Miner Petrol (2009) 97:203–222
DOI 10.1007/s00710-009-0088-8
ORIGINAL PAPER
Assimilation and diffusion during xenolith-magma
interaction: a case study of the Variscan Karkonosze
Granite, Bohemian Massif
Marta Adamuszek & Timm John & Marcin Dabrowski &
Yuri Y. Podladchikov & Ralf Gertisser
Received: 24 February 2009 / Accepted: 16 October 2009 / Published online: 12 November 2009
# Springer-Verlag 2009
Abstract Magmatic enclaves from the Rudolfov quarry near
Liberec (Czech Republic) are interpreted to represent
remnants of lamprophyric melt that intruded the Karkonosze
granite at a stage at which the granite was not fully solidified.
Based on the observation that larger enclaves are generally
more circular than the smaller ones, we conclude that bigger
blobs of mafic magma became more spherical during flow
in the gravity field (sink or float). This flow is also interpreted
to be responsible for the incorporation of mineral grains into
the enclaves and may have facilitated the assimilation of
granitic melt. Linear mixing trends on Harker diagrams for
most network-forming and mainly slow-diffusing or fluidimmobile elements indicate such an assimilation process
between granite and lamprophyre. In contrast, all fastdiffusing or fluid-mobile elements display scattered element
distributions, implying that chemical diffusion also played a
role. Pressure and temperature for this late magmatic stage are
estimated at around 1 kbar and 500°C. These results suggest
that two processes modified the composition of the enclaves
Editorial handling: F. Gaidies and T. John
M. Adamuszek (*) : T. John : M. Dabrowski :
Y. Y. Podladchikov
Physics of Geological Processes PGP, University of Oslo,
PO Box 1048, Blindern,
0316 Oslo, Norway
e-mail: marta.adamuszek@fys.uio.no
T. John
Institut für Mineralogie, Universität Münster,
Correnstrasse 24,
48149 Münster, Germany
R. Gertisser
School of Physical and Geographical Sciences,
Earth Sciences and Geography, Keele University,
Keele, Staffordshire ST5 5BG, UK
in the Karkonosze granite: (1) assimilation (mechanical
mixing) of granitic melt during the injection of the
lamprophyric melt and the subsequent flow of the forming
enclaves in the gravity field (responsible for the linear
mixing trends) and (2) diffusion-controlled redistribution of
elements between both solidifying rock types at the
magmatic stage and/or due to late-stage magmatic fluids
(responsible for the scattering and deviation from the linear
mixing trends).
Introduction
The occurrence of magmatic enclaves in granitic plutons is
a very common feature. It is typically explained by
mechanical mingling of two coexisting magmas (Vernon
1984; Frost and Mahood 1987; Castro et al. 1990; Vernon
1990; Williams and Tobish 1994; Wiebe and Ulrich 1997;
Arvin et al. 2004). During injection of the enclave forming
melt and subsequent cooling, various mechanical and
chemical processes influence the shape and size of the
distribution of the enclaves as well as their bulk composition and consequently their mineral assemblages. Mechanical mingling or chemical mixing are widely documented in
different enclave-granite systems based on detailed petrological analysis and various geochemical techniques (e.g.
Vernon 1983, 1984, 1990; Bateman 1995; Elburg 1996;
Wiebe and Ulrich 1997; Kumar et al. 2004; Paterson et al.
2004; Barbarin 2005). However, little is known about the
effect of the interplay between both mechanical and
chemical processes (e.g. assimilation and diffusion) on the
distribution of elements between enclaves and their host.
For the purpose of this investigation we chose the Rudolfov
quarry (located within the Karkonosze granite, Czech
Republic), where clear field evidence is preserved for the
204
mixing and mingling of two compositionally distinct
magmas within the Karkonosze granite (Słaby and Götze
2003). Our investigation integrates field observations with
petrological and geochemical studies of magmatic enclaves
and their host granite. Magmatic enclaves are the most
striking feature found in the Rudolfov quarry and they
display different sizes, shapes, and compositions. This
study shows geochemical evidence that defines the precursor melt of the enclaves as lamprophyric. We further
present a diffusion model and propose a model of enclave
formation. Finally, we identify the processes, which are
likely to affect the chemical composition of the enclaves
and thus are responsible for magma mixing and mingling.
Both mechanically dominated and purely chemical interactions between the granitic and lamprophyric magmas are
examined by petrological and geochemical methods that
place constraints on mixing-mingling and late-magmatic
hydrothermal processes.
The Karkonosze granite
The Karkonosze granite is located in the eastern part of the
European Variscides (NE margin of Bohemian Massif,
Fig. 1). The emplacement took place during a postcollisional extension stage in the Early Carboniferous
(Mazur and Aleksandrowski 2001) and is dated using the
Rb-Sr method at 329±17 Ma (Duthou et al. 1991). The
granite forms a large, longitudinally aligned body with a
Fig. 1 Geological map of the Karkonosze granite and its metamorphic
envelope (after Kryza and Mazur 1995; Žák and Klomínský 2007)
M. Adamuszek et al.
length of 70 km and a width of up to 20 km. Since the
pluton narrows significantly in the middle section in the
map view (Fig. 1), it is commonly divided into two domes:
the Karkonosze dome in the east, and the Liberec dome in
the west. The contact between the granite and country rock,
being mainly intrusive, is interrupted by two tectonic
dislocations: the Intra-Sudetic Fault in the north-east and a
minor dislocation in the south-west. The pluton is embedded into various pre-Permian tectonostratigraphic terranes
juxtaposed during the Variscan orogeny (Matte et al. 1990;
Aleksandrowski 1995; Franke and Żelaźniewicz 2000).
Based on different lithostratigraphies and a contrasting
metamorphic evolution, four different structural units have
been identified within the Karkonosze granite, namely
Izera-Kowary, Ještěd, South Karkonosze, and Leszczyniec
(Mazur and Aleksandrowski 2001).
Petrological and geochemical investigations of the
Karkonosze granite revealed that it is internally inhomogeneous. Due to different textural features, Borkowska (1966)
distinguished three main facies: (1) a central—coarse to
medium grained porphyritic facies, (2) a ridge—medium to
fine grained facies, and (3) a granophyric facies. Based on
recent geochemical investigations, Słaby and Martin (2005,
2008) have defined only two granite facies: (1) an
equigranular purely felsic facies (largely covering the ridge
granite) and (2) a porphyritic facies (mainly correlating
with the central and granophyric facies). The fine to
medium grained, equigranular granite represents the less
abundant facies and occurs mainly in the central and eastern
part of the pluton (Fig. 1). It consists of a small number of
feldspar megacrysts, schlieren, and enclaves. On the other
hand, the porphyritic granite is the most common and
widespread facies (Fig. 1), which was affected by magma
mixing and mingling processes with a mafic magma prior
to emplacement. It contains alkali feldspar megacrysts,
numerous biotite schlieren, and mafic magmatic enclaves.
Detailed petrological and geochemical studies of the
enclaves, alkali feldspars and different rock facies from the
Karkonosze granite indicate the occurrence of mixingmingling processes between granitic and lamprophyric
melts (Słaby and Martin 2008). It is estimated that over
75 km3 of mafic magma were injected into the granitic
magma chamber over the whole crystallization history.
Moreover, various lithologies occurring within the granite
provide a record of magma evolution (fractional crystallization) in both granitic and lamprophyric reservoirs
(Słaby and Martin 2008). Syn-kinematic lamprophyre
dykes have been found in the eastern part of the pluton.
They are enriched in water (Kozłowski and Słaby 2004)
and some alkali and LIL elements (Słaby and Martin 2005).
