Caledonian Orogenesis
Geological Evidence
FAULTS
FOLDS
OPHIOLITES
METAMORPHISM
INTRUSIONS
VOLCANIC ACTIVITY
ACCRETIONARY PRISM
OVERALL EVALUATION
Description
Moine Thrust Belt – Northern Highlands [200km long, 0-12km wide, 150km NW movement]
Great Glen Fault (GGF) – sinistral strike-slip
Highland Boundary Fault (HBF) – reverse then normal fault after reactivation
Southern Uplands Fault (SUF) - reverse then normal fault after reactivation
Evaluation
 Evidence of foreland outer zone of collision zone but not exactly at NE-SW Caledonian
trend, more NNE-SSW
 NE–SW trend suggest plates converging from SE and NW
 Thrust and reverse faults formed by compression, which backs up continental collision.
 Normal faults formed later due to reactivation as a result of gravitational collapse of
mountain range.
 Principle of Uniformitarianism – similar faults found today in Himalayas and Alps.
Variscan Orogenesis
Name of Evidence
Faults
Folds
Ophiolites
Metamorphism
Intrusions
Volcanic Activity
Accretionary Prism
Overall Evaluation
Description
Evaluation
Alpine Orogenesis
Name of Evidence
Faults
Description
East-West trending faults – Mere Fault in Chalk Downs is a reverse fault.
Evaluation
Reverse faults suggest compression so are
consistent with continental collision and could
be the ripple effect of the Alpine Orogenesis.
Folds
East-West trending folds – Weald Anticline, Hampshire Basin, London Basin.
Gentle
Folds suggest compression so are consistent
with continental collision and could be the
ripple effect of the Alpine Orogenesis.
Ophiolites
None
Have to look at evidence from the Alps in
central Europe.
Metamorphism
None
Have to look at evidence from the Alps in
central Europe.
Intrusions
None
Have to look at evidence from the Alps in
central Europe.
Volcanic Activity
None
Have to look at evidence from the Alps in
central Europe.
Accretionary Prism
None
Have to look at evidence from the Alps in
central Europe.
Overall Evaluation
The fold mountains of the Alps were formed in the Tertiary. It has often been assumed that ripple effects of these Alpine movements
caused the Tertiary folding and faulting of southern England. However, it is not certain that crustal movements as far north as Britain could
have resulted from Alpine compression. The structures formed over southern England could reflect crustal readjustments following the start
of sea-floor spreading in the North Atlantic.
North Atlantic Igneous Tertiary Province (NATP)
Name of Evidence
Extrusive Igneous
Activity
Plutonic Igneous
Activity
Tensional
Structures
Description
Trotternish Peninsular, Isle of Skye
Low viscosity flood basalts – forming horizontal plateaux & distinctive flat topped hills.
Each lava flow 4-8m thick
Overall thickness of the Skye Main Lava Series – 2000m
Columnar jointing – Kilt Rock
Vesicular basalt
Weathering of lava flows in the hot, humid climate of early Tertiary caused red laterite
(soils) to form.
Cuillin Hills, Isle of Skye
Gabbro plutons – large, coarse-grained intrusions (10km wide)
Layering – cumulates of Peridotite
Evaluation
Basaltic flood basalts consistent with the
rifting of a continent due to a mantle plume
head.
Red Hills, Isle of Skye
Granite plutons – large, coarse-grained intrusions (10km
wide)
Younger than gabbro intrusions
Granite plutons due to fractional
crystallisation of slow cooling basaltic magmas.
Isle of Skye
Dyke swarms
NW-SE trend
Dyke swarms indicate tensional stress as gaps
have to be created for dykes to be intruded
into the country rock. However, trend of NWSE not consistent with a NE-SW plate
boundary through Iceland now. Possibly an
aulacogen (a failed arm of a triple junction of
a plate tectonics rift system).
Isle of Arran
300 dykes in 3km
Overall Evaluation
Gabbro plutons consistent with slow cooling of
basaltic magma deep underground. Layering
(cumulates) consistent with slow cooling and
fractional crystallisation.
Very good evidence for a constructive plate margin and tensional stress.
Similar rocks can be found being formed now in Iceland which sits over the mantle plume now (Principle of Uniformitarianism).
Same types and ages of rocks in Greenland, which was once joined to Scotland before rifting.
Hotspot trail either side of Iceland – (Greenland-Faroes Ridge) evidence for plate movement.