6. Results
6.1. Petrographic analysis of magmatic rocks
Magmatic rocks of evaporite melange in Dinarides have been divided in four main types
according to ratio of the primary amphibole/pyroxene amount in the sample. Different ratios
of these minerals vary likely from magma fractionation. Pyroxene crystallized prior to
amphibole and thus the information of ratio between two minerals shows evolution of magma
in the selected area.
The texture of the samples is mostly hypiomorphic-granular. Samples are characterized by
pseudomorphs of plagioclase, pyroxene and brown amphibole partially or completely
substituting by hornblende or actinolite, while still maintaining the habit of primary minerals.
This is shown on Figure 6.1.d. According to different grain sizes samples are in Table 1
divided on fine-grained with sizes of approximate range from 0.1x0.05 mm to 0.3x0.1 mm
(Figure 6.1.a), medium-grained with size range from 0.45x0.2 to 0.7x0.3 (Figure 6.1.b) and
coarse grained textures with size range from 0.9x0.5 to 1.2x0.6 mm (Figure 6.1.c). Based on
primary mineral assemblage these rocks are classified as amphibole bearing gabbro/diorite
according to IUGS classification.
Figure 6.1. Display of different grain sizes of the magmatic rocks within the evaporite
melange in Dinarides- ( a- sample CRO 47 D, Sinjsko polje, b- sample CRO 45, Vrličko polje
c- sample CRO 40) and pseudomorph of plagioclase- (d- sample CRO 46, Vrličko polje).
(N+) Aberrations: Plag- Plagioclase, Ser-Sericite
Important mineralogical data on primary and secondary minerals of all magmatic rock
samples are shown in Table 6.1. Along with their primary and secondary mineral association,
the structure/texture and the type of alteration is used for classification. Different colours of
rows show different ratios of primary amphibole and pyroxene, presented in the legend of the
Table 6.1. Minerals will be described according to belonging mineral association. There are
two different mineral associations detected during petrographic analysis: High-temperature
primary mineral association and secondary mineral association, which is composed of
medium grade alterations and low grade alterations.
Primary magmatic association is composed predominantly of plagioclase, Cpx, brown
amphibole, and minor amount of opaque minerals, zircon and titanite. It is overprinted by
medium-grade secondary hornblende after Cpx or brown amphibole. Low-grade secondary
mineral assemblage is predominantly composed of sericite, and chlorite, smaller amount of
other amphiboles (actinolite, tremolite) and minor amount of prehnite, clinozoisite, secondary
quartz, cristobalite, pumpellyite
On figure 6.2 are shown most represented minerals of the high-temperature primary
association: plagioclase, Cpx and brown amphibolesuppressed by secondary hornblende
belonging to medium-grade assemblage.
Figure 6.2. (CRO 42B, Kosovo polje) Display of primary minerals plagioclase, clinopyroxene
and brown amphibole surrounded by hornblende. (N+)
Aberrations:, Cpx- clinopyroxen, bAmp- brown amphibole, Hbl- hornblende,
6.1.1. Primary magmatic association
Plagioclase minerals are most common minerals occupying 40-45 vol % to maximum 60 vol
% of the sample. Although there are different sizes, plagioclase grains have mostly the same
characteristics. Twining lamellas are mostly thick and there are no more than three of them
throughout a single grain. Almost all plagioclase grains are weathered and altered to sericite,
chlorite and kaolinite. Figure 6.1 d, shows pseudomorph of sericite after plagioclase.
Pyroxene minerals are rare and mostly altered. They represent 5-10 vol % of the rock sample.
Generally they are attacked by hornblende, chlorite or some other secondary mineral. The
amount of pyroxene in the samples is variable. Usually Cpx predominates over Opx except
within sample CRO 42, where is more Opx than Cpx. Since pyroxene grains suffer a lot of
weathering and alteration, it is often possible to detect fragments of pyroxene grains which
are characterized with extremely high interference colour. Figures 6.3 a, b, c, show Cpx
supressed by hornblende.
Figure 6.3. a), c) (CRO 49 A (N), CRO 48, Sinjsko polje) Two types of hornblende around
Cpx, b) (CRO 42 B, Kosovo polje) growth of hornblende after Cpx ,d) (CRO 42b, Kosovo
polje) Brown amphiboles. (N+)
Brown amphibole, (shown on figure 6.3. d), is a titanium bearing amphibole, characterized
with brownish colour and pleochroism. Approximately it represents 10 vol % of the rock. It
has prismatic habit and very good cleavage on {110}. In some cases is possible to see double
cleavage (Fig 6.3. d). It appears to be similar to hornblende and in most samples is partly
replaced by hornblende along rims (Figure 6.3. a). Inclusions of titanite are often found
randomly distributed throughout mineral.
