4. Alpine Orogeny
3. North Atlantic Tertiary
Igneous Province (NATP)
2. Variscan Orogeny
1. Caledonian Orogeny

4. Alpine Orogeny
3. North Atlantic Tertiary
Igneous Province (NATP)
2. Variscan Orogeny
1. Caledonian Orogeny

Evidence for the interpretation that northern and southern Britain were on two different continents:
1. Major differences in the age and character of the Precambrian (basement) rocks.
2. Palaeomagnetic evidence.
(Palaeomagnetism is magnetism trapped in certain rocks at their time of formation. It can give an indication of a continent’s palaeolatitude.)
Precambrian rocks as old as 2500 MYA in northern
Britain
10ºS
Precambrian rocks no older than 700 MYA in most of southern Britain and Ireland

Evidence for the existence of a widening oceanic area separating northern and southern Britain:
1. Palaeomagnetic evidence gives latitude.

Evidence for the existence of a widening oceanic area separating northern and southern Britain:
1. Palaeomagnetic evidence gives latitude.
2. Fossil contrasts, especially trilobites such as Olenellus, found only in Scotland.
3. Contrasts in sedimentary environments between the two areas e.g. Durness Lst.

Evidence for the existence of a widening oceanic area separating northern and southern Britain:
1. Palaeomagnetic evidence gives latitude.
2. Fossil contrasts, especially trilobites such as Olenellus, found only in Scotland.
3. Contrasts in sedimentary environments between the two areas e.g. Durness Lst.
4. Absence of andesitic and rhyolitic volcanic lavas suggests a widening ocean and no subduction.

•Northern Britain & Southern Britain separated by the 3,500km Iapetus Ocean
•Laurentia remained stationary approx 10ºS of
Equator whilst Avalonia (containing England & Wales) drifted away from Gondwana to approx 40ºS.
•Subduction occurring under both continents, causing the Iapetus to close.
Island-arc volcanism
Evidence:
• Palaeomagnetism
• Distinct trilobite faunal provinces
• Durness Lst in Scotland
• Volcanic rocks in Lake
District
• Ophiolites at Ballantrae and Arran in Scotland
• Accretionary prism – Southern Uplands in Scotland

1. Name the orogenic belt that formed in Britain during the Lower Palaeozoic.
2. When was this orogenesis completed by?
3. What two continents collided during this orogenesis?
4. What was the ocean that was destroyed?
5. What areas in Britain were affected?
6. What is the general trend of the structures formed in this orogenesis?
7. What is the name of the continent that formed after this collision?
8. What was the name of the mountain chain formed?
9. At what latitude did these two continents collide at?

Laurentia
(Northern Britain)
Iapetus Suture
Avalonia
(Southern Britain)
Cambrian ~550 Ma

Laurentia
(Northern Britain)
Iapetus Suture
Avalonia
(Southern Britain)
Early Ordovician ~490 Ma

Laurentia
(Northern Britain)
Iapetus Suture
Avalonia
(Southern Britain)
Early Silurian ~440 Ma

Laurentia
(Northern Britain)
Iapetus Suture
Avalonia
(Southern Britain)
Devonian ~400 Ma

Reabsorbed into mantle by subduction
Cooling, thickening & becomes denser as it moves away from MOR
Dewatering of slab lowers
MTP of mantle wedge causing it to partially melt
Does not melt unless young (<3 Ma)
Dehydration of slab cools it and increases its density
Slab pull forces increase
400km phase change olivine to spinel (10% denser)
670km phase change spinel to perovskite (10% denser)

Caledonian Orogenesis (Lower Palaeozoic)
Foreland Outer Zone Inner Zone Hinterland

Igneous Rocks – Andesites &
Rhyolites in Cumbria (BVG) or North
Wales (Snowdonia)
Metamorphic Rocks – Slate in North
Wales & Cumbria, & Schists in
Scotland
Sedimentary Rocks – Black Shales
(Skiddaw Slates)
Folds – Harlech Dome, Shap Fell,
Tebay & Tay Nappe
Faults – Moine Thrust
Trends -
Intrusions – Skiddaw Granite or
Cairngorms
Accretionary Prism – Southern
Uplands
Ophiolites – Ballantrae Complex

