Contrib Mineral Petrol (2010) 160:313–325
DOI 10.1007/s00410-009-0479-1
ORIGINAL PAPER
The role of H2O in rapid emplacement and crystallization
of granite pegmatites: resolving the paradox of large crystals
in highly undercooled melts
Peter I. Nabelek • Alan G. Whittington
Mona-Liza C. Sirbescu
•
Received: 1 July 2009 / Accepted: 5 December 2009 / Published online: 25 December 2009
Ó Springer-Verlag 2009
Abstract Granite pegmatite sheets in the continental
crust are characterized by very large crystals. There has
been a shift in viewing pegmatites as products of very slow
cooling of granite melts to viewing them as products of
crystal growth in undercooled liquids. With this shift there
has been a renewed debate about the role of H2O in the
petrogenesis of pegmatites. Based on data on nucleation of
minerals and new viscosity models for hydrous granite
melts, it is argued that H2O is the essential component in
the petrogenesis of granite pegmatites. H2O is key to
reducing the viscosity of granite melts, which enhances
their transport within the crust. It also dramatically reduces
the glass transition temperature, which permits crystallization of melts at hundreds of degrees below the thermodynamic solidus, which has been demonstrated by fluid
inclusion studies and other geothermometers. Published
experimental data show that because H2O drastically
reduces the nucleation rates of silicate minerals, the minerals may not be able to nucleate until melt is substantially
undercooled. In a rapidly cooling intrusion, nucleation
starts at its highly undercooled margins, followed by
inward crystal growth towards its slower-cooling, hotter
core. Delay in nucleation may be caused by competition for
crystallization by several minerals in the near-eutectic
melts and by the very different structures of minerals and
the highly hydrated melts. Once a mineral nucleates,
however, it may grow rapidly to a size that is determined
by the distance between the site of nucleation and the point
in the magma at which the temperature is approximately
that of the mineral’s liquidus, assuming components necessary for mineral growth are available along the growth
path. Granite pegmatites are apparently able to retain H2O
during most of their crystallization histories within the
confinement of their wall rocks. Pegmatitic texture is a
consequence of delayed nucleation and rapid growth at
large undercooling, both of which are facilitated by high
H2O (±Li, B, F and P) contents in granite pegmatite melts.
Without retention of H2O the conditions for pegmatitic
textural growth may be difficult to achieve. Loss of H2O
due to decompression and venting leads to microcrystalline
texture and potentially glass during rapid cooling as seen in
rhyolites. In contrast, slow cooling within a large magma
chamber promotes continuous exsolution of H2O from
crystallizing magma, growth of equant crystals, and final
solidification at the thermodynamic solidus. These are the
characteristics of normal granites that distinguish them
from pegmatites.
Communicated by T. L. Grove.
Introduction
P. I. Nabelek (&) A. G. Whittington
Department of Geological Sciences,
University of Missouri, Columbia, MO 65211, USA
e-mail: [email protected]
M.-L. C. Sirbescu
Department of Geology, Central Michigan University,
314 Brooks Hall, Mount Pleasant, MI 48859, USA
Keywords Granite Pegmatite H2O Undercooling Nucleation Crystal growth
Granite pegmatites in the upper crust typically occur as
tabular sheets, either dikes or sills, ranging in thickness
from centimeters to decameters. They occur in a variety of
host rocks, including metamorphic rocks and other plutons.
For example, in the San Diego County of California,
USA, Li–Cs–Ta-type (LCT) pegmatites occur mostly as
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subhorizontal sheets within calc-alkaline plutons of the
Mesozoic Peninsular Ranges batholith. These sheets served
as a foundation for the classic pegmatite crystallization
model of Jahns and Burnham (1969) in which H2O plays a
prominent role in differentiation of pegmatites. In the
Black Hills of South Dakota, USA, granite pegmatites
occur as sheets within schists of the Proterozoic Black Hills
orogen (Norton and Redden 1990). They occur as individual sheets or multiple sheets constructing plutons (Duke
et al. 1988; Rockhold et al. 1987).
Large variations in crystal size, elongated crystal shapes,
and strong mineralogical and chemical zoning across
sheets, are a hallmark of most granite pegmatites (Jahns
and Tuttle 1963; London 1996). The zoning may include a
rhythmically crystallized aplitic border zone, pegmatite
zone(s), and pockets (Fig. 1). Pockets represent the space
that was once filled by accumulated supercritical fluid.
Pockets occur only in some pegmatite districts, as in San
Diego County, where sheets have intruded impermeable
granitic rocks at relatively low pressures. In other districts,
such as the Black Hills, where pegmatites were emplaced
at relatively high pressures, pockets do not occur.
Pegmatites can range from simple to highly zoned even
in single districts and the texture of individual sheets is
often asymmetric as are the mineral zones (Norton and
Redden 1990). When an aplite border zone (commonly
called ‘‘line-rock’’ because of its rhythmic variation in
mineral modes) is present, it is most prevalent at the
bottoms of sheets. Rockhold et al. (1987) proposed that a
line-rock is generated by enrichments of rejected, slowly
diffusing components such as B, Mg, and Fe ahead of the
crystallization front of quartz and plagioclase that lead to
rhythmic saturation of tourmaline or garnet. In pegmatites
minerals typically grow inward, perpendicularly to contacts, and blades of minerals such as tourmaline and
spodumene often grow radially on preexisting substrates
(Fig. 1). The fact that crystals grow inward and are rarely
broken, except by late hydrothermal fractures, demonstrates that granite pegmatites are emplaced wholly as
liquids rather than partially crystallized magmas. Elongated crystals and mineral zones in pegmatite sheets are
inherently disequilibrium features. They show that after
emplacement, pegmatites crystallize very rapidly. Large
ranges in d7Li in tourmalines across individual pegmatite
sheets suggest kinetic control on Li isotope fractionation
and crystallization rates that exceed the diffusion rate of Li
(Maloney et al. 2008).
The range of crystallization temperatures of individual
sheets can be spectacularly large, from[700°C to\400°C.
The liquidus temperatures come from stable isotope
fractionations among minerals in line-rock portions of
aplite–pegmatite sheets (Nabelek et al. 1992) and remelting
of crystal-rich melt inclusions (Sirbescu et al. 2008). They
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Contrib Mineral Petrol (2010) 160:313–325
Fig. 1 Illustration of some crystal growth features in granite pegmatites.
a Section of a Jacumba sheet in the San Diego pegmatite district,
California. Lower portion is aplitic with banding (line-rock) highlighted
by tourmaline. Above the aplite is a pegmatite zone. Black minerals are
tourmaline. A chisel is shown for scale. b Top portion of the Stewart dike
in the San Diego pegmatite district showing several pegmatite zones,
each apparently nucleated on a thin aplitic band, and each of which may
indicate intrusion of a new pulse of magma or a new episode of
nucleation and growth in a single sheet. Note the unidirectional growth of
black tourmaline blades. A hammer is shown for scale. c Radially grown
tourmaline blades in the Carol Creek pegmatite, Black Hills, South
Dakota. The blades appear to have nucleated on a relatively fine-grained
muscovite-rich layer which wraps around a large K-feldspar crystal. The
tourmaline blades are *20-cm long
are also consistent with temperatures of muscovite dehydration-melting of schists (Patiño-Douce and Harris 1998),
and they imply that at least some pegmatites may be partial
Contrib Mineral Petrol (2010) 160:313–325
melts instead of late-stage differentiates of parental granite
magmas. Occurrence of multitudes of subvertical pegmatite dikes in the Black Hills, some of which may have been
feeders for granite plutons, suggests that they were melts
that ascended through the folded metasedimentary host
rocks directly from a source region. Similar pegmatite
dikes occur in the high Proterozoic walls of the Black
Canyon of the Gunnison in Colorado. Extremely large
differences between d7Li of pegmatites and nearby leucogranites preclude simple fractionation relationships
between parental granites and pegmatites (Maloney et al.
