Large igneous provinces and silicic large igneous provinces: Progress in our understanding over the last 25 years

Abstract

Large igneous provinces are exceptional intraplate igneous events throughout Earth’s history. Their significance and potential global impact are related to the total volume of magma intruded and released during these geologically brief events (peak eruptions are often within 1–5 m.y. in duration) where mil- lions to tens of millions of cubic kilometers of magma are produced. In some cases, at least 1% of Earth’s surface has been directly covered in volcanic rock, being equivalent to the size of small continents with comparable crustal thicknesses. Large igneous provinces thus represent important, albeit episodic, periods of new crust addition. However, most magmatism is basaltic, so that contributions to crustal growth will not always be picked up in zircon geochronology studies, which bet- ter trace major episodes of extension-related silicic magmatism and the silicic large igne- ous provinces. Much headway has been made in our understanding of these anomalous igneous events over the past 25 yr, driving many new ideas and models. (1) The global spatial and temporal distribution of large igneous provinces has a long-term average of one event approximately every 20 m.y., but there is a clear clustering of events at times of supercontinent breakup, and they are thus an integral part of the Wilson cycle and are becoming an increasingly important tool in reconnecting dispersed continental fragments. (2) Their compositional diversity in part reflects their crustal setting, such as ocean basins and continental interiors and margins, where, in the latter setting, large ig- neous province magmatism can be dominated by silicic products. (3) Mineral and energy re- sources, with major platinum group elements (PGEs) and precious metal resources, are hosted in these provinces, as well as magma- tism impacting on the hydrocarbon potential of volcanic basins and rifted margins through enhancing source-rock maturation, providing fluid migration pathways, and initiating trap formation. (4) Biospheric, hydrospheric, and atmospheric impacts of large igneous prov- inces are now widely regarded as key trigger mechanisms for mass extinctions, although the exact kill mechanism(s) are still being re- solved. (5) Their role in mantle geodynamics and thermal evolution of Earth as large igne- ous provinces potentially record the trans- port of material from the lower mantle or core-mantle boundary to the Earth’s surface and are a fundamental component in whole mantle convection models. (6) Recognition of large igneous provinces on the inner planets, with their planetary antiquity and lack of plate tectonics and erosional processes, means that the very earliest record of large igneous province events during planetary evolution may be better preserved there than on Earth.

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Geological Society of America Bulletin
doi: 10.1130/B30820.1 2013;125, no. 7-8;1053-1078Geological Society of America Bulletin
Scott E. Bryan and Luca Ferrari
understanding over the last 25 years
Large igneous provinces and silicic large igneous provinces: Progress in our
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Large igneous provinces and silicic large
igneous provinces: Progress in our understanding
over the last 25 years
Scott E. Bryan1,† and Luca Ferrari2,3,†
1School of Earth, Environmental and Biological Sciences, Queensland University of Technology, GPO Box 2434,
Brisbane, 4001, Australia
2Centro de Geociencias, Universidad Nacional Autonoma de Mexico, Boulevard Juriquilla 3001, Querétaro, 76230, Mexico
3Instituto de Geología, Universidad Nacional Autonoma de Mexico, Circuito Investigacion Cientifi ca, Ciudad Universitaria,
Mexico City, 04510, Mexico
ABSTRACT
Large igneous provinces are exceptional
intraplate igneous events throughout Earth’s
history. Their signifi cance and potential
global impact are related to the total volume
of magma intruded and released during these
geologically brief events (peak eruptions are
often within 1–5 m.y. in duration) where mil-
lions to tens of millions of cubic kilometers
of magma are produced. In some cases, at
least 1% of Earth’s surface has been directly
covered in volcanic rock, being equivalent to
the size of small continents with comparable
crustal thicknesses. Large igneous provinces
thus represent important, albeit episodic,
periods of new crust addition. However, most
magmatism is basaltic, so that contributions
to crustal growth will not always be picked up
in zircon geochronology studies, which bet-
ter trace major episodes of extension-related
silicic magmatism and the silicic large igne-
ous provinces. Much headway has been made
in our understanding of these anomalous
igneous events over the past 25 yr, driving
many new ideas and models. (1) The global
spatial and temporal distribution of large
igneous provinces has a long-term average
of one event approximately every 20 m.y.,
but there is a clear clustering of events at
times of super continent breakup, and they
are thus an integral part of the Wilson cycle
and are becoming an increasingly important
tool in reconnecting dispersed continental
fragments. (2) Their compositional diversity
in part refl ects their crustal setting, such as
ocean basins and continental interiors and
margins, where, in the latter setting, large ig-
neous province magmatism can be dominated
by silicic products. (3) Mineral and energy re-
sources, with major platinum group elements
(PGEs) and precious metal resources, are
hosted in these provinces, as well as magma-
tism impacting on the hydro carbon potential
of volcanic basins and rifted margins through
enhancing source-rock maturation, providing
fl uid migration pathways, and initiating trap
formation. (4) Biospheric, hydro spheric, and
atmospheric impacts of large igneous prov-
inces are now widely regarded as key trigger
mechanisms for mass extinctions, although
the exact kill mechanism(s) are still being re-
solved. (5) Their role in mantle geodynamics
and thermal evolution of Earth as large igne-
ous provinces potentially record the trans-
port of material from the lower mantle or
core-mantle boundary to the Earth’s surface
and are a fundamental component in whole
mantle convection models. (6) Recognition of
large igneous provinces on the inner planets,
with their planetary antiquity and lack of
plate tectonics and erosional processes, means
that the very earliest record of large igneous
province events during planetary evolution
may be better preserved there than on Earth.
INTRODUCTION
Silicic large igneous provinces, along with
their umbrella grouping of large igneous prov-
inces, represent one the outstanding areas of
major advance in the earth sciences over the past
25 yr. Large igneous provinces are currently de-
fi ned as magmatic provinces with areal extents
>0.1 Mkm2, igneous volumes >0.1 Mkm3, and
maximum life spans of 50 m.y. that have intra-
plate tectonic settings and/or geochemical affi n-
ities, and are characterized by igneous pulse(s)
of short duration (1–5 m.y.), during which a
large proportion (>75%) of the total igneous
volume was emplaced (Bryan and Ernst, 2008).
Continental fl ood basalt provinces, such as the
Deccan Traps, Siberian Traps, and Columbia
River fl ood basalt province, are some of the best
recognized examples of continental large igne-
ous provinces (Fig. 1). While continental fl ood
basalt provinces had been widely recognized
prior to 1988, it was not until the formative
work of Coffi n and Eld holm in the early 1990s
and the recognition of major igneous provinces
submerged along continental margins and in
ocean basins that a global record of episodic but
relatively frequent catastrophic igneous events
was identifi ed and collated (Coffi n and Eld-
holm, 1991, 1992, 1993a, 1993b, 1994, 2005).
Much of this initial recognition of large igneous
provinces focused on the relatively well-pre-
served Mesozoic and Cenozoic record (Fig. 1),
which has been critical to the development of
many key concepts for large igneous provinces
(Ernst, 2007a). Plate-tectonic theory has fo-
cused our attention on plate-boundary processes
to explain magmatism, but the realization that
large igneous province events recorded major
mantle melting processes unrelated to “nor-
mal” seafl oor spreading and subduction has
been an important addition to plate-tectonic
theory. Consequently, large igneous provinces
have been critical to the development of the
mantle plume hypothesis (e.g., Morgan, 1971;
Richards et al., 1989; Griffi ths and Campbell,
1990; Ernst and Buchan, 1997; Campbell,
2007) to explain intra plate magmatism, includ-
ing hotspots, far removed from plate boundar-
ies. Many large igneous provinces have been
attributed to deep mantle plumes (e.g., Richards
et al., 1989; Griffi ths and Campbell, 1990, 1991;
For permission to copy, contact editing@geosociety.org
© 2013 Geological Society of America
1053
GSA Bulletin; July/August 2013; v. 125; no. 7/8; p. 1053–1078; doi: 10.1130/B30820.1; 8 fi gures.
†E-mails: scott.bryan@qut.edu.au (corresponding
author); luca@unam.mx.
Invited Review
CELEBRATING ADVANCES IN GEOS CIENCE
1888 2013
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Bryan and Ferrari
1054 Geological Society of America Bulletin, July/August 2013
Figure 1. Global distribution of large igneous provinces (LIPs) following assembly of Pangea ca. 320 Ma. Annotated ages denote the onset
of the main phase or fi rst pulse of magmatism to the large igneous province event; note that some large igneous provinces may have pre-
cursor magmatism at lower intensity up to 10 m.y. prior, and age constraints on maximum ages for oceanic large igneous provinces remain
poorly constrained. Green tie lines connect oceanic large igneous provinces subsequently rifted apart by seafl oor spreading. The inferred
extent of some of the oldest large igneous province events is shown by a dashed line, as many remain poorly mapped and studied. Some
large igneous provinces are shown in small typeface to aid in fi gure clarity. Abbreviations: CAMP—Central Atlantic magmatic province;
EUNWA—European, northwest Africa; HALIP—High Arctic large igneous province; NAIP—North Atlantic igneous province; OJP—
Ontong Java Plateau; RT-ST—Rajmahal Traps–Sylhet Traps; SRP—Snake River Plain; KCA—Kennedy-Connors-Auburn. Figure is up-
dated and modifi ed from Bryan and Ernst (2008).
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Large igneous provinces and silicic large igneous provinces
Geological Society of America Bulletin, July/August 2013 1055
Campbell, 1998, 2001, 2005, 2007; He et al.,
2003). However, observed geological inconsis-
tencies with predictions of the mantle plume
theory (e.g., Frey et al., 2000; Korenaga, 2005;
Ukstins Peate and Bryan, 2008) have led many
authors to propose alternative models, including
decompression melting in a rift setting (White
and McKenzie, 1989, 1995), slab roll-back and
backarc extension (Carlson and Hart, 1987;
Rivers and Corrigan 2000; Long et al., 2012),
edge-driven convection (Anderson, 1996, 1998;
King and Anderson, 1998; Hames et al., 2003),
meteorite impact (Jones et al., 2002; Ingle and
Coffi n, 2004; Hagstrum, 2005), and mantle
lithospheric instabilities where downwellings
may occur in response to mantle plume impact
and fracturing/heating of the base of the litho-
sphere (e.g., Sengör, 2001), or which may be
generated by gravitational instabilities (e.g.,
Hales et al., 2005; Elkins Tanton, 2005, 2007).
AREAS OF ADVANCEMENT
IN OUR UNDERSTANDING OF
LARGE IGNEOUS PROVINCE
EVENTS SINCE 1988
Since 1988, substantial headway has been
made in many aspects of large igneous prov-
inces. Underpinning the significance of this
topic and as a global research focus over the
past 25 yr, fl ood basalt volcanism, and its link-
age to mass extinction events, represented one
of the top 100 research fronts in geosciences in
2012 (Web of Knowledge, accessed 30/1/2013).
The aim of this review paper is to fi rst provide
a “then and now” snapshot of our understanding
of the importance of large igneous provinces. In
the second part of the paper, we then discuss in
more detail, one of the new classes of large ig-
neous provinces recognized in the past 25 yr—
silicic large igneous provinces—with the Sierra
Madre Occidental of western Mexico used as
an example to illustrate the inter-relationships
between magmatism and continental rifting.
Two topics that are not discussed in detail here
are the substantial advancement in knowledge
of the physical volcanology of large igneous
provinces, particularly continental large igneous
provinces, and magnitude of large igneous prov-
ince basaltic and silicic supereruptions. These
topics have recently been extensively reviewed
by White et al. (2009) and Bryan et al. (2010),
respectively. To summarize, it is now gener-
ally recognized that fl ood basalt eruptions are
not the catastrophic and fast-fl owing fl oods of
lava originally envisaged (Shaw and Swanson,
1970), but instead, they are more analogous to
the largest historic basaltic eruptions in terms of
effusion rate, but where eruption life time is sus-
tained for years or decades along very long fi s-
sures (Swanson et al., 1975) to build up >1000 km3
lava fl ow fi elds (e.g., Self et al., 1996, 1997,
1998). Large igneous provinces are home to the
largest known basaltic and silicic eruptions (or
supereruptions) on Earth, with eruption magni-
tudes up to ~10,000 km3 or magnitude 9.4 now
recognized; many examples of both basaltic and
rhyolitic supereruptions are now known that far
exceed the erupted volume of the ~5000 km3
Fish Canyon Tuff, which is widely reported as
the largest known eruption (Bryan et al., 2010).
Large Igneous Province Events in the
Geologic Record
The large igneous province record has now
been extended back through the Paleozoic and
into the Precambrian, with the oldest recog-
nized large igneous province potentially as old
as 3.79 Ga (Isley and Abbott, 1999, 2002; Ernst
and Buchan, 2001; Ernst, 2013). For ancient
examples, this task has been made more dif-
fi cult due to the effects of erosion, burial, and
tectonic fragmentation, where only the plumb-
ing systems may now be preserved or remnants
now exist on different continents (e.g., Ernst
and Buchan, 1997; Bryan and Ernst, 2008).
As observed for the Mesozoic–Cenozoic large
igneous province record, many large igneous
provinces have been deconstructed by subse-
quent tectonic fragmentation, reducing their
size and preserved volumes such that it be-
comes unclear if the dispersed igneous rocks
were originally part of a large-volume igneous
event, and where its conjugate parts now reside.
Establishing the full extent of Paleozoic and
older large igneous provinces requires well-
constrained plate reconstructions, and a precise
knowledge of pre-Pangean supercontinental
confi gurations is currently lacking (Pisarevsky
et al., 2003; Bryan and Ernst, 2008; Ernst et al.,
2008; Li et al., 2008; Evans, 2009; Evans and
Mitchell, 2011; Meert, 2012; Zhang et al.,
2012). Paleomagnetic, geochemical, and espe-
cially geochronological studies have been piv-
otal to show that widely distributed dikes, sills,
layered intrusions, batholiths, and any erosional
remnants of volcanic rocks were emplaced syn-
chronously, have geochemical similarity, and,
therefore, likely to belong to the same event.
This is the large igneous province barcode ap-
proach of Bleeker and Ernst (2006), Ernst et al.
(2008), Ernst and Bleeker (2010), and Ernst
et al. (2013). One successful example of the
way in which an ancient, deeply eroded large
igneous province has been reconstructed is the
ca. 1270 Ma Mackenzie large igneous province
of North America (LeCheminant and Heaman,
1989; Ernst and Baragar, 1992; French et al.,
2002). High-precision radiometric (e.g., U-Pb)
age constraints of extensive, widely scattered
igneous rocks and dikes at a range of distances
along the >2400 km strike of the dike swarm
(>2.7 million km2 area) have helped to establish
that emplacement was essentially contempora-
neous across the enormous geographical extent.
Large Igneous Province Clusters
Large igneous province events are not dis-
tributed evenly through geologic time, and
from the Phanerozoic record, their frequency
is clearly linked to the supercontinent cycle,
being principally related to the period of Pan-
gea breakup (Fig. 1; e.g., Storey, 1995; Ernst
et al., 2005; Bryan and Ernst, 2008). Based on
the well-defi ned large igneous province record
for the past 150 m.y., a rate of ~1 large igneous
province per 10 m.y. has been estimated (Cof-
fi n and Eldholm, 2001), whereas a longer-term
rate of 1 large igneous province per 20 m.y. has
been estimated from the Proterozoic–Phanero-
zoic continental large igneous province record
(Ernst and Buchan, 2002; Ernst et al., 2005).
