Eruptive history andage of magmatic processes in the
Cãlimani volcanic structure (Romania)
, ALEXANDRU SZAKÁCS
, ZOLTÁN PÉCSKAY
and PAUL R.D. MASON
Institute of Geodynamics, str. Jean-Luis Calderon 1921, 70201 Bucharest, Romania; firstname.lastname@example.org
Institute of Nuclear Research of the Hungarian Academy of Sciences, P.O. Box 51, Bem tér 18/c, H-4001 Debrecen, Hungary
Vening Meinesz Research School of Geodynamics, Department of Earth Sciences, Utrecht University, Budapestlaan 4, 3584 CD Utrecht,
(Manuscript received July 15, 2003; accepted in revised form March 16, 2004)
Abstract: The Cãlimani Mountains represent the largest and most complex volcanic structure at the northern part of the
CãlimaniGurghiuHarghita range in Romania. Sixty-eight K-Ar ages (thirty-three new) provide constraints on the
eruptive history of the Cãlimani volcanic structure between 11.3 and 6.7 Ma. The oldest rocks are from shallow exhumed
intrusions, which pierced the basement between 11.39.4 Ma. The oldest stratovolcano was centered on the presently
recognizable main volcanoes, Rusca-Tihu and the Cãlimani Caldera and grew very large (ca. 300 km
), generating a
large-volume (26 km
) debris avalanche. Debris avalanche blocks dated between 10.27.8 Ma, suggest an edifice failure
event at 8.0±0.5 Ma. The Drãgoiasa Formation (9.38.4 Ma), Budacu Formation (9.08.5 Ma), Lomaº Formation (8.6 Ma),
a number of Peripheral Domes (8.77.1 Ma) and Sãrmaº basalts (8.58.3 Ma) were also active before the debris ava-
lanche event. Volcanic activity continued from the Rusca-Tihu Volcano between 8.06.9 Ma, generating the Rusca-
Tihu Volcaniclastic Formation. The Cãlimani Caldera structure including pre-caldera and post-caldera stages was gen-
erated between 7.56.7 Ma, with an inferred collapse event at 7.1±0.5 Ma. Monzodioritic-dioritic bodies in the central
part of the caldera show ages between 8.87.3 Ma, implying several episodes of intrusions. Fractional crystallization
was important in the generation of different magma series at lower crustal to shallow crustal depths, where plagioclase
was the main crystallizing phase. Crustal assimilation affected most of the analysed samples to some degree through
assimilation-fractional-crystallization (AFC) processes. Isotopic enrichment of the most basic rocks suggests that con-
tamination processes affected the source of most parental magmas, except those of the Lomaº Formation. The initial
stages of volcanism were most complex from the petrological point of view. The Drãgoiasa Formation (represented only
by felsic rocks), for instance, suggests either fractionation from a basic parental magma and mixing with partial melts of
(lower) crustal origin, or represents direct melting of the garnet bearing lower crust. The Lomaº Formation represents the
most primitive magma, which reached the surface recording minimal interaction with crustal material and most closely
characterizes the isotopic composition of the mantle source beneath the Cãlimani Volcano. The youngest volcanic rocks
represented by the Cãlimani Caldera structure were derived from magmas that show a lower degree of partial melting
and were largely affected by assimilation processes.
Key words: Eastern Carpathians, Cãlimani Mountains, petrology, volcanology, K-Ar data.
The Cãlimani Mountains represent the northernmost and larg-
est volcanic area amongst the 160 km long CãlimaniGur-
ghiuHarghita range in Romania (Fig. 1). The basement of
this complex volcanic-magmatic centre is represented by: 1
metamorphic rocks belonging to the Crystalline-Mesozoic
zone of the Eastern Carpathians in the east, 2 Cretaceous-
Paleogene sediments in the north, pierced by a complex of shal-
low intrusions, belonging to the southern extension of the so-
called subvolcanic zone of the Rodna-Bârgau area, and 3
Neogene Molasse sediments of the Transylvanian Basin in the
west. The largest and most prominent volcanic structure is the
Cãlimani Caldera (Seghedi 1982, 1987). It is situated in the
north of the area and covers almost one third of the Cãlimani
K-Ar ages were previously published by Rãdulescu et al.
