A palaeomagnetic study of different lithologies exposed along the Moine Thrust Zone from Skye to Durness, Scotland, has identified three chemical remanent magnetizations (CRMs), a potential fourth CRM, and one possible primary component that all reside in hematite. Local and regional fold tests suggest that the CRMs are post-folding and post-thrusting. A contact test in the Torridon Group sandstone indicates that a Permian CRM is localized in and near the fault zone. The Permian CRM, which is also found in the Durness Group, and associated alteration are direct evidence for post-orogenic activity, in which the thrusts vented excess heat during regional crustal extension. On the Isle of Skye, sandstones (Sleat, Torridon and Eriboll Groups) in and around the fault zone contain a Tertiary CRM interpreted to be related to hydrothermal fluids associated with Tertiary intrusions. A possible Mesozoic CRM is also present but it could represent the vector addition of the Permian and Tertiary CRMs. A Devonian CRM is interpreted to be related to hydrothermal fluids associated with Devonian volcanic rocks or to fluids triggered by late stages of the Caledonian orogeny. Geochemical and petrographical studies provide supporting evidence for multiple fluid flow events along the Moine Thrust Zone. These results show that palaeomagnetism can be used to date multiple fluid migration events and that dormant fault zones can act as conduits for flow.
Sedimentary basins developed along the European margin during the earliest, Permian, stage of protoAtlantic rifting, during a phase of high heat flow. The proximity of some basins to Caledonian thrusts has implied that rifts locally utilized the basement fabric. New mineralogical and palaeomagnetic data show that thrust planes in the Moine Thrust Zone channelled a pulse of hot fluid in Permian time. The fluids precipitated kaolin in fractures in the thrust zone, and with decreasing intensity away from the zone. The high-temperature polytype dickite is largely confined to major thrust planes. Stable H and O isotope analyses indicate that the parent fluid included meteoric water involved in a hydrothermal system. Coeval hydrothermal hematite has a chemical remanence that dates the fluid pulse as Permian. This is direct evidence for post-orogenic activity in the thrust zone, in which the thrusts vented excess heat during regional crustal extension. The example from the European margin exemplifies the importance of deep-seated structures in the release of heat, and the value of kaolinite polytype mapping as a tool to record anomalous palaeo-heat flow.
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