As the record has been expanded and improved
over the past 25 yr, principally driven by many,
and higher-precision geochronology studies,
researchers have realized the temporal coinci-
dence of several large igneous province events
(large igneous province clusters of Ernst et al.,
2005; see also Ernst and Buchan, 2002; Pro-
koph et al., 2004). Although with temporally
overlapping igneous activity, these events have
independently occurred on different tectonic
plates (large igneous province nodes of Bryan
and Ernst, 2008; Ernst et al., 2008). Four clear
examples of a temporal clustering of events in-
clude clusters at ca. 130 Ma, 120 Ma and 90 Ma,
with the most recent at 30 Ma (Fig. 2). Large
igneous provinces with dated igneous activity
at ca. 130 Ma include: (1) the Paraná-Etendeka
(Fig. 3), (2) Comei-Bunbury (Di-Cheng et al.,
2009), (3) High Arctic (Maher, 2001), (4) the
onset of magmatism in the Whitsunday; and
(5) terminal magmatism in the Shatsky Rise
(Papanin Ridge). Within 10 m.y., another major
large igneous province cluster had developed,
by ca. 120 Ma, with (1) the emplacement of the
megaoceanic plateau of Ontong Java, Manihiki,
and Hikurangi, (2) Pigafetta–East Marianas
ocean basin fl ood basalts (Tarduno et al., 1991;
Pringle, 1992) and probably the onset of Nauru
Basin fl ood basaltic volcanism (e.g., Saunders,
1989; Mochizuki et al., 2005); (3) Kerguelen–
Rajmahal Traps ± Wallaby Plateau (Kent et al.,
2002); (4) the onset of the peak of volcanism
in the Whitsunday silicic large igneous province
(Bryan et al., 1997, 2012), (5) formation of the
Mozambique Ridge (Gohl et al., 2011); and
(6) continued tholeiitic volcanism in the High
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Bryan and Ferrari
1056 Geological Society of America Bulletin, July/August 2013
Figure 2. Examples of large igneous province (LIP) clusters formed at ca. 130 Ma, ca. 120 Ma, ca. 90 Ma, and the most recent at 30 Ma.
Large igneous province types: CFB—continental fl ood basalt; OBFB—ocean basin fl ood basalt; OP—oceanic plateau; SLIP—silicic large
igneous province; VRM—volcanic rifted margin. Abbreviations: HALIP—High Arctic large igneous province; MP— Madagascar Plateau;
MR—Mozambique Ridge; OJP—Ontong Java Plateau; RT—Rajmahal Traps; ST—Sylhet Traps; WP—Wallaby Plateau; ODP—Ocean
Drilling Program.
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Large igneous provinces and silicic large igneous provinces
Geological Society of America Bulletin, July/August 2013 1057
C
D
AB
Figure 3. Outcrop characteristics of the continental fl ood basalt provinces, the most intensely studied large igneous provinces. (A) View
across mesas in the Awahab region in the southern Etendeka (Paraná-Etendeka) large igneous province, exposing fl at-lying fl ood basalt
lavas with the ~6866 km3 Springbok quartz latite rheomorphic ignimbrite capping mesas in the distance. (B) A deeply incised section
through the central part of the Permian Emeishan fl ood basalt province near Lijang, Yunan Province (China), where an ~1-km-thick,
gently tilted fl ood basaltic lava succession is exposed and rises to elevations >3000 m above sea level. The Emeishan large igneous
province has come to prominence over the last 10 yr due to interpretations that it provides the best-documented example of mantle
plume–induced domal uplift (He et al., 2003; Campbell, 2007), but this has recently been discounted (Ukstins Peate and Bryan, 2008).
(C) A cliffed section of mainly Wanapum Basalt Formation lavas from the Columbia River large igneous province exposed at Blue Lake,
Washington. The cliff height is 120 m from lake to top. Photo courtesy of Steve Self. (D) Panoramic view of the imposing ca. 132–130 Ma
Brandberg anorogenic granitic massif of the Paraná-Etendeka large igneous province, Namibia, which is ~23 km diameter, rises
~2000 m above the surrounding plains, and is fl anked by fl ood basalt lavas (FB) that gently dip in toward the intrusive complex.
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Bryan and Ferrari
1058 Geological Society of America Bulletin, July/August 2013
Arctic large igneous province (Maher, 2001;
Buchan and Ernst, 2006). The ca. 90 Ma large
igneous province cluster includes the Mada-
gascar fl ood basalt province (and probably the
offshore Madagascar Ridge, Crozet Plateau, and
Conrad Rise), the fi rst peak of volcanism in the
Caribbean large igneous province (Colombia-
Caribbean oceanic plateau; see review of age
data in Serrano et al., 2011), and terminal phases
of the High Arctic large igneous province and
Ontong Java oceanic plateau (see also Ernst
and Buchan, 2002). Oceanic plateaus emplaced
at 90 Ma were volumetrically substantial, with
an estimated combined igneous volume of >18
million km3 (Kerr, 2013). The youngest large ig-
neous province cluster at 30 Ma is represented
by the overlap of peak activities in the Afro-Ara-
bian continental fl ood basalt and Sierra Madre
Occidental silicic large igneous provinces (e.g.,
Hofmann et al., 1997; Ukstins et al., 2002;
Cather et al., 2009; Bryan et al., 2013).
The occurrence of large igneous province
clusters is signifi cant for a number of reasons.
First, it has led to the suggestion of superplumes,
where large igneous province events are inter-
preted to record one or more large core-mantle
boundary–derived mantle plumes, triggering in-
creased convection in the outer core, halting the
magnetic reversal process for tens of millions
of years, and increasing oceanic crust produc-
tion and mantle outgassing (Larson, 1991; cf.
plume-clusters of Ernst and Buchan, 2002). It
is now clear that any Cretaceous “superplume”
event was not restricted to the Pacifi c Basin
(Larson, 1991), but was much more global in
its extent (Fig. 2), and other explanations have
been proposed (e.g., Anderson, 1994). Second,
large igneous provinces are playing a key role
in Precambrian supercontinent reconstructions
(e.g., Bleeker and Ernst, 2006), where ages of
large igneous provinces present on different
terranes are compared, and age matches in a
given interval are established. These are then
used as supporting evidence for those terranes
being nearest neighbors during that time inter-
val (Ernst, 2007a). Reconstruction is further
enhanced by paleomagnetic studies, geochemi-
cal comparisons, and identifi cation of intraplate
compositions, and the use of the geometry of
dike swarms (linear, radiating) to orient the ter-
ranes (Bleeker and Ernst, 2006; Ernst, 2007a).
However, the Mesozoic–Cenozoic record high-
lights the problem of deciding whether coeval
magmatic units that are located on different
cratons actually should be reconstructed into a
single large igneous province or whether they
represent simultaneous but independent events
(Bryan and Ernst, 2008). Temporal overlaps
and geochemical similarities will not be suf-
fi cient for robust terrane reconstructions in the
Precambrian (see also Ernst et al., 2008). Third,
large igneous province events have been consid-
ered important drivers of environmental change,
coinciding with mass extinctions (e.g., Cour-
tillot and Renne, 2003; Wignall, 2001, 2005).
Therefore, the co-occurrence of multiple large
igneous province events globally and both in the
oceans and on the continents would be predicted
to greatly enhance their capacity to drive mass
extinctions. Interestingly, the 130 and 120 Ma
large igneous province clusters, which represent
in excess of 100 million km3 of new, dominantly
mafi c igneous crust, and which account for
the majority of new igneous rock produced by
large igneous province events in the breakup of
Pangea, do not correlate with the largest mass
extinction events or extreme environmental
changes (see following). Instead, the largest
mass extinction events have coincided with a
single continental large igneous province event,
and why a single large igneous province event
may be more signifi cant than global clusterings
of events remains unclear.
Large Igneous Province Events and
Continental Breakup
Large igneous provinces are intimately linked
to continent and supercontinent plate breakup
(e.g., Courtillot et al., 1999; Ernst and Bleeker,
2010). Large igneous province–related breakup
produces volcanic rifted margins, new and large
(up to 108 km2) ocean basins, and new, smaller
continents that undergo dispersal and ultimately,
reassembly (e.g., India). It is now recognized
that up to 90% of the global rifted continental
margins are volcanic rifted margins (Skogseid,
2001; Menzies et al., 2002), with only a few
margin segments characterized as being unusu-
ally magma poor. Most continental-scale rifts
that proceed to seafl oor spreading develop in
association with large igneous provinces, and
recent studies are recognizing the importance of
magmatism and dike intrusion in rift evolution,
such that large magma volumes can facilitate the
transition to tectonic rifting (Corti et al., 2003;
Bialas et al., 2010). Nevertheless, the rift stage
for many volcanic rifted continental margins
lasts between ~20 and 40–50 m.y. (Umhoefer,
2011). More recently, large igneous province
fragmentation has also been recognized as an
important process in the oceanic realm, where
propagation of mid-ocean-ridge spreading cen-
ters and ridge jumps break up oceanic large ig-
neous provinces, as suggested for the Ontong
Java–Manihiki and Hikurangi plateau fragments
(Taylor, 2006). Rifting apart of oceanic large ig-
neous provinces by new oceanic spreading cen-
ters seems commonplace (Fig. 1), and in some
cases, rifting appears to occur soon after the
termination of large igneous province magma-
tism (within 5–20 m.y.; e.g., Worthington et al.,
2006; Parsiegla et al., 2008). It remains unclear
why thickened and strengthened oceanic crust
of an oceanic plateau should be preferentially
rifted apart, where crustal thicknesses may be
up to 40–45 km (Coffi n et al., 2012). It is inter-
esting to note that at the fi rst-order, the sequence
of events in lithospheric rupturing shows little
difference between continental and thickened
oceanic crust.
However, not all continental large igneous
provinces lead to continental rupture, and the
controls on which large igneous provinces lead
to breakup remain poorly understood. This is
despite the fact that all Mesozoic to Cenozoic
continental large igneous provinces were em-
placed into regions of either prior or coeval ex-
tension (Bryan and Ernst, 2008). One factor that
may prevent continental rupturing is whether or
not the adjacent continental margin is undergo-
ing subduction, such that contractional forces
are transmitted into the overriding plate. How-
ever, evidence for upper-plate contraction at the
time of large igneous province emplacement is
poorly documented, and the relative distance of
large igneous province magmatism to the active
plate boundary (often >500 km), coupled with
evidence for crustal extension, suggests that
plate-boundary forces are not strongly control-
ling the ability of the lithosphere to rupture at
the site of large igneous province magmatism.
As discussed later herein, new research is now
suggesting the Sierra Madre Occidental was
the prerift large igneous province event to the
Gulf of California (Bryan et al., 2013), which
is a young ocean basin that has opened in close
proximity to the plate boundary.
The Central Atlantic magmatic province,
emplaced at ca. 201 Ma, is widely recognized
as heralding the breakup of Pangea (e.g., Mar-
zoli et al., 1999, 2011; McHone, 2000), but in
detail, the earliest magmatism was partly em-
placed into and across preexisting extensional
basin structures (e.g., Olsen, 1997; Schlische
et al., 2003; Marzoli et al., 2004; Nomade et al.,
2007). This is a feature of most late Paleozoic
to Cenozoic continental large igneous provinces
(Bryan and Ernst, 2008; see also Meyer et al.,
2007). Continental large igneous provinces gen-
erally precede continental rupture and ocean
basin opening, and the correlation of eruptive
units across the South Atlantic for the Paraná-
Etendeka large igneous province (Milner et al.,
1995; Marsh et al., 2001; Bryan et al., 2010)
supports, in this case, the large igneous prov-
ince principally being a prerift event. Several
provinces also have synrift igneous pulses (e.g.,
North Atlantic—Saunders et al., 1997; Meyer
et al., 2007). Ancient large igneous provinces
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Large igneous provinces and silicic large igneous provinces
Geological Society of America Bulletin, July/August 2013 1059
are now being used to piece together the ancient
supercontinents of Rodinia, Nuna, and Supe-
rior, and also constrain the timing of ancient
supercontinent cycles (e.g., Ernst, 2007a; Ernst
et al., 2008; Ernst and Bleeker, 2010). Large ig-
neous provinces are thus a critical component
of the Wilson cycle, and the Atlantic, Indian,
and Antarctic Ocean ridge spreading systems
can therefore be considered as the consequence
of large igneous province events (Bryan and
Ernst, 2008).
Crustal Setting of Large Igneous Provinces
Following recognition of large igneous
province events throughout the geologic rec-
ord, a clearer picture of the range of crustal
settings (cratons, continental margins, ocean
basins) has emerged (Bryan and Ernst, 2008).
Although a wide variety of large igneous prov-
ince types were initially recognized by Coffi n
and Eldholm (1992, 1994), this was strongly
infl uenced by Mesozoic to Cenozoic examples,
and by vol canic features on the seafl oor, such
that seamount groups and submarine ridges
dominated the initial large igneous province in-
ventory. However, these province types are no
longer considered to be large igneous provinces
(Bryan and Ernst, 2008), and the term “large ig-
neous province” is now restricted to encompass-
ing the continental fl ood basalts, volcanic rifted
margins, silicic large igneous provinces, oceanic
plateaus, ocean basin fl ood basalts, Archean
greenstone-komatiite belts, and giant continen-
tal dike swarms, sills, and mafi c-ultra mafi c in-
trusive provinces (Bryan and Ernst, 2008). Many
Proterozoic–Paleo zoic large igneous provinces
occur as eroded fl ood basalt provinces, exposing
their intrusive underpinnings, while the green-
stone belts of the tholeiite-komati ite association
most likely represent Archean large igneous
provinces (Ernst, 2007a; see also Campbell
and Hill, 1988). Silicic large igneous provinces
refl ect their crustal setting along young, fertile
continental margins (Fig. 1) built up by paleo-
subduction processes, and where crustal par-
tial melting overwhelmed the igneous system
(Bryan et al., 2002; Bryan, 2007).
