www.geologicacarpathica.sk
GEOLOGICA CARPATHICA, APRIL 2009, 60, 2, 181—190 doi: 10.2478/v10096-009-0012-5
Geochronology of the Neogene calc-alkaline intrusive
magmatism in the “Subvolcanic Zone” of the
Eastern Carpathians (Romania)
ZOLTÁN PÉCSKAY
1
, IOAN SEGHEDI
2
, MARINEL KOVACS
3
, ALEXANDRU SZAKÁCS
2, 4
and ALEXANDRINA FÜLÖP
3
1
Institute of Nuclear Research of Hungarian Academy of Sciences, Bem tér 18/c, 4026 Debrecen, Hungary; pecskay@atomki.hu
2
Institute of Geodynamics, Str. J.-L. Calderon 19—21, 020032 Bucharest, Romania
3
North University Baia Mare, Faculty of Mineral Resources and Environment, Str. Victor Babe 62/A, 4800 Baia Mare, Romania
4
Sapientia University, Str. Matei Corvin 4, 400112 Cluj Napoca, Romania
(Manuscript received February 11, 2008; accepted in revised form October 23, 2008)
Abstract: The Poiana Botizei— ible —Toroiaga—Rodna—Bârgău intrusive area (PBTTRB), northwest Romania, known
as the “Subvolcanic Zone”, is located between the Gutâi (NW) and Călimani (SE) volcanic massifs. It consists of rocks
displaying a wide range of compositions and textures: equigranular or porphyritic with holocrystalline groundmass
(gabbro-diorites, diorites, monzodiorites and granodiorites), and/or porphyritic with fine holocrystalline or glassy-
cryptocrystalline groundmass, similar with effusive rocks: basalts, basaltic andesites, andesites, dacites and rhyolites.
The time-span of intrusive rocks emplacement is similar with the nearest calc-alkaline volcanic rocks from Gutâi (NW)
and Călimani (SE) massifs. They are represented by stocks, laccoliths, dykes and sills typical for an upper crustal
intrusive environment. In the absence of biostratigraphic evidence, a comprehensive K-Ar study of intrusive rocks
using whole rock samples, groundmass and monomineral fractions (biotite, hornblende) has been carried out in order to
understand the magmatic evolution of the area. The oldest K-Ar ages recorded in the analysed rocks are close to 11.5 Ma
and magmatism continued to develop until about 8.0 Ma. The inception of intrusion emplacement in the PBTTRB is
coeval with intrusive activity spatially related to volcanism within the neighbouring Gutâi and Călimani massifs. How-
ever, its culmination at ca. 8 Ma ago is younger than the interruption of this activity at ca. 9.2 Ma in Gutâi and Călimani
Mts where intrusive activity resumed for ca. 1 Myr. These circumstances strongly suggest that the geodynamic evolu-
tion of the area controlled the development of both volcanic and intrusive activity and their reciprocal relationships. The
overall geological data suggest that in the PBTTRB intra-lithospheric transpressional-transtensional tectonic processes
controlled the generation and emplacement of intrusive bodies between ca. 12—8 Ma.
Key words: Eastern Carpathians, geodynamic aspects, intrusive magmatism, K-Ar dating, Neogene calc-alkaline rocks.
Introduction
The Poiana Botizei— ible —Toroiaga—Rodna—Bârgău intru-
sive area (PBTTRB) represents a particular segment of the
Carpathian Neogene magmatic arc characterized by intrusive
magmatism with no trace of volcanic products in contrast to
the neighbouring segments – the Gutâi and Călimani Mts
(Fig. 1) – where intrusions are closely related to volcanic
activity. This area is traditionally referred to in the Roma-
nian geological literature as the “Subvolcanic Zone” of the
Eastern Carpathians (e.g. Peltz et al. 1972).
The timing of polyphase Miocene tectonics in the Mara-
mure area (Northern Romania), combined with field obser-
vations, stratigraphic arguments and fission-track analysis
suggests that during the Miocene the area was subjected to
geodynamic evolution stages developed in sinistral
transpressional (16—12 Ma) followed by sinistral transten-
sional (12—10 Ma) stress regimes along the major transcrust-
al Bogdan Vodă—Drago Vodă fault system (Tischler et al.
