
The Deccan Traps are a
large igneous province
A large igneous province (LIP) is an extremely large accumulation of igneous rocks, including intrusive ( sills, dikes) and extrusive (lava flows, tephra deposits), arising when magma travels through the crust towards the surface. The format ...
of west-central India (17–24°N, 73–74°E). They are one of the largest
volcanic
A volcano is commonly defined as a vent or fissure in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface.
On Earth, volcanoes are most often fo ...
features on Earth, taking the form of a large
shield volcano
A shield volcano is a type of volcano named for its low profile, resembling a shield lying on the ground. It is formed by the eruption of highly fluid (low viscosity) lava, which travels farther and forms thinner flows than the more viscous lava ...
.
They consist of many layers of solidified
flood basalt
A flood basalt (or plateau basalt) is the result of a giant volcanic eruption or series of eruptions that covers large stretches of land or the ocean floor with basalt lava. Many flood basalts have been attributed to the onset of a hotspot (geolo ...
that together are more than about thick, cover an area of about ,
and have a volume of about .
Originally, the Deccan Traps may have covered about ,
["What really killed the dinosaurs?"](_blank)
Jennifer Chu, MIT News Office, 11 December 2014 with a correspondingly larger original volume. This volume overlies the
Archean
The Archean ( , also spelled Archaean or Archæan), in older sources sometimes called the Archaeozoic, is the second of the four geologic eons of Earth's history of Earth, history, preceded by the Hadean Eon and followed by the Proterozoic and t ...
age
Indian Shield, which is likely the
lithology
The lithology of a rock unit is a description of its physical characteristics visible at outcrop, in hand or core samples, or with low magnification microscopy. Physical characteristics include colour, texture, grain size, and composition. Lit ...
the province passed through during eruption. The province is commonly divided into four subprovinces: the main Deccan, the
Malwa Plateau, the Mandla Lobe, and the Saurashtran Plateau.
The eruptions occurred over a 600–800,000 year time period between around 66.3 to 65.6 million years ago, spanning the
Cretaceous–Paleogene boundary
The Cretaceous–Paleogene (K–Pg) boundary, formerly known as the Cretaceous–Tertiary (K–T) boundary, is a geological signature, usually a thin band of rock containing much more iridium than other bands. The K–Pg boundary marks the end o ...
. While some authors have suggested that the eruptions were the primary cause of the
Cretaceous–Paleogene mass extinction event, which dates to around 66.05 million years ago, this has been strongly disputed, with many authors suggesting that the
Chicxulub impact
The Chicxulub crater is an impact crater buried underneath the Yucatán Peninsula in Mexico. Its center is offshore, but the crater is named after the onshore community of Chicxulub Pueblo (not the larger coastal town of Chicxulub Puerto). I ...
was the primary cause of the extinction.
While some scholars suggest that the eruptions may have been a contributing factor in the extinctions, others suggest that the role of the Deccan Traps in the extinction were negligible or even partially negated the effects of the impact.
The Deccan Traps are thought to have been produced in major part by the still active
Réunion hotspot
The Réunion hotspot is a volcanic hotspot which currently lies under the island of Réunion in the Indian Ocean. The Chagos-Laccadive Ridge and the southern part of the Mascarene Plateau are volcanic traces of the Réunion hotspot.
The hotspo ...
, responsible for the creation of the modern
Mascarene Islands
The Mascarene Islands (, ) or Mascarenes or Mascarenhas Archipelago is a group of islands in the Indian Ocean east of Madagascar consisting of islands belonging to the Republic of Mauritius as well as the French department of Réunion. Their na ...
in the Indian Ocean.
Etymology
The term ''
trap'' has been used in
geology
Geology (). is a branch of natural science concerned with the Earth and other astronomical objects, the rocks of which they are composed, and the processes by which they change over time. Modern geology significantly overlaps all other Earth ...
since 1785–1795 for such
rock formation
A rock formation is an isolated, scenic, or spectacular surface rock (geology), rock outcrop. Rock formations are usually the result of weathering and erosion sculpting the existing rock. The term ''rock Geological formation, formation ...
s. It is derived from the Swedish word for stairs () and refers to the step-like hills forming the landscape of the region.
[Trap](_blank)
at dictionary.reference.com The name ''Deccan'' has Sanskrit origins meaning "southern".
History

The Deccan Traps began forming 66.25
million years ago
Million years ago, abbreviated as Mya, Myr (megayear) or Ma (megaannum), is a unit of time equal to (i.e. years), or approximately 31.6 teraseconds.