2008; Teng et al. 2006a).
Solidification temperatures \400°C are clearly below
the equilibrium solidus of a H2O-saturated granite, yet
there is very good evidence that they occur. The evidence
includes coexisting high and low-density primary fluid
inclusions and melt inclusions in meter to decameter-thick
pegmatite sheets (Sirbescu and Nabelek 2003a; Sirbescu
et al. 2008; Thomas et al. 1988), oxygen isotope fractionation between quartz and K-feldspar from cores of pegmatite sheets (Nabelek et al. 1992; Taylor and Friedrichsen
1983) and feldspar thermometry (Morgan and London
1999). Lack of tartan twinning in K-feldspar implies that
K-feldspar crystallized below the monoclinic–triclinic
inversion. Estimated solidification durations for pegmatite
dikes range from a few days for meter-thick sheets to
several years for tens of meters thick sheets, depending also
on the country rock temperature (Chakoumakos and
Lumpkin 1990; Morgan and London 1999; Simmons and
Webber 2008; Sirbescu et al. 2008).
Although there has been a paradigm shift from viewing
pegmatites as very slowly crystallized melts to viewing
them as melts whose crystallization is driven by kinetic
effects due to boundary layer enrichments and undercooling (Baker and Freda 1999, 2001; London 1992, 1996,
2005, 2009; Rockhold et al. 1987; Sirbescu et al. 2008),
and/or as melts that have unusual chemical properties that
allows them to exist at very low temperatures (Sirbescu
and Nabelek 2003a; Thomas et al. 1988, 2000), the
essential role of H2O in their petrogenesis that was
underscored by Jahns and Burnham (1969) has recently
been downplayed in favor of diffusion control that may
involve constitutional zone-refining by a moving fluxed
boundary layer through a viscous undercooled melt
(London 2005, 2009; Morgan and London 1999). This
model relies on accumulation of fluxing components
ahead of the crystallization front as a means of producing
large crystals by enhancing the lateral diffusive removal
of rejected components from the growing crystal interface.
We argue here, however, that H2O remains the key
component of pegmatites because it controls two critical
aspects of pegmatite petrogenesis: (1) rapid, supraliquidus
emplacement, and (2) rapid growth of large crystals below
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the equilibrium solidus. The presented model is based on
published experimental data pertaining to dynamic crystallization and bubble formation in silicate melts and
recent models for viscosities of silicate melts. The petrogenetic model is supported by data from the San Diego
County, Black Hills, and Wisconsin pegmatite districts
that have been studied by the authors.
Rapid emplacement of pegmatite sheets
Emplacement of granite pegmatite sheets as liquids implies
that they must be emplaced rapidly without cooling below
their liquidi, in spite of the frequent \400°C temperatures
of host rocks. Pegmatite sheets in the San Diego County are
subhorizontal within brittle fractures and are fairly regularly spaced and mutual crosscutting is infrequent (Jahns
and Tuttle 1963). As exposed, the sheets are continuous in
excess of hundreds of meters. The sheets were emplaced at
200–300 MPa based on densities of fluid inclusions trapped
in pockets within the sheets (London 1986). In the Black
Hills, most sheets are sub-vertical to vertical following the
regional foliation and conjugate joints in metapelites and
metagraywackes (Norton and Redden 1990). In map view
they are tabular to lenticular sheets that are often hundreds
of meters long but their vertical extent is unknown. However, some of the largest zoned pegmatites have subhorizontal attitudes that either cut across the generally vertical
foliation or they follow reoriented foliation. Most of these
are \15 m thick, although some are thicker. The large,
zoned pegmatites appear to represent accumulated liquids
along pinched and swelled flow paths. The Black Hills
pegmatites were emplaced at 350–450 MPa, based on
mineral assemblages in the host metamorphic rocks
(Nabelek et al. 2006). Many have extensive metasomatic
aureoles characterized by elevated Li and B concentrations
that represent expulsion of fluids at some stage of the
pegmatites’ solidification (Shearer et al. 1984; Teng et al.
2006b; Wilke et al. 2002).
Rubin (1995) showed that the distance over which
magma can propagate through dikes depends on the temperature gradient along the flow path. A large temperature
gradient depresses the travel distance because the melt
cools faster and eventually stiffens because of crystallization or increase in melt viscosity, preventing further
transport. Dike flow is essentially reduced to the ratio of
the rate at which the melt stiffens at the propagating tip of
the dike relative to the supply rate of the melt at the source.
Using Rubin’s (1995) model, Baker (1998) calculated that
a 700°C hydrous melt dike with viscosity of *106 Pa s
that stiffens at 650°C should be *1 km long in a temperature gradient of 100°C/km that may occur in the
vicinity of a large pluton. Thus, pegmatite sheets must
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remain liquid even as they travel along high dT/dx gradients until their flow is arrested.
The most recent model for viscosity of very hydrous
granite melts (6–12 wt% H2O) suggests that viscosities of
pegmatites should be on the order of 103 to 105 Pa s at
*700°C, depending on water content (Fig. 2; Whittington
et al. 2009), so their mobility should be significantly higher
than predicted by Baker (1998). Elements that are unusually
abundant in pegmatite melts, including Li and B, can further
reduce viscosities of silicate melts. Estimated Li2O concentrations in pegmatite liquids range from 1,300 ppm in
San Diego dikes (Maloney et al. 2008) to [1 wt% in large
spodumene-bearing pegmatites (Norton 1994). The addition of 1 wt% of excess Li2O to a haplogranite melt lowers
the viscosity by about one order of magnitude (Hess et al.
1995). However, Li-bearing pegmatite liquids may be
slightly peraluminous to metaluminous, so a better comparison is with lithium-bearing metaluminous melts. Measurements on supercooled anhydrous liquids show that
LiAlSi3O8 liquid has three orders of magnitude lower viscosity than NaAlSi3O8 liquid at 800°C, and the viscosity of
spodumene (LiAlSi2O6) liquid is almost another factor
of ten lower still (Hofmeister et al. 2009). The addition of
[0.5 wt% B2O3 can cause more than a tenfold decrease in
the viscosity of a granite melt, especially in the temperature
range at which granite pegmatites crystallize (Dingwell
et al. 1992). In the Calamity Peak aplite-pegmatite complex,
Black Hills, most samples have 0.5–1 wt% B2O3 (Duke
et al. 1992; Rockhold et al. 1987). These concentrations
should be considered to be the minimum for the parent melt
because unless all initial B is contained in the crystallized
tourmaline, B is bound to be carried into the wall rocks by
10
800
fluids upon crystallization (Shearer et al. 1984; Wilke et al.
2002). Furthermore, the components F, B2O3 and P2O5 all
increase the solubility of H2O in granite melts (Holtz et al.
1993). Thus high H2O, Li, and B concentrations in pegmatite liquids may reduce viscosity by several orders of
magnitude more compared to values used by Baker (1998)
and therefore favor rapid emplacement of sheets within the
crust, especially if potential pathways such as vertical
foliation and/or joint sets are available to reduce the magma
pressure necessary for propagation of dike fractures.
Because flow velocity is inversely proportional to viscosity,
orders of magnitude viscosity decrease will result in a
proportional velocity increase.
