Igneous Provinces (LIPs)”: Definition, recommended
terminology, and a hierarchical classification
of Earth Sciences, Indian Institute of Technology (IIT)
Bombay, Powai, Bombay
(Mumbai) 400 076 India.
This webpage is a
condensed and modified version of the paper: Sheth,
H.C., ‘Large Igneous Provinces (LIPs)’:
Definition, recommended terminology, and a hierarchical
Reviews 85 (2007) 117–124.
here for Discussion of this page
Click here for a counter
proposal "Proposed Revision
to Large Igneous Province Classification" by
Bryan & Ernst.
The term Large Igneous
Province (LIP) has been widely applied to large
flood basalt provinces (e.g., Deccan), and
the term Silicic Large Igneous Province (SLIP)
to volcanic provinces of dominantly felsic composition
(e.g., Whitsunday, Australia). Neither of these
terms has been applied to the large granitic batholiths
of the world to which both are perfectly applicable.
LIP has also not been applied to broad areas of contemporaneous
magmatism and sizeable layered mafic intrusions. I suggest
use of the term LIP only in its broad sense and propose
a minimum area of 50,000 km2 for a LIP.
I present a simple hierarchical
classification of LIPs that is independent of composition,
tectonic setting, or emplacement mechanism. I suggest
that volcanic provinces such as the Deccan Traps and
Whitsunday (Australia) be called Large Volcanic
Provinces (LVPs), and large mafic intrusions, dyke
swarms, and other intrusive provinces be called Large
Plutonic Provinces (LPPs). LVPs and LPPs together
cover all large igneous provinces (LIPs), having felsic
to ultramafic compositions of sub-alkalic and alkalic
lineages, emplaced in continental and oceanic settings.
I subdivide LVPs into
- the dominantly/wholly mafic Large
Basaltic Provinces (LBPs) (e.g., Deccan,
- the dominantly felsic Large Rhyolitic
Provinces (LRPs) (e.g., Whitsunday,
Sierra Madre Occidental);
- the dominantly andesitic Large
Andesitic Provinces (LAPs) (e.g., Andes,
- the bimodal Large Basaltic-Rhyolitic
Provinces (LBRPs) (e.g., Snake River-High
Lava Plains; Dongargarh, India).
The intrusive equivalent
of LRPs are the Large Granitic Provinces (LGPs)
(e.g., the Andean batholiths), but a corresponding
term for intrusive equivalents of LBPs is not necessary
or warranted. The largest LBP, and LIP, is neither the
Ontong Java, the Siberian Traps, or the Central Atlantic
Province, but simply the ocean floor.
is a Large Igneous Province (LIP)?
Fig. 1. A view
of the spectacular, >1-km-thick exposed section
through the Deccan flood basalts at Mahabaleshwar.
Photo: Hetu Sheth, December 2005.
igneous province (LIP)
implies a province
of igneous origin that is large. Clearly, the
term LIP should cover large volcanic and intrusive
igneous provinces, of whatever emplacement mechanism
and composition. However, the term LIP has been
applied to and used only for “flood basalt”
provinces that have been the subject of great
interest and extensive research recently (e.g.
, 1988; Mahoney & Coffin
; Kerr et al.
, 2005; Foulger
, 2005; Saunders
, 2005; see
They represent the eruption of enormous volumes
of mantle-derived magma on the Earth’s surface
in relatively short time periods. These provinces
Fig. 1, and Siberian Traps
are unquestionably LIPs in the broadest sense
of the term. However, large-volume felsic provinces
such as the Sierra Madre Occidental in Mexico
are also LIPs, as are the huge granodioritic batholiths
of the world, such as those of Tibet-Himalaya,
western North America, or the Andes (Fig. 2),
and the largest mafic layered intrusions such
as the Bushveld Intrusion. Indeed, continental
rift zones such as the Rio Grande Rift and the
Cameroon Line are LIPs. None of these involve
Coffin & Eldholm
(1992, 1993, 1994) were amongst the first to
use the term LIP in the current restrictive
sense. They defined LIPs as “massive crustal
emplacements of predominantly mafic (Mg and
Fe rich) extrusive and intrusive rock which
originate via processes other than “normal”
seafloor spreading … [and] include continental
flood basalts, volcanic passive margins, oceanic
plateaus, submarine ridges, seamount groups
and ocean basin flood basalts.” This cannot
be a suitable definition of LIP since it excludes
most types of LIPs. However, the term LIP continues
to be used in this restrictive sense (Ernst
et al., 2005; Saunders, 2005;
I suggest that the term LIP be retained but
in its broadest sense, but that new, necessary
terms be introduced for various categories of
The definition of “large”
is clearly subjective and flexible, and I suggest
here 50,000 km2 as the lower limit
for LIPs (see below). Volume would be a better
size parameter than area, but area is usually
easier to measure. Most LIPs are much larger
than 50,000 km2. The Deccan,
for example, covers 0.5 million km2
of western-central India today and has an estimated
original extent of 1.5 million km2
(Wadia, 1975). The Siberian province
is vastly larger (Reichow et al., 2002).
The smaller of the flood basalt provinces, such
as the Emeishan province (~250,000 km2;
He et al., 2003) and the Columbia
River province (~164,000 km2;
Hooper, 1988; Ed: See also comment
River Province size), are also well above
the lower size threshold I suggest.
Fig. 2 (at left). A llama overlooks the
ruins of Machu Picchu, situated at 2500 m above
sea level in the Peruvian batholith, a felsic
large igneous province. Photo: Hetu Sheth,
Volcanic Provinces (LVPs) and Large Plutonic Provinces
Just as there are large
mafic volcanic provinces as exemplified by the Deccan
and the Columbia River
Basalts, there are large felsic volcanic provinces
dominated by highly evolved (broadly rhyolitic) lavas.
Several such provinces (the so-called SLIPs)
are described by Bryan et al. (2000, 2002;
SLIPs webpage) and include
the early Cretaceous Whitsunday province and the Sierra
Madre Occidental. There also are large volcanic provinces
dominated by andesite, and others that comprise subequal
volumes of basaltic and rhyolitic lavas. For all these
volcanic provinces, of whatever composition, I propose
the term Large Volcanic Provinces (LVPs).
Obviously, all LVPs are LIPs, but all LIPs are not LVPs.
After Pluto, the Roman
god of the underworld, I suggest the term Large
Plutonic Provinces (LPPs) for all intrusive
provinces meeting the size requirements, whatever their
composition, emplacement depth, and internal structure.
This category includes mafic-ultramafic intrusions such
as the Bushveld Complex, large granite batholiths such
as the Andean and Tibet-Himalayan batholiths, and giant
dyke swarms such as the Mackenzie dyke swarm of Canada
(Ernst et al., 1995).
Rhyolitic Provinces (LRPs) and Large Granitic Provinces
The term “silicic
LIP” or “SLIP” used for rhyolite-dominated
large volcanic provinces (Bryan et al., 2000,
2002; SLIPs webpage) recognizes
the fact that LIPs can be of felsic composition. However,
this term should strictly include the big granitic batholiths
of the world but does not. I propose that large volcanic
provinces dominated by broadly rhyolitic rocks (i.e.,
the rhyolite-rhyodacite-dacite-trachyte compositional
range, both sub-alkalic and alkalic lineages) be called
Large Rhyolitic Provinces (LRPs). Besides
the Whitsunday and the Sierra Madre Occidental provinces,
the Neoproterozoic Malani
province of northwestern India (Sharma,
2004, 2005) is a good example.
Plutonic provinces with
the same compositions can similarly be called Large
Granitic Provinces (LGPs). “Granitic”
implies the compositional range granitegranodiorite-tonalite-trondhjemite.
