Flood BasaltsFrancis, 2013 Baffin Picrites

North Atlantic Igneous Province60 mys

Flood Basalt Provinces(hotspot)

AgeMa

Area km2

Estimated Volume km3

Columbia River(Yellowstone)

Miocene(15 - 17 Ma) 1.7*105 1.7*105

Ethiopian Rift(Afar)

Oligocene(30 1Ma) 5*105 1.0*106

North Atlantic Igneous (Iceland)

Paleocene(60 1Ma) 1.0*l06 2.0+*l06

Deccan, India(Réunion)

K - T Boundary(66 1 Ma) 5.0*l05 1.5+*l06

Caribbean - Colombian(Galapagos?)

Late Cretaceous(88 - 90 Ma)

6.0*105

Ontong Java Ocean Plateau(Louisville)

mid-Cretaceous(122 & 90 4 Ma) 1.9*106 5.0+*l06

Parana –Etendeka(Tristan)

early Cretaceous(120 ± 5 Ma) 1.4*l05 2.0*l06

Karroo – Antarctica(Marion)

early Jurassic(183 ± 1 Ma) 1.4*l05 2.5*l06

Siberian Traps(Jan Mayen?)

late Permian(248 ± 2 Ma) 3.5*l05 1.5*l06

Keeweenawan – Lake Superior

Proterozoic(1100 - 1070 Ma) 1.3*l05 3.0*l05

Coppermine River, NWT.

Proterozoic(1267 ± 4 Ma) -

-

Hart Dolerite, Tasmanian Proterozoic(1751 Ma) -

-

Circum - Ungava foldbelt Proterozoic(1890 Ma) -

-

No particular time association, flood basalts appear to have erupted throughout the Earth’s history. Many flood basalt provinces appear to be associated with continental break up and/or OIB hot-spot traces.

Age

Characteristic features of Flood Basalts:

Flood basalt provinces occur both as 1 – 5 km thick sequences of effusive basalts on continents and as plateau of anomalously thick oceanic crust (20 – 40 km) capped by 5 – 10 km of basaltic lavas (oceanic plateau).

Flood basalt provinces are characterized by thick sheet-like flows, an absence of central volcanic constructs, and very large volumes ( 106 km3). In comparison, the volume of Mauna Loa, the largest volcano on Earth, is only 75,000 km3. Single flows often reach thicknesses of 100m, for example the La Roza flow of Columbia River Flood Province is 100+m thick and has a volume of 160 km3). It is commonly difficult to identify actual eruption vents.

Dominated by remarkably uniform aphyric quartz tholeiites and basaltic andesites that are too

evolved in composition to equilibrate with a pyrolitic mantle. Commonly associated with significant late-stage rhyolitic volcanism in continental settings (Karroo, Parana, Yellowstone), but there is a marked absence of silicic andesites and dacites, ie. flood basalt provinces are distinctly bimodal. Commonly minor associated picrite and alkaline lavas occur low in the volcanic succession.

Picrites associated with flood basalts share the major element characteristics of OIB picrites, in terms of high Fe, and low Al, most falling in the harzburgite residue field of the Al - Si diagram.

Individual flood basalt provinces have remarkably short histories considering the large volumes of erupted lava. The majority of well-dated flood basalt provinces have main stage durations on the order of only 1 - 4 ma. The better the dating, the shorter the time interval. These short eruption durations, combined with the large volumes, correspond to eruption rates that are 10 - 100 times those seen in OIB suites such as Hawaii. Flood basalt provinces thus appear to represent catastrophic events, with their associated hot-spot tracks representing a long waning period.

Duration

Columbia River Flood Basalts ~15 ± 1 mys

North Atlantic Igneous Province60 ± 1 mys

Deccan Traps 66 ± 1 mys

Curacao –Carribean88-90 mys

Ontong Java Ocean Plateau

Mid-Cretaceous122 & 90 mys

Anomalously thick oceanic crust (20 – 40 km) capped by 5 – 10 km of basaltic lavas..

Siberian Traps248 ± 2 mys

Parana – Etendeka 120 ± 5 mys

Karoo Flood Basalts183 ± 1 mys

Despite their relatively small major element compositional ranges, the variations in relatively incompatible elements such as Ti indicate that most flood basalt suites have experienced a relatively large degree of crystal fractionation along a tholeiitic gabbroic cotectic. This implies the existence of voluminous gabbroic cumulates (Xcumulate/Xlava 0.5), most likely in sills at the base

of the crust. These gabbroic cumulates may represent an important contribution to the growth of continental crust.

