GeolCarp_Vol48_No1_19

GEOLOGICA CARPATHICA, 48, 1, BRATISLAVA, FEBRUARY 1997

19–26

SERPENTINES IN THE OPHIOLITE COMPLEXES OF THE

VOURINOS AND KAMVOUNIA MTS. (NORTHERN GREECE)

DUŠAN HOVORKA

, SERAFIM SAVVIDIS

, JOZEF STANKOVIČ

EVA ŠAMAJOVÁ

and LÝDIA TURANOVÁ

Department of Mineralogy and Petrology, Faculty of Natural Sciences, Comenius University,

Mlynská dolina, 842 15 Bratislava, Slovak Republic

Technical Education Institute, 50100 Kila Kozani, Greece

(Manuscript received June 20, 1996; accepted in revised form December 12, 1996)

Abstract:

The Vourinos as well as the Kamvounia ophiolite complexes yielded in origin of the serpentine-group min-

erals of different appearance. In this stage of laboratory studies we have concentrated on: a — filling of shear zones
occurring within ”basal serpentinites” of the Vourinos Complex (lizardite + chrysotile + splintery antigorite), b — the
rock-forming mass of the Kamvounia massif (antigorite), c — slip-fiber ”asbestos” within the Kamvounia massif
(chrysotile + fibrous antigorite). While the Vourinos Complex during its geological history never reached greenschist
facies conditions, the Kamvounia massif underwent metamorphic recrystallization under such conditions.

Key words:

Hellenides, Mesozoic, ophiolites, lizardite, chrysotile, antigorite.

Introduction

Eastern Mediterranean Mesozoic ophiolite complexes are
some of the most intensively studied ones. This is a result of
their economic value (chromites) and their complicated, but
from several points of view instructive geological history.
So, especially in recent decades numerous authors studied
the complex under consideration. Available information is
found in papers by Moores (l969), Rassios et al. (l983) and a
review by Savvidis & Hovorka (1997). Although some pub-
lished papers include micrographs of serpentinites, serpenti-
nization as a problem has not been studied yet. So, the aim of
the performed study was to: a) identify serpentine-group
minerals in the Vourinos and the Kamvounia ophiolitic mas-
sifs, and b) on the basis of serpentine minerals present to
compare their geological history.

Within the Vourinos Complex serpentine minerals occur

especially as:
1)

massive to schistose serpentinites forming the lowermost

section of the complex under consideration (= ”basal serpen-
tinites”),
2)

filling of shear zones (mostly together with carbonates),

massive serpentines are present in the upper part of the

metamorphic harzburgite section,
4)

serpentines accompanying chromite accumulations both in

the harzburgite tectonite as well as in the cumulate complex.
There is a different situation in the Kamvounia Metaultrama-
fite Complex.
5)

The rock-mass of the Kamvounia Complex is formed by

antigorite as the leading serpentine-group mineral,
6)

shear zones l–5 centimetres in thickness filled by slip-fi-

ber asbestos of complicated mineralogy. In this communica-
tion we especially present the results of study of the serpen-
tine-group minerals presented above under 2), 5) and 6).

Serpentine-group minerals: general problematics

Serpentine-group minerals should be classified according

to several classification schemes. The most commonly used
division of the serpentine-group minerals (Whittaker & Zuss-
man l956; Zussman & Brindley l957) is based on their struc-
tures. According to the classification scheme of these au-
thors, serpentines are divided into: chrysotile (ortho-, clino-,
and para-), antigorite, lizardite and 6-layer orthoserpentine.
The fibrous antigorite of Whittaker & Zussman (l956) has
been described under the disignation picrolite in the past (Ri-
ordon l955). 6-layers orthoserpentine is also known as un-
stite (Whittaker & Zussman l956). During recent decades
serpentines in the past described as ”bastite” (pseudomorphs
after orthopyroxenes: Drasche l871) have been identified as
lizardite in places with chrysotile admixture. Among the lat-
est classification schemes is that of Wicks & Whittaker
(l975). According to these authors (l.c.) lizardite, chrysotile
and parachrysotile are polymorphic modifications to which
do not belongs antigorite.

It should be added that in the process of serpentinization of

rocks with an excess of Mg-rich olivines over pyroxenes be-
sides serpentines brucite also originates (Hostetler et al.
l966). It is present in the rock-mass, or is selectively concen-
trated on veinlets.