The origin of the lamprophyres has been related to the
melting of an enriched mantle source (Awdankiewicz et al.
2005).
Assimilation and diffusion during xenolith-magma interaction
Field description
The investigated area, the Rudolfov quarry near Liberec
(Czech Republic), is located in the western part of the
Liberec dome within the Karkonosze pluton (Fig. 1). The
porphyritic granite is the dominating facies, which is there
characterized by pink alkali feldspars (up to 4 cm) and
white plagioclase megacrysts (up to 1.5 cm) surrounded by
a medium-grained matrix. The alkali feldspar megacrysts
are commonly surrounded by a white, 3 mm to 4 mm wide,
plagioclase rim giving rise to a rapakivi texture. Plagioclases only locally form megacrysts. Inclusions within the
megacrysts are rare and mainly occur close to their rims.
The medium to coarse-grained matrix mainly consists of
biotite, plagioclase, and quartz that are locally accompanied
by alkali feldspar, hornblende, and accessory phases such
as: apatite, zircon, titanite, magnetite, and ilmenite. Some of
the globular quartz crystals are rimmed by mafic minerals
forming an ocellar texture. Biotite and hornblende occasionally develop mafic clots.
Mafic magmatic enclaves are widespread in the quarry.
They vary in size up to 40 cm, however, the enclaves with
dimension up to 10 cm are the most common (Figs. 2 and
3a). The enclaves are fine-grained, usually grading into a
darker and finer grained mineral assemblage towards their
rims (Fig. 3b and c). They are composed of hornblende,
biotite, plagioclase, and discrete grains of quartz and alkali
feldspar. Accessory phases include zircon, titanite, apatite,
and Fe-Ti oxides. The contact with the host granite is
generally sharp with lobate surfaces (Fig. 3b).
The shape of the enclaves is commonly elongated with
an average aspect ratio of ~1.6. The smaller enclaves show
a diversity from rounded to markedly stretched, whereas the
205
large ones are, in general, more spherical (Fig. 2). There is
no preferred orientation of the long axis.
The larger enclaves appear to be more hybridized
(Fig. 3c) and often contain smaller enclaves of different
types or xenocrysts. The xenocrysts occur within the
enclave but are also located at the boundary with the host
granite (Fig. 3c and d). As in the host granite, the alkali
feldspar xenocrysts are mantled with a thin plagioclase rim
(rapakivi texture) (Fig. 3d) and the quartz megacrysts are
armoured by mafic minerals (ocellar texture) (Fig. 3a).
Methods
Chemical analyses of minerals (Tables 1, 2, 3, 4, and 5)
were performed on Cameca SX-100 electron microprobes
at the University of Warsaw and at the University of Oslo,
both equipped with five wavelength dispersive spectrometers (WDS). For mineral analyses, these instruments were
typically operated with a 15 kV acceleration voltage, a
15 nA or 20 nA beam current and a slightly de-focused
beam of 5 µm diameter for most minerals. Both natural and
synthetic mineral standards were used as primary standards
to calibrate the instrument and as secondary in-run standards to monitor precision and accuracy during analyses.
Major and trace element compositions (Table 7) were
determined at the Open University by XRF (ARL 8420+
dual goniometer wavelength dispersive XRF spectrometer)
using glass discs (for major elements) and pressed powder
pellets (for trace elements). Loss on ignition (LOI) was
established by weight difference before and after ignition at
1,000°C. Accuracy is within 0.05 wt% for most major
elements. The exceptions are abundances of SiO2 and
Al2O3 for which accuracy is 0.3 wt% and 0.2 wt%,
respectively. For most of the trace elements, the detection
limit is 5 ppm or lower, except Ba for which the limit is
12 ppm. The precision has been monitored using two rock
standards for major elements (WS-E and OUG-94) and four
rock standards for trace elements (BHVO-1, QLO-1, DNC1, and W2).
Mineral chemistry
Feldspars
Fig. 2 The relationship between the size of the enclaves and their
aspect ratios; the aspect ratio is the measure of the ratio between the
longest and shortest axes. The size is expressed by equivalent radius
(geometric mean: square root of their product)
The granite is rich in plagioclase, which occurs as
phenocrysts or forms small grains in the matrix. Plagioclase
commonly shows variable morphologies and compositional
zoning. The variations in shape and composition are best
displayed with BSE images, where the complex internal
structures and homogeneous rims can be distinguished
(Fig. 4). The rounded or patchy cores contain numerous
206
M. Adamuszek et al.
Fig. 3 Representative enclaves
from the Rudolfov quarry. a
Small dark enclave on the
boundary of a larger and more
diffused one. Quartz xenocrysts
occur in the enclave, on the
boundary with the host granite
and in the granite itself. Quartz
in the enclave and also at the
boundary between the enclave
and granite host is armoured by
mafic minerals; b Elongated
mafic magmatic enclave with
characteristic dark chilled margins; c Large elongated enclave
with a chilled margin. The enclave encloses smaller and
darker mafic blobs, alkali feldspar megacrysts with plagioclase
rims (rapakivi texture) and plagioclase megacrysts; d Alkali
feldspar megacrysts mantled
with a white, thin rim of plagioclase. The feldspar grains
occur in the enclave, in the
granite, and at the boundary
between the two. The plagioclase rim occurs only at the side,
which is in contact with the
enclave
inclusions that form irregular spots or are arranged along a
line. The inclusions mainly consist of sericite, biotite or Fe-Ti
oxides, representing a typical alteration assemblage. The core
compositions of the investigated feldspars vary from 22 mol%
to 53 mol% An (Table 1), whereas the outer zones are
generally more sodic (2 mol% and 21 mol% An with a mean
around 16–20 mol%) and devoid of any inclusions (Fig. 5).
Only a few small grains have Ab contents >90 mol%.
Plagioclase is a common phase in the enclaves, generally
showing magmatic growth zoning. The profiles across the
minerals illustrate considerable enrichment in Ca in the core
and Na in the rim (Fig. 6). Plagioclase cores, characterized
by numerous inclusions of sericite, biotite, and Fe-Ti
oxides, clearly differ from inclusion-free rims (Fig. 6).
The inclusions mainly consist of biotite, apatite, Fe-Ti
oxides, and zircon, again indicating alteration of the
primary magmatic plagioclase. The compositional range
of plagioclase spans between 37 mol% and 58 mol% An in
the cores and between 10 mol% and 26 mol% An in the
rims (Table 1; Fig. 5). The most frequently occurring rim
compositions are between 18 mol% and 22 mol% An.
Alkali feldspar is common in the granite and occurs
locally in the enclaves. It shows a distinct bimodal size
distribution represented by megacrysts with a plagioclase
rim and smaller crystals in the matrix. The composition of
small grains varies from Or87Ab12An1 to Or97Ab3An0 for
both textural types (Table 2), whereas the composition of
the megacrysts is beyond the scope of the investigation.
Amphibole
Amphibole is an abundant phase in the enclaves but it
locally also occurs in the granite. According to the
classification of Leake et al. (1997), the amphiboles from
the enclaves and the host granite are both Ca-amphiboles
and they both show rather homogeneous intermediate
compositions between magnesiohornblende and ferrohornblende (Table 3; Fig. 7).
The amphiboles often occur in aggregates that are
commonly accompanied by biotite and contain inclusions
of Fe-Ti oxides (Fig. 8a and 8b). These mafic clots are
especially common in the margins of enclaves and in the
host granite adjacent to the contact with the enclaves.
Moreover, all these mafic minerals form the reaction rims
around the larger quartz crystals (Fig. 8b and c).
