5. North Atlantic Tertiary Igneous Province (NATP)

Iapetus Suture

Southern Uplands Faults

Highland Boundary Fault

Great Glen Fault

Moine Thrust

Tertiary ~65 Ma

North Atlantic Tertiary Igneous Province (NATP)

Tertiary 65 – 2 MYA

Isle of Skye

Ardnamurchan

Isle of Mull

Isle of Arran

Antrim

• Giant’s Causeway basalt with columnar jointing

• Basaltic lava flows of Trotternish Penisular (Skye Main Lava Series)

• Granite intrusions of Red Hills

• Gabbro intrusions of Cuillin Hills

• Granite intrusions of Goat Fell

Isle of Staffa

• Fingal’s Cave basalt with columnar jointing

Tertiary Igneous Province Rocks

Basaltic lava flows (SMLS)

Plutonic granite intrusions(Red Hills)

Plutonic gabbro intrusions(Cuillin Hills)

(overall 2 km thick of lava erupted, each individual flow was 4 – 8 m thick & interbedded with pyroclastics & sediment)

                                                                                                            

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 swarms6. 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

Mantle Plume

North Atlantic Ocean opening

Uplift of continentExtension & fracture of continental crust

Plume head

Plume tailCauses flood basalts due to large volume of plume head.

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.

“Describe the geological characteristics of the Tertiary Igneous Province of north west Britain in relation to its plate tectonic setting”. (25 marks)

• Write an essay on Britain in the Tertiary linking these two areas.

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

• 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)

• Plutons of basaltic magma cooled slowly to form gabbro – layered with olivine at base due to gravity settling during cooling – Cuillin Hills, Skye

• Fractional crystallisation & magmatic underplating caused granitic plutons to form – Red Hills, Skye & Goat Fell, Arran

• Plutons of basaltic magma were magma chambers for more outpourings of basaltic lava

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