Download An introduction to magma dynamics Geological Society, London

Geological Society, London, Special Publications
An introduction to magma dynamics
Georg F. Zellmer and Catherine Annen
Geological Society, London, Special Publications 2008; v. 304; p. 1-13
doi:10.1144/SP304.1
Email alerting
service
click here to receive free email alerts when new articles cite this
article
Permission
request
click here to seek permission to re-use all or part of this article
Subscribe
click here to subscribe to Geological Society, London, Special
Publications or the Lyell Collection
Notes
Downloaded by
on 24 August 2008
© 2008 Geological Society of
London
An introduction to magma dynamics
GEORG F. ZELLMER1,2 & CATHERINE ANNEN3
1
Institute of Earth Sciences, Academia Sinica, 128 Academia Road Sec. 2, Nankang,
Taipei 11529, Taiwan, ROC (e-mail: [email protected])
2
Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades,
NY 10964, USA
3
Département de Minéralogie, Université de Genève, Rue des Maraı̂chers 13,
1205 Genève, Switzerland
Abstract: A variety of methods have been employed to decipher magmatic systems, including
geophysical, petrological, textural and geochemical approaches, and these elucidate a large
variety of characteristics of different plumbing systems and magmatic differentiation processes.
A common theme to the papers presented in this book is the observation of transport of small
volume magma batches with a relatively high frequency, as opposed to less frequent transport
of larger magma volumes that would require storage in large crustal reservoirs for long periods
of time. The implications of this observation are discussed in the context of a possible tectonic
control on crustal magma dynamics.
This book addresses the rapidly developing fields of
crustal magma transfer, storage and evolution.
During both transfer trough and storage within the
crust, magmas are subject to a series of processes
that lead to their differentiation. Depths and mechanisms of differentiation, crustal contributions to
magma generation through wall-rock assimilation,
rates and timescales of magma generation, transfer
and storage, and how these link to the thermal
state of the crust, are subject to lively debate and
controversy. This volume presents a collection of
papers that provide a balanced overview of the
diverse approaches available to elucidate these
topics, and includes both theoretical models and
case studies. By integrating petrological, geochemical and geophysical approaches, it provides the
reader with new insights to the subject of magmatic
processes operating within the Earth’s crust, and
reveals important links between subsurface
processes and volcanism.
This volume is divided into four sections:
‘Magma transfer: from mantle to surface’ addresses
the ascent and evolution of magmas from the zone
of melt generation in the mantle to eruption at the
surface, forming a backdrop for the detailed
studies of distinct parts of magma plumbing
systems addressed later. ‘Dynamics of magma
transport’ focuses on theoretical and geophysical
approaches to understanding magma movement
through the crust. ‘Magma reservoir dynamics’
provides insights from petrographic and mineral
chemical studies into the processes occurring in
crustal magma chambers. Finally, ‘Processes of
silicic melt generation’ concludes the book with a
dedicated section on the long-standing question of
where and how magma differentiation may take
place. In nature, these issues are of course intimately related, and some of the papers in this
volume address more than one of these aspects.
Therefore, the reader may obtain additional insights
to a particular theme by referring to the other sections of the book.
With the exception of two contributions
(Leeman et al.; Wright & Klein), all case studies
presented in this volume deal with subduction
zone magmatism. The inferences made here on
the dynamics of magma ascent, storage and differentiation are therefore biased towards this tectonic
setting. It may be argued that subduction-related
magmatic systems are likely to have very different
petrogenetic characteristics than ocean ridge and
intraplate volcanism. Firstly, the primary magmas
are produced at different depths within the mantle,
and have different temperatures and compositions,
particularly with regard to their volatile contents.
Secondly, as a result of these differences, their petrogenetic evolution within crustal magma systems
will differ significantly. For example, crystallization of volatile-rich arc magmas may be triggered
by rapid decompression-induced degassing during
magma ascent through the crust, a process that is
not readily applicable for ocean ridge and intraplate
magmatic systems. Thirdly, tectonic controls on the
geometry of the plumbing systems differ considerably. Ocean ridges are in extension, resulting in
rapid magma ascent through dykes and movement
From: ANNEN , C. & ZELLMER , G. F. (eds) Dynamics of Crustal Magma Transfer, Storage and Differentiation.
Geological Society, London, Special Publications, 304, 1–13.
DOI: 10.1144/SP304.1 0305-8719/08/$15.00 # The Geological Society of London 2008.
2
G. F. ZELLMER & C. ANNEN
of newly created crust away from the heat source. In
contrast, intraplate magmatism may favour magma
storage and differentiation within the crust due to
repeated sill intrusion and resulting progressive
elevation of the geothermal gradient. Arcs, on the
other hand, may be situated within extensional,
transtensional or compressional regimes, potentially resulting in differences between the plumbing
systems of different arcs (cf. Zellmer). Further
work will be required to gain a balanced understanding of the dynamics of magma plumbing
systems within different tectonic settings.
approach is used by Cigolini et al. to elucidate the
plumbing system of Stromboli volcano from upper
mantle to surface. The data suggest that phenocrysts
nucleate within a few days in a magma reservoir
that extends vertically from 11 to 5.4 km below
the summit of Stromboli. A new model is proposed
where the magma chamber takes the shape of a vertically elongated ellipsoid that is penetrated by a
feeder dyke sourced from over 30 km depth, i.e.
in the mantle. According to this model, the instantaneous elastic rebound of the walls of the depressurizing subvolcanic reservoir explains the
occurrence of intermittent paroxysmal eruptions at
this volcano.
Magma transfer: from mantle to surface
Studies of igneous processes often focus on those
parts of the crustal plumbing system that are best
elucidated by the samples or methods available. It
is rare that systems have been studied in sufficient
detail to inform the entire process from magma generation in the mantle to eruption at the surface. This
book starts with two studies where the amount of
data is sufficient to provide such insights, on one
hand using global volcanological, geophysical and
geochemical datasets to present a broad overview
of magma transfer (Zellmer), on the other hand
focussing on the single edifice of Stromboli
Volcano to a gain detailed understanding of the petrogenetic processes occurring along the entire
mantle-crust section beneath this volcano (Cigolini
et al.). These papers address the dynamics of
igneous processes operating at sites of ongoing
volcanic activity, and therefore form a backdrop
for the detailed studies of the distinct parts of magmatic plumbing systems focused on in the later sections of this book.
From global correlations between eruptive style,
surface heat flux and convergence rates of different
volcanic arcs, Zellmer infers that the rate of melt
production in the mantle wedge ultimately controls
the dynamics of magma transfer through the crust,
and thereby the chemical and physical properties
of magmas and eruption products. It is shown that
a deep crustal hot zone (Annen et al. 2006) does
not buffer the effects of subduction velocity on
melt production, and that the rate of magma
generated in and released from the hot zone is proportional to the magma advected to the hot zone
from the mantle wedge.
Crystal size distributions, bubble content and
magma rheology, petrology and chemistry are a
number of parameters that – when studied in
combination – may offer a very detailed picture
of the processes operating within magma plumbing
systems, and can be used to quantify pressures,
temperatures and the rates of preeruptive crystallization and gas exsolution. Such a multi-faceted
Dynamics of magma transport
Background
The second section of this book deals with insights
that can be gained from theoretical and geophysical
research. Direct observations of eruptions along
fractures, ground deformation and the distribution
of seisms associated with magma intrusion (e.g.