2006). Although Miocene magmatic rocks are widely dis-
tributed in the PBTTRB, the emplacement history of these
intrusive rocks remained obscure up to now because of the
scarcity of radiometric age data (e.g. Pécskay et al. 1995b)
and uncertainty of stratigraphical relationships with the host
Miocene sedimentary rocks.
Comparative radiometric data of the intrusive rocks and
related mineralizations from Poiana Botizei, ible and Oa -
Gutâi Mts were published by Kovacs et al. (1997). During
the last decade K-Ar age data have been accumulated mak-
ing it possible for the first time to discuss the evolution of
magmatism in the PBTTRB. For chronostratigraphic assign-
ment we refer to the time-scale of the Central Paratethys ac-
cording to Vass & Balogh (1989).
Geological setting
The study area is located in the internal Eastern Car-
pathians (Northern Romania) (inset in Fig. 1). It consists of
the northeastern part of the Tisia (Biharia Unit) and Dacia
blocks (Bucovinian nappes) that have been deformed in mid-
Cretaceous times (“Austrian” phase) until Late Cretaceous
182
PÉCSKAY, SEGHEDI, KOVACS, SZAKÁCS and FÜLÖP
times (“Laramide” phase) (Săndulescu 1984, 1994). Upper
Cretaceous-Paleocene sediments unconformably cover all
tectonic contacts between the Tisia and Dacia blocks and are
unconformably covered by Eocene-Lower Miocene strata.
The Tisia and Dacia blocks, together with their cover, were
overthrust by the Pienides during Early Miocene times (Săn-
dulescu et al. 1981). The post-Lower Miocene deposits of
the Pannonian and Transylvanian Basins begin with the dep-
osition of the Middle Miocene (Badenian) Dej tuff during a
period of mainly explosive rhyolitic volcanism (Szakács
2000). Intermediate calc-alkaline magmatism started during
Middle Miocene times in the Eastern Carpathians (13.5 Ma,
Pécskay et al. 1995a,b). The most obvious tectonic feature in
the study area is the > 75 km long E-striking left-lateral
Bogdan Vodă—Drago Vodă fault system (e.g. Săndulescu et
al. 1981). Most of the intrusive bodies in the PBTTRB, ex-
cept for those in the south Bărgâu Mts, which are related to a
NW-SE strike slip tectonic system beneath the Călimani vol-
canic area (e.g. Fielitz & Seghedi 2005; Seghedi et al. 2005),
have been emplaced in relation to this E-W strike-slip tec-
tonic system (Fig. 1).
General features of the intrusive magmatism
Poiana Botizei, ible , Toroiaga and Rodna—Bârgău areas
are each characterized by a cluster of isolated intrusive bod-
ies of varied size and composition. The Poiana Botizei intru-
sions are situated in the eastern extension of the Gutâi massif
where both intrusive and volcanic products occur (Kovacs et
al. 1995) (Fig. 1). Similarly, in the south-east the intrusions
in the Bârgău area appear as the northward extension of the
Călimani Massive. It has been pointed out that intrusive ac-
tivity predated volcanism in the Călimani volcanic area
(Török 1961; Seghedi et al. 2005) and postdated the early
volcanic activity in the Gutâi-Oa area (Kovacs et al. 1995).
The areas of intrusive magmatism are briefly described in
the following sections while their petrographic summary and
Fig. 1. Simplified geological map of the Poiana Botizei— ible —Toroiaga—Rodna—Bârgău area (northern Eastern Carpathians) showing the oc-
currences of intrusive bodies. The inset shows the location of the area in Romania. 1 – Outcrop areas of the main intrusive bodies; 2 – Out-
crop areas of volcanic rocks belonging to the Gutâi and Călimani massifs; 3 – Post-Miocene sediments; 4 – Middle to Upper Miocene sedi-
ments; 5 – Eocene to Lower Miocene sediments; 6 – Pienides units; 7 – Moldavides units; 8 – Transylvanides units; 9 – Bucovinian
units; 10 – Faults; 11 – Thrust/reverse faults. The large frames correspond to figures 2 and 3, respectively. The smallest frame shows the oc-
currence area of small intrusions in the Poiana Botizei area.