During recent decades a wealth of new experimental re-

sults on serpentinization as well as on serpentine polytypes
have been published (for review see papers by Wicks &
O’Hanley l988 and Banfield et al. l994).

Although the P-T fields of lizardite-chrysotile on one side

and antigorite on the other one (Johannes l975) partly over-
lap their stabilities are generally not identical (Wicks &
Whittaker l977 and others). The origin of lizardite and
chrysotile is generally connected with hydration at low tem-

20 HOVORKA et al.

perature (approx. up to 250

C). Antigorite is stable up to

higher (approx. up to 500

C) temperatures. Taking into ac-

count the description of picrolite (splintery antigorite) given by
Riordon (1955): ”...common variety of fibrous material that oc-
curs along fault planes ... It is made of bundles and sheaves of
coarse fibers that lie roughly parallel to the plane of fissure. It is
generally soft, and white to pale yellowish green in color, and
has splintery fracture. The fibers separate with difficulty and
generally break easily” we identify a part of serpentine studied
with that of splintery antigorite (= picrolite).

The different P-T conditions of the origin of various ser-

pentine minerals are reflected in differences in water content,
specific gravity, chemical composition, remanent magnetiza-
tion and other physical parameters of lizardite/chrysotile ver-
sus antigorite serpentinites.

Mode of occurrence of the studied samples

The identification of serpentine-group minerals is often

complicated by their small size and the simultaneous pres-
ence of several mineral polytypes (Cressey l979; Veblen &
Buseck l979) in the studied sample.

In this stage we have studied serpentines from the follow-

ing modes of occurrences listed in the Introduction:

l) Serpentines forming a substantial part of the basal ser-

pentinites of the Vourinos Ophiolite Complex. This rock
suite crops out especially on the slopes of the Aliakmon Riv-
er as well as on the new (l996) road cut between Chromio
and Museum on the eastern rim of the complex under consid-
eration. Serpentinization within this unit is mostly very in-
tensive, although within massive to schistose serpentinite
”cobbles” (blocks) of less intensively serpentinized peridot-
ite occur. These occurrences exhibit pseudomorphic replace-
ment of primary olivines and ortho- as well as clinopyroxenes
forming lizardite pseudomorphs after orthopyroxenes on one
side and a mixture of lizardite and chrysotile with characteristic
mesh texture on the other. During serpentinization processes
brown (Cr-rich) spinel survived. Magnetite ”powder” distribut-
ed regularly or concentrated on veins and veinlets of younger
generation serpentines is characteristic.

2) Within the basal serpentinites abundant shear zones oc-

cur, which rim blocks of darkgrey, greyish-black to dark-
green serpentinites with lizardites of ”bastite” appearance.
Shear zones are of various (mostly a few centimetres) thick-
ness, and variable color (mostly yellowish-green, apple-
green). In places within mentioned mass, light-colored car-
bonate vein and hair-like veinlets of hap-hazard orientation
are also present.

5) The Kamvounia serpentinite massif, represented by

samples from the open quarry at Zindani, have been studied.
The leading rock-type is massive, darkgrey (with bluish tint)
homogeneous serpentinite. Its leading rock-forming mineral
is antigorite.

6) The last textural type studied is represented by slip-fiber

asbestiform aggregates of light yellowish-green to silver-
white long-columnar and felty character. Being compact it
behaves as hard, but easily desintegrated splintery blades and
long columns. The thickness of the slip fiber serpentine fill-
ing of tectonized zones is variable — it reaches l0 cm in plac-

es. The contacts of the shear zones under consideration are
sharp with no evidence of mineralogical or textural changes in
orientation perpendicular to the contact planes.

Methods applied

The result of study of several dozen thin sections served

as the main discriminant for advanced studies. The present-
ed micrographs represent the most common types of fabrics
of studied serpentines/serpentinites.

X-ray powder diffraction

X-ray powder diffraction (XRD) patterns were obtained

using DRON-3 Bragg-Brentano diffractometer with CuK
radiation wavelength 0.154051 nm, step size 0.1

, time per

step 1 sec. The diffractometer was operated with the com-
mercially distributed software.

