GeolCarp_Vol55_No4_325

325

NEOGENE GURGHIU MOUNTAINS VOLCANIC RANGE (EASTERN CARPATHIANS)

GEOLOGICA CARPATHICA, 55, 4, BRATISLAVA, AUGUST 2004

325332

EVOLUTION OF THE NEOGENE GURGHIU MOUNTAINS VOLCANIC

RANGE (EASTERN CARPATHIANS, ROMANIA), BASED ON

K-Ar GEOCHRONOLOGY

IOAN SEGHEDI

, ALEXANDRU SZAKÁCS

, NORMAN J. SNELLING

and ZOLTÁN PÉCSKAY

Institute of Geodynamics, str. Jean-Luis Calderon 1921, 70201 Bucharest, Romania; seghedi@geodin.ro

Lechlade Rd. 46, Faringdon, Oxon SN7 8AQ, United Kingdom; (formely at Faculty of Geology, University Complutense Madrid, Spain)

Institute of Nuclear Research of the Hungarian Academy of Sciences, Bem Tér 18c, pf. 51, H-4001 Debrecen, Hungary

(Manuscript received February 18, 2003; accepted in revised form October 2, 2003)

Abstract: K-Ar ages of rocks from the Gurghiu Mountains, the middle part of the longest volcanic chain in the Eastern

Carpathians (CãlimaniGurghiuHarghita), indicate an interval of volcanic activity between 9.45.4 Ma. Magmatic

activity migrated from North to South and built the following volcanic centres: Jirca (J), Fâncel-Lãpuºna (FL), Bacta (B),

Seaca-Tãtarca (ST), Borzont (BZ), ªumuleu (S) and Ciumani-Fierãstraie (CF). The timing of volcanic activity in each

volcanic centre reflects the previously recognized overlapping age progression from North to South along the arc: J=9.2

7.0 Ma; FL=9.46.0 Ma; B=7.57.0 Ma; ST=7.35.4 Ma; BZ=6.8 Ma; S=6.86.2 Ma; CF=7.16.3 Ma. Two periph-

eral small intrusive bodies have also been dated (Ditrãu 7.9 Ma and Corund 7.4 Ma). The duration of volcanic

activity of each centre is ca. 1 Ma, with a larger interval of 2.5 Ma for the Fâncel-Lãpuºna volcano. Volcanic activity in

the southernmost volcanic centres (ST; BZ; S; CF) between 76 Ma was contemporaneous. Certain volcanological prob-

lems are pointed out: (i) the voluminous debris-avalanche deposit assumed to belong to the Cãlimani Mountains includes

blocks of ca. 8 Ma up to the Gurghiu Valley and between 7.57.8 Ma south of the Gurghiu Valley (ii) the Fâncel-

Lãpuºna caldera was generated around 6.9 Ma and involved a post-caldera uplift and/or erosion of the caldera floor and

younger domes; and (iii) the model based on volcanic facies distribution is consistent with the new age-data.

Key words: Eastern Carpathians, Gurghiu Mountains, K-Ar data, volcanology, debris-avalanche.

Introduction

The CãlimaniGurghiuHarghita (CGH) chain is the southeast-

ern segment of the Neogene/Quaternary magmatic arc adjoining

the Carpathians from Slovakia, through Hungary and Ukraine,

to Romania. Gurghiu Mountains represent the middle segment

of the ~160 km-long CGH volcanic chain located along the in-

ner (western) side of the East Carpathian orogenic zone (Fig. 1).

Its geographical boundaries are the Mureº Valley in the north,

and the upper reaches of the Târnava Mare Valley in the south,

embracing a ~60 km-long, 40 km-wide mountain range with its

highest elevation at Seaca Peak (1776 m). The Gurghiu Moun-

tains volcanic area is located along the structural boundary be-

tween the Inner Eastern Carpathians including the so-called

Crystalline-Mesozoic zone (Dacides Unit, Sãndulescu 1984)

of the Eastern Carpathians in the east, and the Neogene sedi-

ment-filled Transylvanian Basin in the west. The Quaternary

Gheorgheni intra-mountain depression is situated between the

volcanic area and the Crystalline-Mesozoic zone at the east-

ern margin of the Gurghiu Mountains.

