Large igneous provinces are regions where multiple volcanic eruptions over a short period have resulted in a thick layer of basaltic rock. They are caused by mantle plumes and can release over a million cubic kilometers of material. Famous examples include the Deccan and Siberian Traps, which coincided with mass extinctions. Large igneous provinces only occur once every 50 million years.
A large igneous province is a region of the Earth’s surface in which a series of large eruptions over a geologically short period (~1 million years) has resulted in a thick layer of volcanic rock covering the surface. Many scientists believe the large igneous provinces are caused by mantle plumes, where plumes of magma from deep in the ground rise near the surface, like bubbles in a lava lamp. These are also sometimes called basaltic flood events or basaltic flood provinces, because most of the rock deposited is basalt.
As a mantle plume approaches the surface, the magma is under compression. Pressure builds and volcanic eruptions occur. More than a million cubic kilometers of volcanic material can be released from a large igneous province. A certain percentage of the material, usually between 5% and 20%, is released pyroclastically, ie ejected violently into the air. The rest oozes slowly from the large igneous province like lava. Often, large igneous provinces do not originate from a unified province, but rather from multiple sub-provinces in the same general area. A few large igneous provinces represent some of the geologically youngest areas of the continental surface, as most continents are composed of billion-year-old crust known as shields.
Famous large igneous provinces include the Deccan Traps, a 2 km thick layer of igneous rock (of volcanic origin) covering 15% of modern India, and the Siberian Traps, of similar depth and extent. These areas are called “Traps” from the Swedish word for “stairs” (trappa, or sometimes trapp), due to the large, stair-like basalt hills found throughout the formations. The Deccan Traps and Siberian Traps are associated with eruptions lasting less than a million years, occurring about 65 and 250 million years ago, respectively.
The large igneous provinces of the Deccan and Siberian Traps coincided with two of the worst mass extinctions in the planet’s history, and the eruptions are thought to be the main contributing causes. In the case of the mass extinction 250 million years ago, lava from the Traps is thought to have seeped into the margins of the ocean’s continental shelves, releasing huge amounts of methane clathrate; methane gas trapped in ice cages by microbes over tens of millions of years. Methane is a greenhouse gas tens of times more potent than carbon dioxide, and its mass release is thought to have increased global temperature, leading to a feedback process of further clathrate release and continued warming, eventually killing up to 99.5 % of life in the oceans.
Fortunately for us, the creation of large igneous provinces is rare. They only appear once every 50 million years.
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