Origin and Features of the North Atlantic Igneous Province

Origin and Features of the North Atlantic Igneous Province

Derek Gosney

April 22, 2013

Emporia State University

ES 767

Introduction

The North Atlantic Igneous Province (NAIP) is a result of physical processes within the mantle ejecting magma up through the crust and spilling onto the lithosphere. It is one of the most immense Large Igneous Provinces (LIP) on the planet. The NAIP covers well over a million square kilometers from Baffin Island west of Greenland to northern United Kingdom. The NAIP is a huge area of flood basalts, plateaus, ridges, and rifted margins fueled by a complex system of dykes, sills, fissures, and intrusions. This volcanic plumbing system in the NAIP also includes a plume of magma thought to have a diameter of 1,200 km in the upper reaches of the mantle that increases to 2,500 km as it spreads into the lithosphere. The following information will explain the origin of the NAIP as well as highlight some notable geologic features across the province.

Example of processes at work within a LIP.

Example of processes at work within a LIP. Image courtesy of Large Igneous Provinces Commission.

Layers of the Earth

First, to explain the origin of the NAIP, it is necessary to describe the outer layers of the Earth that lie below. The asthenosphere is fluid and greatly contributes to the convective motion that forces magma from the mantle toward the surface. The mantle is approximately 2,900 km thick with a temperature in the thousands of degrees centigrade that warms with depth.

Layers of the Earth

Layers of the Earth. Image courtesy of USGS.

The hottest magma nearest the core is less dense than the cooling magma near the lithosphere so as the hotter magma flows upward, the cooler, denser magma sinks back towards the lower mantle. These convective belts can be seen in the image below.

Convection.

Mantle convection. Image courtesy of USGS.

The lithosphere contains the upper mantle and the crust (continental and oceanic). The upper mantle is rigid compared to the more fluid asthenosphere and is up to 200 km thick. The continental crust varies widely at 25-90 km in thickness, while the oceanic crust is quite thin in comparison at 6-11 km. The crust contains a wide variety of igneous, metamorphic, and sedimentary material. Upon the crust, six geologic provinces were conceived by scientists. Provided below are short definitions of each province and a US Geological Survey map showing the worldwide distribution of the province types.

Shield: Large flat areas of extremely old rock that have been exposed to erosion since the Precambrian era.

Platform: An area of ancient bedrock overlain by a layer of horizontal or slanted rocks. Portions of the platform and shield that have been largely undisturbed since Precambrian times are also called Craton.

Orogen: Crust that has buckled up and created mountains.

Basin: Large areas that are the result of tectonic deformation and takes on a concave structure.

Extended Crust: A thinned out extension of continental crust.

Large Igneous Provinces: Extensive area of flood basalt from volcanic eruption.

Geological Provinces

Map of geological provinces. Image courtesy of USGS.

Large Igneous Provinces

A product of volcanism, these are huge areas of flood basalt that occur over millions of years. Current LIPs are not thought to be as extensive or impactful as their ancient cousins, some of which are thought to have caused widespread extinction events. The LIP of primary focus here is located in the northern Atlantic Ocean. The Mid-Atlantic Ridge is depicted in the image below. It splits the ocean in two along a north-south seam nearly 10,000 km long. As the North American and Eurasian plates separate on either side of the ridge, dikes form at the seam and a fissure eruption spills vast amounts of lava onto the oceanic crust. This is one example of how Large Igneous Provinces are formed.

Mid-Atlantic Ridge

The Mid-Atlantic Ridge. Image courtesy of Oceanus.

Additionally, magma will sometimes bore through weak areas of the crust. This results in magma plumes as seen in the figure below. Magma plumes may create a plume head just below the upper crust or it can result in flood basalt magmatism that make their way to the surface and produce LIPs as seen in the illustration below.

Formation of plumes and LIPs

Formation of plumes and LIPs. Image obtained at Wikimedia Commons.

North Atlantic Igneous Province

LIPs are divided into silicic and mafic provinces, which essentially just means igneous rock mostly made of silica or mostly not made of silica. A hugely complex topic in itself, three generalization can be applied to describe Mafic and Silicic LIPs. 1) Generally, most LIPs are mafic; 2) Most continental LIPs contain more silicic material than oceanic LIPs do; and 3) some continental LIPs are mostly silicic. The NAIP is a Mafic LIP, though there is evidence of localized silicic dominance within the region. Though the NAIP is indeed the LIP seen on the USGS map above, note that its area is much wider on the map below.

Worldwide LIPs.

Worldwide LIPs. Image courtesy of USGS, obtained at Wikimedia Commons.

The NAIP is further divided into four major locations: the British Tertiary igneous province, Greenland Tertiary igneous province, the Jan Mayen hotspot, and the Iceland hotspot. The NAIP was largely formed by the processes described above over the course of about six million years. From c. 60.5 Ma to c. 54.5 Ma between the Cretaceous-Palaeogene and early Eocene epoch the NAIP’s area saw the most significant increase in size.

Location and age of the NAIP.

Location and age of the NAIP. Image adapted from original NOAA poster, obtained at Wikimedia Commons.

Geologic Landmarks within NAIP

Iceland, located in an active rift zone, lies along the Mid-Atlantic Ridge. Positioned above a mantle plume, which is key to the “hotspot” designation, the island is the jewel of the North Atlantic Igneous Province. Here is a clever graphic illustration of Iceland and the column it sits atop.

Iceland atop a hotspot.

Iceland atop a hotspot. Image courtesy of Icelandic Met Office.