Biotite
Biotite is the dominant Fe-Mg silicate in the enclaves and
the main mafic constituent in the granite. It commonly
appears in aggregates with hornblende but also forms
chains around the feldspar megacrysts. Biotite usually
Assimilation and diffusion during xenolith-magma interaction
207
Table 1 Representative analyses of plagioclase
Measurement
Granite/Enclave
Core/Rim
#6
Granite
Rim
#7
Granite
Rim
oxides [wt%]
62.86
64.08
SiO2
Al2O3
22.47
22.75
FeO
0.37
0.20
CaO
4.67
3.94
Na2O
9.44
9.26
K2O
0.25
0.22
BaO
0.00
0.00
Σ
100.06
100.45
cations [normalized to 8 O]
Si
2.793
2.819
Al
1.176
1.179
Fe
0.014
0.007
Ca
0.222
0.186
Na
0.813
0.790
K
0.014
0.012
Ba
0.000
0.000
Σ
5.032
4.993
An
Ab
Or
21.19
77.48
1.33
18.80
79.95
1.25
#15
Enclave
Rim
#20
Enclave
Rim
#24
Granite/Enclave
Rim
#29
Granite/Enclave
Rim
#192
Granite
Rim
#193
Granite
Core
#217
Encalve
Rim
#218
Enclave
Core
62.32
22.94
0.23
5.67
8.73
0.18
0.00
100.07
63.34
22.89
0.24
4.54
9.43
0.20
0.00
100.64
63.09
22.55
0.41
4.79
9.25
0.20
0.00
100.29
63.30
22.56
0.34
4.70
9.31
0.23
0.00
100.44
64.36
22.91
0.22
3.83
9.02
0.23
0.02
100.59
63.14
23.68
0.11
4.83
8.61
0.25
0.09
100.71
63.63
23.44
0.39
4.60
8.56
0.18
0.00
100.80
54.50
29.40
0.12
11.45
4.76
0.07
0.03
100.33
2.769
1.201
0.010
0.270
0.752
0.010
0.000
5.012
26.16
72.88
0.96
2.792
1.189
0.009
0.215
0.806
0.011
0.000
5.022
20.80
78.13
1.07
2.795
1.177
0.015
0.227
0.795
0.011
0.000
5.020
22.01
76.92
1.07
contains inclusions of zircon and Fe-Ti oxides. Occasionally, sieve-textured biotite megacrysts occur (Fig. 8d).
The biotite compositions generally show relatively
small variability within the investigated enclaves and
their host. They are characterized by moderate Si contents
(5.65±0.07 p.f.u.) and low AlVI (0.02-0.21 p.f.u.) (Table 4;
Fig. 9). The Fetot/(Fetot +Mg) and Mg/(Fetot +Mg) ratios
are constant within individual grains and vary between
0.58–0.64 and 0.36–0.42, respectively. Biotite is rich in
AlIV and poor in Ti, which ranges from 2.28 p.f.u. to
2.42 p.f.u. and from 0.33 p.f.u. to 0.54 p.f.u., respectively.
A slight change in Ti is negatively correlated with AlIV
content (Fig. 9).
Quartz
Quartz is usually an interstitial phase or it forms a
myrmekitic texture with plagioclase. Ocellar mafic-mantled
quartz is widespread in the enclaves (Fig. 3a and 8a).
Accessory phases
Titanite, apatite and Fe-Ti oxides are the most common
accessories in both, granite and enclaves (Table 5). Titanite
2.798
1.175
0.012
0.223
0.798
0.013
0.000
5.019
21.55
77.22
1.23
2.823
1.184
0.008
0.180
0.767
0.013
0.001
4.976
18.74
79.94
1.32
2.776
1.227
0.004
0.227
0.734
0.014
0.001
4.983
23.31
75.24
1.45
2.791
1.212
0.014
0.216
0.728
0.010
0.002
4.973
22.68
76.30
1.02
2.449
1.557
0.004
0.551
0.415
0.004
0.000
4.980
56.81
42.76
0.43
often occurs as inclusions or as isolated crystals. Small
apatite crystals show a prismatic habit in the granite,
whereas in the enclaves they occur as needles enclosed in
larger minerals. Fe-Ti oxides mainly form inclusions in
biotite or amphibole and are rarely individual crystals.
Re-equilibration conditions between enclave and host
granite
The formation of amphibole and Ab-rich plagioclase
represents the latest recorded stage of granite-enclave
interaction. In order to calculate the corresponding pressure
and temperature conditions, the amphibole and plagioclase
rim compositions of both, the granite and the enclaves were
used. The data were acquired using mineral grains that are
in textural equilibrium with each other, as indicated by their
grain boundary relations.
Based on various calibrations (Hammarstrom and Zen
1986; Hollister et al. 1987; Johnson and Rutherford 1989;
Anderson and Smith 1995), our pressure estimates range
from 1.1 kbar and 1.5 kbar for the granite and from 0.8 kbar to
1.2 kbar for the enclaves (Table 6). The pressure calibrations
show the maximum standard deviation of ±0.25 kbar
208
M. Adamuszek et al.
Table 2 Representative analysis of alkali feldspar
Measurement
Granite/Enclave
Core/Rim
#37
Enclave
Core
oxides [wt%]
65.02
SiO2
Al2O3
18.56
FeO
0.07
CaO
0.04
Na2O
0.31
K2O
16.31
BaO
0.00
Σ
100.31
cations [normalized to 8 O]
Si
2.995
Al
1.008
Fe
0.003
Ca
0.002
Na
0.028
K
0.958
Ba
0.000
Σ
4.994
An
Ab
Or
0.20
2.80
97.00
#67
Granite
Core
#68
Granite
Rim
#208
Granite
Core
#209
Granite
Rim
#210
Granite
Core
#235
Enclave
Rim
#236
Enclave
Core
65.23
18.62
0.00
0.00
0.29
16.31
0.00
100.45
65.20
18.40
0.05
0.06
0.62
15.96
0.00
100.29
65.41
18.56
0.00
0.00
0.66
16.03
0.00
100.66
64.16
18.37
0.23
0.00
0.76
16.11
0.00
99.63
64.76
19.17
0.04
0.11
1.30
14.52
0.00
99.90
65.31
18.88
0.03
0.02
0.57
15.63
0.00
100.44
65.32
18.72
0.09
0.00
0.58
15.75
0.00
100.46
2.998
1.009
0.000
0.000
0.026
0.956
0.000
4.989
0.00
2.63
97.37
3.001
0.998
0.002
0.003
0.055
0.937
0.000
4.996
0.29
5.54
94.17
(Table 6). The temperatures estimated following Spear
(1980) yielded values between 490±20°C and 530±20°C
for both, the granite and the enclaves. The thermobarometer
of Plyusnina (1982) gives similar temperatures ranging from
500°C to 550°C and pressures below 2 kbar for the granite
and the enclaves (Fig. 10). All thermobarometers are based on
amphibole-plagioclase equilibria. These estimates are significantly lower than the wet solidus temperatures of granitic
melt, which is 680°C for 2 kbar (e.g. Brown et al. 1992) and
consequently also much lower for the mafic melt (Table 7).
