Flood Basalt, Deccan Traps, Large Igneous Province, and Ontong-Java-Province

Flood Basalt            Plateau basalt extrusion extending many kilometers in vast, flat, layered flows that erupted from numerous volcanic fissures. Flood basalts form one type of large igneous province. See also fissure eruption, mantle plume, and mass extinctions. Real World Examples: The Deccan Traps in India and the Siberian Traps are two of the world’s largest and best examples of flood basalts (see the Table below for additional data) but if you want to see first-hand what one looks like the Columbia River Flood Basalt Province in Washington, Oregon, and Idaho is much more accessible to North Americans. Many geochemists and geologists are convinced that all three of the flood basalts mentioned as examples above had their origins as mantle (magma) plumes.

FLOOD BASALT FLOWS

Event                                                                    Date                         Volume

Ontong Java/Nauru                                       21-124 mya               38-55 x 106 km³

Kerguelen Plateau/Broken Ridge               114-109.5 mya          15-25 x 106 km³

North Atlantic                                                  57.5-54.5 mya           6.6 x 106 km³

Deccan Traps                                                65-69 mya                  8.2 x 106 km³

Columbia River                                             6-17.5 mya                 1.74 x 106 km³

Ethiopian Traps                                             31± 1 mya                  7.5 x 105 km³

Siberian Traps                                              249-216 mya             2.3 x 106 km³

Parana Plateau Brazil                                  119-149 mya             12 x 105 km²

CAMP                                                            200 mya                     2 x 106 km³

Karoo Basalts                                               166-206 mya             >1.4 x 105 km²

Snake River Plain                                         16 mya                       0.5 x 105 km²

        Recent evidence collected from the Siberian Traps by geochemists Asish Basu (University of Rochester), Stein Jacobsen (Harvard University), and Robyn Hannigan (then at the University of Rochester) demonstrated that more than a half-dozen chemical elements and rare isotopes distributed throughout the basalts are now rare on the Earth’s surface but are common in parts of the lower mantle that originated soon after the birth of the solar system. They concluded that the Siberian flood basalt arose from super-heated, buoyant rock that rose in a narrow column from a depth of 1,800 miles into a gigantic mushroom-shaped mass of hot material just 40 to 50 miles below present-day Siberia. Then, some 250 mya, 12 to 16 percent of that rock suddenly melted (probably from depressurization or decompression) and broke through fissures in the Earth’s crust, resulting in a vast flood of lava. The total area of the Tian Shan Cretaceous-Paleogene Large Igneous Province (LIP) basalt distribution is 285 000 sq. km, a number that is comparable to other large igneous provinces (Ernst and Buchan, 2001), such as the Emeishan Traps in China at 250 000 sq. km. Data on the Tian Shan LIP basalts indicate that they were formed as a result of a large mantle plume during a relatively short time. The Deccan Traps were emplaced practically synchronously with the Tian Shan LIP basalts, a synchronicity that suggests that the Deccan Traps and same-aged basaltic rocks of the Tian Shan represent a plume cluster that originated from the same deep mantle source in the form of a superplume rising from the core-mantle boundary.

        For more information, see the following articles. Don L. Anderson. “The Sublithospheric Mantle as the Source of Continental Flood Basalt: The Case against the Continental Lithosphere and Plume Head Reservoirs,” Earth and Planetary Science Letters, vol. 123: pp. 269-280, 1994; Richard E. Ernst and Kenneth L. Buchan, “Large mafic magmatic events through time and links to mantle-plume heads; in: Richard E. Ernst and Kenneth L. Buchan (eds.), Mantle Plumes: Their Identification through Time, Geological Society of America, Special Paper 352, pp. 483-575, 2001; and Richard E. Ernst and Kenneth L. Buchan, “Maximum Size and Sistribution in Time and Space of Mantle Plumes: Evidence from Large Igneous Provinces,” Journal of Geodynamics (Special Issue) vol. 34: pp. 309-342, 2002. Aleksander V. Mikolaichuk and Vladimir A Simonov, “Cretaceous-Paleogene basalts of the Tian Shan,” March 2006, online at: http://www.largeigneousprovinces.org/LOM.html.

        For those geoscientists infected by wanderlust but desirous of a more salubrious climate than frigid Siberia or the Tien Shan, a trip to Brazil’s Rio Grande do Sul flood basalt province might be instructive.

        Author’s Note: In several places the Columbia Plateau basalt is about 10,000 feet thick. Individual flood layers typically range between 50 and 350 feet thick so it is easy to see how many individual flows would be needed to accumulate 10,000 feet of volcanic materials. Road cuts and areas where the basaltic layers have exposed by erosion demonstrate their characteristic parallel, vertical columnar jointing, which is usually hexagonal, though areas of six-sided columns are not uncommon. Enough lava flowed out of the Siberian Traps to cover Europe in thousands of feet of lava; in another perspective, that lava flow was so extensive that it could have covered the entire surface of the Earth with a layer of basaltic rock ten feet thick.

