Multiple post-Caledonian exhumation episodes across NW Scotland revealed by apatite fission-track analysis

Abstract

14The post Caledonian exhumation history of northwest Scotland is a controversial issue, with 15 some studies advocating largely continual emergence while others suggest dominantly early Abstract 36The origin and development of the high topography bordering the Atlantic margin of NW 37 Europe has long been the subject of debate (Geike, 1901; George, 1966; Doré et al., 2002). 38 The mountains of Scotland and western Scandinavia are characterized by rugged topography 39 and elevations that exceed 1.3 km and 2.4 km respectively and largely comprise rocks that 40 were formed and/or deformed during the Caledonian Orogeny. Numerous lines of evidence 41 indicate that the present-day topography of both regions was initiated by tectonic uplift that 42 began during the Cenozoic or late Mesozoic and which also affected peripheral sedimentary 43 basins (Doré et al., 2002). These include; the transition from deposition of shallow-marine 44 carbonates in the late Cretaceous to rejuvenated clastic sedimentation in the early Palaeogene 45 (Doré et al., 2002)); the easterly tilt of Britain (Brodie & White, 1994) Cretaceous rocks are less widely distributed (Fig. 1), but this is considered to be due 137 Cenozoic uplift and erosion rather than non-deposition (Hallam, 1983 This igneous activity has been attributed to the proto-Iceland mantle plume, and petrological 150 data suggest that a significant proportion (up to 70%) of the melt generated around the British Post-Caledonian exhumation of northwest Scotland 8We present AFTA data from 78 samples collected from onshore and offshore northwest 177 Scotland (Fig. 1 The majority of measured fission track ages are younger than the respective stratigraphic ages 187 (Table 1). Overall there is a consistent trend between fission track age and mean track length, totally anneal all tracks (typically >110°C), followed by a subsequent peak around 90-100°C 245 which leads to shortening of tracks formed after the initial cooling to a mean length of ~10 246 μm. Finally, cooling to a low temperature is followed by reheating to ~70°C, sufficient to 247 reduce track lengths formed after the second episode to ~12-13 μm. Post-Caledonian exhumation of northwest Scotland 11 West Orkney Basin 252Of six Permian-Lower Jurassic samples from offshore shallow boreholes in the WOB, most 253 require two discrete episodes of heating and cooling (Table 2) Post-Caledonian exhumation of northwest Scotland 12The variation of palaeotemperature with depth for the two separate episodes (Fig. 4b (Table 2). An onset of cooling beginning between 225 319 and 190 Ma satisfies all samples that show evidence for this episode (Fig. 3). on this basis for sample GC369-6 predicts total annealing, whereas this sample contains 353 tracks and gives a finite (though very young) fission track age (Fig. 5a) superimposed on a "background" linear profile (Fig. 5b). The rapid fluctuations clearly 366 reflect contact heating around the igneous intrusions. AFTA data in GC369-2 is also 367 interpr...

Quaternary evolution of glaciated gneiss terrains: pre-glacial weathering vs. glacial erosion

“…The uplift history of NW Scotland is complicated and closely linked to the subsidence history of the Minch Basin. Some four phases of subsidence and uplift during the Mesozoic and Cenozoic have been recorded by apatite fission-track dating in the west of Scotland (Holford et al 2010). It is possible the study area was inundated and partially covered by marine sediments during the late Mesozoic, but any such sedimentary rocks have disappeared since.…”

Petroleum generation and migration in the Cambro-Ordovician Laurentian margin succession of NW Scotland

“…The Jurassic units may have been deposited widely over NW Scotland, including the Moine Thrust Zone (Holford et al 2010). The Devonian source rocks consistently contain high proportions of C 28 ααα steranes (Fig.…”

Progress in marine geoconservation in Scotland’s seas: assessment of key interests and their contribution to Marine Protected Area network planning

“…Along with Rosemary Bank and the Hebrides Terrace Seamount, Anton Dohrn is one of the few accessible remnants of such early mantle plume activity. In addition, the region has provided a range of sedimentary and geophysical evidence that reveals the dynamic evolution of a supposed 'passive' continental margin in response to changes in upper mantle convective flow Stoker et al, , 2010aHolford et al, 2009Holford et al, , 2010. In turn, the associated tectonic movements have driven responses in erosion, sedimentation and deep-ocean circulation and provided the topographic conditions to support glaciation.…”

“…Consequently, the greater part of the footprint of the last British-Irish Ice Sheet and its earlier counterparts lies offshore, as revealed in remarkable detail by the recent development of new underwater survey techniques, such as multibeam swath bathymetry (Bradwell and Stoker, 2015;Dove et al, 2015). More generally, understanding of the complex geological and geomorphological evolution of the NW European continental margin since the magmatism and rifting that led to the separation of Europe and North America in the early Eocene is fundamentally dependent on integrating onshore and offshore evidence (Hall and Bishop, 2002;Stoker et al, , 2010aHolford et al, 2009Holford et al, , 2010. A significant part of Scotland's geodiversity and geoheritage therefore lies offshore, as documented, for example, in British Geological Survey UK Offshore Regional Reports.…”