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Introduction
When magma interacts with unconsolidated sediment, brec-
cia is generated by disintegration of magma and mingling
with the host sediment. This breccia facies is called peperite
(White et al. 2000; Skilling et al. 2002). Peperite develops in
a wide variety of successions but it is very commonly associ-
ated with intrusions and lavas in subaqueous (submarine)
sedimentary sequences. Peperite occurs in any tectonic set-
ting where magma or lava and unconsolidated sediment are
able to interact, especially where volcanism is accompanied
by continuous sedimentation in a subsiding basin. A wide
variety of peperite compositional and textural types are
known (Skilling et al. 2002).
The recognition of peperite in a succession provides the evi-
dence for the interaction of magma with unconsolidated, com-
monly wet, sediment and is an effective way of determining
the synchronism of magmatism and sedimentation. Therefore,
it contributes to the relative chronology and is a valuable tool
in reconstructing facies architecture and paleoenvironments.
Moreover, the presence of peperite at the roof of a concordant
igneous body helps distinguish true lavas from intrusions
(Skilling et al. 2002 and references therein).
In this paper, we study the products of magma—sediment
interaction in a Permo-Triassic volcano-sedimentary com-
plex at the eastern part of the Vardar (Axios) Zone, within
the Circum-Rhodope Belt, northern Greece. Although the
rocks are recrystallized under conditions of greenschist fa-
cies, their original fabrics are well preserved and much can
Magma—sediment interaction during the emplacement of
syn-sedimentary silicic and mafic intrusions and lavas into and
onto Triassic strata (Circum-Rhodope Belt, northern Greece)
ARGYRO ASVESTA
1
and SARANTIS DIMITRIADIS
2
1
Department of Geotechnology and Environmental Engineering, Technological Educational Institute (TEI) of Western Macedonia, Kila,
50100 Kozani, Greece; asvesta@teikoz.gr
2
Department of Geology, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece; sarantis@geo.auth.gr
(Manuscript received April 5, 2012; accepted in revised form December 11, 2012)
Abstract: Within the Circum-Rhodope Belt in northern Greece, Middle Triassic neritic carbonate metasediments are
locally intercalated with quartz-feldspar-phyric metarhyolites. In the same belt, Upper Triassic pelagic lime-marl-layered
metasediments are similarly intercalated with low-grade metamorphosed basalt, dolerite and minor andesite and
trachydacite. We interpret these sequences as due to magmatism active during the rifting event that eventually led to the
opening of the Vardar Ocean. Despite the overprint of Late Jurassic deformation and low greenschist metamorphism,
peperitic textures produced by magma—wet sediment interaction are well preserved at the contacts between the silicic
volcanic rocks and the originally wet unconsolidated neritic carbonate sediments, suggesting contemporaneous magmatism
and sedimentation. The mafic and intermediate volcanic rocks lack peperitic textures at their contacts with the pelagic
sedimentary rocks. Thin margin parallel banding in the sedimentary members of the sequence indicates thermally af-
fected original contacts with the mafic volcanic rocks only locally and at a microscopic scale. The absence of peperite in
this case is attributed to the consolidated state of the sediments at the time of the mafic magma emplacement.
Key words: Triassic, Circum-Rhodope Belt, contact metamorphism, low greenschist metamorphism, carbonate sediments,
basalt and dolerite, rhyolitic peperites.
be inferred about their origin. Peperites were formed where a
quartz-feldspar-phyric partly extrusive rhyolitic crypto-dome
and rhyolitic sills intruded Triassic neritic carbonate sedi-
ments. Descriptions of the newly recognized peperite occur-
rences are provided. Specific criteria to discriminate peperite
from other mixed volcanic-sediment breccia facies are dis-
cussed. Where mafic and intermediate rocks are in contact
with Triassic pelagic sediments, peperite is absent; instead,
small scale contact metamorphic phenomena are present.
The cause of the absence of peperite in this case is discussed.
Geological setting
In the easternmost part of the Vardar (Axios) Zone in
Greece (the Peonias subzone of Mercier 1966/68), within the
Circum-Rhodope Belt of Kockel et al. (1971, 1977), a Permo-
Triassic volcano-sedimentary complex ( ~ 85 km long and
4—7 km wide) crops out discontinuously in NNW—SSE direc-
tion (Fig. 1). It bounds the western margin of the Vertiscos
Complex, which contains orthogneisses of Early Paleozoic
age (Kockel et al. 1971, 1977; Kauffmann et al. 1976; Kourou
1991; Sidiropoulos 1991; Asvesta 1992; Himmerkus et al.
2009; Asvesta & Dimitriadis 2010a). The Vertiscos Gneiss
Complex is in contact with the Permo-Triassic volcano-sedi-
mentary complex in a series of north-eastwards steeply dip-
ping reverse faults which also run parallel to the NNW—SSE
oriented belt of the Peonian Ophiolites (Mercier 1966/68;
Asvesta & Dimitriadis 2010a). The Permo-Triassic volcano-
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sedimentary complex is now over-
turned, telescoped and tectonically
sandwiched between the south-
westwards steeply thrusted Vertis-
cos Gneisses and the Peonian
Ophiolites, within which, as well
as within the Vertiscos itself, west-
ward or south-westward directed
thrusts are also present. This tec-
tonic picture is the end result of
probably two similarly directed
compression events, a first one of
Late Jurassic and a second one of
Early Tertiary age (Mercier 1966/68;
Kockel et al. 1971, 1977).
Local stratigraphy
The Permo-Triassic volcano-sedi-
mentary complex comprises sub-
aerial to submarine volcanic and
sedimentary rocks. From bottom to
top (Fig. 2), it is composed of:
a) The Examili Formation; b) The
Silicic Volcano-Sedimentary (SVS)
succession; c) The neritic and pel-
agic carbonate sedimentary facies
of the Svoula Formation.
All the contacts between the
above formations are now tectonic
but it is generally accepted (Mercier
1966/68; Kauffmann et al. 1976;
Kockel et al. 1977; Stais & Ferri
e
re
1991; Asvesta 1992; Dimitriadis
& Asvesta 1993; Ferri
e
re & Stais
1995; Meinhold et al. 2009;
Asvesta & Dimitriadis 2010a) that
they represent secondarily tecton-
ized original stratigraphic contacts.
