Earth and Planetary Science Letters 411 (2015) 131–141
Contents lists available at ScienceDirect
Earth and Planetary Science Letters
www.elsevier.com/locate/epsl
Kimberlite emplacement temperatures from conodont
geothermometry
Jennifer Pell a,∗ , James K. Russell b , Shunxin Zhang c
a
b
c
Peregrine Diamonds Ltd., Vancouver, BC, V6B 1C6, Canada
Volcanology and Petrology Laboratory, Earth, Ocean and Atmospheric Sciences, University of British Columbia, Vancouver, BC, V6T 1Z4, Canada
Canada-Nunavut Geoscience Office, Iqaluit, NU, XOA OHO, Canada
a r t i c l e
i n f o
Article history:
Received 27 March 2014
Received in revised form 15 October 2014
Accepted 3 December 2014
Available online xxxx
Editor: T. Elliott
Keywords:
kimberlite
volcanology
conodont
CAI
emplacement temperatures
Baffin Island
a b s t r a c t
Kimberlites are mantle-derived ultramafic rocks preserved in volcanic and sub-volcanic edifices and
are the main primary source of diamonds. The temperatures of formation, transport, eruption and
deposition remain poorly constrained despite their importance for understanding the petrological and
thermodynamic properties of kimberlite magmas and styles of volcanic eruption. Here, we present
measured values of Colour Alteration Indices (CAI) for conodonts recovered from 76 Paleozoic carbonate
xenoliths found within 11 pipes from the Chidliak kimberlite field on Baffin Island, Nunavut, Canada.
The dataset comprises the largest range of CAI values (1.5 to 8) and the highest CAI values reported to
date for kimberlite-hosted xenoliths. Thermal models for cooling of the Chidliak kimberlite pipes and
synchronous heating of conodont-bearing xenoliths indicate time windows of 10–20 000 h and, for these
short time windows, the measured CAI values indicate heating of the xenoliths to temperatures of 225 to
>925 ◦ C. We equate these temperatures with the minimum temperatures of the conduit-filling kimberlite
deposit (i.e. emplacement temperature, T E ). The majority of the xenoliths record CAI values of between
5 and 6.5 suggesting heating of xenoliths to temperatures of 460 ◦ C–735 ◦ C. The highest CAI values are
consistent with being heated to 700 ◦ C–925 ◦ C and establish the minimum conditions for welding or
formation of clastogenic kimberlite deposits. Lastly, we use T E variations within and between individual
pipes, in conjunction with the geology of the conduit-filling deposits, to constrain the styles of explosive
volcanic eruption.
© 2014 Elsevier B.V. All rights reserved.
1. Introduction
Kimberlites are mantle-derived, xenocryst-rich, ultramafic rocks
preserved as volcanic pipes or vents, intrusive sheets or dykes, and,
less commonly, as volcanic cones, craters or lavas (Dawson, 1971;
Mitchell, 1986). They are the principal natural source of diamonds and diamondiferous kimberlites occur almost exclusively
on Archean cratons (Clifford, 1966; Janse, 1991). Diamond exploration and mining have provided us with a unique opportunity to
study these conduit-filling deposits, which are largely inaccessible
in other volcanic systems.
Kimberlites sensu stricto range from Archean to Tertiary in age
(Janse, 1984; Dawson, 1989; Kiviets et al., 1998) and, if the Igwisi Hills volcanoes are included (Sampson, 1953; Reid et al., 1975;
Dawson, 1994), into the Quaternary (Brown et al., 2012). Their distribution in time is not uniform and there are clearly periods of
*
Corresponding author.
E-mail address: [email protected] (J. Pell).
http://dx.doi.org/10.1016/j.epsl.2014.12.003
0012-821X/© 2014 Elsevier B.V. All rights reserved.
increased kimberlitic volcanism (e.g. Cenozoic/Mesozoic, Heaman
et al., 2003). In most cases, the kimberlite volcanoes are largely
eroded away or otherwise absent leaving only vestiges of the original edifice and its deposits (Cox, 1978; Harris, 1984) which are
preserved intracrater or found within the deeper seated portions
of the original volcanic conduit or vent system. They are highly
susceptible to alteration and weathering and, in some cases, many
of the original diagnostic structures, textures, and other properties
of the kimberlite deposits are lost or compromised (Sparks et al.,
2006; Stripp et al., 2006; Porritt et al., 2012).
Our knowledge of kimberlite volcanism and emplacement processes is limited because there have been no observed historic
eruptions and, therefore, we cannot directly measure formation,
transport, or eruption temperatures. Temperatures of 1350 to
1450 ◦ C (Priestly et al., 2006; Sparks, 2013) have been estimated
for the base of the lithosphere which is the assumed source area
for kimberlite melts and, based on experimental data, it has been
argued that temperatures in excess of 1500 ◦ C are required to
generate kimberlite melts (Sparks, 2013). Experimental studies
and transport modelling have estimated that kimberlites erupt at
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J. Pell et al. / Earth and Planetary Science Letters 411 (2015) 131–141
Fig. 1. Location maps for Chidliak kimberlite field. (A) Simplified geological map of southern Baffin Island showing the major tectonostratigraphic assemblages and bounding
crustal structures (from Pell et al., 2013, after St-Onge et al., 2006 and Whalen et al., 2010). (B) Enlarged map for delineated area in (A) showing locations of kimberlites in
the Chidliak kimberlite province. Kimberlite pipes comprising this study are denoted by filled symbols.
temperatures of ∼1000 to <1200 ◦ C (Fedortchouk and Canil, 2004;
Sparks et al., 2006, 2009; Sparks, 2013; Kavanagh and Sparks,
2009). These estimates are dependent on many assumptions, including the original melt composition, the dissolved volatile contents and compositions (e.g., H2 O vs. CO2 ), and ascent rates.
There are, however, reliable methods of recovering paleotemperatures, which approximate emplacement temperatures (T e )
and place bounds on the minimum eruption temperatures. The T E
has been estimated for volcaniclastic kimberlite deposits using a
variety of methods, including:
pipe cooling and xenolith heating to provide the appropriate time
scales for converting CAI values to temperature. The CAIs establish
the temperatures to which the xenoliths were heated and held,
thereby providing direct evidence of the minimum T E for these inpipe kimberlite deposits. The CAI derived temperatures are used to
establish the minimum conditions needed for welding or sintering
of clastogenic kimberlite deposits and to constrain the styles and
nature of explosive kimberlite eruption at Chidliak.
i) thermal effects recorded by coal inclusions (380 ◦ C, Sosman,
1938);
ii) the absence of demonstrable thermal metamorphic effects in
entrained crustal xenoliths or in adjacent country rocks (e.g.
<500 ◦ C; Mitchell, 1986; Skinner and Marsh, 2004);
iii) thermal demagnetisation studies of wall rocks and accidental xenoliths in four South African pipes (∼300 ◦ C; McFadden,
1977);
iv) vitrinite reflectance of contemporaneous organic material
within kimberlites (e.g., tree fragments) and of organic matter in older Cretaceous and Tertiary shale xenoliths preserved
within Lac de Gras kimberlites (150 to 650 ◦ C, Stasiuk et al.,
1999, 2006);
v) calculated temperature stability fields of alteration assemblages within kimberlite pyroclastic rocks (estimated minimum temperatures of ∼250–400 ◦ C; Stripp et al., 2006;
Afanasyev et al., 2014);
vi) thermoremanent magnetic studies of basaltic lithics within
South African kimberlite pipes suggesting emplacement temperatures for conduit-filling (diatreme zone) pyroclastic deposits of >570 ◦ C to >660 ◦ C and cooler temperatures for
pyroclastic crater-filling deposits (∼200–440 ◦ C). The authors
speculate that the initial bulk temperature of the pyroclastic
mixture may have been 300–400 ◦ C hotter because of potential cooling effects of lithic clasts (10–30 vol.%) (Fontana et al.,
2011).
Chidliak, Canada’s newest diamond district, comprises seventy kimberlites on the Hall Peninsula of southern Baffin Island
(Fig. 1) discovered between 2008 and 2013. Based on reconnaissance studies (Blackadar, 1967), the geology of the Hall Peninsula has been divided into three major crustal entities (Scott,
1996, 1999; St-Onge et al., 2006). From west to east, these
are: 1) granulite facies intracrustal (I-type) granitoids of the
∼1.865–1.845 Ga Cumberland Batholith, 2) a central belt of Paleoproterozoic metasediments and, 3) an eastern terrain underlain by
Archaean orthogneissic and supracrustal rocks of ∼2.92–2.80 Ga
age and, possibly, tectonically reworked younger clastic rocks
(Scott, 1999) now termed the Hall Peninsula block (Whalen et
al., 2010) (Fig. 1). The Chidliak kimberlites are mainly hosted by
rocks of the Hall Peninsula block (Fig. 1b). At present, the Chidliak
area lacks Phanerozoic sedimentary cover, except for unconsolidated glacial deposits; however, Ordovician carbonate rocks crop
out on southwestern Baffin Island, some 150–280 km west of the
Chidliak area. Perovskite U–Pb dating of 25 of the kimberlites indicates kimberlite magmatism spanned a period of approximately
18 million years, from 156 to 138 Ma (Late Jurassic to Early Cretaceous) (Heaman et al., 2012).