The general features of the patterns recall the previous

data published by Whittaker & Zussman (1956): chrysotile
is characterized by reflexes at d = 0.259 nm (4) and d =
0.245 nm (8) together with a discriminant reflex at d =
0.1534 nm (9), lizardite by an intensive reflex d = 0.248 nm
(9) and a less intensive doublet at d = 0.153 nm (6) and d =
0.l504 nm (4), antigorite by a strong reflex at d = 0.253 nm
(9) and two reflexes at d = 0.156 nm (6) and d = 0.1536 nm
(4). If antigorite is less well ordered many weak reflexes are
hardly visible, and the pattern may look very similar to that
of lizardite. The strong line at d = 0.156 nm in antigorite has
no counterpart in the chrysotile or lizardite patterns.

Differential thermal analysis

Differential thermal analysis (DTA) also offer discrimina-

tion between lizardite-chrysotile serpentines on one side and
that of antigorite on the other. In combination with thermal

Fig. 1.

Sampling localities: 1 — Museum, 2 — Zindani, 3 — Riso,

— Tsouka.

SERPENTINES IN THE OPHIOLITE COMPLEXES OF THE VOURINOS AND KAMVOUNIA MTS. 21

gravimetric analysis (TGA), this method has been used in the
past for determination (Faust & Fahey l962; Ivanova et al.
l974) of serpentines in rock-mass or vein filling. Thermic
analyses were operated on the MOM (Budapest) derivato-
graph (system Paulik – Paulik – Erdey). The treatment (of
1200 mg of powdered samples) was performed under air
conditions. Speed of heating: 10

C/min

–1

Generally DTA patterns show shallow endothermic reac-

tions under low temperatures mostly below 150

C. Broad

and shallow endothermic peaks are the consequence of the
gradual release of mechanically adsorbed (surface) water in
studied samples. The loss of the weight from this endother-
mic reaction is in range 0.8–3.0 per cent.

The DTA patterns of serpentine-group minerals, especially

those of lizardite and chryzotile are characterized by large
endothermic peak adequate to the temperature range 600–
820

C. Within this temperature range processes of dehydra-

tion took place caused by the breakdown of serpentine struc-
ture. On the DTA records of serpentine minerals with ideal
structure a third very weak endothermic peak is observable at
temperature 830

Another characteristic exothermic peak corresponds to the

temperature of 820

C and represents the formation of for-

sterite on the expense of lizardite and chrysotile. In the case
of serpentine minerals with imperfect structure only the first
two endotherms are expressed. With the decrease of the order
of the crystal structures the increase of the intensity of this
exothermic peak is visible. Simultaneously the beginning of
the endothermic effect is shifted to higher temperatures.

Other methods

To obtain information on the morphology of some of the

serpentines studied we present selected TEM and scanning
electron microscope micrographs. The index of refraction
have been determined on several samples.

Fig. 2.

X-ray diffraction patterns of: a — predominant chrysotile;

b — chrysotile-lizardite mixture; c — less ordered antigorite.

X-ray powder diffractometre traces (Fig. 2) were used to

compare different proportions of serpentine minerals
present in the samples examined. In sample ”A” (Fig. 2a)
chrysotile is strongly predominant while sample ”B” (Fig.
2b) represents chrysotile-lizardite mixture, which is the
most common situation in the samples of this group. For all
samples of this genetic group presence of white, or whitish
carbonates is characteristic. In one sample (a) except of
chrysotile and antigorite also chlorite has been determined
(Fig. 3).

Serpentine-group minerals studied belonging to this cate-

gory are characterized by weak low-temperature endotherm
with maximum 115

C and intensive endothermic peak at

maximum at 695

C and 712

C. According to the intensity

of the exotherm with its maximum usually at 820

C, which

Fig. 3.

X-ray diffraction pattern of chlorite occurring in sample ”A”.

Results

1 — Serpentines forming the column of ”basal serpen-

tinites” are represented by lizardite and chrysotile mixture
of variable quantitative proportions of these serpentine poly-
types. Beside serpentines also relic ortho- and especially cli-
nopyroxenes are present in variable amounts.

Lizardite pseudomorphs after orthopyroxene crystals and

mesh texture are characteristic for this type of studied sam-
ples. The serpentinites under consideration correspond to the
3rd type described by Wicks & Whittaker (l977) which origi-
nate under falling or constant temperature, the absence of
substantial shearing and no antigorite nucleation.

2 — The filling of shear zones within the basal serpen-

tinite of the Vourinos Complex is of variable thickness, com-
position, fabric and general appearance.

Chrysotile and lizardite are the most abundant polymorphs

of these samples, while antigorite except the sample ”C”
(Fig. 2c) is the least common and simultaneously belongs to
the less ordered one. Carbonates forming net-like veinlets
belong to calcite and dolomite (Pl. I: Figs. a–d).