Pollard et al. 1983; Rubin & Pollard 1987; Peltier
et al. 2005; Yamaoka et al. 2005; Aloisi et al.
2006; Mattia et al. 2007) provide evidence for the
role of dykes in mafic magma transport (cf.
Figs 1a & 2). In the case of andesitic volcanism,
effusive or explosive, eruptions are more focused
and the conduits are more cylindrical (cf. Fig. 1b).
This may be explained through melting of host
rocks (Quareni et al. 2001), and may also be
related to a sharp increase in magma viscosity
close to the surface due to decompression, degassing and crystallization. Rhyolitic magma, when
associated with caldera formation, is transported
to the surface through ring dykes.
It has also been suggested that interconnected
sills could transport magma through the crust
(Marsh 2004; Cartwright & Hansen 2006; e.g.
Fig. 3a). Interpretation of geochemical and geophysical data suggests that the plumbing system of
many volcanoes may be a complex plexus of
interconnected sills and dykes (Hildreth 1981;
Lahr et al. 1994; Donoghue et al. 1995; La Delfa
et al. 2001; Preston 2001; Dawson et al. 2004;
Sanchez et al. 2004; cf. Fig. 1c).
For granitic magma, diapirism was thought to be
a common mechanism of magma transport and
emplacement within the crust (e.g. Whitehead &
Luther 1975; White & Chappell 1977; Pitcher
1979; Hildreth 1981; Marsh 1982; cf. Figs 1f &
3b). However, Hot-Stokes diapirism, characterized
by ductile flow of host rock around the rising
magma mass, is regarded as thermally and mechanically unrealistic within the mid to upper crust, and
INTRODUCTION
3
Fig. 1. Summary of possible crustal magma plumbing systems as inferred through studies in this volume. Magmas
may have been processed within a lower crustal hot zone (Annen et al. 2006), although some mantle melts may
be transferred instantly into and through the crustal section (cf. Straub). (a) Magma transport through dykes
(cf. Martin-Del Pozzo et al.; Wright & Klein), at rates of centimetres to tens of kilometres per day. (b) Development of
small vertical chambers (cf. Cigolini et al.; Dosseto et al.; Wright & Klein), with storage times between days and a few
thousand years. (c) Magma transport through interconnected dykes and sills (cf. Bunger; Leeman et al.), with sill
solidification timescales of the order of 10–100 years. (d) Development of small horizontal chambers, e.g. through
repeated sill intrusion (cf. Ban et al.; Leeman et al.), with storage times between tens of years and thousands of years.
(e) Development of plutons through repeated addition of small magma batches over long timescales of up to 105 –107
years (cf. Burgess & Miller; Gray et al.). Large magma chambers may form through rapid (a few hundred years, e.g.
Michaut & Jaupart 2006) large-scale crustal melting when enough thermal energy has accumulated (cf. Leeman et al.).
(f) Diapirism as a mechanism to emplace felsic magma reservoirs. For emplacement into the mid to upper crust,
visco-elastic diapirism as suggested by Miller and Paterson (1999) would be required. Note that none of the studies in
this volume find evidence for diapirism. Although the stalling of magma is not only controlled by the stress field, but
also by the rheological properties and densities of crustal lithologies, the studies presented in this volume suggest that
(a) and (b) may be favoured in extensional or transtensional settings, while (c)–(e) are more likely to occur in
compressional tectonic regimes (see also Zellmer).
dyking as a magma transfer mechanism is favoured
by a number of studies (Clemens & Mawer 1992;
Clemens et al. 1997; Petford et al. 2000). Hutton
et al. (1990) observed granite intrusion along
ductile extensional shear zones and noted that it
was solving the room problem posed by pluton
emplacement, making diapirism unnecessary.
Conversely, Miller & Paterson (1999) introduced
4
G. F. ZELLMER & C. ANNEN
Fig. 2. Geophysical observations indicate subvolcanic magma transport through dykes. This example shows modelled
sources obtained from dynamic inversion of Mount Etna tilt data and seismicity recorded during intrusion propagation,
as taken from Aloisi et al., ‘Imaging composite dike propagation (Etna, 2002 case)’, Journal of Geophysical
Research, 111, paper B06404, DOI:10.1029/2005JB003908, 21 June 2006. Copyright 2006 American Geophysical
Union. Reproduced by permission of American Geophysical Union.
the term ‘visco-elastic diapir’ and argued that, if
diapirism is defined as the upwelling of mobile
material through or into overlying rocks (Van den
Eeckhout et al. 1986), then it remains an important
emplacement mechanism of felsic plutons. The following field observations are used to support the
model of visco-elastic diapirism: downward movement of host rocks through multiple processes,
including brittle deformation and stoping; involvement of multiple magma batches; and controls of
regional deformation on pluton emplacement.
Visco-elastic diapirism is called upon in a number
of recent case studies of felsic plutons (e.g.
Cabello et al. 2006; Farris et al. 2006; Zak &
Paterson 2006).
In the case of magma transport through fractures, crustal magma transfer can be very fast on
the order of days to years (Clemens & Mawer
1992; Clemens et al. 1997; Petford 2003; Annen
et al. 2006). Large excesses in 226Ra in mafic volcanic products indicate ascent from source to surface
in the order of 1 ka or less (Turner et al. 2000;
Zellmer et al. 2005). In exceptional cases, magma
ascent rates through the crust can be extremely
fast: 26 km per day have been estimated for
some Mexican andesites that carry hornblende –
peridotite xenoliths, which reached the surface so
rapidly that they were not affected by dissolution
in their host magma during ascent from the
mantle (Blatter & Carmichael 1998). In the case
of felsic magma transport through visco-elastic
diapirs, crustal magma transfer rates may be significantly slower, of the order of 1022 to 1 m year21
(Miller & Paterson 1999).
Contribution of this volume
Independent of storage depth and composition of
the magma, many magma bodies are thought to be
established through repeated sill intrusions (Bridgwater et al. 1974; Benn et al. 1999; Cruden &
McCaffrey 2001; de Saint-Blanquat et al. 2006;
Pasquare & Tibaldi 2007). The work of Bunger
provides insights into the parameters that govern
sill propagation. It is shown that, during sill
growth, fracture behaviour is strongly influenced
by viscous flow within the near-tip region, and
that the physics of viscous dissipation must therefore be taken into account when modelling
sill growth.
INTRODUCTION
5
Fig. 3. (a) The cartoon depicts a ‘magmatic mush column’, where colour hotness (see HTML version) portrays magma
temperature and small black squares depict large crystals. The mush column is characterized by a complex variety of
local crystallization environments with different cooling rates, in which crystal inheritance from earlier crystallization
episodes is common. Taken from Marsh, ‘A magmatic mush column Rosetta Stone: the McMurdo Dry Valleys of
Antarctica’, EOS, 85, 497–508, 23 November 2004. Copyright 2004 American Geophysical Union. Modified by
permission of American Geophysical Union. (b) In early models of lithospheric magmatism, intermediate composition
magmas were thought to rise through the crust by diapiric mobilization before coalescing in shallow subvolcanic
reservoirs. Idealized cartoon taken from Hildreth, ‘Gradients in silicic magma chambers: implications for lithospheric
magmatism’, Journal of Geophysical Research, 86, 10153– 10192, 10 November 1981. Published 1981 American
Geophysical Union. Modified by permission of American Geophysical Union.