The common implicit assumption in models for melt
ascent as dikes is that any cooling along the flow path will
result in crystallization and therefore stiffening of the
magma. That, however, is not necessarily the case for silicate liquids because their liquidi typically have positive
dT/dP slopes (Fig. 2; Holtz et al. 2001; Johannes and Holtz
1996). H2O solubility isopleths are nearly horizontal at mid
to upper-crustal pressures. Consider a melt with 6 wt%
H2O generated at 550 MPa and at a temperature just above
its liquidus. If this melt ascends rapidly and adiabatically as
a dike to a lower pressure, it will become effectively
superheated. If its ascent is arrested at P [ 200 MPa, it will
remain H2O-unsaturated. If it ascends to \200 MPa, it
should become H2O-saturated and will be superheated by
*50°C. The superheating provides a mechanism for
emplacement of low-viscosity H2O-bearing granite melts
without crystallization during ascent. As long as the ascent
rate is fast enough to preclude significant cooling, a
pegmatite dike will remain wholly liquid. Moreover, any
8
6
4
2
1
10 4
10 2
pressure (MPa)
600
10 6
10
400
8
10 8
6
1010
200
0
4
1012
2
0
400
500
600
700
800
900
1000
temperature (ºC)
Fig. 2 Phase relationships of granite (after Holtz et al. 2001) and
melt viscosities, calculated using the water solubility model of Zhang
et al. (2007) combined with viscosity model for peraluminous granites
from Whittington et al. (2009). Heavy line is the granite solidus in the
presence of H2O fluid. Solid diagonal lines are granite liquidi as
function of wt% of H2O in the system (marked near top of each line).
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Subhorizontal dashed lines are H2O solubilities in granite melt (in
wt% indicated by bold letters). Curved gray solid lines are viscosities
with values in Pa s marked by italics. The heaviest, partially dashed
line with arrow shows a path of a pegmatites melt discussed in the
text
Contrib Mineral Petrol (2010) 160:313–325
Undercooled crystallization of hydrous magma
Equilibrium phase diagrams for a haplogranite melt at 200
and 300 MPa are shown in Fig. 3 (after Holtz et al. 2001).
The phase relations are effectively eutectic. The liquidi and
solidi correspond to the phase relations in Fig. 2. The
negative slope of the melt - melt ? vapor boundary arises
from increasing solubility of melt components in vapor
with increasing temperature. The phase diagrams show that
under equilibrium conditions, melt with 6 wt% H2O that is
at 725°C and 300 MPa is initially above the liquidus, but
only *14% crystallization is needed before the magma
reaches the eutectic and becomes H2O-saturated. Crystallization of an already H2O-saturated melt at 200 MPa is
effectively wholly eutectic, meaning that all melt will
crystallize at 680°C. Thus, under equilibrium conditions,
crystallization of a melt with 6 or more wt% H2O should be
accompanied by the presence of a separate vapor phase
along most of its crystallization path.
1000
300 MPa
200 MPa
melt
900
vapor + melt
800
104 Pa·s
crystals + melt
temperature (˚C)
crystal nuclei or polymer structures that resemble structures of liquidus minerals that may have existed in the melt
may become eliminated with increased superheating during
decompression.
During decompression when a H2O-saturation isopleth is
exceeded, bubbles should form under equilibrium conditions. However, experiments on rhyolite melts show that an
effective supersaturation pressure of 120–150 MPa is needed for homogeneous bubble nucleation to occur and the
melt can retain as much as twice the equilibrium H2O concentration during ascent (Mangan and Sisson 2000). Baker
et al. (2006) observed rapid nucleation of bubbles in albite
melt upon 100–150 MPa decompression from 550 MPa
when the melt was held at 1,200°C. However, decompression of the melt at 800°C produced only small bubbles that
did not change in size or amount even after 32 h at the lower
pressure. Baker et al. (2006) attributed the difference to
change in viscosity of the melt and/or water diffusion, estimated to be 20 Pa s and 5 9 10-11 m2 s-1, respectively at
1,200°C and 9,000 Pa s and 2910-13 m2 s-1 at 800°C. Thus
a pegmatite melt with a viscosity of 103 to 105 Pa s that is
under a confining pressure of its wall rocks should be
inhibited from losing its H2O prior to crystallization, which
begins only after melt transport is arrested. Indeed, there is
scant evidence that pegmatite melts become H2O-saturated
prior to crystallization. Once crystallization begins, however, bubble nucleation should become easier as bubbles can
nucleate heterogeneously on growing crystals (Hurwitz and
Navon 1994; Mangan et al. 2004). Heterogeneous nucleation of bubbles is evident by the presence of primary fluid
inclusions trapped in pegmatite minerals (Sirbescu and
Nabelek 2003b; Thomas et al. 1988).
317
700
crystals + vapor
600
106 Pa·s
500
400
supercooled melt
1012 Pa·s
glass
300
0
2
4
6
wt.% H2O in system
8
10
Fig. 3 Temperature–wt% H2O diagram for a haplogranite at
200 MPa (dashed lines) and 300 MPa (solid lines) (after Johannes
and Holtz 1996; Holtz et al. 2001). Gray curved lines are viscosities
of peraluminous granite calculated using the model of Whittington
et al. (2009). A viscosity of 1012 Pa s is considered to be the onset of
glass transition. At temperatures above the glass transition, a
supercooled melt can exist metastably below the equilibrium solidus.
Heavy black line with dot and arrow shows an equilibrium
crystallization path of a melt as discussed in the text
Equilibrium phase relationships may, however, have only
a limited importance to crystallization and exsolution of a
vapor phase in highly undercooled pegmatite liquids. The
term ‘‘undercooling’’ (DT) is used here in its usual sense as
the difference between the liquidus temperature of a mineral
and the actual temperature of magma. In a highly undercooled system, the equilibrium liquidus and solidus lose
their importance as crystal nucleation is retarded and kinetic
effects, especially diffusion of mineral constituents in the
melt, begin to gain importance. In general, there are maxima
in nucleation and growth rates of minerals at different
amounts of undercooling (Fig. 4; Fenn 1977; Lofgren 1974).
In dry systems, at small undercooling a few nuclei will grow
slowly into euhedral crystals. At larger undercooling many
nuclei will grow relatively fast into small elongated crystals.
At very large undercooling where diffusion rates in melt
become extremely slow, very few crystals will form and the
melt will become glass if it is cooled below the glass transition temperature (Tg), which corresponds approximately to
the melt reaching a viscosity of 1012 Pa s. For anhydrous
granite liquids Tg is *850°C but for H2O concentrations of
[6.5 wt% it is \350°C (Fig. 3).
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Contrib Mineral Petrol (2010) 160:313–325
0
x 103 nuclei/cm3
x 10-6 cm/sec
2
4
0
x 103 nuclei/cm3
x 10-6 cm/sec
2
4
0
undercooling (ΔT)
4.3% H2O
9.5% H2O
100
200
300
nucleation density
growth rate
400
Fig. 4 Nucleation densities and growth rates in an alkali feldspar
melt (Ab70Or30) as a function of undercooling (DT), as determined by
Fenn (1977). His results also show consistent decrease in nucleation
density with addition of H2O for melts with higher and lower Na/K
ratios
Aplite–pegmatite transition
The crystal size in rhythmic bands (line-rock) that occur in
aplite portions of aplite–pegmatite sheets is consistent with
high nucleation rates that occur in highly undercooled,
relatively dry systems. Millimeter to centimeter-scale
banding that occurs along walls of subvertical granite–
pegmatite sheets or upper walls of subhorizontal sheets
cannot be attributed to a sedimentary process within the
sheets. An Ostwald ripening process, where smaller crystals of a mineral become unstable relative to larger crystals
of the mineral, could potentially result in bands where the
mineral is enriched and depleted (Boudreau and McBirney
1997). However, in undercooled systems, where the difference between the Gibbs free energy of a mineral that
should be crystallizing and the melt is large and negative,
dissolution of already-formed crystal nuclei is difficult.
