Effect of intrusion of the Tianlongshan Granite Body on coal seam deform- ation and metamorphism characteristics in Xinhua Area,Hunan Province

Coal is sensitive to stress,strain and temperature. Under the multi-stage and multi-layer tectonic-thermal movement,there will inevitably be various traces of stress (static pressure and structural stress). This paper discusses the effect of intrusion of the Tianlongshan granite body on coal seam deformation and metamorphism,molecular struc- ture,trace elements migration and aggregation in detail by proximate and ultimate analysis,XRD,SEM,ICP-MS meth- ods. The results show that the coal turned itself into aphanitic graphite with the increase of coalification degree under the local stress field which was caused by Tianlongshan granite body intrusion and magmatic hydrothermalism,and the large quantities of thermal metamorphic minerals appeared in the coals and surround rock. Radial compressive stress concentration zone was applied to the rock mass emplacement,σ1 orientation of joint and petrofabric was perpendicular to the granite body boundary,under the ductile-brittle deformation with low temperature,low stress,and high strain rate. The superposition of tectonic stress and magmatic thermal metamorphism had a significant effect on the macromo- lecular structure of the coals,and the value of d002 and La / Lc reduction with the decrease of metamorphism degree and away from the magmatic intrusion,respectively. The coal seam near the granite body was obviously affected by magmat- ic heat. Structural effects of magmatic intrusion ( mechanical energy, thermal energy and chemical energy) caused structural damage to coal petrography,the increase of metamorphism degree,and element enrichment and migration, REE content obviously increased,chondrite-normalized REE patterns could be divided into three types,Type A and C1 superimposed magmatic thermal metamorphism near the rock mass,similar to the distribution pattern curve of rare earth elements in Devonian limestone and silicified limestone. Magmatic hydrothermal fluid mineralized the surround- ing rock,but was limited to the alteration zone. The magmatic thermal metamorphism led to an enrichment of LREE, while structural stress led to an enrichment of HREE,the concentration of local stress in the east side of Tianlongshan granite body caused the lower value of ΣL / ΣH.