183
GEOCHRONOLOGY OF THE NEOGENE CALC-ALKALINE INTRUSIVE MAGMATISM (ROMANIA)
modal composition are given in the Appendix. The most im-
portant bodies are of stock or laccolith type surrounded by a
complex system of sills and dykes. Also individual dykes or
sills of different size, from several km to several meters, can
be found. At the contact with sedimentary strata haloes of
hornfelses or breccias occur. At the margin of the large bod-
ies, as well as in the dykes or sills, the porphyritic texture
with fine holocrystalline or glassy-cryptocrystalline ground-
mass is dominant suggesting rapid cooling; therefore, the ef-
fusive nomenclature was used. A large petrographic
spectrum was identified: rhyolites, dacites, andesites, basaltic
andesites and basalts. In central parts the large intrusions show
medium to large equigranular or porphyritic texture with ho-
locrystalline groundmass (gabbro-diorites, diorites, quartz di-
orites, monzodiorites and granodiorites), which are altered by
hydrothermal solutions (i.e. propylitic and argillic facies).
Poiana Botizei area
Small-size (up to 800 m) intrusive bodies of various
shapes pierce Paleogene sedimentary deposits (Săndulescu
1984). The intrusions cluster within a ca. 5 km wide and ca.
10 km long east-west-oriented area (Fig. 1). Typical calc-al-
kaline rocks are represented by diorites, quartz diorites,
quartz monzodiorites, porphyritic microgranodiorites, andes-
ites and dacites. According to geological evidence, the mi-
crogranodiorites and dacites are apparently younger than
other rocks.
ible area
This area, situated between the Gutâi and Rodna Moun-
tains, is represented by a complex succession of intrusive
bodies, which pierce Paleogene and Lower Miocene sedi-
mentary deposits, south of the Drago Vodă fault (Figs. 2,
3B). The ible Mts represent a polyphase intrusive complex
consisting of a few large km-sized and numerous small-sized
bodies (up to several hundred meters across) emplaced dur-
ing several magmatic pulses (e.g. Pop et al. 1984). The large
intrusions in the north-western and central part of the area
(e.g. Hudin and Tomnatec, Fig. 3) are composed of micro-
granodiorites and dacites; the south-eastern part is dominat-
ed by the monzodioritic intrusion
ible -Bran-Măgura
Neagră (5 km in length) surrounded by a ring composed of
Arcer quartz diorites, microdiorites and andesites (Fig. 3B)
(Uduba a et al. 1983; Pop et al. 1984). A large number of
small intrusions composed of diorites, quartz diorites, mi-
crodiorites and andesites are clustered around the main intru-
sions throughout the whole area (Fig. 2). The main
monzodioritic intrusion pierces the amphibole dacites near
Tomnatec Peak, as also proved in the underground mining
gallery. Crustal contamination is suggested by Pop et al.
(1984) based on the presence of cordierite in the Hudin mi-
crogranodiorites.
Contact phenomena form hornfelses and skarn accumula-
tions (magnesian skarns with phlogopite described by
Uduba a et al. 1982). Ore deposits associated with the main
intrusion are represented by (1) a vein system mostly orient-
ed NE—SW, showing a lower temperature outer belt (Sb, As,
Ag) and a higher temperature internal belt (Zn, Pb, As, Cu),
and (2) a core with disseminated copper-enriched ore (Cu,
Zn, Pb) related to a deep, hidden porphyry system with mag-
netite and chalcopyrite (Uduba a et al. 1983).
