Magmatic flow paths and palaeomagnetism of the Miocene Stoddard Mountain laccolith, Iron Axis region, Southwestern Utah, USA
M. S. Petronis, D. B. Hacker, D. K. Holm, J. W. Geissman, S. S. Harlan, 2004. "Magmatic flow paths and palaeomagnetism of the Miocene Stoddard Mountain laccolith, Iron Axis region, Southwestern Utah, USA", Magnetic Fabric: Methods and Applications, F. Martín-Hernández, C. M. Lüneburg, C. Aubourg, M. Jackson
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The Stoddard Mountain laccolith is part of a complex of Early Miocene laccoliths intruded along the western edge of the Colorado Plateau in the Iron Axis region of Southwestern Utah. Most Colorado Plateau laccoliths (e.g. Henry and La Sal Mountains) are considered to be fed by a central axial feeder system. However, detailed mapping in the Iron Axis region suggests that the Stoddard Mountain laccolith was fed laterally from the west. Structural and field data suggest the quartz monzonitic magma initially migrated laterally eastward at ∼1 km depth as a sill before spreading laterally north-south where it inflated to ∼1–1.5 km thickness. To test the model of a lateral feeder system, data were collected from 32 palaeomagnetic sites and 76 AMS stations (763 accepted specimens) sampled over the ∼54 km2 exposed part of the N-S oval-shaped laccolith. The in situ AMS fabrics, inferred to correlate with magmatic fabrics, typically show NE trending lineations in the north and S-SE trending lineations in the south part of the intrusion. The palaeomagnetic data are interpreted to indicate a very minimal amount of post-emplacement deformation of the intrusion. The overall lack of westerly-directed and steep magnetic lineations argues against emplacement via a central axial feeder system.
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Fabric is a ubiquitous and significant feature of geological materials. The processes involved in the formation and deformation of rocks and sediments leave their mark on the orientations of the constituent mineral grains. Petrofabrics thus provide essential keys to understanding the history of geological materials. Magnetic anisotropy is directly related to petrofabric, and has become one of the most rapid, sensitive and widely used tools for its characterization. The relationship between magnetic fabric and petrofabric is complex and depends on various factors including the composition, concentration and grain size of mineral grains. Ongoing research in geological applications is paralleled by studies of the fundamental mineral magnetic phenomena involved.
The papers in this book represent the current state of investigations in magnetic anisotropy studies as a discipline that integrates geological interpretations, mineral fabric development, technical advances and rock-magnetic properties.