Era
Cenozoic
Mesozoic
Upper
Palaeozoic
Lower
Palaeozoic
Period
Quaternary
Tertiary
Cretaceous
Jurassic
Triassic
Permian
Carboniferous
Devonian
Silurian
Ordovician
Cambrian
Orogeny
ALPINE
(40 MYA)
VARISCAN
(300 MYA)
CALEDONIAN
(400 MYA)

Sedimentary Rocks – Black Shales
(Skiddaw Slates)
Igneous Rocks – Andesites &
Rhyolites in Cumbria (BVG) or North
Wales (Snowdonia)
Metamorphic Rocks – Slate in North
Wales & Cumbria, & Schists in
Scotland
Folds – Harlech Dome, Shap Fell,
Tebay & Tay Nappe
Faults – Moine Thrust
Intrusions – Skiddaw Granite or
Cairngorms
Accretionary Prism – Southern
Uplands
Ophiolites – Ballantrae Complex

• Moine Thrust Belt
• Great Glen Fault
• Highland Boundary Fault
• Southern Uplands Fault
• Tay Nappe

Moine Thrust Belt
• NE-SW strike
• 200km long
• 0-12km wide
• up to 150km displacement
• 435-425 Mya

Great Glen Fault
• NE-SW strike
• 150km long
• strike-slip fault
• sinistral
• >100km displacement
• 430-425 Mya
Highland Boundary Fault
• NE-SW strike
• Reverse fault
• Allowed Midland Valley to descend as major rift by 4,000m
• Sinistral displacement
• 430-424 Mya

Southern Uplands Fault
• NE-SW strike
• Reverse fault
• Allowed Midland Valley to descend as major rift by 4,000m
• Sinistral displacement
• 430-424 Mya

1. North-west Highlands
Torridonian rocks – 1 billion – 770 million years old
Fragmental, red-brown in colour.
Coarse-grained sand & pebbles, with some thin layers of finer grained red mudstone. Grains sub-rounded to rounded.
Sandstone layers are many metres thick and commonly show clear cross-bedding.
Horizontal to gently dipping strata.
Eriboll rocks – 500 million years old
Rocks white to pink on fresh surfaces, but typically weathers to a grey colour.
Made up of almost entirely of grains of quartz, which are cemented tightly together to form a very hard rock.
These rocks are broken into loose, angular blocks forming scree slopes.
The lower layers (oldest) show cross-bedding and fossilised symmetrical ripples. The upper (younger) layers contain vertical “pipes” a few centimetres in length and ½cm to 1 cm wide. Fossil trilobite Olenellus can also be found.
Lewisian rocks – 3 – 1.8 billion years old
Coarse-grained, crystalline rock, in which the crystals can easily be seen with the naked eye.
Stripy appearance – with alternating darker and paler stripes. Darker stripes made of minerals such as hornblende and biotite, white or pink stripes made up of quartz and feldspar.
Durness rocks – 450 million years old
Grey, crystalline rock which is creamy yellow in places.
Dissolves fairly readily in rainwater to produce caves.
Fizzes with HCl acid.
Rock contains stromatolites (sediment mounds bound together by algae) and ooliths (small-spherical growths of CaCO
3 upto 2mm).

Lewisian rocks – 3 – 1.8 billion years old

Torridonian rocks – 1 billion - 770 million years old

Eriboll rocks – 500 million years old
Lower layers

Eriboll rocks – 500 million years old
Upper layers

Durness rocks – 450 million years old

2. Northern Highlands
Moine rocks – 1 billion – 870 million years old
Crystalline rocks, medium to coarse-grained. Silvery grey in colour. Abundant flakes of muscovite and biotite mica, which are aligned into parallel layers (foliated).
Intensely deformed and folded dating to
450 million years.
Lower layer of Moine rocks
Hard, crystalline & fine-grained rock. Light grey in colour with a streaked out texture due to the elongation of the minerals.

