The kinematic linkage of the Dent, Craven and related faults of Northern England

New mapping of the southern part of the Dent Fault reveals three segments, each 5–6 km long, overlapping at two left-stepping zones 1–2 km wide. The main fault strands probably dip steeply WNW. A faulted footwall syncline in Carboniferous strata indicates reverse dip-slip, with a stratigraphic throw of at least 750 m. Locally developed plunging folds and imbricate fault duplexes developed at fault bends reveal a strike-slip component, indicated to be sinistral from limited slickenline data. Silurian strata in the hanging wall lack the Variscan folds observed further north. The northern overstep hosts up-faulted slivers of older Silurian and Ordovician rocks. The southern overstep zone hosts a younger faulted block compatible with releasing kinematics in sinistral strike-slip. The Dent Fault converges at its southern end with the Barbon Fault; an upfaulted wedge of Silurian strata lies between them near the branch point. The two faults swing southeastward, joining the Craven fault system via splays and linkages. Regionally, the Dent and Barbon faults form the innermost pair of a fan of ~N–S striking faults splaying off the northwest end of the South Craven–Morley-Campsall Fault System around the southwestern corner of the Askrigg Block. The kinematics of the Dent, Barbon and Craven faults fit shortening orientated NNW–SSE during late Carboniferous Variscan deformation. The rigid Askrigg Block focussed displacements around its west and south margins where fault and fold orientations were influenced by pre-existing structures, at least Acadian in age to the west and early Carboniferous to the south

Geological notes and local details for 1:10 000 sheet SD69NE (Westerdale), and parts of sheets SD69NW (Howgill), SD69SW (Firbank) and SD69SE (Sedbergh) : part of 1: 50 000 sheets 39 (Kendal) and 40 (Kirkby Stephen)

This report describes the bedrock and superficial deposits geology of the southern parts of Howgill Fells, a picturesque upland area located at the easterly extent of the Lake District Lower Palaeozoic inlier in Cumbria. The bedrock geology consists mainly of a thick succession of mudstone and sandstone assigned to the upper Ordovician and Silurian Windermere Supergroup. These rocks are partially overlain by a variable thickness of glacial and post-glacial deposits. This description and an earlier one by the same authors (Woodcock and Rickards, 1999) accompanies, and should be read in conjunction with, the 1:10 000 scale geological sheets SD 69 NW, NE, SW, SE. These maps are components of the 1:50 000 Geological Series sheets 39 (Kendal) and 40 (Kirkby Stephen). The first part of the report provides an extensive review of previous research into the Quaternary geology of the area, which complements a similar review of research into the bedrock geology of the area presented in Woodcock and Rickards (1999). Each of the Lower Palaeozoic bedrock units identified within the area are then described, along with the biostratigraphy and an outline of the depositional history. An account of the various dolerite, felsite and lamprophyre minor intrusions follows. The ?Upper Devonian and Carboniferous rocks around the margin of the area are described briefly for completeness. A description of the structures present and an analysis of the deformation history forms a major section. The final section describes the Quaternary deposits. The Howgill Fells lies immediately to the west of the Dent Fault, a major zone of east-northeast-trending faults which has the form of a positive flower-structure in cross-section and a contractional strike-slip duplex in map view. Associated with the fault zone, structural domes cored by Ordovician rocks were the result of westerly plunging Early Devonian, Acadian folds affected by interference from Late Carboniferous (‘Variscan’) east-north-east-trending folds. The Ordovician Dent Group here is represented by the Cautley Mudstone and Ashgill formations. The Silurian succession is similar to that found in the Lake District, though significant variations in thickness are recorded for some of the units. The lower part of the Bannisdale Formation comprises the youngest strata represented. The Windermere Supergroup here is up to 3400 m thick. Extensive till deposits overlie the bedrock in many of the upland valleys and alongside the River Lune. Alluvium and River Terrace deposits occupy most of the main streams. Peat blankets the flatter upland areas

Tectonic controls on post-subduction granite genesis and emplacement : the late Caledonian suite of Britain and Ireland

Rates of magma emplacement commonly vary as a function of tectonic setting. The late Caledonian granites of Britain and Ireland are associated with closure of the Iapetus Ocean and were emplaced into a varying regime of transpression and transtension throughout the Silurian and into the early Devonian. Here we evaluate a new approach for examining how magma volumes vary as a function of tectonic setting. Available radiometric ages from the late Caledonian granites are used to calculate probability density functions (age spectra), with each pluton weighted by outcrop area as a proxy for its volume. These spectra confirm an absence of magmatic activity during Iapetus subduction between c. 455 Ma and 425 Ma and a dominance of post-subduction magmas between c. 425 Ma and 380 Ma. We review possible reasons why, despite the widespread outcrop of the late Caledonian granites, magmatism appears absent during Iapetus subduction. These include shallow angle subduction or extensive erosion and tectonic removal of the arc. In contrast to previous work we find no strong difference in the age or major element chemistry of post-subduction granites across all terranes. We propose a common causal mechanism in which the down-going Iapetus oceanic slab peeled back and detached beneath the suture following final Iapetus closure. The lithospheric mantle was delaminated beneath the suture and for about 100 km back beneath the Avalonian margin. While magma generation is largely a function of gravitationally driven lithosphere delamination, strike-slip dominated kinematics in the overlying continental crust is what modulated granitic magma emplacement. Early Devonian (419–404 Ma) transtension permitted large volumes of granite emplacement, whereas the subsequent Acadian (late Early Devonian, 404–394 Ma) transpression reduced and eventually suppressed magma emplacement

Geological notes and local details for 1:10 000 scale Sheet SD 68 NW (Middleton) and part of Sheet SD 68 NE (Gawthorp)

The mapped area of Cumbria represented on Sheets SD 68 NW and NE includes the settlements of Killington, Middleton and Gawthrop. Larger settlements border the area: Sedbergh 2 km to the north, Dent 0.5 km to the east and Barbon 2.5 km to the south. The area is bounded to the east by the Dent Fault, and is completely traversed by two other major faults, the Barbon Fault and the Firbank Fault. These faults divide the solid geology into three major sectors and one minor sector, the stratigraphical continuity of which can only be inferred outside the area. The oldest rocks at outcrop occur as a small sliver along the Dent Fault, comprising Dent Group calcareous mudstones and volcanic rocks and Tranearth Group laminated mudstones; the two groups are also separated by a fault. The major outcrop sector between the Dent and Barbon fault zones comprises turbidite sandstones and subordinate mudstones of the uppermost Coniston Group and a lower division of the Bannisdale Formation, passing up into a mudstone-rich upper Bannisdale Formation. The distinction between the Coniston and lower Bannisdale units is difficult, and based mainly on the lamination characteristics of the their hemipelagic mudstone. The outcrop between the Barbon and Firbank faults comprises mudstones with thin sandstones assigned to the upper part of the Bannisdale Formation. This lithology is also present at the base of the succession west of the Firbank Fault, though most of the outcrop here comprises the overlying sandstone-rich Kirkby Moor Formation. Reddening of the upper parts of this formation also affects part of the upper Bannisdale Formation across the Firbank Fault: the reddening is therefore interpreted as secondary, and not diagnostic of a ‘Scout Hill Formation”. The Lower Palaeozoic rocks are deformed by a weak Acadian cleavage striking generally ESE, and by open kilometric-scale folds. These structures are cut by the major north-south Variscan faults. Till occurs in upland valleys and in the major valleys of the Lune and Dee, where it is moulded into drumlins. The River Lune has extensive spreads of post-glacial alluvium