geological evolution of britain

Question 1

rocks from all the major subdivisions of geological time occur in Britain and surrounding shelf areas: PRECAMBRIAN

Answer 1

• key areas: NW scotland, parts of anglesey, malvern hills
• rock types: highly metamorphosed gneisses and schists, and some volcanic and sedimentary rocks
• significance: represents some of the oldest continental crust in europe; basement rocks on which later sediments were deposited

Question 2

rocks from all the major subdivisions of geological time occur in Britain and surrounding shelf areas: EARLY PALAEOZOIC (cambrian, ordovician, silurian)

Answer 2

• key areas: welsh basin, lake district, southern uplands of scotland
• rock types: deep marine sediments (shales, turbidites), volcanics, fossil-rich limestones and slates
• tectonics: associated with subduction and closure of the iapetus ocean, leading to the caledonian orogeny
• fossils: trilobites, graptolites, brachiopods

Question 3

rocks from all the major subdivisions of geological time occur in Britain and surrounding shelf areas: LATE PALAEOZOIC (devonian, carboniferous, permian)

Answer 3

DEVONIAN
- key areas: old red sandstone in S wales and scotland
- environment: terrestrial deposits from arid conditions in the post-caledonian landscape

CARBONIFEROUS
- key areas: pennines, S wales, mendips
- rock types: limestones (marine), sandstones, coal measures (deltaic and swamp)
- significance: formation of major coalfields

PERMIAN
- key areas: NE england e.g. zechstein sea deposits
- environment: arid desert and evaporitic marine settings after the variscan orogeny

Question 4

rocks from all the major subdivisions of geological time occur in Britain and surrounding shelf areas: MESOZOIC (triassic, jurassic, cretaceous)

Answer 4

TRIASSIC
- key areas: midlands and cheshire basin
- rock types: red beds (sandstones, mudstones), evaporites

JURASSIC
- key areas: jurassic coast (dorset), cleveland basin
- depositional environment: shallow marine and deltaic; rich in ammonites and marine reptiles

CRETACEOUS
- key areas: chalk downs of southern england
- rock types: chalk and flint nodules from deep marine conditions

Question 5

rocks from all the major subdivisions of geological time occur in Britain and surrounding shelf areas: CENOZOIC (palaeogene, neogene & quaternary)

Answer 5

PALAEOGENE
- key events: volcanic activity in NW britain (e.g. isle of skye) associated with the opening of the N atlantic

NEOGENE & QUATERNARY
- quaternary: glacial and interglacial deposits, shaping the modern british landscape
- key features: glacial till, morains, raised beaches, river terraces

Question 6

caledonian orogeny

Answer 6

AGE
late silurian → early devonian

CAUSE
closure of the iapetus ocean due to the collision of lauentia, baltica and avalonia

LOCATION & GEOLOGY
- affects scotland, northern ireland, northern england and wales
- formation of mountain belts and regional metamorphism
- major granitic intrusions

MAJOR STRUCTURES & TRENDS
- major faults: great glen fault, highland boundary fault, moine thrust
- trend: NE - SW
- deformation: folding, thrusting, low-grade metamorphism

KEY FEATURES
- dalradian supergroup (metamorphosed sediments)
- old red sandstone basins formed as post-orogenic deposits

PLUTONIC ROCK, LOCATION & TECTONIC INTERPRETATION
- caledonian granites
- cairngorms, NW highlands
- partial melting of crust during continent-contient collision (laurentia-avalonia)

VOLCANIC ROCK, LOCATION & TECTONIC INTERPRETATION
- ordovician volcanics
- lake district, snowdonia
- island arc volcanism above a subduction zone as the iapetus ocean closed

METAMORPHIC ROCK, LOCATION & TECTONIC INTERPRETATION
- dalradian supergroup (scottish highlands); moine thrust
- regional metamorphism and thrusting due to continental collision

Question 7

variscan orogeny

Answer 7

AGE
late carboniferous → early permian

CAUSE
collision of gondwana and laurussia during the assembly of pangea

LOCATION & GEOLOGY
- strongest effects in SW england, south wales, devon-cornwall and isle of purbeck
- granite batholiths emplaces
- folding and faulting of previously flat-lying carboniferous rocks