Usage
Myr is in common use in fields such as Earth science and cosmology. Myr is also used w ...
,
at the end of the
Cretaceous
The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...
period, although it is possible that some of the oldest material may underlie younger material.
The bulk of the volcanic eruption occurred at the
Western Ghats between 66 and 65 million years ago when lava began to extrude in
fissure eruptions. Determining the exact age for Deccan rock is difficult due to a number of limitations, one being that the transition between eruption events may have lasted only a few thousand years and the resolution of dating methods is not sufficient to pinpoint these events. In this way, determining the rate of magma emplacement is also difficult to constrain.
This series of eruptions may have lasted for less than 30,000 years.
The original area covered by the
lava flow
Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a Natural satellite, moon onto its surface. Lava may be erupted at a volcano or through a Fissure vent, fractu ...
s is estimated to have been as large as , approximately half the size of modern
India
India, officially the Republic of India, is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area; the List of countries by population (United Nations), most populous country since ...
. The Deccan Traps region was reduced to its current size by
erosion
Erosion is the action of surface processes (such as Surface runoff, water flow or wind) that removes soil, Rock (geology), rock, or dissolved material from one location on the Earth's crust#Crust, Earth's crust and then sediment transport, tran ...
and plate tectonics; the present area of directly observable lava flows is around .
The Deccan Traps are segmented into three stratigraphic units: the Upper, Middle, and Lower traps. While it was previously interpreted that these groups represented their own key points in the sequence of events in Deccan extrusion, it is now more widely accepted that these horizons relate more closely to paleotopography and distance from the eruption site.
Effect on mass extinctions and climate
The release of
volcanic gas
Volcanic gases are gases given off by active (or, at times, by dormant) volcanoes. These include gases trapped in cavities (Vesicular texture, vesicles) in volcanic rocks, dissolved or dissociated gases in magma and lava, or gases emanating from ...
es, particularly
sulfur dioxide
Sulfur dioxide (IUPAC-recommended spelling) or sulphur dioxide (traditional Commonwealth English) is the chemical compound with the formula . It is a colorless gas with a pungent smell that is responsible for the odor of burnt matches. It is r ...
, during the formation of the traps may have contributed to
climate change
Present-day climate change includes both global warming—the ongoing increase in Global surface temperature, global average temperature—and its wider effects on Earth's climate system. Climate variability and change, Climate change in ...
. An average drop in temperature of about was recorded during this period.
Because of its magnitude, some scientists (notably
Gerta Keller) have speculated that the gases released during the formation of the Deccan Traps played a major role in the
Cretaceous–Paleogene (K–Pg) extinction event (also known as the Cretaceous–Tertiary or K–T extinction). It has been theorized that sudden cooling due to sulfurous volcanic gases released by the formation of the traps and toxic gas emissions may have contributed significantly to the K–Pg mass extinction. However, the current consensus among the scientific community is that the extinction was primarily triggered by the
Chicxulub impact event in North America, which would have produced a sunlight-blocking dust cloud that killed much of the plant life and reduced global temperature (this cooling is called an
impact winter).
A 2014 study suggested the extinction may have been caused by both the volcanism and the impact event. This was followed by a similar study in 2015, both of which consider the hypothesis that the impact exacerbated or induced the Deccan volcanism, since the events occurred approximately at
antipodes
In geography, the antipode () of any spot on Earth is the point on Earth's surface diametrically opposite to it. A pair of points ''antipodal'' () to each other are situated such that a straight line connecting the two would pass through Ea ...
. A 2020 study questioned the idea that the Deccan Traps were a contributory factor at all, suggesting that the Deccan Traps eruptions may have even partially negated the climatic change induced by the impact.
A major criticism of the Deccan Traps as the primary cause of the extinctions is that the extinction event appears to be globally geologically instantaneous and simultaneous in both marine and terrestrial environments, as would be expected from an impact cause, rather than staggered as would be expected from an LIP cause.
A more recent discovery appears to demonstrate the scope of the destruction from the impact alone, however. In a March 2019 article in the
Proceedings of the National Academy of Sciences
''Proceedings of the National Academy of Sciences of the United States of America'' (often abbreviated ''PNAS'' or ''PNAS USA'') is a peer-reviewed multidisciplinary scientific journal. It is the official journal of the National Academy of Scie ...