Using seismic, geodetic and eruption data from
Kilauea volcano, Wright & Klein evaluate the
interplay between magma supply and spreading of
associated rift zones that provide room for intrusions
into the subvolcanic reservoirs. It is shown that the
dynamics of magma supply affects spreading rate,
intrusion frequency and degree of summit inflation,
resulting in varying characteristics of intrusive and
eruptive activity at this volcano.
In a case study of the 2006 eruptions of Popocatepetl volcano, Martin-Del Pozzo et al. use
varying magnetic anomalies to gain insights into
magma ascent and lava dome extrusion. The magnetic signatures of these and associated processes
are superimposed, but they can be distinguished
on the basis of signal morphology, and correlated
with data from other monitoring techniques. It is
deduced from magnetic, seismic and petrological
data that the plumbing system beneath Popocatepetl
is essentially formed by dykes. The stagnation level
is constituted from a series of interconnected dykes
and does not involve a large magma chamber.
Magma reservoir dynamics
Background
The third section of this book focuses on petrographic, petrological and mineral chemical
approaches to elucidate crustal magma reservoirs
and plumbing systems (e.g. Fig. 1d). Magma reservoirs have been inferred to occur at a range of
depths, from the base of the lower crust right up
to near the surface beneath volcanic edifices. The
temperatures and melt fractions within a magma
reservoir depend on its volume and depth. If the
melt fraction is below a critical value (40 –60%),
the crystals form a rigid network (Vandermolen &
Paterson 1979; Marsh 1981; Lejeune & Richet
1995). This mush is a porous medium where melt
and gases may move independently through the
crystal framework. In contrast, if the melt fraction
is above the critical value, the crystals are suspended and the magma is a multiphase fluid able
to convect. In a mush, the separation of the residual
6
G. F. ZELLMER & C. ANNEN
melt from the crystals is mostly by compaction and
deformation (McKenzie 1984; Sparks & Huppert
1984; Petford 2003; Bachmann & Bergantz 2004).
In a liquid magma this separation can be related
to crystal sedimentation or floating, although
thermal convection in the magma chamber can
prevent crystal settling. In a convecting magma
chamber, crystals and liquids can be separated by
crystallization on the magma chamber walls and
convection of the adjacent fluid (Sparks &
Huppert 1984; Sparks et al. 1984).
The shapes and sizes of magma reservoirs are
not well known. Many plutons are roughly circular
in outcrop with steep sides (Pitcher 1979), and
magma chambers and plutons are often represented
as spherical bodies. However, geophysical and
structural studies show that some plutons are silllike, low aspect-ratio, tabular bodies (Bridgwater
et al. 1974; Lefort 1981; Cruden 1998; Petford
et al. 2000), while others are elongate intrusive
bodies of a few kilometres vertical extent (e.g.
Farris et al. 2006). The Socorro magma body,
which can be seen on seismic profiles, is sill-like
(Rinehart et al. 1979; Brocher 1981). Further,
most igneous bodies may have been emplaced by
the incremental assembly of discrete pulses
(Coleman et al. 2004; Vigneresse 2004; de SaintBlanquat et al. 2006). Geochronological data indicate that the assembly of some plutons and batholiths lasted several millions years. For example,
according to U – Pb geochronological data, the Tuolumne Intrusive Suite of the Sierra Nevada, California, was emplaced over 10 millions years (Coleman
et al. 2004), and the Mount Stuart batholith and
Tenpeak intrusion in the Northern Cascades were
emplaced over 5.5 and 2.6 Ma, respectively
(Matzel et al. 2006). Long emplacement timescales
led Glazner et al. (2004) to question the relationship
between plutons and large magma chambers: if
plutons are emplaced slowly by amalgamation of
discrete pulses of magma, the volume of molten
rock during the construction of the pluton might
not greatly exceed the volume of a single pulse.
However, Matzel et al. (2006) argue that the construction of the Mount Stuart batholith was discontinuous and punctuated by high magma flux
intervals that may have led to the formation of
large magma reservoirs (cf. Fig. 1e). The existence
of calderas, the distribution of vents around these
calderas, the large volumes of ignimbrites and the
common occurrence of zoning within these ignimbrites support the existence of large and shallow
felsic magma chambers (Chapin & Elston 1979;
Lipman 1984). In a recent paper, Lipman (2007)
provides a series of arguments that support the
link between plutons and large-volume ignimbrite
volcanism associated with caldera formation, but
stresses that large upper crustal magma reservoirs
may be short-lived, and that in some arcs the volcanic products may come directly from the mid or
lower crust without involving shallow crustal
magma chambers. The view that magma reservoirs
shallower than 20 km are rare is supported by the
absence of detected ground deformation associated
with several eruptions in the Andes (Pritchard &
Simons 2004), and the view that shallow reservoirs
are short-lived is supported by the short residence
time of crystals at magmatic temperatures recorded
by trace element profiles in zones crystals
(e.g. Zellmer et al. 1999, 2003; Costa et al. 2003;
Morgan et al. 2004; Morgan & Blake 2005;
Zellmer & Clavero 2006).
Contribution of this volume
The variety of crystal populations that are found
in volcanic products indicate that crustal magma
transfer processes may in detail be complicated
through uptake of xenocrysts, crystal recycling
within the magmatic system of individual volcanoes, and crystal growth and resorption triggered
by processes such as magma cooling, recharge,
decompression and degassing. Jerram & Martin
provide a review of how these processes may be
deciphered and quantified, and outline avenues for
future research, where a combination of textural
and microgeochemical techniques may provide
an ever more detailed picture of the magma
plumbing system beneath individual volcanoes.
Santorini, one of the decade volcanoes, is used as
a well-studied example.
The evolution of a shallow stratified magma
chamber beneath Zao volcano in NE Japan is
studied by Ban et al., using the petrology and geochemistry of eruption products within a c.
5.8 ka-old tephra layer. The authors deduce high
rates of crystallization and infer that this chamber
was short-lived. They also provide evidence for
magma mixing due to intrusion of a new pulse of
basaltic magma, which ultimately triggered
the eruption.
Processes of silicic melt generation
Background
Since the seminal work of Bowen (1915), it is
known that, when magmas crystallize, the separation of crystals from the residual melt leads to a
chemical evolution of this melt and to the genesis
of evolved magmas. Basalts generated by partial
melting of the mantle, when cooling down and crystallizing at the crust-mantle boundary or within the
crust, can differentiate and produce intermediate
and silicic magmas. However, intermediate and
INTRODUCTION
silicic magmas can also be produced by partial
melting of the crust. Experimental petrology
shows that partial melting of amphibolites in the
lower crust can produce calc-alkaline melts (Rapp
& Watson 1995; Sisson et al. 2005). I-type granites
are thought to be generated by this mechanism
(Chappell & White 2001). The partial melting of
crust of granodioritic, pelitic or greywacke composition produces more aluminous melts that are
thought to be the origin of S- and some A-type
melts (Clemens & Wall 1981; Patiño Douce
1997). Assimilation of crust and fractional crystallization may act concomitantly (AFC, DePaolo
1981), and these processes are variably important
in the evolution of some silicic magmas.