Toroiaga area
The Toroiaga intrusive area, situated north of the Rodna
Mountains and north of the Drago Vodă fault, consists of a
complex of subvolcanic intrusions that pierce metamorphic
rocks and in its southern part, Paleogene and Miocene sedi-
mentary deposits, suggesting a multiphase intrusive activity
(Berza et al. 1982, 1984). In the Toroiaga Massif, five dis-
Fig. 2. Geological map of the
ible Mts. 1 – Biotite mi-
crogranodiorites (Hudin type)
and amphibole-bearing dac-
ites (Tomnatec type); 2 –
Quartz monzodiorites ( ible
type); 3 – Pyroxene andes-
ites (Arcer type); 4 – Dior-
ites, quartz diorites, mi-
crodiorites and andesites; 5 –
Paleogene flysch; 6 – Oli-
gocene-Miocene sedimentary
deposits; 7 – Thrust faults;
8 – K-Ar sample locations;
9 – Geological cross-sec-
tion (Fig. 3B).
184
PÉCSKAY, SEGHEDI, KOVACS, SZAKÁCS and FÜLÖP
tinct phases of calc-alkaline rocks (diorites, quartz diorites,
microgranodiorites, microdiorites and andesites) (Berza et
al. 1982) intrude metamorphic rocks of the Median Dacides
belonging to Bucovinian units (Săndulescu 1994). Hydro-
thermal activity and mineralization processes are related to
the second and third intrusion phases.
Rodna—Bârgău area
This area is situated south of the Drago Vodă fault
(Fig. 1) and extends from the southern part of the Rodna
Mountains and continues over 75 km NE—SW below the
Călimani Mountains volcanic edifice. The main contribu-
tions to the knowledge of magmatic rocks in this area come
from Kräutner (1930), Athanasiu et al. (1956), Mânzăraru
(1965), Teodoru et al. (1973), Istrate in Kräutner et al.
(1978), Seghedi in Kräutner et al. (1990), Ureche (2000),
Ni oi et al. (2002), Papp et al. (2005).
A cluster of many subvolcanic intrusions with highly vari-
able geometries intrudes metamorphic rocks and Paleogene
and Miocene sedimentary deposits (Fig. 4), either as results
of a single moment of intrusion or multiphase intrusive ac-
tivity. Laccoliths are the most common type, as at Bucnitori,
Cornii, Heniu, Oala, Căsarul, Colibi a (e.g. Mânzăraru 1965;
Seghedi in Kräutner et al. 1990). They are always surround-
ed by swarms of smaller bodies which form an intricate sys-
tem of sills and dykes. Individual dykes and sills can be
followed along strike from several meters to several kilome-
ters. Hornfelses and, less frequently, breccias are present at
the contact with sedimentary rocks. Porphyritic texture with
fine-grained groundmass, allowing the usage of the effusive
nomenclature, is the most common rock fabric, suggesting
rapid cooling of magma in a shallow environment. The larg-
est dioritic-andesitic bodies (up to 10 km across) such as
Cornii, Heniul and Colibi a are mostly equigranular, fine-
grained or less frequently coarse-grained in their central part.
They commonly affected by propylitic and argillic hydro-
thermal alterations, sometimes associated with Cu, Pb, (Au)
mineralization. The rock-types of small individual bodies
range across a large petrographic spectrum: basalts, basaltic
andesites, andesites, dacites and rhyolites. The intrusions of
acidic composition (rhyolites and dacites, sometimes garnet-
bearing) mostly occur in the south-eastern part of the Rodna
Mts. A few of them with small dimensions (several tens or
hundred of meters in length) are located close to the Căli-
mani volcanic area. Frequent xenoliths are present mainly in
the intermediate to basic types (microdiorites, diorites, basal-
tic andesites and andesites) (Ni oi et al. 2002).
Radiometric age determination
Experimental techniques and sample preparation
About 200 g of each rock sample was crushed and sieved
to 300 µm. Adhering fine particles were removed by rinsing
in distilled water. Approximately 0.8 g of sieved rough sam-
ple was weighed for whole rock and amphibole and about
0.2 g for biotite. The amount of radiogenic
40
Ar was deter-
mined by the isotope dilution method using
38
Ar as a spike.
Mass discrimination of Ar isotopes was corrected by measur-
ing atmospheric Ar.