Enclave and granite geochemistry
A comprehensive study of the interaction between mafic
and felsic magmas for the whole Karkonosze granite has
been presented by Słaby and Martin (2008). They suggest
that the equigranular granite and the lamprophyric rocks
represent the end-members in the mixing process, which
formed all the different magmatic rock types observed
within the entire granite body (Fig. 11). Injection of the
mafic magma occurred throughout the whole crystallization
period of the granitic magma, during which both magma
sources show evidence for a chemical evolution by
2.999
1.003
0.000
0.000
0.059
0.938
0.000
4.999
0.00
5.89
94.11
2.984
1.007
0.009
0.000
0.069
0.956
0.000
5.025
0.00
6.69
93.31
2.976
1.038
0.002
0.006
0.116
0.851
0.000
4.989
0.56
11.91
87.53
2.993
1.020
0.001
0.001
0.051
0.914
0.000
4.980
0.10
5.25
94.65
2.996
1.012
0.004
0.000
0.052
0.922
0.000
4.986
0.00
5.30
94.70
fractional crystallization over time. Early injection of the
lamprophyric magma resulted in complete mixing and the
formation of porphyritic granite, hybrid quartz-diorite, and
granodiorite, whereas later injection triggered mingling and
appearance of enclaves and composite dykes. The mafic
end-member for the later interactions has not been
identified, however the hybrid rocks point towards a rock
composition that is genetically related to the lamprophyre.
By applying the chemical evolution diagram of Słaby
and Martin (2008) to the data of the enclaves from the
Rudolfov quarry it is evident that all samples align on a
mixing trend between lamprophyre and granite close to the
hybrid quartz-diorite and granodiorite field (Fig. 11). Such
a relation indicates that the hybrid quartz-diorite, granodiorite and thus also the enclaves from the Rudolfov quarry
most likely resulted from the mixing between compositionally similar felsic and mafic end-members as in early stage
of granite crystallization. For this reason, the enclaves from
Rudolfov quarry are exceptional for the Karkonosze pluton,
as they allow the detailed investigation of magma minglingmixing processes with both end-members involved in these
processes identified.
For further discussion about the granite-lamprophyre
interaction, we chose one granite sample from the Rudolfov
Assimilation and diffusion during xenolith-magma interaction
209
Table 3 Representative analyses of amphibole
Measurement
Granite/Enclave
Core/Rim
#8
Granite
Rim
#12
Granite
Rim
oxides [wt%]
46.65
46.22
SiO2
TiO2
1.02
1.08
Al2O3
6.02
6.20
Cr2O3
0.03
0.04
FeO
21.35
21.39
MnO
0.71
0.68
MgO
8.99
8.89
CaO
11.08
11.35
Na2O
1.45
1.36
K2O
0.66
0.72
Σ
97.96
97.93
cations [normalized to 23 O and 13 CNK*]
Si
7.020
6.979
Aliv
0.980
1.021
Σ T-site
8.000
8.000
#13
Granite
Rim
#18
Granite/Enclave
Rim
#22
Enclave
Core
#28
Granite/Enclave
Rim
#231
Enclave
Rim
#232
Enclave
Core
46.56
0.94
6.05
0.02
21.27
0.65
8.71
11.45
1.30
0.72
97.67
47.57
1.05
5.73
0.04
19.36
0.50
9.94
11.72
1.19
0.72
97.82
46.45
0.95
5.69
0.01
20.06
0.48
9.44
11.86
1.09
0.71
96.74
47.04
0.95
5.21
0.05
19.54
0.50
9.81
11.71
1.04
0.61
96.46
46.93
0.84
6.02
0.01
20.80
0.46
9.18
11.56
1.04
0.68
97.52
47.12
0.83
6.00
0.05
20.82
0.61
9.40
11.49
1.03
0.69
98.04
7.060
0.940
8.000
7.143
0.857
8.000
7.093
0.907
8.000
7.167
0.833
8.000
7.083
0.917
8.000
7.058
0.942
8.000
Alvi
Ti
Cr
Feiii
Feii
Mn
Mg
0.087
0.115
0.003
0.537
2.150
0.091
2.017
0.082
0.123
0.005
0.481
2.221
0.086
2.002
0.141
0.107
0.003
0.339
2.358
0.083
1.969
0.157
0.118
0.005
0.203
2.229
0.063
2.225
0.117
0.109
0.001
0.229
2.333
0.062
2.149
0.103
0.108
0.006
0.257
2.233
0.064
2.229
0.153
0.095
0.001
0.401
2.225
0.059
2.066
0.118
0.093
0.005
0.515
2.093
0.078
2.098
Σ C-site
5.000
5.000
5.000
5.000
5.000
5.000
5.000
5.000
Ca
Na
Σ B-site
1.786
0.214
2.000
1.836
0.164
2.000
1.860
0.140
2.000
1.886
0.114
2.000
1.940
0.060
2.000
1.912
0.088
2.000
1.869
0.131
2.000
1.844
0.156
2.000
Na
K
Σ A-site
0.210
0.126
0.336
0.234
0.138
0.372
0.243
0.140
0.383
0.233
0.138
0.371
0.263
0.138
0.401
0.220
0.119
0.339
0.172
0.131
0.303
0.142
0.132
0.274
15.336
15.372
15.383
15.371
15.401
15.339
15.303
15.274
Σ
*Leake et al. (1997)
quarry as a representative example and two lamprophyre
compositions from the literature (Awdankiewicz 2007;
Słaby and Martin 2008). These selected mafic samples
represent the lamprophyres that have silica contents lower
than those of the Rudolfov quarry enclaves, as only these
rocks are suitable mafic end-members for the mixing and
mingling processes (Fig. 11).
Variation diagrams for selected major and trace elements
versus SiO2 are presented in Figs. 12 and 13. Amongst all
analysed elements only TiO2, MgO, Al2O3, Th, V, and Zn
display good linear correlations relative to SiO2. The other
elements show scattered data (CaO, U, and Pb) or an extreme
deviation from the linear trends (K2O, Na2O, Sr, Rb, and Ba).
Since the lamprophyres’ data have been acquired from a
different part of the pluton, the chemical change across the
zone of granite-lamprophyre interaction has been determined
through hypothetical compositional profiles (Fig. 14). For this
purpose, we selected four reference samples: the granite, two
enclaves—MA21C and MA6C, and an averaged lamprophyre. The enclaves MA21R and MA6C were chosen as