The Archaean-Proterozoic charnockite (hypersthenegranite)
massifs of southern India (Rajesh
2004) are included in the LGP category. Both LRP
and LGP are independent of the geodynamic origins and
tectonic settings of these rocks.
Basaltic Provinces (LBPs)
I suggest that large volcanic provinces of
dominantly basaltic composition be called
Large Basaltic Provinces (LBPs). “Basaltic”
implies the compositional range basaltic andesite-basalt-picrobasalt
(and their alkalic equivalents). The rock type
basaltic andesite belongs in this category because
many flood “basalts” are in fact
basaltic andesites. Examples include many Deccan
lavas from the Western Ghats (see Fig. 4a on
page) and the Grande Ronde lavas of the
Columbia River basalt province that constitute
85% of the volume of that province (Hooper,
1997; Ed: See also comment on Columbia
River Province size).
Fig. 3 (at right). A thick
pile of Palaeogene flood basalts on the Isle
of Skye, Scotland. Photo: Hetu Sheth, September
Fig. 4. The Ofaerufoss
in the great Eldgja (A.D. 934) fissure in southern
Iceland. Photo: Hetu Sheth, September 2003.
It is to be noted that the
term “LBP” refers not only to exclusively
basaltic provinces that lack felsic rocks (e.g.,
the Columbia River province; Hooper, 1997) but
equally well to dominantly basaltic
provinces with subordinate amounts of more evolved
rocks such as rhyolite and trachyte. Most continental
flood basalt (CFB) provinces are of this
type. Examples of LBPs thus include the Deccan,
Emeishan, Madagascar, Karoo, Parana-Etendeka,
Yemen-Ethiopia and North
Atlantic Tertiary provinces (Fig. 3). The
oceanic flood basalt provinces, the so-called
oceanic plateaus (e.g., Ontong
and Kerguelen; Fig. 4), are also LBPs. Large
oceanic island-seamount chains such as the Hawaii-Emperor
(Fig. 5) and the Ninety East Ridge also belong
in the LBP category, as do broad areas of diffuse
basaltic volcanism on the continents (e.g.,
et al., 2003) and in the oceans (e.g.,
the South Pacific
Superswell; Janney et al., 2000).
The term “LBP” is independent of
Fig. 5. Red-hot Kilauea lava in action.
Photo: Hetu Sheth, July 2002.
Basaltic-Rhyolitic Provinces (LBRPs)
When felsic lavas and
mafic lavas in an LVP each constitute nearly half of
the total volume, they constitute a bimodal LVP with
intermediate compositions more or less absent. These,
I call Large Basaltic-Rhyolitic Provinces (LBRPs).
There are fewer members in this category than the LBPs.
Examples are the Snake River Plain-Oregon High
Lava Plains province of the western U.S.A. (e.g.,
Jordan, 2005), and the Palaeoproterozoic (2.5
– 2.2 Ga) Dongargarh Group in central India (Sensarma
Andesitic Provinces (LAPs)
I suggest the term Large
Andesitic Province (LAP) for any andesite-dominated
province that meets the LIP size requirement. No tectonic
setting is implied, but it is clear that most andesites
are erupted in subduction zones (Gill, 1981).
This category includes as members andesitic belts along
island arcs (e.g., Indonesia, Japan), active
continental margins (e.g., the Ecuadorian-Colombian
Andes, Peruvian-Chilean Andes, Cascades, and Mexico-central
America), and continental collision zones (e.g.,
is the largest LIP?
The largest LBP and LIP
is not the Ontong Java,
Siberian Traps, or the Central
Atlantic Magmatic Province. It is, of course, the
ocean floor. Though Coffin & Eldholm (1992,
1993, 1994) would exclude volcanic provinces formed
by “normal” seafloor spreading from their
definition of LIPs, this exclusion is not warranted.
Though the formation of the ocean floor is gradual and
very long-lived, the production rate is high. It takes
only a 500-km-long ocean ridge segment spreading with
a half-rate of 5 cm/yr to create a 100-km-long (or 50,000
km2 area) expanse of new oceanic lithosphere
in only 1 million years. The 50,000-km-long worldwide
network of ridges, with this average half-spreading
rate, creates 5 million km2 of oceanic lithosphere
in just 1 million years. The average thickness of the
modern oceanic crust is 7 ± 1 km (e.g.,
White et al., 1992), of which the basaltic part (pillow
basalts and sheeted dykes) makes up ~2 km (Boudier
& Nicolas, 1985; Nicolas, 1989). Thus,
the lower size limit of 50,000 km2 proposed
here for a LIP, and the areas and volumes of most LIPs,
are small in relation to the output of the mid-ocean
ridge system over comparable time scales.
hierarchical classification of large igneous provinces
The foregoing discussion
shows that the term LIP is broad and vague. For this
reason I suggest the hierarchical classification of
LIPs described above, which is summarised in Table 1.
I note the following:
The terms in boldface
in Table 1, with the exception of “Large Igneous
Province (LIP)” are proposed here for the
first time. The terms in italics are either formal
terms (e.g., flood basalts, island
arcs) currently in vogue for these provinces,
or informal (e.g., diffuse provinces).
proposed is independent of tectonic setting. No
tectonic setting is excluded a priori,
though most of the provinces listed belong to intraplate
(continental/oceanic) or rifted continental margin.
The LAP category includes members only from subduction
Any LAP may include
other rock types – the only criterion to be
satisfied by any province for inclusion in the LAP
category is dominantly andesitic compositions of
volcanic products and an area of at least 50,000
. Thus, the andesite-dominated, 1000-km-long
and 50-60-km-wide Mexican
with its considerable amount of
alkalic, ocean-island-basalt-type magmatism (e.g.
and references therein; Verma
2002; see also Mexico
) is included in this category.
Large Basaltic Provinces
(LBPs) or Large Volcanic Provinces (LVPs) in general
will necessarily include, besides the lavas, their
associated dyke swarms and intrusive complexes.
The category of
dominantly mafic, intrusive, continental LIPs includes
the layered mafic intrusions and the giant dyke
swarms. Both types of features may have been feeders
to flood basalt provinces now lost to erosion. The
famous Skaergaard Intrusion is quite small (100
km2) and forms part of the East Greenland
flood basalt province, and thus does not feature
in Table 1. The Dufek and Forrestal Intrusions of
Antarctica that cover ~6,600 km2 (Ferris
et al., 2003) similarly belong to the Jurassic
Ferrar flood basalt province. Worldwide, only the
Precambrian Bushveld Complex of South Africa (60,000
km2; Winter, 2001) reaches the
lower proposed size limit for a LIP. Other well-known
layered mafic intrusions (Duluth, Stillwater, Muscox,
Kiglapait) are well below this size.
Granitic Provinces (LGPs)” is an apt term
for broadly granitic (granite-granodiorite-tonalite)
batholiths, a corresponding short and single term
for dominantly mafic, intrusive, continental category
(e.g., “Large Gabbroic Provinces”)
does not seem possible. This is because many layered
mafic intrusions have significant volumes of ultramafic
rocks, and associated giant dyke swarms (e.g.,
Ernst et al., 1995) are mostly dolerite.