The generation of evolved magma by differentiation of mafic magma in shallow reservoirs is
favoured by many authors (e.g. Sisson & Grove
1993; Grove et al. 1997; Pichavant et al. 2002).
However, on the basis of geochemical data,
Hildreth & Moorbath (1988) proposed that magma
diversity is acquired at the mantle–crust interface
in MASH zones, i.e. produced by processes of
Mixing, Assimilation, Storage and Homogenization. Recently, more arguments based on petrological, geochemical and thermal data were
presented in favour of differentiation in long-lived
deep hot zones located in or below the lower crust
where multiple sills of basalt are intruded and crystallise (Petford & Gallagher 2001; Bryan et al.
2002; Annen & Sparks 2002; Annen et al. 2006).
In these studies, basalt differentiation and partial
melting of the crust can happen simultaneously,
although this is not necessarily the case. Thermal
evolution and differentiation of each successive
sill depend on its position on the geotherm, which
changes with time as sills transfer heat to their
surroundings. The geochemical and petrological
characteristics of the melt depend on the time
between sill emplacement and melt extraction. If
melt segregation and extraction are by compaction,
the melt can evolve further during segregation
(Jackson et al. 2003).
In recent years, isotopic data have elucidated the
timescales of magmatic differentiation processes
(cf. Turner & Costa 2007): decrease of 226Ra
excesses during small degrees of differentiation
within individual volcanic centres indicate that
magmatic evolution may occur in the order of 103
years at some sites (George et al. 2003, and references therein). However, the general decrease of
238
U excesses from mafic towards andesitic compositions in arc lavas suggests that, in order to produce
andesitic compositions from less evolved magmas,
timescales of the order of 105 years are required,
unless open system processes such as magma
mixing are involved (Zellmer et al. 2005). Open
system processes that involve mixing of young
7
mafic with older more felsic composition do
appear to operate in many cases: they are evidenced
through macroscopic and microscopic mixing
and disequilibrium textures within intermediate
volcanic products, and are suggested by the
occasional persistence of 226Ra excesses to dacitic
compositions (Zellmer et al. 2005, and references
therein). Finally, the generation of some rhyolites
has been shown to be associated with large scale rejuvenation of previously intruded felsic magmas from
mid to upper crustal levels (Charlier et al. 2005;
Lipman 2007). The rates of generation of such felsic
magmas are more difficult to constrain, but evidence
of assimilation of ancient crustal rocks indicates that
thermal incubation times of the order of several
hundred ka may be required (Zellmer et al. 2005).
However, once the right thermal conditions are
attained, rhyolite generation from basaltic magmas
may proceed on timescales of the order of 104 years
in some systems (Lowenstern et al. 2006).
Contribution of this volume
Using uranium-series isotope constraints, Dosseto
et al. show that differentiation from mafic to intermediate and felsic magmas is a rapid process at
some arc volcanoes (e.g. ,2500 years for Mount
St Helens). In contrast to suggestions of a longlived, deep-crustal hot zone as a key site for magmatic differentiation (Annen et al. 2006), the
authors suggest that in the case of Mount
St Helens, the magmatic evolution is constrained
to the cooler environment of the mid crust.
In their study of the Tuolumne Intrusive Suite of
the Sierra Nevada Batholith, California, Gray et al.
provide thermobarometric evidence for subsolidus
exsolution of crystal phases at depths near 6 km,
and argue that the scatter of trace element and isotopic signatures precludes fractional crystallization
of a large magma chamber as the dominant
process in the generation of the intrusive suite.
Instead, the authors suggest a petrogenetic model
based on mixing of mantle-derived mafic with
granitic melts. Because the Tuolumne Intrusive
Suite was emplaced slowly over at least 10
million years (Glazner et al. 2004), successive
magma batches that formed the batholith were not
molten simultaneously and could not mix after
emplacement, which suggests that the magmas
mixed at source level or during transport.
In contrast, Burgess & Miller focus their study
on the Cathedral Peak granodiorite, which is the
largest unit of the Tuolumne Intrusive Suite. It is
found that the Cathedral Peak was emplaced
rapidly, suggesting that it may have represented a
large mushy magma reservoir, where fractional
crystallization and magma mixing did operate.
8
G. F. ZELLMER & C. ANNEN
The last two papers of the volume focus on
bimodal volcanism. In the Snake River Plain –
Yellowstone bimodal magmatic system, Leeman
et al. argue that isotopic data on the initially
erupted voluminous rhyolites indicate a dominant
crustal component. Rhyolite petrogenesis is modelled through massive input of basalts into the mid
to upper crust over several million years, leading
to partial melting of several kilometres of the
upper crust.
Finally, Straub studied the composition of
tephras of the central Izu –Bonin volcanic arc
(NW Pacific) using mineral chemical data from an
ODP drill core. Her work provides evidence for a
remarkable constancy in tephra compositions over
42 Ma of eruptive history at this arc and, by inference, constancy in petrogenetic and eruptive processes over this timescale.
Discussion
Integrating the evidence
The processes of crustal magma transfer, storage
and differentiation are inherently complex (Marsh
2004): ‘The local size, shape, and age of the
system coupled with magma crystallinity, integrated flux, flushing frequency, and nature of wall
rock involvement determines the local and systemwide products.’ The papers collected in this volume
may serve as a means to move on from that
acknowledgment towards an understanding of the
dominating characteristics of magmatic systems.
Despite the variety of systems addressed (Fig. 1),
the overall theme of the papers in this volume is
the importance of small volume magma batches
that are transported through plumbing systems
with a relatively high frequency, as opposed to
less frequent transport of larger magma volumes
that would have to be stored in larger crustal reservoirs for longer periods of time. This corroborates
results from previous work on small volume
systems (Bacon et al. 1981; Hildreth 1981;
Detrick et al. 1987), and is consistent with studies
of magma mixing (e.g. Sparks et al. 1977), and
chamber replenishment and inflation (Björnsson
et al. 1977; Blake 1981). Frequent transport of
small magma batches is directly evident at Popocatepetl, where magma transport to the surface occurs
through repeated dyke injection (Martin-Del Pozzo
et al.); at Santorini, where crystal size distribution
and textural constraints indicate the presence
of one or more small reservoirs that repeatedly
experience recharge (Jerram & Martin); at
Stromboli, where upper crustal magma residence
times of a few days are inferred (Cigolini et al.);
at Zao volcano and Mount St Helens, where rapid
crystallization indicates that the subvolcanic
chambers are small and short-lived (Ban et al.;
Dosseto et al.); and at Kilauea, where repeated
injections into the volcanic edifice can be geophysically observed and correlated with the eruptive
behaviour of the volcano (Wright & Klein). Highfrequency transport of small magma batches is
also evident within the structurally less mature
intra-oceanic Izu –Bonin volcanic arc, where
Straub argues that the large number of tephra
deposits with distinct compositions implies
magma transfer processes that do not involve longterm storage within large crustal reservoirs. Further,
it is consistent with the global study of Zellmer,
which suggests that magma throughput through a
lower crustal hot zone is close to steady state,
with magma input from the mantle proportional to
magma output into the overlying crust. Even the
generation of large volumes of evolved melts
forming the Snake-River Plain rhyolites (Leeman
et al.) is seen as a result of repeated injection of
relatively small volume magma batches into mid
to upper crustal levels over millions of years.