Rhythmic banding in aplite-pegmatite sheets can best be
ascribed to depletions and enrichments of slow-diffusing
mineral species at interfaces of growing minerals as have
been observed in crystal-growth experiments (Donaldson
1975). For example, consider a line-rock in the sheets that
make up the Calamity Peak pluton. The line-rock is primarily defined by abundance of schorl tourmaline, whereas
the proportion of other phases is subequal in dark and light
bands (Rockhold et al. 1987). In a few places near schist
inliers the banding is defined by almandine-spessartine
garnet instead of tourmaline. Garnet also defines line-rock
in some pegmatites in San Diego County (Kleck and Foord
1999; Webber et al. 1999). These banding patterns are
consistent with slow diffusion of Fe, Mg, and Mn in silicate
melts in comparison with alkali elements, especially Li and
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Na, which diffuse orders of magnitude more rapidly
(Acosta-Vigil et al. 2005; Dunn and Ratliffe 1990; Watson,
1982). Chemical diffusion of B that involves exchange
with Si in the melt structure is also very slow (Chakraborty
et al. 1993). Therefore, crystallization of tourmaline will
lead to depletion of divalent cations and potentially B in a
boundary layer ahead of the tourmaline crystallization front
as these elements will not have time to be replenished in
the boundary layer during cooling (Rockhold et al. 1987;
Webber et al. 1997). Tourmaline crystallization will cease
until temperature will drop sufficiently at some distance
away from the heat-dissipation boundary where the concentration of constituents necessary for tourmaline crystallization is again sufficiently high. Experiments on
peraluminous leucogranites similar in composition to
tourmaline-bearing pegmatites show that they are nearly
multiply saturated on the liquidus with tourmaline, plagioclase, quartz, and K-feldspar at high H2O concentrations
(Scaillet et al. 1995). Therefore, cessation and reactivation
of tourmaline crystallization in particular is consistent with
concentration gradients of the slowest-diffusing elements,
which moreover are only minor components in a typical
granite melt.
In a sheet emplaced into colder rocks, the melt at the
margins will be undercooled the most so that many nuclei
may form to generate an aplite. Following initial undercooled crystallization, the rate of temperature decrease may
be moderated by heat of crystallization. A more hydrous
residual liquid that will concentrate toward the center of a
sheet may in fact crystallize at a higher temperature than
the liquid at the margins. Evidence for this pattern of
crystallization temperature comes from the Animikie Red
Ace pegmatite, Wisconsin, where primary fluid inclusions
were trapped at the margins at *480°C, that is at *240°C
of undercooling, and are then postdated by secondary
inclusions that were trapped between 580 and 720°C and
that represent fluid exsolved from the hotter, later-crystallized core of the sheet (Fig. 5; Sirbescu et al. 2008). This
trend in trapping temperatures is consistent with crystallization of a conductively-cooled pegmatite sheet emplaced
into colder wall rocks. A similar trend is apparent for the
San Diego dikes, in which primary inclusions in wall zones
suggest colder fluid-trapping temperatures than in intermediate pegmatite zones. However, in the core and pocket
zones the temperatures are similar to temperatures in the
wall zones, suggesting a delayed crystallization of the inner
zones, probably in the presence of accumulated exsolved
vapor. There is a marked increase in the size of quartzhosted fluid inclusions by one to two orders of magnitude
in the inner zones of the pegmatites compared to the
marginal zones, which generally correlates with an increase
of crystal size. These textural changes may mark the
occurrence of massive fluid exsolution.
Contrib Mineral Petrol (2010) 160:313–325
319
5
pressure(kbar)
4
BI
3
2
c
wz
TM
wz
ARA
CG + LT
p
c
iz
300
400
1
0
200
500
600
700
800
temperature (˚C)
Fig. 5 Fluid inclusion constraints on the conditions of crystallization
for five granite pegmatites: TM Tin Mountain and BI Bob Ingersol,
Black Hills, South Dakota (Sirbescu and Nabelek 2003b); ARA
Animikie Red Ace, WI (Sirbescu et al. 2008); CG Cryo-Genie and LT
Little Three, San Diego County, California (Lyter and Sirbescu 2006
and unpublished data). Pegmatite zones: wz wall zone, iz intermediate
zone, c core, and p pocket zone. P–T paths of crystallization are
suggested by arrows. The crystallization temperatures are represented
by fields of inclusion isochores (trapezoid shapes) limited by
pressures estimated from independent methods. The dashed portions
of the isochoric fields are uncertain crystallization conditions because
they were constructed based on secondary inclusions (core of ARA)
or inclusions of ambiguous primary character (wz of CG and LT). TM
crystallization conditions (oval shape) are on the solvus of a CO2(H2O?NaCl) fluid
In thicker sheets such as the Tin Mountain and Bob
Ingersoll pegmatites in the Black Hills, the apparent trapping temperatures of primary inclusions, and hence crystallization temperatures of the host minerals, are more
homogeneous. Nevertheless, rapid growth of the large
crystals in such thick pegmatites is indicated by their often
radial growth morphology (Fig. 1c) and by captured low
and high-density primary fluid inclusions together with
melt inclusions (Sirbescu and Nabelek 2003b; Thomas
et al. 1988).
Role of H2O in depressing crystal nucleation
A critical question is why growth of large crystals that
characterize pegmatites occurs at very large DT’s and not
near equilibrium temperatures even in cores of large pegmatites that must cool at a slower rate than the margins? A
2.5 m dike cools in 2 weeks from 720 to 410°C at the
margins but only to 590°C in the core when emplaced into
220°C host rocks (Sirbescu et al. 2008). Crystal growth in
undercooled melts has been addressed in numerous previous studies (e.g. Dowty 1980; Lofgren and Donaldson
1975), and has frequently been used to explain mineral
morphologies in granite pegmatites (e.g. Baker and Freda
1999, 2001; London 2005, 2009; Webber et al. 1999).
Although the role of H2O in promoting the morphologic
features of pegmatites has recently been deemphasized in
favor of a diffusion-controlled process (London 2005,
2008, 2009; Morgan and London 1999), we nevertheless
suggest that H2O plays a critical role in delaying mineral
nucleation to large DT’s, which then results in rapid growth
of large crystals. Crystal growth experiments on alkali
feldspars in hydrous melts demonstrate a strong effect of
H2O on the rate of nucleation (Fig. 4; Fenn 1977). For a
given feldspar composition, the maximum in nucleation
density dramatically decreases in magnitude and occurs at
a smaller DT relative to the feldspar liquidus with
increasing H2O, while remaining at approximately the
same absolute T. We suggest that it is the difficulty of
mineral nucleation in melts that retain their H2O that
causes undercooling even in thick sheets of pegmatite
liquids that may cool relatively slowly.
Indeed, without seeding experimental charges or
inducing nucleation by temperature cycling, experimentalists often have difficulty producing any crystallization in
hydrous granitic melts, even if experimental charges are
held for many days at undercooled temperatures (e.g.,
Baker and Freda 2001; Fenn 1977; Swanson and Fenn
1986). Experiments on komatiite melts show that nucleation rate is dramatically decreased while the growth rate is
increased when the melts are hydrated and this leads to
development of spinifex texture (Grove et al. 2002; Grove
and Parman 2006). The longest olivine crystals grew in
centers of experimental charges where nucleation was
depressed the most due to accumulation of H2O.
New experiments on the haplogranite–B–Li–H2O system at 300 MPa show that crystal nucleation is sluggish at
temperatures between liquidus and glass transition (Sirbescu et al. 2009b). For example, time-series of isothermalisobaric, unseeded experiments constrained nucleation
delays between 9 and 14 days for a haplogranite melt
containing 2% Li2O, 4.6% B2O3 and 6.5% H2O at 400°C.
The nucleation delay exceeded 14 days for haplogranite
with only 1% Li2O, 2.3% B2O3 and 6.5% H2O at 400°C.
The results also suggest that water supersaturation reduces
the nucleation density, but it enhances crystal growth.