Opaque minerals, zircon and titanite represent important accessory minerals. Opaque minerals,
represent 2-5 % of the rock samples, (Figure 6.4. c) are found in most of the samples and
most likely contain iron oxides (hematite or magnetite) judging by their occasional slightly
red colour. Hematite is shown on figure 10 b. Titanite (Figure 6.5. a) and zircon (Figure 6.4.d)
are very scarce (< 2 vol % of the rock), and usually found as inclusions within amphibole or
pyroxene. Figure 6.4 presents all accesory minerals mostly as inclusions within larger grains
such as hornblende, pyroxene or plagioclase of the high-temperature association.
Figure 6.4. a) (CRO 45, Kosovo polje), titanite in Cpx, b) (CRO 47 C, Sinjsko polje (N)), Feoxide and opaque minerals c) (CRO 45, Vrličko polje), opaque minerals in plagioclase and
hornblende, d) (CRO 42, Kosovo polje), zircon in brown amphibole. (N+)
Abberations: , Ttn- titanite, Hmt- Hematite, Opq- Opaque mineral, Zrc- Zircon,
6.1.2. Secondary mineral associations
6.1.2.1 Medium-grade alterations
Secondary hornblende is formed after pyroxenes and brown amphibole. They represent
approximately 30 vol % of the rock. At some places, hornblende completely substitutes
pyroxene or brown amphibole but mostly partial alteration can be observed. This is presented
on figure 9 a), b), c) where cores contain remnants of the pyroxene or brown amphibole,
whereas external sectors are completely supressed by hornblende. This core to rim change in
amphibole crystal chemistry is presented much better on SEM figures (Figure 6.5 a-d).
Opaque minerals are also present as inclusion within hornblende most probably inherited
from pyroxene.
Figure 6.5. (a-d) SEM figures of samples CRO 42 B (Kosovo polje) and CRO 49 A (Sinjsko
polje). Aberrations: Chl-Chlorite, Pre-prehnite
6.1.2.1. Low grade alterations
Sericite represent approximately 30% of rock minerals. It is made due to hydrothermal
alteration of plagioclases (40 to 60 vol %) and thus is abundant in the rock samples. It
typically occurs as fine-grained aggregates with high interference colours within plagioclase
grains. In most cases is visible core to rim suppression of plagioclase by sericite.
Chlorite occupy 15 % of rock. Chlorite mostly occurs within fine-grained diorite samples as
fine-grained aggregate growing over amphiboles and pyroxenes. Generally, chlorite is formed
due to low-temperature hydrothermal alteration of iron-bearing minerals (e.g. Howie et al,
1992).
Amphiboles are in some places suppressed by actinolite/tremolite, which represent 5-10 vol
% of minerals in rock. Figure 6.6 b shows overgrown of tremolite over hornblende. The
reaction provides good geothermometer parameters that will be described further in the text.
Furthermore, another type of alteration and weathering of hornblende is prehnitization.
Prehnite, shown on figure 6.6a, occupy 2-5vol % of the rock minerals. Mostly, is found after
hornblende in the fibrous shape of radial grains. Each grain has different extinction angle
which creates impression of undulose extinction. Prehnite mostly grows enveloping
hornblendas rims. Clinozoisite represents 2-5 vol % of the rock. It usually occurs between the
plagioclase grains, possibly as alteration product of plagioclase. (Fig 6.6 b). Secondary quartz
and cristobalite, represent 2-5 vol % of the rock. Cristobalite is likely created as a result of
surplus of SiO2 after previous hydrothermal alterations or as a result of stress deformations
(e.g. Howie et al, 1992). Figure 6.6 d presents cristobalite with recognizable circular habit.
Quartz is fresh and lacks undulose extinction. Figure 6.6 c shows pumpellyite with radial
growth of mineral aggregates. Pumpellyite occupy < 2 vol % of the rock.
Figure 6.6. a) (CRO 42, Kosovo polje) Prehnite between plagioclase grains, b) (CRO 42 B,
Kosovo polje) tremolite on hornblende, c) (CRO 47 D, Sinjsko polje), pumpellyite, d) (CRO
46, Vrličko polje) cristobalite. (N+) Abberations: Tmt/Akt- Tremolite/actinolite, PmpPumpellyite, Cr-Cristobalite.
Table 6.1. Petrography of the analyzed magmatic rocks of evaporite melange within
Dinarides..