The CGH volcanic chain, including the Gurghiu Mountains

is a typical andesite-dominated calc-alkaline volcanic range,

displaying a subduction-type geochemical signature (Rãdulescu

& Sãndulescu 1973; Seghedi et al. 1995; Mason et al. 1996).

Compared with other segments of the chain, the volcanic

rocks of the Gurghiu Mountains are both petrographically and

chemically monotonous. With minor exceptions (basaltic

andesites and dacites), andesites are dominant and pyroxene

andesite is the most common rock type. Magmas were frac-

tionated with typical mineral assemblages found in calc-alka-

line suites and also experienced limited crustal assimilation

and mixing processes (Seghedi et al. 1995; Mason et al. 1996).

The volcanism in the Gurghiu Mountains was first dated by

Rãdulescu et al. (1972) and later by Michailova et al. (1983)

and Pécskay et al. (1995). The present geochronological study

draws upon these data (36 measurements), as well as on a

number of additional K-Ar age determinations (30) performed

at the Complutense University of Madrid (Spain) (13) and

ATOMKI, Debrecen (Hungary) (14) (Table 1). Collectively,

these K-Ar ages allow a more detailed understanding of the

evolution of volcanism in the Gurghiu Mountains. The dated

samples represent all the volcanic edifices, as well as their pe-

ripheral volcaniclastic aprons (Fig. 1). Lava flows, andesite

lithic blocks in volcaniclastic rocks, as well as intrusive rocks

have been sampled to better constrain the age of different vol-

canoes and of the principal volcanic events.

Six samples in this study were analysed both in Madrid and

Debrecen, enabling us to assess the possible analytical prob-

lems that might bear on the reliability and reproducibility of

K-Ar dating of Neogene calc-alkaline volcanics.

327

NEOGENE GURGHIU MOUNTAINS VOLCANIC RANGE (EASTERN CARPATHIANS)

Experimental methods, precision and errors

All the potassium determinations reported herein were made

in the Debrecen laboratories. Approximately 0.1 g of finely

powdered sample was dissolved in acids and the residue was

taken into solution; potassium concentration was determined by

flame photometry with a Na buffer and a Li internal standard.

Conventional experimental methods were used in the deter-

mination of argon. In both laboratories, argon was extracted

from 0.20.3 mm fraction of whole-rock samples (initial

sample weight = 35 kg) by induction heating in Mo crucibles

and purified in a previously baked glass and stainless steel

vacuum system. Argon 38-spike was added from conventional

pipette systems (calibrated against international reference

samples Asia 1/65, LP-6, HD-B1, GL-0), and the evolved

gases were purified using Ti getters, molecular sieves, hot

CuO and liquid nitrogen traps. The purified argon was mea-

sured in the static mode using a Micromass 6 mass spectrom-

eter in Madrid and a 15 cm-radius sector instrument built in

the Institute of Nuclear Research (Hungarian Academy of Sci-

ences) in Debrecen (Balogh 1985). Both instruments were

checked regularly by inter-laboratory reference samples:

HDB1, LP-6, G1-O, Asia 1/65, and Bern 4M and 4B. When

checking against any particular reference sample, the influ-

ence of that sample was deleted from the calculation of the

spike calibration constants.

Since the radiogenic argon content of these reference

samples is about 10 times greater than that of the rock being

analysed, systematic errors may be difficult to detect. How-

ever, during the course of this investigation, 10 samples were

analysed in both laboratories for inter-laboratory comparison.