There may be two reasons for the apparent inability of
minerals to nucleate and grow near their equilibrium
crystallization conditions in pegmatite melts. The first
reason is that the structure of a very hydrous silicate melt is
very different from the structure of the mostly anhydrous
minerals attempting to nucleate from it, so that there are
fewer polymer structures in the melt that can readily
develop into crystal nuclei. Water dissolves in silicate
melts and glasses in two species, hydroxyl (OH-) and
molecular water (H2Om), with the former dominating at
low water contents and the latter being more abundant at
high water contents (Stolper 1982). However, water speciation in melts moves towards increasing OH- content
with increasing temperature (Nowak and Behrens 1995;
123
320
Growth of large elongated crystals
Figure 7 shows schematically how delayed crystal nucleation in an undercooled melt can lead to unidirectional
123
~700
rate
~660
rate
temperature ( C)
Shen and Keppler 1995). The effects of water dissolution
on aluminosilicate glass structure, and presumably melt,
include depolymerization to form Si–OH and Al–OH
groups, protonation of bridging oxygens, and formation of
alkali hydroxides (e.g. Robert et al. 2001; Schmidt et al.
2001; Xue and Kanzaki 2006). All of these dissolution
mechanisms require dissociation of H2Om to form OH-,
and produce structures that are not found in anhydrous
silicates, including quartz or feldspar. Therefore, OH- that
is present in very hydrous melts will hinder nucleation of
framework silicate minerals. For pegmatites in particular,
the presence of significant quantities of other elements,
such as B, F and P, further complicates the melt structure
and inhibits nucleation of aluminosilicate minerals.
The second reason is that because pegmatite melts have
essentially eutectic compositions, there is a competition
among several minerals for appropriate polymers with the
consequent inability of any of the competing minerals to
nucleate. This ‘‘principle of confusion’’ is well known in
the literature on metallic glasses, and the effect is pronounced when rival cations have very different sizes (Greer
1993). In the case of Li-bearing pegmatite melts, the
presence of large amounts of Li competing with Na and K
may be significant. Due to its low atomic weight, 1 wt%
Li2O is equivalent to *2 mol.%, comparable with
*5 mol.% Na2O and *3 mol.% K2O in a typical minimum melt granite composition.
Transitions from aplite border zones to pegmatite zones
that occur in some pegmatite sheets represent transitions
from zones of high nucleation density and rapid growth to
zones of low nucleation density and even more rapid
crystal growth (Webber et al. 1999), as schematically
shown in Fig. 6. Noting that aplite line-rock usually occurs
on the bottoms of sheets, Jahns and Burnham (1969) and
Burnham and Nekvasil (1986) suggested that vertical
bubble transport may be responsible for this and other
asymmetries in horizontal sheets. Indeed, bubbles generated at the crystallization front at the bottom of the sheet
are expected to move upward away from the front, whereas
at the top of the sheet generated bubbles are expected to
migrate in opposite direction from the downward-propagating crystallization front, thus keeping the top of the
sheet saturated in H2O vapor. The asymmetry cannot be
ascribed to vertical transport of dissolved H2O in melt
because its diffusion rate is too slow (*10-11 m2/s at
700°C; Zhang and Behrens 2000) compared to the diffusion rate of heat in silicic melt (*0.6 9 10-6 m2/s;
Hofmeister et al. 2009), which will control its cooling rate.
Contrib Mineral Petrol (2010) 160:313–325
º
~350
aplite
growth
nucleation
pegmatite
Fig. 6 Schematic illustration showing how rapid undercooling of an
initially H2O-undersaturated margin of a granite dike can lead to high
nucleation density and development of aplite. With build-up of H2O
ahead of the aplite crystallization front, the nucleation density will be
diminished, eventually resulting in the development of only few
crystal nuclei that can grow into large crystals. The vertical axis is
labeled with absolute temperature instead of undercooling that was
used in Fig. 4. Approximate liquidus and glass transition temperatures
are shown. The small difference in liquidus temperatures of aplite and
pegmatite reflects the effect of higher activity of H2O in pegmatite.
The gray fields show crystallization regimes that are consistent with
indicators of crystallization temperatures discussed in the text
rapid growth of large crystals and to mineral zones in
pegmatites. Consider tourmaline that nucleates below its
liquidus at its nucleation temperature at a time t1 after
emplacement of a pegmatite sheet. The nucleation will
probably be heterogeneous on the walls of the sheet. Once
nucleated, the crystal will grow rapidly inward into the
sheet, to a distance at which the temperature in the melt is
approximately that of tourmaline’s liquidus or a distance
where the boundary layer enriched in rejected components
forming ahead of the growing tourmaline will prevent its
further growth. In essence, the size of the crystals will be
determined by the distance between the nucleation temperature and liquidus temperature of the mineral along the
temperature profile in the sheet at the time of the mineral’s
nucleation and growth, assuming the mineral’s components
are available for its growth along the whole distance.
Following this episode of growth of tourmaline, there will
probably be only a short time-period before another mineral, for example albite, will begin to grow in the interstices of the tourmaline at time t2 when albite is able to
nucleate. Once nucleated, it will grow to a distance at
which the temperature in the sheet is approximately that of
its liquidus temperature. It is also possible that the two
minerals will grow at the same time. On the new crystallization front, there may be a new episode of growth of
tourmaline at t3 when temperature at the new front will
again drop to the nucleation temperature of tourmaline
after some hiatus in time. Growth of a new mineral, for
example K-feldspar, may begin shortly after at t4 when it is
able to nucleate. Subsequently, another episode of mineral
growth will begin on new crystallization front. As a consequence of the flattening of the temperature profile with
Contrib Mineral Petrol (2010) 160:313–325
wall
321
t1
center
wall
t2
center
o
temperature
temperature
liquidus of tourmaline
nucleation T of tourmaline
liquidus of albite
nucleation T of albite
distance into center of sheet
t3
center
liquidus of tourmaline
nucleation T of tourmaline
distance into center of sheet
wall
temperature
temperature
wall
distance into center of sheet
t4
center
liquidus of K-feldspar
nucleation T of K-feldspar
distance into center of sheet
Fig. 7 Schematic diagram showing how undercooling can result in
growth of large crystals and mineral zones within pegmatite sheets.
Each set of panels represents time at which growth of a mineral
begins (t1, t2, t3, t4). The top panel of each set shows growth of a
mineral toward the center of a sheet. The bottom panel of each set
shows the temperature profile at each time. Thick black line is the
temperature profile at time tx and thin dashed line is temperature
profile from previous time, shown for reference. A mineral will begin
to grow when the temperature at a nucleation side drops sufficiently
for the mineral to nucleate. The length of each crystal that begins to
grow at a particular time (t1, t2, etc.) will be limited by the distance
between the site of the mineral’s nucleation and the position of its
liquidus temperature within the sheet. The figure shows a case that is
discussed in the text: crystallization of the pegmatite begins with
growth of tourmaline at t1, and is followed shorty by crystallization of
albite at t2 between the tourmaline crystals. After a hiatus in time
when temperature at the crystallization front drops to the heterogeneous nucleation temperature of tourmaline, tourmaline begins to
grow again from the crystallization front toward center of the sheet,
and its growth is followed shortly by growth of K-feldspar around the
tourmaline. This episodic growth is then followed by a new
generation of crystals at t5 (not shown)
time, later generations of crystals should become longer,
which is a frequent feature of zoned pegmatites.
Boundary layer enrichments of slowly diffusing components ahead of crystallizing feldspars and quartz may be
important in promoting rapid crystallization of minerals
such as tourmaline, garnet, or apatite because a boundary
layer enriched in these components will effectively raise
the liquidi of these minerals and hence induce larger DT’s.
