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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