Magmatic rocks of evaporite melange within Dinarides
Maximum Minimum
Rock Magmatic
Primary
Secondary
Sample
Texture
grain size grain size Alteration
name
fabric
minerals
minerals
(mm)
(mm)
CRO 47 gabbro/
fine
hypidiomorph- Plag, bAmp,
sercitization,
Chl,
0.3x0.1
0.1x 0.05
B
diorite
grained
granular
Opq
chloritization
CRO 47 gabbro/
C
diorite
fine
grained
hypidiomorph- Plag, bAmp,
granular
Cpx
Ser, Q, Chl
0.3x0.1
0.15x0.02
chloritization
CRO 47 gabbro/di
D
orite
fine
grained
hypidiomorphgranular
Ser, Chl, Q,
Cr, Pre,
0.3x0.05
0.15x0.02
sericitization,
chloritization
CRO 47 gabbro/di
E
orite
fine
grained
hypidiomorph- Plag, bAmp,
granular
Cpx
Ser, Chl, Q,
0.3x 0.1
0.1x0.03
sericitization,
chloritization
CRO 46
gabbro/di
orite
coarse
grained
hypidiomorphgranular
Hbl, Tml, Pre,
Ser, Q, Cz,
Cr
1.2x0.5
0.7x0.3
sericitization,
prehnitization
CRO 45
gabbro/di
orite
coarse
grained
hypidiomorphgranular
Hbl, Ser, Q,
Ep, Cz, Cr
0.6x0.3
0.45x0.2
sericitization
CRO 42 gabbro/di
B
orite
coarse
grained
Hbl, Act, Ser,
Cz, Tml, Pmp
0.75x0.4
0.5x0.3
sericitization
CRO 42
gabbro/di
orite
fine
grained
Hbl, Ser, Pre,
Chl,
0.8x0.35
0.5x0.2
sericitization,
chloritization,
prehnitization
CRO 48
gabbro/di
orite
coarse
grained
Plag, Cpx,
bAmp, Ttn,
Opq
Plag, Opx,
hypidiomorphCpx, Ttn,
granular
bAmp
Opx, Plag,
hypidiomorphbAmp,Opq,
granular
Zrc
hypidiomorph- Cpx, Opx,
granular
Plag, bAmp
Hbl, Ser, Cz,
1.2x0.5
0.8x0.35
sericitization
CRO 49
gabbro/di
orite
coarse
grained
hypidiomorphgranular
Cpx, Opx,
Pl, bAmp
Hbl, Ser,
Act,Tml, Cz,
1x0.55
0.85x0.45
sericitization
CRO 40
gabbro/di
orite
coarse
grained
hypidiomorphgranular
Plag, Cpx
Chl, Cz
1.2x0.5
0.85x0.4
chloritization
Plag, Opq,
bAmp
Plag,
Cpx,bAmp
Act - actinolite;bAmp-brown Amphibole; Chl - chlorite; Cpx- clinopyroxen, Cz - clinozoicite; Cr-cristobalite; Hbl hornblende; Opx- orthopyroxen, Opq - opaque; Plag – plagiocase; Pmp- pumpeylite Pre - prehnite; Q - quartz; Ser Sericite; Tml - tremolite;Ttn - titanite; Zrc- zircon
primary amphibole/pyroxen: 90/10
primary amphibole/ pyroxen: 70/30
primary amphibole/ pyroxen: 50/50
primary amphibole/ pyroxen: 10/90
6.2. Petrography of evaporite rocks
Microanalysis of thin sections of the evaporite rocks from Knin area has shown that they are
consist of three main components: anhydrite, gypsum and carbonate mineral (mostly
dolomite). According to (Kulušić and Borojević Šoštarić, 2013), evaporites show basically
two types of macro-faciese:
1)
laminated
evaporite-carbonate
facies,
composed
of
millimeter
to
centimeter
gypsum/anhydrite laminas intercalated with dolomite/dolomicrite ± organic matter ± siltite,
the dolostone member usually beeing several times thinner (Figs 5a,b); and
2) evaporite-carbonate breccia facies, composed of millimeter to decameter-sized fragments
of laminated evaporites, carbonate and siltite cemented by massive gypsum and occasionally
sulfur, most likely originated during the emplacement. Evaporite-carbonate breccia containing
below 5 vol% of carbonate prevails at the uppermost levels of the evaporite succession,
succeeding by the laminated facies downdeep.
Here is given similar, but a bit more detailed classification of evaporite facies. The sections
can be divided into several distinct groups on the basis of the mineralogical composition and
fabric type:
1) Massive anhydrite
2) Nematoblastic anhydrite
3) Porphyroblastic gypsum
4) Granoblastic gypsum
5) Breccia facies
Basic features like grain sizes, aspect ratio and other characteristics are presented in the Table
6.2.
6.2.1. Massive anhydrite
Massive anhydrite is characterized with equidimensional subrounded grains of anhydrite that
have average size of 0.6x0.5 mm (Figure 6.7. a). Most of the grains have serrated boundaries
where some of the grains start to recrystallize (Figure 6.7. a). Around the larger grains there
are few smaller recrystallized grains sizes of 0.04x0.03 mm, probably of the same
composition as the larger grains. This appearance is especially represented in sample CRO 44
D. Also it can be seen that these sections were exposed to stresses, which is reflected as
undulose extinction and twinning in some grains.