For example, reoccurrence in layers and rhythmic variations in Fe/Mn ratios in garnet in the George Ashley Block
pegmatite, San Diego County (Kleck and Foord 1999) and
in Ca/Mn ratios in apatite in the Animikie Red Ace pegmatite (Sirbescu et al. 2009a, b) may be the consequence of
boundary layers enriched in Fe, Mn, Ca, and P.
We believe that this delayed nucleation model explains
features such as growth of tourmaline blades on a crystal of
K-feldspar (Fig. 1c), reoccurrence of individual minerals in
multiple zones with widely variable crystal dimensions
(Fig. 1b), zoning defined by growth of new minerals, and
growth directions that are generally perpendicular to contacts of pegmatite sheets.
Crystallization below the thermodynamic solidus
Aside from causing delays in mineral nucleation, another
critical aspect of H2O in granite pegmatites is that it
permits growth of crystals at temperatures deeply below
the thermodynamic solidus. In contrast to dry rhyolites,
123
322
which upon rapid undercooling develop a very finegrained matrix, large crystals are able to grow from pegmatite liquids at apparently highly undercooled conditions.
H2O strongly depresses the Tg of silicate liquids (Fig. 3).
For example, Tg of an albite melt with only 6 wt% H2O is
360°C, whereas Tg of a dry albite melt is 820°C (Romano
et al. 1994; Whittington et al. 2009) and Tg of a haplogranite with 5 wt% H2O is depressed by 400°C relative to
an anhydrous haplogranite (Dingwell et al. 1996). The
effect of other fluxes on Tg of silicate melts is less well
known but Tg of B2O3 is only 284°C (Moynihan 1995).
Baker and Freda (2001) demonstrated experimentally the
ability of K-feldspar and quartz to grow in hydrous
eutectic melts at DT of 200°C at 540°C. They were able to
reproduce small versions of textures seen in granite pegmatites. We suggest that the very low Tg’s of hydrous
silicate melts allow growth of large crystals at highly
undercooled conditions, particularly in centers of sheets
where other fluxing components that lower silicate melt
viscosity, particularly Li, may be accumulated by fractional crystallization.
Discussion
The shift in viewing granite pegmatite sheets as products of
very slow cooling of magma to viewing them as products
of rapidly cooled intrusions is fundamentally based on the
simple fact that when emplaced into relatively cold rocks,
pegmatite sheets must cool rapidly (Chakoumakos and
Lumpkin 1990; Morgan and London 1999; Sirbescu et al.
2008; Webber et al. 1999). It is during undercooling that
kinetically-controlled crystal growth becomes important
(Rockhold et al. 1987; Webber et al. 1999). The postulated
importance of water in the petrogenesis of pegmatites by
Jahns and Burnham (1969) has not diminished since their
model was proposed, but in fact becomes more important
because it allows crystals to grow in highly undercooled
granite melts that can remain liquid at hundreds of degrees
below the equilibrium solidus for extended periods of time.
Moreover, water appears to promote rapid growth of large
crystals because it drastically diminishes the rate of
nucleation so that the few nuclei that eventually grow into
large crystals do not form until the melt is highly undercooled. Recent viscosity models for hydrous granite melts
(e.g. Whittington et al. 2009) and data for Li-bearing melts
(Hofmeister et al. 2009) suggest that the transport distance
of pegmatite melts should be significantly larger than
previously estimated. If during ascent bubbles have difficulty nucleating and growing at equilibrium saturation
pressures (Baker et al. 2006; Mangan and Sisson 2000),
pegmatite melts may retain anomalously high concentrations of H2O during cooling. The retention of H2O,
123
Contrib Mineral Petrol (2010) 160:313–325
particularly when magma is confined by impermeable wall
rocks, and its role in depressing crystal nucleation, may be
the essential features that distinguish pegmatites from more
typical granites and rhyolites. This is supported by occurrences of thick rhyolite flows, such as the topaz rhyolites of
western United States that have similar compositions to
granite pegmatites, except for H2O content (Christiansen
et al. 1983; Congdon and Nash 1988), and some of which
probably cooled over longer time periods than many pegmatite sheets.
In our model, once a mineral nucleates, its growth is
driven by the large negative difference between the Gibbs
free energies of the growing mineral and the melt because
of a large DT. The growth ceases in the hotter interior of a
sheet where DG is small but then restarts again at the new
interface when DG becomes large again because of delayed
nucleation. In the model of London (2008, 2009), growth
of large single crystals, although initiated in an undercooled melt, is promoted by enhanced lateral diffusivities
of Si and Al in a fluxed boundary layer which allow segregation of these two elements within rapidly-cooled melt.
The enhanced diffusivities of these two elements are
attributed to equilibration of their activities due to ‘‘field
diffusion’’ of other melt components, especially the alkalis
(Morgan et al. 2008). Indeed, the growth of large crystals
requires rapid removal of incompatible components from
the growing crystal interface and London’s (2008, 2009)
model provides a mechanism for this to occur. However,
enhanced diffusion by itself does not provide the driving
force for crystallization, which must be the difference in
the Gibbs free energy between the growing crystal and the
melt. Because fluxes enhance diffusivities and decrease
free energies of melts relative to minerals, effectively
reducing undercooling, they promote slow growth of
equant crystals instead of elongated and/or skeletal crystals
that characterize pegmatites. Euhedral or massive crystal
morphologies that occur in the cores and pockets of some
LCT pegmatites may result from slower growth at reduced
amounts of undercooling in highly fluxed, hydrous residual
melt. In addition, the cooling rate in inner pegmatite zones
decreases as the intrusion approaches thermal equilibrium
with its surroundings. Therefore, crystal morphology in
cores of pegmatites, where fluxes are accumulated during
crystallization, may be controlled more by high diffusivity
in melt than temperature gradients.
We believe that pegmatitic texture is primarily the
consequence of slow nucleation and rapid growth at large
undercooling in a crystal-poor melt, all of which are
facilitated by high H2O concentrations, and Li, B, F and P
if they occur in significant abundances because they contribute to increasing water solubility and also alter the melt
structure promoting a delay in crystal nucleation. As
illustrated in Fig. 8, retention of H2O in undercooled melts
Contrib Mineral Petrol (2010) 160:313–325
323
crystals and complete solidification of magma at the solidus, both of which characterize granites. Therefore, we
suggest that the differences in textures among granites,
rhyolites, and pegmatites are largely due to differences in
retention of H2O by melts and the degree of undercooling.
1000
melt
50 MPa
300 MPa
900
vapor + melt
crystals
+ melt
temperature (˚C)
800
Acknowledgments The presentation of ideas in this paper was
helped by reviews of Don Baker and an anonymous reviewer. The
work was supported by NSF grants EAR-911116 and EAR-0821152.
granite
700
crystals + vapor
References
600
rhyolite
pegmatite
500
supercooled melt
400
glass
1012 Pa·s
300
0
2
4
6
wt.% H2O in system
8
10
Fig. 8 Temperature–wt% H2O paths for a generic granite, rhyolite
and pegmatite (heavy lines with arrows) illustrating the differences in
undercooling and H2O retention. Large black dots show beginnings of
the paths. The diagram is similar to that shown in Fig. 3. Solid thin
black lines are phase boundaries for 300 MPa and dashed lines for
50 MPa. A granite in a large pluton will cool slowly to the
crystals ? melt ? vapor eutectic where it will exsolve H2O during
slow crystallization. A rhyolite will lose most of its H2O in volcanic
conduits because of decreased H2O solubility in melt with decompression. A rhyolite may cross into the glass field because of the
relatively high glass transition temperature of H2O-poor melts. A
H2O-rich melt that is initially superheated but subsequently is rapidly
undercooled will retain most of its H2O during rapid crystallization if
the H2O cannot be efficiently vented from the system. This process
will lead to a pegmatite
is probably the most salient aspect of pegmatites that differentiates them from normal granites and rhyolites.