Although the amount of lava pumped onto the Earth’s surface by the flood basalts is truly staggering, that’s only the tip of the iceberg in terms of other effects these phenomena would have had on the Earth. Terrence M. Gerlach of Sandia National Laboratory in Albuquerque used one of the Kilauea eruptions as a model and estimated that the Deccan Traps injected up to 30 trillion tons of carbon dioxide, six trillion tons of sulfur (start thinking sulfuric acid) and 60 billion tons of halogens (reactive elements such as chlorine and fluorine) into the lower atmosphere over a period of a few hundred years (reported by Vincent E. Courtillot in “A Volcanic Eruption,” Scientific American, October, 1990, pp. 85-92). Now, think of all the flood basalts listed in the table above and their combined effects on the Earth’s surface and atmosphere. And then think about what would happen to the Earth if ALL that volcanic activity occurred almost simultaneously, like the Young Earth advocates and creationists would have us believe. Exactly what would all that carbon dioxide, sulfuric acid, nitric acid, and other noxious chemicals do to living organisms? Have you heard the term, volcanic-nuclear winter? Nearly every organism in the ocean would die since the various acids would lower the pH of seawater to levels that wouldn’t sustain life. And the C0₂ injected into the atmosphere would be in the range of many thousand parts per million (perhaps 50,000 to 60,000 ppm or more), meaning that Earth’s surface temperature would be intolerably hot, as in several hundred degrees. In other words, in that unbelievable scenario nearly all life on Earth would die. Yet, here we are. It must be a miracle.

Deccan Traps                 Enormous flood basalt lava outflow in central and western India and one of the Earth’s largest volcanic provinces. In their pre-erosional state, the Traps may have covered as many as 200,000 square miles of basalt estimated to range in volume from 200,000 cubic miles to well over 1,000,000 cubic miles. The most precise date yet for the end of the main pulse of Deccan volcanism has been estimated at 64.9 mya, give or take 100,000 years, and shows that the volcanic activity occurred precisely at the Cretaceous and Tertiary boundary (see Cretaceous-Tertiary extinction in mass extinctions). In addition, several independent studies have documented the presence of iridium (a platinum group element thought to indicate the effects of a bolide impact on the Earth) between layers of the flood basalts. Author’s Note: Although many scientists have thought that the Traps were caused by a hot spot or mantle plume, other evidence collected in the late 1990s by Indian geophysicists has called into question the widely accepted mantle plume model. According to their theory, the Deccan continental flood basalt province is more correctly related to continental rifting in a non-plume, plate tectonic environment. Recently, however, additional evidence has been presented by Richard Muller and others that points to an impact origin that may have brought about both decompression melting as well as the extinction event; see core-mantle boundary for additional related information. Since this debate is far from settled, be sure to watch the professional literature for additional research. The word trap is derived from a Sanskrit word meaning a step, which is in reference to the step-like topography produced by the flat, stacked layers of lava.

Large Igneous Province (LIP)                 Enormous outpourings of predominantly basaltic magma that commonly cover areas of 105 km² or more in a continuum of voluminous magmatic constructions that include continental flood basalts and associated intrusive rocks, volcanic passive margins, oceanic plateaus, submarine ridges, seamount groups, and ocean basin flood basalts. Although plate tectonic theory provided a breakthrough in understanding how the continuous opening and closing of ocean basins reflects convection in the Earth’s upper mantle, it is now known that LIPs form independently of plate settings on continents, in oceans, along margins between the two, and either wholly within plates or at plate boundaries. A number of geophysicists believe that the alternative mode of convection manifested by LIPs may be how other terrestrial planets and moons lost most, if not all, of their interior heat. However, a growing number of geophysicists have proposed an alternate method of formation for LIPs: bolide impact-induced melting. According to this theory, decompression melting would occur almost simultaneously upon impact, triggering long-lived mantle upwelling and eruption that may in many respects resemble a mantle plume or hot spot and have plume-like geochemical signatures. Decompression melting and the upwelling magma would quickly auto-obliterate the craters and would explain their conspicuous absences on Earth when compared to other planets in the solar system.

        The largest LIPs occur in ocean basins, especially the giant plateaus such as the Ontong-Java Plateau and Shatsky Rise in the western Pacific and the Kerguelen Plateau in the Indian Ocean. Flood basalts also erupted along many “volcanic passive margins” (e.g., Greenland, eastern North America, Brazil, Norway, Namibia, and northwest Australia) during continental breakup, as well as in continental settings, such as the Columbia River Flood Basalt Province, Deccan Traps in India, Karoo/Ferrar in South Africa/Antarctica, Parana in Brazil, and the Siberian Traps.