The results, when plotting against each other, generally fall on

or close to the line of no significant difference. Some anoma-

lous data are apparent, but we are confident that they result

from failure to completely outgas the fused rock samples,

rather than systematic instrumental bias.

Replicate analyses made in Madrid on young volcanic

samples from the Canary Islands, with an average radiogenic

Ar content of about 0.12 nl/gm (17 replicates on 7 samples),

yielded a pooled standard deviation of ±0.0123 nl (one

sigma). The average radiogenic

Ar content of the samples

studied in this investigation is about 0.35 nl/gm, and the afore-

mentioned replicate data would suggest that the precision on

the analytical data reported here is likely to be between 5 %

and 10 %. Such an estimate agrees well with the errors in the

age calculated for each individual analysis by the classical

method of partial differentiation of the analytical errors at-

tached to the variables (see for example Baker et al. 1967;

Mahood & Drake 1982 and references therein). In calculating

the individual age errors, we have assumed errors (one sigma

standard deviation) of ±1 % on the measured isotope ratios

(

Ar/

Ar and

Ar/

Ar), ±2 % on the spike calibration and

±3 % on the K determinations. Although we consider that

these error estimates are overestimates (probably by a factor of

2), we believe that such conservative assumptions will avoid

misleading chronological conclusions that may arise from un-

derestimated errors.

The new data are given in the Table 1. For six samples, ar-

gon determinations have been made independently in both

Debrecen and Madrid. These samples yield radiogenic argon

values that do not differ significantly using the criterion devel-

oped by McIntyre (1963). The critical value for the difference

between analyses in Debrecen and Madrid should not exceed

2.772 × sigma (0.034 nl), where sigma is taken to be the

pooled standard deviation on replicates of ±0.0123 nl, as dis-

cussed above. This criterion is developed from the conven-

tional t-test and assumes a normal distribution of experi-

mental errors. For these samples, the adopted age is the

weighted mean (and weighted standard deviation) of the two

determinations.

Volcanic edifices

Although the morphological boundaries are obvious, the

Gurghiu Mountains, as a geological entity is more difficult to

define, because volcanic rocks (especially volcaniclastic

rocks) originating from volcanic edifices located in both the

geographically defined Cãlimani and Gurghiu Mountains,

interfinger with each other along the Mureº Valley and its

tributaries (Szakács & Seghedi 1996). The Rusca-Tihu De-

bris Avalanche Deposit (a volcanic debris-avalanche deposit)

and the Rusca-Tihu Volcaniclastic Formation, originating

from the Cãlimani Mountains crop out south of the Mureº

Valley, while the Fâncel-Lãpuºna Volcaniclastic Formation,

derived from the northern Gurghiu (Fâncel-Lãpuºna volcano)

occurs north of the Mureº Valley. These formations have been

defined by Szakács & Seghedi (1996, 2000) (Fig. 2).

As in the other parts of CGH volcanic chain, the volcanic

structure of the Gurghiu Mountains consists of an axial,

roughly NWSE row of adjoining composite volcanic edifices

(e.g. Davidson & De Silva 2000) surrounded by extensive

merged volcaniclastic aprons (Figs. 1, 2). The peripheral

volcaniclastic pile, which was formerly described in terms of a

volcano-sedimentary formation (Rãdulescu et al. 1964a,

1973) consist of a ring-plane-type volcaniclastic association

including volcanic debris flow deposits, volcanic debris-ava-

lanche deposits and rarely pyroclastic fall and pyroclastic flow

deposits. It represents the medial to distal facies related to the

volcanic edifices in the Gurghiu Mts (Szakács & Seghedi

1995).

The types of volcanic edifices in the Gurghiu Mountains in-

clude composite volcanoes with or without a caldera, shield

volcanoes, and lava dome complexes. Individual or complex

intrusive bodies are also present in the centre or at the periph-

ery of the edifices. Adjoining and partially overlapping com-

posite cones are located in the axis of the Gurghiu Mountains.