22 HOVORKA et al.

in some cases gradually pass into a very weak endotherm, it
is possible to conclude, that minerals with various degrees
of structural order are present (Figs. 4a, 4b). The weight loss
observed by thermogravimetry (TG) in the majority of sam-
ples studied is over l3 weight per cent which is the conse-
quence of the calcite and dolomite present (Fig. 4c). The
content of carbonate minerals in this sample ranges up to 55
weight per cent (manometric determination).

Optical studies of powder samples brought evidence that

the studied samples represent inhomogeneous material com-
posed of chrysotile, lizardite and antigorite in variable pro-

portions. Antigorite is present in substantial amounts only
in samples E, G, but its presence is evident for all the sam-
ples studied.

3 — The Kamvounia massif is composed of antigorite

serpentinites. Total serpentinization of the primary mineral
association is characteristic. Lathy antigorite has haphazard
orientation and is pigmented by tiny magnetites (Pl. II:
Fig. a). The presented X-ray diffraction pattern of the rock-
forming antigorite (Fig. 5) is in good agreement with the data
of Whittaker & Zussman (l956). The presented DTA pattern
prove this optical thin sections determination (Fig. 4d). It is

Plate I: Fig. a.

Tectonically crushed and recrystallized lizardite-chrysotile serpentinite from the shear zone (type 2). Serp I = serpentine

of the 1st generation (dark), serp. II = serpentine of the 2nd generation (light). Enlarg. 27

, crossed nicols. Fig. b. Cross fiber chrysotile

from the shear zone within lizardite-chrysotile serpentinite (type 2). Enlarg. 46

, crossed nicols. Fig. c. Net-like veinlets of carbonates

from the shear zone within lizardite-chrysotile serpentinite (type 2). Enlarg. 26

, crossed nicols. Fig. d. Plates of antigorite and fibers of

chrysotile from the shear zone within lizardite-chrysotile serpentinite (electron microscope, suspension). All micrographs are from the shear
zone of the Vourinos Complex.

SERPENTINES IN THE OPHIOLITE COMPLEXES OF THE VOURINOS AND KAMVOUNIA MTS. 23

characterized by absence of the first (low-temperature) ser-
pentine-group endotherm (Ivanova et al. l974). The maxi-
mum of the second intensive endotherm is shifted to the tem-
perature of 760

C and the consequent exothermic peak,

which is characteristic for chrysotile, is missing. At 870

C a

very weak endothermic peak is expressed, which together
with the above mentioned features of DTA curve determine
antigorite. This is also in accordance with published results.

4 — Slip fiber asbestos from the Kamvounia massif. The

thickness of the splintery and fibrous serpentine (Pl. III) fill-
ing of shear zones within the Kamvounia Complex is vari-
able — it reaches l0 centimetres on places. The contacts of
the shear zones under consideration are sharp with no evi-
dence of mineralogical as well as textural changes in orienta-
tion perpendicular to contact planes. Two main substances
make up the shear zones in the antigorite serpentinites of Ka-
mvounia: serpentines of fibrous and splintery character as
well as pale carbonates. Mutual proportions of serpentines
and carbonates varies. Within the fibrous filling of the shear
zones we have picked up two main types of material: a) sil-
ver-white to yellowish-white long-fibrous asbestos of the
textile type quality and several centimetres in length. They
have been determined as chrysotile (Fig. 6b), b) light-green,

splintery, in the case of natural occurrence hard aggregates,
which have X-ray patterns of a mixture of antigorite (”picro-
lite”) and chrysotile (Fig. 6a). On the DTA records (Fig. 4e)
of the set of samples of this group, a low temperature endot-
hermic peak (by l00

C) together with a broad endothermic

peak, or two endotherms with maxima at 690

C and at

740

C are observable. Endothermic reactions are expressed

by the loss of weight in the range 1.5 to 15.5 per cents. Such
high loss of weight is caused by the presence of carbonates.
The exothermic peak with its maximum at 830

C is connect-

ed with a very low (0.4 %) loss of weight.

This DTA pattern is typical for a mixture of fibrous antig-

orite, chrysotile or lizardite. Measured indexes of refraction
(N = l.55 and N = 1.53 or N = 1.457 and N = 1.535) and high
birefringence (0.012) prove the presence of chrysotile in this
mineral mixture forming the slip-fiber asbestos occurring in
shear zones.