Large Igneous Province Events and
Crustal Growth
Large igneous province events typically rep-
resent the outpouring of >1 Mkm3 of magma,
which can cover millions of square kilometers of
the Earth’s surface. However, a large proportion
of the igneous volume generated during a large
igneous province event does not reach the sur-
face and remains stored at all depths in the litho-
sphere. Deeply eroded large igneous provinces,
as represented by the giant continental dike
swarms and mafi c-ultramafi c intrusive prov-
inces (Ernst and Buchan, 1997; Ernst, 2007a;
Bryan and Ernst, 2008; Ernst and Bleeker,
2010), provide windows into the plumbing
system and subsurface storage of large igneous
province magmas. Some estimates suggest that
the ratio of extruded to intruded magma is 1:10
(White and McKenzie, 1989; Bryan and Ernst,
2008). Oceanic plateaus are the largest large
igneous provinces preserved on Earth in terms
of area and igneous volume, and the Cretaceous
marked a peak in oceanic plateau formation
(e.g., Larson, 1991; Kerr, 1998, 2003, 2005). To
emphasize the continental scale of some large
igneous province events, the prerift reconstruc-
tion of the oceanic plateau fragments of Ontong
Java, Manihiki, and Hikurangi (Taylor, 2006)
results in a single plateau originally the size
of the Indian subcontinent. Due to their excess
crustal thicknesses, oceanic plateaus are dif-
fi cult to subduct (e.g., Cloos, 1993, but cf. Liu
et al., 2010), such that at least their uppermost
sections are accreted to continental margins,
and thus, the accretion of oceanic plateaus is an
important contributor to crustal growth (Kerr,
2013). Consequently, large igneous province
events represent major, juvenile lithosphere-
building episodes and are important to factor
into crustal growth models (e.g., Condie, 2001;
Hawkesworth and Kemp, 2006) and orogenesis
(van Hunen et al., 2002; Liu et al., 2010). The
clustering of large igneous province events at
times of supercontinent breakup, when hun-
dreds of millions of cubic kilometers of magma
are emplaced, and the substantial development
of volcanic rifted margins during the breakup
of Pangea (e.g., Skogseid, 2001; Menzies et al.,
2002) confi rm that magma volumes are actu-
ally very high in continental breakup settings
(cf. Cawood et al., 2013). However, because
magmatism is fundamentally basaltic, large
igneous province magmatism typically yields
little to no age signature of new zircon growth
(except for silicic large igneous provinces), and
their substantial mafi c igneous contribution to
crustal growth will largely go unrecorded in zir-
con-based crustal growth studies (e.g., Condie,
1998; Condie et al., 2009; Condie and Aster,
2010; Iizuka et al., 2010; Cawood et al., 2013).
Although the long-term average is ~1 event
every 20 m.y. (Ernst et al., 2005), large igneous
province events are relatively strongly linked to
supercontinent breakup and, for example, show
a very strong clustering in the last ~300 m.y.,
related to Pangea breakup (Fig. 1). For example,
25 continental large igneous provinces are rec-
ognized from 325 to 0 Ma, but only fi ve have
so far been recognized from 325 to 550 Ma, a
period of Pangea assembly (Bryan and Ernst,
2008; Grofl in and Bryan, 2012). In contrast, six
well-defi ned large igneous province events can
be recognized for the relatively short breakup
history of Rodinia between ca. 825 Ma and
700 Ma, which may also include another two
possible fragments of continental large igneous
provinces (Ernst et al., 2008). This large igneous
province episodicity is consistent with a more
pulsed history to lithospheric growth.
Large Igneous Provinces and Mass
Extinction Events
The origin of sudden mass extinction events
has attracted substantial research effort, and extra-
ordinary and geologically rapid events such as
large igneous provinces and large, high-veloc-
ity impacts of asteroids or comets with Earth
are widely considered to be the most plausible
causes for the fi ve major mass extinction events
at the end-Ordovician, mid-Devonian (Fras-
nian–Fammenian), end-Permian, end-Triassic,
and end-Cretaceous (Hallam and Wignall,
1997). In particular, a near-perfect association
exists between extinction events and large ig-
neous province events over the last 300 m.y.,
such that the general consensus now is that large
igneous province events are suffi ciently global
in their occurrence and impact that they can
trigger mass extinction events (Courtillot and
Renne, 2003; Wignall, 2005). This is because
large igneous provinces are unique in being the
loci for both basaltic and silicic supereruptions
(magnitude >8 or >360 and >410 km3 of basaltic
and rhyolitic magma, respectively) throughout
Earth history, and for the substantial cumulative
volumes (>105–107 km3) of magma emplaced
over brief periods (1–5 m.y.), which ultimately
results from tens to hundreds of M >8 eruptions
and intrusions (Bryan et al., 2010).
However, it has also been recognized that
many large igneous province events do not co-
incide with major environmental change or a
mass extinction. This is also the case for large
asteroid impacts (White and Saunders, 2005),
with only the end-Cretaceous extinction event
being clearly linked with an asteroid impact
(e.g., Alvarez et al., 1980; see review in Schulte
et al., 2010), although greater numbers of large
meteorite impacts are now being recognized
that have coincided with extinction events (e.g.,
Tohver et al., 2012). Additionally, no correla-
tion exists between the magnitude of the large
igneous province event and the corresponding
mass extinction (see Fig. 9 in Wignall, 2001),
as might be predicted for the severity of an
extinc tion event due to an asteroid impact. For
example, the end-Permian mass extinction was
the most devastating in Earth history and was
characterized by the sudden loss of >90% of
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1060 Geological Society of America Bulletin, July/August 2013
marine species and >70% of terrestrial species
(Erwin, 1994), yet the Siberian Traps large igne-
ous province, which is proposed as the trigger
for this mass extinction, with an estimated size-
able volume of ~4 million km3 (Fedorenko et al.,
2000), is dwarfed by many of the oceanic large
igneous provinces, such as the prerifted Ontong
Java–Manihiki–Hikurangi megaplateau, which
has an igneous volume of up to 77 million km3
(Kerr and Mahoney, 2007). In addition, large
igneous province clusters (e.g., Fig. 2) do not
seem to correlate with mass extinction events.
Consequently, proof of the nature of the causal
links between large igneous provinces and ex-
tinction events, and whether the juxtaposition of
effects from large igneous province volcanism
and an asteroid impact is required to cause the
largest mass extinctions (White and Saunders,
2005), is far from resolved (Wignall, 2005).
There are three main issues in establishing
a causal link between large igneous province
event(s) and a mass extinction: (1) The large ig-
neous province event(s) must coincide with an
extinction event, and this temporal coincidence
is strongly dependent on our ability to precisely
date the duration and peak(s) of large igneous
province events, as well as the timing of the
mass extinction, which is generally thought to
last ~100,000 yr or less (e.g., Rampino et al.,
2000; Rampino and Kaiho, 2012; cf. Huang
et al., 2011); (2) the kill mechanism(s) must be
constrained; and (3) the eruptive mechanisms by
which large igneous province eruptions can per-
turb global climate or modify the environment
must be identifi ed, and their impact on a wide
variety of terrestrial and marine ecosystems
must be explored.
Contemporaneity of Large Igneous Province
Events and Mass Extinctions
Linking mass extinction with the onset and
tempo of large igneous province eruptions
has proved diffi cult because of the geographic
separation between large igneous provinces and
stratigraphic sequences preserving evidence of
the extinction (Blackburn et al., 2012). Conse-
quently, an accurate temporal relationship be-
tween the onset of eruption and the main pulse
of large igneous provinces and a correlated
mass extinction requires precise geochronol-
ogy, but this remains unclear for a number of
large igneous provinces (see Fig. 3 in Kelley,
2007, for example ), despite improved instru-
mentation (e.g., see review by Corfu, 2013) and
geo chrono logi cal advances (e.g., Mundil et al.,
2004). This includes the Siberian Traps (Bow-
ring et al., 1998; Kamo et al., 2003; Black et al.,
2012), the Afro-Arabian large igneous prov-
ince (Ukstins et al., 2002), and until recently,
the Central Atlantic magmatic province (e.g.,
Nomade et al., 2007), as recent studies are now
more clearly establishing peak volcanic activity
at the Triassic-Jurassic boundary (Marzoli et al.,
2011; Blackburn et al., 2012; Kerr, 2012). Early
work, including sampling of fl ood basalt lava
piles, assumed overly simplistic layer-cake stra-
tigraphies for large igneous provinces, and much
more complex lava stratigraphies and facies
architectures are now apparent (e.g., Jerram ,
2002; Jerram and Widdowson, 2005; Jay et al.,
2009); the consequence is that while the main
phase or some pulses of volcanism in some parts
of the large igneous province may be well con-
strained, the entire eruptive history of a large
igneous province in many cases still remains
very poorly constrained. This is particularly the
case for oceanic large igneous provinces, where,
often, only the top few hundred meters in a few
widely separated locations have been sampled
by ocean drilling programs (e.g., Tejada et al.,
2004). Furthermore, recent studies are now fi nd-
ing missing pieces to large igneous provinces
where they had been rifted away following
continental breakup (e.g., Comei province; Di-
Cheng et al., 2009), raising the possibility that
any one fl ood basalt province may be a partial
record to a larger large igneous province event.
For older large igneous provinces where sig-
nifi cant erosion has removed much of the vol-
canic pile (e.g., giant continental dike swarms,
sills and mafi c-ultramafi c intrusive provinces
of Bryan and Ernst, 2008), identifi cation of the
main eruptive pulse(s) is dependent on the ex-
posed intrusive record. Studies of younger large
igneous provinces such as the Afro-Arabian
have shown that temporal differences can exist
between extrusive and intrusive events, such
that the exposed hypabyssal, plutonic rocks and
dike swarms are younger and biased toward dat-
ing crustal extension (Menzies et al., 1997).
High-resolution chronology using zircon or
feldspar is commonly hindered in large igneous
provinces because phenocrystic zircon is not
present in the fl ood basalt lavas/volcaniclastic
rocks (but can be present in intrusions), and the
basalts are commonly either aphyric or altered,
lacking fresh feldspar for 40Ar/39Ar dating. A
further complication arises in that where fl ood
basalt lavas do contain crystals, they can be
recycled (i.e., antecrystic; Ramos et al., 2005;
Vye et al., 2009). Dating stratigraphic bound-
aries has also been fraught with diffi culties
(e.g., Mundil et al., 2004). Other studies have
drawn attention to issues regarding interlabora-
tory variability (e.g., Thiede and Vasconcelos,
2010) or discrepancies in the comparison of
U-Pb and 40Ar/39Ar ages (e.g., Min et al., 2000;
Nomade et al., 2007) in pinning down the main
eruptive phase(s) of large igneous provinces and
their coincidence with time boundaries. Con-
sequently, while more recent studies are now
illus trating that some key large igneous prov-
ince events, based on the dated main phase of
volcanism, may slightly either pre- or postdate
the corresponding mass extinction event (e.g.,
Kelley, 2007), the true age duration of large
igneous province events and the way in which
they precisely correspond to extinctions and en-
vironmental changes require further study, and
still face geological (i.e., preservation) and ana-
lytical limitations.
Kill Mechanisms of Large Igneous
Province Events
While large igneous province events are
considered the trigger mechanism initiating
reactions that lead to environmental conditions
resulting in the death of organisms (Knoll et al.,
2007), the kill mechanism(s) or the nature of
the actual environmental condition that caused
death and mass extinction remains unclear. This
is because of the observation that only some
large igneous province events have coincided
with mass extinctions and others have not,
and that little correlation exists between the
magnitude of the large igneous province event
and the corresponding mass extinction. The
implications are that large igneous province
events may not always be triggers, the coinci-
dence with an asteroid impact may be required
(White and Saunders, 2005), ecosystems may
have already been under stress in those cases
where mass extinction occurred, or large ig-
neous provinces may lead to more than one
type of kill mechanism. Several specifi c kill
mechanisms have been identifi ed (e.g., Wignall,
2005), such as greenhouse warming and ocean
acidifi cation resulting from CO2 overloading
of the atmosphere; atmospheric cooling due to
stratospheric SO2 injections; oceanic anoxia/
euxinia (e.g., Kump et al., 2005) triggered by
ocean warming, increased atmospheric carbon
dioxide or H2S levels and nutrient supply, and
decreased ocean circulation; ozone depletion
and mutagenesis (Visscher et al., 2004; Beerling
et al., 2007); methane clathrate release (e.g.,
McInerney and Wing, 2011); and thermogenic
methane release due to large igneous province
magma inter action with coal-rich sedimentary
basins (Svensen et al., 2004, 2007, 2009).
Volcanic aerosol release associated with fl ood
basaltic volcanism during large igneous province
events is thought to have infl uenced the environ-
ment in two ways (Self et al., 2005): (1) Sulfuric
acid (H2SO4) aerosols generated from volcanic
SO2 emissions that scatter and absorb incom-
ing solar radiation increase atmospheric opacity
and cause atmospheric cooling (e.g., Rampino
and Self, 2000); or (2) greenhouse gas CO2
emissions contribute to atmospheric warming
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Large igneous provinces and silicic large igneous provinces
Geological Society of America Bulletin, July/August 2013 1061
(e.g., Olsen, 1999; Wignall, 2001, 2005). For
oceanic plateaus, CO2 emissions are thought to
be particularly important, contributing to ocean
acidifi cation, global warming, and potentially
runaway greenhouse conditions (see summary
in Kerr, 2013). Oceanic plateaus are commonly
related to periods of black shale deposition
and evidence for oceanic anoxia (e.g., Sinton
and Duncan, 1997; Kerr, 1998, 2005, 2013),
and the combination of subsurface anoxia and
ocean acidifi cation may have been important
in marine extinctions at the end of the Permian
Period (see summary in Knoll, 2013). In addi-
tion, the physical emplacement of the basaltic
plateaus in the oceans is thought to have resulted
in sea-level rises, disturbance of oceanic circula-
tion systems and thus nutrient upwelling events,
causing increased biological productivity in
surface waters, and the catastrophic release of
ocean-fl oor clathrates, all of which contribute to
ocean anoxia (Kerr, 1998, 2005, 2013). How-
ever, other studies, based on continental fl ood
basalt provinces have concluded that warming
due to CO2 release from lava/magmas is likely
to have been insignifi cant because the mass of
CO2 was less than that already present in the
atmosphere for some large igneous province
events (Self et al., 2005). Furthermore, it also
appears that annual anthropogenic CO2 emis-
sions may already exceed the estimated annual
CO2 emissions of continental fl ood basalt erup-
tions (Gerlach, 2011).
In contrast, SO2 emissions and the atmo-
spheric burden of sulfate aerosols generated
during large igneous province events appear
to be unprecedented at any other time in Earth
history (Self et al., 2005, 2006). The mass of
H2SO4 aerosols injected into, and produced in,
the stratosphere (and the upper troposphere)
appears to be the single most signifi cant factor
controlling the magnitude of the climatic impact
(Thordarson et al., 2009); acid rain (Self et al.,
2005) and ocean anoxia (Kump et al., 2005) are
also likely consequences. Petrologic estimates
of SO2 released during large igneous province
fl ood basaltic eruptions would have formed
considerable amounts of sulfate aerosols, with
effects lasting at least as long as the eruptions
persisted (decades and possibly longer ; Self
et al., 2005, 2006), and recent melt inclusion–
based studies of the Siberian Traps have es-
timated that magmatic degassing contributed
prodigious amounts of sulfur (~6300–7800 Gt)
to the atmosphere (Black et al., 2012). However,
strong atmospheric cooling trends are not ap-
parent for all large igneous province events and
those correlated with mass extinctions (Wignall,
2005), and delivery to the stratosphere, which
is dependent on eruptive mechanisms, is a criti-
cal prerequisite for ozone depletion and global
climatic effects (Thordarson et al., 2009; Black
et al., 2012). It has also been suggested that an
upper limit may exist as to how much sulfate
aerosol can be stored in the stratosphere as
larger, negatively buoyant sulfate particles may
form through coagulation and rain out, limiting
the potential increase in the optical depth of the
atmosphere (Pinto et al., 1989; Timmreck et al.,
2010). However, this potential self-limiting
process will depend on the location(s), rate, and
height of aerosol delivery into the stratosphere,
and stratospheric wind patterns that can quickly
disperse aerosols globally and minimize aerosol
particle interactions.