For the determination of K content, about 1 g of the identi-
cal sample that was used for Ar measurement was grounded
in an agate mortar to the grain size finer than 50 µm. About
100 mg of this powdered sample was dissolved in hydrofluo-
ric acid and nitric acid using a Teflon bomb. Potassium con-
tents were determined using flame photometry with Li
internal standard. The decay constants of Steiger & Jäger
(1977) were used in the age calculation. The inter-laboratory
standards Asia 1/65, HD-B1, LP-6 and GL-O as well as at-
mospheric Ar were used for control and calibration of analy-
ses. All analytical errors represent one standard deviation
(i.e. 68% analytical confidence level). Details of the instru-
ments, the applied methods and results of calibration have
been described elsewhere (Balogh 1985).
We dated whole rock samples, mono-minerals (amphibole
and biotite) or groundmass following thin section investiga-
tions. A standard technique (i.e. heavy liquids, magnetic sep-
arator) for mineral separation was used. The purity of the
mineral fraction was improved by handpicking. Biotite was
cleaned in ethyl-alcohol with ultrasonic cleaner with addi-
Fig. 3. Geological cross-sections showing age relationships between intrusive bodies. A – Runca intrusive body in the Poiana Botizei
area. B – The main intrusive body of the ible Mts. 1 – Pyroxene microdiorites; 2 – Biotite dacite/microgranodiorites; 3 – Amphib-
ole-bearing dacites (Tomnatec type); 4 – Quartz monzodiorites ( ible type); 5 – Pyroxene andesites (Arcer type); 6 – Paleogene flysch;
7 – K-Ar ages.
185
GEOCHRONOLOGY OF THE NEOGENE CALC-ALKALINE INTRUSIVE MAGMATISM (ROMANIA)
Fig. 4. Geological map of the Rodna—Bârgău area (according to the Geological map of Romania, scale 1 : 200,000; Geological Institute of
Romania). 1 – Metamorphic formations; 2 – Eocene sediments; 3 – Oligocene sediments; 4 – Oligocene—Lower Miocene sediments;
5 – Lower Miocene sediments; 6 – Middle-Upper Miocene sediments; 7 – Pleistocene sediments; 8 – Quaternary alluvial deposits;
9 – Intrusive bodies; 10 – K-Ar sample locations.
186
PÉCSKAY, SEGHEDI, KOVACS, SZAKÁCS and FÜLÖP
tional shaking. For the whole rock dating we selected the
samples that have not been affected by secondary alteration.
Results
Analytical results of 54 K-Ar age determinations of intru-
sive rocks from the PBTTRB are presented in Table 1 (new
results) and Table 2 (data previously published by Pécskay
et al. 1995b). Holocrystalline rocks are normally excellent
for dating as the high temperature mineral phases retain ra-
diogenic argon quantitatively. However, coarse-grained in-
trusive rocks can sometimes give inconsistent ages. The
most suitable radiometric datings have been acquired by anal-
ysing biotite and amphibole. Feldspars have not been used
since they easily lose radiogenic argon due to thermal effects.
Intrusive rocks are prone to slow cooling after emplacement
and may undergo thermal metamorphism that can rejuvenate
the rock and give younger apparent ages. Low
40
Ar-rad (%)
increase dramatically the analytical errors (e.g. sample BR-21;
Table 1). Therefore, our most important conclusions were
based on the samples with the highest
40
Ar-rad (%).
Figure 5 displays a synoptic view of all the available K-Ar
age data grouped according to the occurrence areas and rock
types. Although the intrusions in the Rodna and Bârgău ar-
eas suggest a quite homogeneous area, we presented them in
two groups according to a geographical divide separating the
Rodna Mts with metamorphic host rocks from the Bârgău
Mts with sedimentary host rocks. It is obvious that the em-
placement of intrusions spans a time interval of ca. 3.5 Myr
between ca. 11.5 and 8 Ma, entirely belonging to the Pan-
nonian time (according to Vass & Balogh 1987). Except for
Toroiaga, where very few data are available, there is no sig-
nificant difference between the age distributions of intrusive
rocks in the different areas. However, the intrusions in the
western part of the study area (Poiana Botizei and ible ) ap-
pear to have been generated during a shorter time interval
(2.5 Myr) since the youngest dated rocks are about 9 Ma old.