Moine rocks – 1 billion to 870 million years old

Moine rocks – 1 billion to 870 million years old
Lower layer

3. Grampian Highlands
Dalradian rocks – 750 – 480 million years old
A mixture of rocks which have been intensely folded and metamorphosed.
Repeated fining-upward sequences, with coarse-grained sands at the base often with flute casts and tool marks, and fine-grained silts and clays at the top.
Hard and re-crystalline in places.
Cairngorm rocks – 400 million years old
Crystalline rocks, interlocking and coarse-grained.
Mineralogically composed of quartz and feldspar, which are randomly orientated. Relatively undeformed and approximately 400 mya.
Lochranza, Isle of Arran – Greenish tinge to rocks. Fine-grained and re-crystalline.
Chlorite mica minerals which are clearly aligned.
Ballachulish, Glencoe – dark grey and black in colour, very fine-grained. Re-crystalline muscovite mica minerals.
Fine layering visible throughout rock.
Tay Nappe
Complex overfolds and huge nappes.
Locally geology has become inverted.
Trend of fold axis is NE to SW, with fold amplitudes of up to 10km from trough to crest.

Cairngorm rocks – 400 million years old

Dalradian rocks – 400 million years old

5. Southern Uplands
Southern Uplands – 470 -420 million years old
Rocks have been weakly metamorphosed. Great majority of older rocks are coarse-grained greywackes with smaller amounts of finer siltstones, mudstones, shale, volcanic ash and lavas.
Metamorphism of fine-grained rocks (mudstone and shale) has produced slate.
Greywacke, a grey, black, dark-green or deep-purplish hard rock, is coarse-grained and poorly sorted. It contains angular fragments of quartz, feldspar, ferromagnesian minerals and igneous and metamorphic rock fragments held together in a dark mud or clay matrix.
Low grade metamorphism has re-crystallised the cement to produce a tough hard rock which often looks like an igneous rock.
Southern Upland greywackes are divided into 3 main zones, separated by faults that run NE-SW, parallel to the strike of the beds.
Overall the beds get younger to the SE.
The many NE-SW trending faults all have their downthrow side on the SE. Within each of the 30 or so fault blocks, the oldest beds are on the SE side, but the blocks get progressively older towards the NW.
These faults dip towards the NE and get progressively steeper towards the NE.
Fossils are restricted to the fine sediments, where dead animal remains would have been preserved by slow accumulation of mud in an oxygen-deficient environment. The most abundant fossils are the graptolites. No fossils occur in the greywackes.

6. Lake District
Skiddaw Group – 470 million years old
Weakly metamorphosed greywackes, sandstones, siltstones and mudstones. Fine-grained rocks clearly foliated.
Uniform grey colour.
Approx. 3km thick. Very few fossils. Intensely folded.
Igneous Intrusions – 400 million years old
Undeformed batholith emplaced at a depth of 5kn. Now exposed due to erosion and uplift. Coarse-grained and felsic in colour. Found at
Shap. Skiddaw, Ennerdale and Eskdale. Gravity anomaly data suggests that these intrusions all join up to form one large batholith.
Borrowdale Volcanic Group – 450 million years old
6km thick sequence of volcanic rocks – mostly andesite and tuffs, with ignimbrites and welded tuffs.
Windermere Supergroup – 440 - 420 million years old
Limestones and thick turbidite sequences of sandstones, siltstones and mudstones, weakly metamorphosed and folded.
e.g. Shap Fell and Jeffrey’s Mount, Tebay – evidence of tectonic folding, with fold axes trending NE-SW.

7. North Wales & Anglesey
Anglesey Rocks – 580 – 550 million years old
Schists with metamorphic minerals indicating high pressure and low temperature conditions. These schists were orinally fine-grained shales and medium-grained sandstones.
Cambrian Rocks – 500 million years old
Thick sequences of marine sandstones and shales, weakly metamorphosed. Many of the sandstones such as the Rhinog Grits are greywackes.
Above this the sediments grade into fine-grained shales now forming the Llanberis Slates.
Ordovician Rocks – 450 million years old
Volcanic rocks containing rhyolites and andesites, and tuffs. Outcrops trend in a NE to SW direction. In some areas many of the volcanic rocks are welded ash flows.
All sediments have been gently folded into large open antiforms and synforms. E.g Harlech Dome. The strike of the axial planes is NE-SW.