Recent studies have focused on the emplace-
ment environments of those large igneous prov-
inces that were contemporaneous with mass
extinction events. In particular, large igneous
province emplacement through, and onto,
hydro carbon- and/or evaporite-rich sedimentary
basins particularly distinguishes those events
at the Permian-Triassic and Paleocene-Eocene
boundaries (e.g., Svensen et al., 2004, 2009).
In these cases, contact metamorphism of coal
and other carbonaceous sediments generated
carbon gases and probably halocarbons, bolster-
ing the volcanic aerosol emissions (Retallack
and Jahren, 2008; Svensen et al., 2009; Black
et al., 2012). In the case of the end-Permian
mass extinction, the end-Permian negative car-
bon isotope excursion and global warming are
consistent with basinwide thermogenic meth-
ane generation resulting from contact meta-
morphism with intruded fl ood basaltic magmas
(Svensen et al., 2009). Additional evidence for
ozone destruction at the time of the end-Permian
extinction comes from the prevalence of mutant
pollen tetrads, which has been related to vol-
canic emissions of chlorine and fl uorine com-
pounds (Visscher et al., 2004). Recent studies
support substantial F, Cl, and Br emissions from
Siberian Traps eruptions that would have had
profound effects on atmospheric chemistry and
substantial ozone destruction (Beerling et al.,
2007; Svensen et al., 2009; Black et al., 2012).
Virtually all these kill mechanisms have been
linked to basaltic magmas intruded and extruded
in large igneous province events. However, re-
cent studies (e.g., Cather et al., 2009) are draw-
ing attention to the role of large-volume silicic
magmatism during large igneous province
events that can more effi ciently contribute to
aerosol loading of the stratosphere. In addi tion,
the large-volume explosive silicic vol canism
during large igneous province events can signifi -
cantly force global cooling by iron fertili za tion
of oceans triggered by volcanic ash deposition
(Cather et al., 2009; Olgun et al., 2011). Iron
fertilization may decrease oceanic and subse-
quently atmospheric CO2 concentrations by in-
creasing the photosynthetic conversion of CO2
to organic carbon (e.g., Cooper et al., 1996).
In summary, rather than thermal perturba-
tions to global climate, large igneous province
events may have their greatest environmental
impact through prolonged ozone-layer destruc-
tion. Directions for future research will be in
examining the paired effects on atmospheric
chemistry/structure and ocean chemistry of re-
peated closely spaced and even synchronous
large-volume mafi c and silicic eruptions that can
characterize the main pulses of continental large
igneous province events, determining the gases
that are most effective in causing environmental
damage/deterioration, or ascertaining whether it
is a cocktail of gases and the combined effects
of S, Cl, F, Br, and CO2/CH4.
Large Igneous Province Eruptive
Mechanisms
Delivery of volcanic aerosols to the strato-
sphere is a critical prerequisite for ozone deple-
tion and global climatic effects (Black et al.,
2012). This is because precipitation will remove
volcanic aerosol contributions from the tropo-
sphere quickly, and effects will be only regional
in extent (Thordarson et al., 2009). Work over
the past 15 yr on continental fl ood basalt prov-
inces has shown that the massive lava fl ows that
typify large igneous provinces (Figs. 3 and 4) are
giant pahoehoe and rubbly pahoehoe fl ow fi elds
produced by many, but prolonged supererup-
tions that most likely lasted for years to decades
(Self et al., 1996, 1997, 1998; Thordarson and
Self, 1996, 1998; see review in White et al.,
2009). Importantly, aerosol emissions associ-
ated with these eruptions would also have lasted
over the eruption duration, lasting several years
to a few decades (Thordarson et al., 2009). This
contrasts with silicic explosive supereruptions,
including those during large igneous province
events, where magma and volatile discharge is
brief (days to weeks; e.g., Bryan et al., 2010),
and based on observations of modern explosive
eruptions, aerosol and ash residence times in the
stratosphere are expected to be in the order of
a few years. While basaltic supereruptions are
prolonged, the eruptions that feed fl ood basalt
lava fi elds have generally low eruption heights
(≤10 km), and estimated effusion rates approach
the largest witnessed basaltic eruptions (Self
et al., 1997). Unlike silicic explosive eruptions,
fl ood basalt eruptions therefore lack obvious
eruptive mechanisms to inject huge volumes
of ash and aerosols directly and quickly into
the stratosphere (Bryan, 2007), even if they are
asso ciated with large SO2 and other gas emis-
sions (Self et al., 2005, 2006; Black et al., 2012).
Mafi c volcaniclastic deposits are common
to many large igneous provinces, and the most
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1062 Geological Society of America Bulletin, July/August 2013
signifi cant deposit volumes are present where
they result from phreatomagmatic eruptions
(see reviews by Ross et al., 2005; White et al.,
2009; Fig. 4B). In these cases, explosivity and
thus potentially higher eruption column heights
have resulted from the water interaction, thus
enabling Plinian-type dispersal and strato-
spheric delivery of aerosols (Ross et al., 2005;
Black et al., 2012). Several tephra layers in
the North Atlantic large igneous province have
Plinian-like distributions, indicating that tall ba-
saltic eruption plumes were developed (see Ross
et al., 2005, and references therein). However,
unlike magmatically driven explosive eruptions,
the ingestion of cold water and a potentially
high content of cold rock fragments increases
plume density, such that they will be prone to
collapse, producing density currents. Refl ect-
ing this, in many large igneous provinces, mafi c
volcaniclastic deposits of phreatomagmatic ori-
gin commonly include abundant coarse lapilli-
tuffs and tuff-breccias (e.g., Ferrar, Emeishan,
Karoo, Siberia; Fig. 4B), which are interpreted
to have been deposited proximal to the source
vents (White et al., 2009). Therefore, basaltic
phreatomagmatic volcanism does not appear
to be a primary mechanism for sustained deliv-
ery of aerosols to the stratosphere from fl ood
basaltic magmas.
The general model interpreted for effusive
fl ood basalt eruptions is that they are fi ssure-
fed eruptions and often scaled-up versions of
relatively large historic eruptions (e.g., Self
et al., 1996, 1997; White et al., 2009). Important
aspects of this analogy are that: (1) each fl ood
basalt eruptive event likely featured multiple
eruption episodes, where each episode began
with a relatively short-lived (hours to days?)
explosive phase, followed by a longer-lasting ef-
fusive phase; and (2) at any one time, eruptive
activity was confi ned to distinct segments on the
fi ssure vent system, such that estimated mean
eruption rates of ~4000 m3 s–1 would have been
able to maintain 5–9-km-high columns through-
out the eruption and potentially penetrate into the
stratosphere with up to 20-km-high columns, but
only during periods of peak lava fl ux and under
favorable atmospheric conditions (Thordarson
et al., 2009). A critical factor, then, to the success
of fl ood basalt eruptions in delivering aerosols to
the stratosphere is the height of the tropopause,
which is strongly latitude and climate dependent,
and currently varies from 17 km at the equator to
<10 km near the poles. Flood basaltic eruption
plumes may have been able to regularly inject
SO2 and other aerosols into the stratosphere at
high latitudes, where the tropopause boundary is
lower. However, large-scale subsidence through
the stratosphere dominates at high latitudes (e.g.,
Holton et al., 1995), preventing interhemispheric
circulation and effectively limiting aerosol and
ash dispersion to the high latitudes and tropo-
sphere (Bryan, 2007). At low latitudes, it appears
less likely that eruption plumes from fl ood ba-
salt eruptions would be able to penetrate into the
stratosphere and for any length of time.
Silicic supereruptions during large igneous
province events are expected to have produced
substantial and tall plumes, both at the vent,
given the tremendously high eruptive mass fl ux
(up to 1011 kg s–1; Bryan et al., 2010), and as
buoyant coignimbrite ash plumes that would
have reached the stratosphere, collectively de-
livering prodigious amounts of ash and aerosols
at multiple locations over large areas (up to 105
km2). In addition, the magnitude and frequency
of silicic supereruptions were far greater during
large igneous province events than when com-
pared to global, long-term averaged frequencies
of silicic supereruptions (Bryan et al., 2010). As
several recent studies have demonstrated, silicic
volcanic rocks represent a signifi cant cumu la-
tive eruptive volume of continental large igneous
provinces and were principally erupted during
the peak and fi nal stages of fl ood vol canism
(e.g., Marsh et al., 2001; Bryan et al., 2002;
Ukstins Peate et al., 2005). While the silicic
super erup tions have an obvious eruption mech-
anism for stratospheric aerosol injection, the
much shorter duration (days to weeks) suggests
that their impact may not have been as long-last-
ing as potentially decadal fl ood basalt eruptions
(Thordarson et al., 2009). However, this may be
less of an issue if the main kill mechanism is
ozone destruction rather than thermal perturba-
tions. The penecontemporaneity of mafi c and
AB
Figure 4. (A) Cliffed section of the 2660 km3 (M8.86) Sand Hollow fl ood basalt fl ow from the Columbia River large igneous province
(Palouse Falls, Washington), illustrating the internal morphology and potential thickness (~60 m height) of a single, large-magnitude sheet
lobe (from Bryan et al., 2010). (B) Close-up of a proximal mafi c volcaniclastic deposit of phreatomagmatic origin from the Emeishan large
igneous province (Daqiao, near Huidong, China), produced by the explosive interaction between fl ood basaltic magmas, seawater, and living
carbonate reefs during the early stages of volcanism (Ukstins Peate and Bryan, 2008). Note the ragged shapes to the basaltic lava clasts (dark
colored) and textural evidence for their ductile state at time of emplacement, such as indentations from limestone clasts (light colored). Mafi c
volcaniclastic deposits can provide sensitive records of eruption and emplacement environments and subtle variations in tectono-volcanic
evolution not found in a thick and extensive fl ood basalt lava stratigraphy. Figure 4A is reprinted from Earth-Science Reviews, vol. 102,
Bryan, S.E., Ukstins Peate, I.A., Self, S., Peate, D., Jerram, D.A., Mawby, M.R., Miller, J., and Marsh, J.S., The largest volcanic eruptions on
Earth, p. 207–229, 2010, with permission from Elsevier.
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Large igneous provinces and silicic large igneous provinces
Geological Society of America Bulletin, July/August 2013 1063
silicic magmatism is now recognized in con-
tinental large igneous provinces (Bryan et al.,
2010), raising the possibility that large-volume
mafi c and silicic eruptions may have worked
together in causing aerosol loading of the tropo-
sphere and stratosphere, as well as causing addi-
tional effects such as iron fertilization of oceans
(Cather et al., 2009). No quantitative constraints
currently exist on volatile degassing from large
igneous province–related silicic explosive
super erup tions that can be used to compare with
the fl ood basalts, and to constrain better the total
volatile loads generated during large igneous
province events. These would be ideal topics for
future investigation.
Large Igneous Province Events and
Mantle Dynamics
Large igneous provinces fundamentally
record major mantle melting events and thus
require large amounts of thermal energy ex-
pended over a geologically short period of time
(Saunders, 2005). Because of the vast spatial
dimensions of large igneous provinces, under-
stand ing why such magmatism takes place
could potentially provide fi rst-order constraints
on mantle dynamics (Korenaga, 2011), such as
instability at the core-mantle boundary (e.g.,
Richards et al., 1989; Larson, 1991; Hill et al.,
1992) and the effi ciency of convective mix-
ing (e.g., Takahahshi et al., 1998; Korenaga,
2004). Studies of large igneous provinces have
been fundamental to development of the mantle
plume theory (e.g., Richards et al., 1989; Camp-
bell and Griffi ths, 1990; Campbell, 2005, 2007),
and also to whole-mantle convection models, as
mantle plumes represent a rising counter fl ux to
deep subduction into the lower mantle, which
is increasingly being supported by seismic evi-
dence (e.g., van der Hilst et al., 1997; Grand,
2002; Ren et al., 2007).
Large igneous provinces have generally been
interpreted to be the result of decompression
melting of the large spherical head of a new
mantle plume (Richards et al., 1989; Campbell
and Griffi ths, 1990), likely originating from the
core-mantle boundary, while associated hotspot
trails or aseismic ridges are related to melt-
ing of the narrow plume tail (Wilson, 1963;
Morgan 1971). This theory gained ascendancy
through the 1990s, and potentially some of the
strongest evidence for mantle plumes may come
from studies of planetary large igneous prov-
inces (e.g., Ernst et al., 2001; Hansen, 2007).
The common spatial-temporal connection of
large igneous provinces with age-progressive
hotspots or aseismic ridges representing chains
of overlapping hotspot-type volcanoes (e.g.,
Paraná-Etendeka large igneous province–Tristan
de Cunha hotspot; Deccan large igneous prov-
ince–Reunion hotspot; North Atlantic large ig-
neous province–Iceland hotspot) provided an
initial compelling argument (e.g., Richards et al.,
1989). The isotopic and trace-element composi-
tional similarities between large igneous prov-
inces and associated hotspot-related igneous
rocks are consistent with melt derivation from
similar sublithospheric mantle source regions,
and they are distinct from magmas typically
produced at plate boundaries (Hawkesworth and
Scherstén, 2007).
There are several geologically testable pre-
dictions of the mantle plume theory: (1) Is
there a connection between a large igneous
province and (active) hotspot representing the
products of melting of the plume head and
tail, respectively? (2) What is the extent of the
rift zone? Large igneous province magmatism
and the length of thickened oceanic crust de-
veloped within a rift zone should have extents
of ~2000–2500 km, which will represent the
calculated dimensions of a core-mantle bound-
ary–derived plume head that fl attens beneath
the lithosphere. (3) Is there evidence of the
presence of high-temperature, magnesium-
rich igneous rocks (picrites, komatiites) within
the large igneous province and hotspot, which
would have erupted early and be most abun-
dant near the inferred center of the province
(plume head)? (4) Is there regional domal uplift
of 1000 ± 500 m preceding fl ood volcanism?
(5) Is there a short duration to the main pulse of
fl ood volcanism (Campbell, 2005, 2007)?