All the rocks are deformed with a
northeast dipping cleavage and
have been metamorphosed to low-
greenschist facies during a Late Ju-
rassic Alpine event. Despite this,
primary sedimentary and volcanic
features are well preserved and the
prefix “meta-” is omitted in the fol-
lowing descriptions.
The Examili Formation consists
of terrigenous, immature, poorly
sorted, unfossiliferous, slightly
metamorphosed arkosic sandstones
and conglomerates. It is generally
believed to be Permian—Scythian in
age (Kauffmann 1976; Kauffmann
et al. 1976; Kockel et al. 1977)
because of the time constraints im-
posed by the stratigraphically over-
Fig. 1. Geological map of Permo-Triassic volcano-sedimentary complex in the Circum-Rhodope
Belt illustrates the main lithostratigraphic units. Studied locations (1, 2, 3, 4) are noted. Modified
after Mercier (1966/68), Kockel & Ioannides (1979) and Asvesta (1992).
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Fig. 2. Synthetic columnar tectonostratigraphic succession of Permo-Triassic volcano-sedimentary complex in the Circum-Rhodope Belt of
northern Greece. Modified after Mercier (1966/68), Kockel & Ioannides (1979), Asvesta (1992), Meinhold et al. (2009) and Asvesta &
Dimitriadis (2010a).
lying Silicic Volcano-Sedimentary (SVS) succession. The
volcanic rocks of the SVS succession are probably Early to
Middle Triassic in age, based on the finding of micro- and
macro-fauna in the overlying and interbedded limestones
(e.g. Dimitriadis & Asvesta 1993; Ferri
e
re & Stais 1995) and
on U-Pb dating of rhyolitic zircons, which has yielded an age
of 240 Ma (R. Frei, unpublished report; in Kostopoulos et al.
2001). Furthermore, Meinhold et al. (2009) based on U-Pb
(in zircon) geochronology propose a Permian—Triassic age
for the sedimentary rocks of the Examili Formation, in ac-
cordance with previous studies.
The Silicic Volcano-Sedimentary (SVS) succession (Asvesta
& Dimitriadis 2010a) or “Volcanosedimentary series” (Mercier
1966/68; Kockel et al. 1977) or “Pirghoto Formation” ( Ferri
e
re
& Stais 1995; Meinhold et al. 2009) can be divided into two
parts (Asvesta & Dimitriadis 2010a). The lower part comprises
rhyolitic pyroclastic rocks (lapilli and minor accretionary
lapilli tuffs) and aphyric and porphyritic lavas, most likely
emplaced in a subaerial—coastal environment. The upper part
comprises rhyolitic quartz-feldspar-phyric lavas, domes, hyalo-
clastites, sills interbedded with neritic carbonate sedimentary
facies, peperites and finally polymictic epiclastic sedimentary
rocks composed of rhyolitic and carbonate fragments, all sug-
gesting emplacement in a submarine environment. Peperites
were found near Nea Santa (Loc. 1 in Fig. 1) and Akritas
(Loc. 2 in Fig. 1) villages. They reveal original contacts be-
tween rhyolitic porphyries and carbonate sedimentary facies
of the overlying Triassic neritic limestone of Svoula Forma-
tion (Asvesta 1992; Dimitriadis & Asvesta 1993; Asvesta &
Dimitriadis 2010a,b) and are a topic of this work.
Rhyolitic porphyry dykes intruding the Vertiscos Gneisses
near Nea Santa (Asvesta 1992; Asvesta & Dimitriadis
2010a) and Zagliveri (Kauffmann et al. 1976) villages, not
far from the exposed SVS succession, are probably feeder
dykes to the volcanic rocks.
The part of the SVS succession that is exposed in the area
between Akritas village and the city of Kilkis comprises in
addition rhyodacitic amygdaloidal K-feldspar-phyric lavas
(named as “Doiranite” by Osswald 1938). In the area be-
tween Akritas village and Cherson village (Fig. 1), these si-
licic lavas are locally intercalated (intruded or interstratified)
with subordinate basalt, dolerite, andesite and trachydacite,
named herein as “Triassic Rift Basic Volcanics” (Asvesta
1992; Dimitriadis & Asvesta 1993). Small exposures of these
lavas also occur further south, near Sana village (Fig. 1). A
banded iron formation (Mavros Vrachos Hill) near Akritas vil-
lage (Fig. 1) is genetically associated with this volcanism
(Tsamadouridis & Chorianopoulou 1990; Asvesta 1992).
The neritic carbonate sedimentary facies of the Svoula
Formation (Kauffmann et al. 1976; Kockel et al. 1977) con-
tains conodonts, brachiopods, echinoderms, foraminifera,
corals and crinoids of Middle and Late Triassic age (Mercier
1966/68; Kauffmann et al. 1976; Stais & Ferri
e
re 1991; Fer-
ri
e
re & Stais 1995). It is composed of:
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a) Dark grey bedded limestone carrying lenses of reddish
to pink flaser limestone rich in conodonts (age Carnian);
b) White, massive or thick-bedded, recrystallized lime-
stone (age Ladinian);
c) Yellow to whitish, thick-bedded dolomite, alternating
with limestone;
d) Black, ferruginous, thin-bedded limestone with brachio-
pods (age Anisian);
e) Dark grey, thin-bedded, detrital limestone alternating
with whitish sandstone layers and fine-grained conglomerate.
The neritic limestone facies pass upwards into the pelagic
sedimentary facies of the Metallikon and Megali Sterna Units.
The pelagic sedimentary facies of the Metallikon Unit is com-
posed of dark grey, in places red, thin-bedded, micritic and
biosparitic limestones with intercalations of yellow marls,
dark grey shales and calc-schists. In the area near Metallikon
village (Loc. 3 in Fig. 1) it contains interstratifications of altered
dolerite and basalt of the Triassic Rift Basic Volcanics (Stais &
Ferri
e
re 1991; Asvesta 1992; Dimitriadis & Asvesta 1993;
Ferri
e
re & Stais 1995). According to Ferri
e
re & Stais (1995)
these mafic rocks are probably of Late Ladinian—Late Trias-
sic age, as is indicated by the occurrence of the foraminifera
“Aulotortus ex. gr. communis” (Kristan) and “Agathammina
austroalpina” (Kristan-Tollmann & Tollmann) in intercalated
sedimentary units and the presence of Carnian conodonts in
the overlying limestone. Mercier (1966/68) and Kauffmann et
al. (1976) had attributed an Early Jurassic age to these rocks.
