GCR block - Ordovician Igneous Rocks (ORD-IGN)

Ordovician Igneous Rocks

Block Description

UK map showing distribution of GCR sites of GCR block ORD-IGN
Distribution of GCR sites of GCR block Ordovician Igneous Rocks

The GCR sites selected for this GCR Block represent a major episode of intrusive and extrusive igneous activity in the UK that occurred as a result of the ‘Caledonian Orogeny’, lasting from about 500 million years ago (Ma) to around 360 Ma (see CAL-STR-LD; CAL-STR-SU; CAL-STR-WL), which was a period of mountain building and continental collision that began in the Ordovician Period (which lasted from 495 to 440 Ma) and continued through Silurian (440–417 Ma) and Devonian (417–354 Ma) time.

There is at present no agreed definition of the term ‘Caledonian’, but is taken here to include all of the convergent tectonic and magmatic events arising from the closure of the ‘proto-Atlantic’ Iapetus Ocean in which many of the rocks of Late Proterozoic and early Palaeozoic age had been deposited. It therefore encompasses subduction beneath the continental margins; the accretion or obduction of oceanic crust and island-arc material onto these margins; and ultimate collision of the continents, uplift and development of extensional molasse basins. Within this broad orogenic framework many separate ‘events’ are identified, such as the ‘Grampian Event’ and the ‘Acadian Event’. By this definition, most Caledonian igneous rocks of Britain range in age from about 500 Ma (earliest Ordovician) to around 390 Ma (end Early Devonian), with related activity continuing to around 360 Ma (end Late Devonian) in Orkney and Shetland.

For details of stratigraphy related to the Caledonian Orogeny see GCR Blocks for Ordovician, Silurian and Devonian Stratigraphy: ARE-LLV; ARE-TRE; CAR-ASH; LDO; LDY; LUD; MAR-DEV; NMAR-DEV).

Tectonic setting and evolution

The Iapetus Ocean was created in Late Proterozoic time by the rifting and pulling apart of a large supercontinent known as ‘Rodinia’. The opening started sometime around 650 million years (Ma) ago and, by the beginning of Ordovician time, at 510 Ma, the ocean was at its widest development of possibly up to 5000 km across. On one side of the ocean lay the supercontinent of Laurentia, which is represented today largely by the Precambrian basement rocks of North America, Greenland, the north of Ireland and the Scottish Highlands. On the opposite side lay the supercontinent of Gondwana, consisting of the basements of South America, Africa, India, Australia, East Antarctica and Western Europe (including south Ireland, England and Wales). A separate continent, Baltica (the basement of Scandinavia and Russia), was separated from Gondwana by an arm of the Iapetus Ocean, known as the ‘Tornquist Sea’. The wide separation is supported by palaeontological data which shows distinctly different faunal assemblages in the Lower Palaeozoic rocks of each continent and by palaeomagnetic interpretations.

The continental plates of Laurentia, Gondwana and Baltica started to converge during the early part of the Ordovician Period, initiating new tectonic and magmatic processes which marked the start of the Caledonian Orogeny. The Iapetus oceanic crust was consumed in subduction zones beneath oceanic island arcs and beneath the continental margins.

Magma was being created by the melting of mantle and oceanic crustal material within and above the subduction zones and by melting within the thickened continental crust.

The exact sequence and timing of events as the three plates converged is the subject of much debate, in which the distribution, nature and timing of the igneous activity are crucial evidence.

The tectonic history of the Caledonian Orogeny in Britain can be divided into the following time intervals, linking together coeval magmatic events in the various terranes across the whole orogenic belt.

• Early Ordovician –Tremadoc and Arenig

• Mid-Ordovician –Llanvirn and Llandeilo

• Late Ordovician –Caradoc and Ashgill

• Early and mid-Silurian –Llandovery and Wenlock

• Late Silurian and Early Devonian –Ludlow to Emsian

• Mid- and Late Devonian –Eifelian to Famennian

GCR site selection

Within this GCR Block, sites fall into natural ‘networks’, which are based upon petrological or tectonic affinites, age and geographical distribution. The ten networks are:

• Ordovician Volcanic Rocks and Ophiolites of Scotland

• Ordovician intrusions of the NE Grampian Highlands of Scotland

• Ordovician Igneous rocks of the Lake District

• Ordovician Igneous rocks of Central England

• Ordovician Igneous rocks of Wales

• Silurian and Devonian Plutonic rocks: alkaline ntrusions of the NW highlands of Scotland

• Silurian and Devonian Plutonic rocks: granitic intrusions of Scotland

• Silurian and Devonian Plutonic rocks: northern England

• Silurian and Devonian volcanic rocks: Scotland

• Silurian and Devonian volcanic rocks: Wales

Sites that are important for unravelling the geological history of these major igneous events will also be important for demonstrating general processes of igneous rock petrology, magma evolution and emplacement, and vulcanology (e.g. Cauldron Subsidence theory at Glencoe) irrespective of their role in building up a picture of the sequence of events of geological history of the UK.

