THREE-DIMENSIONAL MAGMATIC FABRIC OF A SHEETED LACCOLITH, HENRY MOUNTAINS, UTAH
The fabric of this intrusion was determined using field measurements of aligned elongate minerals and laboratory determination of anisotropy of magnetic susceptibility (AMS). The agreement between field and AMS measurements was corroborated with image analysis and X-ray computed tomography. Petrographic work indicates a lack of solid-state deformation, allowing the fabric data to be interpreted in terms of magmatic flow direction. The data indicate consistent directions of movement, even along a series of vertical cross-sections.
The field and magnetic data indicate that the thin Maiden Creek laccolith is composed of multiple sheets of porphyry emplaced in rapid succession, rather than a single injection pulse. Field evidence further suggests that each sheet solidified before the next sheet was emplaced. From these data, we infer that magmas intruded near their solidus temperature and rapidly solidified after emplacement. The constant orientation of the fabric throughout the intrusion suggests that each pulse of magma originated from a single source area.