Both steeply dipping sheet-like and larger pipe-like bodies have
been discovered at Chidliak. The sheet-like bodies comprise mainly
coherent kimberlite (CK, cf. Scott Smith et al., 2013) dykes, which
may contain basement xenoliths. Most of the pipe-like bodies contain, in addition to basement xenoliths, Late Ordovician to Early
Silurian carbonate and clastic rock xenoliths derived from the paleosurface and incorporated into an open vent structure (Zhang
and Pell, 2014). The occurrence of these Paleozoic xenoliths in the
Chidliak pipes proves that this part of Hall Peninsula was overlain
by Lower Paleozoic sedimentary rocks at the time of kimberlite
Here, we present measured values of conodont Colour Alteration Indices (CAI) recovered from Paleozoic carbonate xenoliths
within kimberlite pipes from the Chidliak kimberlite field on Baffin
Island, Nunavut, Canada. We use thermal modelling of kimberlite
2. Geology of the Chidliak kimberlites
J. Pell et al. / Earth and Planetary Science Letters 411 (2015) 131–141
133
Fig. 2. Schematic diagrams of Chidliak kimberlite pipes. (A) Pipe with volcaniclastic kimberlite infill only. (B) Pipe with mixed in-fill, dominated by volcaniclastic kimberlite.
(C) Pipe with mixed in-fill, dominated by apparent coherent kimberlite.
eruption. The sedimentary succession is estimated to have been
270 to 305 m in thickness and removed by erosion between the
Early Cretaceous and the present (Zhang and Pell, 2013, 2014).
The Chidliak kimberlite pipes are ovoid, steeply plunging to
near vertical, cylindrical-shaped volcanic bodies that are predominantly 50–150 m in radius and estimated to be >500 m deep.
They have a range of textural types of infill and, broadly, can be
assigned to two main types: pipes containing only layered volcaniclastic kimberlite (VK) infill; and, pipes infilled by a combination
of VK, CK, and more enigmatic kimberlite deposits.
The enigmatic deposits are dark, competent, and massive and
show some features of CK such as a finely crystalline groundmass; however, they lack sharp intrusive contacts and contain
well-dispersed Paleozoic sedimentary xenoliths. They also exhibit
other textural features, including olivine grain size variations, close
packing of olivine and other components, occasional broken garnet and olivine grains, diffuse magmaclasts and subtle layering
(cf. Scott Smith et al., 2013). Here, we refer to these rocks as “ap-
parent coherent” kimberlite (ACK) to distinguish them from the
deposits that are clearly VK (e.g., visible pyroclasts) or CK (e.g.,
lavas, sills, dykes) that are devoid of Paleozoic xenoliths.
The layered VK-only pipes tend to be larger (≥125–150 m
radius) than the mixed infill pipes and are dominated by pyroclastic kimberlite (Fort à la Corne-type pyroclastic kimberlite,
cf. Scott Smith et al., 2013) and lesser resedimented pyroclastic
material (Fig. 2A). They are internally variable with respect to
olivine abundance and grain size and commonly contain readily
recognized juvenile pyroclasts. They can comprise up to 15 vol.%
inhomogeneously distributed crustal and mantle xenoliths; Paleozoic carbonates are commonly much more abundant than gneissic
basement, which are, in turn, more abundant than mantle xenoliths.
The mixed infill pipes are commonly 50–75 m in radius, stratified, and range from VK-dominated, with lesser CK and ACK
(Fig. 2B), to dominantly infilled by ACK, with minor amounts of
CK and VK (Fig. 2C). The VK and ACK deposits in the mixed infill
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J. Pell et al. / Earth and Planetary Science Letters 411 (2015) 131–141
pipes have a lower Paleozoic and gneissic basement xenolith content (commonly only 1–2 vol.%) than the VK-only pipes. The CK
units contain only gneissic basement xenoliths and lack Paleozoic
xenoliths. Mantle xenoliths are found in all types of pipe infill. The
VK deposits in the mixed infill pipes are internally variable with
respect to olivine content, packing and grain size, have inhomogeneously distributed xenoliths and easily recognized pyroclasts.
The CK units are dark, massive and have a crystalline groundmass.
They are more homogeneous and have a more uniform olivine
distribution than in the VK or ACK deposits; however, no sharp intrusive contacts are observed and these units may also be effusive,
not intrusive (Pell et al., 2013). Massive volcaniclastic kimberlite
(MVK, also referred to as Kimberley-type pyroclastic kimberlite,
cf. Scott Smith et al., 2013), which is characteristic of many African
kimberlites, does not occur at Chidliak.
3. Conodonts in xenoliths within Chidliak kimberlites
3.1. Introduction to conodonts
Conodonts are phosphatic marine microfossils which are commonly preserved in carbonate rocks; they first appear in the Cambrian period but are extinct by the end of the Triassic. The fossils
themselves are believed to be the skeletal elements of the feeding
apparatus of conodont animals (Aldridge et al., 1986, 1987).
Conodonts have characteristics that are useful in a variety of
geological applications. Most conodont species have substantially
shorter temporal ranges than other fossil groups and, thus, are
commonly the first choice in biostratigraphic dating of Paleozoic and Triassic marine sedimentary rocks (Sweet and Bergström,
1981). Conodonts also change colour with increasing temperature
under burial conditions (Epstein et al., 1977) or when metamorphosed (Rejebian et al., 1987). Unweathered and unheated conodonts are pale yellow and, with increasing temperature, their
colour ranges from pale yellow to light to dark brown, black, grey,
opaque white and, finally, crystal clear (Harris, 1981). Crystal clear
elements, which are generally found in carbonate rocks interbedded with garnet-grade metamorphic rocks, have been produced
experimentally in high temperature runs as the last stage before
decomposition (Harris, 1981).
Conodont elements contain trace amounts of organic matter
and the changes in colour from pale yellow to black are related
to a carbon-fixing process, while the changes from black to clear
are related to carbon loss, the release of water, and recrystallisation (Lindström, 1964; Clark and Miller, 1969; Harris, 1981;
Rejebian et al., 1987). The CAI scale of 1 to 8 relates these colour
changes to temperature and was developed and calibrated experimentally by Epstein et al. (1977) and Rejebian et al. (1987). Conodont colour alteration is time and temperature dependent, the
colour changes are progressive, cumulative and irreversible, thus
making CAI values a good tool for estimating maximum temperatures (Harris, 1979). CAI values are mainly used as geothermometers by the petroleum exploration industry to estimate the thermal maturation history of sedimentary basins (e.g., Voldman et
al., 2010). Some conodont species have relatively long stratigraphic
ranges and are not useful for age dating; however, each element
has a specific colour and provides a reliable CAI value.
3.2. Conodont sample suite
A total of 109 carbonate xenolith samples were collected from
19 diamond drill holes intersecting 11 of the Chidliak kimberlite
pipes and then processed for conodonts (Zhang and Pell, 2013,
2014). Xenoliths were recovered from VK-only pipes and from both
VK and ACK units within mixed infill pipes. All drill cores were
47.6 mm in diameter except for those from two holes which were
63 mm in diameter. The lengths of core samples for most of the
Fig. 3. Histogram of CAI values recovered from carbonate xenoliths in all Chidliak
kimberlite bodies. Vertical lines coincide with CAI scale of 1.5 to 8. Most CAI values
are for xenoliths from volcaniclastic kimberlite (VK); shaded bars denote CAI values
from apparent coherent kimberlite (ACK). CAI data are adopted from Zhang and Pell
(2014).
carbonate xenoliths varied in length from 3 to 50 cm, a few were
as large as 2 m. Conodonts were recovered from the residue resulting from complete sample dissolution within a weak acid solution. More than 1300 conodont elements were recovered from
76 of the 109 samples processed, the other 33 samples were barren. A total of 32 species ranging in age from Late Ordovician to
Early Silurian have been identified (Zhang and Pell, 2014), which
is approximately 280 Ma older than the emplacement ages of the
kimberlites. The recovered conodonts represent the xenolith as a
whole and cannot be ascribed to a specific position within the
xenolith.
Thirty-six of the 109 conodont-bearing xenoliths studied were
from a single, 417 m long inclined (−38◦ ) drill hole (CHI-48210-DD01) in the CH-31 kimberlite pipe, which is one of the largest
bodies at Chidliak (∼4 ha). The pipe contains VK infill that is dominated by primary (Fort à la Corne-type) pyroclastic kimberlite but
includes subordinate amounts of recycled or resedimented pyroclastic kimberlite (Pell et al., 2013). Carbonate xenoliths up to 12 m
in size locally comprise >15 vol.% of the pipe infill. The drill hole
intersects seven VK units, defined on the basis of subtle variations
in macroscopic features, including xenolith sizes, abundance, types
and distribution, juvenile componentry, and magnetic susceptibility. Full descriptions of these units are presented in Supplementary
Appendix A. Conodonts were recovered from xenoliths taken from
six of the seven VK units in this drill core; the seventh unit contained only one xenolith large enough to sample and process but
no conodonts were recovered.
3.3. CAI results
The conodont elements recovered from the Chidliak kimberlites
have CAI values ranging from 1.5 to 8 (Supplementary Appendix B,
Table B1, Fig. B1). In contrast, conodonts from present-day outcrops
of the correlative Ordovician and Silurian strata in the Hudson Bay
and Foxe Basin areas all have CAI values of 1 (Zhang and Barnes,
2007; Zhang, 2013). No systematic variations were noted between
xenolith size and CAI, nor were any systematic variations noted between xenolith abundance and CAI. The conodonts recovered from
xenoliths within VK deposits record a wide range of CAI values,
from 1.5 to 7 (Table B1, Fig. 3). CAI values of <4 are found exclusively in VK-only pipes (CH-31 and CH-58, Table B1). CAI values of
4 to 7 are recorded in xenoliths from VK in VK-only and mixed infill pipes. Xenoliths from ACK within mixed infill pipes contained
conodonts having the most elevated CAI values, from 6 to 8 (Table B1, Fig. 3).