Table 1. Proposed
terminology and hierarchical classification of the
large igneous provinces (LIPs), with examples (Sheth,2007)
LARGE IGNEOUS PROVINCES (LIPs)
Extrusive/intrusive provinces of any
composition and tectonic setting with a minimum
area of 50,000 km2
(lavas: pyroclastics = 100:0 to 0:100, sub-alkalic:
alkalic = 100:0 to 0:100)
LARGE VOLCANIC PROVINCES (LVPs)
LARGE PLUTONIC PROVINCES (LPPs)
Dominantly or wholly felsic:
Large Rhyolitic Provinces (LRPs)
Dominantly or wholly andesitic:
Large Andesitic Provinces (LAPs)
Dominantly or wholly mafic:
Large Basaltic Provinces (LBPs)
Dominantly or wholly felsic:
Large Granitic Provinces (LGPs)
Dominantly or wholly mafic:
Both continental & oceanic
Both continental & oceanic
Sierra Madre Occidental,
North Atlantic Tertiary,
Central Atlantic (CAMP)
Oceanic island-seamount chains:
South Pacific Superswell
River Plain-Oregon High Lava Plains,
Peru-Chile Coastal Batholith,
Coast Range Batholith NW USA
portions of oceanic plateaus
The term Large Igneous
Province (LIP) is loosely defined (Saunders,
2005), and no attempts have hitherto been made to evolve
a more appropriate and accurate classification. In my
opinion, LIP covers a very broad category of provinces
larger than 50,000 km2 in area. I suggest
separate terms for each of the several categories of
LIPs and define them here on the basis of dominantly
extrusive or intrusive emplacement and rock compositions.
Correct terminology is important as it influences the
way we approach scientific problems. The classification
proposed here is simple and easy to use. I hope that
it will be adopted and lead to more accurate and effective
communication among scientists working in this field.
I am grateful to Ian Skilling,
James White, and Thor Thordarson for valuable and thought-provoking
reviews, and to Ninad Bondre, Kamal Sharma, Sarajit
Sensarma and Gillian Foulger for several helpful comments.
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last updated 3rd
9th March, 2006, Andy Saunders
Without getting into a protracted debate, I find the
new classification interesting but too broad.
It seems to encompass all large provinces that
have protracted magmatism and, technically, should also
include the entire ocean floor, as Hetu says. An
important feature of LIPs, and one which makes their
defintion rather more restrictive, is the period of
emplacement which I have always assumed to be geologically
short [here, 'short' is as fairly loosely defined as
Any useful classification scheme needs to give a least
a glance towards process. Thus LIPs are produced
by unusual processes (plume or not), and are thus distinct
from subduction – and MOR-related systems (but
can overlap geographically and tectonically with these
(viz Iceland and CRB).
I think Hetu has hit on an interesting topic; existing
definitions are vague, as a number of us have indicated
(see recent issue of Elements). I'm not sure that
this is necessarily a bad thing – we've
all tried to define the terms 'plume' or 'lithosphere'
- but the definition should not be too all-embracing.
If it does, it becmes unwieldy and won't, I believe,
help further our understanding.
9th March, 2006, Mike Coffin
Here are two relatively recent encyclopedia articles
M.F., and Eldholm, O., 2001. Large igneous provinces,
in Steele, J.H., Thorpe, S.A., and Turekian, K.K., eds.,
Encyclopedia of Ocean Sciences, Academic Press, London:
M.F., and Eldholm, O., 2005. Large igneous provinces,
in Selley, R.C., Cocks, R., and Plimer, I.R., eds.,
Encyclopedia of Geology, Elsevier, Oxford: 315-323.
9th March, 2006, Don Anderson
I always thought that the duration and rapidity had
to be controlled by the lithosphere (stress-valve) rather
than mantle temperature, and that large-scale ponding
prior to release was implied. I don't know if this glance
toward process can be built into a definition. LIPs
differ from non LIPs in that the process is finite in
duration (the rates and volumes are not exceptional).
This could, of course, reflect the size of the fertile
blobs, or the duration of extension. The tectonic context
is also necessary.
An updated definition of LIP may be in order ( and
plume! ). Lavoisier said that you cannot pretend to
have a science unless you have a language and definitions.
Things have moved along since the Encyclopedia artiicles
were published. The Elements volume is a fantastic update
of the situation. But the ideas that mantle convection
controls the plates rather than vice versa , and that
magma volume and rate is a proxy for high T are still
around. You have to decide whether volcanism, anomalous
or not, and uplift and rifting, is cause or effect.
The main changes in thinking are papers on melting instabilities
and on the possibility that high homologous temperature,
rather than high absolute temperature, is the key variable.
Papers by Tackley, Stevenson, Raddick, Parmentier...on
melt instabilities, and Abt, Rudnick, Kays, Cin-Ty Lee,
Humphreys etc. on delamination, are important in the
Although LIPs MAY require very large absolute temperature
(rather than ponding, fertility, shallow recycling,
delamination, homologous T, melting instabilities and
lithospheric control), this should not be part of the
definition. If short duration is part of the definition
it should not then be stated that this is a characteristic
of a plume, as Richards and Courtillot did; this is
circular reasoning. Stress and fertility can change
rapidly; temperature cannot.
9th March, 2006, Andy Saunders
I agree with you that process (source T or fertility,
fundamental cause such as plume, EDGE convection, delamination
etc) should not play a role in the definition or classification
of a LIP. My initial comment was intended to mean that
a definition or classification, to be useful, should
bear the processes in mind. A similar approach is taken
with the classification of most rocks, especially igneous
(e.g, the broad division into volcanic and plutonic
nods towards a recognition of emplacement style, but
is not in itself dependent upon that process).
9th March, 2006, Richard Ernst
Here is my contribution to the current discussion
of LIP definition. There are three points relevant to
a definition of LIPs:
To these Hetu has proposed subclassifications based
on magmatic composition (mafic, felsic intermediate)
and whether the main magmatism is volcanic or intrusive
SIZE OF LIPS: See a proposal for a new classification
of magmatic events (including LIPs) based on size which
is extracted from the attached paper by Bleeker
& Ernst (2006). Note that we retain the
conventional minimum size of 100,000 km2,
in disagreement with Hetu's suggestions of 50,000
Bleeker & Ernst (2006) "We suggest the following
classification of event sizes, compatible with common
usage in large igneous province terminology (e.g. Coffin
& Eldholm 1994, 2001):
Giant (LIP): >107
Major (LIP): 106
- 107 km3
Substantial (LIP): 105
- 106 km3
- 105 km3
The first three categories (giant, major, and substantial)
qualify the size of what are generally considered large
igneous provinces (LIPs), with (eruptive) volume estimates
on the order of one to several million cubic kilometres.
When intrusive and underplated volumes are considered
as well, some of the largest LIPs would classify as
true giants, e.g. the Ontong Java plateau at ca. 45x106
km3. The two smaller categories (moderate
to small) describe sub-LIP scale events.
 Coffin & Eldholm (1994, 2001) and others (e.g.
Ernst et al. 2005) have generally used a surface area
of >105 km2, rather than volume
estimates, to define LIPs.
DURATION OF LIPS:
Some LIPs are clearly very short duration events,
Deccan, Siberian Traps, Mackenzie (1270 Ma). However,
other events are clearly more protracted; Keweenawan
(1116-1085 Ma), probably Parana, Iapetus-margin (615-550
Ma), Matachewan (2500-2450 Ma), and many potential Archean
analogues. Many of the protracted events are actually
characterized by multiple pulses (e.g. the NAIP, Blekinge
Dalarna (975-948 Ma; main pulse at 948 Ma), and Central
Scandinavian Dolerite Group event (1270-1248; 3 pulses)).
So a short duration is not a required component of the
Ideally, LIP definition and classification should be
based on observable/measurable characteristics, not
be based on interpreted origin, plume, rifting, delamination.
So Hetu's classification based on magmatic type (dominantly
mafic, felsic intermediate, extrusive, intrusive) is
interesting in that regard. I certainly agree
that discussion of the LIP definition is required. Do
we go toward something similar to Hetu's, or do we stay
with the traditional definition (e.g. Coffin & Eldholm
definition) which links LIPs to process other than normal
sea floor spreading, and which implicitly excludes
normal subduction-related magmatism. I look forward
to further discussion on this.