210
M. Adamuszek et al.
Table 4 Representative analyses of biotite
Measurement
Granite/Enclave
Core/Rim
#190
Granite/Enclave
Rim
oxides [wt%]
35.50
SiO2
TiO2
3.97
Al2O3
13.19
Cr2O3
0.00
FeO
24.00
MnO
0.35
MgO
8.18
CaO
0.03
Na2O
0.05
K2O
9.42
H2O
3.79
Σ
98.49
cations [normalized to 24 O]
Si
5.620
Ti
0.473
Al
2.463
Cr
0.000
Fe
Mn
Mg
Ca
Na
K
H2O
Σ
#191
Granite/Enclave
Core
#196
Enclave
Rim
#211
Granite
Rim
#212
Granite
Core
#213
Granite
Rim
#214
Granite
Core
#225
Enclave
Rim
#226
Enclave
Core
#228
Enclave
Core
36.73
3.47
13.21
0.03
24.05
0.29
8.74
0.00
0.04
9.49
3.86
99.91
36.43
2.78
13.82
0.02
24.65
0.29
8.66
0.00
0.01
9.50
3.85
100.01
36.17
3.96
13.29
0.00
24.46
0.35
8.44
0.05
0.02
9.49
3.85
100.08
36.10
4.02
13.13
0.04
23.90
0.31
8.56
0.00
0.09
9.46
3.83
99.44
37.32
4.08
13.37
0.00
22.71
0.25
9.28
0.02
0.05
9.40
3.91
100.39
36.12
3.78
13.28
0.00
23.40
0.24
8.98
0.03
0.04
9.39
3.83
99. 09
36.88
3.81
13.34
0.03
23.86
0.39
8.67
0.00
0.04
9.49
3.88
100.39
36.18
4.11
13.32
0.00
23.73
0.28
8.60
0.00
0.09
9.46
3.85
99.62
36.70
3.22
13.51
0.00
23.72
0.29
8.92
0.00
0.04
9.80
3.87
100.07
5.708
0.405
2.421
0.004
5.671
0.325
2.536
0.002
5.633
0.464
2.441
0.000
5.647
0.473
2.421
0.005
5.721
0.470
2.417
0.000
5.650
0.444
2.449
0.000
5.698
0.442
2.430
0.004
5.641
0.482
2.447
0.000
5.694
0.375
2.471
0.000
3.178
0.047
1.930
0.006
0.016
1.902
3.127
0.038
2.024
0.000
0.012
1.882
3.209
0.038
0.010
0.000
0.002
1.886
3.186
0.046
1.958
0.008
0.005
1.885
3.127
0.041
1.996
0.000
0.026
1.888
2.912
0.032
2.121
0.003
0.014
1.838
3.062
0.032
2.093
0.005
0.013
1.873
3.082
0.051
1.995
0.000
0.010
1.870
3.093
0.037
1.998
0.000
0.028
1.881
3.078
0.039
2.062
0.000
0.013
1.939
4.001
19.636
4.000
19.621
4.000
19.679
4.000
19.626
4.000
19.624
4.000
19.528
4.000
19.621
4.000
19.582
4.000
19.607
4.000
19.671
Table 5 Representative analyses of titanite, apatite and ilmenite
titanite
Core/Rim
Sample
Granite/Enclave
apatite
Core
MA12
Enclave
Core/Rim
Sample
Granite/Enclave
oxides [wt%]
SiO2
TiO2
Al2O3
29.75
33.89
1.73
oxides [wt%]
P2O5
SiO2
CaO
CaO
FeO
H2O
V2O2
Nb2O5
Cr2O3
26.17
1.92
4.84
0.21
1.41
0.02
Na2O
MnO
FeO
Na2O
H2O
F
Σ
99.94
Σ
ilmenite
Core
MA12
Granite
41.90
0.53
54.29
0.03
0.10
0.07
0.03
0.07
3.61
100.63
Core/Rim
Sample
Granite/Enclave
Rim
MA12
Enclave
oxides [wt%]
SiO2
TiO2
V2O3
0.06
51.39
0.29
FeO
MgO
CaO
MnO
FeO
Cr2O3
1.75
0.03
0.11
4.57
41.53
0.01
Σ
99.74
Assimilation and diffusion during xenolith-magma interaction
211
Fig. 4 Backscattered images of:
a granite and b enclave. The
plagioclases in both the granite
and the enclave have similar rim
compositions as indicated by
comparable grey tones. The
mineral cores display different
compositions, which are related
to an earlier magmatic stage.
The plagioclase cores show typical hydrothermal alteration
features
they have the highest and lowest SiO2 concentrations
among the analysed enclaves and are interpreted to reflect
the most and the least affected and chemically modified
enclaves. As stated before, the data for the granite are
taken from the Rudolfov quarry, while those for the
lamprophyres are taken from Awdankiewicz (2007) and
Słaby and Martin (2008).
The chemical profiles for SiO2, Al2O3, TiO2, MgO, Zr,
and Th show linear trends, with the concentrations of these
elements in the enclaves lying between the values of the
average lamprophyre and the host granite. Other elements
(e.g. Na2O, K2O, and Rb) display distinct concave-upward
or concave-downward patterns. CaO is the only element
that shows a discrepancy between the average and chemical
approach and represents either a concave-upward or a linear
trend on the diagram.
Fig. 5 Various compositions of
feldspars from the host granite
and the enclaves are shown, core
and rim compositions are shown
separately
Analysis of mechanical and chemical mixing
Mixing between two magmas can be driven by both
mechanical and chemical processes. In this section we
evaluate the relative contribution of these two processes on
the element distribution between two interacting magmas
and the formation of a hybrid mixture.
Mechanical mixing
Mechanical mixing is responsible for the formation of
heterogeneous mixtures with discrete portions of the endmember magmas. The mixture can have various intermediate compositions, which are related to the proportions of the
mixing magmas. The magma series formed during the
hybridization are always aligned between their end-
212
M. Adamuszek et al.
Fig. 6 Representative chemical
profile across a plagioclase in an
enclave. The core has an andesine to labradorite (37–58 mol%
An) composition, whereas the
rim has an oligoclase composition (18–23 mol% An). Note the
altered core of the plagioclase
members. Such a relation shows a geochemical massbalance law (Rollinson 1993)
cmix ¼ wA cA þ ð1 wA ÞcB ;
where cmix is the concentration of the element in the
mixture, cA and cB are the concentrations of the element in
the end-member magmas A and B, respectively, and wA is a
weight fraction of the magma A in the mixture.
(e.g. Costa et al. 2003) show that diffusion in natural
systems can also proceed against concentration gradients
leading to ‘uphill’ diffusion. The ‘uphill’ sharpening of a
concentration gradient can be described by using a wellestablished generalization of the Fick’s law (e.g. Nauman
and He 2001), which defines that diffusion is driven by the
gradient of the chemical potential, μ:
J ¼ Dc
Chemical mixing
@m
:
@x
The chemical potential is often expressed as
Chemical mixing leads to the formation of a chemically and
physically homogeneous mixture and is governed by
diffusion. Diffusion in ideal mixtures obeys Fick’s law
and the flux of species is proportional to the concentration
gradient:
J ¼ D
@c
;
@x
where J is the flux of a single component with a
concentration c, D is the diffusion coefficient, and x is the
spatial coordinate. The evolution of the concentration
profiles according to Fick’s law results in equalization of
any compositional differences across the system. However,
experimental results (e.g. Watson 1976, 1982; Johnston and
Wyllie 1988; Bindeman and Davis 1999), petrological
examples (Schreiber et al. 1999), and numerical studies
m ¼ m0 ðP; T Þ þ RT ln½gðxÞ cðxÞ;
where γ and μ0 are the activity coefficient and the chemical
potential in the reference state, respectively. Here, we study
a two-phase system (phases α and β) where the chemical
potential is now given by
mðxÞ ¼ ma0 ðP; T Þ þ RT ln fg a cðxÞg in phase a
mðxÞ ¼ mb0 ðP; T Þ þ RT ln fg b cðxÞg in phase b:
When the pressures and temperatures are constant, the
chemical diffusion in the bulk of each phase is driven by a
Fickian-type of flux. However, a jump in the activity
coefficient γ or in the reference chemical potential μ0
results in a non-Fickian type of diffusion across the phase
boundaries. The thermodynamic equilibrium between two
phases, α and β, is reached when the chemical potential of
a component in phase α is equal to the chemical potential
of the same component in phase β, namely
ma0 ðP; T Þ þ RT ln½g a ca ðxÞ ¼ mb0 ðP; T Þ þ RT ln g b cb ðxÞ :
From the above local thermodynamic equilibrium relation, the equilibrium partitioning of the component between
phases is determined by the partition coefficient
ma ðP;T Þ
0
Fig. 7 Calcic amphiboles classification diagram (Leake et al. 1997).