(1972), Peltz et al. (1987) and Pécskay et al. (1995). Petrologi-
cal studies have been performed by Peltz et al. (1974, 1984),
Seghedi (1987), Seghedi et al. (1995) and Mason et al. (1995,
The present study is based on 33 new K-Ar ages and re-
views another 35 previously published ages produced in the
same laboratory. Age data of Rãdulescu et al. (1972) have not
been used in this study. This new extended K-Ar data-base en-
ables more constraints to be applied to the eruptive history of
the volcanic edifice, as established by previous volcanological
studies. An additional aim of this study is to discuss the petro-
logical evolution of the area on the basis of existing geochemi-
cal data (Mason 1995; Mason et al. 1996).
Rock samples dated in this study (Table 1) were taken from
different types of magmatic rocks including those from lava
flows, intrusions and blocks in volcaniclastic deposits. They
were systematically collected using the methodology of Péc-
GEOLOGICA CARPATHICA, FEBRUARY 2005, 56, 1, 6775
68 SEGHEDI, SZAKÁCS, PÉCSKAY and MASON
Fig. 1. Simplified volcanological sketch map of the Cãlimani and northernmost Gurghiu Mountains (according to Seghedi & Szakács in Sza-
kács & Seghedi 1996) with location of sampling points for K-Ar determination. 1 Pre-volcanic basement (a in the interior of the volca-
nic area); 2 Early intrusions (basaltic-andesites, andesites, microdiorites); 3 Drãgoiasa Formation (dacites, rhyolites); 4 Lomaº For-
mation (low-K andesites and dacites); 5 Budacu Formation (andesites); 6 Sãrmaº basalt lavas; 7 Rusca-Tihu stratovolcanic edifice
(basaltic andesites and andesites); 8 Aphyric andesite lavas; 9 Rusca-Tihu debris avalanche deposit; 10 Rusca-Tihu Volcaniclastic
Formation with lava intercalations (andesites, basaltic andesites); 11 Peripheral Domes (andesites and dacites); 12 Cãlimani Caldera
lava flows (andesites); 13 Post-Cãlimani-Caldera rocks: a monzodiorites, diorites, b andesites, dacites; 14 Upper PlioceneQua-
ternary sedimentary basins; 15 Jirca volcanic edifice: a andesites, b diorites; 16 Fâncel-Lãpuºna pre-Caldera rocks: a volcani-
clastics, b andesite and basaltic andesite lavas; 17 Fâncel-Lãpuºna Volcaniclastic Formation (andesites, dacites); 18 a Caldera
rim according to present topography, b Crater rim according to present topography; 19 Volcanic vent; 20 Sample location.
skay et al. (1995). Rock samples were optically examined in
thin sections and only the freshest or least altered material was
prepared (crushed and sieved) for geochemical and geochro-
nological study. One portion of the sieved fraction was used
for the Ar analysis and another portion from the same sample
was ground and used for K determination. All of the K-Ar
work was carried out in the Institute of Nuclear Research of
the Hungarian Academy of Sciences (ATOMKI), Debrecen,
Hungary, using the methods previously described by Pécskay
et al. (1995). Further details of analytical methods and calcula-
tions of analytical errors are described in Balogh (1985). The
decay constants used in the age calculations are given in
Steiger & Jäger (1977).
The reconstruction of the volcanic structure of the Cãlimani
Mountains has been carried out by reinterpreting previously
published data (Peltz 1969; Teodoru et al. 1970; Seghedi
1982, 1987) using a set of 5 geological maps at scale of
1:50,000. Two of these have been published (ªarul Dornei,
Poiana Stampei) whilst the other three (Bilbor, Negoiul Româ-
nesc, Topliþa) are as yet unpublished. A volcanological map of
the Cãlimani volcanic area was first proposed in Szakács &
Seghedi (1996) and is presented in Fig. 1.