Clearly, rhyolites are also undercooled melts, but rhyolites
are microcrystalline or glassy because they had very little
H2O to begin with or they have lost it during decompression within volcanic conduits because the solubility of H2O
is diminished with decrease in pressure (Fig. 8). Loss of
H2O raises the melt viscosity, the glass transition temperature, and promotes high nucleation density. These are the
features that characterize rhyolites. Thus, while both
pegmatites and rhyolites are undercooled melts, the
essential difference between them is that pegmatite melts
have retained H2O whereas rhyolites have not. In contrast
to rapid cooling of rhyolites and pegmatites, slow cooling
of granite melts within large plutons provides the opportunity for continuous loss of H2O without significant
undercooling. Slow cooling also favors growth of equant
Acosta-Vigil A, London D, Morgan GB VI (2005) Contrasting
interactions of sodium and potassium with H2O in haplogranitic
liquids and glasses at 200 MPa from hydration–diffusion
experiments. Contrib Mineral Petrol 149:276–287
Baker DR (1998) Granite melt viscosity and dike formation. J Struct
Geol 20:1395–1404
Baker DR, Freda C (1999) Ising models of undercooled binary system
crystallization: comparison with experimental and pegmatite
textures. Am Mineral 84:725–732
Baker DR, Freda C (2001) Eutectic crystallization in the undercooled
orthoclase-quartz-H2O system: experiments and simulations. Eur
J Mineral 13:453–466
Baker DR, Lang P, Robert G, Bergevin JF, Allard E, Bai L (2006)
Bubble growth in slightly supersaturated albite melt at constant
pressure. Geochim Cosmochim Acta 70:1821–1838
Boudreau AE, McBirney AR (1997) The Skaergaard layered series.
Part III. Non-dynamic layering. J Petrol 38:1003–1020
Burnham CW, Nekvasil H (1986) Equilibrium properties of granite
pegmatite magmas. Am Mineral 71:239–263
Chakoumakos BC, Lumpkin GR (1990) Pressure-temperature constraints on the crystallization of the Harding pegmatite, Taos
County, New Mexico. Can Mineral 28:287–298
Chakraborty S, Dingwell DB, Chaussidon M (1993) Chemical
diffusivity of boron in melts of haplogranitic composition.
Geochim Cosmochim Acta 57:1741–1752
Christiansen EH, Burt DM, Sheridan MF, Wilson RT (1983) The
petrogenesis of topaz rhyolites from the western Unites States.
Contrib Mineral Petrol 83:16–30
Congdon RD, Nash WP (1988) High-fluorine rhyolite: an eruptive
pegmatite magma at the Honeycomb Hills, Utah. Geology
16:1018–1021
Dingwell DB, Knoche R, Webb SL, Pichavant M (1992) The effect of
B2O3 on the viscosity of haplogranite liquids. Am Mineral
77:457–461
Dingwell DB, Hess K-U, Knoche R (1996) Granite and granitic
pegmatite melts: volumes and viscosities. Trans R Soc Edinburgh: Earth Sci 87:65–72
Donaldson CH (1975) Calculated diffusion coefficients and the
growth rate of olivine in a basalt magma. Lithos 8:163–174
Dowty E (1980) Crystal growth and nucleation theory and the
numerical simulation of igneous crystallization. In: Hargraves
RB (ed) Physics of magmatic processes. Princeton University
Press, Princeton, pp 419–485
Duke EF, Redden JA, Papike JJ (1988) Calamity Peak layered
granite–pegmatite complex, Black Hills, South Dakota. Part I.
Structure and emplacement. Bull Geol Soc Am 100:825–840
Duke EF, Papike JJ, Laul JC (1992) Geochemistry of a boron-rich
peraluminous granite pluton: the Calamity Peak layered granite–
pegmatite complex, Black Hills, South Dakota. Can Mineral
30:811–834
123
324
Dunn T, Ratliffe WA (1990) Chemical diffusion of ferrous iron in a
peraluminous sodium aluminosilicate melt: 0.1 MPa to 2.0 GPa.
J Geophys Res 95:15665–15673
Fenn PM (1977) The nucleation and growth of alkali feldspars from
hydrous melts. Can Mineral 15:135–161
Greer AL (1993) Confusion by design. Nature 366:303–304
Grove TL, Parman SW (2006) The development of spinifex textures
in komatiites. Geol Assoc Can Abstr 31:61
Grove TL, Parman SW, Nuka P, deWit M, Dann J (2002) Influence of
H2O on the development of spinifex texture in komatiites.
Geochim Cosmochim Acta 66(Suppl 15A):294
Hess KU, Dingwell DB, Webb SL (1995) The influence of excess
alkalis on the viscosity of a haplogranitic melt. Am Mineral
80:297–304
Hofmeister AM, Whittington AG, Pertermann M (2009) Transport
properties of high albite crystals, near-endmember feldspar and
pyroxene glasses, and their melts to high temperature. Contrib
Mineral Petrol 158:381–400. doi:10.1007/s00410-009-0388-3
Holtz F, Dingwell DB, Behrens H (1993) Effects of F, B2O3 and P2O5
on the solubility of water in haplogranite melts compared to
natural silicate melts. Contrib Mineral Petrol 113:492–501
Holtz F, Johannes W, Tamic N, Behrens H (2001) Maximum and
minimum water contents of granitic melts generated in the crust:
a reevaluation and implications. Lithos 56:1–14
Hurwitz S, Navon O (1994) Bubble nucleation in rhyolitic melts:
experiments at high pressure, temperature, and water content.
Earth Planet Sci Lett 122:267–280
Jahns RH, Burnham CW (1969) Experimental studies of pegmatite
genesis. I. A model for the derivation and crystallization of
granitic pegmatites. Econ Geol 64:843–864
Jahns RH, Tuttle OF (1963) Layered pegmatite–aplite intrusives.
Mineral Soc Am Sp Pap 1:78–92
Johannes W, Holtz F (1996) Petrogenesis and experimental petrology
of granitic rocks. Springer, Berlin
Kleck WD, Foord EE (1999) The chemistry, mineralogy, and
petrology of the George Ashley Block pegmatite body. Am
Mineral 84:695–707
Lofgren GE (1974) An experimental study of plagioclase morphology: isothermal crystallization. Am J Sci 273:243–273
Lofgren GE, Donaldson CH (1975) Curved branching crystals and
differentiation in comb-layered rocks. Contrib Mineral Petrol
49:309–319
London D (1986) Formation of tourmaline-rich gem pockets in
miarolitic pegmatites. Am Mineral 71:396–405
London D (1992) The application of experimental petrology to the
genesis and crystallization of granitic pegmatites. Can Mineral
30:499–540
London D (1996) Granitic pegmatites. Trans R Soc Edinb: Earth Sci
87:305–319
London D (2005) Granitic pegmatites: an assessment of current
concepts and directions for the future. Lithos 80:271–303
London D (2008) Pegmatites. Can Mineral Sp Publ 10, p 347
London D (2009) The origin of primary textures in granitic
pegmatites. Can Mineral 47:697–724
Lyter M, Sirbescu MC (2006) Fluid evolution in a gem-bearing
pocket pegmatite at the Cryo-Genie Mine, San Diego County,
California. A novel method of gemstone exploration. Geol Soc
Am Abstr Prog 38:558
Maloney JS, Nabelek PI, Sirbescu MC, Halama R (2008) Lithium and
its isotopes in tourmaline as indicators of the crystallization
process in the San Diego County pegmatites, California, USA.