The pelagic facies of the Megali Sterna Unit is of Late No-
rian age (Kauffmann et al. 1976) and is composed of grey,
bluish and white thin-bedded recrystallized pelagic platy
limestones, with lenses of white-grey thick-bedded lime-
stones and layers of shales and calc-schists. In the lower part
of the series, which is intensely folded, alternations of phyl-
lites and platy limestones occur (Mercier 1966/68; Kauff-
mann et al. 1976). In the area to the south of Akritas village
(Loc. 4 in Fig. 1) intercalations of basalt and dolerite and mi-
nor andesite and trachydacite of the Triassic Rift Basic Vol-
canics (now-metamorphosed to greenschist facies) have been
found in among the pelagic lime-marl-layered sedimentary
facies of Megali Sterna Unit (Asvesta 1992; Dimitriadis &
Asvesta 1993). The interaction between mafic units and pe-
lagic sedimentary units is a topic of this work.
Syn-sedimentary intrusions and lavas
Representative chemical analyses of the silicic porphyries
associated with peperites and the mafic and intermediate vol-
canic rocks are given in Table 1. The immobile element ra-
tios provide reliable information on primary geochemistry
and petrogenetic affinity. On the basis of classification dia-
grams (Winchester & Floyd 1977), the silicic porphyries of
Nea Santa and Akritas areas are characterized as rhyolites
and rhyodacites, the mafic volcanic rocks of Akritas—Metal-
likon as sub-alkaline basalts, and the intermediate volcanic
rocks of Akritas as andesites and trachydacites (Fig. 3). All
magma types have Nb/Y ratios less than 0.67 indicating their
sub-alkaline affinity. The silicic volcanic rocks show a within
plate granite (WPG) to volcanic arc granite (VAG) chemical
character and represent a calc-alkaline silicic suite (Asvesta
1992; Asvesta & Dimitriadis 2010a). The mafic volcanic
rocks show mid-ocean ridge basalt (MORB) to within plate
basalt (WPB) affinity and are interpreted as volcanic rocks
of a Triassic rift-related tholeiitic suite (“Triassic Rift Basic
Volcanics”; Asvesta 1992; Dimitriadis & Asvesta 1993).
Silicic rocks
Silicic syn-sedimentary volcanic rocks are porphyritic and
contain quartz and K-feldspar phenocrysts (1 to 4
mm in
size) and fewer small-sized albite crystals. Phenocrysts
amount to about 30 % of the rock. Accessory minerals are
zircon, oxidized biotite and disseminated microgranules of
magnetite. Subhedral quartz phenocrysts show round edges
and embayments filled with the groundmass. They display
undulose extinction; some crystals, however, have been an-
nealed and recrystallized to granoblastic aggregates. K-feld-
spar phenocrysts are kaolinized and sericitized, partly
corroded, euhedral to subhedral perthitic microcline (ex-
sanidine) and some of them are twinned. The groundmass is
mostly composed of quartz and sericite, as a result of low-
grade metamorphism. A curved, stringy sericite mesh
Fig. 3. On the SiO
2
vs. Nb/Y and SiO
2
vs. Zr/TiO
2
classification
diagrams (after Winchester & Floyd 1977), silicic porphyries asso-
ciated with peperites are classified as rhyolites—rhyodacites, mafic
volcanic rocks as sub-alkaline basalts and intermediated volcanic
rocks as andesites and trachytes or dacites.
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Table 1: Representative chemical analyses of Triassic syn-sedimentary volcanic rocks.
Location Nea
Santa
Akritas
Rock silicic
silicic
Sample
A49 A66 A626 A629 A630 A631 A637 A678 A5 A757 A670 A671
SiO
2
(wt. %)
74.41 74.15 69.45 69.79 77.33 72.20 72.37 76.52 75.09 74.53 75.89 74.26
Al
2
O
3
12.20 12.96 5.96 15.98 11.27 13.46 13.58 11.83 12.08 12.71 12.07 12.65
Fe
2
O
3
1.41 1.05 2.08 2.11 1.25 1.55 1.53 0.67 1.81 1.97 2.07 2.05
MgO
0.11 0.41 0.79 0.75 0.06 0.00 n.d. 0.23 0.42 0.55 0.15 0.19
CaO
0.20 0.12 0.16 0.15 0.31 0.01 0.01 0.14 0.05 0.06 0.01 0.01
Na
2
O
1.00 0.56 2.18 2.01 1.52 0.14 0.13 n.d. 0.18 2.02 n.d. 0.00
K
2
O
9.20 9.10 7.55 7.59 7.44 11.76 11.77 9.40 8.57 7.12 9.00 10.10
TiO
2
0.18 0.17 0.22 0.22 0.13 0.12 0.12 0.25 0.18 0.36 0.18 0.19
MnO
0.00 0.01 n.d. 0.00 0.01 0.01 0.01 n.d. 0.02 0.00 0.01 0.00
P
2
O
5
0.05 0.06 0.04 0.04 0.02 0.02 0.02 0.13 0.02 0.05 0.04 0.03
Total
98.76 98.59 98.43 98.64 99.34 99.27 99.54
99.17 98.42 99.37 99.42 99.48
Ni (ppm)
4
5
11
6
6
8
8
9
4
11
21
8
Cr
1
1
n.d.
2
2
3
1
6
7
0
2
V
7
8
1
4
1
0
5
6
5
10
4
4
Sc
1
3
1
4
1
2
n.d.
5
4
4
4
5
Cu
4
3
28
n.d.
1
11
n.d.
9
17
n.d.
n.d.
n.d.