The largest identifiable stratovolcanoes are represented by
Rusca-Tihu and Pietrele Roºii and are built up mostly of ba-
MAGMATIC PROCESSES IN THE CÃLIMANI VOLCANIC STRUCTURE (ROMANIA) 69
saltic andesites. They supplied huge volumes (~300 km
of 420 km
for all Cãlimani Mountains volcanics) of volcanic
deposits found all over the Cãlimani volcanic area on a surface
larger then 900 km
(Szakács et al. 1997). Detailed volcano-
logical survey supports the occurrence of large-volume debris
avalanche deposits belonging to the Rusca-Tihu Volcano
) (Szakács & Seghedi 1996, 2000) (Figs. 1, 3). This
evidence implies that during its early history, the Rusca-Tihu
Volcano (RTV) was much more imposing than today. Its
height has been estimated at ca. 3000 m by Szakács & Seghe-
di (2000). Tectonic instability most likely led to edifice failure
and the resulting debris avalanche reached distances of up to
55 km southwards and almost 40 km westwards. After this de-
structive episode, which would have resulted in a major topo-
graphic change, the volcanic activity continued from the cen-
tral vents as well as from NS-directed peripheral ones. The
composition remained constant with the eruption of the same
basaltic andesitic lavas, becoming more andesitic in the final
stages. The post-debris avalanche proximal facies is represent-
ed by lava flows, in places autobrecciated, pyroclastic (mainly
phreatomagmatic) flow and fall deposits and block-and-ash-
flow deposits. The Rusca-Tihu stratovolcano then supplied
debris flow deposits associated with hyperconcentrated flood-
flow and normal stream flow deposits or lacustrine deposits
(well exposed along the Mureº Valley) emplaced at intermedi-
ary to distal locations (Szakács & Seghedi 1996, 2000).
Besides the products of the Rusca-Tihu stratovolcano, other
contemporaneous complex volcaniclastic formations, such as
the Budacu Formation (at the western periphery), the Drã-
goiasa Formation (eastern part) and the Lomaº Formation
(southern-central part) have been identified. They are distinct
from each another, according to their geochronological, petro-
graphical, geochemical and volcanological features (Peltz et
al. 1970, 1987; Peltz & Seghedi 1984; Seghedi 1987; Szakács
& Seghedi 1996). Peripheral lava centres have been found all
around the main volcanic edifices. The Drãgoiasa Formation
is a dome-complex of aphyric dacites (occasionally rhyolites),
associated with pyroclastic rocks in the east (Niþoi 1986). In
the north and east, aphyric and normal andesitic lava vents are
present (e.g. Mãgura, Scaunul), whereas in the south basaltic-
andesitic and dacitic lava domes prevail (e.g. Leul, Bãieºul,
Tarniþa, Mogoºul). They are referred to as Peripheral Domes
(PD). In the south-easternmost part a large area of basalts
(Sãrmaº basalts SB), which formed a shield volcano, are
found and younger volcaniclastic deposits of basaltic-andesite
composition cover them.
The Cãlimani Caldera structure represents the final major
volcanic episode in this area. Its products, mainly lava flows,
partially cover the series of NNE-trending older stratocones
(Rusca-Tihu, Tãmãul, Pietrele Roºii, Lucaciul) in the west, the
Drãgoiasa dacite Formation, the volcaniclastic deposits of the
older Rusca-Tihu Volcano and the Lomaº Formation in the
east and south. The pre-caldera Cãlimani edifice consists of
large-volume andesitic lavas, rich in silica and alkalies (Se-
ghedi 1987; Mason et al. 1996). Flow directions of the lavas
were dependent on local topography, with south and east-di-
rected slopes, originating from at least four independent vents
(Seghedi 1987). A huge volume of lava, estimated to be in ex-
cess of 10 km
, was erupted in a relatively short interval of
time, constrained by K-Ar data at ca. 300 ka (Pécskay et al.
1995). The actual caldera, with a summit rim altitude of ca.
2000 m a.s.l., was a result of the collapse initiated by the
above mentioned effusive eruption. The horseshoe shape is as-
sumed to be related to a half-block tilting downward the
southeastern part from a NESW oriented hinge, resulting in a
trap-door type caldera (Seghedi 1995). Post-caldera volcanism
is represented by a few andesitic stratocones (e.g. Negoiul
Românesc) in the interior of the caldera. A large monzodiorit-
ic-dioritic intrusion is exposed in an area of about 11 km
the central part of the caldera. Dacitic domes located on the
caldera rim (Pietricelul) and outer slopes (Drãguºul, Puturo-
sul) are also post-caldera features. The central area has under-
gone extensive hydrothermal alteration (Teodoru & Teodoru
1966; Stanciu & Medeºan 1971a,b; Seghedi et al. 1985).