Figure 6 shows a statistical representation of the K-Ar data
available for the PBTTRB according to rock types and in
comparison with age ranges of volcanic activity and intru-
sive magmatism in the neighbouring Oa -Gutâi and Căli-
mani volcanic areas. More than 50 % of the K-Ar ages
cluster in the 10.5—9 Ma age interval. The two peaks appar-
ently reflect the most important pulses of intrusive activity in
the area. A third peak at the youngest ages around 8 Ma sug-
gests a sudden end of the intrusion emplacement after a short
final pulse. Although no systematic correlation between rock
types and age can be observed, it is worth mentioning that the
only dated rhyolite occurring at the boundary between the
Rodna and Bârgău Mts belongs to the youngest age group.
According to the available data, the inception of the intru-
sion emplacement in the PBTTRB is coeval with intrusive
activity spatially related to volcanism within the neighbour-
ing Gutâi and Călimani massifs (Fig. 6). On the other hand,
Sample# Lab#
Location
Rock
type
Dated
fraction
K
(%)
40
Ar rad
(ccSTP/g)
×10
–7
40
Ar rad
(%)
K-Ar age
(Ma)
BR-1
5956 Valea
Strâmbă-B mDi
wr
1.07
4.317
20.6
10.4±0.7
BR-2
5957
Valea Strâmbă-B
mDi Am
wr
0.71
2.371
31.9
8.6±0.4
BR-3
5958
Valea Strâmbă, forest road-B
mDi Am
wr
1.12
4.167
21.5
9.5±0.6
BR-4
5959 Sângeorz-Băi, Quarry-R
D Bi
wr
1.49
6.271
52.9
10.8±0.4
BR-5
5960 Măgura Rodnei, Someş v. quarry-R
D AmBi
wr
2.45
7.630
54.1
8.0±0.4
BR-6
5961
Vinului v., lower -R
A Am
wr
1.71
6.416
42.4
9.6±0.4
BR-7
5962
Vinului v., Upper-R
D BiAm
wr
Bi
2.74
7.21
8.504
22.51
25.7
68.5
8.0±0.4
8.0±0.3
BR-8
5963 Pleşilor v.-R
BA
wr
0.46
2.053
17.9
11.4±0.9
BR-9
5964 Pleşilor v., upstream-R
A GrAm
wr
0.94
3.755
52.2
10.3±0.4
BR-10
5965 Pleşilor v., Măgura Porcului-R
A Am (Bi)
wr
2.23
7.838
43.2
9.0±0.4
BR-11
5966
Vinului v., (Cormaia tributary) -R
D BiAm
Bi
7.17 22.39
45.4
8.0±0.3
BR-12
5967
Cormaia v., downstream Vinului v.-R
D Bi
Bi
7.04 27.23
30.2
9.9±0.5
BR-13
5968
Poiana Ilvei, quarry before tunnel-R
D AmGr
wr
1.10
4.085
52.1
9.5±0.4
BR-14
5969 Lunca
Ilvei,
Şant road-old quarry-B
A Am
wr
Am
1.51
0.67
5.188
3.344
50.2
11.9
8.9±0.4
12.7±1.5
BR-15
5970 Măgura Neagră Ivăneşti -B
A Am (Bi)
gm
1.52
6.563
31.1
11.1±0.5
BR-16
5981 Ivăneşti- Ivăneşti valley-B
BA Px
gm
1.92
6.956
14.7
9.3±1.0
BR-17
5972 Arsişa quarry, Măgura Arsiţei-B A
AmBi
wr
1.49
5.729
36.2
9.8±0.5
BR-19
5974
