Monday Musings: Large Igneous Provinces
As the name suggests, large igneous provinces are very large accumulations of igneous rocks. Sometimes referred to as LIPs to shorten it (have I mentioned that geologists really like to abbreviate things?) they are often attributed to mantle plumes or divergent plate tectonics. The current minimum threshold to be a LIP is a coverage of 100,000 square km.
Large igneous provinces are created during short-lived igneous events. They often coincide with mass extinction events, global environmental and climatic changes and changes in the hydrosphere and atmosphere. They have played a major role in cycles of continental breakup and formations, new crustal additions from the upper mantle and supercontinent cycles.
So, how are LIPs formed? It’s important to understand how the mantle works and how it interacts with the crust along with lithospheric plate interactions. The mantle is very viscous, more solid than liquid. Its flow is driven by cold crust sinking into it through subduction of lithospheric plates while hot mantle plumes flow upward. We call this mantle convection. Most volcanism occurs due to plate tectonics.
Now, sometimes the plumes rise and spread out radially beneath the plate causing regions of uplift. We call these hotspots. The most famous ones are Hawaii and Yellowstone but there are numerous hotspots across the globe.
The origin of these are hotly contested (pun intended). There are three origins that have been proposed. One is deep, originating near the mantle-outer core boundary.
Another one says some originate from hot lava domes within the mantle. Lastly, some appear to originate in the upper mantle possibly due to the break up of lithospheric plates that have been subducted.
A competing hypothesis to mantle plumes is plate ruptures. Basically, stresses in the lithosphere cause fractures in the plates allowing melt to reach the surface through mantle convection.
Another hypothesis on the formation of hotspots and LIPs involves meteorite impacts. Seven pairs of hotspots and LIPs located on opposite sides of the globe from each other of the same age have been located. When a meteorite impacted oceanic crust, it allowed melt to reach the surface. At the same time, the energy released from the impact converted into seismic waves and propagated across the globe, converging on the exact opposite side of the planet fracturing the crust enough to let massive amounts of magma to erupt.
Likely, there is a LIP in your neck of the woods. In the U.S., we have the Columbia River Flood Basalts in Washington, Oregon and Idaho. It’s actually the youngest and smallest LIP covering about 81 square miles (210,000 km₂). It erupted during the Late Miocene Epoch for about 10-15 Ma.
In Europe, there is the North Atlantic Igneous Province centered on Iceland (for obvious reasons). It erupted from the mid Paleocene to the early Eocene epochs between 60.5 and 54.5 Ma. It covers around 500,000 sq miles (1.3 million sq km). It is one of the few that consists of both onshore and offshore flood basalts, sills, dikes, and plateaus.
In Asia, there are the Emeishan Traps a flood basalt in southwestern China. It erupted between 262 and 259 Ma during the Middle Permian Period. It covers 155,343 sq miles (250,000 sq km2). It is associate with a minor mass extinction event.
The Gondwana LIP is associated with the breakup of the supercontinent of Gondwana about 183 Ma which now consists of South America, Africa, Antarctica and Australia. The flood basalts are mostly in South Africa and Antarctica. It erupted during the Early Jurassic Period and is associated with the major Triassic-Jurassic extinction event. It spans about 3x10 ^6 km2 before the supercontinent broke apart.
During the early Cretaceous about 136-132 Ma and=other flood basalt occurred in South America (and a bit in Africa) called the Paraná-Etendeka Plateau. It covered 390.000 sq miles (1,000,000 sq km2). There was also a silicic component to this province, ignimbrites (hardened tuff) from explosive eruptions. The pyroclastic sheet has a thickness between 130-980 ft (40-300 m). This makes it the largest known explosive eruption on Earth.
In India are the famous Deccan Traps which erupted during the Late Cretaceous and early Paleogene Period meaning it spanned the K-Pg Extinction Event that killed the non-avian dinosaurs. They cover an area of 200,000 square miles (500,000 sq km) and may have contributed to the extinction event.
The Siberian Traps cover a vast majority of Russia (which is impressive considering the size of Russia. It is one of the biggest volcanic events, spanning 500 million years and covering 3 million sq miles (7 million sq km2). It spanned the Periman-Triassic boundary and may have contributed to the Great Dying, the largest mass extinction ever.
Thanks for joining me today to learn about igneous rocks and tune in tomorrow for some trivia fun. Fossilize you later!