Discussion of the K-Ar ages and eruptive history
The new K-Ar age data are presented in Table 1. The volca-
nological sketch (Fig. 1) shows the sampling locations, in-
cluding those of published ones, used in this study. The time
distribution of the main age intervals of different volcanic
and intrusive formations given by K-Ar data is summarized
in Fig. 2.
The time span of the magmatic activity in the whole Cãli-
mani volcanic area is between 11.3 and 6.7 Ma. The oldest
dated rocks are the exhumed subvolcanic intrusions of diverse
composition basaltic andesites, andesites and microdior-
ites, which pierced the metamorphic and Cretaceous-Paleo-
gene sedimentary basement of the region (hereafter referred to
as Early Intrusions EI), confirming previous geological in-
terpretations of their relative age (Török 1961). The ages of
Fig. 2. K-Ar age histogram and time-space distribution of Neogene
magmatic rocks in the Cãlimani Mountains (each block represents
one sample). Abbreviations: C Cãlimani Caldera-forming event;
DA Debris-avalanche event.
70 SEGHEDI, SZAKÁCS, PÉCSKAY and MASON
various bodies belonging to this intrusive activity range be-
tween 11.39.4 Ma, covering a 2 million years time interval
and coeval with the subvolcanic intrusions belonging to the
Bârgãu area (11.98.6 Ma) developed northward (Pécskay et
al. 1995). They also crop out inside the volcanic area on the
Zebrac Valley (10.110.6 Ma) or along the Mureº Valley in
the Stânceni Quarry (9.5 Ma). In all these occurrences the
cross-cutting relationships of the intrusive rocks with Miocene
sedimentary strata are clear (e.g. Peltz et al. 1981).
As inferred from volcanological observations, the oldest
stratovolcano was probably centered at the actual location of
the main volcanoes Rusca-Tihu and Cãlimani Caldera.
This stratovolcano shows the largest age interval among all
the volcanic structures of the Cãlimani Mountains (10.1
6.8 Ma). The most striking feature of the volcanic evolution of
Rusca-Tihu is its synchronicity with the subvolcanic intru-
sions in the 10.19.1 Ma interval (Fig. 2), a critical time-peri-
od for the transition from intrusive to extrusive activity. The
Rusca-Tihu Volcano, built up mostly of basaltic andesites,
grew very large and voluminous between 107 Ma when it
supplied a huge volume of volcaniclastic deposits, part of
them related to a large debris avalanche event (Szakács & Se-
ghedi 1996, 2000). The dating of the debris avalanche blocks
gives an age interval between 10.27.8 Ma, similar to that
found in the western side of the Gurghiu Mountains area (Se-
ghedi et al. 2004). The youngest dated block in the debris ava-
lanche suggests edifice failure of the Rusca-Tihu Volcano at
ca. 8.0±0.5 Ma.
According to our volcanological field evidence, small-vol-
ume effusive and explosive volcanic activity was active in the
surrounding area during the generation of the Rusca-Tihu Vol-
cano. It produced the dacitic-rhyolitic Drãgoiasa Formation
Table 1: Whole rock K-Ar ages for selected samples from Cãlimani Mountains volcanic area. The samples represent different formations or
edifices generated during the evolution of the volcanic activity. Abbreviations: vcl volcaniclastic deposit, Aph aphyric, B basalts,
BA basaltic andesite, A andesite, D dacite, Mzd monzodiorite, Py pyroxene, Am amphibole, Ga garnet, Bi biotite.
Lab. No. Sample
Rock type Rock body
Ar rad (%)
CLM-22 Colibiþa Valley
12 Apostoli Valley
Rusca-Tihu volcanic edifice
Piatra Dornei Peak
CLM-42 Repedea Valley
12 Apostoli summit
CLM-21 Podiºorenilor Hill
CLM-34 Piatra lui Orban Peak
CLM-31 ªoimul de Jos Valley
Buza ªerbii-Pinþii Crest Py-BA
CLM-61 Secu Valley
Gãlãoaia Mica Valley
Gãlãoaia Mica Valley
MAGMATIC PROCESSES IN THE CÃLIMANI VOLCANIC STRUCTURE (ROMANIA) 71
lated lavas, and secondary reworked sequences (debris flow,
hyperconcentrated flood flow and fluvio-lacustrine deposits).