Zn
14
42
12
46
25
41
19
34
39
47
20
19
Sr
12
14
32
33
12
12
9
23
10
17
14
7
Rb
305
312
20
297
240
270
310
204
240
152
235
258
Ba
455
367
24
230
152
156
726
1381
734
618
632
575
Pb
18
13
32
3
25
25
5
1
8
n.d.
2
3
Th
23
25
21
28
19
19
13
10
25
18
19
18
Zr
132
124
187
287
149
166
102
263
180
435
184
202
Nb
9
10
18
20
16
16
10
13
13
16
13
13
Y
37
40
63
70
54
59
32
46
52
50
44
44
La
33
35
37
61
33
32
23
29
36
12
43
45
Ce
62
68
92
116
62
66
55
55
81
29
97
103
Nd
29
31
41
48
29
29
27
40
42
18
42
45
Location Metallikon
Akritas
Akritas
Rock mafic
mafic
intermediate
Sample
KM A681 B39 B43 B80 B127 B128 B46 B116 B121 B122
SiO
2
(wt. %)
48.38
46.55 46.70 48.19 46.95 46.00 46.17 55.16 53.57 61.90 63.47
Al
2
O
3
14.91
16.40 15.89 15.16 17.27 15.78 16.03 13.20 13.18 14.21 13.67
Fe
2
O
3
10.14
9.02 11.31 10.22 8.82 11.09 12.24 13.50 13.30 8.94 9.73
MgO
7.57
8.95 8.54 6.89 10.75 9.08 8.03 4.20 3.92 1.65 0.87
CaO
6.08
10.10 9.23 10.26 6.53 10.74 8.49 2.13 3.32 2.15 1.69
Na
2
O
4.78
1.44 2.20 3.52 1.45 1.91 3.19 3.81 4.01 6.96 5.77
K
2
O
0.06
2.20 1.37 0.34 3.09 0.80 0.29 3.28 1.93 0.39 1.37
TiO
2
1.49
1.24 1.94 1.72 1.20 1.72 2.22 2.50 2.50 0.96 0.84
MnO
0.14
0.18 0.17 0.19 0.17 0.18 0.20 0.19 0.23 0.17 0.18
P
2
O
5
0.13
0.11 0.19 0.17 0.10 0.16 0.25 0.39 0.40 0.23 0.20
Total
93.68
96.19 97.54 96.66 96.33 97.46 97.11 98.36 96.36 97.56 97.79
Ni (ppm)
61
143
122
54
152
142
92
8
7
6
7
Cr
145
317
319
430
381
359
254
2
0
1
1
V
242
204
259
280
197
257
281
154
135
3
2
Sc
38
33
39
55
34
38
40
30
32
23
20
Cu
42
38
25
101
52
94
44
n.d.
n.d.
n.d.
n.d.
Zn
71
86
84
84
71
103
111
156
156
132
163
Sr
270
580
313
631
100
1156
1047
71
98
120
194
Rb
1
68
38
9
133
33
12
110
51
18
51
Ba
2
269
131
52
337
124
56
161
207
99
183
Pb
1
n.d.
3
4
2
2
n.d.
1
2
3
6
Th
2
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
6
5
16
15
Zr
137
77
132
127
72
146
201
359
354
784
732
Nb
4
2
6
5
2
4
7
15
12
26
25
Y
32
23
30
29
24
31
36
82
71
111
99
La
16
n.d.
0
1
5
1
5
26
26
37
44
Ce
22
9
16
12
6
8
17
64
69
104
101
Nd
9
8
12
10
9
7
12
38
41
66
57
Whole-rock analyses were performed with a Phillips PW1450/20 X-ray fluorescence spectrometer (XRF) at the Department of Geology
and Geophysics of the University of Edinburgh using standard procedures. Major elements were analysed on fused glass discs and trace el-
ements on pressed powder pellets. n.d.– not detected.
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present in some places mimics perlite cracking, suggesting
an originally glassy character of the groundmass.
Mafic and intermediate rocks
Mafic volcanic rocks, exposed near Akritas and Metal-
likon villages, are altered doleritic dykes and basaltic lavas
(Fig. 4A). In many places, they preserve relict ophitic texture
and have disequilibrium mineral assemblages, characterized
by relict subhedral plagioclase crystals, enclosed in relict cli-
nopyroxene crystals. The clinopyroxene is diopside, largely
converted to actinolite and chlorite (Fig. 4B), as a result of
greenschist facies metamorphism. Microprobe analyses of
pyroxene and amphibole are present in Table 2. Albite,
zoisite, clinozoisite and calcite have been formed after the
primary plagioclase. Sphene and leucoxene (TiO
2
· nH
2
O)
have replaced ilmenite; relics of the last are seen in the cen-
tre of leucoxene assemblages. Quartz, pyrite and magnetite
crystals are also present.
Intermediate volcanic rocks are exposed only near Akritas
village. They have relict hyalo-ophitic texture. Plagioclase
crystals occur in a mass of stilpnomelane that has probably
been formed by crystallization of ferrous glassy groundmass
(Fig. 4C). In the andesites, metamorphic biotite has grown
parallel to schistosity and tiny magnetite crystals are concen-
trated in laminas.
Field evidence for magma—sediment interaction
A variety of magma—wet sediment interaction features are
well preserved at many locations of the studied area (Fig. 1).
Peperitic textures of the Nea Santa and Akritas rhyolites re-
veal interaction between silicic magma and wet unconsoli-
dated neritic carbonate sediment. Thermal contact phenomena
in pelagic sedimentary rocks suggest interaction between mafic
magma and pelagic lime-marl-layered sediment.
Peperitic textures and hyaloclastite associated with the Nea
Santa rhyolite
The Nea Santa rhyolitic porphyry is mostly represented by
a partly extrusive dome ( ~ 1 km in diameter) (Loc. 1 in
Fig. 1) that had intruded into wet unconsolidated carbonate
sediments (Asvesta & Dimitriadis 2010a,b). The dome is co-
herent and non-vesicular in its core but its external upper
marginal sector is perlitic and contains lithophysae in-filled
with quartz. In places, the contact between the rhyolitic por-
phyry and the carbonate sedimentary rock is gradational,
forming a mixed breccia facies. This breccia is composed of
rhyolite clasts in a carbonate matrix and is interpreted as
peperite (Asvesta & Dimitriadis 2010a).
