The Cretaceous Superplume
The following topical questions and selected resources are designed to guide you in an introductory exploration of the Cretaceous superplume event. The resources linked from this page include an assortment of web- and non-web resources, published papers, abstracts, graphics, and animations. Direct links to web resources are followed by a "more info" link that gives a short description of the web resource. These resources by no means comprise a comprehensive treatment of the literature on the subject, but should at least give you a place to start in your study of the Cretaceous superplume event.
Background: What are mantle plumes?
Mantle plumes are thought to be zones of upwelling hot mantle rock, the surface expressions of which often include large igneous provinces, oceanic islands, seamounts, continental flood basalts, and linear volcanic chains in the oceans and on the continents called "hotspot tracks". The mantle plume concept was first proposed by Morgan (1971) (more info) and was based on Wilson's (1963) ideas that stationary hotspots in the shallow mantle underlay island/seamount chains in the deep ocean, and that the motion of crustal plates over these hotspots was what produced hotspot tracks. The Wilson-Morgan hotspot-plume theory comprised a key piece of evidence for the new theory of global plate tectonics which emerged during the late 1960's and early 1970's.
For some background information on the evidence and development of the hotspot and mantle plume theories, please see the chapter on hotspots and mantle thermal plumes (more info) in the online text "This Dynamic Earth: The Story of Plate Tectonics", published by the U.S. Geological Survey.
Be warned! A growing number of geoscientists doubt the very existence of mantle plumes! For more in-depth information concerning current controversies about mantle plumes, the mantleplumes.org (more info) website is a good place to start.
What is a superplume?
In their preface to a special issue of the Journal of Geodynamics on "Superplume events in Earth history: causes and effects", Condie et al. (2002) discuss the terms superplume and superplume event, the various ways these terms have been used in the literature, and suggest their own definitions. The text that follows is largely based on their discussion.
The term superplume has been used in different ways in the literature as..
- a broad zone of mantle upwelling (many thousands of km's across) comprising the return flow from subduction (Larson, 1991b )
- a mantle plume sufficiently large that, when the plume head spreads at the base of the lithosphere, it achieves a diameter of 1500-3000 km (Condie et al., 2002) .
According to Condie et al. (2001) , a superplume event is a
- a short-lived mantle event (100 Ma) during which many superplumes as well as smaller plumes bombard the base of the lithosphere
Who originated the superplume concept?
As pointed out by Sheridan (1991) , the concept of a 'pulsating' pattern of global geological processes (transgressions and regressions, mountain building, etc.) is not new, but the link between global cycles of geologic change and mantle processes was not made until the development of the mantle plume concept by Morgan (1971) (more info) . Morgan's plume theory was based on the emerging theory of global plate tectonics and the idea proposed by Wilson (1963) that hotspots in the shallow mantle underlay island/seamount chains in the deep ocean.
During the 1980's, a few publications noted the correlation between periods during which the Earth's magnetic field did not switch polarity (as it normally does on an irregular basis) and major episodes of geologic activity. The most developed of these was a paper by Sheridan (1987) , in which he hypothesized that these correlations could be explained by cyclic eruptions of plumes from the core-mantle boundary. Sheridan called this mechanism pulsation tectonics.
The term superplume was coined by Roger Larson in the early 1990's, and his two short papers published in Geology--Larson (1991a) and Larson (1991b) --are commonly cited as the origination of the superplume concept. To his credit, however, Larson (1992) has acknowledged Sheridan's priority in linking mantle plumes to major cycles in Earth history.
What was the cause of the Cretaceous superplume event?
No one really knows what causes superplume events, but it is believed that some mechanism that traps and then catastrophically releases heat from the core-mantle boundary may be responsible. One possibility which has been proposed involves the sinking of subducted slabs to the core-mantle boundary where they trap and build up heat over long periods of time. An animation (more info) illustrating this model of superplume formation has been created by Eh Tan and Michael Gurnis at Cal Tech: Superplume Formation Beneath An Ancient Slab (more info) .
What is the evidence for a superplume event in the Cretaceous?
Sheridan's (1987) and Larson's (1991a , 1991b ) original formulations of the "pulsation" or "superplume" event during the mid-Cretaceous are based on a number of correlations between various Earth processes during this time:
- a dramatic decrease in magnetic reversals
- increased production of oceanic crust
- increased seafloor spreading rates
- increased global temperature
- increased eustatic sea levels
- increased deposition of black shales
- increased oil generation
- shallowing of the carbonate compensation depth (CCD) (Sheridan, 1987 ; but see the reply by Larson, 1991a )
What were the effects of the Cretaceous superplume?
The Cretaceous superplume event was truly an Earth system-wide event, as it had pronounced affects on the Earth's deep interior, lithosphere (including tectonics), biosphere and atmosphere/climate. To explore how the Cretaceous earth system responded to the superplume event, see the following resources:
- Deep interior and geomagnetism: Larson (1991a) , Larson (1991b)
- Lithosphere: Larson (1991a) , Larson (1991b) , Cox and Van Arsdale (2002)
- Biosphere: Jahren (2002) (more info)
- Atmosphere and climate: Caldeira and Rampino (1991) , Jahren (2002) (more info)
Have some of the effects of the Cretaceous superplume persisted to the present day?
In his original paper on the Cretaceous superplume, Larson (1991a) characterizes the Cretaceous superplume as "primarily a Pacific Ocean phenomenon", and interprets the "superswell" of anomalously shallow oceanic crust under the present-day South Pacific as "nearly exhausted remnant of the original upwelling".
Have other superplume events occurred in geologic time?
The Cretaceous superplume was the first superplume event to be identified, but there is no reason to believe that it was a unique event in Earth history. Evidence for other superplume events is somewhat controversial, but geologists have proposed superplume events during the following periods of geologic history:
- Arguments against: Larson (1992)
- Permian-Pennsylvanian: Larson (1991b)
- Proterozoic: Condie (2002)
- Archean: Eriksson et al. (2002)
Have superplume events occurred on terrestrial bodies other than the Earth?
Perhaps the best example of superplume activity on other planets is the Tharsis region on Mars, an elevated volcanic plateau containing the largest shield volcanoes in the solar system:
- Tharsis Superplume(1): Why Superplume? (more info)
- Tharsis Superplume (2): Earthlike Evolution of the Tharsis Magmatic Complex (more info)
- Superplume Concept Applies To Tharsis Area On Mars (more info)
Superplume activity has even been proposed for the early history of the Moon.