All amphiboles have similar compositions ranging between magnesioand ferrohornblende
KDba
cb
g a e RT
¼ a¼
:
b
m ðP;T Þ
c
0
g b e RT
Assimilation and diffusion during xenolith-magma interaction
213
Fig. 8 Microstructures of
enclaves: a Biotite and amphibole aggregate; b Quartz megacryst rimmed by amphibole
grains; c An ocellar
texture—quartz surrounded by a
fine-grained amphibole and
biotite rim; d Sieve-textured
biotite megacryst
The evolution of the concentration c(t,x) is described by
a diffusional transport with the flux derived above.
i m0 ðx;P;T Þ
@cðt; xÞ
@
@ h
RT
¼
D cðt; xÞ R T ln gðxÞ e
cðt; xÞ
:
@t
@x
@x
Fig. 9 Compositions of biotite
in the granite and enclaves. Four
plots show various relations between elements that form the
mineral formulae: Ti, AlIV, AlVI
and also iron (Fe/(Fe + Mg)) or
magnesium (Mg/(Fe + Mg))
numbers. All biotites from
granite and enclaves have similar composition
The equation can be simplified for constant temperature
and pressure:
h
i
@cðt;xÞ
@
@
e
; where
@t ¼ R T @x D cðt; xÞ @x ln K D cðt; xÞ
e D ¼ KD for pahse a:
K
1 for phase b
214
M. Adamuszek et al.
Table 6 Pressure estimations according to various calibrations
Authors
P (kbar)
Standard deviation
P (kbar)
Granite
Standard deviation
Enclave
Hammarstrom and Zen (1986)
1.53
0.09
1.17
0.21
Hollister et al. (1987)
Johnson and Rutherford (1989)
Anderson and Smith (1995) for T=500°C
1.35
1.10
1.42
0.10
0.08
0.11
0.95
0.79
1.00
0.24
0.18
0.25
For illustration purposes, we show the modelling of
diffusion between the host magma and the enclaves, which
has been developed in one-dimension. The modelling aims
at a better understanding of the possible influence of
chemical diffusion on element distribution within the
investigated reacting systems. The evolution of hypothetical concentration profiles across the enclave-granite
contact has been studied using different activity models.
We simulate only half of the profile assuming the symmetry
of the model. In order to compare the results, the same
initial distribution of element concentrations was used in
each case:
cð0; xÞ ¼ 2 for
cð0; xÞ ¼ 1 for
0 x < 15 L
1
5 L x L:
and
where L corresponds to the size of the model. We also
assumed that the size of the enclave is much smaller than the
granite, so that the effect of the diffusion is most pronounced
in the enclave but only locally in the granite. Thus, the
boundary conditions are zero flux at the symmetry axis and a
constant undisturbed value at the other end:
J ðt; 0Þ ¼ 0
cðt; LÞ ¼ 1:
Fig. 10 a Temperature estimates for the enclaves and their
host granite based on Spear
(1980); b Pressure and temperature estimates based on the
calibration of Plyusnina (1982)
Diffusion is simulated for constant pressure and temperature conditions and for varying KD, which is a single
parameter quantifying the relative difference of γ(x) and
m0 ðxÞ variation between two phases. Diffusion likely
occurred in an overall very similar medium (fluid or melt)
and consequently, the diffusion coefficient D was assumed
to be equal in the granite and the enclave and set at D=1.
Results of the modelling are presented in Fig. 15, where
the chemical evolution through time with initial (t0),
transition (t1) and steady state (t2) profiles are shown. The
first diffusion model (Fig. 15a) illustrates the evolution of
the concentration profiles when the distribution coefficient
is KD =1. In this case, diffusion proceeds according to the
Fick’s law smoothing the concentration gradient (t1) and
flattening the profile (t2). In the second model (Fig. 15b),
we applied a distribution coefficient KD =3. In the first step
the concentration profile bends sharply at the boundary
between the two phases turning it upward from the enclave
side (increasing the concentration) and downward from the
granite side (decreasing the concentration). This initializes
an uphill diffusion and increases the concentration ratio
between two phases. As the gradient of concentration does
not change orientation, we refer to this type of diffusion as
normal uphill diffusion. In the transient stage (t1) the
diffusion tends to equalize the concentration gradient within
1.74
0.86
0.34
2.40
3.92
5.96
4.05
0.20
10.24
15.99
0.79
0.32
2.52
3.99
5.74
3.91
0.20
10.08
15.84
1.71
56.03
134
37.8
162
16.7
360
24
22
8
9
48
35
7
8
7
47
Sr
Y
Zr
Nb
Ba
Pb
Th
U
Sc
V
Cr
Co
Ni
Cu
Zn
141
24
21
28
43
162
21
b.d
11
18
298
24.2
225
53.5
138
305
189
28
23
29
44
181
24
4
11
24
192
33.5
221
129.3
124
387
139
28
22
27
52
169
22
3
11
16
223
20.4
218
43.3
164
266
133
26
19
25
40
166
19
3
10
14
243
19.9
209
43.1
162
276
99.90
0.91
0.26
4.00
3.86
4.35
3.18
0.15
7.95
15.38
1.27
58.58
106
11
19
20
32
129
16
5
12
24
380
18.3
202
34.2
139
305
n.d. = not determined, b.d. = below detection limit
232
Rb
ppm
1.12
0.36
3.31
4.06
4.82
4.20
0.22
11.58
16.34
55.66
108
11
21
22
48
128
16
7
13
21
356
19.1
188
34.2
139
305
100.92
1.04
0.27
3.95
3.80
4.48
3.33
0.15
8.15
15.61
1.34
58.80
1.52
0.33
2.63
4.45
5.00
3.99
0.21
11.53
16.07
1.79
53.82
2.26
0.34
1.74
4.61
4.36
3.83
0.21
11.60
16.13
1.81
53.56
0.78 0.00
0.31 0.30
2.96 2.36
3.69 3.90
5.55 5.66
3.77 3.87
0.21 0.23
10.34 10.91
15.78 15.98
1.62 1.70
55.67 55.43
0.77
0.30
2.55
4.08
5.50
3.41
0.16
8.76
15.67
1.52
58.29
132
27
21
28
51
152
20
b.d
11
14
281
19.2
195
37.0
170
261
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
141
31
18
25
46
157
18
4
9
23
307
23.9
205
63.4
161
264
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
111
23
19
25
37
154
20
b.d
11
15
309
19.3
217
36.5
170
254
110
19
18
24
44
152
17
b.d
12
17
293
20.1
218
37.2
169
251
98.98
0.82
0.30
2.41
3.95
5.29
3.36
0.16
8.86
15.50
1.54
56.80
151
17
22
24
45
164
22
5
11
16
252
27.0
228
78.8
133
349
100.37
1.03
0.33
2.88
4.59
4.28
3.47
0.19
9.86
16.13
1.74
55.87
0.96 1.00
0.28 0.39
2.97 2.71
4.10 4.23
3.98 5.52
3.37 4.04
0.13 0.21
9.58 11.40
15.40 16.50
1.50 1.96
58.50 54.27
0.70
0.27
2.54
4.01
4.64
2.99
0.15
8.18
15.47
1.34
60.47
157
26
21
22
40
146
23
5
10
19
257
26.8
190
66.9
130
292
136
18
24
24
31
165
19
5
11
15
443
25.6
219
33.9
132
315
159
22
21
28
46
185
21
b.d
9
18
226
28.8
233
68.1
137
290
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
101.62 100.77 102.24 100.75
0.67
0.31
2.64
4.04
4.92
3.61
0.19
10.48
15.92
1.57
57.29
113
21
15
21
52
133
17
b.d
13
16
235
23.6
216
52.1
143
259
101.08
0.53
0.29
2.38
4.36
4.61
3.09
0.15
8.85
15.59
1.43
59.78
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
101.01
0.34
0.26
2.33
4.23
3.93
2.72
0.13
7.83
15.44
1.23
62.57
MA9A MA9B MA11 MA12 MA13C MA13R MA15R MA16 MA19 MA20 MA21C MA21R MA24
100.11 101.34 100.44 100.68 100.33 101.02
0.95
0.29
2.61
4.03
5.75
3.56
0.15
9.12
16.00
1.57
56.10
MA6C MA6-R MA7-C MA7-R MA8
100.77 99.32 101.28 101.34 101.13
0.74 0.61
LOI
Total
0.14 0.30
P2O5
CaO
3.48 4.00
2.40 4.80
MgO
4.11 2.74
1.19 3.69
MnO
Na2O
0.06 0.18
Fe2O3
K2O
3.45 10.28
Al2O3
1.89
0.53 1.68
13.68 15.65
TiO2
53.38
70.99 55.39
MA3 MA5
SiO2
wt. %
GRA
NITE
Table 7 Whole-rock major and trace element compositions of the Karkonosze granite and its enclaves obtained by X-ray fluorescence analysis