As more detailed studies of large igneous
provinces and hotspot-related seamount vol-
canoes, and geophysical imaging of deep Earth
have been undertaken, particularly in the last 10–
15 yr, it has been realized that many large igneous
provinces and seamounts do not show geologic
evidence for these predictions and for vol canism
to have formed above a mantle plume (e.g.,
Czamanske et al., 1998; Ingle and Coffi n, 2004;
Korenaga, 2005; Ukstins Peate and Bryan, 2008;
Koppers, 2011; Serrano et al., 2011). Mantle
plumes have proven diffi cult to image down to
the core-mantle boundary using seismology (e.g.,
Hwang et al., 2011), with several appearing to be
restricted to the upper mantle (e.g., Yellowstone,
Iceland; Christiansen et al., 2002; Montelli et al.,
2004). In some cases, the predictions may be too
simplistic; it has been suggested that the type and
passage of a mantle plume through the mantle
and the way in which a plume interacts with
lithosphere may explain, for example, the general
absence of pre volcanic domal uplift (e.g., Leng
and Zhong, 2010; Sobo lev et al., 2011). Never-
theless, many geological inconsistencies have
resulted in a variety of models being proposed
to explain the origin of large igneous provinces
(see summaries in Saunders , 2005; Ernst et al.,
2005; Bryan and Ernst, 2008; and the Introduc-
tion section herein). Recently, opposing sets of
literature on the existence of mantle plumes have
been published (for example, compare Campbell
and Kerr [2007] with Foulger et al. [2005] and
Foulger and Jurdy [2007]; and Humphreys and
Schmandt [2011] with Anderson [2012]). The
debate about whether mantle plumes exist or not,
and what other mechanisms could cause melting
anomalies that generate large igneous provinces
and hotspots has led to the establishment of the
Web site www.mantleplumes.org, where wide
varie ties of ideas and theories are presented, serv-
ing as a valuable resource on this topic.
Part of the issue stems from a “one size fi ts
all” approach to interpreting the origin of large
igneous provinces (and hotspots; see Courtillot
et al., 2003; Foulger, 2007), because large ig-
neous province events may have a number of
origins. The fact that all large igneous province
events show a number of key features (Bryan
and Ernst, 2008) that make them distinctive and
unique in Earth history, and are fundamentally
intraplate igneous events, does suggest a com-
mon origin. If planetary large igneous province
examples are validated (see following), then this
common process for large-volume magma gen-
eration in the mantle cannot be intimately linked
to plate-boundary processes. It is underappreci-
ated that much of what is observed and sampled
in large igneous provinces refl ects processes at
crustal depths, including magma generation and
extraction, transport, storage, contamination,
crystallization, and emplacement (Bryan et al.,
2010); the revelation that large igneous prov-
ince magmas can undergo substantial lateral
transport in the crust over distances exceeding
3000 km and be so far removed from their place
of origin in the mantle is also quite astounding
(Ernst and Baragar, 1992; Elliot et al., 1999).
Province-specifi c models (e.g., Ingle and Coffi n,
2004; Long et al., 2012) that might satisfactorily
explain geologic observations locally remain
unsatisfying in providing a broader framework
for understanding the origin of all large igne-
ous provinces. If large igneous provinces (and
hotspots) do have different origins, then a future
challenge will be recognizing geologic features
that can unequivocally discriminate the different
models; otherwise, these models become untest-
able. Vigorous debate is expected to continue
for many years to come on this topic.
Resource Signifi cance of Large
Igneous Provinces
Over the past 25 yr, large igneous provinces
have been increasingly explored for mineral
and energy resources. They are a key target
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1064 Geological Society of America Bulletin, July/August 2013
for magmatic Ni-Cu and platinum group ele-
ments (PGEs), Cr, Fe-Ti-V, and other mineral
deposit types (Naldrett, 1997, 1999; Pirajno,
2000, 2007; Schissel and Smail, 2001; Bori-
senko et al., 2006; Eckstrand and Hulbert,
2007; Ernst, 2007b; Begg et al., 2010; Jowitt
and Ernst, 2013). In terms of ore-forming sys-
tems, two general end members are rec og nized:
(1) those associated with magma, and (2) hydro-
thermal systems powered by the thermal en-
ergy released by the cooling of anorogenic
magmas in the crust (Pirajno, 2007). Ortho-
magmatic ore deposits are typically hosted by
mafi c-ultramafi c layered intrusions or volcanic
rocks in large igneous provinces, with key ore
deposit types being: (1) intrusion-hosted Cu-
Ni-PGE–rich sulfi des, chromite, and Fe-Ti-V
oxides (e.g., Bushveld Complex—Bushveld
large igneous province, Great dike of Zim-
babwe, southern Africa); (2) Cu-Ni sulfi de min-
eralization in basaltic and gabbroic rocks (e.g.,
Duluth—Keweenawan large igneous province,
USA; Noril’sk-Talnakh—Siberia Traps, Rus-
sia; Jinchuan—Guibei large igneous province,
China); and (3) Archean komatiite Ni sulfi des
(e.g., Kambalda, Western Aus tralia) (Pirajno,
2007). Two styles of ortho magmatic ore depos-
its are now also known from granitic rocks in
large igneous provinces: iron-oxide copper gold
(IOCG), and Sn, W, U, Nb, Ta, and Th mineral-
ization associated with A-type granites (Pirajno ,
2007; McPhie et al., 2011). Voluminous banded-
iron formations that formed between 2.6 and
1.8 Ga along intracratonic passive margins or
in platform basins likely have temporal and
genetic links to large igneous province events
(e.g., Barley et al., 1997). Consequently, two
specifi c ore systems ( komatiite-hosted Ni-Cu
deposits and iron formations) associated with
large igneous provinces are age dependent,
being restricted to Archean and Paleoprotero-
zoic-Mesoproterozoic rocks. Hydro thermal ore
systems are also associated with large igneous
provinces, particularly where active rift systems
act as major conduits for both magmas and
hydrothermal fl uids. Carlin and epithermal Au
mineralization are key expressions of hydro-
thermal mineralization asso ciated with large
igneous provinces, but they appear to be more
commonly associated with silicic large igneous
provinces (Bryan, 2007; Pirajno, 2007).
Petroleum exploration over the past 25 yr has
had considerable focus on a number of hydro-
carbon-rich volcanic rifted margins such as the
North Atlantic, South Atlantic, and Northwest-
ern Australia. The nature and timing of large
igneous province magmatism have several im-
plications for hydrocarbon generation/matura-
tion and storage, as well as creating “volcanic
risk” for exploration companies in ultradeep-
water (>2000 m) environments. Consequently,
this has driven an improved understanding of
the thickness, architecture, and timing of large
igneous province–related volcanism in these
sedimentary basins (e.g., Mohriak et al., 2002;
Nelson et al., 2009; Aarnes et al., 2011), and it
will continue to be an area of applied research in
the foreseeable future. In addition, oceanic pla-
teau volcanism has been linked to the deposition
of organic-rich sediments during anoxic condi-
tions, such that many of the world’s most impor-
tant occurrences of mid-Cretaceous oil source
rocks may owe their existence to the formation
of oceanic plateaus at this time in the Pacifi c and
Indian Oceans (Kerr, 2013).
Planetary Large Igneous Provinces
Following analysis of fl y-by data from the
inner planets over the last four decades, and re-
covery of mare rocks from the Moon, it has been
concluded that Mars, Venus, Mercury, and the
Moon have had a signifi cant history of large ig-
neous province–scale basaltic to ultramafi c vol-
canism (Head and Coffi n, 1997; Wilson, 2009;
Thordarson et al., 2009; Head et al., 2011; Head
and Wilson, 2012). Planetary large igneous
provinces can provide important contributions
to our understanding of terrestrial large igne-
ous provinces and geodynamics because they
record planetary evolution and the transport of a
signifi cant amount of internal heat and material
(Wilson, 2009). Furthermore, unlike on Earth,
the lack of convincing evidence for Earth-like
plate tectonics on the other rocky planets means
the planetary large igneous provinces have not
been affected by tectonic deformation or frag-
mentation (e.g., Hansen, 2007), and exposure
and preservation will be better due to fewer
erosional agents and minimal erosional rates.
The antiquity of the other inner planets means
that the very earliest large igneous province rec-
ord of a planet is likely to be better preserved
than on Earth (Head and Coffi n, 1997). Con-
sequently, the inner planets are considered to
preserve an excellent record of large igneous
provinces in space (their areal distribution over
the planet) and through time, providing infor-
mation on temporal variations of large igneous
province events over the geological history of
a planet.
Potential planetary analogues to terrestrial
large igneous province types include the lunar
maria (continental fl ood basalt provinces), Ve-
nusian crustal plateaus (oceanic plateaus), and
rift-dominated volcanic rises on Mars and Venus
(volcanic rifted margins) (Head and Coffi n ,
1997; Ernst et al., 2001; Hansen, 2007). Unlike
Earth, no silicic large igneous provinces or large-
volume silicic magmatism associated with plan-
etary large igneous provinces have so far been
recognized. The recent discovery and documen-
tation of laterally and areally extensive sets of
narrow ridges that are interpreted to be shallowly
exhumed major dike systems (Head et al., 2006)
and extensive radial graben systems interpreted
to be a surface manifestation of mantle-derived
dike intrusion complexes (Wilson and Head,
2002) provide interesting planetary analogues to
the giant dike swarms recognized on Earth (e.g.,
Ernst and Buchan, 1997; Ernst et al., 2001).
The lateral extents of the giant dike swarms,
the Martian ridges, and other dike-related fea-
tures (Ernst et al., 2001) are similar (hundreds
of kilome ters and discontinuously for thousands
of kilometers), as are thicknesses: Dike widths
are typically up to 20–40 m, with maximum
widths of 100–200 m on Earth, and high-reso-
lution imagery indicates ridge crests ~60 m
wide across the Hesperian plains of Mars (Head
et al., 2006). The continuity and thickness of the
dikes are consistent with being developed dur-
ing very high-effusion-rate, large-volume fl ood
basalt–type eruptions (Head et al., 2006), and as
on Earth, signifi cant lateral transport (>1000 km)
is inferred for magma along these planetary giant
dike swarms (Ernst et al., 2001).
Planetary large igneous province recognition
so far has been based primarily on areal extent,
which is generally well constrained from the
high-resolution surface images now available.
Several regions on the planets with areas >1 mil-
lion km2 have been interpreted as large igneous
provinces (e.g., Head and Coffi n, 1997; Hansen,
2007; Head et al.., 2011), and, internally, lava
fi elds on the scale of fl ood basalts exhibiting a
variety of fl ood basaltic lava surface features,
such as extensive and lobate fl ow fronts and
sinuous rilles or evidence for thermal erosion
by lava channels, have been identifi ed in images
(see summary in Head and Coffi n, 1997). In the
extreme, early studies had suggested that up to
80% of the surface of Venus had been covered
by massive outpourings of fl ood basaltic lava to
a depth of ~2.5 km, taking 10–100 m.y., mak-
ing this the largest large igneous province in the
solar system (e.g., Strom et al., 1994; Basilevsky
and Head, 1996; Head and Coffi n, 1997). How-
ever, the basis for this event has recently been
challenged (Hansen, 2007), and it highlights
the diffi culties in constraining igneous volumes
and event durations for planetary large igneous
provinces. As has been discussed for terrestrial
large igneous provinces, volume, duration, and
evidence for brief, large-volume igneous pulses
are critical and distinguishing features (Bryan
and Ernst, 2008).
Volume, both of individual eruptions and at
the provincial scale, and eruption rate/duration
are critical parameters to establish equivalence
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Large igneous provinces and silicic large igneous provinces
Geological Society of America Bulletin, July/August 2013 1065
to terrestrial large igneous provinces. Ghost
craters, which are preexisting craters that have
been partially or completely buried by lava, pro-
vide a useful approach in constraining deposit
thickness, as well as potentially informing the
mode of emplacement of the concealing vol-
canic rocks (Head et al., 2011). While the inner
planets essentially lack weathering, erosion,
sediment transport, and deposition processes
that play dominant roles in shaping Earth’s sur-
face (Hansen, 2007), these processes actually
provide a vital role in helping us to identify the
products and scale of individual large igneous
province eruptions (Bryan et al., 2010), poten-
tially important time breaks during large igneous
province events, and also the relative chronol-
ogy of large igneous provinces based on their
state of preservation. Consequently, large igne-
ous province–sized volcanic constructs such as
Olympus Mons on Mars, with an edifi ce volume
of ~2 million km3, may simply result from long-
term mantle melting anomalies lasting billions
of years (Head and Coffi n, 1997) and the lack
of plate tectonics and erosional processes. The
lunar maria, widely considered to be large ig-
neous provinces and which cover ~17% of the
Moon, are interpreted to have been emplaced
over periods of time (108 to 109 yr) substan-
tially longer than for terrestrial large igneous
provinces (<50 m.y.; Bryan and Ernst, 2008),
and at very low averaged magma emplacement
rates (~0.01 km3/yr; Head and Coffi n, 1997).
As pointed out by Bryan and Ernst (2008), all
plate-boundary processes generating magma
(i.e., mid-ocean ridges, subduction zones, con-
tinental rifts), as well as other mantle-melting
processes on planets, given suffi cient time and
space, can also produce igneous rock of large
igneous province–scale dimensions. While vol-
canic coverage of the inner planets is extensive,
it remains unclear if many of the provinces result
from very long-term or more rapid (<50 m.y.)
accumulations akin to terrestrial large igneous
provinces. At present, absolute geologic time
cannot be constrained for the inner planets, and
the surface density of impact craters provides
the only means by which to constrain absolute
time on planet surfaces (Hansen, 2007).
SILICIC LARGE IGNEOUS PROVINCES
Within the broad research area of large ig-
neous provinces, one particular advance over
the past 25 yr has been in the recognition and
understanding of “silicic” large igneous prov-
inces, including their geologic/tectonic settings,
key characteristics, origins of the magmas, and
economic resources. In some cases, the scale of
these provinces had been recognized for some
time (e.g., Sierra Madre Occidental; McDowell
and Keizer, 1977; McDowell and Clabaugh,
1979). In other cases, the true size and immen-
sity of silicic magmatism were revealed through
an integration of igneous and sedimentary rec-
ords that now reside both onshore and offshore
(e.g., Whitsunday; Bryan et al., 1997, 2012),
or on adjacent continents (e.g., Chon Aike;
Pankhurst et al., 1998, 2000) following tectonic
fragmentation (Fig. 1). Many early studies sim-
ply considered the silicic-dominant magmatism
as a continental magmatic arc emplaced above
an active subduction zone (e.g., Cameron et al.,
1980; Jones and Veevers, 1983; Wark et al.,
1990; Wark, 1991). Such interpretations on the
tectonic setting of the magmatism have been
strongly infl uenced by the continent-margin
position, calc-alkaline affi nity, relatively primi-
tive isotopic characteristics, the presence of
ande sitic or intermediate composition volcanic
rocks, and a subduction heritage along the conti-
nental margin (Bryan et al., 2013). A fundamen-
tal revision then has been our understanding of
a tectonic setting for the silicic magmatism that
is often remote (up to or >500 km) and discon-
nected from suprasubduction-zone processes
and relative plate motions (Bryan et al., 1997,
2008; Pankhurst and Rapela, 1995; Pankhurst
et al., 1998, 2000; Bryan, 2007; Wong et al.,
2010), and that spatial-temporal relationships
exist with ocean basin formation (Bryan et al.,
2012, 2013).
The potential long-term signifi cance of silicic
(granitoid) magmatism during large igneous
province events has been the ever-growing rec-
ord of U-Pb igneous zircon ages derived from
granitoid and sedimentary rocks, which has par-
ticularly delineated major silicic granitoid igne-
ous events at ca. 2.7 Ga and 1.9 Ga (e.g., Gastil,
1960; Campbell and Hill, 1988; Condie, 1998;
Condie et al., 2009, 2011; Iizuka et al., 2010).