But I disagree strongly on at least two points in Hetu's
1) It is a mistake to group the 1270 Ma Mackenzie with
the Tibet-Himalayan batholiths as LPPs. There
is no insight or understanding gained by grouping a
classic mafic-ultramafic event (rifting/plume
related) with a classic felsic event (collision/subduction
2) I think the 100,000 km2 minimum size for
LIPs should be retained (see my point above).
10th March, 2006, Don Anderson
Size should not be in the definition if it is arbitrary.
Is there a natural cut off? Likewise for
duration and rate and thickness. If these merge into
non LIPs then there may be a continuum and artificial
limits would not be helpful. LIPs occur when continents
are converging and diverging. They also overlap MORB,
back arc basin and arc basalts in chemistry. The
temperatures of the magmas or parents or source mantle
would be helpful.
10th March, 2006, Gillian Foulger
Clearly size, duration, rate and thickness are all a
continuum from very small to very large. Maybe instead
of proliferating categories we should just dump the
term "LIP" – it might be misleading
10th March, 2006, Hetu Sheth
I am pleased to see the amount of discussion my contribution
has generated. In this common Reply, I provide some
clarifications on the issues raised by the readers above.
First, there seems to be complete (and fortunate) agreement
that LIP is a broad and vague term. Dr. Saunders’
words, “the definition should not be too all-embracing.
If it does, it becmes unwieldy and won't help further
our understanding” are perfectly true of LIP.
LIP IS an all-embracing term, though it has always been
used in the incorrect, restrictive sense. By itself,
LIP conveys very little to me.
I would disagree with Dr. Saunders’ implication
that “LIPs” are unusual because they form
in plume/rift settings, whereas subduction and MOR are
“normal” settings. I see no reason why they
should be separated, or discussed separately. What is
the basis to exclude this or that province? And surely
there is no requirement in the Earth machine that “LIPs”
cannot be formed by subduction. As he notes, and so
does Dr. Anderson, there is a real continuum in tectonic
settings and size. In fact, LIPs may not be all that
In contrast to LIP, the new term I have coined, “Large
Basaltic Province”, is specific and accurate.
When one says LBP, one can’t mean the Andean granite
batholith. Similarly for LRP, and so on. When one says
LVP, one is aware that the term includes all volcanic
provinces and excludes all plutonic provinces. My contribution
goes further than a mere criticism of the current inappropriate
usage of the basket term LIP, by providing new terminology
and a classification, and is therefore, I believe, a
Regarding proposals to incorporate a tectonic context
or geodynamic origin into the classification, I think
that this is not only unnecessary in a viable classification,
but that the classification should be free of these
features, themselves often the subject of heated debate.
The classification is particularly meant to be independent
of the plume/non-plume debate. An LIP is not an LIP
because someone believes it to have come from a plume,
and does not cease to be an LIP if someone rejects the
I strongly believe that an LIP definition should be
based on size (how “large”) and not eruptive
duration or tectonic setting. An LIP classification
should be based on observable, non-contentious characteristics
of igneous provinces. Chemical composition (felsic,
mafic…) and emplacement depth (volcanic or plutonic)
are two such parameters and so form the bases of my
scheme. Eruptive durations for many LBPs are debated
(e.g., Deccan, whose total duration is no less than
8-9 m.y., Sheth et al., GRL, 2001, and Ivanov et al.
Terra Nova 2005 reach similar conclusions for the Siberian
Traps). The tectonic setting and geodynamic origin are
even more debated and by no means well known. This is
the reason why such subjective parameters should not
be the guiding factors while constructing a classification.
Regarding the minimum LIP size: A good classification
scheme should be able to encompass as many examples
worldwide as possible. I chose 50,000 km2
as the minimum size limit because with a higher limit
(say, 100,000 km2, to which I did give a
thought), provinces like the Mexican Volcanic Belt (50-60,000
km2 area) would not find a place in the classification
and no “Large Andesitic Province” category
could be formulated. Why such exclusion? 100,000 km2
is not “better” than 50,000 km2,
but as arbitrary, and because there IS a continuum in
igneous provinces in terms of size or tectonic setting,
such bounds are necessarily artificial. I chose 50,000
km2 as the limit merely because it is by
all means “large”, in absolute terms, and
any higher limit would result in exclusion of several
important provinces. With MY classification, 50,000
km2 is a much more suitable cut-off. I will
be happy to discuss this aspect more.
Regarding LPPs: I have by no means equated or compared
mafic dyke swarms with granite-granodiorite batholiths.
They are very different things, as Dr. Ernst points
out. However, by saying that they should not be together
because the former are plume/rifting-related and the
letter subduction-related, we are again creating all
sorts of nightmares by going into geodynamic origins/tectonic
settings. There are Proterozoic granite batholiths in
India, for example, that are (or appear to be) anorogenic.
They still are batholiths and SLIPs in every sense of
the term. Do we place them in a different category from
the (presumably) subduction-related batholiths and SLIPs?
No, because descriptively, physically, they are all
granite-granodiorite batholiths and SLIPs. In the same
way, giant mafic dyke swarms and SLIPs are plutonic
(in the sense of “intrusive”) and so come
under the same LPP category, just as two contrasting
types of volcanic provinces – LBPs and LRPs –
come under the LVP category.
Finally, I am not recommending dropping the term LIP.
I merely indicated its inappropriate and thoughtless
use, and recommended proper use and newly coined acronyms
for many LIP types. Acronyms are good as long as they
are accurate and used correctly. If LIP is dropped,
then so be it, but there is no reason to abandon the
new ones, specific and accurate as they are. For the
first time, we have a classification and accurate terms
that are specific, easy, and unambiguous. The contribution
was meant as a constructive one, not a criticism of
the term “LIP”. My efforts will be well
spent if the new terms and classification goes into
2006, Richard Ernst
With respect, size MUST be part of a definition
of LARGE Igneous Provinces. Some possible natural cutoffs
100,000 km2 – which seems to be the
minimum areal extent for flood basalt events based on
the initial work of Coffin & Eldholm. Furthermore,
our work on dyke swarms suggests that there is a natural
break in dyke swarm length. Those less than about 100
km in length have more local origin (e.g. individual
volcano), while those more than 300 km in length have
regional origin (rift zone, plume, etc.). Furthermore,
a swarm 300 by 300 km is 90,000 km2, which
is similar to the flood basalt value – this is
a reason that we have also endorsed the 100,000 km2
minimum for LIPs..
That being said, we are really at early days in understanding
the size of LIP – even the youngest ones: The
Siberian traps nearly doubled in known size a few years
ago, from about 2.6 million km3 to >3.9
million km3 with the dating of basalts under
the West Siberian Basin (Reichow & Saunders and
others; see March 2004 LIP
of the Month on our website). Furthermore, there
are estimates of 16 million km3 (i.e. by
scientists in Novosibirsk, Dobretsov and Vernikovsky)
if all the possible Siberian Trap equivalents are included,
in the Ural mountains, and in the Central Asia fold
belt. The same 'changing size' is true for Ontong Java.
Brian Taylor's recent EPSL paper (see also his February
of the Month) indicates that Ontong Java, Manihiki
Plateau and Hikurangi plateaus were originally formed
as a SINGLE LIP that was subsequently fragmented.
If events at 250 Ma and 120 Ma can be so uncertain
in size, then the many Paleozoic and Proterozoic LIPs
dominated by dykes and sills are even more uncertain
in their extents. So the order of magnitude size estimates
for LIPs and other rmagmatic provinces, that Wouter
Bleeker and I have adopted (and contributed earlier
in this discussion) seem the best way to go for now
until the database is more robust and natural breaks
become more apparent.
