Go with the Flow : Investigating Petrofabric Evidence for Hydrothermal Flow in Thermal Aureoles

Fluid flow in the Earth’s crust governs heat and mass transfer, critical metal mineralisation, rock rheology, and the development of deep, non-photosynthetic biospheres, yet its direction and mechanical drivers remain poorly constrained in natural systems. Conventional approaches infer fluid pathways from fractures, models, or geochemical tracers but rarely capture flow direction or mechanism directly. This PhD project develops a novel combination of fabric-based methods—integrating anisotropy of magnetic susceptibility and remanence (AMS/ARM), crystal preferred orientation analysis, and hyperspectral mineral mapping—to directly identify and quantify fluid-induced petrofabrics within the thermal aureoles of igneous intrusions, independent of fault kinematics. Similar integrated approaches have demonstrated their ability to track volatile-rich liquid migration through texturally layered intrusions, where permeability contrasts control fluid focusing and the development of REE-enriched horizons. Together, these methods provide new constraints on how fluids modify host-rock properties, localise permeability, and generate chemical enrichment, representing a step-change in our ability to observe and model crustal fluid flow.We present new petrofabric data from the Sherwood Sandstone Group, Northern Ireland, to assess fluid flow in permeable sandstones surrounding basaltic dykes. The study examines: (i) the geometry and extent of hydrothermal flow pathways, (ii) the interaction between thermally driven fluid circulation and pre-existing sedimentary anisotropy, and (iii) the impact of alteration on host-rock porosity and permeability. The Sherwood Sandstone Group forms the lowermost unit of the Triassic New Red Sandstone succession and is cross-cut by Palaeogene basaltic dykes related to North Atlantic rifting. Preliminary field observations and hyperspectral data identify laterally zoned alteration halos defined by systematic variations in clay, mica, and Fe-oxide mineralogy. AMS and ARM data reveal that primary sedimentary fabrics are preserved more than ~10 m from the dyke but are progressively overprinted toward the intrusion. Ongoing analyses test whether these overprinting fabrics record convective hydrothermal flow, with fluids ascending along dyke margins before dispersing laterally along bedding planes. We further evaluate the controls on stratigraphic fluid focusing and blockage, constraining the reciprocal relationship between fluid flow and evolving rock properties.