These periods have been linked to catastrophic
superplume events in the mantle (e.g., Camp-
bell and Hill, 1988; Condie, 1995), based on the
presence of 2.8–2.7 Ga fl ood basalts (e.g., Blake,
1993; Cheney and Winter, 1995) and widely oc-
curring fl ood basalt volcanics and mafi c-ultra-
mafi c intrusive rocks at 1.9 Ma (e.g., Ernst and
Buchan, 2001, and references therein). How-
ever, the temporally related granitoid magma-
tism, the source for the detrital zircons, has been
considered as orogenic and thus unrelated (e.g.,
Condie and Aster, 2010). An important observa-
tion that has been evident from zircon studies
in volcanic rocks (Charlier et al., 2005; Bryan
et al., 2008) is that zircon generally only appears
as a new crystallizing phase in silicic magmas
(~>70 wt% SiO2; see also Watson and Harrison,
1983). Suprasubduction-zone magmatism is
dominantly basaltic ande site to andesite-dacite
at modern oceanic and continental arcs, respec-
tively; the consequence is that these magma
compositions are zircon under saturated and will
not crystallize new zircon. Large-volume silicic
(new zircon-bearing) magmatism that will have
a measurable effect on the detrital zircon age
record occurs in intraplate continental regions,
and along continental margins or island arcs
undergoing rifting. Thus, major peaks in new
igneous zircon ages more likely refl ect crust
instability, extension, and possible successful
rupturing events, and should not be so closely
tied to periods of supercontinent assembly (cf.
Condie and Aster, 2010; Cawood et al., 2013).
Consequently, the origin of the widespread 2.7
and ca. 1.9 Ga zircon peaks may alternatively be
linked to large igneous province events at this
time and enhanced melting of continental crust
that would have been composed of larger vol-
umes of juvenile material (e.g., Campbell and
Hill, 1988).
The following section focuses on western
Mexico and the Sierra Madre Occidental si-
licic large igneous province to illustrate some
of these major advances in understanding of
large igneous province magmatism, associated
crustal extension, and subsequent ocean basin
formation.
Sierra Madre Occidental
The Sierra Madre Occidental (SMO, Fig. 5)
is the largest silicic igneous province in
North America (McDowell and Keizer, 1977;
McDowell and Clabaugh, 1979; Ward, 1995),
and it is contiguous with silicic volcanism
through the Basin and Range Province of the
western United States to the north (Lipman
et al., 1972; Gans et al., 1989; Best and Chris-
tiansen, 1991), and also with the ignimbrite
province of the Sierra Madre Sur, south of the
Trans-Mexican volcanic belt (Morán-Zenteno et
al., 1999, 2007; Cerca-Martínez et al., 2007). It
forms a prominent elevated plateau region up to
3 km high, where ignimbrite sections are at least
1 km thick (Fig. 6), and, notably, crustal thick-
nesses are their highest in Mexico (up to 55 km;
Fig. 5). Through this elevated core of the prov-
ince, ignimbrite sections are fl at lying, but along
the fl anks, ignimbrite sections are increasingly
faulted and tilted. Along the eastern edge of the
Gulf of California, crustal thicknesses have been
reduced to ~22 km (Fig. 5).
A minimum volume of 400,000 km3 of domi-
nantly rhyolitic ignimbrite was erupted mostly
between ca. 38 and 18 Ma, but age dating over
the past 40 yr has identifi ed two main pulses or
“fl are-ups” of ignimbrite activity (Fig. 7): at ca.
34–28 Ma and ca. 24–18 Ma (Ferrari et al., 2002,
2007; Bryan et al., 2013). Signifi cantly, age dat-
ing has further revealed the very rapid (~1 m.y.
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Bryan and Ferrari
1066 Geological Society of America Bulletin, July/August 2013
duration), large igneous province–like emplace-
ment rates for kilometer-thick sections of ig-
nimbrite across the province (e.g., McDowell
and Keizer, 1977; Ferrari et al., 2002; Swanson
et al., 2006; McDowell and McIntosh, 2012),
attesting to rapid rates of silicic magma gen-
eration and eruption (Bryan et al., 2008). The
Oligocene pulse is thought to be responsible for
at least three quarters of the erupted volume,
whereas a volume of at least 100,000 km3 was
erupted in the early Miocene. Rhyolitic ignim-
brite represents at least 85%–90% of the erupted
volume, with the remaining volume being rhyo-
litic lavas/domes and basaltic lavas.
The early Miocene pulse was largely super-
imposed on the Oligocene volcanic pulse, but it
also extended further west (Fig. 5) to be pres-
ent on Baja California (e.g., Umhoefer et al.,
2001). Recent dredge surveys and age dating
of recovered rocks through the southern Gulf
of California have confi rmed the presence of
early Miocene bimodal volcanic and exhumed
intrusive rocks offshore (Fig. 5), improving
the prerift connection between Baja California
and mainland Mexico (Orozco-Esquivel et al.,
2010; Ferrari et al., 2012). The early Miocene
pulse shows signifi cant differences from north
to south. Silicic volcanism appears to have been
more volumetrically dominant in the SW part of
the Sierra Madre Occidental, with thick rhyo-
litic ignimbrite packages, similar to the Oligo-
cene sections, characterizing some areas (e.g.,
Espinazo del Diablo and El Salto successions—
McDowell and Keizer, 1977; Mesa del Nayar
area—Ferrari et al., 2002). Elsewhere, graben-
focused bimodal volcanism was characteristic
(Ferrari et al., 2002; Ramos Rosique, 2013).
Graben margins are commonly defi ned by rhyo-
lite domes, whereas basaltic lava packages up
to 200 m thick and rhyolitic ignimbrites (some
fi ssure fed; Aguirre-Díaz and Labarthe-Hernán-
dez, 2003; Murray et al., 2010) partly infi ll the
grabens (Ramos Rosique et al., 2010; Ramos
Rosique, 2013). In contrast, early Miocene vol-
canism was less abundant and dominantly mafi c
in composition across the northern Sierra Madre
Occidental (McDowell et al., 1997).
Association with Synvolcanic Extension
A general temporal and spatial overlap be-
tween volcanism and extension has been rec-
ognized for many continental large igneous
provinces (Bryan and Ernst, 2008), includ-
ing the silicic large igneous provinces (Bryan,
2007), but large igneous province initiation may
be prerift, with no initial surface expression of
rifting. Some large igneous provinces such as
the North Atlantic large igneous province have
pulses of igneous activity that correspond to pre-
rift (62–58 Ma) and synrift phases (56–53 Ma;
Saunders et al., 1997). Since many large igne-
ous provinces, both continental and oceanic, are
subsequently ruptured to produce new ocean
basins (Fig. 1) and coincide with superconti-
nent breakup (e.g., Bryan and Ernst, 2008; Ernst
et al., 2008), lithospheric extension is a funda-
mental part of large igneous province events.
Crustal extension is generally considered to be
important for generating large volumes of si-
licic magma (e.g., Hildreth, 1981; Ward, 1995;
Hanson and Glazner, 1995; Gans and Bohrson,
1998), and petrogenetic studies have demon-
strated the substantial contribution to silicic large
igneous province magmatism by crustal partial
melting (e.g., Ewart et al., 1992; Pankhurst and
Rapela, 1995; Riley et al., 2001; Bryan et al.,
2002, 2008). However, for many large igneous
provinces, the relative timings of the onset of
large igneous province magmatism and exten-
sion remain unclear, as well as if signifi cant
changes in the rate of synvolcanic extension
also occur, and how this may affect magmatism
in terms of magma production, magmatic pro-
cesses, eruptive styles, and eruptive products.
Previous studies have suggested that synvolcanic
extension can promote smaller-volume effusive
eruptions over larger caldera-forming eruptions
(e.g., Axen et al., 1993), intermediate magma
Bo
6A
6B
Figure 5. Tectonic map of northwestern Mexico showing the main volcano-tectonic ele-
ments, including: (1) the preserved extents of the Oligocene–early Miocene silicic-dominant
volcanic activity of the Sierra Madre Occidental (Ferrari et al., 2002; Bryan et al., 2008);
(2) extents of the dominantly bimodal early Miocene pulse that coincided with the wide
development of grabens and rift basins (McDowell et al., 1997; Ferrari et al., 2002), and a
restricted belt of metamorphic core complexes in the state of Sonora (Nourse et al., 1994;
Wong et al., 2010); (3) distribution of the middle Miocene Comondú Group andesites (from
Umhoefer et al., 2001); and (4) recently dated Miocene igneous rocks from offshore (Orozco-
Esquivel et al., 2010). Lithospheric variation across the region is also shown, including un-
extended and extended continental regions, and transitional to new oceanic crust formed by
the propagating spreading center in the Gulf of California. Red boxed areas near Mazatlán
and Chihuahua-Sinaloa state border refer to locations of photographs in Figure 6. Abbre-
viations: EPR—East Pacifi c Rise; H—Hermosillo; Nay.—Nayarit; Bo—Bolaños graben.
Figure is modifi ed from Bryan et al. (2013).
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Large igneous provinces and silicic large igneous provinces
Geological Society of America Bulletin, July/August 2013 1067
compositions instead of bimodal magma compo-
sitions (Johnson and Grunder, 2000; Bryan et al.,
2012, 2013), and, where extension is rapid (high
magnitude), a suppression of volcanism (Gans
and Bohrson, 1998).
Signifi cant extension began across the north-
ern Sierra Madre Occidental at ca. 30 Ma,
marked by the eruption of basaltic andesite lavas
chemically resembling fl ood basalts (Southern
Cordilleran Basaltic Andesite [or SCORBA] of
Cameron et al., 1989), followed by the devel-
opment of grabens at 27 Ma (McDowell et al.,
1997), and by 25 Ma, a prominent belt (>300 km
long) of high-magnitude extension was initiated
in the state of Sonora (Gans, 1997; Wong et al.,
2010), producing metamorphic core complexes
(Fig. 5). This high-magnitude extension may
have contributed to a suppression of large-
volume silicic volcanism (Gans and Bohrson,
1998) through the NE Sierra Madre Occidental
during the latest Oligocene and early Miocene,
when volcanism was occurring along strike to
the south in the Sierra Madre Occidental (Bryan
et al., 2013). As inferred by Cameron et al.
(1989), the potential initiation of upper-crustal
extension at ca. 30 Ma was marked by the wide-
spread and increased eruption of the SCORBA,
and immediately followed the peak in silicic ex-
plosive volcanism and coincided with a decline
in silicic explosive volcanism (Fig. 7).
Bimodal volcanism during the early Miocene
pulse was clearly enhanced by active extension,
particularly across the southern Sierra Madre
Occidental at this time (Ferrari et al., 2002;
Bryan et al., 2013). Typically crystal-poor,
high-silica rhyolites were emplaced as both nu-
merous lava domes sited along active faults or
graben-bounding structures and as ignimbrites
from fault-controlled explosive fi ssure erup-
tions (Aguirre-Díaz and Labarthe-Hernández,
2003; Murray et al., 2010; Ramos Rosique,
2013). Welded pyroclastic dikes exposed within
faults demonstrate that graben faults were uti-
lized by silicic magmas for explosive eruptions
(Aguirre-Díaz and Labarthe-Hernández, 2003;
Ramos Rosique, 2013). Basaltic dikes are also
found intruding along graben-bounding faults,
and relatively thick lava piles (up to 200 m in
the Bolaños graben, Fig. 5) ponded within the
grabens, and in some locations invaded devel-
oping lacustrine sedimentary sequences. The
active faulting thus provided enhanced path-
ways for basaltic magmas to invade the upper
crust and erupt at the surface. Previously, during
the Oligocene pulse, while material and thermal
inputs from the upper mantle were requisite to
generate the widespread crustal partial melting
and silicic ignimbrite fl are-up, an extensive zone
of silicic magma generation would have acted as
a density barrier to the mafi c magmas, prevent-
ing their substantial eruption.
Relationship of Silicic Large Igneous
Province Magmatism to Gulf of
California Rifting
Sierra Madre Occidental silicic volcanism
and opening of the Gulf of California have pre-
viously been considered two separate phenom-
ena. This has mainly been due to two linked
reasons. The fi rst is that despite different models
of opening (see review in Fletcher et al., 2007),
rifting to open the Gulf of California has been
considered to have developed rapidly following
cessation of subduction of the Guadalupe and
Magdalena plates at about ca. 12.3–12.5 Ma
(Stock and Hodges, 1989; Ferrari et al., 2007;
Fletcher et al., 2007; Lizarralde et al., 2007;
Umhoefer , 2011; Sutherland et al., 2012). Sec-
ondly, the margins of the Gulf of California
were the site of eruption of distinctive, albeit
A
B
Figure 6. Examples of elevated, dissected plateaus of fl at-lying ignimbrite along the core
of the Sierra Madre Occidental silicic large igneous province. This “step-like” topography,
a product of posteruption erosion, is also characteristic of many continental fl ood basalt
provinces (cf. Fig. 3). (A) Approximately 1-km-thick Oligocene ignimbrite pile exposed on
the southeastern side of Copper Canyon, northern Sierra Madre Occidental (27°31.670′N,
107°49.687′W), reaching an elevation of 2240 m above sea level (asl), with the base of the
canyon at 1320 m asl. The lowermost exposed unit is the Copper Canyon Tuff (29.6 Ma),
for which the intracaldera facies is up to 1 km thick (Swanson et al., 2006). (B) View west
from the Mazatlán-Durango old highway (23°39.927′N, 105° 43.340′W) to the fl at-lying
24.0–23.5 Ma Espinazo–El Salto sequence (McDowell and Keizer, 1977) with a thick section
of basaltic lavas at the base overlain by numerous rhyolitic welded ignimbrites; the exposed
cliff section is ca. 250 m high, and the prominent cliffed and columnar jointed rhyolitic
ignim brite near the top of the section has been mapped up to 150 m thickness.
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Bryan and Ferrari
1068 Geological Society of America Bulletin, July/August 2013
relatively volumetrically minor, andesitic vol-
canic rocks in the early to middle Miocene (the
Comondú arc; Hausback, 1984; Sawlan and
Smith, 1984; Sawlan, 1991; Umhoefer et al.,
2001). This andesitic magmatism was widely
interpreted to mark the termination of the Sierra
Madre Occidental, and its broad zone of silicic-
dominant magmatism and extension beginning
ca. 40 Ma (Fig. 7), and the re-establishment of
typical suprasubduction-zone arc magmatism
(e.g., Ferrari et al., 2007). Consequently, mag-
matism and Oligocene–early Miocene exten-
sion observed in the Sierra Madre Occidental
were thought to be temporally separated from
Gulf of California opening by a suprasubduc-
tion-zone volcanic arc occupying the site of the
future Gulf of California (Fig. 5).