10th March, 2006, Andy Saunders
I agree with Richard. Size matters.
10th March, 2006, Gillian Foulger
I would expect the sizes of magmatic provinces to be
a continuum and I think it would be most ill advised
to make assumptions regarding origin, let alone incorporate
them in definitions. If we ever become 100% sure of
the origins of all of them, it'll be a sign we are not
doing our jobs properly.
10th March, 2006, Scott Bryan
Sheth has erected an unnecessary subdivision with regards
to Large Rhyolitic Provinces and Large Granitic Provinces.
The term "igneous" includes plutonic and volcanic
rocks; there is absolutely no requirement to coin terms
for separate plutonic and volcanic provinces. As noted
by the other commentators, there are spectrums in many
aspects of LIPs; there certainly is between the proportion
of volcanic rocks (preserved) and plutonic rocks (exposed)
in mafic and silicic LIPs. Any LIP with a volcanic expression,
will also have a plutonic component; therefore trying
to make a subdivision into volcanic or plutonic is unnecessary
splitting. The first-level division of Sheth's nomenclature
reflects more on the exhumation history of a LIP rather
than any fundamental differences in terms of emplacement,
relative proportions of magma emplaced at depth or erupted,
areal extents, volume, duration etc.
Sheth has misrepresented the definition of Silicic
Large Igneous Provinces (SLIPs) as given in Bryan et
al. (2002) and on the SLIPs webpage.To
reiterate the definition, the term “Silicic Large
Igneous Province” was used to describe silicic
volcanic-plutonic provinces with voluminous
magmatism >105 km3. The original
definition did specify extrusive volumes, and it should
be revised to be "igneous" volumes to account
for provinces where silicic intrusive rocks may be voluminous
(e.g., Kennedy-Connors-AuburnSilicic LIP; Table 1 of
SLIPs webpage). All the listed
examples of Silicic LIPs (Whitsunday, Chon Aike, Sierra
Madre, Kennedy-Connors-Auburn) have both volcanic and
intrusive rocks exposed, with the proportion largely
dependent on the depth of erosion. Therefore, any extensive
granitic batholiths that have areal extents, emplacement
rates and intrusive volumes comparable to LIPs may be
just deeper level features or plumbing/chamber systems
of silicic LIPs. This is no different to the argument
Ernst et al. have made for ancient mafic LIPs where
dyke swarms, sills and layered intrusions are the deeper
level plumbing structures to mafic LIPs (eg, continental
flood basalt provinces).
It is a very dangerous approach to add confusion
to the term LIP by simply using it to refer to a large
mass of similar composition igneous rock or lithology
(e.g. oceanic crust, large granitic batholith). Using
a tectonic-based term like "igneous or volcanic
terrane" would be much better for this purpose.
It is well-known that many granitic batholiths (that
can be on the scale of LIPs) have intrusive phases that
can span 100's of Myr but which were emplaced during
completely different tectonothermal regimes. To me,
LIPs are discrete, huge volume igneous events - they
are the sites of the largest individual eruptions (both
mafic and silicic) and cumulative erupted volumes in
Earth history that are the result of very high melt
production and eruption rates.
There are fundamental differences between the
Silicic LIPs and other large silicic volcanic systems
such as the SRP, Altiplano-Puna, TVZ, and although the
volcanism has been extensive, and erupted volumes prolific,
these latter provinces are still an order of magnitude
smaller in just about every respect to the Silicic LIPs
(see Table 1 of SLIPs webpage).
A critical part of the original LIP definition
is that they "originate via process other than
‘normal’ seafloor-spreading or those associated
with ‘normal’ subduction processes".
This reflects the fact LIPs form independently of plate
setting and fundamentally differ in style and geochemical
characteristics from MOR and subduction zone magmatism.
Therefore, the statement that subduction-related arc
igneous accumulations or MORB are LIPs is contradictory
and adds confusion. Magma flux rates at subduction zones
do not come close to those of LIPs.
I also agree with Ernst & Saunders that "size
does matter". For Silicic LIPs, a natural cut-off
is apparent at present; eruptive/intrusive volume is
more useful than Area and the Whitsunday, Sierra Madre
Occidental, Chon Aike & Kennedy-Connors-Auburn provinces
all have volumes >250,000 km3. Other provinces
with large volume silicic volcanism (eg TVZ, Altiplano-Puna,
SRP) all have (extrusive) volumes <50,000 km3.
The 100,000 km2 area cut-off used for mafic
LIPs also seems currently applicable for Silicic LIPs.
11th March, 2006, Don Anderson
Better define 'production rate' and 'eruption rate'.
This implies a very specific mechanism, steady state
and equilibrium ("melt upon demand").
If there is already melt in the asthenosphere, or ponding,
then the eruption (and intrusion) rate need not equal
the rate at which the mantle melts. In the plume hypothesis
and in the adiabatic ascent hypothesis for melting,
there is a steady state, but this is not general. Even
in the more general case, eruption + intrusion + underplating
need not equal the rate at which melt is produced although
it is likely to be close. For example, in the delmaination
case, dense eclogite can bottom out at 400-km, warm
up and partially melt, become buoyant, melt more upon
ascent, and then underplate, pond and start to intrude
when stress condtions are right, and then extrude (erupt)
at a later time, but 100% efficiency is not required,
or a steady-state. This may be nit picking but some
current theories assume steady-state, or assume that
ALL melting has to be due to adiabatic ascent. I suspect
that no current theory can produce melt from scratch
at the rates at which it is erupted, except possibly
Some LIPs form at RRR triple junctions, and in back-arc
settings and at incipient plate boundaries or
at new ridges. Most LIPs are NOW midplate but this is
because ridges migrate.
11th March, 2006, Sami Mikhail
I think the recent page by Hetu Sheth entitled Large
Igneous Provinces (LIPs)”: Definition, recommended
terminology, and a hierarchical classification is long
I have been quite upset by the lack of constraints
used by authors regarding the umbrella term (LIPs);
it’s like the whole plume thing part 2. We as
a scientific community must be specific and concise
to avoid confusion and misinterpretation. Its not complicated
science, but utilising our ability to communicate by
setting up definitive parameters based on terminology,
which are governed by definition, otherwise know as
words (‘Large’ & ‘Igneous’
are pre-existing words with definitions). The term LIP
does incorporate all Sheth was talking about (LBP, LRP,
LPP, LVP, LBP…) but Sheth’s paper is exhibiting
that the term LIP (by definition) is Igneous Geology
as a whole. The use of the term ‘LIP’ was
set up with basaltic flood lavas in mind. These have
large volumes extruded over short periods of time, which
is why I think the bulk of research is biased towards
CFB & oceanic plateaus. This is probably because
they are quite odd, interesting and with regard to biota-DANGEROUS
as we all know are linked to extinction.
Workers must see that using pre-existing words in any
order to define something previously undefined is proven
by the use of the term plume to be hazardous and a constant
nuisance. The idea of inventing words for new discoveries
is not sensible, but is useful. For example we didn’t
call electrons ‘little moon like things’!
But where do we draw the line? Who decides?
We do not really need the term as we use localised
names such as Siberian Traps, Emeishan flood basalts,
NAIP etc. The term (LIP) is set up to classify these
large igneous episodes as a whole. Sheth has just exposed
a problem with this system in this field of research
(LIPs). Similar to Scott Bryan (& others) who put
an S in front of LIP and simply said what about SLIPs,
but unlike Scott, Sheth gave an accelerated expansion
of the term that future workers would ‘inevitably’
do using the new hierarchical classification and terminology
one by one (first LGP then LRP etc…) he just said
them all at once. I feel it’s a clear sign that
the field is alive and growing with each publication,
which is fascinating.