Finally, according to Gray et al., the Tuolumne
Intrusive suite was generated by mixing of a
number of successive magma batches.
If movement of small volume melt batches is a
common phenomenon in the generation and evolution of crustal magmatic systems, critical parameters responsible for variations in magma
dynamics are the intrusion frequency and the melt
segregation threshold. These will ultimately
control the thermal structure of the crust, and therefore the amount and composition of magmas transferred through the plumbing system. Intrusion
frequency is dependent on the rate of melt generation within the mantle. Further studies are required
to determine the controls on melt segregation,
although there is some indication that the local
and regional stress regimes are important. These
in turn will differ considerably between different
tectonic settings.
Considerations regarding the tectonic setting
The tectonic controls on magma ascent and storage,
and links to differentiation mechanisms, have not
yet been investigated in sufficient detail, and
promise to yield many insights into the operation
of crustal magma plumbing systems. Future
research should therefore include studies that
specifically focus on melt differentiation at ocean
ridges with variable spreading rates, including onand off-axis sites of volcanic activity; at intra-plate
volcanoes sampled at variable distance from the
plume centre; and at arcs situated within contrasting
tectonic regimes, e.g. extensional v. compressional.
Traditionally, research in ocean ridge and intraplate
INTRODUCTION
settings has focused on the origin of the melts, the
melting process, and insights that may be gained
into the dynamics and composition of the underlying mantle. Studies of crustal magma evolution
may, however, yield many important additional
insights. For example, detailed results on oceanic
rhyolitic volcanism in Iceland show that differentiation mechanisms range from near-liquidus
processes (crystal fractionation + assimilation,
e.g. Carmichael 1964; Macdonald et al. 1990;
Nicholson et al. 1991; Lacasse et al. 2007) to nearsolidus scenarios (crustal melting, e.g. O’Nions &
Grönvold 1973; Sigvaldason 1974; Hèmond et al.
1988; Sigmarsson et al. 1991; Jónasson 1994;
Lacasse et al. 2007; Martin & Sigmarsson 2007;
Zellmer et al. 2008). Future studies of melt evolution at ocean ridge and intraplate settings, as
well as above subduction zones, will further refine
our understanding of the processes and timescales
operating during crustal magma transfer, storage
and differentiation, and how they are affected by
tectonic controls.
Conclusions
1.
2.
3.
4.
Crustal magma plumbing systems are characterized by a variety of processes that include
dyke and sill propagation; magma accumulation, segregation, and mixing; crystallization,
crystal resorption and recycling; magmatic
volatile exsolution and degassing; and
various assimilation processes that involve
both old and juvenile crust. These can be
linked to eruptive behaviour and the chemistry
and petrology of erupted or intruded
magmatic products.
Despite the complexity and variety of crustal
magmatic systems, a common theme in the
dynamics of magma transfer and storage
mechanisms appears to be the high-frequency
processing of small melt batches, as opposed
to long-term storage of large volumes of melt
accumulated in crustal reservoirs. This evidence is mainly based on studies of subduction
zone magmatism.
Tectonic setting has the potential to exert a
strong control on the geometry and evolution
of crustal magma plumbing systems, and on
the dynamics of magma transfer and storage
within these systems. Future studies should
address the links between magmatism and tectonism to improve our understanding of the
crustal magmatic processes that operate in
different tectonic regimes.
The length and timescales governing the development of crustal magma reservoirs remain
key to the understanding of the petrogenetic
9
processes operating in crustal magmatic
systems.
The authors would like to acknowledge all colleagues who
have contributed to the many advances in our understanding of igneous processes through constructive discussions
led throughout the last few years. We are grateful for the
opportunity to present some of this progress within a
dedicated volume. Our initial book proposal was improved
through constructive comments by N. Petford, M. Wilson
and an anonymous reviewer. This introduction benefited
from reviews by P. Leat and P. Kokelaar. A. Hills provided
administrative support throughout the editorial process.
G. F. Z. thanks J. Erzinger at the GeoForschungsZentrum
Potsdam for his hospitality during a productive sabbatical
visit in summer 2007, and acknowledges support by the
Institute of Earth Sciences, Academia Sinica and the
National Science Council of Taiwan (NSC 96-2116-M001-006).
References
A LOISI , M., B ONACCORSO , A. & G AMBINO , S. 2006.
Imaging composite dike propagation (Etna, 2002 case).
Journal of Geophysical Research–Solid Earth, 111,
DOI: 10.1029/2005JB003908.
A NNEN , C. & S PARKS , R. S. J. 2002. Effects of repetitive
emplacement of basaltic intrusions on thermal
evolution and melt generation in the crust. Earth and
Planetary Science Letters, 203, 937– 955.
A NNEN , C., B LUNDY , J. D. & S PARKS , R. S. J. 2006.
The genesis of intermediate and silicic magmas in
deep crustal hot zones. Journal of Petrology, 47,
505– 539.
B ACHMANN , O. & B ERGANTZ , G. W. 2004. On the
origin of crystal-poor rhyolites: extracted from
batholithic crystal mushes. Journal of Petrology, 45,
1565– 1582.
B ACON , C. R., M ACDONALD , R., S MITH , R. L. &
B AEDECKER , P. A. 1981. Pleistocene high-silica
rhyolites of the Coso volcanic field, Inyo County,
California. Journal of Geophysical Research, B86,
10223–10241.
B ENN , K., R OEST , W. R., R OCHETTE , P., E VANS , N. G.
& P IGNOTTA , G. S. 1999. Geophysical and structural
signatures of syntectonic batholith construction: the
South Mountain Batholith, Meguma Terrane, Nova
Scotia. Geophysical Journal International, 136,
144– 158.
B JÖRNSSON , A., S AEMUNDSSON , K., E INARSSON , P.,
T RYGGVASON , E. & G RÖNVOLD , K. 1977.
Current rifting episode in north Iceland. Nature, 266,
318– 323.
B LAKE , S. 1981. Volcanism and the dynamics of open
magma chambers. Nature, 289, 783–785.
B LATTER , D. L. & C ARMICHAEL , I. S. E. 1998. Hornblende peridotite xenoliths from central Mexico reveal
the highly oxidized nature of subarc upper mantle.
Geology, 26, 1035–1038.
B OWEN , N. L. 1915. Crystallization – differentiation in
silicate liquids. American Journal of Science, 39,
175– 191.
10
G. F. ZELLMER & C. ANNEN
B RIDGWATER , D., S UTTON , J. & W ATTERSON , J. 1974.
Crustal downfolding associated with igneous activity.
Tectonophysics, 21, 57–77.
B ROCHER , T. M. 1981. Geometry and physical properties
of the Socorro, New Mexico, Magma bodies. Journal
of Geophysical Research, 86, 9420– 9432.
B RYAN , S. E., R ILEY , T. R., J ERRAM , D. A., S TEPHENS ,
C. J. & L EAT , P. 2002. Silicic volcanism; an
undervalued component of large igneous provinces
and volcanic rifted margins. In: M ENZIES , M. A.,
K LEMPERER , S. L., E BINGER , C. J. & B AKER , J.
