Flood Basalts
Francis, 2013
Baffin Picrites
North Atlantic Igneous Province
60 mys
Flood Basalt Provinces
Age
(hotspot)
Ma
Area
km2
Columbia River
(Yellowstone)
Miocene
(15 - 17 Ma)
1.7*105
Ethiopian Rift
(Afar)
Oligocene
(30  1Ma)
5*105
North Atlantic Igneous
(Iceland)
Paleocene
(60  1Ma)
1.0*l06
Deccan, India
(Réunion)
K - T Boundary
(66  1 Ma)
5.0*l05
Caribbean - Colombian
(Galapagos?)
Late Cretaceous
(88 - 90 Ma)
Ontong Java Ocean Plateau
(Louisville)
1.9*106
early Cretaceous
(120 ± 5 Ma)
1.4*l05
Karroo – Antarctica
(Marion)
early Jurassic
(183 ± 1 Ma)
1.4*l05
Siberian Traps
(Jan Mayen?)
late Permian
(248 ± 2 Ma)
3.5*l05
Proterozoic
(1100 - 1070 Ma)
1.3*l05
Keeweenawan –
Lake Superior
Coppermine River,
NWT.
Hart Dolerite, Tasmanian
Circum - Ungava foldbelt
1.7*105
1.0*106
2.0+*l06
1.5+*l06
6.0*105
mid-Cretaceous
(122 & 90 4 Ma)
Parana –Etendeka
(Tristan)
Estimated
Volume
km3
Proterozoic
(1267 ± 4 Ma)
-
Proterozoic
(1751 Ma)
-
Proterozoic
(1890 Ma)
-
5.0+*l06
2.0*l06
2.5*l06
1.5*l06
3.0*l05
-
Age
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.
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 latestage 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.
Duration
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.
Columbia River Flood Basalts
~15 ± 1 mys
North Atlantic Igneous Province
60 ± 1 mys
Deccan Traps
66 ± 1 mys
Curacao –Carribean
88-90 mys
Ontong Java Ocean Plateau
Mid-Cretaceous
122 & 90 mys
Anomalously thick oceanic crust (20 –
40 km) capped by 5 – 10 km of basaltic
lavas..
Siberian Traps
248 ± 2 mys
Parana – Etendeka
120 ± 5 mys
Karoo Flood Basalts
183 ± 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 latestage 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
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
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
Age
(hotspot)
Ma
Area
km2
Columbia River
(Yellowstone)
Miocene
(15 - 17 Ma)
1.7*105
Ethiopian Rift
(Afar)
Oligocene
(30  1Ma)
5*105
North Atlantic Igneous
(Iceland)
Paleocene
(60  1Ma)
1.0*l06
Deccan, India
(Réunion)
K - T Boundary
(66  1 Ma)
5.0*l05
Caribbean - Colombian
(Galapagos?)
Late Cretaceous
(88 - 90 Ma)
Ontong Java Ocean Plateau
(Louisville)
1.9*106
early Cretaceous
(120 ± 5 Ma)
1.4*l05
Karroo – Antarctica
(Marion)
early Jurassic
(183 ± 1 Ma)
1.4*l05
Siberian Traps
(Jan Mayen?)
late Permian
(248 ± 2 Ma)
3.5*l05
Proterozoic
(1100 - 1070 Ma)
1.3*l05
Keeweenawan –
Lake Superior
Coppermine River,
NWT.
Hart Dolerite, Tasmanian
Circum - Ungava foldbelt
1.7*105
1.0*106
2.0+*l06
1.5+*l06
6.0*105
mid-Cretaceous
(122 & 90 4 Ma)
Parana –Etendeka
(Tristan)
Estimated
Volume
km3
Proterozoic
(1267 ± 4 Ma)
-
Proterozoic
(1751 Ma)
-
Proterozoic
(1890 Ma)
-
5.0+*l06
2.0*l06
2.5*l06
1.5*l06
3.0*l05
-
Age
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.
A Role for Eclogite?
Large Volume of Monotonous
Si-rich Compositions
Plume Head
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