As an undergrad seeking a PhD place I feel this Sheth
system is exciting. It opens doors for future research
projects like identification and petrogenesis of LBP,
LRP, LPP, LVP, LBP… comparisons, histories and
expansion of the database & website www.largeigneousprovinces.org.
11th March, 2006, Hetu Sheth
It is good to be able to provide some
further clarifications. My apologies to Dr. Bryan if
I misread or misquoted his work and definitions.
I maintain that LRP and LGP should be separate categories,
just as LBP and large mafic-ultramafic intrusive complexes
are separate categories. It is true that a flood basalt
province/LBP does include the associated intrusive complexes
WHEN EXPOSED (see my explanation to Table 1), and this
is similarly true of LRPs. What I had in mind, however,
was situations when the intrusive counterparts of an
LBP or LRP are not yet exposed by erosion, or when only
the intrusive counterparts (mafic dyke swarms or granite-granodiorite
batholiths) remain and the upper levels have been lost
to erosion. Ample examples exist of each. Of the latter,
take the many giant dyke swarms (the Mackenzie and many
others) that may well have fed flood basalts, now eroded,
or the felsic batholiths that may simply be the root
zones of rhyolitic stratovolcanoes/flood provinces (many
examples in the southern Indian shield, e.g., the charnockite
massifs I have mentioned). The latter is indeed due
to exhumation – it is immaterial, and the classification
addresses what is seen at the surface.
I have tried to define or coin terms for what I see,
without any conjectures or guess-work. Whether a granite
batholith exposed today at the surface fed rhyolitic
volcanoes at the top, or did not, is immaterial, and
should not affect the classification. Similarly, giant
dyke swarms in all probability fed surface flood basalts,
but whether they actually did or not we may never know.
In any case, it is immaterial, in this classification,
and should be. I emphasize once again that the classification
is purely descriptive, based on what is at the surface
and what can readily be seen and what is not contentious.
This is nothing but the emplacement depth and the compositions.
Tectonic setting, geodynamic origin, even the age and
eruptive duration, are sufficiently contentious, and
likely to remain so. In whichever direction our ideas
and knowledge evolve regarding these issues, ten years,
twenty years from now, the basic characteristics (volcanic/intrusive,
chemical composition) are not going to change.
Whether the community will adopt this classification,
or a modified version of it, or none of it, the future
that’s not too far off will tell, but I really
think that if the term LIP is to continue (and there
is no reason why it shouldn’t), then the various
categories defined and named here are the best thing
available. If the classification is basically faulty,
or deemed unappealing despite the explanations and clarifications,
then the option we are left with perhaps is to blow
LIP and all other acronyms up and end up with no terms
and nothing to work with. Just use the plain “flood
basalt provinces”, “granite batholiths”,
and so on. This may be counter-productive however. After
all a classification is meant to simplify things, and
this one does it.
I still fail to see how sea-floor spreading and subduction
are “normal”, whereas plume/rift/rifted
margin are not “normal”. How do we define
“normal”? As DeLaughter et al. in the P3
book note, “the main problem is satisfactorily
defining normal”. Today may be “normal”
with a hundred active volcanoes worldwide, or we may
be living in a particularly “abnormal” time
in Earth history with only a hundred volcanoes active.
Even notions of “normal” and “not
normal” may be prejudices rather than real. I
see no basis to separate subduction and MOR from the
other features if there is no physical basis for this.
And as I note in my article, the crustal production
is not in any way less along a moderately fast-spreading
ridge than it is in a flood basalt, over time scales
of 5 m.y. or 10 m.y. Many flood basalts do have such
durations, as Dr. Ernst notes. Is 5 m.y. short or long?
Is 10 m.y. short or long? These things are bound to
remain subjective and debatable.
In any case, the ocean floor does satisfy perfectly
the LIP (and LVP and LBP) definitions. It is the largest
igneous, volcanic, and basaltic province, in every sense
of these English terms. Including it in the LIP definition
does not create confusion. It is the thoughtless use
of the term LIP for over a decade that is the cause
of ample confusion. Not including the ocean floor in
the LIP definition basically means we are not prepared
for clear and accurate terminology. There’s no
escaping the fact that the ocean floor is an LIP, and
the largest one. If this is not appealing, then one
should stop using LIP for the other things as well.
It is somewhat ironic that some of us who think that
“size does matter” are recommending exclusion
of the ocean floor, a true LIP and in fact the largest
LIP, from the LIP definition itself.
2006, Scott Bryan
Eruption rate (Note: we made comments
on this in our 2002 GSA Spec Publ 362 paper, see conclusions
on p. 115) - this varies depending on if it is a mafic
or silicic eruption. We now know the mafic flood basalt
eruptions from the CFBPs are very large volume (1 to
~5000 km3, may be larger if Steve Self et
al are correct for some eruptions from the Deccan),
long-lived (yrs to 10s of yrs) and although the effusion
rates are high (~4000 m3/s), they may not
be too dissimilar to recent eruptions (eg comparisons
between Laki and Columbia River flood basalt eruptions
by Self, Thordarson et al). The big silicic eruptions
(eg Parana-Etendeka & Afro-Arabia) represent similar
and much larger erupted volumes (up to 6340 km3
and possibly much larger, up to 10,000 km3).
Although no detailed work has been done on their eruption
rates, they are no doubt going to be similar or greater
to other well-constrained large plinian/explosive eruptions.
Probably a key point in both (mafic & silicic) cases
is that the individual eruptions will have been far
more sustained (primarily by virtue of the tremendous
volume that had to have been erupted) than any other
non-LIP eruption. Therefore, if we argue or interpret
that eruption rates are not dissimilar to those observed
in recent times, then the eruptions had to be far more
sustained. If we interpret much higher eruption rates,
then eruption duration will be less. There is currently,
insufficient age resolution to constrain recurrence
rates of both mafic and silicic eruptions in LIPs. This
may well be the crucial distinctor for LIPs compared
to other igneous provinces (arcs, MORs etc).
Melt production rates - I am coming at this from the
silicic LIP point of view. We know that they require
massive thermal inputs into the crust to drive crustal
melting, and if you look at Table 1 on the Whitsunday
LIP of the month web page, you'll see that the magma
flux rate is substantially higher for the Whitsunday
LIP when compared to what is the most productive silicic
volcanic province on the Earth today (TVZ). There does
seem to be a basic difference here between the silicic
LIPs when compared with other volumetrically significant
and hyperactive silicic volcanic provinces (TVZ, Altiplano-puna,
I note your points, and agree on the potential
complexities on how melt is generated. That is why I
think silicic LIPs have an important contribution to
make here in understanding the origin of mafic LIPs.
"Some LIPs form at RRR triple junctions,
and in back arc settings and at incipient plate
boundaries or at new ridges. Most LIPs are NOW midplate
but this is because ridges migrate." Agreed,
but the point I was making and that I think Mike Coffin
was making was that LIPs can occur anywhere and everywhere
- ie are independent of plate setting. Supra-subduction-zone
arcs or MORs are not. "Back-arc" is vague
- do you mean back-arc setting (could be anywhere from
0 to >1000 km inboard of the volcanic arc), or do
you mean it has a tectonic connection to the subduction
zone and plate boundary processes? Yes, the CRFBG are
back-arc (in terms of setting), but it is a big call
to say they are subduction-related. The Sierra Madre
Occidental can also be argued to be erupted in a back-arc
setting; many have argued (wrongly) that the volcanism
was arc- or back-arc related - this is primarily due
to the erroneous assumption that calc-alkaline = arc/subduction
signature (a similar story for the Whitsunday Silicic
LIP), but this is a whole other topic of discussion.
