Relationship between metamorphism and structure in the Skiddaw Group, English Lake District

Fortey, N. J.; Робертс, Б.; Hirons, Steven

doi:10.1017/s0016756800020938

Cited by 12 publications

(6 citation statements)

References 33 publications

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“…(2) A thin-skinned fold and thrust belt developed over the central Lake District from mid-Ludlow onwards. Deformation of the Skiddaw Group does not show genetic linkage of the folding and thrusting: the thrusts are superimposed on the 'D1' folds (Hughes, Cooper & Stone, 1993) and disrupt the metamorphic pattern (Fortey, Roberts & Hirons, 1993). Nor is there compelling evidence that the structure is thin-skinned: exposed thrusts in the Skiddaw Group are steeply inclined, as shown correctly in the cartoon.…”

Section: B Critique Of the Flexural Model In Northwest Englandmentioning

confidence: 84%

The lost Lower Old Red Sandstone of England and Wales: a record of post-Iapetan flexure or Early Devonian transtension?

Soper

Woodcock

2003

Geol. Mag.

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Illite crystallinity data from the Silurian slate belts of England and Wales indicate anchizone to low epizone metamorphism during the Acadian deformation in late Early Devonian time. This metamorphic grade implies a substantial overburden, now eroded, of Lower Devonian non-marine sediments of the Old Red Sandstone (ORS) magnafacies. A minimum 3.5 km pre-tectonic thickness of ‘lost’ ORS is estimated in the southern Lake District and comparable thicknesses in North Wales and East Anglia. Tectonically driven subsidence of the underlying Avalonian crust is required to accommodate such thicknesses of non-marine sediment. One proposed mechanism is flexure of the Avalonian footwall during convergence that continued from Iapetus closure in the Silurian until Acadian cleavage formation in the Emsian. The evidence for this model in the critical area of northwest England is reviewed and found to be unconvincing. An alternative model is developed following a recent suggestion that the Early Devonian was a period not of continued convergence but of orogen-wide sinistral transtension. Transtensional accommodation of the lost ORS is evidenced by Early Devonian extensional faults, by synchronous lamprophyric magmatism, and by compatibility with previously diagnosed sediment provenance patterns. A summary of Siluro-Devonian tectonostratigraphy for Britain south of the Highland Border emphasizes that, unlike the Scottish Highlands, this area was not affected by the Scandian Orogeny, but was by the Acadian. An important period of sinistral transtension in the Early Devonian (c.420–400 Ma) was common to both regions. This was a time of high heat flow, lamprophyric and more evolved magmatism, and major southward sediment transport, involving mainly recycled metamorphic detritus from the Highlands and from contemporaneous volcanicity. Old Red Sandstone, deposited in coalescing transtensional basins over much of Britain from the Midland Valley to the Welsh Borders, was largely removed and recycled southward during Acadian inversion.

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Section: B Critique Of the Flexural Model In Northwest Englandmentioning

confidence: 84%

The lost Lower Old Red Sandstone of England and Wales: a record of post-Iapetan flexure or Early Devonian transtension?

Soper

Woodcock

2003

Geol. Mag.

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“…These Lower Palaeozoic rocks are intruded by a number of igneous bodies, most notably the Ennerdale Granophyre (mid-Ordovician), and Eskdale and Wasdale granites and granodiorite (late Ordovician). The Lower Palaeozoic strata are affected by NE-SW trending folding and regional sub-greenschist facies metamorphism (Fortey 1989;Fortey et al 1993) which developed during the late Caledonian (late Silurian to mid-Devonian) 'Acadian' orogeny.…”

Section: Geological Settingmentioning

confidence: 99%

The petrology and paragenesis of fracture mineralization in the Sellafield area, west Cumbria