        Field investigations, laboratory research, and modeling efforts to understand LIP formation and development have been initiated only recently. Those efforts are comparable to investigations of the mid-ocean ridge system that preceded development of the plate tectonics paradigm. At this time no single theory adequately explains the Earth’s large-volume basaltic magmatism. However, recent geophysical research involving the core-mantle boundary may have provided theoretical arguments that eventually are capable of tying together the now disparate threads. Understanding the processes in the Earth’s mantle and crust and the effects of LIPs on the oceans, atmosphere, and biosphere is of particular importance. Because the scientific problems associated with LIPs range widely, scientists from many disciplines are involved in their study. A list of fields involved in LIP research is extensive and includes among others geophysics, geochemistry, geochronology, petrology, mineral physics, rock deformation, oceanic and atmospheric chemistry, physical volcanology, paleomagnetics, tectonics, seismology, geodynamics and hydrodynamics, micropaleontology, paleoclimatology, paleoceanography, sedimentology, planetary geology, astrogeology, and remote sensing. For additional and fascinating technical information online, see http://www.largeigneousprovinces.org/frontiers

Ontong-Java Plateau (OJP)              Massive outpouring of igneous rock formed about 120 mya near the Solomon Islands in the western Pacific. The OJP may be the Earth’s largest such province, with a surface area roughly the size of Alaska. Although it is generally believed that igneous provinces such as the OJP were formed as part of the initial plume-head stage of hot-spot development, other theories are extent, as is illustrated below. The most widely accepted plume-head model predicts that such plateaus were formed in massive eruptions of basaltic magma (see magma, types of) that lasted only a few million years or less, most likely resulting in major atmospheric, oceanographic, and biospheric effects. Nearly all of the large igneous provinces in the oceans were formed in the Cretaceous period, suggesting a method of mass and energy transfer from the Earth’s interior to the surface that was considerably different from the mid-ocean ridge mode of the Cenozoic. If, as evidence to date suggests, most of the greater OJP was formed in a single volcanic episode lasting a few million years, then the magma production rate required for its formation would have rivaled that of the entire global mid-ocean ridge system at the time. The OJP may therefore represent the largest igneous event of the last 200 million years. The principal characteristics of the greater OJP may be summarized as follows.

Formed in the early Cretaceous, about 120 mya

Presently obducting along the Solomon Islands Trench

Includes the Ontong-Java Plateau and neighboring basin basalts

The most voluminous LIP on Earth at ~ 60 million cubic kilometers

Aerially extensive, covering about 0.8 percent of the total surface area of the Earth

Geochemically and structurally homogeneous with no evidence of continental lithosphere

Presently in isostatic equilibrium with the sea-floor except for the obducting margin

Widely believed to have been formed by the Louisville hot spot, a large mantle plume head

        However, with respect to the origin of the greater OJP, recent research has demonstrated that many geophysical, geodynamic, and geochemical results from studies of the greater OJP are at odds with various mantle plume origin models. A fascinating and recently made suggestion is that an extraterrestrial impact model is much more consistent with existing data and results than the mantle plume explanation. That model would include the following elements:

Penetration depth of about 36 miles

Initial crater diameter of about 120 miles

Massive decompression melting in the upper mantle to a minimum depth of 180 miles assuming 100 percent partial melting as a result of the removal of lithospheric overburden

Solid asthenospheric mantle, moving laterally inward and upward from below to replace the extracted mantle may have experienced a catastrophic decrease in pressure during its emplacement beneath the OJP, resulting in the low shear-wave velocities observed by Richardson et al.

        The authors of the research paper that has been summarized above (Ingle, S. and M. F. Coffin, 2004.  “Impact origin for the Ontong Java Plateau, Earth Planet,” Science Letters, vol. 218, pp. 123-134) note that the absence of recognized bolide impact craters on the deep ocean floor is remarkable. Reliable estimates based on the present-day terrestrial cratering rate predict that up to three bolides at about six miles in diameter should have struck the deep ocean basins in post-Jurassic times. The greater OJP may be the evidence of one such impact. tholeiitic basalt

        Author’s Note: Of course, a great deal of field and lab research will have to be performed to test such an impact model. For example, if tsunamis deposits, disturbed abyssal sediments, and spherules and highly-siderophile element anomalies are discovered in contemporaneous, local sediments then the model will become much more interesting to geophysicists. However, I have included this information on the OJP not because the idea has been thoroughly tested and has been shown to be correct but because it is the highly exciting, cutting-edge stuff that makes science so spell-binding and flat out irresistible. Additional closely related information can be found under large igneous province and large igneous province, silicic-dominated. Recent research (2006) of sea-floor fabric data by Brian Taylor of the University of Hawaii concluded that the OJP and the nearby Manihiki Plateau and Hikurangi Plateau were at one time continuous and formed a single entity until sea-floor spreading separated them and moved them apart. Interested observers should keep their eyes on the literature for more information.