Depositional environments ranged from terrestrial to lacus-
trine. The Cãlimani Caldera is the youngest and most impor-
tant post-debris-avalanche volcanic feature and partially cov-
ers a series of NNE trending older stratocones of the RTV,
toward the west. The pre-caldera volcanic rocks (PC) have
been dated between 7.16.8 Ma, while volcanologically rec-
ognized post-caldera volcanic events (CP) suggest a similar
age interval between 7.36.7 Ma (Fig. 3). The short time-in-
terval of pre- and post-caldera evolution is notable (several
hundred thousand years). However, the monzodioritic-dioritic
intrusion exposed in the central part of the caldera shows a
larger age interval, between 8.07.3 Ma, which in part over-
laps with the pre- and post-caldera volcanic events (Fig. 2).
Taking into account the youngest age of pre-caldera lava flows
we can infer the caldera collapse event around 7.1±0.5 Ma.
Fig. 3. Cartoons (A, B, C, D) showing the evolution of volcanism in the Cãlimani and northern Gurghiu Mountains (according to Szakács &
Seghedi 1995, with modifications). Areas of active volcanic processes are represented by grey shadings for each time interval. A. EI Ear-
ly intrusions, DF Drãgoiasa Formation, LF Lomaº Formation, BF Budacu Formation, RTV Rusca-Tihu Volcano, SB Sãrmaº
basalts, PD Peripheral Domes, J Jirca Volcano. B. Generation of Rusca-Tihu debris avalanche and volcanic activity at PD Periph-
eral Domes, SB Sãrmaº basalts, J Jirca Volcano. Thick cross in B cartoon indicates tectonic uplift. Arrows show assumed dispersion
path directions of volcaniclastics. C. RTF Rusca-Tihu Volcaniclastic Formation, FL Fâncel-Lãpuºna Volcano. Arrows show assumed
dispersion path directions of volcaniclastics. D. CC Cãlimani Caldera Volcano, PD Peripheral Domes, FL Fâncel-Lãpuºna Volca-
niclastic Formation, B Bacta Dome Complex.
(9.38.4 Ma), andesitic-dacitic Budacu Formation (9.0
8.5 Ma), low-K andesitic-dacitic Lomaº Formation (8.6 Ma),
andesitic-dacitic Peripheral Domes (8.77.1 Ma) and Sãrmaº
basalts (8.78.3 Ma). All these peripheral volcanic centres
were active before the main debris avalanche event (Fig. 3).
Following the inferred debris avalanche event (at ca. 8 Ma),
the volcanic activity continued from the same Rusca-Tihu
Volcano, as well as other peripheral vents during an interval
between 8.06.8 Ma. The deposits of post-debris-avalanche
volcanic activity have been denominated as the Rusca-Tihu
Volcaniclastic Formation RTVF (Szakács & Seghedi
1996) and RTF hereafter (Fig. 3). On the basis of the K-Ar
data presented here we have split the RTV and the RTF units.
Basaltic andesites and other andesites were generated in this
interval and a peripheral volcaniclastic apron was constructed
consisting of a complex lithological assemblage of proximal
pyroclastics (of both fall and flow origin) with several interca-
72 SEGHEDI, SZAKÁCS, PÉCSKAY and MASON
One sample of an amphibole-pyroxene-bearing andesite,
collected from volcaniclastic deposits attributed to the Fâncel-
Lãpuºna Volcaniclastic Formation FLVF (Szakács & Seg-
hedi 1996) yields an age of 7.1 Ma, which is in the same range
with dated samples of this formation from the northern Gur-
ghiu Mountains, which designate the moment of Fâncel-
Lãpuºna Caldera generation, as a consequence of a major Plin-
ian eruption (Szakács & Seghedi 1996; Seghedi et al. 2004).