On the basis of the dominant shape of the juvenile clasts,
two different textural types of peperite are recognized at the
Nea Santa rhyolite dome: (1) the fluidal and (2) the blocky,
according to the nomenclature of Busby-Spera & White
(1987). Both the fluidal and the blocky peperites have been
subjected to mineralogical and textural modifications proba-
bly due to hydrothermal alteration (coeval to or following the
peperite genesis) and later low-grade regional metamorphism.
Apart from the dome itself, syn-sedimentary rhyolitic por-
phyry stubby sills or hyaloclastic lavas are intercalated with
the neritic carbonate sedimentary rocks and present micro-
peperitic textures at their margins. Resedimented hyaloclastite
breccia facies and polymictic rhyolite-carbonate epiclastic
sedimentary facies in the vicinity testify to the partly extrusive
nature of the rhyolitic dome (Asvesta & Dimitriadis 2010a,b).
Fig. 4. A – Spheroidal weathering in mafic volcanic rock exposed
near Metallikon village. B – Relict clinopyroxene (Cpx) and plagio-
clase (Pl) crystals (ophitic texture). Actinolite (Act) and chlorite
(Chl) are products of greenschist metamorphism (crossed polars).
C – Intermediate volcanic rock showing hyalo-ophitic texture with
plagioclase crystals and stilpnomelane (Stlp) (recrystallized ferrous
glass). Note high concentration of magnetite grains (crossed polars).
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Rhyolitic fluidal peperite
Fluidal peperite is exposed over some tens of meters on the
eastern lower side of the Nea Santa rhyolite dome along its
contact with a coarse-grained bio-calcirudite limestone (FP in
Fig. 5). The contact is nearby and almost parallel to the north-
ern bank of the Xiropotamos Creek and most of the year a
large part of it is covered by water. Fluidal peperite has a
thickness up to 2 meters and consists of ragged, wispy, seric-
ite-altered rhyolite clasts and stringers mingled with the
coarse-grained bio-calcirudite host sediment (Fig. 6). There
are gradational contacts between coherent rhyolite and host
sediment. The host sediment involved in the peperite is homo-
geneous in texture and unstratified, whereas away from peper-
ite it is bedded (Fig. 6A,B). It is dominated by recrystallized
bio-calcirudite facies, composed of carbonate granules, peb-
bles and limey mud, probably deposited by debris flows in a
shallow submarine environment. Fossils of coral colonies of
the genus Thecosmilia (Milne-Edwards & Haime) have been
found in this facies. They are probably derived from a nearby
carbonate shelf (Asvesta & Dimitriadis 2010a).
The rhyolite clasts in fluidal peperite vary in size from
millimeter to decimeter. They are green in colour with small
pale spots giving a speckled appearance to them. The spots
are calcite-altered feldspar phenocrysts (1—3 mm in size)
whereas chert-like quartz and microsparry calcite assemblages
replace quartz phenocrysts, in a strongly foliated sericite-al-
tered groundmass. The rhyolite clasts involved in fluidal
peperite are more altered than the main mass of rhyolite.
Ductile deformation and cleavage development have modi-
fied the primary texture and shape of the rhyolite clasts.
Table 2: Representative electron microprobe analyses of pyroxene
and amphibole from mafic volcanic rocks and garnet (product of
contact metamorphism) from the lime-marl-layered sedimentary
rocks (Akritas area).
Crystal compositions were analysed on a Cambridge Microscan 5 electron
microprobe (EMP) at the Geological Institute, in the Department of Geology
and Geophysics of the University of Edinburgh, using a 20 kV accelerating
potential, 30 nA incident current. Pure metals, oxides and silica combina-
tions were used as standards. *FeO = total Fe. Fe
3+
is determined based on
stoichiomerty and charge balance. Mineral formula calculated on a 6 Oxy-
gen basis for pyroxene, a 23 Oxygen basis for amphibole and a 12 Oxygen
basis for garnet.
Fig. 5. Detailed map of the location 1 at Figure 1 showing rhyolite and carbonate sedimentary facies along the Xiropotamos Creek near Nea
Santa village. Fluidal peperite (FB) is exposed on the eastern lower side of the dome and blocky peperite (BP) occurs in the western part of
the dome.
Mineral Pyroxene
Amphibole
Garnet
Sample no.
B58
B58
B59
Location
(4) in Fig. 1
(4) in Fig. 1
(4) in Fig. 1
SiO
2
(wt. %)
TiO
2
Al
2
O
3
Cr
2
O
3
*FeO
MnO
MgO
CaO
Na
2
O
K
2
O
Total
52.69
0.00
0.40
0.09
9.34
0.39
11.95
24.30
0.37
–
99.53
53.26
0.01
1.68
–
13.70
0.28
14.24
12.64
0.32
0.11
96.24
38.74
0.11
16.76
0.00
6.82
0.13
0.08
36.52
–
–
99.16
Normalized mineral composition
Si
Al
IV
Al
VI
Ti
Cr
Fe
3+
Fe
2+
Mn
Mg
Ca
Na
K
Total
1.989
0.011
0.007
0.000
0.003
0.028
0.267
0.012
0.673
0.983
0.027
–
4.000
7.835
0.165
0.126
0.001
–
0.000
1.685
0.035
3.123
1.992
0.091
0.021
15.074
2.990
–
1.525
0.006
0.000
0.440
0.000
0.008
0.009
3.020
–
–
7.998
Molecular percent end members
Wollastonite
Enstatite
Ferrosilite
50.40
34.48
15.12
Grossular
Andradite
Pyrope
Spessartine
Uvarovite
Almandine
Schorlomite
77.60
21.60
0.30
0.28
0.00
0.00
0.21
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Fig. 6. Outcrops of fluidal peperite on the eastern lower side of the Nea Santa rhyolite dome exposed in the Xiropotamos Creek (FP in
Fig. 5) showing details of the mingled domains: sericite-altered rhyolite clasts (R) and bio-calcirudite host sediment (S). Where it is possible,
contacts between them are outlined. The small pale spots in the rhyolite domains are phenocrysts. A – Unstratified texture of the host sed-
iment in peperite. B – Tongue of rhyolite (outlined) and detached clasts (two of them outlined) from the main mass of rhyolite (bottom
left) within bio-calcirudite host sediment (top right). Bedding of the sediment away from rhyolite is horizontal. Cleavage is dipping 45° to
the northeast. The outcrop is viewed to the east-northeast. C – Outcrop showing three-dimension relations between rhyolite and bio-calciru-
dite domains. Note a carbonate pebble is enclosed in the rhyolite (bottom left). D – Fluidal rhyolite clasts detached from the main mass of
rhyolite set in bio-calcirudite host sediment. E – Irregular and aligned shape of the rhyolite domains is not entirely primary but a conse-
quence of compaction and deformation. F – Closer view of Fig. 6E – Note bleached bands (arrows) in the host sediment that mirror the
contact parallel to rhyolite clast/sediment matrix interface as a result of baking.