(eds) Volcanic Rift Margins. Geological Society of
America, Special Papers, 362, 97–118.
C ABELLO , G. C., G ARZA , R. M. ET AL . 2006. Geology
and paleomagnetism of El Potrero pluton, Baja
California: Understanding criteria for timing of deformation and evidence of pluton tilt during batholith
growth. Tectonophysics, 424, 1 –17.
C ARMICHAEL , I. S. E. 1964. The petrology of Thingmuli,
a Tertiary volcano in eastern Iceland. Journal of
Petrology, 5, 435 –460.
C ARTWRIGHT , J. & H ANSEN , D. M. 2006. Magma
transport through the crust via interconnected sill
complexes. Geology, 34, 929–932.
C HAPIN , C. E. & E LSTON , W. E. (eds). 1979. Ash Flow
Tuffs. Geological Society of America, Boulder, CO,
Special Papers.
C HAPPELL , B. W. & W HITE , J. R. 2001. Two contrasting
granite types: 25 years later. Australian Journal of
Earth Sciences, 48, 489–499.
C HARLIER , B. L. A., W ILSON , C. J. N., L OWENSTERN ,
J. B., B LAKE , S., VAN C ALSTEREN , P. W. &
D AVIDSON , J. P. 2005. Magma generation at a large,
hyperactive silicic volcano (Taupo, New Zealand)
revealed by U–Th and U–Pb systematics in zircons.
Journal of Petrology, 46, 3 –32.
C LEMENS , J. D. & M AWER , C. K. 1992. Granitic magma
transport by fracture propagation. Tectonophysics,
204, 339–360.
C LEMENS , J. D. & W ALL , W. J. 1981. Origin and crystallization of some peraluminous (S-type) granitic
magmas. Canadian Mineralogist, 19, 111–131.
C LEMENS , J. D., P ETFORD , N. & M AWER , C. K. 1997.
Ascent mechanisms of granitic magmas: causes and
consequences. In: H OLNESS , M. B. (ed.) Deformationenhanced Fluid Transport in the Earth’s Crust and
Mantle. Chapman & Hall, London, 145–172.
C OLEMAN , D. S., G RAY , W. & G LAZNER , A. F. 2004.
Rethinking the emplacement and evolution of zoned
plutons: Geochronologic evidence for incremental
assembly of the Tuolumne Intrusive Suite, California.
Geology, 32, 433–436.
C OSTA , F., C HAKRABORTY , S. & D OHMEN , R. 2003.
Diffusion coupling between trace and major elements
and a model for calculation of magma residence
times using plagioclase. Geochimica et Cosmochimica
Acta, 67, 2189–2200.
C RUDEN , A. R. 1998. On the emplacement of tabular
granites. Journal of the Geological Society, 155,
853– 862.
C RUDEN , A. R. & M C C AFFREY , K. J. W. 2001. Growth
of plutons by floor subsidence: Implications for rates
of emplacement, intrusion spacing and melt-extraction
mechanisms. Physics and Chemistry of the Earth Part
a – Solid Earth and Geodesy, 26, 303–315.
D AWSON , P., W HILLDIN , D. & C HOUET , B. 2004.
Application of near real-time radial semblance
to locate the shallow magmatic conduit at Kilauea
Volcano, Hawaii. Geophysical Research Letters, 31.
DE S AINT -B LANQUAT , M., H ABERT , G., H ORSMAN , E.,
M ORGAN , S. S., T IKOFF , B., L AUNEAU , P. &
G LEIZES , G. 2006. Mechanisms and duration of nontectonically assisted magma emplacement in the upper
crust: The Black Mesa pluton, Henry Mountains, Utah.
Tectonophysics, 428, 1– 31.
D E P AOLO , D. 1981. Trace element and isotopic effects of
combined wallrock assimilation and fractional crystallisation. Earth and Planetary Science Letters, 53,
189–202.
D ETRICK , R. S., B UHL , P., V ERA , E., M UTTER , J.,
O RCUTT , J., M ADSON , J. & B ROCKER , T. 1987.
Multi-channel seismic imaging of a crustal magma
chamber along the East Pacific Rise. Nature, 236,
35–41.
D ONOGHUE , S. L., G AMBLE , J. A., P ALMER , A. S. &
S TEWART , R. B. 1995. Magma mingling in an
andesite pyroclastic flow of the Pourahu member,
Ruapehu volcano, New Zealand. Journal of Volcanology and Geothermal Research, 68, 177– 191.
F ARRIS , D. W., H AEUSSLER , P., F RIEDMAN , R.,
P ATERSON , S. R., S ALTUS , R. W. & A YUSO , R.
2006. Emplacement of the Kodiak batholith and
slab-window migration. Geological Society of
America Bulletin, 118, 1360–1376.
G EORGE , R. M. M., T URNER , S. P., H AWKESWORTH ,
C. J., B ACON , C. R., N YE , C., S TELLING , P. &
D REHER , S. 2003. Chemical versus temporal controls
on the evolution of tholeiitic and calc-alkaline magmas
at two volcanoes in the Alaska– Aleutian arc. Journal
of Petrology, 45, 203 –219.
G LAZNER , A. F., B ARTLEY , J. M., C OLEMAN , D. S.,
G RAY , W. & T AYLOR , Z. T. 2004. Are plutons
assembled over millions of years by amalgamation
from small magma chambers? GSA Today, 14, 4– 11.
G ROVE , T. L., D ONNELLY -N OLAN , J. M. & H OUSH , T.
1997. Magmatic processes that generated the rhyolite
of Glass Mountain, Medicine Lake volcano,
N. California. Contributions to Mineralogy and
Petrology, 127, 205–223.
H ÈMOND , C., C ONDOMINES , M., F OURCADE , S.,
A LLÈGRE , C. J., O SKARSSON , N. & J AVOY , M.
1988. Thorium, strontium and oxygen isotopic
geochemistry in recent tholeiites from Iceland:
crustal influence on mantle-derived magmas. Earth
and Planetary Science Letters, 87, 273–285.
H ILDRETH , W. 1981. Gradients in silicic magma
chambers: implications for lithospheric magmatism.
Journal of Geophysical Research, 86, 10153–10192.
H ILDRETH , W. & M OORBATH , S. 1988. Crustal contribution to arc magmatism in the Andes of Central
Chile. Contributions to Mineralogy and Petrology,
98, 455–489.
H UTTON , D. H. W., D EMPSTER , T. J., B ROWN , P. E. &
B ECKER , S. D. 1990. A new mechanism of granite
emplacement – intrusion in active extensional shear
zones. Nature, 343, 452– 455.
J ACKSON , M. D., C HEADLE , M. J. & A THERTON , M. P.
2003. Quantitative modeling of granitic melt generation
and segregation in the continental crust. Journal of Geophysical Research, B7, DOI: 10.1029/2001JB001050.
INTRODUCTION
J ÓNASSON , K. 1994. Rhyolite volcanism in the Krafla
central volcano, north-east Iceland. Bulletin of Volcanology, 56, 516– 528.
L ACASSE , C., S IGURDSSON , H., C AREY , S. N., J ÓHANNESSON , H., T HOMAS , L. E. & R OGERS , N. W.
