Silurian–Devonian magmatism, mineralization, regional exhumation and brittle strike-slip deformation along the Loch Shin Line, NW Scotland

Abstract

The Loch Shin Line is a geological–geophysical lineament associated with a zone of mantle-derived appinites, granites and strike-slip faulting that runs NW–SE across the Moine Nappe, northern Scotland. U–Pb zircon and Re–Os molybdenite dating of the Loch Shin and Grudie plutons, which lie immediately SW of the NW–SE Loch Shin–Strath Fleet fault system, yield c . 427–430 Ma ages that overlap within error. They also coincide with previously obtained U–Pb zircon ages for the Rogart pluton, which lies along-strike to the SE. Field and microstructural observations confirm the similarity and contemporaneous nature of the plutons and associated sulphide mineralization. Fluid inclusion analyses place further constraints on the P – T – X conditions during regional late Caledonian exhumation of the Moine Nappe. Synchronous to slightly younger brittle dextral strike-slip faulting along the WNW–ESE Loch Shin–Strath Fleet Fault System was probably antithetic to sinistral movements along the nearby Great Glen Fault Zone. Our findings support the hypothesis that the Loch Shin Line acted as a deep crustal channelway controlling the ascent and emplacement of Silurian magmas into the overlying Moine Nappe. We propose that this deep structure corresponds to the southeastern continuation of the Precambrian-age Laxford Front shear zone in the buried Lewisian autochthon. Supplementary Material: Field photographs, photomicrographs and fluid inclusion information are available at http://www.geolsoc.org.uk/SUP18859 .

Quartz-Amethyst Hosted Hydrocarbon-Bearing Fluid Inclusions from the Green Ridge Breccia in the Snoqualmie Granite, North Cascades, WA, USA

“…wt % NaCl) with the majority of TH values between ~270 °C and 310 °C. This fluid is similar to hydrothermal fluids recorded in granite quartz and their mineralised veins from granites throughout Great Britain and Ireland [46][47][48][49][50][51]. These fluids invariably involve mixing between late-stage magmatic fluids and meteoric fluids.…”

Timing of strain partitioning and magmatism in the Scottish Scandian collision, evidence from the high Ba–Sr Orkney granite complex

“…The Orkney granite complex also yields the hitherto oldest age for the Scottish high Ba-Sr granite magmatism (cf. Rogers and Dunning 1991;Stewart et al 2001;Olivier et al 2008;Holdsworth et al 2015), apart from an 433.5 ± 1.8 Ma Re-Os age interpreted as a minimum age for the Ballachulish complex (Conliffe et al 2010). The age of the Orkney granite complex thus constrains the onset of the tectonic process (-es) that led to the widespread production of high Ba-Sr magmas below the Scottish highlands, and suggests that this process is coeval with the onset of transpressional deformation in northern Scotland.…”

“…For example, the stick-point sketch in Fig 6a is adapted from an interpretation of the Clunes granite published by Stewart et al (2001), the jog on a subsidiary fault parallel to the Great Glen / Leannan fault has been proposed for the Donegal pluton (Fig 6c;Hutton 1982;Arthur 1982), and a jog on an anti-Riedel shear zone has been proposed for the Rogart pluton (Fig 6e; Kocks et al 2013). These conceptual models do not take into account the potential for strain rotation in a strike slip setting or effects of preexisting basement structures (for examples of the latter, see Jacques and Reavy 1994;Holdsworth et al 2015). In contrast to the aforementioned examples, the Orkney granite complex lacks steeply dipping fabrics commonly reported in proximity to subvertical strike slip faults.…”

A revised age, structural model and origin for the North Pennine Orefield in the Alston Block, northern England: intrusion (Whin Sill)-related base metal (Cu–Pb–Zn–F) mineralization

“…Fault-slip slickenline data associated with each of the mineralized fault groups identified in the field were used to carry out a conventional palaeostress inversion analysis (Angelier 1979(Angelier , 1984Michael 1984) implemented using MyFault® software following the protocols set out by Holdsworth et al (2015) and Dichiarante et al (2020). Importantly, any analysis of this kind is viable only in regions where finite strains are modest and the presence of major fault block rotations can be ruled out.…”

“…Pyrite is commonly enriched with rhenium (Re) so that the 187 Re-187 Os geochronometer can be used to date mineralization and better constrain the timing of brittle deformation (e.g. Holdsworth et al 2015Holdsworth et al , 2020Dichiarante et al 2016). Furthermore, the determined 187 Os/ 188 Os composition of the sulfide minerals at the time of formation can yield insights into the origins of the fracture-hosted fluids (e.g.…”