New studies have questioned the nature and
tectonic setting of the middle Miocene andesitic
volcanism (Bryan et al., 2013). Several dating
studies from the Sierra Madre Occidental, the
Gulf of California margins and Baja California
indicate bimodal volcanism of the early Miocene
pulse continuing to ca. 17 Ma (Hausback, 1984;
Martín-Barajas et al., 2000; Umhoefer et al.,
2001; Drake, 2005; Bryan et al., 2008; Ferrari
et al., 2012; Ramos Rosique, 2013). However, the
onset of “arc” volcanism along Baja California
has been interpreted at ca. 19.5 Ma (Umhoefer
et al., 2001), whereas others have suggested that
“arc” volcanism began earlier in northern Baja
California at ca. 21 Ma (e.g., Martín-Barajas
et al., 1995). These new age data also indicate
that, regionally, mafi c to weakly bimodal vol-
canism continued during the middle Miocene,
although at much lower intensity (Fig. 7). Con-
sequently, this age overlap suggests no abrupt
termination to Sierra Madre Occidental bimodal
volcanism (and extension) when rejuvenation
of suprasubduction-zone arc volcanism was ap-
parently initiated, despite some of the bimodal
and andesitic volcanism spatially overlapping.
Nevertheless, a strong compositional shift from
dominant bimodal volcanism to more intermedi-
ate-composition volcanism beginning ca. 19 Ma
is evident, as is a concentration of volcanic ac-
tivity around the future position of the Gulf of
California (Figs. 5 and 7).
The onset of extension in the Gulf Extensional
Province, a region of Basin and Range–style ex-
tension bordering the Gulf of California (Henry
and Aranda-Gomez, 2000), was thought to have
been ca. 13–12 Ma, being associated with the
termination of subduction along this part of the
western North American plate boundary (e.g.,
Stock and Hodges, 1989; Henry and Aranda-
Gomez, 2000; Umhoefer, 2011). Recent stud-
ies along the southeastern and eastern margins
of the Gulf of California through Sinaloa and
Nayarit, however, have revealed that kilometer-
thick ignimbrite sections of the Sierra Madre
Occidental, dated to as young as 20 Ma, have
been tilted by up to 35°. These large tilt blocks
of Sierra Madre Occidental ignimbrite face a
low-relief coastal plain where fl at-lying and
undeformed basaltic lava fi elds distributed for
at least 700 km along the eastern margin of the
Gulf of California were emplaced between 12
and 9 Ma (Fig. 5; Ferrari et al., 2012; see also
Gastil et al., 1979). Similar-aged basalts have
also been dredged from the submerged conti-
nental margins to the southern Gulf of Califor-
nia (Ferrari et al., 2012).
The fundamental implication of these struc-
tural-eruption timing relationships is that large-
magnitude extension instrumental to successful
rifting of the Gulf of California must have oc-
curred between ca. 25 and 12 Ma. Along the
southeastern Gulf of California margin, this ex-
tension must have postdated the fi nal phases of
bimodal and ignimbrite-dominant activity of the
early Miocene pulse of the Sierra Madre Occiden-
tal (ca. 20–18 Ma), and preceded the widespread
eruption of fl at-lying, (undeformed) transitional
intraplate basaltic lavas along the eastern margin
of the gulf (Fig. 5). Importantly, most of the ob-
served variation in crustal thickness across the
region (Fig. 5) must also have been achieved by
this time, occurring prior to the termination of
subduction along the plate boundary at ca. 12 Ma
and emplacement of the intraplate basaltic lava
fi elds along the eastern Gulf of California coast
(Bryan et al., 2013). Consequently, the period of
enhanced andesitic volcanism during the middle
Figure 7. Probability density plot of igneous ages from western Mexico for the period
40–12 Ma. Dated rocks have been grouped into four main compositional groupings: basalt
(includes basaltic andesites and tholeiitic, calc-alkaline and rare alkaline varieties), ande-
site, dacite, and rhyolite (includes high-silica rhyolites and rare peralkaline compositions).
Important features of the diagram are: (1) the silicic-dominant character of the Oligocene
Sierra Madre Occidental pulse; (2) the appearance of basalts (Southern Cordilleran Ba-
saltic Andesite [SCORBA] of Cameron et al., 1989) during the Oligocene silicic ignimbrite
pulse and an increase in the frequency of basaltic eruptions up to the start of the early
Miocene pulse ca. 25–24 Ma; (3) the bimodal character of the early Miocene pulse; (4) the
increase in andesitic compositions beginning ca. 20 Ma until ca. 14 Ma; and (5) the abrupt
decline in rhyolite magma generation and eruption beginning ca. 19–18 Ma, when dacite-
andesite eruptions were more predominant, representing the Comondú period of igneous
activity centered on the Gulf of California. Figure is modifi ed from Bryan et al. (2013); age
data were plotted using Isoplot (Ludwig, 2003).
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Large igneous provinces and silicic large igneous provinces
Geological Society of America Bulletin, July/August 2013 1069
Miocene (ca. 20–12 Ma) was spatially and tem-
porally coincident with this extension and crustal
thinning, which was principally localized in
space and time around the nascent Gulf of Cali-
fornia, and where crustal thicknesses were being
reduced by up to 50%.
The middle Miocene period of andesitic vol-
canism is now alternatively interpreted to be a
consequence of the active extensional environ-
ment. By ca. 18 Ma, rift modes had changed
from wide to narrow as extension became fo-
cused in the Gulf of California region (Fig. 8).
Several early Miocene grabens that had formed
to the east were magmatically abandoned by
ca. 18 Ma (Ferrari et al., 2002; Ramos Rosique ,
2013). Bimodal magma systems, which had
been active across the Gulf of California region
(Ferrari et al., 2012), were now being more ac-
tively disrupted by extensional faulting, which
was promoting large-scale magma mixing
(Bryan et al., 2013) and the generation of in-
termediate magma compositions (e.g., Johnson
and Grunder, 2000). This switch had an impor-
tant effect on silicic magma generation rates,
which appear to have signifi cantly decreased
during this period as mafi c magma inputs to the
crust became more focused in the gulf region,
where eruption tendency increased (Fig. 7).
In summary, new age, stratigraphic, and
structural data are confi rming a spatial-temporal
overlap and connections between silicic large
igneous province volcanism of the Sierra Madre
Occidental and extension that led to the open-
ing of the Gulf of California. Like other large
igneous provinces, the Sierra Madre Occidental
igneous record was pulsed, with the early Mio-
cene pulse clearly synrift in character (Ferrari
et al., 2002, 2012; Murray et al., 2010; Ramos
Rosique , 2013). As extension rate increased
and/or became focused on the gulf region at ca.
18 Ma, this had a profound effect on magma-
tism, which was greatly reduced or switched off
at the regional scale, but continued locally in
and around the gulf. Here, the active extensional
faulting modifi ed erupted magma compositions,
which were dominantly intermediate, and erup-
tion styles became dominantly effusive, produc-
ing lavas and domes. At the same time, eruptive
volumes were lowered as a consequence of
reduced rates of crustal partial melting, which
had been required to produce the large vol-
umes of rhyolite that had previously dominated
the Oligo cene and early Miocene pulses of the
Sierra Madre Occidental. Crustal rupturing to
open the Gulf of California and form the Baja
California microplate took at least 25 m.y., a
time span comparable to the opening of the Red
Sea (Menzies et al., 1997).
Crustal Melting and Igneous Recycling
Many previous studies have emphasized the
fundamental role of crustal partial melting to
generate the observed volumes and geochemical
characteristics of the fl ood rhyolites that com-
prise silicic large igneous provinces (e.g., Ewart
et al., 1992; Pankhurst and Rapela, 1995; Riley
et al., 2001; Ferrari et al., 2007; Bryan, 2007;
Bryan et al., 2008). The main controlling fac-
tor in the generation of large igneous province
volumes of rhyolite, rather than basalt, is crustal
setting (Bryan et al., 2002). The Phanerozoic si-
licic large igneous provinces, for example, are all
restricted to continental margins, where fertile,
hydrous lower-crustal materials (graywacke,
ande site; e.g., Tamura and Tatsumi, 2002;
Clemens et al., 2011) were built up by long-lived
subduction. Large-scale and sustained mantle
thermal and material inputs into the crust gen-
erate widespread crustal partial melting of these
hydrous crustal materials and igneous underplate
formed during previous episodes of subduction.
The generation and accumulations of those melts
within the crust will act as density barriers to the
rise of fl ood basaltic magma. Additional basal-
tic magma fl uxes from the mantle will provide
additional heat for further crustal melting, and
this concept supports interpretations that basaltic
magmas erupted in large igneous provinces can
also have signifi cant crustal melt contributions
(Carlson and Hart, 1987; Coble and Mahood,
2012). Consequently, the potentially widespread
silicic melt density barrier that develops pro-
motes mafi c magma intrusion and crustal pond-
ing and inhibits a substantial and more typical
mafi c surface expression for large igneous prov-
ince events along paleo- and active continental
margins (Bryan et al., 2002; Bryan, 2007). This
has recently led to the notion that silicic large
igneous provinces represent “hidden mafi c large
igneous provinces,” where the mafi c-ultramafi c
magmatic component becomes stalled in the
lower crust (Ernst, 2013).
A new discovery from recent U-Pb zircon
chronochemical data for Sierra Madre Occi-
dental rhyolites has been the identifi cation of
a very distinctive zircon age and chemical sig-
nature for the synextensional early Miocene
rhyolites (Bryan et al., 2008; Ferrari et al., 2012;
Figure 8. Space-time map of northwestern Mexico showing the
progressive switch from wide rift and silicic-dominant to bimodal
volcanic modes from ca. 30 Ma to 18 Ma, to a narrow rift and in-
termediate composition volcanic mode after 18 Ma focused on the
current site of the Gulf of California. Dashed purple line denotes
current extents of Sierra Madre Occidental Oligocene–early Mio-
cene volcanism on mainland Mexico (see Fig. 5).
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Bryan and Ferrari
1070 Geological Society of America Bulletin, July/August 2013
Ramos Rosique, 2013). Most igneous zircons
typically have U concentrations between 100
and 2000 ppm (e.g., Harley and Kelly, 2007),
but many of the dated early Miocene rhyolites
contain zircons showing many orders of mag-
nitude variation in U concentrations that range
up to ~1.5 wt% U (~15,000 ppm). The chemi-
cal variation is commonly age related, with the
youngest zircons showing the highest U and Th
enrichments (Bryan et al., 2008). However, stan-
dard statistical treatments of the concordant age
populations (e.g., Isoplot; Ludwig, 2003) fail to
provide geologically reasonable emplacement
age estimates for the rhyolites. The high mean
square of weighted deviates (MSWD) values
and polymodal age distributions, coupled with
the extreme chemical variation, indicate sub-
stantial zircon inheritance. Recognition of zircon
inheritance and the magnitude of inheritance is
diffi cult because of often subtle age differences
amongst the dated populations and because indi-
vidual zircon grain ages overlap with the general
duration of Sierra Madre Occidental igneous
activity (i.e., 38–18 Ma; Bryan et al., 2008). A
key approach to recognizing inheritance and
confi rming the magnitude of inheritance has
been a “double-dating” approach by pairing
the U-Pb zircon ages with 40Ar/39Ar feldspar or
biotite ages from the same sample, supported
by detailed stratigraphic information (Bryan
et al., 2008; Ferrari et al., 2012; Ramos Rosique,
2013). The key assumption of the double-dating
approach has been that the 40Ar/39Ar ages con-
strain the eruption age and serve as a reference
age for the U-Pb zircon age data. Recent stud-
ies have recognized age discrepancies between
the two dating techniques of up to 8 m.y., which
are well outside the analytical errors of the two
techniques (Bryan et al., 2008; Ferrari et al.,
2012; Ramos Rosique , 2013). Lithologically,
many of the samples showing the strongest age
discrepancies are crystal-poor rhyolite to high-
silica rhyolite lavas/domes, and thus represent
relatively small-volume magma batches. The
zircon population ages are consistently older
than the corresponding 40Ar/39Ar age, and this
leads to the conclusion that the majority, if not
all, of the zircons present in these silicic magmas
are inherited and antecrystic (Bryan et al., 2008).
The ages of the antecrystic zircons indicate that
they have been derived from mostly solidifi ed
plutonic rocks formed during earlier phases of
silicic magmatism. The zircon chemistries give
insight into the degree of differentiation of the
remelted igneous rocks, and the high-U zircon
subpopulations indicate highly fractionated ig-
neous rock representing a component of the
source region undergoing remelting. Additional
outcomes of these studies are that these ante-
crystic zircon-bearing rhyolites:
(1) represent Zr-undersaturated magmas,
where little to no new zircon crystallized prior
to eruption;
(2) may contain other inherited crystal popu-
lations (e.g., feldspar, apatite);
(3) have most likely been generated and
emplaced rapidly, based on zircon dissolution
modeling (Bryan et al., 2008), which is a fi nd-
ing from studies of other rhyolitic magmatic
systems (e.g., Charlier et al., 2005); and
(4) show A-type geochemical signatures
(Ramos Rosique, 2013).
These age data thus indicate that while, at the
fi rst-order, silicic large igneous provinces, like
the mafi c large igneous provinces, record new
crustal additions from the mantle through basal-
tic underplating and intrusion, and potentially
substantial igneous crustal thickening (Fig. 5),
with time, much of the silicic igneous activity
instead refl ects signifi cant crustal remelting and
recycling. This is also a feature of continental
fl ood basalt provinces, where some workers
have interpreted the origin of the associated
fl ood rhyolites to be due to crustal remelting,
including the basaltic igneous underplate (e.g.,
Garland et al., 1995; Ewart et al., 2004; Miller
and Harris, 2007). For the Sierra Madre Occi-
dental, rhyolites with high antecrystic zircon
contents appear to be characteristic of the early
Miocene pulse, but they do not dominate the
zircon age populations of ignimbrites related to
the Oligocene pulse. While zircon inheritance
is present in the Oligo cene ignimbrites, these
inherited zircons are more xenocrystic in
character, being sourced largely from Meso-
zoic and older crustal materials (Bryan et al.,
2008). This difference in zircon inheritance
between the two silicic volcanic pulses may
refl ect a long-term trend in changing crustal
source regions for the silicic magmas. The
dominance of antecrystic zircons, often with
highly fractionated chemistries, indicates deri-
vation from plutonic rocks emplaced at mid-
to upper-crustal levels, whereas Mesozoic to
Proterozoic xenocrystic zircons in the Oligo-
cene ignimbrites may refl ect derivation from
partially melted lower-crustal source regions
(Bryan et al., 2008).
A key question then is: What promoted crustal
partial melting at mid- to upper-crustal levels in
the early Miocene, where crustal lithologies had
apparently become volumetrically dominated by
young igneous rocks? Many of the antecryst-
rich early Miocene rhyolites occur as domes or
lavas emplaced along synvolcanic normal faults
defi ning grabens and half grabens, or they occur
as fi ssure-fed ignimbrites fed from these syn-
vol canic extensional fault systems (Bryan et al.,
2008; Ferrari et al., 2012; Murray et al., 2010;
Ramos Rosique , 2013). Spatially and tem-
porally associated with these rhyolites, basaltic
lavas and dikes also appear to have been fed
from graben-bounding fault structures (Ferrari
et al., 2002, 2012; Ramos Rosique, 2013). The
active extensional faulting therefore appears to
have been fundamental to generating much of
the silicic volcanism in the early Miocene pulse
of the Sierra Madre Occidental. The working
hypothesis that requires further examination is
that synvolcanic extension allowed basaltic mag-
matism to invade higher structural levels in the
crust and cause remelting of largely Oligocene
granitic rocks residing in the middle to upper
crust. Here, relatively small volumes of rhyolite
magma were generated rapidly and ascended
quickly because of the active extensional regime.