Weighting of site selection has focussed on identifying those sites where the contribution of Caledonian igneous rocks of Great Britain to igneous petrology and the understanding of igneous processes and have played a major role in the initiation, testing and evolution of many theories of igneous processes.

Volume Introduction

Ordovician Igneous Rocks

Site List

Your selection found 58 GCR sites. Sites are sorted alphabetically by country, local authority and then by site name -
CodeNameCountryLocal AuthorityGrid RefGCR Site Account
295Carrock FellEnglandEast CumbriaNY352327Site Account
292ConistonEnglandEast CumbriaSD296985Site Account
291Eycott HillEnglandEast CumbriaNY386295Site Account
286HaweswaterEnglandEast CumbriaNY492147Site Account
2607Pets QuarryEnglandEast CumbriaNY392073Site Account
2608Side PikeEnglandEast CumbriaNY290053Site Account
297Beckfoot QuarryEnglandWest CumbriaNY164003Site Account
296Bowness KnottEnglandWest CumbriaNY112156Site Account
288Bramcrag QuarryEnglandWest CumbriaNY320220Site Account
287Falcon CragEnglandWest CumbriaNY272206Site Account
2710Ray Crag & Crinkle CragsEnglandWest CumbriaNY243042Site Account
289Rosthwaite FellEnglandWest CumbriaNY258122Site Account
294Sour Milk GillEnglandWest CumbriaNY230122Site Account
290Waberthwaite QuarryEnglandWest CumbriaSD112944Site Account
2563Garron Point to Slug HeadScotlandAberdeen City and AberdeenshireNO893872Site Account
2399North Glen SannoxScotlandEast Ayrshire and North Ayrshire MainlandNR995465Site Account
2564Balmaha and Arrochymore PointScotlandPerth and Kinross and StirlingNS419915Site Account
2417Ham NessScotlandShetland IslandsHP636017Site Account
2416Qui Ness to Pund StacksScotlandShetland IslandsHP622033Site Account
2420Skeo Taing to CluganScotlandShetland IslandsHP640084Site Account
2421The Punds to Wick of HagdaleScotlandShetland IslandsHP642113Site Account
2418Tressa Ness to ColbinstoftScotlandShetland IslandsHU620949Site Account
2419VirvaScotlandShetland IslandsHU645920Site Account
2412Balcreuchan Port to Port VadScotlandSouth AyrshireNX100878Site Account
2407Bennane LeaScotlandSouth AyrshireNX091861Site Account
2410Byne HillScotlandSouth AyrshireNX180945Site Account
2406Games LoupScotlandSouth AyrshireNX103880Site Account
2405KnocklaughScotlandSouth AyrshireNX168920Site Account
2415KnockormalScotlandSouth AyrshireNX134885Site Account
2409MillenderdaleScotlandSouth AyrshireNX177905Site Account
2408Sgavoch RockScotlandSouth AyrshireNX073808Not available
2411Slockenray CoastScotlandSouth AyrshireNX135911Site Account
270Capel CurigWalesCONWY AND DENBIGHSHIRESH700575Site Account
279Curig HillWalesCONWY AND DENBIGHSHIRESH729583Site Account
277Cwm IdwalWalesCONWY AND DENBIGHSHIRESH645585Site Account
271Llyn DulynWalesCONWY AND DENBIGHSHIRESH703661Site Account
275SarnauWalesCONWY AND DENBIGHSHIRESH775595Site Account
281PandyWalesFLINTSHIRE AND WREXHAMSJ195362Site Account
2711Cadair IdrisWalesGWYNEDDSH750149Site Account
274Craig y GarnWalesGWYNEDDSH511444Site Account
1351Ffestiniog Granite QuarryWalesGWYNEDDSH696453Site Account
2403Foel GronWalesGWYNEDDSH301309Site Account
278LlanbedrogWalesGWYNEDDSH337307Site Account
2404MoelypenmaenWalesGWYNEDDSH338386Site Account
273Mynydd PenarfynyddWalesGWYNEDDSH214259Site Account
2402Nanhoron QuarryWalesGWYNEDDSH287329Site Account
276Pared y Cefn-hirWalesGWYNEDDSH666152Site Account
2401Penrhyn BodeilasWalesGWYNEDDSH318422Site Account
280Rhobell FawrWalesGWYNEDDSH787257Site Account
2400Trwyn-y-Gorlech to Yr-Eifl QuarriesWalesGWYNEDDSH348455Site Account
272Yr ArdduWalesGWYNEDDSH626462Site Account
2712Carneddau & Llanelwedd RocksWalesPOWYSSO050520Site Account
284Aber Mawr to Porth LleuogWalesSOUTH WEST WALESSM695234Site Account
283Castell Coch to TrwyncastellWalesSOUTH WEST WALESSM775303Site Account
2414Deer ParkWalesSOUTH WEST WALESSM756091Site Account
282Pen CaerWalesSOUTH WEST WALESSM887391Site Account
2413Skomer IslandWalesSOUTH WEST WALESSM722088Site Account
285St David`s HeadWalesSOUTH WEST WALESSM740280Site Account
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