4. variscan orogenesis. 1. caledonian orogeny 2. variscan orogeny 4. alpine orogeny 3. north...

4. Variscan Orogenesis

1. Caledonian Orogeny

2. Variscan Orogeny

4. Alpine Orogeny

3. North Atlantic Tertiary Igneous Province (NATP)

Mid-Devonian ~400 Ma

Old Red Sandstone Continent

Pre-Cambrian ~ 850 MaCarboniferous ~300 Ma

Pangaea

Supercontinent

Upper Carboniferous 300 MYA – Variscan Orogenesis

1. Intense Folding

2. Batholiths

e.g. Dartmoor

3. Regional Metamorphism

e.g. Delabole Slate, North Cornwall

4. Faulting

e.g. Lizard Thrust Fault

5. Ophiolites

e.g. Lizard Ophiolite Complex

e.g. Hartland Quay

CornwallDevonSomersetSouth Wales

•Very complex folding & extensive thrusting.

•65% shortening of crust

•Very strong cleavage

•Complex folding & thrusting.

•50% shortening of crust

•Good cleavage

•Open, asymmetric folds with steep southern limb

•10% shortening of crust

•No cleavage

•Gentle folds

•2% shortening of crust

•No cleavage

Less intense, more irregular folds, Bude, Devon

Recumbent folds, Millook Haven, north Cornwall

Gentle open folds, Broad Haven, South Wales

Granite Batholith

Carboniferous rocks

Lizard Thrust

Lizard Ophiolite Complex

Recumbent folds, Millook Haven, north Cornwall

Less intense, more irregular folds, Bude, Devon

Gentle open folds, Broad Haven, South Wales

Plates Involved

Location in Britain

Age Geological Structures & Trends

Igneous Rocks Metamorphic Rocks

Caledonian

Variscan

Alpine

Avalonia

Laurentia

ORS continent

Gondwana

Europe Africa

Scottish Highlands

Lake District

North Wales

Anglesey

South Wales

Cornwall

Devon

Somerset

SE England

Lower Palaeozoic

400 mya

Upper Palaeozoic

300 mya

Cenozoic

40 mya

Faults:

Moine Thrust Belt e.g. Glencoul Thrust

Great Glen

Folds:

Tay Nappe

Shap Fell

Harlech Dome

NE-SW trend

Faults:

Lizard Thrust

Folds:

Millook Haven

Hartland Quay

Broad Haven

E-W trend

Folds:

North & South Downs

E-W trend

Granite batholiths:

Cairngorms

Skiddaw

Shap

Eskdale

Ennerdale

Ophiolites – Ballantrae

Granite batholiths:

Dartmoor

Bodmin Moor

Land’s End

Scilly Isles

Regional:

Dalradian schists

Ballachulish slates

Easdale slates

Llanberis slates

Skiddaw slates

Dynamic:

Mylonite

Regional:

Delabole slates