Assimilation and diffusion during xenolith-magma interaction
215
216
M. Adamuszek et al.
Fig. 11 Composition diagrams (Słaby and Martin 2008) showing the
evolution of Karkonosze granite magma and suggested mixingmingling trends with lamprophyric magma prior to and after
emplacement (solid lines indicate mixing whereas dashed line indicate
evolution of the granite and lamprophyre composition). The host
granite sampled in the Rudolfov quarry (diamond) overlaps with the
porphyritic granite composition. The enclaves’ compositions indicate
a precursor similar to a lamprophyre, which experienced various
degrees of mixing and mingling with the host granite. Two lamprophyre compositions (hexagon) are shown to illustrate possible
enclave precursor compositions (Awdankiewicz 2007; Słaby and
Martin 2008)
the two phases without any changes of the concentration
ratio at the boundary. The final profile (t2) shows the step
function with KD =3. A KD ¼ 1=3 is used in the third model
(Fig. 15c). Here, the flux of the diffusing components
causes a rapid shift of the concentration at the enclavegranite boundary. This significant bend in the concentration
profiles occurs opposite to the initial concentration gradient,
thus it introduces a reverse uphill diffusion. During the
Fig. 12 Major element variations of the enclaves versus
SiO2 (wt.%). The host granite
and the compositional field
of the potential enclave
precursor—lamprophyre (see
Fig. 11) are shown to illustrate
possible mixing trends. All
values are in wt%. See text for
discussion
Assimilation and diffusion during xenolith-magma interaction
217
Fig. 13 Trace element compositions (ppm) of the enclaves
versus SiO2 (wt.%). The host
granite and the compositional
field of the potential enclave
precursor lamprophyre (see
Fig. 11) are shown to illustrate
possible mixing trends. See text
for discussion
transient stage (t1) the concentration profile is smoothing
within the phases and maintaining a constant partition
coefficient. The final profile (t2) demonstrates the step
function with KD ¼ 1=3.
Diffusion is the process that can smooth the concentration gradient between phases only when it acts according to
Fick’s law. Otherwise, it is a process that can generate or
maintain the compositional difference. In both cases
diffusion is a process responsible for the transient systematic deviations from the linear mixing trends.
Discussion
Petrological and geochemical data indicate that the
enclaves found in the Rudolfov quarry were formed
during hybridization processes between the granite host
and injected lamprophyric magma. The interaction between the enclaves and the host granite was complex and
involved thermal and chemical diffusion as well as
mechanical mixing.
Mechanical interaction between the enclave and the host
granite
The temperature of the lamprophyric and the granitic
magma at the time of interaction has been estimated at
around 890°C and 770°C, respectively (Słaby et al. 2008).
Quenched textures in the mafic blobs are commonly
observed in the Rudolfov quarry. The thermal contrast
between both melts is commonly accepted as the reason for
the development of the fine-grained texture on the
218
M. Adamuszek et al.
Fig. 14 Chemical variation of
selected elements plotted along
a hypothetical profile across the
host granite, enclaves (MA21C,
MA6C), and lamprophyre. The
two enclaves are chosen
according to their silica contents, relatively high (left side in
the enclave field) and low (right
side in the enclave field).
Lamprophyre data are taken
from literature (Awdankiewicz
2007; Słaby and Martin 2008).
See text for discussion
enclaves’ margins due to an undercooling of the mafic
magma and rapid crystallization of the minerals in the
enclaves (e.g. Vernon 1984; Altherr et al. 1999; Tepper and
Kuehner 2004; Kumar and Rino 2006). However, the
lobate shape of the enclaves indicates that both magmas
coexisted at least in partially molten states (Vernon et al.
1988). The lamprophyric magma batch in the Karkonosze
massif contained high water contents (Kozłowski and Słaby
Fig. 15 Diffusion profiles showing the time evolution (initial,
transient and steady state) of the element concentration (X) in the
granite and the enclave in one-dimension for different diffusion
models: a Fickian diffusion, b normal uphill diffusion, and c reverse
uphill diffusion. Fickian diffusion leads to a decrease in the
concentration in the enclave and the smoothing of the concentration
gradient with time. Normal uphill diffusion increases the difference in
concentration in the two phases. Reverse uphill diffusion causes a
significant inflection in the profile at the contact between the granite
and the enclave opposite to the initial concentration gradient. With
time, a reverse gradient in concentration is established
Assimilation and diffusion during xenolith-magma interaction
2004), hence a lowered crystallization temperature is
expected (Sparks and Marshall 1986), leading to a
prolonged time span available for mechanical interaction.
Xenocryst capturing
Magmatic enclaves in Rudolfov quarry contain alkali
feldspar and quartz megacrysts with rapakivi and ocellar
textures indicating a rapid change of crystallization
conditions. The feldspar megacrysts in the enclaves
and in the host granite share the same crystallization
path as evident from mineral, chemical, and cathodoluminescence data (Słaby and Götze 2004). These observations point to a mechanical introduction of the feldspar
and quartz crystals into the mafic melt from the surrounding granitic crystal mush. Partially incorporated xenocrysts have been observed, with reaction rims developing
exclusively on the enclave side. Hence, it proves that
crystal capturing was active during the formation of the
enclaves (Fig. 3). However, some xenocrysts are also
enclosed by the quenched margins of enclaves (Fig. 3c),
suggesting that they must have been incorporated into the
mafic melt before the enclave was created (Bacon and
Metz 1984; Vernon 1984; Bateman 1995; Paterson et al.
2004).
Shape evolution of enclaves
The elongation of enclaves occurring in the Rudolfov
quarry is size-related. The small enclaves can reach an
aspect ratio of three, whereas the larger ones are equidimensional. The enclave aspect ratio-size scaling has been
widely discussed in relation to magmatic flow, surface
tension and thermal re-equilibration (Paterson and Vernon
1995; Blake and Fink 2000; Paterson et al. 2004). Large
enclaves do not quench as rapid as smaller ones and are
expected to experience more deformation during magmatic
flow. If present, the surface tension can relax more the
shapes of small objects. Therefore, these processes cannot
explain the observed aspect ratio-size distribution.
We propose a density-driven rising or sinking model of
enclaves as the potential mechanism for their deformation.
The shape evolution of isolated ascending deformable
droplets was studied numerically by Koh and Leal (1989)
and experimentally by Whitehead and Luther (1975) and
Kojima et al. (1984). They concluded that ascending
droplets develop an overall equidimensional shape after
rising a distance of few radii even for a negligible surface
tension. Large objects rise or sink faster and preserve high
temperature and low viscosity longer. Therefore, we expect
the shape relaxation as a result of the buoyant flow to be
more efficient for large enclaves. In the numerical modelling of Koh and Leal (1989), vertically elongated droplets
219
were developing spherical heads and long thin tails behind
them. Tail and head pairs have not been observed in the
quarry. However, chemical diffusion may, in fact, have
obliterated the tail and head relation completely. We
tentatively suggest that some schlieren commonly observed
in the Karkonosze granite may represent the remnants of
such tails. Furthermore, it was found that during the
numerical simulations horizontally elongated inclusions
were folded, leading to the formation of embayments. Later
due to internal circulation these embayments were closed
forming an overall spherical object.