Different Mantle Sources or

Extensive Fractionation?

Trace Element Characteristics of Flood Basalts

Unlike OIB and MORB basalts and picrites, continental flood basalts are commonly characterized by negative high field strength element anomalies (eg. Nb) and positive Pb anomalies, and are characteristically enriched in LIL elements (K, Rb, & Ba).

Continental alkaline basalts associated with flood basalt provinces, however, are virtually indistinguishable from those of OIB suites, exhibiting neither Nb nor Pb anomalies, and relative depletions in LIL elements.

Oceanic plateau, in contrast, have relatively flat, unfractionated trace element profiles, with relative depletions in LIL elements, and lack Nb and Pb anomalies. This may in fact be an observational problem, because we do not have much in the way of samples from the lower parts of ocean plateau successions.

Individual continental flood basalt provinces commonly exhibit chemically and isotopically polarised stratigraphic successions, with picrites and basalts that are trace element and isotopically enriched near the base of the succession, but with trace element and isotopic enrichment, and Nb and Pb anomalies, decreasing up section to late-stage basalts that have MORB-like trace element and isotopic characteristics (Deccan, Karroo, Coppermine). This pattern suggests that the effects of crustal contamination (or lithospheric mantle?) are most common in the early stages of flood basalt volcanism.

Continental Flood Basalts Ocean Plateau

Continental flood tholeiites have relatively high 87Sr/86Sr and low 143Nd/144Nd ratios, that typically extend from near Bulk Earth into the lower right quadrant of the mantle array. Some continental tholeiites actually have lower Pb isotopic ratios than MORB, and thus appear to contain very old Pb (Yellowstone), derived from continental crust or lithospheric mantle.

Ocean plateau provinces, in contrast, are characterized by relatively low 87Sr/86Sr and high 143Nd/144Nd isotopic ratios, commonly plotting in the upper left hand quadrant of the mantle array, similar to many apparently plume-related OIB tholeiites.

Rhyolites in continental flood basalt provinces are typically even more isotopically enriched in terms of Sr and Nd, and clearly distinct from their associated basalts. Such rhyolites appear to be melts of the crust.

Some of the Columbia River flood basalts and associated Yellowstone basalts and rhyolites contain very old lead, presumably derived from the North American Proterozoic crust.

1 Ga

Flood Basalt Provinces(hotspot)

AgeMa

Area km2

Estimated Volume km3

Columbia River(Yellowstone)

Miocene(15 - 17 Ma) 1.7*105 1.7*105

Ethiopian Rift(Afar)

Oligocene(30 1Ma) 5*105 1.0*106

North Atlantic Igneous (Iceland)

Paleocene(60 1Ma) 1.0*l06 2.0+*l06

Deccan, India(Réunion)

K - T Boundary(66 1 Ma) 5.0*l05 1.5+*l06

Caribbean - Colombian(Galapagos?)

Late Cretaceous(88 - 90 Ma)

6.0*105

Ontong Java Ocean Plateau(Louisville)

mid-Cretaceous(122 & 90 4 Ma) 1.9*106 5.0+*l06

Parana –Etendeka(Tristan)

early Cretaceous(120 ± 5 Ma) 1.4*l05 2.0*l06

Karroo – Antarctica(Marion)

early Jurassic(183 ± 1 Ma) 1.4*l05 2.5*l06

Siberian Traps(Jan Mayen?)

late Permian(248 ± 2 Ma) 3.5*l05 1.5*l06

Keeweenawan – Lake Superior

Proterozoic(1100 - 1070 Ma) 1.3*l05 3.0*l05

Coppermine River, NWT.

Proterozoic(1267 ± 4 Ma) -

-

Hart Dolerite, Tasmanian Proterozoic(1751 Ma) -

-

Circum - Ungava foldbelt Proterozoic(1890 Ma) -

-

No particular time association, flood basalts appear to have erupted throughout the Earth’s history. Many flood basalt provinces appear to be associated with continental break up and/or OIB hot-spot traces.

Age

A Role for Eclogite?

Plume Head

Large Volume of Monotonous Si-rich

Compositions

Olivines in MORB, OIB, and

Continental Flood Basalts

Olivine Compositions

Multi-Stage Melting Model:

Lithosphere

Lithosphere

Lithosphere

Melting of peridotite containing eclogite or

pyroxenite pods