Digital mapping of accommodating structures and deformation associated with the emplacement of high level magmatic intrusions, Henry Mountains, Utah

High-level sill and laccolith complexes form an important part of volcanic plumbing systems in which magma is emplaced as a series of sub-horizontal tabular sheet-like intrusions. Few studies of these intrusion types have looked in detail at the host rock, emplacement-related deformation structures, and how the additional volume of rock is accommodated within the crust, i.e. the 'space problem'. The aim of this study is to develop an understanding of the stages of emplacement (style of emplacement versus style of host rock deformation) and the internal textural evolution of Tertiary sills and laccoliths in the Henry Mountains, whilst also attempting to resolve the 'space problem'. Conventional field mapping, outcrop studies and detailed data collection of deformation structures has been combined with digital mapping using FieldMove™ and terrestrial laser scanning (TLS) in order to enable 3D modelling of the intrusive bodies and emplacement-related host rock deformation. Kinematic and geometrical studies of emplacement-related structures in the host rocks are supplemented by micro-scale textural and geochemical studies of deformed host rocks, plagioclase feldspar and amphibole phenocryst populations within the intrusions, and the intrusion-host rock contact zone. Fabric studies recognise micro-structural fabrics (associated with accommodating structures) from magmatic fabrics (associated with magma flow). Crystal size distribution (CSD) studies help constrain the crystal:molten rock ratio and mechanical properties of the intruding magma, in addition to helping identify individual magma pulses. Fieldwork to date has focused on two satellite intrusions to Mt. Hilliers: Trachyte Mesa (the most distal intrusion; simple geometries); and Maiden Creek (closer to Mt. Hilliers; more complex geometries) both of which are emplaced into the Jurassic Entrada Formation sandstone. Preliminary results highlight the importance of faults, fractures, deformation bands and newly identified shear zones in accommodating the extra volume of magma at depth.