From north to south, there are five larger edifices of this kind,

namely: Jirca, Fâncel-Lãpuºna, Seaca-Tãtarca, ªumuleu and

Ciumani-Fierãstraie (Fig. 1). In addition, there are two lava

dome complexes (Borzont and Bacta). Except for the late

stage of Fâncel-Lãpuºna, all are essentially lava-dominated

volcanoes. The brief characterization of each of these volcanic

edifices is summarized from Szakács & Seghedi (1995, 1996).

Jirca is the northernmost edifice, whose erosional rem-

nants, displaying steep-sided topography, are covered by

younger products of the neighboring Fâncel-Lãpuºna volcano

and the Cãlimani Mountains volcanic area. A deeply eroded

328

SEGHEDI, SZAKÁCS, SNELLING and PÉCSKAY

central intrusive complex at Jirca, largely affected by perva-

sive hydrothermal alteration, is surrounded by lava flows. The

remnants of a Strombolian scoria cone (Zespezele) are also rec-

ognized. Peripheral volcaniclastic rocks represented by basaltic

andesite and andesite debris flow deposits are present, but are

covered by younger volcanic rocks belonging to the adjacent

larger volcanic structures, Fâncel-Lãpuºna and Cãlimani.

The southward-open amphitheatre-shaped Fâncel-Lãpuºna

caldera, ~10 km across (Rãdulescu et al. 1964b), dominates

the northern half of the Gurghiu Mountains. Unroofed large

complex intrusions (andesites and microdiorites) are found in-

side the caldera. Along and near the topographically-defined

caldera-rim, older lava flows and younger lava domes, rang-

ing from basaltic andesites to amphibole andesites, are clus-

tered. The caldera was identified mostly on morphological

grounds by Rãdulescu et al. (1964b), who suggested the

caldera origin of the huge topographic depression 10 km

across, but no large-volume eruptive products to account for

the missing volume of the presumed pre-caldera volcanic edi-

fice have been recognized by previous researchers. The recent

identification of the voluminous pumice-rich Fâncel-Lãpuºna

Volcaniclastic Formation (FLVF, Szakács & Seghedi 1996)

as the possible candidate for the products of a caldera-forming

eruption (e.g. Walker 1984; Lipman 2000) lent more support

to this hypothesis. Pumice-rich pyroclastic flow and less fre-

quent pumice fall deposits of amphibole or amphibole-pyrox-

ene andesites composition, have been found on the northern

and eastern slopes of the volcanic edifice, including its upper-

most parts surrounding the topographic rim of the presumed

caldera. Their reworked counterparts (mostly pumice-rich

volcanic debris flow deposits) crop out at many locations

along the northern and eastern lower slopes of the volcano.

FLVF is spread to the north and east of the caldera within a ra-

dius of ~25 km; a part of the formation occurs as far as the

southern Cãlimani Mountains (Fig. 2). Its present areal cover-

age is ~490 km

, with 10 m-average thickness and an esti-

mated volume of ~4.9 km

(Szakács & Seghedi 1996), may at

least partially account for the caldera depression. Intrusions

consisting of basaltic andesites, andesites and microdiorites

have been mapped in the centre of the edifice (Figs. 1, 2).

Small amphibole-pyroxene andesite to dacite lava domes (up

to 1.5 km in diameter) are located at the margins or in the inte-

rior of the caldera edifice. A similar amphibole-pyroxene

andesite lava dome cluster, Bacta adjoins the caldera at its

south-eastern side (Fig. 1).

Seaca-Tãtarca is the next volcanic edifice to the south.