Caldera-type edifices Cãlimani and Fâncel-Lãpuºna are the
most important of the CãlimaniGurghiuHarghita range, be-
ing generated in a short time interval at around 7 Ma, almost
contemporaneously (Fig. 3).
Petrological evolution in the light of K-Ar dating
This section discusses the geochemical and petrological
evolution of the distinct volcanic formation identified using
K-Ar geochronology. We use the geochemical data-base from
Mason, (1995) consisting of 67 rock samples, most of them
collected from the same outcrops as the K-Ar samples used for
this study. Seghedi (1987), Mason (1995) and Mason et al.
(1996) already pointed out that the Cãlimani volcanic area is
petrogenetically very complex and is a result of various contri-
butions of mantle and crust materials in the genesis of primary
mafic magmas. In spite of the fact that the area displays huge
volumes of basalt and basaltic andesite, the low-K dacites be-
longing to the Lomaº Formation have been found as the most
isotopically primitive (Mason et al. 1996). The Cãlimani ba-
salts in general show low MgO (<7 wt. %), Ni (<70 ppm) and
Cr (<210 ppm), suggesting fractionation of mafic phases such
as olivine and clinopyroxene during magma ascent.
The TAS (total alkali vs. silica) diagram (Fig. 4) indicates a
broad range of rocks from basalt to rhyolite, dacites and rhyo-
lites are specific for Drãgoiasa Formation and Lomaº Forma-
tion (almost exclusive) and some post-caldera rocks. EI, RTV
and RTF volcanic products range from basalts to andesites.
Pre- and post-caldera rocks are mostly andesitic, but with a
slightly higher alkali content in Budacu Formation and Pe-
ripheral Domes rocks, which plot in the andesitic field. SB
rocks have a slightly elevated alkali content. Incompatible ele-
ment abundances of Cãlimani calc-alkaline basalts normalized
to primitive mantle (Fig. 5) are variably enriched in large ion
lithophile elements (LILE) and light rare earth elements
(LREE) and also show variable Nb depletion, a characteristic
feature for subduction-related magmas. The SB basalts are
most enriched and show a negative spike of Sr as compared to
Sr with SiO
provides evidence for the
occurrence of both source contamination and assimilation in
the volcanic suites of the Cãlimani region (Fig. 6). The frac-
tionating mineral assemblage (i.e. plagioclase, olivine and py-
roxenes) mainly caused the increase in SiO
, whereas the shift
Sr ratios is related to assimilation. Source
contamination is linked to the increasing
Sr ratio of
most primitive rocks (basalts and basaltic andesites). The large
range of geochemical and isotopic characteristics observed be-
tween rocks of the different volcanic formations may have re-
sulted as a consequence of magma evolution at multiple loca-
tions in small-volume pockets. These magmas evolved inde-
pendently from each other on the way to the surface. The
Lomaº Formation dacites show minimal interaction with
crustal material and may represent the evolved composition of
a primitive magma, which did not reach the surface, but which
is isotopically closest to the mantle source. The plot of the
most primitive RTV, RTF and SB (along with an inferred
composition for the Lomaº Formation group) suggests vari-
able source contamination. Increasing
Sr ratios from
this source contamination trend may be related to variable
crustal contamination. The progressive increase of
Fig. 4. TAS diagram for Cãlimani Mountain samples. Symbols and
abbreviations as in Fig. 3. Further symbols: PC pre-caldera stage,
CP post-caldera stage. Data from Mason (1995).
Fig. 5. Primitive mantle normalized incompatible trace element dia-
grams for calc-alkaline basalts from Cãlimani Mountains, using the
normalizing coefficient of Sun & McDonough (1989). Data from
MAGMATIC PROCESSES IN THE CÃLIMANI VOLCANIC STRUCTURE (ROMANIA) 73
Sr vs. SiO
diagram for Cãlimani Mountains samples.
Symbols as in Fig. 4. Symbols and abbreviations as in Figs. 3 and 4.