Each pipe features a unique range of CAI values; for example,
CH-58 produced CAI values ranging from 3–4 to 6, while CH-45
J. Pell et al. / Earth and Planetary Science Letters 411 (2015) 131–141
135
NWT (Table 1); it was originally considered to have a kimberlitic
affinity (Godwin and Price, 1987) but is alkaline basalt (Goodfellow
et al., 1995). The CAI values at Chidliak (Table B1) include the highest reported to date for conodonts recovered from kimberlite or
related rock types and represent the largest range of CAI values
observed within a single pipe (1.5 to 6.5 for CH-31) or within a
single kimberlite field (1.5 to 8 for Chidliak). As postulated in other
studies (e.g., McArthur et al., 1980; Cookenboo et al., 1998; Zhang,
2011), we ascribe the elevated CAI values to post-depositional
heating of the xenoliths hosted by the volcanic deposits infilling the Chidliak kimberlite pipes. However, in contrast to previous
studies, we use the CAI’s as a quantitative geothermometer to establish the temperatures to which the xenoliths were heated and
to constrain kimberlite emplacement temperatures.
4. Pipe cooling and xenolith heating
Fig. 4. CAI values from carbonate xenoliths recovered from drill hole
CHI-482-10-DD01 in the CH-31 kimberlite plotted against down hole depth.
The drill hole intersects 7 mappable units; approximate contacts are indicated by
dashed lines. Photographs of representative NQ cores (diameter = 47.6 mm) for
each descriptive unit in CH-31 are shown (right side). The photos are from depths
of: Unit 1 ∼ 21.5 m; Unit 2 ∼ 69.5 m; Unit 3 ∼ 128.5 m; d) Unit 4 ∼ 181.5 m;
e) Unit 5 ∼ 263 m; f) Unit 6 ∼ 308 m; g) Unit 7 ∼ 361.5 m. CAI data are adopted
from Zhang and Pell (2014).
returned CAI values of 5–6 to 7 (Table B1). Conodonts recovered
from CH-31 showed the widest range of CAI values (1.5 to 6.5) and,
within that pipe, the distribution of CAI values correlates well with
the mapped VK units (Fig. 4, Supplementary Appendix A). Some of
the individual units have a very narrow range of CAI values. For
example, six conodont-bearing xenoliths from Unit 1 yielded CAI
values of 3–4 and Unit 6 (also six conodont-bearing xenoliths) had
CAI values of 1–1.5 or 1.5–2 (Fig. 4, Table B1). Other units show
more CAI variability as exemplified by Unit 4. Conodonts from nine
xenoliths in Unit 4 have CAI values of 3–4 ( N = 2), 4 ( N = 2), 4–5
( N = 2) and 5–6 ( N = 3) (Table B1, Fig. 4). The CAI values do not
show an increase with increasing depth in the pipe nor show a
symmetrical decrease from centre of the pipe to the pipe margins.
The variations in CAI values are interpreted to represent differences
in emplacement temperatures and the post emplacement cooling
history of individual depositional units.
Conodont CAI studies from carbonate xenoliths in kimberlite
have been completed elsewhere in Canada and in Russia; most are
characterised by lower CAI values and restricted ranges of CAI values (Table 1). Conodont results have also been reported for xenoliths from the Mountain Diatreme in the Mackenzie Mountains,
In order to relate CAI values to temperatures, numerical modelling of the times involved in cooling of the pipes after cessation of volcanism and heating of the xenoliths was undertaken
to constrain the time available for transformation of conodonts to
variable CAI values. The Chidliak pipes are expected to cool relatively quickly because of their large surface areas (2π Hr) relative
to their volumes (π Hr2 ), where H = height (>500 m) and r = radius (50–150 m). The surface area to volume ratio (2/r ) decreases
markedly as the diameter of the pipe increases and the timescales
for cooling of the pipe increase.
The cooling model assumes the Chidliak kimberlite pipes to
be filled mainly with primary pyroclastic deposits emplaced at
high temperatures (900–1100 ◦ C). Physical properties of the system
(pipe and country rocks) are simplified and listed in Supplementary Appendix C, Table C1. For example, thermal conductivity (K)
is treated as constant in space and time; an average value (see Table C1) for the range of rock types and temperatures considered
is assigned. Cooling is assumed to occur by conduction alone and
the effects of advection (e.g., fluid circulation, volatile degassing)
are not considered; the overall effects of advection would be to
shorten the overall times scales of cooling. The transient cooling of
the pipe also ignores the endothermic effects of heating of crustal
(granitic and carbonate) xenoliths. The syn-to post emplacement
exothermic heat effects of crystallisation (latent heats of crystallisation) and serpentinization of olivine within the pipe (e.g., Stripp
et al., 2006; Mitchell, 2008; Sparks et al., 2009; Porritt et al., 2012;
Afanasyev et al., 2014) are also ignored. Afanasyev et al. (2014)
note that the inclusion of the heats of serpentinization more than
compensates for the cooling effects of convective fluid flow and
can extend the cooling times slightly beyond the times of purely
conductive cooling. Our main goal is to understand the first order
Table 1
Summary of CAI from conodonts in xenoliths within Canadian and Russian kimberlites and mafic diatremes.
Occurrence
Location
Xenolith ages
CAI in
xenoliths
CAI in
source rock
Reference
Multiple pipes
East European Craton,
Arkhangels’k area, Russia
Ordovician
1 to 2
1 (?)
Tolmacheva et al. (2008, 2013)
Buzz No. 1, A-1, Alfie Creek,
Diamond Lake, Troika,
Guiges, Bucke and
Gravel
Superior Craton, Kirkland
Lake and Lake Timiskaming
area, Ontario and Quebec
Middle to Late Ordovician,
Silurian and Devonian
2
1 to 1.5
McCracken et al. (2000)
Glacial boulders
Superior Craton, Larder Lake,
Ontario
Middle Ordovician to
Middle Devonian
3
1 to 1.5
McCracken et al. (1996), Nowlan (1987)
Jericho
Slave Craton, NWT
Middle Devonian
1.5 to 4
≤1.5
Cookenboo et al. (1998)
JD-03
Slave Craton, NWT
Upper Ordovician
3 to 6
≤1.5
Zhang (2011)
Mountain Diatreme
Mackenzie Mountains, NWT
Early and Middle
Ordovician
6 and 7
<4
McArthur et al. (1980)
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J. Pell et al. / Earth and Planetary Science Letters 411 (2015) 131–141
timescales available for heating of the xenoliths and maturation of
the conodonts at Chidliak. On that basis our model decisions to
exclude the heat loss due to advective fluid flow or the heating of
crustal xenoliths and the exothermic heats of serpentinization are
reasonable as the competing heat effects would essentially cancel
out over the shorter time scales.
The 1-D transient conductive cooling model of the pipe (1st order in time and 2nd order in space) uses a modification of the
node-centred explicit finite difference code developed in cylindrical coordinates as used by Dipple (1995). The kimberlite pipe has
radius r and the deposits have an initial (i.e. emplacement) temperature of (T E ). Heat is conductively transferred from the pipe
into wall rocks; the country rocks are a heat sink but assumed
to maintain a fixed T at an infinite distance away from the pipe
(T ∞ = 25 ◦ C; Table C1). The spatial bounds (i.e. z) on the numerical
model are from the centre of the pipe (z = 0) outwards to the contact (z = r) and into the country rock to a distance of ∼4–5 times
the pipe radius. This ensures that the far boundary condition of
a constant country rock temperature is met and the cooling of the
pipe is not compromised. Operationally, the finite difference model
is run by setting the distance between nodes (e.g., z) to reflect
the spatial scale of the problem and then adjusting the time increments (t) to meet the stability condition t = 0.5 z2 /α where
α is thermal diffusivity (Table C1).
Our numerical modelling suggests that, by conductive cooling
alone, a pipe with a 50 m radius would cool from an emplacement
temperature of 1100 ◦ C to ambient temperature of 50 ◦ C or less in
approximately 40 years, while a pipe with a radius of 100 m would
require approximately 170 years to cool. Shorter times would be
required to cool bodies with lower initial emplacement temperatures (Supplementary Appendix C, Fig. C1). Cooling on the pipe
margins would be more rapid than in the centre of the pipes, but
even in the centre, a pipe with a 50 m radius would only take 4
or 5 years to cool to half its original emplacement temperature,
while a pipe with 100 m radius would take about 20 years. This
model for cooling of the kimberlite pipes represents the maximum
amount of time required to cool the pipe because the influence
of fluid transport in and out of the pipe (e.g. rain, ground water,
etc.) is neglected, and the boundary condition is conductive without any natural convection. The total cooling times of Afanasyev
et al. (2014) are somewhat longer than ours (100s–1000s yrs vs.
10s–100s yrs) reflecting their different model assumptions, including significantly larger pipe sizes (H = 1000 m, r = 270 m) more
appropriate for African kimberlites.
A by-product of the model is the thermal history of the proximal country rocks after the pipe is infilled and volcanism has
terminated. Within 2–5 years, the wall rocks are heated to a maximum of 400–500 ◦ C. However, the heating is a transient event
that is too short-lived to produce a thermal metamorphic overprint which is consistent with the general lack of baking effects at
pipe wall contacts (e.g. Mitchell, 1986; Skinner and Marsh, 2004).