This large, lava-dominated volcano, with a basal diameter of

~16 km, displays a shield-like topography with gentle outer

Fig. 2. Sketch map of volcanic events belonging to the Cãlimani and Gurghiu volcanic areas along the Mureº Valley, emphasizing

Fâncel-Lãpuºna caldera generation (modified after Szakács & Seghedi 1996): 1 Rusca-Tihu Debris Avalanche Deposit; 2 Rusca-

Tihu Volcaniclastic Formation; 3 Jirca volcanic edifice; 4 Fâncel-Lãpuºna volcano: a. Volcanic edifice, b. Central intrusive com-

plex, c. Fâncel-Lãpuºna Volcaniclastic Formation (R: 25 km radius), d. Late-stage domes; 5 Bacta dome-cluster; 6 Seaca-Tãtarca

volcanic edifice; 7 Topographic rim of volcanic edifices.

329

NEOGENE GURGHIU MOUNTAINS VOLCANIC RANGE (EASTERN CARPATHIANS)

slopes and a surprisingly regular, almost circular, central to-

pographic depression (5 km in diameter), whose rim shows a

relatively uniform elevation, breached to the north. Its struc-

ture seems simple, consisting of a pile of lava flows, mostly

pyroxene andesite. Karátson (1999) and Karátson et al. (1999)

describes this depression as an erosion caldera on purely mor-

phological grounds, however, later, Karátson & Thouret

(2001) accept that a true caldera and an erosion caldera can

coexist, as refers to a primary volcanic depression trans-

formed later by erosion.

Since no obvious large-volume pyroclastic deposits are as-

sociated with this edifice, nor voluminous effusive products to

be allocated to one particular eruptive event, Seaca-Tãtarca

central depression is rather a remnant of an eroded crater, then

a caldera (e.g. Szakács & Ort 2001). The southernmost part of

the Gurghiu Mountains consists of a closely-spaced cluster of

smaller edifices which, together with the northernmost North

Harghita volcanoes, are controlled by WNWESE-striking

tectonic alignments (Fig. 1). Borzont is a small amphibole

andesite volcano with a central intrusive core unroofed par-

tially by erosion.

ªumuleu is a composite volcanic edifice, with a basal di-

ameter of ~12 km and ~4 km in diameter central depression

with a well-developed shallow intrusive core-complex. Both

the intrusions domes (amphibole and pyroxene andesites and

microdiorites) and host lava flows are highly altered. Lava

flows (pyroxene andesites), extending beyond the crater show

gentle-dipping slopes and are topped by crater-rim lava domes

(amphibole and pyroxene andesites). A prominent flank vent

that erupted pyroxene andesite lava is present on the lower

southern side of the volcano.

Ciumani-Fierãstraie is a double-crater composite edifice

with pyroxene andesite lavas dominating its lower slopes that

are buttressed westwards against lavas of the neighbouring

ªumuleu volcano (Fig. 1). The Ciumani crater is breached to

the south and Fierãstraie crater to the north. Lava domes oc-

cupy the topographic crest between the two craters on the

western part of the summit area. Both craters have been ero-

sion-modified (enlarged) and host intrusive core complexes

with related hydrothermal alteration zones.

Volcaniclastic deposits, mostly consisting of volcanic de-

bris flow deposits, cover a widespread area to west and south-

west of the Seaca-Tãtarca, ªumuleu and Ciumani-Fierãstraie

volcanoes. It consists of merged volcaniclastic aprons of the

individual volcanoes, which cannot be mapped individually

because of the similar composition of their respective source

volcanoes (Szakács & Seghedi 1995).

Discussion of K-Ar ages and eruptive history

The location of the thirty new K-Ar whole-rock determina-

tions (Table 1) together with 36 previously published K-Ar

determinations (Pécskay et al. 1995), are shown in Fig. 1. The

timing of volcanic structures is summarized in Fig. 3.

Recent observations (Szakács & Seghedi 1996) led to a re-

evaluation of 6 age determinations (Pécskay et al. 1995) on

samples of block-sized lithic clasts collected from the western

periphery of the Gurghiu Mountains from volcaniclastic de-

posits. These deposits have been mapped as a volcanic debris-

avalanche deposit having their origin in the Cãlimani Moun-

tains (Figs. 1, 2). These deposits although extremely chaotic

and heterogeneous contain mainly basaltic andesites, with

large clinopyroxene phenocrysts as a distinctive feature.