Eur J Min 20:905–916
Mangan M, Sisson T (2000) Delayed, disequilibrium degassing in
rhyolite magma: decompression experiments and implications for explosive volcanism. Earth Planet Sci Lett
183:441–455
123
Contrib Mineral Petrol (2010) 160:313–325
Mangan MT, Sisson TW, Hankins WB (2004) Decompression
experiments identify kinetic controls on explosive silicic eruptions. Geophys Res Let 31:L08605
Morgan GB VI, London D (1999) Crystallization of the little three
layered pegmatite–aplite dike, Ramona District, California.
Contrib Mineral Petrol 136:310–330
Morgan GB VI, Acosta-Vigil A, London D (2008) Diffusive
equilibration between hydrous metaluminous–peraluminous haplogranite liquid couples at 200 MPa (H2O) and alkali transport in
granitic liquids. Contrib Mineral Petrol 155:257–269
Moynihan CT (1995) Structural relaxation and the glass transition.
Rev Mineral 32:1–19
Nabelek PI, Russ-Nabelek C, Haeussler GT (1992) Stable isotope
evidence for the petrogenesis and fluid evolution in the
Proterozoic Harney Peak leucogranite, Black Hills, South
Dakota. Geochim Cosmochim Acta 56:403–417
Nabelek PI, Labotka TC, Helms TS, Wilke M (2006) Fluid-mediated
polymetamorphism related to Proterozoic collision of Archean
Wyoming and Superior provinces in the Black Hills, South
Dakota. Am Mineral 91:1473–1487
Norton JJ (1994) Structure and bulk composition of the Tin Mountain
Pegmatite, Black Hills, South Dakota. Econ Geol 89:1167–1175
Norton JJ, Redden JA (1990) Relations of zoned pegmatites to other
pegmatites, granite, and metamorphic rocks in the southern
Black Hills, South Dakota. Am Mineral 75:631–655
Nowak M, Behrens H (1995) The speciation of water in haplogranitic
glasses and melts determined by in situ near-infrared spectroscopy. Geochim Cosmochim Acta 59:3445–3450
Patiño-Douce AE, Harris N (1998) Experimental constraints on
Himalayan anatexis. J Petrol 39:689–710
Robert E, Whittington A, Fayon F, Pichavant M, Massiot D (2001)
Structural characterization of water-bearing silicate and aluminosilicate glasses by high-resolution solid-state NMR. Chem
Geol 174:291–305
Rockhold JR, Nabelek PI, Glascock MD (1987) Origin of rhythmic
layering in the Calamity Peak satellite pluton of the Harney Peak
Granite, South Dakota: the role of boron. Geochim Cosmochim
Acta 51:487–496
Romano C, Dingwell DB, Sterner MS (1994) Kinetics of quenching
of hydrous feldspathic melts: quantification using synthetic fluid
inclusions. Am Mineral 79:1125–1134
Rubin AM (1995) Getting granite dikes out of the source region.
J Geophys Res 100:5911–5929
Scaillet B, Pichavant M, Roux J (1995) Experimental crystallization
of leucogranite magmas. J Petrol 36:663–705
Schmidt BC, Riemer T, Kohn SC, Holtz F, Dupree R (2001) Structural
implications of water dissolution in haplogranitic glasses from
NMR spectroscopy: influence of total water content and mixed
alkali effect. Geochim Cosmochim Acta 65:2949–2964
Shearer CK, Papike JJ, Simon SB, Laul JC, Christian RP (1984)
Pegmatite/wallrock interactions, Black Hills, South Dakota:
Progressive boron metasomatism adjacent to the Tip Top
pegmatite. Geochim Cosmochim Acta 48:2563–2580
Shen A, Keppler H (1995) Infrared spectroscopy of hydrous silicate
melts to 1000 C and 10 kbar: Direct observation of H2O
speciation in a diamond-anvil cell. Am Mineral 80:1335–1338
Simmons WB, Webber KL (2008) Pegmatite genesis: state of the art.
Eur J Min 20:421–438
Sirbescu MC, Nabelek PI (2003a) Crustal melts below 400°C.
Geology 31:685–688
Sirbescu MC, Nabelek PI (2003b) Crystallization conditions and
evolution of magmatic fluids in the Harney Peak Granite and
associated pegmatites, Black Hills, South Dakota—Evidence
from fluid inclusions. Geochim Cosmochim Acta 67:2443–2465
Sirbescu MC, Hartwick EE, Student JJ (2008) Rapid crystallization of
the Animikie Red Ace Pegmatite, Florence county, northeastern
Contrib Mineral Petrol (2010) 160:313–325
Wisconsin: inclusion microthermometry and conductive-cooling
modeling. Contrib Mineral Petrol 156:289–305
Sirbescu MLC, Leatherman MA, Student JJ (2009a) Apatite textures
and compositions as records of crystallization processes in the
Animikie Red Ace pegmatite dike, Wisconsin, USA. Can
Mineral 47:725–743
Sirbescu MC, Wilke M, Veksler I (2009b) Understanding pegmatite
texture: kinetics of crystallization in the haplogranite–Li–B–H2O
System. EOS Trans AGU 90 Fall Meet(Suppl):V43B-2233
Stolper E (1982) The speciation of water in silicate melts. Geochim
Cosmochim Acta 46:2609–2620
Swanson SE, Fenn PM (1986) Quartz crystallization in igneous rocks.
Am Mineral 71:331–342
Taylor BE, Friedrichsen H (1983) Light stable isotope systematics of
granitic pegmatites from North America and Norway. Isot
Geosci 1:127–167
Teng F, McDonough WF, Rudnick RL, Walker RJ (2006a) Diffusiondriven extreme lithium isotopic fractionation in country rocks of
the Tin Mountain pegmatite. Earth Planet Sci Lett 243:701–710
Teng F, McDonough WF, Rudnick RL, Walker RJ, Sirbescu MC
(2006b) Lithium isotopic systematics of granites and pegmatites
from the Black Hills, South Dakota. Am Mineral 91:1488–1498
Thomas AV, Bray CJ, Spooner ETC (1988) A discussion of the
Jahns–Burnham proposal for the formation of zoned granitic
pegmatites using solid–liquid–vapour inclusions from the Tanco
Pegmatite, S.E. Manitoba, Canada. Trans R Soc Edinb: Earth Sci
7:299–315
325
Thomas R, Webster JD, Heinrich W (2000) Melt inclusions in
pegmatite quartz: complete miscibility between silicate melts
and hydrous fluids at low pressure. Contrib Mineral Petrol
139:394–401
Watson EB (1982) Basalt contamination by continental crust: some
experiments and models. Contrib Mineral Petrol 80:73–87
Webber KL, Falster AU, Simmons W, Foord EE (1997) The role of
diffusion-controlled oscillatory nucleation in the formation of
line rock in pegmatite–aplite dikes. J Petrol 38:1777–1791
Webber KL, Simmons WB, Falster AU, Foord EE (1999) Cooling rates
and crystallization dynamics of shallow level pegmatite–aplite
dikes, San Diego County, California. Am Mineral 84:708–717
Whittington AG, Bouhifd MA, Richet P (2009) The viscosity of
hydrous NaAlSi3O8 and granitic melts: configurational entropy
models. Am Mineral 94:1–16
Wilke M, Nabelek PI, Glascock MD (2002) B and Li in metapelites
from the Proterozoic Terrane in the Black Hills, South Dakota,
USA: implications for the origin of leucogranitic magmas. Am
Mineral 87:491–500
Xue X, Kanzaki M (2006) Depolymerization effect of water in
aluminosilicate glasses: direct evidence from 1H-27Al heteronuclear correlation NMR. Am Mineral 91:1922–1926
Zhang Y, Behrens H (2000) H2O diffusion in rhyolitic melts and
glasses. Chem Geol 169:243–262
Zhang Y, Xu Z, Zhu M, Wang H (2007) Silicate melt properties and
volcanic eruptions. Rev Geophys 45:RG4004. doi:10.1029/
2006RG000216
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