The heating of xenoliths is modelled using a 1-D transient
heat conduction model for a sphere based on a MATLAB code
by Recktenwald (2006). All model input parameters are listed in
Table C1. The xenoliths are treated as spheres of fixed diameter
and the times required for conductive heating from 25 ◦ C to the
emplacement temperature of the pipe are computed. The models
were run for a 50 m radius kimberlite and emplacement temperatures of 1000 ◦ C, 900 ◦ C and 500 ◦ C (Fig. 5A).
Modelling also shows that carbonate xenoliths entrained within
hotter material will achieve pipe temperatures in a matter of hours
for small cm sized xenoliths and about two months for xenoliths up to 2 m in diameter. In the simplistic case where the
host remains at a constant temperature, the original emplacement
temperature has a limited effect on time taken to thermally equilibrate (Fig. 5A). Extremely rapid thermal equilibration has also
Fig. 5. Heating times for xenoliths in a kimberlite pipe. (A) Temperature–time heating paths for different sized carbonate xenoliths within a kimberlite pipe with
emplacement temperatures of 1000 ◦ C, 900 ◦ C and 500 ◦ C. Model runs are for xenoliths having diameters of: 5, 10, 25, 50, 100 and 200 cm. The heating times rise
slightly with decreasing pipe temperature but all xenoliths achieve the ambient
emplacement temperature of the pipe in under a month. (B) Model heating and
cooling paths of different sized carbonate xenoliths as a function of location in a
cooling kimberlite pipe with a 50 m radius assuming an emplacement temperature
of 1000 ◦ C. Xenoliths are heated along dashed curves (left to right) until they intersect the pipe cooling path; two extreme cooling paths (solid lines) are shown for
the exterior and centre of the pipe. At this point the xenolith has reached its maximum temperature and then follows the cooling path of the kimberlite. Xenoliths
near the centre of the pipe will be heated to the pipe emplacement temperature
whilst those on the margins of the pipe will be heated to ∼600–750 ◦ C depending on their size. (C) The same modelling is shown for a kimberlite pipe having a
100 m radius; a larger pipe will heat xenoliths on the margin of the pipe faster and
to slightly higher temperatures.
been modelled for mantle xenoliths entrained in kimberlite magmas (Mitchell et al., 1980).
In reality, xenoliths entrained in kimberlites will be heating
while the pipe is cooling. Xenoliths in the centre of the body
would heat to the temperature of the host and remain at that temperature until this part of the pipe begins to cool (Fig. 5B and C).
Given a 1000 ◦ C emplacement temperature, this would occur over
times of ∼10 000 h in a 50 m pipe and ∼20 000 h in a 100 m
pipe. Xenoliths situated near the centre of the body should record
J. Pell et al. / Earth and Planetary Science Letters 411 (2015) 131–141
the temperature of emplacement. Xenoliths near the wall of the
pipe would intersect the pipe cooling curve and start cooling before they can be heated to the original emplacement temperature
(Fig. 5B and C).
Limestone xenoliths are entrained at low temperatures (25–
50 ◦ C) and, as discussed by Fontana et al. (2011), will help to
cool the host deposit while they are being heated. This effect is
most pronounced where xenolith contents are high or near the
margins of the kimberlite body where deposits are already being
quenched before the xenoliths reach emplacement temperatures.
We have modelled the effects of the limestone xenoliths on the
thermal budget of kimberlite deposits as they cool and explored
the implications for interpreting the CAI values as estimates of emplacement temperatures of the resultant deposits (Supplementary
Appendix D). We follow the work of Philpotts (1990), and Marti
et al. (1991) and use the physical constants employed by Fontana
et al. (2011). We examine the heat lost, and the corresponding
temperature reduction, that occurs as xenoliths are heated during
the period that the pipe is cooling. Our modelling shows that, at
lower temperatures (e.g. <400 ◦ C), the cooling effect of the xenoliths is minimal even for high xenolith contents. Approximately
5 vol.% xenoliths would result in a <10 ◦ C lowering of the temperature, while up to 25 vol.% xenoliths would only result in a
temperature reduction of ∼60 ◦ C. This is because the thermal cost
of heating the xenoliths to such low temperatures is not extreme.
Conversely, at high equilibration temperatures (e.g., >650 ◦ C) the
effects of xenolith heating on the overall cooling can be substantial (>100 ◦ C) if the xenolith content is high (e.g., >20 vol.%). This
reflects the fact that there was substantial thermal cost to heat the
xenoliths up to the higher equilibration temperature. Lower xenolith contents will have less effect on the cooling of the body.
5. Discussion
Fig. 6. Arrhenius plot of time vs. reciprocal T (K) defining CAI fields from 1 to 8
(modified from Rejebian et al., 1987). Diagonal lines bound CAI fields: 1–5 from
Epstein et al. (1977); 6–8 from Rejebian et al. (1987). Upper grey shaded area indicates the typical ranges of geological time for heating in sedimentary basins and
burial or contact metamorphism. Lower grey shaded field indicates the time period applicable to xenolith heating in kimberlites involving higher temperatures and
shorter times (cf. Table 2). Corresponding temperature ranges are defined by the
maximum and minimum times on each CAI field.
Table 2
Summary of minimum and maximum temperatures ascribed to each CAI for different time scales (e.g. Fig. 6).
CAI
5.1. Conodont geothermometry
The conventional use of CAI values as geothermometers generally involves burial, contact or regional metamorphic events having durations of tens of thousands to millions of years. In such
studies, the CAI scale of 1–8 corresponds to a temperature range
from <50 ◦ C to >600 ◦ C reflecting the extended time required for
the conodont to achieve a specific index (Epstein et al., 1977;
Rejebian et al., 1987; Voldman et al., 2010). The changes in CAI are
both time and temperature dependent; this is particularly the case
with respect to the lower CAI values. On an Arrhenius (T -time)
plot, the iso-CAI lines for CAI values >5 are steep, indicating that
the CAI thermometry is weakly dependent on time; conversely
iso-CAI lines for CAI <5 have shallow slopes indicating a strong
dependence on time (Fig. 6).
The thermal modelling of pipe cooling and xenolith heating
(Fig. C1 and Fig. 5) indicate a restricted range of times available
to heat the xenoliths prior to joining the pipe cooling path. In
contrast to the window of tens of thousands to millions of years
traditionally used to assess thermal maturation or metamorphism
of sedimentary basins, a time window of 10–20 000 h is more appropriate for converting CAI values to temperatures for conodonts
in xenolith heated in kimberlite pipes (Fig. 6). This time range actually overlaps the field of experimentation upon which the T -time
calibration of CAI values was based (Harris, 1981), thus, allowing for accurate temperature prediction. Given these significantly
shorter durations of heating, conodonts must be exposed to significantly higher temperatures to attain the same CAI values as those
formed in diagenetic or metamorphic environments, especially at
lower CAI values.
Modelling of xenolith heating and pipe cooling (Fig. 7) shows
that a 50 cm carbonate xenolith entrained into a 50 m radius pipe
137
1
1.5
2
3
4
5
6
6.5
7
8
a
b
T
(◦ C)
103 –108 yrs
100 –105 hrs
<50–80
<225
190–480
225–515
305–600
365–610
455–625
525–670
650–775
675–850
>780–>960
50–90a
60–140a
110–200a
190–300a
300–480b
360–550b
440–610b
490–720b
>600b
From Epstein et al. (1977).
From Rejebian et al. (1987).
with an emplacement temperature of 1000 ◦ C would be heated
to approximately 600 ◦ C if it were situated at the margin of the
pipe before beginning to cool; if it were in the centre of the pipe
it would be heated to the emplacement temperature of 1000 ◦ C.
Conodonts within the xenolith situated at the margin of the pipe
would attain CAI values of approximately 5–6, those in the interior
would have CAI values of 8.
5.2. Geothermometry of the Chidliak kimberlites
Xenoliths within the Chidliak VK (predominantly pyroclastic)
deposits contain conodonts with CAI values from 1.5 to 7, with
the majority recording values of between 5 and 6.5 (Fig. 3; Table B1). All nine pipes in which VK was sampled returned CAI
values in this range. This suggests that the majority of the xenoliths were heated to temperatures of at least 460 ◦ C–735 ◦ C and
the one sample with CAI value of 6.5–7 records minimum temperatures of between 625 ◦ C and 815 ◦ C (Fig. 6, Table 2).
138
J. Pell et al. / Earth and Planetary Science Letters 411 (2015) 131–141
Fig. 7. CAI values implied by model thermal histories of carbonate xenoliths distributed in a 50 m radius kimberlite pipe. (A) CAI window for a kimberlite emplaced
at 900 ◦ C. Temperature–time heating–cooling paths for xenoliths are as in Fig. 5A
and CAI fields are as in Fig. 6. Xenoliths in the centre of the pipe can potentially
reach CAI values of 8, while xenoliths located at the pipe margin will have variable
CAI values (4–6) depending on size (see text). (B) CAI window for a kimberlite emplaced at 1000 ◦ C. Xenoliths in the centre of the pipe would potentially have CAI
values of 8 and greater, while xenoliths located at the pipe margin would have CAI
values 5–6.5. Lower CAI values could occur in xenoliths from deposits with lower
original emplacement temperatures or having accelerated cooling rates.
The ACK rocks at Chidliak all record CAI values of 6 to 8, indicating that these xenoliths were heated to temperatures of between 700 ◦ C and 925 ◦ C, which is hotter than seen in the majority of the VK deposits. Carbonate xenoliths in the ACKs are often
recrystallised and commonly show features such as irregular outlines with impinging olivine grains or irregular, convoluted, fluidalshaped margins (Pell et al., 2013), observations that are consistent
with the xenoliths being subjected to high temperatures and supporting the CAI results.
