Download 5. North Atlantic Tertiary Igneous Province (NATP)

5. North Atlantic Tertiary Igneous Province
(NATP)
Moine Thrust
Great Glen Fault
Highland Boundary Fault
Iapetus Suture
Southern Uplands Faults
Tertiary ~65 Ma
North Atlantic Tertiary
Igneous Province (NATP)
Tertiary 65 – 2 MYA
Isle of Skye
• Basaltic lava flows of Trotternish
Penisular (Skye Main Lava Series)
Isle of Mull
Ardnamurchan
• Granite intrusions of Red Hills
• Gabbro intrusions of Cuillin Hills
Isle of Arran
• Granite intrusions of Goat Fell
Isle of Staffa
• Fingal’s Cave basalt with columnar jointing
Antrim
• Giant’s Causeway basalt with columnar jointing
Tertiary Igneous Province Rocks
Basaltic lava flows (SMLS)
(overall 2 km thick of lava erupted, each
individual flow was 4 – 8 m thick &
interbedded with pyroclastics & sediment)
Plutonic granite intrusions
(Red Hills)
Plutonic gabbro intrusions
(Cuillin Hills)
Tertiary
Tertiary Igneous Province Rocks
1. Initiation of the Iceland mantle plume 65 mya
2. 63 mya uplift & updoming of continental crust raises
Britain high above sea-level & actively eroded
3. 60 mya eruption from fissures onto continental crust of extensive
sheets of basaltic lava (flood basalts)
4. 58 mya large volcanoes erupted more lavas onto the land. The
roots of these volcanoes can be seen in Skye, Mull & Ardnamurchan
as outcrops of granite & gabbro
5. Igneous material was also injected into the country rocks as dykes.
Often they were so numerous as to occur in what are called dyke
swarms
6. 55 mya continental rifting over hot spot & ocean-floor spreading
started & North Atlantic opened
7. 50 mya a constructive plate margin developed & can now be seen as
the Mid-Atlantic Ridge
Tertiary
North Atlantic Ocean
opening
Extension & fracture
of continental crust
Uplift of continent
Plume head
Plume tail
Causes flood basalts
due to large volume
of plume head.
Mantle Plume
Causes basaltic eruptions at
oceanic island hot spots such as
Iceland and Hawaii due to more
continuous but less voluminous
plume tail.
Tertiary
Tertiary
• Explain the tectonic setting Britain was in during the Tertiary.
• Describe the rocks and geology of Britain formed during the Tertiary.
• Write an essay on Britain in the Tertiary linking these two areas.
“Describe the geological characteristics of the Tertiary Igneous Province of
north west Britain in relation to its plate tectonic setting”. (25 marks)
Tertiary Essay
“Discuss the geological evidence for the type of plate boundary active in the
British area, during the formation of the Tertiary Igneous Province.” (25
marks)
Extrusive Igneous Activity:
• Extensive upwelling of basalts (flood basalts) – Antrim 1500 square miles of lava still preserved
• Low viscosity so lava flowed substantial distances
• Horizontal & flat topped hills/plateaux – northern Skye, Scotland or County Antrim, N Ireland
• Lava flows 10-15metres thick
• Isle of Mull – 2000m overall thickness & Skye – 600m overall thickness
• Sub-aerial weathering of lava flows formed red laterite surface (soil)
• Vesicles (gas bubbles) filled in with calcite later (amygdales)
• Cooling formed contraction and columnar jointing into perfect mathematical patterns – Fingal’s Cave,
Isle of Staffa & Giant’s Causeway, Antrim
• Geology similar to that found in Iceland today.
Tertiary Essay
“Discuss the geological evidence for the type of plate boundary active in the
British area, during the formation of the Tertiary Igneous Province.” (25
marks)
Intrusive Igneous Activity:
• Complex igneous intrusive centres – Skye, Mull, Arran, Rhum & Ardnamurchan
• Plutons of basaltic magma cooled slowly to form gabbro – layered with olivine at
base due to gravity settling during cooling – Cuillin Hills, Skye
• Plutons of basaltic magma
basaltic lava
were magma chambers for more outpourings of
• Rising plutons of basic magma caused localised uplift, tension and crustal extension
• Concentric intrusions of ring dykes & cone sheets through the magma chamber & country rock
(Lewisian Gneiss & Torridonian Sandstone)
• Fractional crystallisation & magmatic underplating caused granitic plutons to form – Red
Hills, Skye & Goat Fell, Arran
Tertiary Essay
“Discuss the geological evidence for the type of plate boundary active in the
British area, during the formation of the Tertiary Igneous Province.” (25
marks)
Tension:
• Dyke swarms due to extension of crust
• Arran 300 dykes in 3km section of coastline – 10% extension of crust
• Trend NW - SE
• Cleveland Dyke – 400km long
• Radiate out from intrusive igneous centres – Arran, Skye, Mull & Ardnamurchan