Fluid history of the Sideling Hill syncline, Hancock County, Maryland.

摘要

Fluid inclusion microthermometry was employed to determine the fluid history of the Sideling Hill syncline in Maryland with respect to its deformation history. The syncline is unique in the region in that it preserves the youngest rocks (Mississippian) in the Valley and Ridge Province and is the easternmost exposure of Mississippian rocks in this portion of the Central Appalachians.;Two types of fluid inclusions were prominent in vein quartz: CH4-rich and two-phase aqueous with the former comprising about 60% of the inclusions observed. The presence of the two fluids in inclusions that appear to be coeval indicates that the migrating fluid was a CH4- saturated aqueous brine that was trapped immiscibly as separate CH4-rich and two-phase aqueous inclusions. Cross cutting relations show that at least two generations of veins formed during deformation. Similarities in chemistry of the inclusions in the different vein generations suggests that a single fluid was present during deformation.;Older veins were found to have formed at depths of at least 5 km while younger veins formed at minimum depths of 9 km. Overburden for older veins is attributed to emplacement of the North Mountain Thrust (NMT) sheet (∼6 km thick). The thickness of the Alleghanian clastic wedge is calculated to be ∼2.5 km in the Appalachian Plateau which accounts for most of the remaining overburden in younger veins. Due to the sediment load imposed by the NMT it is likely that the clastic wedge was thicker at Sideling Hill, with this increased thickness accounting for the remaining 0.5 km.