Our CAI-based geothermometry results for the ACK deposits at
Chidliak (up to 925 ◦ C) are the highest estimates of emplacement
temperatures reported for conduit infilling kimberlites. If we consider the thermal effects (∼50 ◦ C) of heating even a small (∼10%)
fraction of carbonate xenoliths (Supplementary Appendix D), these
temperatures (∼975 ◦ C) are approaching the best estimates of kimberlite eruption temperatures (e.g., Fedortchouk and Canil, 2004;
Sparks et al., 2006, 2009; Kavanagh and Sparks, 2009; Sparks,
2013). It is possible that even higher temperature deposits existed,
but conodonts in the entrained xenoliths would have decomposed,
leaving no record of this. The coherent phases of kimberlite in
these bodies do not contain carbonate xenoliths, so no geothermometry is available for these lithologies; however, they are likely
to have been as hot as or hotter than the ACKs.
5.3. Volcanological implications
The Chidliak kimberlites are stratified bodies and different pipes
contain different types of infill ranging from VK-only to mixed VK,
ACK and CK deposits. None contain massive infill such as seen in
many southern African kimberlites (Field and Scott Smith, 1999;
Skinner and Marsh, 2004; Field et al., 2008; Brown et al., 2008b;
and many others) and the volcanic processes responsible for the
formation of the southern African pipes may not be applicable
at Chidliak. The different infill types have their own characteristic CAI values and value ranges reflecting different emplacement
temperatures and temperature variations. The range of CAI values
and the temperatures they record can also vary within a single
pipe. The CH-31 kimberlite pipe, for example, is a large, layered,
VK-only pipe with distinct mappable units defined by texture and
componentry (Fig. 4, Supplementary Appendix A) and representing discrete accumulation events from episodic volcanism. Multiple samples from individual units displayed either a homogeneous
clustering of CAI values representing a restricted range of emplacement temperatures or more variable CAI values suggesting some
variance in temperature occurred within individual units (Fig. 4,
Table B1). This suggests that each depositional unit had a separate emplacement temperature and thermal cooling path, some
with nearly uniform emplacement temperatures whilst others appear to record some variation in emplacement temperatures that
cannot be explained by stratigraphic position within the unit, proximity to the wall rocks, variations in xenolith abundance or other
factors. These rocks are mainly within-vent, pyroclastic deposits
interpreted to be deposited during the waning phases of eruption when it is possible for material to accumulate in the conduit via processes such as (but not restricted to) column collapse
from highly explosive gas-rich eruptions (Fig. 8A), as have been
described from Lac de Gras (Porritt et al., 2008). Higher temperature units could be deposited from non-dilute (hot) plumes, cooler
ones from more diluted plumes (Fig. 8A). A range in temperatures
could occur within a single unit derived from a stratified plume or
through mixing.
Both the ACK and VK deposits found within the smaller, mixedinfill pipes appear to record more homogeneous and higher temperatures than the corresponding deposits in the larger VK-only
pipes. There are a number of features suggesting that the ACK
deposits at Chidliak are products of explosive volcanism (e.g., clastogenic conduit infill) rather than effusive volcanism (e.g., coherent extrusive kimberlite lava) or intrusion (e.g., coherent hypabyssal kimberlite). These include: the modest but relatively
even distribution of low density Paleozoic xenoliths intermixed
with high density mantle xenoliths; variations in olivine grain
size and abundance; the occasional presence of broken garnet
and olivine grains; and the occurrence of subtle, diffuse magmaclasts (Pell et al., 2013). Post- to syn-depositional agglutination,
welding or sintering (Sumner, 1998; Grunder and Russell, 2005;
Vasseur et al., 2013) of these “apparently coherent” conduit infilling clastogenic kimberlites accounts for their enigmatic character. Although not common, similar coherent-like pipe-infill has
been recognized in several other instances, and has also been assigned an explosive or effusive origin (e.g. Brown et al., 2008b;
Hayman et al., 2008; Nowicki et al., 2008; Hayman and Cas, 2011;
van Straaten et al., 2009, 2011; Kurszlaukis and Fulop, 2013).
The high temperatures recorded by CAI geothermometry, support the ACKs being clastogenic deposits resulting from a lower
energy, less explosive fire fountaining style of eruption (Fig. 8B).
Pyroclasts accumulated within the conduit at uniform temperatures closely approximating to the eruption temperature. The CAI
values recorded by these xenoliths in the ACK deposits constrain
the temperatures required for welding to occur, material deposited
at temperatures less than 700 ◦ C do not weld, whilst deposition
at temperatures in excess of 700 ◦ C facilitates welding and formation of clastogenic kimberlite deposits. Coherent kimberlite deposits that lack Paleozoic xenoliths and occur within the pipe infill
may represent an extreme, even hotter end-member of these processes and may also have a pyroclastic origin (e.g., Sumner, 1998).
J. Pell et al. / Earth and Planetary Science Letters 411 (2015) 131–141
139
Fig. 8. Schematic diagram illustrating the eruption styles resulting in the types of pipe infill observed in the Chidliak kimberlites. (A) Highly explosive gas-rich eruptions
could produce VK-only pipes. Associated plumes can have hot, non-dilute sections closer to the vent and cooler more diluted portions (higher, marginal). Resulting deposits
would be within-vent, column collapse pyroclastics and could have variable in temperatures resulting from deposition from different parts of the plume or from different
plume collapse events. (B) Lower energy, fire fountain or spatter-type eruptions could produce apparent coherent and coherent pipe-infill. The majority of the explosive ejecta
remain eruptive temperatures and coalesce upon landing. Pyroclasts formed in the cooler, external parts of the column could be incorporated within the hotter deposits,
resulting in the diffuse magmaclasts seen in some of the ACKs. Cycling between the two eruptive styles could explain the mixed-infill pipes.
6. Conclusions
As applied at Chidliak, using time scales appropriate to volcanic
processes, conodont geothermometry is shown to be an effective
tool for recovering emplacement temperatures (T E ) of volcaniclastic kimberlites and therefore, setting minimum bounds on eruption
temperatures. The determination of T E , combined with textural evidence, have led to a better understanding of the nature of the
conduit filling volcaniclastic kimberlite deposits at Chidliak. For example, CAI geothermometry strongly support the agglutination and
welding of within-pipe pyroclastic kimberlite deposits and establishes the minimum temperatures that facilitate these processes.
The geothermometry also constrains the styles of explosive volcanism for kimberlites within the Chidliak field.
The range of CAI values and the temperatures they record vary
both across the Chidliak kimberlite field and within a single pipe.
The temperature and textural differences recorded both within a
single pipe and between pipes at Chidliak suggest that the styles
and mechanisms of explosive eruptions and depositional processes
can vary both during the formation of a single kimberlite volcano
and across a kimberlite field. By inference, one should expect that
volcanic and depositional processes could also vary between kimberlite fields.
At Chidliak, the conduits collected materials from multiple
eruptive events or during column collapse attending the waning
phases of eruption. Each depositional event would produce deposits having their own thermal budget. The style of eruption
varied from high energy, explosive volcanism producing larger,
cooler VK-only deposits to lower energy fire fountaining produc-
ing smaller pipes with hotter ACK pipe infill. The ACKs were
emplaced at higher temperatures and place minimum bounds on
the temperatures for explosive eruption of kimberlite. Similar internal facies variations have been documented in other Canadian
and some African kimberlites and are also attributed to transitions
from highly to weakly explosive eruptive styles (van Straaten et al.,
2011; Kurszlaukis and Fulop, 2013).
Acknowledgements
Thanks to Peregrine Diamonds Ltd. for giving the authors permission to collect xenolith samples and to Canada-Nunavut Geoscience Office (CNGO) for its financial support for sample processing. Special thanks to P. Krauss (Geological Survey of Canada (GSC),
Vancouver) and J. Barrick (Texas Tech University) for processing
conodont samples and to S. Kurszlaukis, A. Fulop (De Beers Canada,
Toronto) and Barbara Scott Smith (Scott Smith Petrology, Vancouver) for constructive discussions on the geology and volcanology
of the Chidliak kimberlites. Cathy Fitzgerald kindly helped with
the figures. Brooke Clements, Lucy Porritt, Alan O’Connor, Cathy
Fitzgerald, Herman Grütter, Tim Elliott, Tatiana Tolmacheva and an
anonymous reviewer provided constructive criticism and helped
improve the manuscript.
Appendix A. Supplementary material
Supplementary material related to this article can be found online at http://dx.doi.org/10.1016/j.epsl.2014.12.003.
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J. Pell et al. / Earth and Planetary Science Letters 411 (2015) 131–141
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Appendix A: Descriptions of volcaniclastic units infilling Chidliak pipe CH-31 in terms of subsurface depth, textures, componentry, and xenolith contents. The two side panels summarize the downhole variations in magnetic susceptibility measured every metre (left panel) and the abundance and size of all xenoliths over 6 cm in diameter (right panel).
Coloured green bars denote different mappable units within pipe; width of coloured bars represents relative abundance of Paleozoic (i.e. carbonate) xenoliths (blue squares). Red line (on the right panel) denotes relative abundance of basement gneiss xenoliths (red circles).