, an international team of twelve scientists revealed the contents of the
Tanis fossil site discovered near
Bowman, North Dakota, that appeared to show a devastating mass destruction of an ancient lake and its inhabitants at the time of the Chicxulub impact. In the paper, the group reports that the geology of the site is strewn with
fossil
A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserve ...
ized trees and remains of fish and other animals. The lead researcher, Robert A. DePalma of the
University of Kansas
The University of Kansas (KU) is a public research university with its main campus in Lawrence, Kansas, United States. Two branch campuses are in the Kansas City metropolitan area on the Kansas side: the university's medical school and hospital ...
, was quoted in the New York Times as stating that "You would be blind to miss the carcasses sticking out... It is impossible to miss when you see the outcrop". Evidence correlating this find to the Chicxulub impact included
tektite
Tektites () are gravel-sized bodies composed of black, green, brown or grey natural glass formed from terrestrial debris ejected during meteorite impacts. The term was coined by Austrian geologist Franz Eduard Suess (1867–1941), son of Eduar ...
s bearing "the unique chemical signature of other tektites associated with the Chicxulub event" found in the gills of fish fossils and embedded in
amber
Amber is fossilized tree resin. Examples of it have been appreciated for its color and natural beauty since the Neolithic times, and worked as a gemstone since antiquity."Amber" (2004). In Maxine N. Lurie and Marc Mappen (eds.) ''Encyclopedia ...
, an
iridium
Iridium is a chemical element; it has the symbol Ir and atomic number 77. This very hard, brittle, silvery-white transition metal of the platinum group, is considered the second-densest naturally occurring metal (after osmium) with a density ...
-rich top layer that is considered another signature of the event, and an atypical lack of evidence for scavenging, perhaps suggesting that there were few survivors. The exact mechanism of the site's destruction has been debated as either an impact-caused
tsunami
A tsunami ( ; from , ) is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquakes, volcanic eruptions and underwater explosions (including detonations, ...
or lake and river
seiche
A seiche ( ) is a standing wave in an enclosed or partially enclosed body of water. Seiches and seiche-related phenomena have been observed on lakes, reservoirs, swimming pools, bays, harbors, caves, and seas. The key requirement for formatio ...
activity triggered by post-impact earthquakes, though there has yet been no firm conclusion upon which researchers have settled.
A 2024 study of
glycerol dialkyl glycerol tetraether levels in fossilized peat found that the Deccan Traps caused long-term warming of around 3°C over the course of the final 100,000 years of the
Maastrichtian
The Maastrichtian ( ) is, in the International Commission on Stratigraphy (ICS) geologic timescale, the latest age (geology), age (uppermost stage (stratigraphy), stage) of the Late Cretaceous epoch (geology), Epoch or Upper Cretaceous series (s ...
, as well as about 5°C drop in temperature for less than 10,000 years around 30,000 years prior to the K-Pg boundary (coinciding with the peak of the Poladpur eruptive phase), but by the time of the K-Pg boundary, global temperatures had returned to previous levels. This suggests that the Deccan Traps were not the primary cause of extinction.
Petrology

Within the Deccan Traps, at least 95% of the lavas are
tholeiitic basalts. Major mineral constituents are
olivine
The mineral olivine () is a magnesium iron Silicate minerals, silicate with the chemical formula . It is a type of Nesosilicates, nesosilicate or orthosilicate. The primary component of the Earth's upper mantle (Earth), upper mantle, it is a com ...
,
pyroxene
The pyroxenes (commonly abbreviated Px) are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. Pyroxenes have the general formula , where X represents ions of calcium (Ca), sodium (Na), iron ( ...
s, and
plagioclase
Plagioclase ( ) is a series of Silicate minerals#Tectosilicates, tectosilicate (framework silicate) minerals within the feldspar group. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a continu ...
, as well as certain
Fe-
Ti-rich oxides. These magmas are <7%
MgO. However, many of these minerals are observed as highly altered forms.
Other rock types present include
alkali basalt,
nephelinite,
lamprophyre
Lamprophyres () are uncommon, small-volume ultrapotassic igneous rocks primarily occurring as dikes, lopoliths, laccoliths, stocks, and small intrusions. They are alkaline silica- undersaturated mafic or ultramafic rocks with high magnesium o ...
, and
carbonatite
Carbonatite () is a type of intrusive rock, intrusive or extrusive rock, extrusive igneous rock defined by mineralogic composition consisting of greater than 50% carbonate minerals. Carbonatites may be confused with marble and may require geoche ...
.
