The Siberian Traps, also called Сибирские траппы in Russian, are a large area of volcanic rock in Siberia, Russia. This region is part of a large igneous province, which is a term for areas covered by vast amounts of volcanic rock. A flood basalt event, where huge amounts of basaltic lava spread across Siberia, formed the Siberian Traps. This eruption was one of the largest volcanic events in the last 500 million years. The eruptions lasted about two million years and happened during the time when the Permian and Triassic periods changed, around 251.9 million years ago. Scientists believe the Siberian Traps were the main cause of the Permian–Triassic extinction event, which was the most severe extinction in Earth’s history. Later eruptions from the Siberian Traps are linked to smaller extinction events, such as the Smithian-Spathian, Olenekian-Anisian, Middle-Late Anisian, and Anisian-Ladinian extinctions. Today, the area is covered by about 7 million square kilometers (3 million square miles) of basaltic rock, with a volume of approximately 4 million cubic kilometers (1 million cubic miles).
Etymology
The word "trap" has been used in geology since 1785–1795 to describe certain rock structures. It comes from the Swedish word "trappa," which means "stairs." The term refers to hills that form step-like shapes in the landscape of the region.
Formation
The basaltic rock of the Siberian Traps is believed to have come from a mantle plume, which rose until it reached the Earth's crust, causing volcanic eruptions through the Siberian Craton. It is thought that as Earth's lithospheric plates moved over the mantle plume (the Iceland plume), the plume created the Viluy Traps to the east, then the Siberian Traps during the Permian and Triassic periods. Later, it caused volcanic activity on the floor of the Arctic Ocean during the Jurassic and Cretaceous periods, and eventually led to volcanic activity in Iceland. Other tectonic causes have also been proposed. Another possible cause may be the impact that formed the Wilkes Land crater in Antarctica, which is estimated to have occurred around the same time and was nearly opposite the Siberian Traps.
The main rock type in this formation is basalt, but mafic and felsic rocks are also present. Because of this, the formation is officially called a Flood Basalt Province. The presence of mafic and felsic rocks shows that multiple eruptions happened alongside the one-million-year-long series of eruptions that created most of the basalt layers. The traps are divided into sections based on their chemical, layering, and rock type composition.
The Siberian Traps lie above the Tungus Syneclise, a large sedimentary basin containing thick layers of Early-Mid-Paleozoic carbonate and evaporite deposits, as well as Carboniferous-Permian coal-bearing clastic rocks. When heated, such as by igneous intrusions, these rocks can release large amounts of toxic and greenhouse gases.
Effects on prehistoric life
The Siberian Traps happened around the same time as the Permian–Triassic extinction event, which is the worst extinction event ever recorded in Earth's history. Evidence from rocks, fossils, and chemical studies shows that this mass extinction was caused by a series of environmental changes. Volcanic eruptions released large amounts of carbon dioxide, sulfur dioxide, halogens, and metals into the atmosphere. These emissions led to global warming, oceans without oxygen, ocean acidification, thinning of the ozone layer, acid rain, and toxic metals in the environment. These changes caused the extinction of many species on land and in the ocean, though the timing of these events differed slightly between land and sea. The connection between the massive volcanic activity and the extinction, along with the ability of this activity to produce large amounts of greenhouse gases, suggests that the Siberian Traps were the main cause of the extinction. However, scientists still disagree about why this extinction was so severe. Other possible causes or factors that may have contributed to the event have also been proposed.
Dating
The volcanism in the Siberian Traps caused large amounts of magma to be released from Earth's crust, leaving rock layers that formed during the same time as the mass extinction. These rocks can still be studied today. In some of these volcanic rocks, a mineral called zircon is found. To better determine the age of the zircon, scientists arranged different zircon samples into a timeline based on when each one formed. A method called CA-TIMS, which removes errors caused by changes in lead levels over time, was used to accurately measure the age of the zircons in the Siberian Traps. By removing the effect of lead, this method focused on uranium in the zircon to connect the volcanic activity in the Siberian Traps, which produced large amounts of magma, to the Permian–Triassic mass extinction.
To strengthen the link between the Permian–Triassic extinction and other events, scientists looked at other disasters that happened around the same time, such as changes in sea levels, meteor impacts, and volcanism. Focusing on volcanism, rock samples from the Siberian Traps and other southern regions were collected and compared. Basalt and gabbro samples from southern areas near and far from the Siberian Traps were dated using the argon-argon method. Scientists specifically studied feldspar and biotite in these samples to determine their ages and the time magma was present during the volcanic event. Most of the basalt and gabbro samples were dated to 250 million years ago, covered an area of 5,000,000 square kilometers (1,900,000 square miles) in the Siberian Traps, and formed quickly with rapid rock hardening and cooling. Studies showed that similar samples from other southern regions also matched the age of Siberian Traps samples. This confirms that volcanic rocks from the Siberian Traps and other southern regions are connected to the Permian–Triassic mass extinction event.
Mineral deposits
The giant Norilsk-Talnakh nickel-copper-palladium deposit formed inside the channels of magma in a well-preserved area of the Siberian Traps. Scientists have connected this deposit to the Permian-Triassic extinction event because large amounts of nickel and other elements were found in rock layers that formed after the extinction. Researchers compare the timeline of volcanic activity in the Siberian Traps with the timeline of the extinction to link them. Before this connection was discovered, scientists thought the mass extinction and volcanic eruptions happened at the same time because the rocks from both events had similar compositions.