2007. Bimodal volcanism at the Katla subglacial
caldera, Iceland: insight into the geochemistry and
petrogenesis of rhyolitic magmas. Bulletin of Volcanology, 69, 373– 399.
L A D ELFA , S., P ATANE , G., C LOCCHIATTI , R., J ORON ,
J. L. & T ANGUY , J. C. 2001. Activity of Mount Etna
preceding the February 1999 fissure eruption: inferred
mechanism from seismological and geochemical data.
Journal of Volcanology and Geothermal Research,
105, 121– 139.
L AHR , J. C., C HOUET , B. A., S TEPHENS , C. D., P OWER ,
J. A. & P AGE , R. A. 1994. Earthquake classification,
location and error analysis in a volcanic environment
– implications for the magmatic system of the
1989–1990 eruptions at Redoubt volcano, Alaska.
Journal of Volcanology and Geothermal Research,
62, 137–151.
L EFORT , P. 1981. Manaslu leucoganite – a collision signature of the Himalya – a model for its genesis and
emplacement. Journal of Geophysical Research, 86,
545–568.
L EJEUNE , A. & R ICHET , P. 1995. Rheology of crystalbearing silicate melts: an experimental study at high
viscosity. Journal of Geophysical Research, 100,
4215–4229.
L IPMAN , P. 1984. The roots of Ash flow calderas in
Western North America: windows into the tops of
granitic batholiths. Journal of Geophysical Research,
89, 8801– 8841.
L IPMAN , P. W. 2007. Incremental assembly and prolonged consolidation of Cordilleran magma chambers:
evidence from the Southern Rocky Mountain volcanic
field. Geosphere, 3, 42– 70.
L OWENSTERN , J. B., C HARLIER , B. L. A., C LYNNE ,
M. A. & W OODEN , J. L. 2006. Extreme U–Th disequilibrium in rift-related basalts, rhyolites and granophyric granite and the time scale of rhyolite
generation, intrusion and crystallization at Alid Volcanic Center, Eritrea. Journal of Petrology, 47,
2105–2122, DOI: 10.1093/petrology/egl038.
M ACDONALD , R., M C G ARVIE , D. W., P INKERTON , H.,
S MITH , R. L. & P ALACZ , Z. A. 1990. Petrogenetic
evolution of the Torfajökull Volcanic Complex,
Iceland I. Relationship between the magma types.
Journal of Petrology, 31, 429–459.
M ARSH , B. 2004. A magmatic mush column Rosetta
Stone: the McMurdo dry valleys of Antarctica. EOS
Transactions, American Geophysical Union, 85,
497–508.
M ARSH , B. D. 1981. On the crystallinity, probability of
occurrence, and rheology of lava and magma. Contributions to Mineralogy and Petrology, 78, 85–98.
M ARSH , B. D. 1982. On the mechanics of igneous diapirism, stoping, and zone-melting. American Journal of
Science, 282, 808–855.
M ARTIN , E. & S IGMARSSON , O. 2007. Crustal thermal
state and origin of silicic magma in Iceland: the case
of Torfajökull, Ljósufjöll and Snæfellsjökull volcanoes. Contributions to Mineralogy and Petrology,
153, 593– 605.
11
M ATTIA , M., P ATANE , D., A LOISI , M. & A MORE , M.
2007. Faulting on the western flank of Mt Etna and
magma intrusions in the shallow crust. Terra Nova,
19, 89–94.
M ATZEL , J. E. P., B OWRING , S. A. & M ILLER , R. B.
2006. Time scales of pluton construction at differing
crustal levels: Examples from the Mount Stuart and
Tenpeak intrusions, North Cascades, Washington.
Geological Society of America Bulletin, 118,
1412– 1430.
M C K ENZIE , D. 1984. The generation and compaction of
partially molten rock. Journal of Petrology, 25,
713– 765.
M ICHAUT , C. & J AUPART , C. 2006. Ultra-rapid formation
of large volumes of evolved magma. Earth and Planetary Science Letters, 250, 38– 52.
M ILLER , R. B. & P ATERSON , S. R. 1999. In defense of
magmatic diapirs. Journal of Structural Geology, 21,
1161– 1173.
M ORGAN , D. J. & B LAKE , S. 2005. Magmatic residence
times of zoned phenocrysts: introduction and application of the binary element diffusion modelling
(BEDM) technique. Contributions to Mineralogy and
Petrology, 151, 58–70.
M ORGAN , D. J., B LAKE , S., R OGERS , N. W., D E V IVO ,
B., R OLANDI , G., M ACDONALD , R. & H AWKESWORTH , C. J. 2004. Timescales of crystal residence
and magma chamber volume from modelling of diffusion profiles in phenocrysts: Vesuvius 1944. Earth and
Planetary Science Letters, 222, 933– 946.
N ICHOLSON , H., C ONDOMINES , M., F ITTON , J. G.,
F ALLICK , A. E., G RÖNVOLD , K. & R ODGERS , G.
1991. Geochemical and isotopic evidence for crustal
assimilation beneath Krafla, Iceland. Journal of Petrology, 32, 1005–1020.
O’N IONS , R. K. & G RÖNVOLD , K. 1973. Petrogenetic
relationships of acid and basic rocks in Iceland:
Sr-isotopes and rare-earth elements in late and postglacial volcanics. Earth and Planetary Science Letters,
19, 397– 409.
P ASQUARE , F. & T IBALDI , A. 2007. Structure of a
sheet-laccolith system revealing the interplay
between tectonic and magma stresses at Stardalur
Volcano, Iceland. Journal of Volcanology and
Geothermal Research, 161, 131 –150.
P ATIÑO D OUCE , A. E. 1997. Generation of metaluminous
A-type granites by low-pressure melting of
calc-alkaline granitoids. Geology, 25, 743– 746.
P ELTIER , A., F ERRAZZINI , V., S TAUDACHER , T. &
B ACHELERY , P. 2005. Imaging the dynamics of
dyke propagation prior to the 2000–2003 flank eruptions at Piton de La Fournaise, Reunion Island. Geophysical Research Letters, 32, DOI: 10.1029/
2005GL023720.
P ETFORD , N. 2003. Rheology of granitic magmas during
ascent and emplacement. Annual Review of Earth
and Planetary Sciences, 31, 399–427.
P ETFORD , N. & G ALLAGHER , K. 2001. Partial melting of
mafic (amphibolitic) lower crust by periodic influx of
basaltic magma. Earth and Planetary Science
Letters, 193, 483– 499.
P ETFORD , N., C RUDEN , A. R., M C C AFFREY , K. J. W. &
V IGNERESSE , J. L. 2000. Granite magma formation,
transport and emplacement in the Earth’s crust.
Nature, 408, 669– 673.
12
G. F. ZELLMER & C. ANNEN
P ICHAVANT , M., M ARTEL , C., B OURDIER , J.-L. &
S CAILLET , B. 2002. Physical conditions, structure,
and dynamics of a zoned magma chamber: Mount
Pelée (Martinique, Lesser Antilles Arc). Journal of
Geophysical Research, 107, DOI: 10.1029/
2001JB000315.
P ITCHER , W. S. 1979. The nature, ascent and emplacement of granitic magmas. Journal of the Geological
Society, 136, 627– 662.