Mantle
xenolith
A xenolith ("foreign rock") is a rock (geology), rock fragment (Country rock (geology), country rock) that becomes enveloped in a larger rock during the latter's development and solidification. In geology, the term ''xenolith'' is almost exclusi ...
s have been described from
Kachchh (northwestern India) and elsewhere in the western Deccan and contain spinel
lherzolite
Lherzolite is a type of ultramafic igneous rock. It is a coarse-grained rock consisting of 40 to 90% olivine along with significant orthopyroxene and lesser amounts of calcic chromium-rich clinopyroxene. Minor minerals include chromium and alumi ...
and
pyroxenite constituents.
While the Deccan traps have been categorized in many different ways including the three different
stratigraphic
Stratigraphy is a branch of geology concerned with the study of rock layers (strata) and layering (stratification). It is primarily used in the study of sedimentary and layered volcanic rocks.
Stratigraphy has three related subfields: lithost ...
groups, geochemically the province can be split into as many as eleven different formations. Many of the petrologic differences in these units are a product of varying degrees of crustal contamination.
Fossils
The Deccan Traps are famous for the beds of fossils that have been found between layers of lava. Particularly well-known species include the frog ''
Oxyglossus pusillus'' (Owen) of the
Eocene
The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...
of
India
India, officially the Republic of India, is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area; the List of countries by population (United Nations), most populous country since ...
and the toothed frog ''
Indobatrachus'', an early lineage of modern frogs, which is now placed in the Australian family
Myobatrachidae
Myobatrachidae, commonly known as Australian ground frogs or Australian water frogs, is a family of frogs found in Australia and New Guinea. Members of this family vary greatly in size, from species less than long, to the second-largest frog in ...
. The
Infratrappean Beds (Lameta Formation) and
Intertrappean Beds also contain fossil freshwater
molluscs
Mollusca is a phylum of protostome, protostomic invertebrate animals, whose members are known as molluscs or mollusks (). Around 76,000 extant taxon, extant species of molluscs are recognized, making it the second-largest animal phylum ...
.
Theories of formation
It is postulated that the Deccan Traps eruption was associated with a deep
mantle plume
A mantle plume is a proposed mechanism of convection within the Earth's mantle, hypothesized to explain anomalous volcanism. Because the plume head partially melts on reaching shallow depths, a plume is often invoked as the cause of volcanic ho ...
. High
3He/
4He ratios of the main pulse of the eruption are often seen in magmas with
mantle plume
A mantle plume is a proposed mechanism of convection within the Earth's mantle, hypothesized to explain anomalous volcanism. Because the plume head partially melts on reaching shallow depths, a plume is often invoked as the cause of volcanic ho ...
origin. The area of long-term eruption (the
hotspot), known as the
Réunion hotspot
The Réunion hotspot is a volcanic hotspot which currently lies under the island of Réunion in the Indian Ocean. The Chagos-Laccadive Ridge and the southern part of the Mascarene Plateau are volcanic traces of the Réunion hotspot.
The hotspo ...
, is suspected of both causing the Deccan Traps eruption and opening the
rift
In geology, a rift is a linear zone where the lithosphere is being pulled apart and is an example of extensional tectonics. Typical rift features are a central linear downfaulted depression, called a graben, or more commonly a half-graben ...
that separated the
Mascarene Plateau
The Mascarene Plateau is a submarine plateau in the Indian Ocean, north and east of Madagascar. The plateau extends approximately , from Seychelles in the north to Réunion in the south. The plateau covers an area of over of shallow water, wi ...
from India. Regional
crustal thinning supports the theory of this rifting event and likely encouraged the rise of the plume in this area.
Seafloor spreading
Seafloor spreading, or seafloor spread, is a process that occurs at mid-ocean ridges, where new oceanic crust is formed through volcanic activity and then gradually moves away from the ridge.
History of study
Earlier theories by Alfred Wegener ...
at the boundary between the Indian and
African Plates subsequently pushed India north over the plume, which now lies under
Réunion
Réunion (; ; ; known as before 1848) is an island in the Indian Ocean that is an overseas departments and regions of France, overseas department and region of France. Part of the Mascarene Islands, it is located approximately east of the isl ...
island in the
Indian Ocean
The Indian Ocean is the third-largest of the world's five oceanic divisions, covering or approximately 20% of the water area of Earth#Surface, Earth's surface. It is bounded by Asia to the north, Africa to the west and Australia (continent), ...
, southwest of India. The mantle plume model has, however, been challenged.
[Sheth, Hetu C.]
The Deccan Beyond the Plume Hypothesis
" ''MantlePlumes.org,'' 2006.