As suggested for synextensional volcanism in
the western United States, the active faulting
may have promoted degassing of magmas and
thus more effusive eruptive styles (e.g., Gans
et al., 1989; Axen et al., 1993). However, in the
Sierra Madre Occidental, the differentiated and
potentially degassed plutonic source rocks may
also have contributed to generating gas-poor si-
licic magmas that promoted effusive eruption.
CONCLUSIONS
Large igneous provinces record episodic, but
commonly multiple synchronous major mantle
melting events during which large volumes (106
to 107 km3 at the provincial scale; >108 million
km3 for event clusters or periods of supercon-
tinent breakup) of mafi c, and generally sub-
ordinate silicic and ultramafi c, magmas were
generated and emplaced by processes distinct
from those observable at modern plate bound-
aries, and predicted in a simple way by plate-
tectonic theory. This anomalous igneous volume
is aided by an elevated frequency of large-vol-
ume eruptions or supereruptions during large
igneous province events, where individual erup-
tions of basaltic and silicic magma commonly
range from hundreds of cubic kilometers up to
~10,000 km3 in volume, such that large igneous
provinces are the only known locus of basal-
tic supereruptions on Earth (Thordarson et al.,
2009; Bryan et al., 2010).
Research over the past 25 yr has focused
on several aspects of large igneous provinces,
often raising more questions than have been
answered . These aspects include:
(1) Large igneous provinces in the geologic
record. A terrestrial large igneous province rec-
ord has been interpreted as far back as 3.79 Ga
(Isley and Abbott, 1999, 2002; Ernst and Buchan ,
2001), and an older and better-preserved record
of large igneous provinces may occur on the
inner planets (Head and Coffi n, 1997). A long-
term average of ~1 large igneous province every
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Geological Society of America Bulletin, July/August 2013 1071
20 m.y. has been estimated (Ernst and Buchan,
2002), but the lack of an oceanic large igneous
province record older than 200 Ma, and the in-
creasing fragmentation of Paleozoic to Archean
large igneous provinces by erosion and tec-
tonism hinder efforts to constrain whether
this long-term average has remained constant
(Prokoph et al., 2004) or changed over Earth
history. Importantly, the Late Proterozoic and
Phanerozoic record highlights a strong cluster-
ing of large igneous province events, coinciding
with supercontinent cycles.
(2) Large igneous provinces and continental
breakup. Most large igneous province events are
spatially and temporally linked to supercontinent
cycles and their breakup (Fig. 1). Volcanic rifted
margins are a major expression of supercon-
tinent breakup, with up to 90% of the present-
day rifted margins that developed in response
to Pangea breakup being characterized by large
igneous province magmatism. In some cases, the
onset of new seafl oor spreading may be delayed
by up to 50 m.y. from the onset of large igne-
ous province magmatism, preventing a recogni-
tion of clear links between the magmatism and
subsequent ocean basin–forming processes. Not
all large igneous provinces are succeeded by
continental breakup, however, and the reasons
why some large igneous provinces are torn apart
and others are not remain unclear. Based on the
breakup history of Pangea, greater proportions
of large igneous provinces unrelated to breakup
appear to occur during and initially after super-
continent assembly (Grofl in and Bryan, 2012).
(3) Large igneous province clusters. Large ig-
neous province events are not evenly distributed
over geologic time, and even during periods of
higher frequency, such as the breakup stage of
supercontinents, multiple, temporally coincident
but spatially separate large igneous province
events have occurred (large igneous province
cluster). Volumetrically, the largest known clus-
ter of large igneous province events began ca.
120 Ma, when a volume of ~100 million km3
of magma was added to the lithosphere. Put in
perspective, this is equivalent to half the crustal
volume of the Australian continent or ~1.5% of
the total estimated volume of continental crust
(Cogley, 1984) forming within 30 m.y. While
the clustering of large igneous province events
is strongly linked to supercontinental breakup,
rather surprisingly, a very poor correlation
exists between large igneous province cluster-
ing and the magnitude of these events with mass
extinctions.
(4) Large igneous provinces and crustal
growth. Large igneous provinces represent
substantial but episodic additions of juve-
nile crust, such that the crust has had periodic
growth spurts in addition to more steady-state
growth by subduction processes (cf. Cawood
et al., 2013). Large igneous provinces have
large and extensive volcanic expressions, but
the nature and volume of the associated intru-
sive underpinnings are less well known and are
poorly constrained. Previous studies have esti-
mated that the intrusive component to a large
igneous province may be up to ten times the
extrusive volume, and the tremendous crustal
thicknesses developed for oceanic plateaus
support this (e.g., Coffi n and Eldholm, 1994).
The contribution of large igneous provinces to
crustal growth will often be absent in zircon-
based studies (e.g., Condie, 1998; Condie et al.,
2009, 2011; Cawood et al., 2013) because the
fl ood basalts will almost always remain zircon
undersaturated. However, it remains under-
appre ciated that the silicic large igneous prov-
inces will make major contributions to detrital
zircon records. This is because the volumetri-
cally silicic-dominant magmas are typically zir-
con saturated and contain abundant zircon, and
the eruptive processes result in tremendous vol-
umes of dominantly sand-grade pyroclastic ma-
terial that can easily be resedimented and dictate
the sediment provenance of many large basins
(e.g., Bryan et al., 1997, 2012). While the best
known examples of silicic large igneous prov-
inces are found in the Phanerozoic (Bryan et al.,
2002; Bryan, 2007), there is no reason why they
would not also have occurred extensively in the
Protero zoic and Archean.
(5) Large igneous provinces and mass extinc-
tions. As a result of an improved understanding
of the location, dimensions, age, and volcanic
aerosol budgets of large igneous provinces,
there is a growing consensus that large igne-
ous province eruptions can cause environmental
and climatic effects that are suffi ciently severe
to trigger mass extinctions (Wignall, 2005).
Key aspects underpinning this are an improved
under standing of the frequency and magnitude
of basaltic and silicic supereruptions from large
igneous provinces (Bryan et al., 2010), the envi-
ronmental setting of the large igneous province
(e.g., Svensen et al., 2004), and the substantial
aerosol and ash budgets emitted (e.g., Self et al.,
2005; Svensen et al., 2009; Cather et al., 2009;
Black et al., 2012). However, many uncertainties
and challenges remain to demonstrate that the
onset and peak eruptions of large igneous prov-
inces coincide with all extinction events, to de-
termine the kill mechanism(s), and to integrate
their effects on land and in the oceans, where the
kill mechanisms may be different and multiple
(e.g., Archibald et al., 2010). While most atten-
tion has been given to quantifying the aerosol
budgets of large igneous province eruptions, is-
sues still exist on the ways in which fl ood basal-
tic eruptions can sustain aerosol delivery to the
stratosphere for maximum climatic effect over
the eruption duration (years to decades).
(6) Large igneous provinces and mineral and
energy resources. Large igneous provinces are
major repositories for a range of orthomagmatic
ore deposits, in particular PGEs and Cu-Ni sul-
fi de mineralization. Given the tremendous heat
fl uxes associated with large igneous province
magmatism, large ore-forming hydrothermal
systems can also develop (Pirajno, 2007), and
the silicic large igneous provinces are host
to precious metal hydrothermal ore deposits.
Large igneous province magmatism is also inte-
gral to many sedimentary basins, with the igne-
ous rocks and emplacement processes exerting
a major control on petroleum prospectivity.
As petroleum exploration extends into deeper-
water regions along rifted continental margins,
future efforts will be required to reduce “vol-
canic risk”; volcanism can signifi cantly impact
reservoir presence and effectiveness, depending
on its timing and mode of emplacement (i.e., in-
trusive or extrusive).
(7) Planetary large igneous provinces. Large
igneous province–scale magmatism is now rec-
ognized on the Moon and inner planets. These
examples can provide important constraints on
terrestrial large igneous province origins be-
cause of their near-intact preservation due to
minimal erosion rates and the lack of plate tec-
tonics. Several fl ood basaltic lavas, the products
of M >8 supereruptions, have also been mapped
out. A variety of planetary igneous provinces
have been identifi ed that morphologically rep-
resent analogues to terrestrial large igneous
province types; these include lunar maria and
terrestrial continental fl ood basalts, mafi c ig-
neous crustal plateaus on Venus and terrestrial
oceanic plateaus, rift-dominated volcanic rises
on Mars and Venus and terrestrial volcanic rifted
margins, and extensive radial grabens and ridges
on Mars and dike swarms on Earth. Silicic large
igneous provinces, however, appear to be ab-
sent from the other planets due to the absence
of plate tectonics and subduction, which are
required to build up hydrated crust for later par-
tial melting. While the areal extent and inferred
volume of planetary large igneous provinces are
large, covering >5% of the surface area of each
planet, few constraints currently exist on the ab-
solute age and duration of the igneous activity
and whether they record geologically rapid (<50
m.y.) events as on Earth, or if they are the end
product of prolonged planetary mantle melting
events lasting 108–109 m.y.
(8) Large igneous provinces and mantle geo-
dynamics. Large igneous provinces have be-
come integral to our understanding of mantle
dynamics, and, along with hotspots, they poten-
tially provide samples of, and windows into, the
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Bryan and Ferrari
1072 Geological Society of America Bulletin, July/August 2013
lower mantle. Large igneous provinces have al-
most become synonymous with mantle plumes
in the literature. It is widely accepted that large
igneous provinces record major mantle melting
events, but signifi cant debate over the past 15 yr
has largely become polarized into models pro-
posing an origin from core-mantle boundary–
derived mantle plumes (e.g., Campbell, 2007),
or from shallow processes controlled by stress,
plate tectonics, and upper-mantle fertility (e.g.,
Foulger, 2007). Large igneous provinces show
a suffi cient commonality and suite of features
(Bryan and Ernst, 2008) that distinguish them
from magmatism generated at modern plate
boundaries, and this leads to the conclusion
that a common process promoting excess and
rapid mantle melting exists in their formation.
At present, existing models remain unsatisfac-
tory in explaining the key geologic features of
all large igneous provinces, and, in particular,
contrasts exist between models for oceanic and
continental large igneous provinces and be-
tween those formed in the interiors and on the
margins of continents.
(9) Silicic large igneous provinces. These rep-
resent a new class of large igneous provinces rec-
ognized in the past 25 yr, where the scale of the
silicic magmatism is similar to the better-known
continental fl ood basalt provinces and basaltic
volcanic rifted margins, and eruptive volumes
are an order of magnitude larger than silicic
volcanism generated in arc-rift to backarc ex-
tensional settings (Bryan et al., 2002). The large
volumes of rhyolite generated in these events
require partial melting of the crust, and this is
achieved by the underplating and intrusion of
large igneous province–scale intraplate basaltic
magmas, and thus silicic large igneous provinces
can be thought of as “hidden” mafi c large igne-
ous provinces (Ernst, 2013). The Sierra Madre
Occidental of western Mexico is the most recent
silicic large igneous province event, and new
research is revealing important links and feed-
backs among the volcanism, extension, and con-
tinental rupture that recently opened the Gulf of
California. In particular, the large-volume silicic
volcanism coincided with wide rifting, but a
change to a narrow rift mode resulted in the ter-
mination of large-volume silicic volcanism and a
change in eruptive styles and to more intermedi-
ate magma compositions, promoted by the inter-
action between bimodal magma systems and
active extensional faulting (Bryan et al., 2013).
In addition, long-term temporal-compositional
trends in the silicic magmas suggest a greater
degree of crustal recycling as basaltic magmas
penetrated higher crustal levels as extension pro-
ceeded to partially remelt igneous rocks formed
during earlier phases of the silicic large igneous
province (Bryan et al., 2008).
ACKNOWLEDGMENTS
The International Association of Volcanology and
Chemistry of the Earth’s Interior (IAVCEI) estab-
lished the Large Igneous Province Subcommission,
which maintains a Web site with up-to date informa-
tion that is a tremendous resource on large igneous
provinces. See http://www.largeigneousprovinces.org.
Bryan has been supported by a Vice Chancellor’s
Fellowship to Queensland University of Technology,
and we acknowledge support by grant CONACyT
82378 to Ferrari. The submarine samples shown
on Figure 5 were collected by cruises supported by
the U.S. National Science Foundation (NSF; grants
0203348 and 0646563 to co–principal investiga-
tors Peter Lonsdale and Paterno Castillo), as well
as grants to Peter Lonsdale and Jared Kluesner for
the BEKL, ROCA, and DANA cruises in the Gulf
of California. David Gust is thanked for support and
general discussions on silicic magmatism. Valuable
discussions with Aldo Ramos Rosique, complet-
ing his Ph.D. thesis in the southern Sierra Madre
Occidental, and Jose Duque Trujillo, undertaking
a thermochronological Ph.D. study in the southern
Gulf of California, are acknowledged, and their work
has contributed to our new understanding of silicic
magma generation in the Sierra Madre Occidental
and Gulf of California. This manuscript has also
benefi ted from discussions with Stefan Grofl in and
outcomes from his ongoing Ph.D. research into the
Early Permian Panjal large igneous province and
Irina Romanova who is undertaking Ph.D. research
on Shatsky Rise oceanic plateau. Valuable discus-
sions with Steve Self and Charlotte Allen on aspects
of this manuscript are appreciated. We thank Richard
Ernst and Martin Menzies for constructive reviews of
this manuscript, and Brendan Murphy, editor of the
GSA Bulletin 125th anniversary celebration articles,
for his invitation and support.
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SCIENCE EDITOR: J. BRENDAN MURPHY
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REVISED MANUSCRIPT RECEIVED 5 FEBRUARY 2013
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Errata
Granite: From genesis to emplacement
Michael Brown
(v. 125, no. 7/8, p. 1079–1113, doi: 10.1130/B30877.1)
In the third column on p. 3, line 34, the phrase should read “granular framework–controlled fl ow behavior.”
In the third column on p. 26, the sentence, deleting “Furthermore,” should read: “This issue has been discussed in detail by De Paoli et al. (2012), who
concluded that limitations of the haplogranite melt model become pronounced for intermediate and mafi c rock compositions, where the calcium, iron
and magnesium contents of the modeled melts in particular do not correspond to those of comparable experimental glasses. The conclusion..”
Large igneous provinces and silicic large igneous provinces: Progress in our understanding over the last 25 years
Scott E. Bryan and Luca Ferrari
(v. 125, no. 7/8, p. 1053–1078, doi: 10.1130/B30820.1)
The correct reference for Zhu et al. in the reference list should read:
Zhu, D.C., Chung, S.L., Mo, X.X., Zhao, Z.D., Niu, Y.L., Song, B., and Yang, Y.H., 2009, The 132 Ma Comei-Bunbury large igneous province: Remnants identifi ed in present-day southeastern
Tibet and southwestern Australia: Geology, v. 37, p. 583–586, doi:10.1130/G30001A.1.
The cover image of the May-June 2013 issue of the Bulletin should be attributed to Jeanette Arkle. It corresponds to the article in the same issue by
Arkle et al.