These rocks show an age interval between 8.08.1 Ma north

of the Gurghiu Valley (GH-51, GH-56, GH-59). Three

samples collected from similar deposits and of similar petrog-

raphy south of the Gurghiu Valley show slightly younger ages

(7.57.8 Ma), but with partially overlapping error-bars

(Fig. 3). The ages measured on volcanic lithic clasts in the

volcanic debris-avalanche deposit indicate ca. 7.58.1 Ma as

the period of pre-avalanche volcanic activity at the source vol-

cano (Figs. 1, 2), which is consistent with the K-Ar ages of

lithologically similar rocks in the Cãlimani volcanic area

(7.48.7 Ma) (Seghedi et al. in print). However, the origin of

some debris-avalanche clasts (in outcrops located at the south

of the Gurghiu Valley) from the early Fâncel-Lapuºna vol-

cano, cannot be ruled out. In the Cãlimani area, as constrained

by K-Ar determinations, 8.0±0.5 Ma is the assumed age for

the edifice failure and related debris-avalanche event (Rusca-

Tihu Debris Avalanche Deposit) (Szakács & Seghedi 1996;

Seghedi et al. in print).

The oldest and northernmost volcanic structure belonging

to the Gurghiu Mountains is Jirca (9.28.4 Ma). An isolated

intrusion, situated close to Jirca volcano toward north, which

consist of pyroxene-bearing aphyric andesite (G-20), was

dated at 7.0 Ma, however it is not clear if this event can be at-

tributed to the Jirca volcano. At its periphery, the Jirca vol-

cano is partially covered by younger volcaniclastic products

belonging to both the North Cãlimani and the Fâncel-Lãpuºna

volcanoes.

The Fâncel-Lãpuºna volcano has been the major focus of

K-Ar studies, since it is the largest volcanic structure of the

Gurghiu Mountains. The oldest volcanic activity is mostly ef-

fusive and represented mainly by basaltic andesites and py-

roxene and amphibole andesites, which corresponds to the

8.77.5 Ma interval (GH-53, GH-80, GH-79, GH-78, 3974).

Fragments of the same petrography belonging to the

volcaniclastic apron around the volcano show an age interval

between 7.77.5 Ma suggesting their generation contempora-

neous with the effusive edifice (GH-49, GH-81, GH-61). This

interval can be considered as the pre-caldera stage. Amphib-

ole, pyroxene-bearing andesites and dacites, found as

volcaniclastic deposits attributed to FLVF show 7.16.91 Ma

and have been generated during the caldera stage (Fig. 3).

Younger ages have been obtained for the amphibole (pyrox-

ene) andesite domes at the border of the caldera (5.99

6.23 Ma), which belong to the post-caldera stage according to

morphological observations. Three different bodies, belong-

ing to an intrusive complex in the caldera interior, showing

various petrography (microdiorite with pyroxene, andesites

with pyroxene and amphibole, basaltic andesites) have been

dated. Results (9.44 Ma, 8.5 Ma and 8.13 Ma) show a wide

range. The small-sized Bacta structure, located southeast of

the Fâncel-Lãpuºna volcano, homogeneous from petrographic

point of view (amphibole, pyroxene-bearing andesites),

evolved between 6.977.52 Ma. It is indicating a relatively

short time interval of extrusion. Similar rock types belonging

330

SEGHEDI, SZAKÁCS, SNELLING and PÉCSKAY

to the Fâncel-Lãpuºna volcano are almost coeval (7.5

6.0 Ma). An isolated small dome on the eastern periphery of

Bacta shows 6.6 Ma.