Evidence of the Iceland hotspot abounds with numerous volcanoes. Eight volcanoes are depicted on the map below, but there are about 130-140 volcanoes in Iceland. The country has about 30-40 volcanoes that have been active at some point in the last few hundred years. Iceland experiences about 25 eruptions on average per 100 years. The most active is mount Hekla which has erupted 18 times in the last 900 years. Mount Lakagigar is thought to have produced the largest eruption currently known to man. In the 1700’s it produced 3 cubic miles of lava, killed hundreds of thousands of domestic animals, and the resulting famine reduced the population by 20%. Also seen on the map below is the tectonic crossroads over which Iceland is positioned. As the North American and Eurasian tectonic plates continue to separate, upwelling of the mantle could continue to add to the NAIP for millions of years to come.

Volcanic island

Iceland: A volcanic island at the junction of Eurasia and North America. Image courtesy USGS, obtained at Wikimedia Commons.

Another notorious feature of the Iceland hotspot, and acting as a sort of pressure valve for the mantle plume below, is the Eyjafjallajökull volcano which is located less than 100 km southeast of the capital, Reykjavik. In April, 2010 a large eruption occurred and spewed ash tens of thousands of feet into the atmosphere. Carried by the jet stream and the general west-to-east wind flow, the ash halted Northern Europe’s air traffic for a week. This was the largest airline shutdown since 9/11.

Eyjafjallajökull

Violent eruption of Iceland’s mount Eyjafjallajökull. Image courtesy of NASA.

Less than 40 km southwest of the capital on the Reykjanes Peninsula is the Blue Lagoon. Though not a naturally occurring body of water, the blue lagoon is one of the biggest tourist attractions in the country. Over 90% of the homes in Iceland are heated by geothermal power. The lagoon is the result of a nearby geothermal power plant that dumps its geothermally heated seawater onto a nearby lava plain. Over time, the minerals in the water plugged the holes in the basalt and a lake formed. The water is mostly opaque and the unusual light turquoise color comes from blue-green algae that thrive in hot water.

Blue Lagoon

Blue Lagoon. Image obtained at Wikimedia Commons.

Below is Baffin Island, the western extent of NAIP. Western Greenland and Baffin Island contain the LIP’s largest volume of picritic lava. Picritic lava contains a high volume of magnesium-rich olivine and is generally believed to be the result of continental breakup; in this case the separation of Baffin Island from Greenland.

Baffin Island

Baffin Island. Image obtained at Wikimedia Commons.

The next image is Surtsey Island located just off Iceland’s southern coast. In November, 1963 a fisherman discovered smoke rising from an expanse of open water. The next day a speck of land was observed and over the next four years the volcanic eruption created a one square mile island. Now home to some plant life and migratory animals, scientists believe the island will last another century before wind and waves erode it away.

Surtsey

Surtsey, a new island. Image courtesy of NASA.

Another awe-inspiring example of the NAIP’s geology lies along the Ireland’s Antrim Coast. The picture below shows an area of distinctive rock formations known as Giant’s Causeway. These hexagonal basalt shapes are called columnar joints. The cooling of the lava flow caused contraction and cracking leaving these geometric columns.

Columnar jointing

Columnar jointing. Image obtained at Wikimedia Commons.

Below is a picture and description of a complex area of lava flows in the NAIP on the Scottish island of Skye. Accompanying it is a description the different types of lava flows and formations. Notice the huge lava tube!

Isle of Skye

Isle of Skye lava flows. Image courtesy of Large Igneous Provinces Commission.

The NAIP’s Rockall perched above the north Atlantic is sometimes called the most isolated rock in the world. Part of the Rockall plateau, this continental splinter was isolated during an era of sea floor spreading.

Rockall

“The most isolated rock in the world”. Image obtained at Wikimedia Commons.

Conclusion

The North Atlantic Igneous Province is the result of millions of years of tectonic movement and mantle convection. Scientists believe the spreading tectonic plates along with mantle plumes will continue to produce flood basalts, plateaus, ridges, and rifted margins for millions of years to come. This Large Igneous Province is here to stay and may someday challenge the Siberian Traps for the title of largest province of flood basalts.

Resources:

Geological Survey of Denmark and Greenland, Copenhagen. 2004. The North Atlantic Igneous Province. Retrieved on 8 April 2013. http://www.geus.dk/departments/geol-mapping/projects/n-atlantic-ign-provin-uk.htm

A.D. Saunders, S.M. Jones, L.A. Morgan, et al. 2007. Regional uplift associated with continental large igneous provinces: The roles of mantle plumes and the lithosphere. Chemical Geology 241, p. 282–318. http://www.le.ac.uk/gl/ads/SiberianTraps/PDF%20Files/Saunders%20et%20al%20Chem%20Geol%202007.pdf

International Association of Volcanology and Chemistry of the Earth's Interior. Retrieved on 9 April 2013.http://www.largeigneousprovinces.org/

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Bentley, C. 2003. Touring tectonics in Iceland. Geotimes. Travels in Geology, Dec 2003. Retrieved 15 April 2013.http://www.geotimes.org/dec03/Travels1203.html

BBC News. 2010. How volcano chaos unfolded: in graphics. Retrieved 16 April 2013.http://news.bbc.co.uk/2/hi/europe/8634944.stm

NASA. Visible Earth. The Infant Island of Surtsey, Iceland. .Retrieved 16 April 2013.http://visibleearth.nasa.gov/view.php?id=4499

Roberts, D.G. 1975. Abstract: Marine Geology of the Rockall Plateau and Trough. Retrieved April 16 2013.http://rsta.royalsocietypublishing.org/content/278/1285/447

The Paleocene Eocene Thermal Maximum. P. 5. Retrieved April 10 2013.https://sites.google.com/site/thepaleoceneeocenethermalmaxim/5-molten-magma-the-north-atlantic-igneous-province

Official Government of Iceland Website. Nature and Environment: Volcanoes. Retrieved April 20 2013. http://www.iceland.is/the-big-picture/nature-environment/volcanoes/

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