6.2.2. Nematoblastic anhydrite
Nematoblastic anhydrite is presented as aggregates of elongated subangular grains with
subparallel orientation resulting in a shape-prefferred orientation and foliation, respectively
figure 6.7. b. The orientation of the grains is perpendicular to the main stress axis. In samples
CRO 44 F and CRO 44 G, boundaries between the grains are seriate with occasional
recrystallization appearance, section CRO 40A has straight boundaries and CRO 40 B has
interlobate. Samples CRO 40 B and CRO 44 F contain carbonatic laminae, which are locally
thicker or thinner. In this type, recrystallisation on the boundaries of larger grains can be
observed. In the Table 6.2. are presented sizes of recrystallized grains. All the recrystallized
grains are of anhydrite composition.
6.2.3.Porphyroblastic gypsum
Porphyroblastic gypsum has characteristic porhyroblastic structure with larger grains
(porphyroblasts) surrounded with smaller grains (matrix). In this case both the larger and
smaller grains are gypsum although belonging to different generations (Figure 6.7. c).
Examining the sample can lead to conclusion that there are more than two generations of
gypsum crystallization, most probably two.
6.2.4. Granoblastic gypsum
Granoblastic gypsum is characterized with equidimensional grains of similar size. This type is
also characterized by more generations of gypsum. As it can be seen on the figure 6.7. d,
various gypsum generations are pointed with numbers (1 for the older generation and 2 for the
younger generation). Boundaries between grains are mostly straight and recrystallization is
often seen around larger grains.
6.2.5 Breccia facies
The breccia facies can be divided into two types. One type of breccia is breccia consists of
gypsum with carbonate minerals (Figure 6.7. e) and the other is gypsum with organic matter
(Figure 6.7. f). ´The first type is characterized by growth of gypsum grains in veins between
carbonate clasts. The second type has much larger and different shape of grains, which are
developed between organic materials.
a
Figure 6.7. Evaporite facies: a) Massive anhydrite b) Nematoblastic anhydrite c)
Porphyroblastic gypsum d) Granoblastic gypsum e) Breccia facies with carbonate f) Breccia
facies with organic material.
Table 6.2.
Sample
Mineralogy
Fabric type
Average
grain size
(mm)
Aspect ratio
Grain boundaries
Recrystalized
grain size
Remarks
CRO 40 a
anhydrite
nematoblastic
0.6x0.15
4:1
straight
/
shape preferred orientation of the grains not developed as good as in other
samples
nematoblastic
0.9x0.15
7:1
interlobate
0.05x0.04
shape preferred orientation
nematoblastic
0.65x0.15
5:1
seriate
0.1x0.08
Shape preffered orientation, some grains show undulose extinction, twinning
nematoblastic
0.6x0.08
6.5:1
seriate
0.02x0.03
massive
0.25x0.2
6:1, 1.5:1
straight
/
Shape preffered orientation of the grains, occasional twinning
different shape of grains: some grains are enlogated ( 6:1 aspect ratio), some
grains are rounded (aspect ratio 1.5:1)
massive
granoblastic
0.6x0.5
0.4x0.3
1.5:1
1:1
seriate
straight
0.04x0.03
/
deformed grains, undulose extinction
porphyroblastic
0.4x0.3
1.5:1
straight
0.01x0.01
3 generatons of gypsum
0.3x0.2
1:1
straight
/
no orientation of the grains
0.25x0.2
1:1
straight
/
no orientation of the grains
0.4x0.35
1:1
straight
/
different grains sizes and shapes, hard to define average size and aspect ratio,
probably more generations of gypsum
0.15x0.08
2:1
straight
/
Variation of grain sizes and shapes, hard to determine average shape an aspect
ratio
anhydrite, org matter,
carbonate
anhydrite, carbonatic
CRO 44 f
lamineas, quartz
CRO 44 g
anhydrite
CRO 40 b
86-AK 3
CRO 44 d
CRO 41 b
CRO 44 a
anhydrite, carbonate,
org matter
anhydrite, carbonate
gypsum
gypsum, org. matter,
anhydrite inclusions,
carbonate
carbonate, gypsum in
veins
carbonate, gypsum in
veins, org. matter
carbonate breccia,
vein type gypsum
carbonate breccia,
CRO 44 c
vein type gypsum
breccia facies with
org. matter, gypsum in
86 AK- 1c
org. matter and
veins,
gypsum
breccia facies with
gypsum, org matter,
CRO 41
org. matter and
qurtz, carbonate
gypsum ??
CRO 44 b
3 generations of gypsum