The bulk of the Seaca-Tãtarca volcano evolved between

7.26.3 Ma. A younger age was detected for a lava flow in-

side the edifice (5.4 Ma) suggesting a last eruption (Pécskay

et al. 1995). There is an excellent agreement between the du-

plicate measurements performed on pyroxene andesite

samples (GH-34, GH-35) from this volcano. Moreover, the

sample collected by Michailova et al. (1983), from the same

outcrop (GH-35), gave the same K-Ar age within error

(7.4 Ma) as the new age (7.25±0.21 Ma).

The only sample dated from the Borzont lava volcano

(6.8 Ma) (Pécskay et al. 1995), brings an age in the same

range as that of the neighbouring volcanic structures (Fig. 3).

Age data for the ªumuleu volcano (6.86.2 Ma) and for the

Ciumani-Fierãstraie edifice (7.16.3 Ma) show a roughly

similar age interval.

The small pyroxene amphibole-bearing andesite bodies

(several meters in diameter), mapped as intrusions, which cut

volcaniclastic deposits at the south-western periphery of the

Gurghiu Mountains, give 7.4 Ma (GH-69) (Pécskay et al.

1995). Similar rocks on the north-eastern margin of the

Gurghiu volcanic (Ditrãu) show 7.9 Ma (GH-84).

Conclusions

The age determinations show an interval of volcanic activ-

ity between 9.45.4 Ma. The distribution of K-Ar data

(Fig. 3) confirms the previously recognized age progression

along the CãlimaniGurghiuHarghita arc (Rãdulescu et al.

1973; Pécskay et al. 1995). The duration of the main volcanic

activity corresponding to each volcanic center is considered to

be about 1 Ma, with a longer interval for the most complex

Fâncel-Lãpuºna volcano (2.5 Ma), which was active mainly

during Pannonian times.

Simultaneous activity of all the volcanoes (Seaca Tãtarca,

Borzont, ªumuleu and Ciumani-Fierãstraie), took place in the

southern part of the Gurghiu Mountains between 76 Ma.

Nr.

crt

Sample

Locality

Volcano Rock

type

K% vol.rg 40 Ar

nl/gm

% atm. Age (Ma) Adopted age Lab.

References

GH-84

Ditrau V.

Apxam 1.88

0.6490

57.63

7.86 ± 0.37

GH-76

Nirajul Mare

Apx

0.64

0.3300

19.29

7.74 ± 0.40

GH-77

Nirajul Mare

Apx

0.92

0.4560

29.23

7.50 ± 0.33

GH-83

Magura de sus V.

Aam

0.90

0.3280

31.24

8.90 ± 0.46

GH-83

Magura de sus V.

Aam

0.81

0.2523

77.90

9.12 ± 0.52

GH-82

Gudea V.

Apx

1.07

0.3497

53.21

8.38 ± 0.31

GH-49

Eszenyo V.

Aam

1.85

0.5538

59.70

5.99 ± 0.31

G-612

Cilnic Ridge

Aam

1.48

0.1830

35.88

6.23 ± 0.50

G-616

Fancel Ridge

Aampx 1.62

0.3300

43.59

6.91 ± 0.34

GRG-28B Coasta Mare Ridge

Dam

1.57

0.4292

42.10

7.01± 0.32

G-354A

Galautas V.

Aam

1.39

0.4088

31.50

7.54 ± 0.30

G-383

Musca Brook

Apx

1.46

0.4300

31.70

7.59 ± 0.30

GH-78

Batrana Ridge

Apxam 1.85

0.5468

37.20

7.59 ± 0.30

GH-81

Mariselu V.

Aam

1.83

0.7440

54.85

7.69 ± 0.29

GH-79

Viclean Ridge

Apx

0.81

0.2752

79.45

7.74 ± 0.56

GH-54

Zambroi Summit

0.82

0.3070

25.83

8.13 ± 0.43

GH-80

Piatra Ridge

Apxam 1.62

0.5474

41.50

8.68 ± 0.35

G-562

Fancel V.