Milodowski

Gillespie

Naden

et al. 1998

PYGS

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SUMMARY The petrology and paragenesis of fracture mineralization hosted in the Ordovician, Dinantian (Carboniferous Limestone) and Permo-Triassic rocks of the Sellafield area were studied as part of the United Kingdom Nirex Limited programme of site investigations around Sellafield in west Cumbria for a deep repository for radioactive waste. This paper summarizes the petrological and mineralogical observations from 23 of the deep (up to 2 km) boreholes drilled by Nirex. A paragenetic sequence of nine Mineralization Episodes (ME1 to ME9) was recognized, and has been interpreted in the context of the geological and hydrogeological history of the Lake District massif and East Irish Sea Basin margin areas. ME1 to ME3 produced silicate and sulphide-dominated Palaeozoic epithermal to mesothermal mineralization associated with pre-Acadian hydrothermal circulation and late-Caledonian (mid-Devonian) intrusions. ME4 to ME7 represent carbonate-sulphate-fluorite-hematite-dominated mineralization associated with warm, complex, Na-Cl-Ca-SO 4 brines expelled from the East Irish Sea Basin area during progressive burial of the thick Carboniferous and Permo-Triassic sedimentary sequence. Sulphate-carrying brines expelled to the basin margin in the Sellafield area mixed locally with cooler, more dilute, sulphate-poor groundwaters carrying barium, resulting in the precipitation of barite. ME8 and ME9, by contrast, are closely related to the development of the present-day groundwater system. ME8 involved telodiagenetic, supergene alteration and weathering by near surface oxidizing groundwaters. Isotopic evidence indicates that ME8 was probably initiated following Late Tertiary uplift and may still be ongoing in some areas. ME9 may be coeval with ME8, but represents mineralization in the deeper, more-reducing groundwater environment. This mineralization episode is dominated by calcite (sometimes associated with pyrite, marcasite, barite, anhydrite or gypsum) precipitated from groundwaters of similar composition to those found in the Sellafield area at the present day. Observations suggest that ME9 mineralization occurred during the Quaternary and is ongoing in the present groundwaters.

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“…Two contrasting settings of low-grade meta morphism are juxtaposed in the Lake District. In the northern Lake District early burial meta morphism of the Skiddaw Group took place at a h ig h er than norm al g eotherm al grad ien t (-35°C km_1) related to extensional high heat flow associated with volcanism and granitic batholith emplacement (Fortey et a/., 1993). Subsequent anchizonal to epizonal metamorphism occurred as the extensional basin was inverted and compressed.…”

Section: Lake Districtmentioning

confidence: 99%

Mineralogical controls on metal distribution in stream sediment derived from the Caledonides of the Scottish Southern Uplands and English Lake District

Stone¹,

Breward²,

Merriman³

2003

Mineral. mag.

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Stream sediment geochemistry provides an innovative method of assessing the basinal history of the Caledonian slate belts. Despite glaciation, the stream sediment geochemical patterns spatially mimic the outcrop of underlying bedrock lithologies. However, erosion from rock to sediment by fluvial processes may either increase or reduce an element’s abundance depending on the nature of its mineral host. An element held in heavy, resistate minerals will be concentrated, whereas one residing in unstable ferromagnesian minerals, which readily break down to clays during weathering, may be preferentially removed. Examples are provided from the Cr-Ni-V-Mg, base metal and Rb-Sr element suites. Primary and secondary bedrock patterns are recognized in the stream sediments. Primary patterns follow the original composition of the source bedrock, with steep gradients in the element distribution coinciding with lithostratigraphical boundaries. Such patterns also reveal subtle divisions within the established geological units for which the main compositional control was the nature of the ancient sedimentary provenance. Secondary patterns reflect remobilization of elements within the bedrock and so may cut across lithostratigraphical boundaries. These patterns (or their absence) are influenced by the thermal histories of the Caledonian basins, and so are indicative of the geotectonic regime in which the sedimentary sequences were originally deposited.

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Relationship between metamorphism and structure in the Skiddaw Group, English Lake District

Cited by 12 publications

References 33 publications

The lost Lower Old Red Sandstone of England and Wales: a record of post-Iapetan flexure or Early Devonian transtension?

The lost Lower Old Red Sandstone of England and Wales: a record of post-Iapetan flexure or Early Devonian transtension?

The petrology and paragenesis of fracture mineralization in the Sellafield area, west Cumbria

Mineralogical controls on metal distribution in stream sediment derived from the Caledonides of the Scottish Southern Uplands and English Lake District

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