In some places, the carbonate sediment in direct contact
with the fluidal rhyolite clasts displays macroscopic bleach-
ing in bands parallel to the rhyolite clast/sediment matrix in-
terface that mirror the contact (Fig. 6F). Microscopically,
neoformed minerals such as microgranular chert-like silica,
albite, biotite and/or chlorite are visible on the rhyolite clast/
sediment matrix interface (Fig. 7). This mineral association
is confined specifically at the contact. The high concentra-
tion of quartz at the contact even though it is recrystallized
and deformed probably represent an original silicification of
the carbonate sediment. Bleaching and silicification of the
host sediment at the contact with the rhyolite clasts are inter-
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Fig. 8. A – Outcrop of the western part of the Nea Santa rhyolite dome at the Xiropotamos Creek (BP in Fig. 5) showing well developed pris-
matic columnar joints and enclosing breccia zones, viewed to the north. Note a big dyke-like breccia zone (arrow) interpreted as blocky peper-
ite filling cooling contraction fracture. B – Closer view of lower middle part of previous figure. Blocky peperite occurs as a dyke-like breccia
zone. The porphyry clasts (light-coloured) are blocky, polyhedral and float in the carbonate sediment matrix (brown). C – Blocky peperite
fills cooling contraction fracture. Angular blocky jigsaw-fitted rhyolite fragments (light-coloured) reveal in situ fragmentation. The interstices
are completely filled with carbonate sediment matrix (brown).
Fig. 7. Reaction rim in the carbonate domain indicated by the presence of neoformed minerals (quartz, albite and biotite) at the rhyolite
clast/sediment matrix interface of the fluidal peperite (crossed polars). 1 – Rhyolite clast, 2 – Reaction rim, 3 – Carbonate host sedi-
ment. Interface is outlined.
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Fig. 9. Rhyolite clast/carbonate sediment matrix interface in the
blocky porphyritic peperite (crossed polars). Rhyolite clast is com-
posed of quartz and K-feldspar phenocrysts setting in a recrystal-
lized groundmass (top left) and sediment matrix is composed of
sparry calcite (bottom right). Boundary is outlined.
Fig. 11. A reaction rim at the
rhyolite clast/carbonate sediment
matrix interface of the Akritas
peperite (crossed polars). Note
the fluidal rim morphology of a
rhyolite clast. 1 – Rhyolite clast,
2 – Neoformed minerals (quartz,
albite and chlorite), 3 – Silici-
fication of carbonate sediment
(baked margin), 4 – Carbonate
sediment.
Fig. 10. Detailed
maps 2, 3, 4 of
the equivalent lo-
cations at Fig. 1.
preted to reflect baking and compositional modification of
the host sediment, as a result of heat and magmatic fluids
rich in SiO
2
released from the rhyolite (cf. Hunns & McPhie
1999; Gifkins et al. 2002). It is a reaction rim at the rhyolite
clast/sediment matrix contact and is formed by interaction of
the hot magma and wet sediment during the formation of
peperite.
Rhyolitic blocky peperite
Blocky peperite occurs as dyke-like breccia zones travers-
ing the western part of the rhyolite dome (BP in Fig. 5) and fills
cooling contraction fractures in prismatic columnar jointing
(Fig. 8A). It consists of quartz-feldspar porphyry clasts sup-
ported in a massive recrystallized carbonate sediment matrix
(Fig. 8B,C). Some fractures in the rhyolite are completely filled
with sediment only. The porphyry clasts (spalls) are up to 40 cm
long and many of them are blocky, polyhedral and angular with
sharp corners; others however, have partly rounded margins. In
places, these clasts form a jigsaw-fit texture, where clasts are
not displaced far from their adjacent clasts and it is possible to
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fit clast shapes back together (Fig. 8B,C). The groundmass of
the blocky porphyry clasts has been pervasively altered and
metamorphosed to chert-like silica and sericite. Sparry calcite
crystals also occur in the recrystallized groundmass. The phe-
nocrysts are mostly quartz with undulose extinction and corro-
sion embayments filled with the recrystallized groundmass.
Perthitic K-feldspar (ex-sanidine) and a small amount of seric-
itized plagioclase phenocrysts also occur (Fig. 9).
The carbonate sediment matrix is composed of coarse-
grained sparry calcite formed by recrystallization of micrite
and is locally silicified (fine-grained quartz) and dolomitized
probably due to hydrothermal alteration. The extensive recrys-
tallization, dolomitization and silicification have obscured the
original sedimentary textures. Angular corroded quartz grains,
kaolinitized K-feldspar and partly sericitized plagioclase from
the porphyry are also dispersed in the carbonate matrix.
Peperitic textures associated with the Akritas rhyolite
To the south of Akritas village, west of Mavros Vrachos
Hill (Loc. 2 in Fig. 1), tectonic slivers of Triassic limestone
belonging to the Svoula Formation are emplaced in between
the rhyolitic rocks of the SVS succession (map 2 in Fig. 10).
A detailed macroscopic observation reveals rhyolite clasts
incorporated into the limestones. Original contacts between
the rhyolite and limestone have not been found.