MAIN STRUCTURES & TRENDS
- trend: E - W
- major structures: folds (e.g. south devon fold belt), thrusts, strike-slip faults
- cleavage and deformation zones in south wales and cornwall

KEY FEATURES
- metalliferous mineralisation e.g. tin and copper in cornwall
- molasse deposits and desert red beds post-orogeny e.g. permian red sandstones

PLUTONIC ROCK, LOCATION & TECTONIC INTERPRETATION
- cornubian batholith
- SW england
- post-collision melting during late-stage variscan convergence

VOLCANIC ROCK, LOCATION & TECTONIC INTERPRETATION
- less extensive; mainly sedimentary and plutonic
- volcanism less prominent in UK sector

METAMORPHIC ROCK, LOCATION & TECTONIC INTERPRETATION
- low-grade slates
- devon and cornwall
- burial metamorphism due to variscan folding and thrusting

Question 8

alpine orogeny

Answer 8

AGE
palaeogene → neogene

CAUSE
africa colliding with eurasia, forming the alps

LOCATION & GEOLOGY
- indirect effects in southern britain
- mainly rejuvenation of pre-existing faults
- uplift of southern england and inversion of mesozoic basins

MAIN STRUCTURES & TRENDS
- trend: generally N - S to NW - SE
- structure: gentle folding and doming

KEY FEATURES
- uplift and erosion in southern england
- reactivation of faults such as the purfleet-sole pit high

PLUTONIC ROCK, LOCATION & TECTONIC INTERPRETATION
- minor uplift and reactivation of faults; no major plutonism
- tectonic compression without deep magmatism

VOLCANIC ROCK, LOCATION & TECTONIC INTERPRETATION
- palaeogene volcanics
- isle of skye, northern ireland
- associated with rifting and north atlantic opening, not alpine compression directly

METAMORPHIC ROCK, LOCATION & TECTONIC INTERPRETATION
- no regional metamorphism; only rejuvenation of old structures
- alpine stress too far from britain to cause metamorphism

Question 9

• plutonic rocks (formed from magma cooling deep underground), tell us:
  - presence of granites and other intrusive igneous bodies indicates continental collision and crustal thickening
  - often linked to mountain-building (orogenic) events and continental arc settings
• volcanic rocks (formed at or near earth’s surface), tell us:
  - help reconstruct subduction zones, island arcs or rift settings
  - lava chemistry (e.g. andesite vs basalt) helps identify tectonic settings
• metamorphic rocks, tell us:
  - indicate burial depth, temperature and tectonic pressures during orogeny
  - help identify subduction, continental collision and thrusting

Answer 9

…

Question 10

palaeogene igneous province of NW britain

Answer 10

is critical evidence for the early stages of north atlantic ocean opening, associated with rift-related basaltic volcanism

AGE
- palaeogene period
- occured during the opening of the north atlantic ocean and linked to the break up of laurasia

LOCATION
- NW britain, especially: isle of skye, mull, ardnamurchan, rum, st kilda, antrim plateau (northern ireland)
- these areas contain the remnants of volcanic centres and lava fields

Question 11

palaeogene igneous province of NW britain — geological evidence for rift-related volcanism

Answer 11

BASALTIC LAVA FLOWS
- thick sequences of tholeiitic basalt flows e.g. antrim plateau basalts, skye lavas
- indicative of high-volume effusive eruptions, typical of rifting environments

CENTRAL COMPLEXES
- volcanic centres with ring dykes, cone sheets, gabbros, granites and diorites
- examples: skye central complex, ardnamurchan ring complex
- suggest repeated magma chamber activity, linked to crustal streching and uplift

DYKE SWARMS
- extensive basic dyke swarms e.g. mull dyke swarm, hebridean swarm
- radiate from central complexes
- formed as magma intruded into fractures created by tectonic extension

GEOPHYSICAL ANOMALIES
- evidence of mantle plume beneath the region
- uplift and crustal doming before volcanism