I think these LIPs emplaced near active continental
margins have a lot to offer on how LIPs are formed -
if from a CMB-derived plume, then how does such a plume
navigate through an actively subsiding slab of oceanic
12th March, 2006, Don Anderson
Scott – Thanks for the clarification.
My point is that 'melting rate' should not be in the
definition, or the assumption that eruption rate equals
the rate of latent heat supply. My terse comment was
just to point out that melting rate does not have to
equal eruption rate, and that high eruption does not
imply the need to melt as fast as it erupts, i.e. high
melt production rate is a prerequisite only in
the plume theory. Some plume advocates argue that high
production is required, and therefore high vertical
plume velocities, and that no non plume theory can give
such high rates of melting. But when calculations are
attempted (Cordery et al., 1997) even a plume cannot
give the implied melting rate and even a plume head
salted with eclogite and made hot instead of warm (ala
Campbell) cannot produce much melt under thick lithosphere.
Some plume modifictions accept ponding and lateral flow
but many current papers demand high melting rates, rather
than the ponding/stress valve release mechanisms. The
SLIP situation is particularly instructive since the
sources of heat and material are clearly different and
something else controls when and where the eruption/intrusion
occurs and eruption rates have little to do with intrusion
rates and ponding volumes. The opposite is usually assumed
"recurrence rates of both mafic and silicic
eruptions in LIPs. This may well be the crucial distinctor
for LIPs compared to other igneous provinces (arcs,
MORs etc)." Good point. And this may be controlled
by stress and litosphere, rather than mantle and temperature.
Any criteria that distinguishes LIPs from ridges and
arcs would be useful.
"Melt production rates - I am coming at this
from the silicic LIP point of view. We know that they
require massive thermal inputs into the crust to drive
crustal melting...you'll see that the magma flux rate
is substantially higher for the Whitsunday LIP when
compared to what is the most productive silicic volcanic
province on the Earth today (TVZ). " Thermal
input into the crust is the key, and this is likely
due to basalt. In the delamination/reheating model the
infinite heat source of the manltle heats and melts
the eclogite blobs but no superheat or high temperature
is needed. In the plume model it is the relatively more
modest core heat that is used; ambient mantle is considered
to be cool and isothermal, as well as having a pyrolite-like
solidus throughout. Geophysics implies mantle potential
temperatures well above the standard 1300 ¾C adiabats
and bringing basalt into the crust at these kind of
temperatures may be adequate for the SLIPs and probably
for the LIPs. But, in any case, the melting rate is
not the eruption rate. Eruption rate and intrusion rate
may be controlled by the lithospheric situation.
"I note your points below, and agree on the
potential complexities on how melt is generated. That
is why I think silicic LIPs have an important contribution
to make here in understanding the origin of mafic LIPs."
"....the point I was making and that I think
Mike Coffin was making was that LIPs can occur anywhere
and every where - ie are independent of plate setting."
I would contest this. Hawaii is a still being worked
on example, but as far as I know ALL LIPs have
a fairly well understood tectonic and stress relationship...
e.g to mobile belts, suture zones, craton edges, new
triple junctions, extension. A long time ago Cox pointed
out that Karooo was in general terms 'back arc' from
the SAMFRAU belt. CRB, Keweenawen, Deccan are
also in convergent situations with a slab somewhere
below and the possibility of arc delamination. You are
right, back arc may be too vague; convergence, slabs,
arc, sutures...and maybe, delamination, plus extensional
stress, are usually involved somehow. But we definitely
do not see a full fledged LIP popping up in the
middle of Canada or Australia or the Pacific plate.
Detailed plate reconstructions show that LIPs have a
tectonic context, often between two cratons, or an evolving
Pacific plate, or ~1000-km offshore of a fragmenting
continent, or at a new ridge (but there is cause and
effect for this one; plumologists have plumes causing
breakup bu this leaves out Karoo, Deccan, CRB etc.)
"Yes, the CRFBG are back-arc (in terms of
setting), but it is a big call to say they are subduction-related."
Delamination is similar to subduction and most candidates
for delamination are in arcs or convergent mountain
belts. The B&R and the Sierras seem to have uplift
and delamination somehow related to the Farallon slab,
and CRB are somehow related to the only active subduction
in this part of the world. Humphreys wants all of western
N America to be related to dewatering of dead slabs.
The Changbei volcanics are 2000 km form a trench but
a slab has been imaged beneath it. Tomography
does show that slabs can bottom out and extend for thousands
of km horizontally. Most of China seems to be underlain
by a flat slab. I prefer to think that the current subduction
is secondary but the stresses and arcs and thick crust
may be involved.
"I think these LIPs emplaced near active continental
margins have a lot to offer on how LIPs are formed."
I AGREE, but the past tectonic context is also
important. Atlantic and Indian ocean LIPs seem to be
related to supercontinent fragmentation (delamination
in my view) but the previous convergent situation
may also be critical.
13th March, 2006, Gillian Foulger
Persons interested in this debate might
be interested in a new Powerpoint presentation I just
breakup of Gondwana: An argument against the deep mantle
plume paradigm by James Sears.
He just gave this at Durham, and he presents a novel
model for the location of LIPs.
13th March, 2006, Don Anderson
The words 'normal', as in normal MORB
or NMORB, and 'anomalous', as in anomalous seafloor
bathymetry or a swell, seem innoculous but are largely
responsible for the present confusion and debate about
plumes. The terms imply that the mantle is isothermal
and homogeneous and two-dimensional. One does not expect
magmatism to be steady in time or uniform in space,
or ridges to be constant depth. In 3D convective simulations
upwellings may start linear but then become concentrated,
as in salt domes from salt beds. The upwelllings do
not need a special theory and they are not anomalies.
Plate tectonics makes the mantle heterogeneous and not
isothermal and this is normal. Some places will make
more basalts than other places. The distinctions between
NMORB, TMORB, EMORB, PMORB and OIB are arbitrary and
have led to the situation where when EMORB is found
along a ridge it means a plume (and lower mantle), even
though the N- and E-MORB distinction is arbitrary. Likewise,
'high 3He/4He' is arbitrarily
defined as >9.5 Ra, and 'therefore' 'high 3He/4He'
is plume (anything greater than 9-10 Ra found at ridges
is excluded from the normal average and when found,
by definition, is a plume).
Every parameter has a statistical range and a standard
deviation. To arbitrarily make a cutoff and then say
that a different theory is needed for things outside
the cutoff is not to appreciate statistics or sampling
theory. If igneous volumes or areas are bimodal
or have many peaks, then different theories may be needed.
But even this can be due to sampling differences. The
standard deviation is sometimes more important than
the parameter. Likewise, if the chemistry (or eruption
rate, or temperature ) does not overlap MORB, or BABB,
IAV... then it should be in the definition. If there
is overlap and if there is uncertainty in the definitions
or cutoffs then this probably tells us a great deal
about the mechanism. LIPs may just be the endgames of
'normal' plate tectonic and seafloor spreading processes;
the transients that occur as spreading starts or as
ocean basins close or when a TJ jumps.
These chronological and timing parameters may be more
important than size, if you eventually want the definition
to help in determining the mechanism. Has a LIP ever
happened in the middle of a plate, away from the current
or future plate boundaries or craton boundaries and
not related to slabs, incipient boundaries etc? Are
LIPs really independent of tectonics and are they ever
midplate? Are they always atop thick sedimentary basins?