Mechanical mixing
The large enclaves in the Rudolfov quarry are more
hybridized than the small ones, but mixing caused by the
static chemical diffusion becomes inefficient for large
objects (Grasset and Albarede 1994). This phenomenon
can be assigned to the embayment process (as described
before), where a significant portion of both fine and coarsegrained granitic material can be incorporated into the
enclaves. Thus, both the crystal capture and the internal
circulation can significantly enhance the rate of the
chemical transfer and large melt blobs are able to hybridize
stronger than smaller blobs due to higher rising velocities
and stirring rates. Variation diagrams (Figs. 12 and 13) and
chemical profiles (Fig. 14) for most major elements (e.g.
Al2O3, TiO2, MgO, TiO2) and some trace elements (e.g. Th,
Zr) are in a good agreement with mechanical mixing
between the granite and a lamprophyre.
Chemical mixing
It is evident that a good correlation among the data and
with the granite-lamprophyre mixing trend is restricted to
the fluid-immobile elements (Figs. 12, 13, and 14). More
scattered data is associated with those elements that have a
low valence and are commonly very mobile, e.g., large ion
lithophile elements LILE (K, Na, Rb, Ba, Sr, Pb) and Ca
(Henderson et al. 1985). Such a different behaviour of
elements can be assigned to the conditions, when the
immobile elements reflect solely mechanical mixing and
the concentrations of the mobile element have been
modified during the melt or the later fluid dominated stage.
The effect of diffusion on the element distribution within
the enclave-granite system is clearly noticeable in the
profiles and diagrams that involve alkali elements
(Fig. 12, 13, and 14). The fast diffusion of Sr and Ba
resulted in a complete shift of their concentration in the
enclaves towards the granitic values. Complete homogenization of concentration gradients corresponds to the Fickian
diffusion model (Fig. 15a). This could have occurred still
during the magmatic, melt-dominated stage or in presence
220
of late magmatic fluids. Experimental results revealed highdiffusivity of these elements (Mungall et al. 1999) and twoliquid partition coefficient close to 1 (Watson 1976). Also,
the partitioning between fluid and minerals (biotite for Ba,
and amphibole and plagioclase for Sr) could bring the
concentrations of the enclaves towards those of the granite.
In contrast, Na2O, K2O, and Rb display concave-upward or
concave-downward patterns due to diffusion processes,
which involved uphill transport either into the enclave or
into the granite. The concentrations of these elements in the
enclaves are significantly enriched for Na2O and Rb, and
depleted for K2O, relative to the concentrations in the
granite and lamprophyre. The numerical simulation of
normal or reverse uphill diffusion shows how such element
distributions may develop (Fig. 15b and c). Since geological observations may suggest and experimental results
show that diffusion of alkalis is extremely fast between
felsic and mafic melts, e.g. minutes to hours (e.g. Watson
1982; Johnston and Wyllie 1988; Wiebe et al. 1997;
Bindeman and Davis 1999), we can expect that rapid
diffusion of these elements may have occurred at the
magmatic stage.
Petrographic observations indicate that the changes in
the composition of the enclaves also took place during latestage magmatic-hydrothermal processes. The increase of
Na2O in the enclaves may be correlated with feldspar
alteration, i.e. the extensive formation of albitic plagioclase,
and thus Na-uptake, may be driven by the chemical
potential. Consequently, only small domains of the rock
(Fig. 4) accommodate most of the mass exchange.
Moreover, the enrichment of Rb could indicate the
accumulation of this element in the newly formed biotite.
On the other hand, the strong depletion of K2O in the
enclaves might be caused by the breakdown of magmatic
ternary feldspar that contains more K than the newly
formed metamorphic albitic plagioclase. It might also be a
result of the partial breakdown of K-feldspar in the
formerly lamprophyre melt, which might have no longer
been stable in the altered metamorphic enclave. This
implies that biotite formation was not sufficient to take up
all the released K.
The effect of fluids on the element concentrations is
clearly noticeable by comparing U and Th (Fig. 13). During
magmatic processes, both elements tend to follow similar
trends. However, they behave differently during fluid
interaction (John et al. 2004). Uranium has a high tendency
to form a very fluid-mobile uranyl complex (UO2)2+, in
which U has the valence of 6+, whereas ThO2 has a very
low solubility in aqueous fluids. Hence, U, in contrast to
Th, is extremely fluid mobile under oxidizing conditions,
which may have caused the scattering and low correlation
of the U data in comparison with Th.
M. Adamuszek et al.
There are no significant chemical differences among the
newly formed alteration minerals in the host granite and the
enclaves (e.g. biotite, amphibole, feldspar rims). This might
be explained by mineral growth under the same physical
and chemical conditions (Lesher 1990; Baker 1991).
However, our sample set of the granite host and its enclaves
reveals similar temperatures of approximately 500°C and
pressures of about 1 kbar for the final equilibration, which
is well below the wet solidus for both systems at the given
pressure conditions. Volume diffusion in, for instance,
plagioclase is much too slow at such temperatures (e.g.
Wayte et al. 1989) indicating that fluid-facilitated mineral
reactions along grain boundaries took place (Vernon and
Paterson 2008). This implies that the latest phase of the
granite-enclave interaction was controlled by a fluid rather
than a melt or solid-state diffusion. Thus, the same
composition of the minerals more likely resulted from the
equilibration of the reactive parts of the granite and the
enclaves through element transport in hydrothermal fluids
and associated mineral growth under the same subsolidus
conditions (Baker 1990; Lesher 1990; Barbarin 2005).
Conclusions
The formation of magmatic enclaves in the Rudolfov
quarry is a consequence of incomplete mixing between an
injected lamprophyric melt and its host granite. The
injection of mafic magma into the partially crystallized
granite host resulted in various interactions, which, due to
compositional and thermal differences, were obstructed and
never accomplished. Buoyancy contrasts may have caused
the blobs of mafic magma to flow into the granitic mush
and this flow had a larger effect on the bigger enclaves
since they stayed open longer for melt-melt interaction than
the smaller ones. As a consequence, the bigger enclaves
became more spherical (as the time for shape relaxation was
longer) and more hybridized (as the longer flow allowed the
enclaves to interact longer mechanically and chemically with
the host). The chemical effect of the mechanical mixing
between granite and lamprophyre is evident only for
immobile or high-valence elements, e.g. Ti, Zr, and Th. The
more mobile and low-valence elements such as Na, Rb, and
Ba show significant deviations from the granite-lamprophyre
mixing trend. This deviation is attributed to diffusion
processes at the partially molten stage and/or fluid control at
subsolidus conditions. The role of fluid-facilitated diffusion
for the compositions of the enclaves is particularly evident for
Na2O and K2O, which display uphill diffusion features either
into or out of the enclave, and for some trace elements such
as Sr and Ba, which reach values in the enclaves similar to
the host granite.
Assimilation and diffusion during xenolith-magma interaction
Acknowledgements We would like to thank Ewa Słaby (Warsaw
University) for showing us the Rudolfov quarry and Stanisław Mazur
and Jacek Szczepański (University of Wrocław) for their collaboration
at the early stages of the project. We wish to thank John Watson (The
Open University) for carrying out the XRF analysis and Piotr
Dzierżanowski (Warsaw University), Lidia Jeżak (Warsaw University), and Muriel Erambert (University of Oslo) for help and assistance
during the microprobe analytical sessions. We are also grateful to
Christoph Beier and an anonymous referee for constructive suggestions and critical comments on the manuscript. This work was partly
funded through a Centre of Excellence grant to Physics of Geological
Processes (PGP).
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