0
5
MAGNETIC SUSCEPTIBILITY (SI UNITS)
10
15
20
25
30
35
0
20
40
XENOLITH SIZE (CM)
60
80
Volcaniclastic Deposit
100
120
140
Unit
0
Description
25
25
Blue-green to blue grey, fairly massive,
competent pyroclastic kimberlite.
Olivine size and content is variable from poor to moderately olivine-rich;
olivines mostly have a sugary texture
50
50
0
75
75
100
100
125
125
KU-1
150
175
175
225
250
200
DEPTH IN HOLE
DEPTH IN HOLE
200
6 - 43.5
300
300
325
350
350
375
375
400
425
425
Comment
0.72
Uniformly
low
8
15 - < 30
32
Complete size gradation from mm scale upwards.
Mostly very fresh, rare xenoliths show concentric
zoning or blue-green serpentinization. Wide
range of colours: white to light grey to light buff
dominant, some medium to dark grey.
32
Inhomogeneously
distributed. Vary from
relatively fresh to
15 - < 30
serpentinized to a light
yellow to dark green
colour. Many have darker
halos in the kimberlite.
75
Paleozoic xenoliths are light grey to buff, with
rare black shales and frequently have blue-green
alteration rims. Complete size gradation from
mm scale to 25 cm; rare larger xenoliths.
2.58
Increases
slightly
downsection
10
Inhomogeneously
distributed, abundance
increases downsection.
Generally serpentinized
yellow-grey to dark
greyish green; often with
20
Commonly white and grey, rare black shales.
Mostly fresh; however, some have thin blue
alteration rims or show distinct zonal alteration
with bleached margins. Smaller xenoliths can
form cores to juvenile pyroclasts. Most are
between a few mm to 11 cm in size; only 1
6.64
Increases
slightly
downsection
95
Close to 15% overall; however, inhomogeneously
distributed wrt amount and size. Mostly very
fresh, white, medium and dark grey, commonly
displaying mottled algal laminations. Some buff
xenoliths and rare black shales. Minor blue
serpentinization along margins, or subtle
concentric zoning.
9.55
Decreases
downsection
15
Inhomogeneously distributed; generally <5% but
locally can comprise close to 15%. Most are
fresh, but some have distinct dirty yellow
alteration rims.
6.52
Fairly
uniform
Very inhomogeneously distributed, generally
increase in size and amount downsection, but not
in a uniform manner. Most are fresh, light to
medium grey or buff, with rare dark grey
carbonate or dark brown/black shale fragments.
6.7
Variable
KU-4
156 - 250
Light green-grey to medium grey to
medium grey-brown, relatively
competent pyroclastic kimberlite, with
predominantly serpentinized to clay
altered olivine.
Two possible types present, one is similar to
above and the second are ameboidal to ovoid in
shape, medium brown in colour and
macrocrystic, slightly more so than in overlying
units and contain larger phenocrysts. Olivine
inside the pyroclasts can be much larger than in
host.
1-<5
22
Large basement xenoliths
mostly look fresh, smaller
ones serpentinized to a
5 - < 15
greyish yellow colour and
frequently have dark halos
in the kimberlite.
KU-5
250 - 284
Overall dark grey, fairly competent,
pyroclastic kimberlite. Inhomogeneous
with respect to olivine content and grain
size and xenolith content.
Relatively abundant curviplanar to ovoid
pyroclasts; commonly have light brown cores
and darker, finer grained rims, up to 15 mm in
size.
1-<5
55
Inhomogeneously
distributed. Most are
fairly fresh; bleached
halos occur in the
kimberlite surrounding
5
Less basement and
smaller fragments than
above; dominantly fresh.
15 - < 30
125
4.5
Dominantly fresh.
5 - < 15
3
Just over 5% white, buff, light grey carbonate
xenoliths. Some very fresh, others baked with
concentric alteration zones.
17.99
Uniformly
high
2
Dominantly fresh.
5 - < 15
4
Just over 5% white, buff, light grey carbonate
xenoliths. Some very fresh, others baked with
concentric alteration zones.
8.01
Fairly
uniform
6.5
Dominantly fresh.
15 - < 30
9
Mainly buff, grey and white carbonate xenoliths.
Very few <2 mm in size.
3.18
Variable
KU-7A
KU-7B
400
Vol. %
Fresh to slightly
serpentinized,
predominantly granitic
gneisses
114 - 156
KU-6
325
Comment
Magnetic
Susceptibility
Average
Comment
(S.I.)
Clay-altered, light grey green kimberlite
unit with ultracoarse juvenile pyroclasts Similar to above; however, ultracoarse (>16
mm) pyroclasts are quite common, and some are
and rare autoliths. Olivine-poor;
as large as 50 mm in diameter.
olivine varies from relatively fresh to
completely clay altered.
250
275
Vol. %
Paleozoic (Carbonate) Xenoliths
Max.
Size
43.5 - 114
KU-2
225
275
Juvenile Pyroclasts
Abundant grey-brown ovoid to curviplanar
juvenile pyroclasts, up to 12mm in size. They
>0-<1
can be cored by coarse olivine grains and are
generally are finer-grained than the surrounding
kimberlite.
Max.
Size
Light blue grey to greenish grey,
pyroclastic kimberlite with some
autoliths. Variable clast and crystal
content but generally olivine-poor;
olivines range from altered to fresh.
KU-3
150
Basement Gneiss Xenoliths
Depth (m)
KU-7C
Dark grey pyroclastic kimberlite, nonuniform with respect to grain size and
Paleozoic xenolith content. Paleozoic
284 - 332.75 xenolith content and size generally
increases down-section, but is not
uniform and there are interbedded fine
and coarse-grained zones.
Overall medium grey brown to green
mottled, competent pyroclastic
kimberlite with fresh to serpentinized
332.75 - 376
olivine. Crystal/clast supported.
Carbonate xenolith content non
uniform, locally bedded.
Overall medium grey brown to green
mottled, competent pyroclastic
376 - 401
kimberlite with fresh to serpentinized
olivine. Crystal/clast supported.
Crystal/clast supported pyroclastic
401 - 416.1 kimberlite with fresh to serpentinized
olivine; lacks small carbonate xenoliths.
Similar to above, but slightly less abundant and
locally, slightly coarser (up to 20 mm)
Similar to above, up to 20 mm in size.
5 - < 15
1-<5
>0-<1
Possibly at least two types. Some are beautiful
ovoid to spherical, mostly c to vc in size, med
grey colour. Commonly cored with olivine or
>0-<1
xenoliths. Something to check with thin section
. Others are common amoeboid, curviplanar to
almost angular shapes. Frequently dark brown
Possibly two types: 1) ovoid to spherical, mostly
coarse to very coarse in size, medium grey
>0-<1
colour. Commonly cored with olivine or
xenoliths; 2) amoeboid, curviplanar to almost
Similar at above.