The enclosed rhyolite clasts are porphyritic with a purple-
coloured groundmass, just like the nearby rhyolite. They lo-
cally present fluidal rim morphology (Fig. 11) suggesting
that they are not reworked or tectonic but juvenile. Pheno-
crysts are mostly quartz, K-feldspar, plagioclase and minor
zircon and oxidized biotite. The groundmass has been re-
crystallized to quartz and sericite. The core and the rim of
the clast have distinct recrystallized textures; original chilled
margins cannot be recognized with certainty. Iron oxide
strings also define margin parallel bands.
At its contact with the rhyolite clasts, the carbonate rock
exhibits mostly microgranular chert-like quartz and little mi-
crosparry calcite. The amount of quartz diminishes away from
the contact whereas sparry calcite increases (Fig. 11). This
probably represents silicification of carbonate host sediment at
the contact and interpreted as a baked margin (reaction rim).
Neoformed minerals such as microgranular chert-like silica,
albite and chlorite preferentially occur at the rhyolite clast/sed-
iment matrix interface (Fig. 11), as in the case of the neo-
formed mineral assemblages of the Nea Santa fluidal peperites.
The host sediment is composed of microsparry calcite con-
taining crinoid bioclasts. Spongy piemontite poikiloblasts
with lacey borders have locally grown and contain inclu-
sions of recrystallized calcite (Fig. 12). There are also por-
phyroblasts of piemontite, biotite and opaque minerals
(magnetite and hematite). The sediment was apparently rich
in Mn and Fe.
Thermal contact phenomena in pelagic sedimentary rocks
associated with the Triassic Rift Basic Volcanics
To the south of Metallikon village (Loc. 3 in Fig. 1, map 3
in Fig. 10), zoisite crystals in a matrix of sparry calcite have
Fig. 13. A – Parallel bands composed of zoisite (anomalous blue)
and garnet (isotropic) porphyroblasts and poikiloblasts in lime-marl-
layered pelagic sedimentary rock that came in contact with a mafic
lava; Akritas area (crossed polars). B – Garnet poikiloblast enclos-
ing calcite from the carbonate matrix (SEM photomicrograph).
Fig. 12. Spongy piemontite poikiloblasts (Pmt) with lacey borders
enclose sparry calcite (Cc) crystals (parallel polars). Note also bio-
tite (Bi) crystals.
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been developed exclusively along the margins of micritic pe-
lagic sedimentary rocks that are in contact with mafic volcanic
rocks. Their presence is taken as likely evidence of a thermal
contact effect. However, more convincing evidence is found
to the south of Akritas village (Loc. 4 in Fig. 1, map 4 in
Fig. 10), where in the marly and limey alternating bands (1 to
10 cm thick) of the pelagic sedimentary rock that are in con-
tact with a ~ 10 m thick mafic volcanic unit, abundant zoisite
and tiny garnet porphyroblasts have grown in equilibrium
with calcite (Fig. 13A). These two minerals are arranged in
bands following the sedimentary banding. Zoisite has grown
mostly in the marly bands, whereas tiny garnets (10 to
200 µm) are abundant in the limey bands, although they have
also been nucleated at the marly bands together with zoisite.
The tiny garnets (Table 2) are rich in grossular and andradite
(Gro
77,6
Andr
21,6
). Some of them are poikiloblasts enclosing
calcite identical to that in the carbonate matrix (Fig. 13B). It is
important that in this case, grossular and zoisite have grown in
the marly and limey pelagic metasediment that are in contact
only with the upper margin of the mafic volcanic unit, inter-
preted as its original base because the sequence is overturned,
whereas these minerals are apparently absent from the margin
of the same metasediment that is in contact with the lower
margin (original top) of the mafic unit. This is convincing
evidence of a thermal contact effect. It also suggests that the
mafic volcanic unit in Akritas is ex-basaltic lava rather than
intrusion. It furthermore weakens the possibility that the de-
scribed mineral association (calcite + zoisite + garnet) is due to
a metasomatic reaction related to greenschist metamorphism
post-dating the basic magmatism, since in this case the reac-
tion rims of the metasediments ought to be equally present at
both their contacts with the mafic unit (with the inferred top
and bottom margins of this unit).
Challis (1992) has described metamorphism of impure cal-
careous sediments at their contacts with a basaltic dyke at
Potikirua Point, Raukumara Peninsula, New Zealand. Contact
metamorphism has produced flint-hard, garnet-rich rocks.
Tiny spherules of garnet of hydrogrossular and grossular-an-
dradite (grandite) composition have been developed in thin
margin parallel bands. No zoisite was formed in this case
however.
Discussion
When magma interacts with wet unconsolidated sediment,
the produced features vary in character and magnitude de-
pending on numerous factors such as: the nature of the in-
truded sediment, the state of its consolidation, the amount of
water it contains, the viscosity of the magma, the magma
volatile content and temperature, and the depth and hence
the confining (lithostatic and hydrostatic) pressure of intru-
sion (Skilling et al. 2002 and references therein).
The positive identification of peperite requires evidence that
the host sediment was unconsolidated, usually wet, at the time
of mingling and that the igneous component was molten
(White et al. 2000; Skilling et al. 2002). Breccia facies which
are texturally similar to peperite but result from different pro-
cesses may be difficult to distinguish, especially in the case of
blocky peperite. In ancient rocks, it may be difficult to distin-
guish blocky/angular clasts generated by tectonic processes or
by fracture-controlled alteration from those generated during
blocky peperite formation (Allen 1992; McPhie et al. 1993;
Skilling et al. 2002). Other processes such as fallout of juve-
nile pyroclasts into unconsolidated sediment, water-settling of
juvenile pyroclasts contemporaneous with deposition of other
sediments, resedimentation of volcaniclastic deposits by mass
flows, and infiltration of sediment into volcaniclastic deposits
can all produce mixtures of igneous clasts and sediment ma-
trix that resemble peperite (cf. Branney & Suthren 1988;
White et al. 2000; Gifkins et al. 2002).
The breccia facies studied here are composed of volcanic
clasts in a sediment matrix. The rhyolite clasts are interpreted
as juvenile and the carbonate host sediment as wet and uncon-
solidated at the time of mingling. The breccias therefore are
characterized as peperites. The major characteristics of the
studied peperites that are assumed to be key criteria (cf. Goto
& McPhie 1998; Hunns & McPhie 1999; Gifkins et al. 2002;
Skilling et al. 2002; Squire & McPhie 2002; Agnew et al.