Data from Mason (1995).
ratios for similar SiO
, may suggest increasing assimilation,
along with fractional crystallization trend (FC), of successive
magma batches, in the evolution of Cãlimani Caldera. The
Sr ratios and SiO
of Drãgoiasa Formation
rocks indicate a strong crustal influence. Since these rocks
also show HREE depletion (Mason 1995) indicating the direct
implication of garnet in their genesis, it is likely that their pa-
rental magma may have mixed with, or represent partial melts
of a garnet-bearing lower crust. The distinction between
source contamination and crustal assimilation can be more
easily recognized using Sr-Nd and O isotopic modelling
(James 1981; Ellam & Harmon 1990), since oxygen isotope
enrichment is a sensitive indicator of crustal contamination
(Mason et al. 1996) (Fig. 7). Assimilation-fractional crystalli-
zation (AFC) curves have been modelled using the most isoto-
pically primitive compositions, which belong to samples C65
(RTV) and C10 (EI) and a crustal assimilant, represented by
the average value for Eastern Carpathians local crust (Mason
et al. 1996). Between 5 and 20 % upper crustal contaminant is
required in the AFC modelling (EI, RTF, Drãgoiasa Forma-
tion, pre-caldera volcanic rocks). Up to 2 % source contamina-
tion can explain the
Sr variability of the basaltic compo-
sition belonging to various formations. Lomaº Formation
dacites are the most unaffected by source contamination.
These variable source contamination processes suggested for
the Cãlimani magmas are perhaps related to differences in the
mantle wedge composition affected by variable sediment and
fluid addition. Extreme
Sr and δ
O values of the Drã-
goiasa Formation rocks suggest a crustal origin of their mag-
mas is most likely.
The ratio of high field strength elements (HFSE) such as Nb
and Zr, can provide insight into variations in magma source
composition (e.g. Davidson 1996; Singer et al. 1996). Nb and
Zr are depleted in subduction-related magmas and are as-
sumed to be dominantly mantle-derived, being relatively im-
mobile under hydrothermal conditions. However, a small de-
gree of modification to these ratios may be possible during
bulk crustal assimilation, to lower Nb/Zr ratios (crustal Nb/Zr
is ~0.06 Mason 1995) corresponding to higher or lower
Th/La (crustal Th/La is ~0.36 Mason 1995). The Nb/Zr-
Th/La diagram (Fig. 8) shows Nb/Zr values starting from
~0.05 (close to a typical MORB value). Higher Nb/Zr ratio
characterizes only the Drãgoiasa Formation rocks. However,
in the same range of Nb/Zr, Th/La is much higher for the Cãli-
mani Caldera rocks. This suggests either lower-degree partial
melting of a similar source, or crustal assimilation, or both. If
crustal assimilation did play a role (as suggested by high
Sr) then the local assimilated crustal component has not
yet been identified in this area (highest crustal Th/La = 0.5; Ma-
son 1995). Co-variance of Ni with Rb (Fig. 9) is considered to
result from partial melting along the Rb trend and fractional
Sr vs. δ
O variation for Cãlimani Mountains samples.
Assimilation-fractional crystallization (AFC) and bulk mixing mod-
els intend to explain Sr and O isotope variation of Cãlimani mag-
mas. For AFC: r = 0.4 trend (degree of assimilation/degree of frac-
tionation) is shown with tick marks for every 5 % of consumed
= 1.2 in all calculations. Symbols and abbreviations as in
Figs. 3 and 4. Data from Mason (1995).
Fig. 8. Nb/Zr vs. Th/La diagram for Cãlimani Mountains samples.
Symbols as in Fig. 4. Data from Mason (1995). Symbols and abbre-
viations as in Figs. 3 and 4. Data from Mason (1995).
74 SEGHEDI, SZAKÁCS, PÉCSKAY and MASON
crystallization along the Ni trend. As the highest Ni content of
Cãlimani basalts does not exceed 60 ppm, it is clear that all the
magmas were affected by fractionation before rising to the
surface and are far from primary melts in their composition.
Crystal fractionation most likely started to occur at the deep
levels, maybe at the crust mantle boundary. Rb variation,
however, suggests higher degrees of partial melting for EI
(11.59.5 Ma), RTV, Lomaº Formation and most of the volca-
nic activity between 108 Ma. Cãlimani Caldera resulted from
magmas, which for the whole Cãlimani Mountains volcanic
structure resulted from a lower degree of partial melting, re-
flecting a general decrease of partial melting through time.