>0-<1
5 - < 15
1-<5
Conodont Geothermometry in Kimberlite [Pell et al., 2014 EPSL] Appendix B: Conodont Alteration Indices from Chidliak Kimberlite Pipes
Table B1: Measured alteration indices of conodonts (CAI) from sedimentary xenoliths in
drill core from specific Chidliak kimberlite pipes, including: volcanic facies1, down-hole
depth of sample midpoint (D), sample length processed (L). Sample
Drill Hole
Pipe
11SZ-18-06
11SZ-18-05
11SZ-18-07
11SZ-18-08
11SZ-18-09
11SZ-18-10
11SZ-18-01
11SZ-18-02
11SZ-18-03
11SZ-18-04
11SZ-19-01
11SZ-20-11
11SZ-20-13
11SZ-20-16
SZ11-21-14
SZ11-21-11
SZ11-21-10
SZ11-21-03
SZ11-21-08
11SZ-01-45
11SZ-01-43
11SZ-01-44
11SZ-01-41
11SZ-01-40
11SZ-01-39
11SZ-01-38
11SZ-01-37
11SZ-01-36
11SZ-01-35
11SZ-01-34
11SZ-01-33
11SZ-01-32
11SZ-01-31
11SZ-01-30
11SZ-01-29
11SZ-01-28
11SZ-01-27
11SZ-01-26
11SZ-01-24
CHI-101-11-DD02
CHI-101-11-DD02
CHI-101-11-DD03
CHI-101-11-DD03
CHI-101-11-DD03
CHI-101-11-DD03
CHI-101-11-DD04
CHI-101-11-DD04
CHI-101-11-DD04
CHI-101-11-DD04
CHI-166-11-DD02
CHI-192-11-DD01
CHI-192-11-DD01
CHI-192-11-DD01
CHI-258-11-DD05
CHI-258-11-DD06
CHI-258-11-DD07
CHI-258-11-DD08
CHI-258-11-DD08
CHI-482-10-DD01
CHI-482-10-DD01
CHI-482-10-DD01
CHI-482-10-DD01
CHI-482-10-DD01
CHI-482-10-DD01
CHI-482-10-DD01
CHI-482-10-DD01
CHI-482-10-DD01
CHI-482-10-DD01
CHI-482-10-DD01
CHI-482-10-DD01
CHI-482-10-DD01
CHI-482-10-DD01
CHI-482-10-DD01
CHI-482-10-DD01
CHI-482-10-DD01
CHI-482-10-DD01
CHI-482-10-DD01
CHI-482-10-DD01
CH-45
CH-45
CH-45
CH-45
CH-45
CH-45
CH-45
CH-45
CH-45
CH-45
CH-17
CH-56
CH-56
CH-56
CH-44
CH-44
CH-44
CH-44
CH-44
CH-31 (U1)
CH-31 (U1)
CH-31 (U1)
CH-31 (U1)
CH-31 (U1)
CH-31 (U1)
CH-31 (U2)
CH-31 (U2)
CH-31 (U2)
CH-31 (U2)
CH-31 (U2)
CH-31 (U2)
CH-31 (U2)
CH-31 (U2)
CH-31 (U2)
CH-31 (U2)
CH-31 (U2)
CH-31 (U2)
CH-31 (U3)
CH-31 (U4)
Facies
D (m)
L (cm)
CAI
VK
ACK
VK
VK
VK
VK
VK
VK
VK
VK
VK
VK
VK
VK
ACK
ACK
ACK
ACK
VK/ACK
VK
VK
VK
VK
VK
VK
VK
VK
VK
VK
VK
VK
VK
VK
VK
VK
VK
VK
VK
VK
14
67.8
33
34
35.1
36.63
35.2
40.66
41.66
52.25
68.4
102.2
114.9
165.08
104.4
63.9
41
21.2
94.3
20.35
28.2
27.9
38.62
39.57
41.23
60.05
62.2
63.63
82
83.89
85.38
85.06
88.13
92. 93
93.25
107.58
110
120
156.5
100
16
125
79
142
80
40
100
100
50
40
27
15
15
100
10
11
200
36
30
118
40
13
40
33
10
20
24
60
23
23
13
10
15
50
15
15
23
30
6-6.5
7
5-6
6.5-7
5-6
6-6.5
6.5
6.5
5-6
6
6-6.5
6-6.5
6
6-6.5
7-8
7-8
7
6
6
3-4
3-4
3-4
3-4
3-4
3-4
6-6.5
6-6.5
6-6.5
6-6.5
5-6
6-6.5
6-6.5
6-6.5
5-6
5-6
5-6
4-5
5-6
3-4
i Conodont Geothermometry in Kimberlite [Pell et al., 2014 EPSL] 11SZ-01-23
CHI-482-10-DD01 CH-31 (U4)
VK
157.9
18
4-5
11SZ-01-22
CHI-482-10-DD01 CH-31 (U4)
VK
159.65
45
4-5
11SZ-01-21
CHI-482-10-DD01 CH-31 (U4)
VK
163
15
3-4
11SZ-01-20
CHI-482-10-DD01 CH-31 (U4)
VK
167.75
55
5-6
11SZ-01-19
CHI-482-10-DD01 CH-31 (U4)
VK
169.9
18
5-6
11SZ-01-18
CHI-482-10-DD01 CH-31 (U4)
VK
186.68
15
5-6
11SZ-01-17
CHI-482-10-DD01 CH-31 (U4)
VK
192
3
4
11SZ-01-16
CHI-482-10-DD01 CH-31 (U4)
VK
210.43
25
4
11SZ-01-14
CHI-482-10-DD01 CH-31 (U5)
VK
251.7
10
3
11SZ-01-13
CHI-482-10-DD01 CH-31 (U5)
VK
261.9
20
2-3
11SZ-01-11
CHI-482-10-DD01 CH-31 (U6)
VK
307.65
50
1-1.5
11SZ-01-09
CHI-482-10-DD01 CH-31 (U6)
VK
311.58
18
1-1.5
11SZ-01-07
CHI-482-10-DD01 CH-31 (U6)
VK
314.2
40
1.5-2
11SZ-01-06
CHI-482-10-DD01 CH-31 (U6)
VK
317
40
1.5-2
11SZ-01-03
CHI-482-10-DD01 CH-31 (U6)
VK
326.75
130
1-1.5
11SZ-01-02
CHI-482-10-DD01 CH-31 (U6)
VK
328.15
14
1-1.5
11SZ-20-05
CHI-488-11-DD02
CH-33
VK
151.09
8
5-6
11-SZ20-17
CHI-400-11-DD01
CH-28
VK
40.05
55
6
11-SZ20-17
CHI-400-11-DD01
CH-28
VK
112.7
33
6
11SZ-20-06
CHI-554-11-DD01
CH-55
VK
84.35
30
6
11SZ-20-10
CHI-554-11-DD01
CH-55
VK
152.1
55
5-6
11SZ-17-01
CHI-557-11-DD02
CH-58
VK
161.91
120
3-4
11SZ-17-02
CHI-557-11-DD02
CH-58
VK
163
100
4
11SZ-17-03
CHI-557-11-DD02
CH-58
VK
163.7
35
4
11SZ-17-04
CHI-557-11-DD02
CH-58
VK
164.06
40
4-5
11SZ-17-06
CHI-557-11-DD02
CH-58
VK
165.57
45
5-6
11SZ-17-07
CHI-557-11-DD02
CH-58
VK
167.3
90
5-6
11SZ-17-08
CHI-557-11-DD02
CH-58
VK
168.3
112
5-6
11SZ-17-09
CHI-557-11-DD02
CH-58
VK
169.35
70
5-6
11SZ-20-03
CHI-557-11-DD02
CH-58
VK
181.4
30
6
SZ12-01-07
CHI-050-11-DD16
CH-06
ACK
87.15
45
6.5-7
SZ12-01-08
CHI-050-11-DD16
CH-06
ACK
88.3
60
6.5-7
SZ12-01-09
CHI-050-11-DD19
CH-06
ACK
79.7
87
7
SZ12-01-01
CHI-251-11-DD08
CH-07
VK
147.5
145
4-5
SZ12-01-02
CHI-251-11-DD14
CH-07
VK
38.47
15
6
SZ12-01-04 CHI-251-11-DD14
CH-07
VK
113.9
20
4-5
1VK = Volcaniclastic kimberlite, dominantly primary pyroclastic kimberlite (Fort a la Corne-type, as per
Scott Smith et al., 2013); ACK = Apparent coherent kimberlite. CAI data and sample numbers are
adopted from Zhang and Pell (2014).
ii Conodont Geothermometry in Kimberlite [Pell et al., 2014 EPSL] Figure B1. Photographs illustrating the range of
colors for conodonts recovered from carbonate
xenoliths preserved in the Chidliak kimberlites
pipes (cf. Zhang and Pell, 2014). The colour
alteration index (CAI) is product of temperature
and time and is scaled from 1-8. The 16 examples
(black bar = 0.25 mm) shown here include: 1. Sa
element of Oulodus panuarensis Bischoff (CAI =
1.5) from SZ1101-23, GSC137600. 2.
ozarkodiniform Pb element (CAI = 1.5) from
SZ11-01-03, GSC137602. 3. Sa element of
Oulodus jeannae Schönlaub (CAI = 2) from SZ1101-41, GSC137603. 4. Sa element of Distomodus
sp. 1 (CAI = 2) from SZ11-01-41, GSC137604. 5
and 6. Pb3 element of Rhipidognathus
symmetricus Branson, Mehl and Branson (CAI =
3) from SZ11-01-43, GSC137566. 7. Pa element
of Ozarkodina elibata (Pollock, Rexroad and
Nicoll) (CAI = 4–5) from SZ11-1709, GSC137605.
8. Pb element of gen. et sp. indet B (CAI = 4–5)
from SZ11-01-27, GSC137571. 9 and 10. Pb and
M elements of Oulodus velicuspis (Pulse and
Sweet) (CAI = 6) from SZ11-01-35, GSC137559
0
and GSC137560. 11. Sc element of
Pseudobelodina v. vulgaris Sweet (CAI = 6.5)
from SZ11-01-35, GSC137547. 12. grandiform
element of Belodina confluens Sweet (CAI = 6.5)
from SZ11-01-26, GSC137541. 13. M element of
gen. et sp. indet A (CAI = 7) from SZ12-01-09,
GSC137567. 14. arcuatiform element of
Panderodus unicostatus (Branson and Mehl) (CAI
1
= 7) from SZ11-18-05, GSC137606. 15. Sc
element of Pseudobelodina? dispensa (Glenister)
(CAI = 8) from SZ11-21-14, GSC137607. 16.
compressiform element of Panderodus
unicostatus (Branson and Mehl) (CAI = 8) from
SZ11-21-14, GSC137608. 1–6 and 8–12 are from
CHI-482-10-DD01, 7 from CHI-557-11DD02, 13
from CHI-050-11-DD19, 14 from CHI-101-11DD02, and 15 and 16 from CHI258-11-DD05.
iii Conodont Geothermometry in Kimberlite [Pell et al., 2014 EPSL] Appendix C: Thermal Models for Cooling of Kimberlite Pipes
Figure C1. Summary of thermal modelling applied to cooling of kimberlite pipes (see
text). Model results are for pipe radii of 50 m (left) and 100 m (right) and original
emplacement temperatures of 900 (top), 1000 (middle) and 1100 oC (bottom).
Temperature-distance isochrons are shown at variable time increments and from the
centre of the pipe and into the country rock. The maximum time reported for each
scenario is the time for the entire pipe to cool to 100-125 oC (red line). A 200 oC
difference in emplacement temperature increases this time by 8 years; doubling of the
pipe diameter raises this time by more than 4 times.
i Conodont Geothermometry in Kimberlite [Pell et al., 2014 EPSL] Table C1. Parameters used to model cooling of kimberlite pipe and heating of xenoliths.
Property
Description
Value
Source
T0 [oC]
Emplacement Temperature
900 - 1100
-
T [oC]
Wall rock temperature
25
-
Tx [oC]
Xenolith initial temperature
25
-
R0 (m)
Pipe radius
50 or 100
Pell et al. (2013), this study
r (cm)
Xenolith radius
5 - 200
Zhang and Pell (2014), this
study
Thermal diffusivity
1-6x10-6
Philpotts (1990)
K [W m-1 K-1]
Thermal conductivity
2.5
Philpotts (1990)
h [W m-2 K-1]
Free convection coefficient
1-10
Carslaw and Jaegar (1959)
α [m2 s-1]
References
Carslaw, H.S., Jaeger, J.C., 1959. Conduction of Heat in Solids. Oxford University
Press, New York.
