Spectral decomposition method for predicting magmatic intrusion into a coal bed

Accurate prediction of magmatic intrusion into a coal bed is illustrated using the method of seismic spectral decomposition.The characteristics of coal seismic reflections are first analyzed and the effect of variable time windows and domain frequencies on the spectral decomposition are examined.The higher domain frequency of coal bed reflections using the narrower STFT time window,or the smaller ST scale factor,are acceptable.When magmatic rock intrudes from the bottom of the coal bed the domain frequency of the reflections is decreased slightly,the frequency bandwidth is narrowed correspondingly,and the response from spectral decomposition is significantly reduced.Intrusion by a very thin magmatic rock gives a spectral decomposition response that is just slightly less than what is seen from a normal coal bed.Results from an actual mining area were used to validate the method.Predicting the boundary of magmatic intrusions with the method discussed herein was highly accurate and has been validated by observations from underground mining.

A Preliminary Research on Skarns of Magmatic Origin

Skarns of magmatic origin, or magmatic skarns as called, are formed by crystallization of skarnic magma injecting into structural fissures. They occur in various rocks (rock formations), mainly in form of veins. Usually, they possess massive structure and cumulative texture. They mainly consist of calc silicate, without or with minor water bearing silicates. The typical minerals in it include alkali feldspar, calcite and anhydrite. Some silicate melt inclusions and high temperature, high salinity poly phase inclusions can be seen in the crystals of their host minerals. The particular members of the magmatic skarns are transitional skarn and skarnic pegmatite. The magmatic skarn and the congenetic alkali rich diorite usually collaborate in a conjugating and complementary manner. They probably are the products of calcic contamination, degassing, desilicification and separation in melt state of deep seated (high level magma chamber) alkali rich intermediate acid magma.

Genesis of High Ba-Sr Yashan Intrusion from the Jiaodong Peninsula,Eastern China:Implications for the Destruction of the North China Craton

The origin of the Mesozoic high Ba-Sr(HBS)granitic magmatism in the Jiaodong Peninsula remains controversial in petrogenesis models and geodynamic settings.Here,we report zircon UPb age,trace element and oxygen isotope compositions,and whole-rock major-trace element and Sr-Nd isotope compositions of the HBS Yashan granodiorite.The zircon U-Pb age of~118 Ma denotes that the Yashan granodiorite belongs to the Weideshan-stage magmatic activity,which is consistent with the age of Mo mineralization in the Yashan intrusion.The low Sr/Y(48.8-115)and high(La/Yb)_(N)(23.8-50.4)ratios of the Yashan granodiorite are analogous to adakitic features derived from the lower-crust.This is also supported by the whole-rock initial^(87)Sr/^(86)Sr ratios(0.7096-0.7103)and zircon δ^(18) O values(6.79‰-8.03‰).Contemporaneous mantle-derived mafic microgranular enclaves indicate the involvement of the metasomatized lithospheric mantle.The high magma oxygen fugacity of the Yashan intrusion as indicated by high zircon Ce^(4+)/Ce^(3+) values suggests the involvement of plate subduction.The obviously lower Dy/Yb,La/Yb and Sr/Y ratios of magmatic rocks in the Weideshan-stage than those in the early-stage imply lithospheric thinning of the eastern North China Craton.We propose that the Yashan HBS granodiorite was formed by crust-mantle interactions during slab rollback.