This may imply a temperature decrease in the mantle-source
toward the end of volcanic activity in the Cãlimani volcanic
area, but in parallel it suggests a temperature increase in the
upper crustal magma chamber (i.e. Cãlimani Caldera), as re-
sult of the ascent of successive magma batches, significant for
increased assimilation along with fractionation.
The Cãlimani volcanic area was active between 11.3 and
6.7 Ma, with a complex magmatic history involving eruptions
from multiple vents. The earliest volcanic activity developed
between 10.59.5 Ma, partially overlapping previous intrusive
magmatism. We suggest the following scenario for the evolu-
tion of this volcanic structure:
1 Shallow intrusions pierced along a NNWSSE trend
the metamorphic and Cretaceous-Paleogene sedimentary base-
ment rocks of the region between 11.39.4 Ma, representing
the southern extension of the intrusive activity in the Bârgau
area (11.98.6 Ma) in the north. Enriched mantle source, frac-
tionation and assimilation at crustal levels were important
petrogenetic processes in the generation for these rocks.
2 Several major volcanic formations were formed
throughout the whole Cãlimani area during the initial stages of
the extrusive activity between ~108 Ma: Rusca-Tihu Volca-
no (which covers the entire interval), Drãgoiasa Formation
(9.38.4 Ma), Budacu Formation (9.08.5 Ma), Lomaº For-
mation (8.6 Ma), Peripheral Domes (8.77.1) and Sãrmaº ba-
salts (8.78.3). The main stratovolcano, centered on the actual
location of the Rusca-Tihu and Cãlimani Caldera structures
was the largest and most voluminous. Its instability led to a
large debris avalanche event at 8.0±0.5 Ma. The magmatic ac-
tivity at this time was complex, with different volcanic forma-
tions resulting as a consequence of magma evolution at multi-
ple locations. Drãgoiasa Formation rocks either fractionated
from a more basic, but enriched parental magma, and mixed
with partial melts from a garnet-bearing lower crust, or repre-
sent direct partial melts of a garnet-bearing lower crust. Lomaº
Formation magmas fractionated in deep-seated magma cham-
bers, but ascended to the surface with minimal interaction with
crustal material. The Rusca-Tihu Volcano suite is the most
representative for the Cãlimani area, suggesting both source
contamination and AFC processes, in shallower larger-volume
magma chambers. The Budacu Formation magmas are similar
to the Rusca-Tihu magmas, but are more fractionated. The
Sãrmaº basalts magmas experienced the largest source con-
3 Following the debris avalanche event, between ~8
7.5 Ma volcanic activity continued at the same Rusca-Tihu
Volcano and other peripheral vents, generating the RTF For-
mation. These magmas represent a new batch and exhibit a
larger degree of source contamination, lower degree of partial
melting and AFC processes in shallow magma chambers. The
magmatic activity at this time tends to concentrate in one ma-
jor volcano as a consequence of magma system evolution to-
wards smaller number of locations.
4 The Cãlimani Caldera was generated between ~7.5
6.7 Ma (collapse at 7.1±0.5 Ma) and is the most important
post-debris avalanche volcanic structure. Pre-caldera volcanic
products show ages between 7.16.8 Ma, while post-caldera
volcanic events are dated between 7.36.7 Ma. A post-caldera
monzodioritic-dioritic intrusion exposed in the central part of
the caldera shows a larger age interval, between 8.87.3 Ma
and, according to field evidence, was probably emplaced in
several intrusive episodes. Some Peripheral Domes were gen-
erated in this interval. These rocks are envisaged as a new
batch of magma giving the pre- and post-caldera stages, as
well as some of the Peripheral Domes. This magma fractionat-
ed from a source characterized by more significant enrich-
ment, evolved AFC and lower degree of partial melting, as
compared with earlier magmas. This implies lower tempera-
Fig. 9. Ni vs. Rb diagram for Cãlimani Mountains samples. Symbols
as in Fig. 4. Symbols and abbreviations as in Figs. 3 and 4. Data
from Mason (1995).
MAGMATIC PROCESSES IN THE CÃLIMANI VOLCANIC STRUCTURE (ROMANIA) 75
tures at the source and higher temperatures in a unique upper
crustal magma chamber, at the termination of volcanic activity.
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