Philpotts, A.R., 1990. Principles of igneous and metamorphic petrology. Prentice Hall,
Englewood Cliffs, New Jersey.
Pell, J., Grütter, H., Neilson, S., Lockhart, G., Dempsey, S. and Grenon, H., 2013.
Exploration and Discovery of the Chidliak Kimberlite Province, Baffin Island,
Nunavut, Canada’s Newest Diamond District. In D.G. Pearson et al., (eds)
Proceeding of the 10th International Kimberlite Conference, Bangalore, India,
Volume 2, Special Issue of the Journal of the Geological Society of India, 209227.
Zhang, S. and Pell, J., 2014. Conodonts recovered from the carbonate xenoliths in
kimberlites confirm the Paleozoic cover on Hall Peninsula, Nunavut. Can. J.
Earth Sci., 51, 142-155.
ii Conodont Geothermometry in Kimberlite [Pell et al., 2014 EPSL] Appendix D: Thermal Model Considerations for the Effects of Carbonate Xenoliths
The Chidliak kimberlite pipes are populated by variable abundances of limestone
xenoliths derived from the explosive disruption of the sedimentary rock sequences overlying the
crystalline basement rocks of Baffin Island by emplacement of the Chidliak kimberlites. The
fragments of limestone were presumably produced by the explosive volcanic eruption of the
kimberlite and, then, entrained and mixed into the flux of erupting kimberlite, prior to being
sedimented or collapsing back into the vent as part of the present-day conduit filling kimberlite
deposit. The pervasive distribution of these limestone xenoliths within the Chidliak pipes and the
fact that they contain conodonts, allows the values of CAI to be used as estimates of the
emplacement temperatures of the kimberlite.
The equilibration temperatures (TC) recorded by the CAI of conodonts represent the
integrated time spent at elevated temperatures. The thermal history of the conodonts is a
complex product of being heated to the temperature of the kimberlite deposit as the deposit
itself is cooled. The CAI's are modified as they are heated and record the maximum
temperature that the xenoliths are held at (TC) within the kimberlite deposits before the deposits
begin to cool. The CAI's therefore inform indirectly on the initial emplacement temperature of the
kimberlite deposits accumulated within the volcanic conduit (i.e. TE).
We take the CAI values, and the temperatures they indicate, as representative of the
peak temperatures the limestone xenoliths reached (TC) prior to being quenched by wholesale
cooling of the kimberlite body/deposit. Ideally, this peak temperature (TC) is a close
approximation of TE for the depositional unit that contains it. In the case of vent filling pyroclastic
deposits deriving from small, non-dilute eruption columns, TC may equal TE and may even
closely approximate eruption temperatures. Within-vent deposits that derive from larger, more
dilute, eruption columns, perhaps featuring convecting plumes, will logically record cooler
temperatures. Such deposits could also record highly variable temperatures because of the
diverse paths imposed on the pyroclastic material within the eruption column prior to falling back
into the conduit.
The position of the kimberlite-hosted limestone xenoliths, relative to the pipe wall, can
also affect the temperature recorded (TC) because the deposits and xenoliths they contain will
cool more rapidly than deposits in the centre of the pipe. Potentially, the xenoliths will be
quenched by cooling of the kimberlite prior to reaching the original TE of the host kimberlite
deposit. Indeed, the cooling times for these kimberlite bodies are short when compared to the
times conodonts in sedimentary basins are held at elevated temperatures. However, as our
modelling shows, the heating of the xenoliths is very rapid relative to the time scale of cooling
for even the marginal kimberlite rocks. Depending on the xenolith size (5-200 cm; Figs. 8,10),
the CAI for samples right at the contact will record temperatures (TC) that are only 20-50% lower
than the deposit's TE.
There is one other consideration that affects how we interpret the CAI values (TC) in
terms of TE's of the individual conduit-filling kimberlite deposits. As discussed by Fontana et al.
(2011), the limestone xenoliths are entrained at low temperatures (25-50 oC) and, thus, will help
to cool the host deposit whilst it is heating the conodont-bearing xenolith. In essence, the
heating of the xenoliths helps quench the deposit at a lower TC prior to the xenolith reaching the
original TE. Clearly, this effect is most important where xenolith contents are high and near the
margins of the kimberlite body where deposits are already being quenched prior to xenoliths
reaching the original TE.
We have modelled the effects of the limestone xenoliths on the thermal budget of
kimberlite deposits as they cool and explored the implications for interpreting the CAI values as
estimates of deposit TE. We follow the work of Phipotts (1990), Russell (1990), Marti et al.
(1991) and use the physical constants employed by Fontana et al. 2011). Our analysis differs
from Fontana et al. (2011). We consider our deposits as resulting from sedimentation and
i Conodont Geothermometry in Kimberlite [Pell et al., 2014 EPSL] collapse of eruption columns back into their conduits, rather than as products of pyroclastic
density current with the attendant cooling during transport. We note that they also used these
calculations to extrapolate their recorded temperatures (i.e. <540 oC) to possible source
temperatures of eruption (760-920oC; see Fig. 10; Fontana et al. 2011).
Here we examine the heat lost, and the corresponding temperature reduction, that
occurs as the xenoliths are heated during the period that the pipe is cooling. We consider the
original heat content of the pre-deposited material (H0) to be:
𝐻! = 𝜌! 𝐶𝑝! 𝑇! (1 − 𝑥! ) + 𝜌! 𝐶𝑝! 𝑇! 𝑥!
(1)
where the subscripts E and L refer to kimberlite and limestone, respectively. Other variables
include temperature (T), density (ρ), heat capacity (Cp) and volume fraction of limestone
xenoliths (x). After thermal equilibration we can rewrite heat content equation for the conditions
of thermal equilibrium (Heq) as:
𝐻!" = 𝜌! 𝐶𝑝! 𝑇!" (1 − 𝑥! ) + 𝜌! 𝐶𝑝! 𝑇!" 𝑥!
.
(2)
Assuming conservation of heat (Heq = H0) implies a minimum reduction of the emplacement
temperature (ΔT) from heating of the xenoliths of:
Δ𝑇 = − !! !"! !! (!!" !!! ) !! !"! (!!!! )
.
(3)
We use the temperatures derived from the observed values of CAI (i.e. TC) as Teq to calculate
the temperature reduction of the deposit (TC - TE) as a function of xenolith content (Fig. D1).
Where the CAI values are low (e.g., < 400 oC), the effect of the xenoliths is minimal (<60
o
C) even for high (~25 vol. %) xenolith contents. This is because the thermal cost of heating the
xenoliths to such low temperatures are not extreme. The implication is that the low values of
CAI cannot be explained alone by the entrainment and heating of xenoliths; the low CAI's have
to be taken as indicative of low emplacement temperatures (e.g., primary volcanic process) or
quenching of hot deposits by a combination of proximity to wall rocks and high xenolith
contents (e.g., post-emplacement processes).
Conversely, where the CAI values indicate very high equilibration temperatures (e.g.,
>650 oC) the effects of xenolith heating on masking the original TE can be substantial (> 100 oC)
if the xenolith content is high (e.g., > 20 vol. %). This reflects the fact that there is substantial
thermal cost to heating cold xenoliths to higher equilibration temperatures (as recorded by the
conodont alteration index).
We have used a modified form of Eq. 3 to compute the original unknown emplacement
temperature (TE) of the kimberlite deposits for a range of xenolith contents using the maximum
equilibration temperature (TC) recovered form our analysis of CAI's (e.g., 900oC) As illustrated in
Figure D1, if the limestone content was high, the original emplacement temperature could have
been ~200oC higher than recorded by the CAI values (e.g., 1090oC).
ii Conodont Geothermometry in Kimberlite [Pell et al., 2014 EPSL] Figure D1. Model effects of carbonate xenolith
content on thermal budgets of kimberlite. (A) The
extent of cooling of kimberlite deposits caused by
heating of cold surface-derived carbonate xenoliths
shown as function of the volume fraction of
xenoliths for different initial deposit temperatures
(100 - 1000oC). (B) The drop in temperature
resulting from heating of different xenolith
abundances (0.025 - 0.25 vol. fraction) is plotted
against the equilibration temperature as would be
recorded by CAI values. (C) The minimum
original emplacement temperatures are
calculated for a deposit having CAI values
corresponding to 900oC as a function of the
volume fraction of carbonate xenoliths.
References
Fontana, G. MacNiocaill, C., Brown, R. J., Sparks, R.S.J., Field, M., 2011.
Emplacement temperatures of pyroclastic and volcaniclastic deposits in
kimberlite pipes in southern Africa. Bull. Volc. 73, 1063-1083.
Marti, J., Diez-Gil, J.L., Ortiz, R., 1991. Conduction model for the thermal influence of
lithic clasts in mixtures of hot gases and ejecta. J. Geophys. Res. 96, 21879–
21885.
Philpotts, A. R.,1990. Principles of Igneous and Metamorphic Petrology, Prentice Hall,
494 pgs.
Russell, J.K., 1990. Magma Mixing Processes: Insights Provided by Thermodynamic
Calculations, in Modern Methods of Igneous Petrology. Mineralogical Society of
America, Rev. Mineral. 23, 153-190.
iii