Data continues to emerge that supports the plume model. The motion of the Indian tectonic plate and the eruptive history of the Deccan traps show strong correlations. Based on data from marine magnetic profiles, a pulse of unusually rapid plate motion began at the same time as the first pulse of Deccan flood basalts, which is dated at 67 million years ago. The spreading rate rapidly increased and reached a maximum at the same time as the peak basaltic eruptions. The spreading rate then dropped off, with the decrease occurring around 63 million years ago, by which time the main phase of Deccan volcanism ended. This correlation is seen as driven by plume dynamics.
The motions of the Indian and
African plates have also been shown to be coupled, the common element being the position of these plates relative to the location of the Réunion plume head. The onset of accelerated motion of India coincides with a large slowing of the rate of counterclockwise rotation of Africa. The close correlations between the plate motions suggest that they were both driven by the force of the Réunion plume.
When comparing the Na
8, Fe
8, and Si
8 contents of the Deccan to other major igneous provinces, the Deccan appears to have undergone the greatest degree of melting suggesting a deep plume origin.
Olivine
The mineral olivine () is a magnesium iron Silicate minerals, silicate with the chemical formula . It is a type of Nesosilicates, nesosilicate or orthosilicate. The primary component of the Earth's upper mantle (Earth), upper mantle, it is a com ...
appears to have fractionated at near-
Moho depths with additional fractionation of
gabbro
Gabbro ( ) is a phaneritic (coarse-grained and magnesium- and iron-rich), mafic intrusive igneous rock formed from the slow cooling magma into a holocrystalline mass deep beneath the Earth's surface. Slow-cooling, coarse-grained gabbro is ch ...
~6 km below the surface.
Features such as widespread
faulting
In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic ...
, frequent
diking events, high heat flux, and positive
gravity anomalies suggest that the extrusive phase of the Deccan Traps is associated with the existence of a triple junction which may have existed during the Late Cretaceous, having been caused by a deep mantle plume. Not all of these diking events are attributed to large-scale contributions to the overall flow volume. It can be difficult, however, to locate the largest dikes as they are often located towards the west coast and are therefore believed to currently reside under water.
Suggested link to impact events
Chicxulub crater
Although the Deccan Traps began erupting well before
the impact, in a 2015 study it was proposed based on
argon–argon dating
Argon–argon (or 40Ar/39Ar) dating is a radiometric dating method invented to supersede Potassium-argon dating, potassiumargon (K/Ar) dating in accuracy. The older method required splitting samples into two for separate potassium and argon measur ...
that the impact may have caused an increase in permeability that allowed magma to reach the surface and produced the most voluminous flows, accounting for around 70% of the volume.
The combination of the asteroid impact and the resulting increase in eruptive volume may have been responsible for the mass extinctions that occurred at the time that separates the Cretaceous and
Paleogene
The Paleogene Period ( ; also spelled Palaeogene or Palæogene) is a geologic period and system that spans 43 million years from the end of the Cretaceous Period Ma (million years ago) to the beginning of the Neogene Period Ma. It is the fir ...
periods, known as the
K–Pg boundary. However this proposal has been questioned by other authors, who describe the suggestion as being "convenient interpretations based on superficial and cursory observations."
Shiva crater
A geological structure that exists in the sea floor off the west coast of India has been suggested as a possible impact crater, in this context called the
Shiva crater. It was also dated approximately 66 million years ago, potentially matching the Deccan traps. The researchers claiming that this feature is an impact crater suggest that the impact may have been the triggering event for the Deccan Traps as well as contributing to the acceleration of the Indian plate in the early
Paleogene
The Paleogene Period ( ; also spelled Palaeogene or Palæogene) is a geologic period and system that spans 43 million years from the end of the Cretaceous Period Ma (million years ago) to the beginning of the Neogene Period Ma. It is the fir ...
. However, the current consensus in the Earth science community is that this feature is unlikely to be an actual impact crater.
[ - original article a]
source
/ref>
See also
* Columbia River Basalt Group
* Emeishan Traps
* Geology of India
* Krishna Godavari Basin
* Lameta Formation
* List of flood basalt provinces
* List of volcanoes in India
*Siberian Traps
The Siberian Traps () are a large region of volcanic rock, known as a large igneous province, in Siberia, Russia. The massive eruptive event that formed the trap rock, traps is one of the largest known Volcano, volcanic events in the last years ...
* Verneshot
* Viluy Traps
References
External links
*
Scientist argues that volcanoes, not meteorite, killed dinosaurs
{{Large igneous provinces
Cretaceous paleontological sites of Asia
Cretaceous–Paleogene boundary
Cretaceous volcanism
Events that forced the climate
Geology of India
Geology of Maharashtra
Large igneous provinces
Paleocene volcanism
Plate tectonics
Volcanism of India