Fig. 4a.

Derivatogram of chrysotile-lizardite mixture. Fig. 4b. Deri-

vatogram of chysotile-lizardite mixture with less ordered structure.
Fig. 4c.

Derivatogram of carbonate minerals from shear zone. Fig. 4d.

Derivatogram of rock-forming antigorite. Fig. 4e. Derivatogram of the
mixture of antigorite + lizardite/chrysotile + carbonates.

Fig. 6.

X-ray diffraction patterns of: a — splintery-shape particles

being mixture of antigorite (picrolite) and chrysotile; b — long
fibers with the predominence of chrysotile. Included Figs. 2, 3, 5
and 6 are parts of diffractograms used for distinction of serpentine-
group minerals present.

Fig. 5.

X-ray diffraction pattern of rock-forming antigorite.

Discussion and conclusion

Within the whole Vourinos ophiolite mass lizardite and

chrysotile are the dominant serpentine-group minerals
present. The degree of serpentinization of harzburgite tecto-

24 HOVORKA et al.

nites generally increases in the direction of its basal plane.
Within the column of ”basal serpentinites” there are numer-
ous shear zones of several generation filled by younger gen-
eration serpentines + carbonates.

The dominant phases of shear zones within the basal ser-

pentinites are chrysotile ± lizardite. In several samples antig-
orite — mostly of fibrous character — has been identified to-
gether with the prevailing chrysotile. Therefore an elevated
temperature, in comparison to that responsible for serpentini-
zation of the rock-mass of the basal part of the ophiolite
complex under consideration, is supposed. The fluids needed
for the origin of serpentines of the younger generation (to-
gether with carbonates) used the shear zones and fractures as
communication paths. The heat responsible for the antig-
orite-chrysotile (± lizardite) filling of the shear zones could
be friction heat generated precisely within those zones.

In contrast to Vourinos, the Kamvounia Complex is

formed by antigorite serpentinites. Thus metamorphic re-
crystallization under greenschist facies conditions is re-
sponsible for the origin of antigorite.

The filling of shear zones (chrysotile and fibous antigorite

of slip-fiber character + carbonates) within the Kamvounia
massif indicate the activities of fluids under lower tempera-
ture conditions (indicative is the presence of chrysotile) in
comparison with the processes responsible for rock-forming
antigorite (± chlorite) formation.

Taking into account the lower water contents in antigorite

in comparison with chrysotile, fluids (with CO

content) in-

flux into mechanically weakened zones during mentioned
tectonic events have been responsible for slip-fiber serpen-
tines (chrysotile and antigorite) + carbonates origin.

Plate II: Fig. a.

Thin section of antigorite serpentinite — the Kamvounia massif. Enlarg. 45

, crossed nicols. Fig. b–d. Natural surfaces

of antigorite serpentinite of the Kamvounia massif. Scanning electron microscope.

SERPENTINES IN THE OPHIOLITE COMPLEXES OF THE VOURINOS AND KAMVOUNIA MTS. 25

Plate III: Fig. a.

Mixture of splintery antigorite and fibrous chrysotile from shear zone — Kamvounia massif. Fig. b. Splintery antigorite

from shear zone Kamvounia massif. Fig. c. Natural surface of the mineral aggregate filling shear zone — Kamvounia massif, Micrographs
b and c = scanning electron microscope. Fig. d. Chrysotile fibers from the shear zone — Kamvounia massif. Transmission electron mi-
croscope.

In accordance with results of Prichard’s (l979) studies

(and studies of numerous authors’ cited here) we consider
that serpentinization process which resulted in the origin of
the rock-forming lizardite and chrysotile in both the massifs
studied occurred in an oceanic environment (= ocean floor
serpentinization). On the basis of the different serpentine
minerals present in these massifs we suppose their different
subsequent history. The Kamvounia massif was subsequently
recrystallized under the greenschist facies P-T conditions,
while Vourinos Complex never underwent recrystallization
under such P-T conditions. During the meso- and probably
neoalpine geological events both massifs were involved in
more-or-less identical P-T conditions. They are documented
by the common appearance of chrysotile (+ lizardite) and

antigorite (mostly of ”fibrous antigorite” character) in shear
zones within both massifs under consideration.

From the petrological point of view the formation of

chrysotile at the expense of antigorite should be classified
(from the temperature point of view) as a retrogressive and
simultaneously hydration process.

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