Are emplacements always followed by uplift? Is it clear
that oceanic plateaus and CFB are the same thing (LIPs)?
How does a (bounded) small ocean basin or BAB
differ from a LIP?
13th March, 2006, Sami Mikhail
LOGIC, LANGUAGE & LIPs.
I have a few questions if anyone would be so kind
to hazard some suggestions, assumptions or propose answers,
but first some points:
LARGE is defined as big in size or amount relative
to a known comparable X which is small (or large is
only large in comparison to small as it is a relative
term, Large > Small). IGNEOUS is defined as rocks
formed from magma. As Anderson quoted from Lavoisier
on 9/3/2006 ‘you cannot pretend to have a science
unless you have a language and definitions!’ So
to have a large igneous province one must classify such
a province relative to a small igneous province. The
umbrella term ‘LIPs’ like it or not does
include all igneous provinces which are ‘anomalously’
large compared to ‘normal’ igneous activity
regardless of tectonic setting, chemical signature and/or
process of formation. This includes almost all orogenic
settings such as Cadomia (N Armorican massif), the Andean
SZ, the plutons of Himalaya (along strike to the collision
zone and back arc) and all ocean floors. Whether or
not this means it is harder to say the term LIP and
inflict a simple mental picture is irrespective of the
terms’ definition using the English language.
Ernst (9/3/06) has put up three constraints on LIP
definition. 1- Size, without a doubt, the term states
a relative description of size using the word LARGE.
2- Duration, well does it? Maybe for the conceptional
idea it plays a part, but what has that got to
do with anything? If it is large (>small) & igneous
it is a LIP by definition of the words in the term.
I understand how it may be helpful to estimate or assume
the petrogenesis of areas such as NAIP, Deccan Traps,
Siberian Traps ect from just being told it’s a
LIP which gives the recipient the idea that the petrogenesis
was fast (rapid eruption rates) and big. But does that
constrain a LIP? Also 3- Setting, how? Recently we have
seen many people publish ideas on LIP petrogenesis with
no indicative conclusion, i.e. OJP. Ingle & Coffin
(2003) proposed impact of an extra terrestrial bolide,
then plume activity was proposed in a geochemical sense.
The OJP basalts contain enough concentrations of Platinum
Group Elements (PGE) to indicate an outer-core origin
transported by a deep mantle plume from D’’
according to Ely & Neal (2003). Also lithospheric
delamination seems plausible as Anderson (2005) states
‘the possibility of delamination is increased
at ridge-ridge-ridge triple junctions’ like the
one surrounding the OJP. Burke & Torsvik (2004)
concluded no relation to continental break-up unlike
most LIPs! So when classifying the OJP as a LIP which
setting was used?
Saunders states (9/3/06) ‘Thus LIPs are produced
by unusual processes’, but are they? According
to Burke & Torsvik (2004) and Ernst et al (2005)
and the LIP
data base LIPs appear almost 1 per 10 Ma over the
last 200 Ma (LIPs >200 Ma may be destroyed by surface
processes) which is not a geologically unusual process.
It is more like a steady occurrence through time which
isn’t anomalous and therefore is not unusual.
A few questions K0228562@kingston.ac.uk:
- 1 Bryan has done a good job of solidifying the
term SLIP, so now we have two ‘agreed’
types of LIP (SLIP & ‘normal-mafic’
LIP). But the proposal put forward in this article
by Sheth is not going to disappear. Now the two terms
(LIP & SLIP) are readily used they will be broken
down. Just like simplifying an algebraic equation.
Thus the possibility of more sub-divisions/umbrella
terms. For example, a SLIP may have both
rhyolitic and andesitic components, but the ratio
of andesite:rhyolite may be (hypothetically) 2:8.
To increase clarity one may call it a Rhyolitic
Large Igneous Province (RLIP). Does this not
improve classification? Example (LIP) =
('normal basaltic' LIP + SLIP) & (SLIP) = (RLIP
+ ALIP[andesitic] + DLIP[dacitic]).
- Are subduction-related LIPs not considered by workers
as our knowledge of the magma generation at subduction
zones is relatively well known & documented compared
to MOR & intra-plate where there is less clarity
- Why is process of formation even considered when
there is no agreement towards either end-member of
the argument with regard to plume vs. non-plume (tectonics,
- With regard to Ernsts’ (9/3/06) comments
and constraints as to LIP definition on this page
there is no mention of geochemistry. So are SLIPs
not SLIPs but LIPs?
- Foulger stated on 10/3/06 ‘Maybe instead
of proliferating categories we should just dump the
term "LIP" – it might be misleading
us’. Saunders (2005) makes a point that LIPs
have no strict definition. So as there is no strict
definition and no set constraints in nature for strict
definitions with regard to Earth sciences. We could
just agree to use the term ‘unofficially’
and off the record. So, why use the term LIP in published
The term LIP is very useful to spread interest of
geoscientists of the future, Scientists and non-geo/scientists.
It also helps current workers to easily identify with
each others field (for example the formation of the
large igneous province commission). The only problem
appears to be in agreeing constraints for the definition.
I put forward a suggestion that a more specific name
or umbrella term may be more useful. Such as ‘Areas
of Rapid Magma Generation’. I am not proposing
this title but simply implying that a more representative
term could be used to replace LIP and better suit the
generally agreed definition (such as the definition
given by Coffin and Eldholm (2005) in the Encyclopaedia
- ANDERSON, D.L. 2005. Large Igneous Provinces, Delamination,
and Fertile Mantle. Elements. 1 (271-275)
- BURKE, K., TORSVIK, T.H. 2004. Derivation of Large
Igneous Provinces of the past 200 million years from
long-term heterogeneities in the deep mantle. Earth
and Planetary Science Letters. 227 (531-538)
- Coffin, M.F., and Eldholm, O., 2005. Large igneous
provinces, in Selley, R.C., Cocks, R., and Plimer,
I.R., eds., Encyclopedia of Geology, Elsevier, Oxford:
- ELY, J.C., NEAL, C.R. 2003. Using Platinum-group
elements to investigate the origin of the Ontong Java
Plateau, SW Pacific. Chemical Geology. 196 (235-257)
- ERNST, R.E., BUCHAN, K.L., CAMPBELL, I.H. 2004.
Frontiers in Large Igneous Province research. Lithos.
- INGLE, S., COFFIN, M.F. 2004. Impact origin for
the greater Ontong Java Plateau. Earth and Planetary
Science Letters. 218 (123-134)
- SAUNDERS, A. D. 2005. Large Igneous Provinces: Origin
and Environmental consequence. Elements. 1
15th March, 2006, Kamal Sharma
Hetu described various categories of LIPs
on the basis of extrusive or intrusive emplacement and
rock compositions. The terminology is a scientific one
and gives an idea of occurrence and rock type of the
igneous body. Adhering to 100, 000 km2 minimum
size for a LIP seems inappropriate. A minimum size of
50, 000 km2 to characterize the LIP is not
improper. The size parameter should be applied loosely,
while defining LIPs.
LIPs developed on Earth in different tectonic settings
during the geological past. If a significant area is
presently preserved, than it can be categorized as an
LIP. The south Indian charnockite massif formation is
a large scale Precambrian igneous province. Similarly,
the Tibet-Himalayan batholith also formed during Precambrian
time. Categorizing both as LIPs will give a better understanding
of the formation of the Large Igneous Provinces on the
Earth through time. In my view, the message will be
more specific through the use of standard LIP terminology
in scientific descriptions.
20th March, 2006
Please visit the webpage "Proposed
Revision to Large Igneous Province Classification"
by Scott Bryan & Richard Ernst where the authors
present a comprehensive proposal for LIP classification.
... for continuation of this discussion, click