2004) for their interpretation with the sense that hot magma
interacted with wet unconsolidated sediment are the following.
The bio-calcirudite sedimentary rock in the Nea Santa flu-
idal peperite is unstratified whereas it grades into bedded sedi-
ment away from the rhyolite. Local destruction of bedding
requires that the host sediment was unconsolidated or weakly
consolidated, allowing easy disruption of grain contacts.
There are gradational contacts between coherent rhyolite
and host bio-calcirudite sedimentary rock in the Nea Santa
fluidal peperite.
The host carbonate sediment is bleached in a zone about
1—2 cm wide adjacent to the rhyolite clasts. The paler sedi-
ment at the contacts is more silicified than the host sedimen-
tary facies elsewhere. Localized silicification is represented
by chert-like quartz grain aggregate along the rhyolite/sedi-
ment interface. The subtle, gradational colour change and lo-
cal silicification of the sediment are interpreted as results of
thermal modification of the sediment (baking) in contact
with hot rhyolite (McPhie 1993; Hunns & McPhie 1999;
Gifkins et al. 2002).
The highly irregular contacts between fluidal rhyolite
clasts and host carbonate sediment (complex clast—matrix re-
lationships) at the Nea Santa fluidal peperite suggest magma
in a ductile stage.
Fluidal peperite is thought to form in cases where a water
vapour film is established and maintained at the interface of
the magma with the sediment. The vapour film insulates the
magma from direct contact with the wet sediment, so both
quench fragmentation of the magma and steam explosions are
suppressed (Kokelaar 1982). According to Erkül et al. (2006),
the presence of chalcedonic rims around juvenile clasts in pep-
erite defines preserved open spaces after removal of the va-
pour film. Open spaces as zones of weakness at the magma/
sediment interface were probably filled by hydrothermal solu-
tions. Field evidence for vapour film development during
fluidal emplacement of magma at Nea Santa and Akritas pep-
erites is found in the presence of neoformed minerals, such as:
microgranular chert-like quartz, albite and biotite or chlorite,
at the rhyolite clast/sediment matrix interface. Chert-like
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quartz is probably the recrystallized product of original chal-
cedonic rims.
The blocky angular polyhedral shape of porphyritic
rhyolite clasts that commonly display jigsaw-fit texture sug-
gests in situ fragmentation and is diagnostic of non-explo-
sive hydroclastic mechanisms resulting from cooling and
solidification of viscous magma with brittle disintegration
along contraction joints.
The presence of host sediment along cooling contraction
fractures of the rhyolite suggests fluidization of sediment, in
the sense of particle support and transport by a fluid, imply-
ing that the sediment was unconsolidated and probably wet
at the time of peperite formation (cf. Kokelaar 1982).
The newly recognized peperite occurrences exposed near
Nea Santa and Akritas villages are deformed and metamor-
phosed rocks, so they are not well suited to exploring some
of the unanswered questions surrounding the formation of
peperite. However, their recognition reveals contemporaneous
magmatism and sedimentation and contributes to facies archi-
tecture and paleoenvironmental reconstruction. Silicic volcan-
ism and accompanying neritic carbonate sedimentation during
the first stages of opening of the Vardar (Axios) Basin in the
Early Triassic provided locally appropriate conditions to form
peperite. When the sedimentation commenced in the basin,
the volcanic activities were waning but had not completely
ceased. Intrusion of porphyritic rhyolitic magma during the
last stage of silicic volcanism took place even contemporane-
ous to sedimentation and interaction between the two resulted
in the formation of peperites. Due to the temporal relationship
between neritic carbonate sedimentation and silicic volcanism
in the Nea Santa and Akritas area, the age of the volcanic
rocks can also provide constraint on the time of commence-
ment of sedimentation in the basin.
As the rift basin evolved, mafic and minor intermediate
volcanism accompanied pelagic sedimentation without
forming peperitic textures. Formation of peperite may have
failed due to a consolidated nature of the sediment as mafic
magma was emplaced late during the evolution of the basin,
when pore water in the sedimentary pile had been lost by
compaction. However, the interaction of mafic magma with
pelagic consolidated sediments formed contact metamorphic
phenomena. The common mineral assemblage of lime-marl-
layered sedimentary rocks at their contacts with the mafic
rocks is: calcite + zoisite + grossular, as a result of contact
metamorphism. If the growth of zoisite and grossular is also
a result of metasomatism, it is difficult to write possible re-
actions of their formation in an open system. Moreover, re-
gional metamorphism probably overprinted the contact
metamorphism mineral assemblage and it is difficult to infer
temperature and pressure conditions.
Conclusions
In less deformed sections of the low-grade metamorphosed
Silicic Volcano-Sedimentary (SVS) succession in the Circum-
Rhodope Belt of northern Greece, near the Nea Santa and
Akritas villages, the identification of peperitic textures at the
contact margins of porphyritic rhyolite intrusions in Middle
Triassic neritic carbonate sedimentary rocks reveals evidence
of interaction of silicic magma with wet unconsolidated car-
bonate sediments. The recognition of rhyolitic peperite is im-
portant for interpreting the facies architecture and stratigraphic
relationships in the Silicic Volcano-Sedimentary (SVS) suc-
cession and timing the Triassic age of the rhyolitic intrusions.
The identification of altered basalt and dolerite intercalated
with pelagic lime-marl-layered sedimentary rocks of the
Metallikon and Megali Sterna Units produced the first argu-
ment for the existence of syn-sedimentary submarine mafic
volcanism during the Triassic in the Circum-Rhodope Belt.
Mafic volcanic rocks lack peperitic textures at their contacts
with Triassic pelagic sedimentary rocks. The generation of
peperite in this case was probably prevented by the consoli-
dated nature of the sediments. However, contact metamor-
phic phenomena, indicated by the presence of grossular and
zoisite in the margins of sedimentary rocks, are evidence of
primary magmatic contacts.
Acknowledgments: Professor Jocelyn McPhie and one
anonymous reviewer are gratefully acknowledged for sug-
gesting significant improvements to the manuscript.
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