Mdpx

1.54

0.1760

56.65

9.44 ± 0.77

G-604

Fagul Ascutit

Aampx 1.29

0.3210

33.08

6.58 ± 0.34

GH-50

Sineu Quarry

Aam

1.46

0.4141

50.10

7.29 ± 0.31

6.97 ± 0.25*

20 "

0.3938

66.10

6.60 ± 0.33

Pécskay et al. 1995

GH-46

Bacta V.

Aampx 1.42

0.4027

15.50

7.29 ± 0.28

GH-47

Bacta V.

Aampx 1.32

0.3903

54.20

7.53 ± 0.33

7.46 ± 0.31*

22 "

0.3608

89.00

7.00 ± 0.88

Pécskay et al. 1995

GH-48

Bacta V.

Aam

1.33

0.3909

44.10

7.55 ± 0.31

7.52 ± 0.21*

23 "

0.3895

29.50

7.50 ± 0.29

Pécskay et al. 1995

GH-34

Tarvez Summit

Apx

0.97

0.2414

45.10

6.39 ± 0.27

6.39 ± 0.21*

24 "

0.2429

67.40

6.40 ± 0.33

Pécskay et al. 1995

GH-35

Bucin Pass

Apx

1.11

0.3124

34.70

7.29 ± 0.29

7.25 ± 0.21*

25 "

0.3095

42.00

7.20 ± 0.30

Pécskay et al. 1995

GH-33

Sumuleul Mare V.

ABpxam 0.99

0.2407

58.30

6.20 ± 0.28

Pécskay et al. 1995

GH-31

Sumuleul Mic V

Apx

1.11

0.2928

51.20

6.70 ± 0.29

Pécskay et al. 1995

GH-32

Sumuleu Mare V.

Apxam 1.11

0.3023

43.10

7.00 ± 0.29

6.80 ± 0.21*

28 "

0.2852

54.30

6.60 ± 0.29

Pécskay et al. 1995

GH-29

Chilieni Quarry

Apx

0.98

0.2669

34.80

7.00 ± 0.28

GH-30

Drumul lui Gavrila V.

Aam

1.18

0.3243

37.10

7.10 ± 0.28

Pécskay et al. 1995

*Calcuted mean age

Table 1: K-Ar ages for rocks from Gurghiu Mountains volcanic area. The samples follow the order of volcanoes from north to south as

they are shown in Fig. 1. Abbreviation: for volcanoes as in Fig. 1, additional: PI peripheric intrusions, DA clasts in debris-ava-

lanche. For rock types: AB basaltic andesite, A andesite, D dacite, Md microdiorite, px pyroxene, am amphibole.

Laboratory: M Madrid, D Debrecen.

332

SEGHEDI, SZAKÁCS, SNELLING and PÉCSKAY

petrography and age as of the pre-volcanic intrusions below

the Cãlimani volcanic area (Seghedi et al. in print) and it can

be attributed to this event. The ages of the most distal lava

flows and volcaniclastic deposits (e.g. in the Fâncel-Lãpuºna

and Seaca-Tãtarca volcanoes) are similar to those of corre-

sponding central edifices, each of which display a central

(proximal) facies and peripheral (distal) facies, as has previ-

ously been reported (Szakács & Seghedi 1995).

Acknowledgments: The Geological Institute of Romania

(GIR) supported fieldwork. Analytical work was supported by

an inter-Academy cooperation project between GIR, Institute

of Geodynamics Sabba S. Stefãnescu and ATOMKI, and by

a bilateral cooperation project between GIR and the CSIC-

University Complutense of Madrid. We thank Robert I. Till-

ing of the U.S. Geological Survey for helpful review and edi-

torial improvements to the earlier version of the manuscript.

We acknowledge the critical and helpful review of the paper

by K. Németh, J. Lexa and V. Koneèný.

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