P OLLARD , D., D ELANEY , P., D UFFIELD , W., E NDO , E. &
O KAMURA , A. 1983. Surface deformation in volcanic
rift zones. Tectonophysics, 94, 541 –584.
P RESTON , R. J. 2001. Composite minor intrusions as
windows into subvolcanic magma reservoir processes:
mineralogical and geochemical evidence for complex
magmatic plumbing systems in the British Tertiary
Igneous Province. Journal of the Geological Society,
158, 47–58.
P RITCHARD , M. E. & S IMONS , M. 2004. An InSARbased survey of volcanic deformation in the central
Andes. Geochemistry Geophysics Geosystems, 5,
DOI: 10.1029/2003GL000610.
Q UARENI , F., V ENTURA , G. & M ULARGIA , F. 2001.
Numerical modelling of the transition from fissureto central-type activity on volcanoes: a case study
from Salina Island, Italy. Physics of the Earth and
Planetary Interior, 124, 213–221.
R APP , R. P. & W ATSON , E. B. 1995. Dehydration melting
of metabasalt at 8– 32 kbar; implications for continental growth and crust– mantle recycling. Journal of
Petrology, 36, 891–931.
R INEHART , E. J., S ANFORD , A. R. & W ARD , R. M.
1979. Geographic extent and shape of an extensive
magma body at mid-crustal depths in the Rio
Grande rift near Socorro, New Mexico, in
Rio Grande Rift. In: R IECKER , R. E. (ed.)
Tectonics and Magmatism. AGU, Washington, DC,
237– 251.
R UBIN , A. M. & P OLLARD , D. D. 1987. Origins of bladelike dikes in volcanic rift zones. In: D ECKER , R. W.,
W IGHT , T. L. & S TUFFER , P. H. (eds) Volcanism in
Hawaii. US Geoligical Survey Professional Papers,
1350, 1449–1470.
S ANCHEZ , J. J., W YSS , M. & M C N UTT , S. R. 2004. Temporal–spatial variations of stress at Redoubt volcano,
Alaska, inferred from inversion of fault plane solutions. Journal of Volcanology and Geothermal
Research, 130, 1– 30.
S IGMARSSON , O., H EMOND , C., C ONDOMINES , M.,
F OURCADE , S. & O SKARSSON , N. 1991. Origin of
silicic magma in Iceland revealed by Th isotopes.
Geology, 19, 621–624.
S IGVALDASON , G. E. 1974. The petrology of Hekla and
origin of silicic rocks in Iceland. Societas Scientarium
Islandica, 5, 1 –44.
S ISSON , T. W. & G ROVE , T. L. 1993. Experimental investigations of the role of H2O in calc-alkaline differentiation
and
subduction
zone
magmatism.
Contributions to Mineralogy and Petrology, 113,
143– 166.
S ISSON , T. W., R ATAJESKI , K., H ANKINS , W. B. &
G LAZNER , A. F. 2005. Voluminous granitic magmas
from common basaltic sources. Contributions to
Mineralogy and Petrology, 148, 635–661.
S PARKS , R. S. J. & H UPPERT , H. E. 1984. Density
changes during the fractional crystallization of basaltic
magmas – fluid dynamic implications. Contributions
to Mineralogy and Petrology, 85, 300– 309.
S PARKS , R. S. J., S IGURDSSON , H. & W ILSON , L. 1977.
Magma mixing: a mechanism for triggering acid
explosive eruptions. Nature, 267, 315– 318.
S PARKS , R. S. J., H UPPERT , H. E. & T URNER , J. S. 1984.
The fluid-dynamics of evolving magma chambers.
Philosophical Transactions of the Royal Society of
London Series a – Mathematical Physical and Engineering Sciences, 310, 511.
T URNER , S., B OURDON , B., H AWKESWORTH , C. &
E VANS , P. 2000. 226Ra– 230Th evidence for multiple
dehydration events, rapid melt ascent and the time
scales of differentiation beneath the Tonga– Kermadec
island arc. Earth and Planetary Science Letters, 179,
581–593.
T URNER , S. P. & C OSTA , F. 2007. Measuring time scales
of magmatic evolution. Elements, 3, 267– 272.
V AN DEN E ECKHOUT , B., G ROCOTT , J. & V ISSERS , R.
1986. On the role of diapirism in the segregation,
ascent and final emplacement of granitoid magmas –
discussion. Tectonophysics, 127, 161– 166.
V ANDERMOLEN , I. & P ATERSON , M. S. 1979.
Experimental deformation of partially-melted
granite. Contributions to Mineralogy and Petrology,
70, 299–318.
V IGNERESSE , J. L. 2004. A new paradigm for granite
generation. Transactions of the Royal Society of
Edinburgh – Earth Sciences, 95, 11– 22.
W HITE , A. J. R. & C HAPPELL , B. W. 1977. Ultrametamorphism and granitoid genesis. Tectonophysics, 43,
7– 22.
W HITEHEAD , J. A. & L UTHER , D. S. 1975. Dynamics of
laboratory diapir and plume models. Journal of Geophysical Research, 80, 705–717.
Y AMAOKA , K., K AWAMURA , M., K IMATA , F., F UJII , N.
& K UDO , T. 2005. Dike intrusion associated with the
2000 eruption of Miyakejima Volcano, Japan. Bulletin
of Volcanology, 67, 231– 242.
Z AK , J. & P ATERSON , S. R. 2006. Roof and walls of the
Red Mountain Creek pluton, eastern Sierra Nevada,
California (USA): implications for process zones
during pluton emplacement. Journal of Structural
Geology, 28, 575– 587.
Z ELLMER , G. F. & C LAVERO , J. 2006. Using trace
element correlation patterns to decipher a
sanidine crystal growth chronology: an example from
Taapaca volcano, Central Andes. Journal of
Volcanology and Geothermal Research, 156,
291–301, DOI: 10.1016/j.jvolgeores.2006.03.004.
Z ELLMER , G. F., A NNEN , C., C HARLIER , B. L. A.,
G EORGE , R. M. M., T URNER , S. P. & H AWKESWORTH , C. J. 2005. Magma evolution and ascent at
volcanic arcs: constraining petrogenetic processes
through rates and chronologies. Journal of Volcanology and Geothermal Research, 140, 171–191.
Z ELLMER , G. F., B LAKE , S., V ANCE , D.,
H AWKESWORTH , C. & T URNER , S. 1999. Plagioclase
residence times at two island arc volcanoes (Kameni
islands, Santorini, and Soufriere, St. Vincent)
determined by Sr diffusion systematics. Contributions
to Mineralogy and Petrology, 136, 345– 357.
INTRODUCTION
Z ELLMER , G. F., R UBIN , K. H., G RÖNVOLD , K. &
J URADO -C HICHAY , Z. 2008. On the recent bimodal
magmatic processes and their rates in the Torfajökull-Veidivötn area, Iceland. Earth and Planetary
Science Letters, 269, 387– 397.
13
Z ELLMER , G. F., S PARKS , R. S. J., H AWKESWORTH , C. J.
& W IEDENBECK , M. 2003. Magma emplacement
and remobilization time scales beneath Montserrat:
insights from Sr and Ba zonation in plagioclase
phenocrysts. Journal of Petrology, 44, 1413–1431.