eruption of the Emeishan basalt.Based on the sedimentary successions and provenance analysis,the tectonic setting for Xuanwei Formation deposition was a volcanic rifted margin.

Experimental study on the acoustic propagation and anisotropy of coal rocks

In order to study the propagation laws of acoustic wave of coal samples from the Upper Permian Xuanwei Formation in the east of Yunnan Province,China,under saturated water and dry conditions,the basic physical parameters,acoustic parameters and anisotropic parameters were obtained through the experiments.Based on FFT and wavelet analysis theory,the spectral characteristics of coal samples under different conditions were studied.The results show that physical parameters of coal samples in different directions have different values,that is,the anisotropy of coal samples is obvious.When the coal samples are saturated with water,the acoustic velocities and the attenuation coefficient increase,whereas the dominant frequency decreases.The signal amplitude of the frequency domain significantly decreases,that is,the internal structure of coal samples is damaged.The P-wave velocity and S-wave velocity increase with the increase of the confining pressure,whereas the anisotropy parameters decrease with the increase of the confining pressure.Overall,this study provides the basis to understand basic acoustic information and anisotropy characteristics of coal samples.