Zagra quarry-B
A Am
wr
1.03
3.492
45.6
8.7±0.4
BR-20
5975 Rebra,
Pietriş Hill-B
R
wr
3.08
9.674
70.1
8.0±0.3
BR-21
5976 Colibiţa, Căsărel Hill-B
BA PxAm
gm
Am
0.45
0.27
1.909
1.115
10.2
16.3
10.8±1.4
10.4±0.9
BR-22
5977 Tihuţa, Zîmbroiu Hill-B
A Am
wr
Am
1.70
0.63
5.979
2.163
43.0
20.8
9.0±0.4
8.8±0.6
BR-23
5978 W
Tihuţa, road side outcrop-B
BA PxAm
wr
0.62
2.253
22.9
9.3±0.6
BR-24
5979 W
Tihuţa, road side outcrop-B
A Am
wr
0.82
3.464
35.7
10.8±0.5
BR-25
5980 Mureşenii Bârgăului, road side quarry-B
A Am
wr
0.93
3.782
20.0
10.4±0.9
Areas: R – Rodna, B – Bârgău; Rock-types: BA – basaltic andesite, mDi – microdiorite, A – andesite, D – dacite, R – rhyolite;
Minerals: Am - amphibole, Px – pyroxene, Bi – biotite, Gr – garnet; Dated fraction: wr – whole rock, Am – amphibole, Bi – biotite,
gm – ground mass.
Table 1: Analytical results of K-Ar age determinations.
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GEOCHRONOLOGY OF THE NEOGENE CALC-ALKALINE INTRUSIVE MAGMATISM (ROMANIA)
Table 2: Published K-Ar age data (according to Pécskay et al. 1995).
Sample #
Location
Rock type
K-Ar age (Ma)
Poiana Botizei
PB-1
Runcaş Peak
mDiPx
11.2±0.9
PB-2
Roţii Valley
APx
11.1±0.7
PB-3
Ulmului Valley
mDiPx
10.4±0.6
PB-4
Poienii Valley
APx
10.3±0.5
PB-5
Rugului Valley
MDiPx
10.3±0.5
PB-6
Prisacele Peak
DBiAmPx
9.7±0.4
PB-7
Runcaş Peak
DBiAmPx
9.3±0.4
PB-8
Pietroasa Peak
QDiPx
9.3±0.5
PB-9
Izvorul Rugului V.
DPxAmBi
9.0±0.4
Ţibleş
T1
Stegioara Peak
QDiPx
11.5±0.5
T2
Stegioara Summit
QDiPx
10.9±0.5
T3
Hudieş Peak
DiPx
10.6±0.7
T4
Hudieş Summit
DiPx
10.2±0.4
T5
Hudin Peak
mGDiBiAmPx
10.0±0.4
T6
Arieşului Valley
mGDiBiAmPx
10.0±0.4
T7
Arcer gallery
MDiPx
9.8±0.5
T8
Cascadelor Valley
MDiPx
9.6±0.4
T9
Arcer Peak
APx
9.4±0.9
Toroiaga
TR1
Secului Valley
GDiBi
9.7±0.5
TR2
Secului Valley
GDiBi
9.6±0.4
TR3
Toroiaga Summit
ABi
9.0±0.6
Rodna
R535
Măgura Rodnei
DAmBi
8.6±0.4
RD7
Cormaia Valley
ABiAm
9.0±0.5
Bârgău
RD5
Măgura Sturzii quarry
DBiAm
10.6±0.7
RD3
Runcu quarry
DiPx
10.4±0.8
RD9
Cornii drill 3/470
DiAm
9.9±0.7
RD8
Cornii drill 11/670
DiAm
9.8±0.8
RD1
Turnuri quarry
DiAm
9.3±0.4
RD6
Zagra quarry
AAm
9.1±0.6
RD2
Chicera-Arşiţa
GbDiPx
8.8±0.5
Rock-types: Di – diorite, mDi – microdiorite, Mdi – monzodiorite,
GDi – granodiorite, mGDi – microgranodiorite, QDi – quartz-diorite,
GbDi – gabbrodiorite, A – andesite, D – dacite;
Minerals: Am – amphibole, Px – pyroxene, Bi – biotite.
Fig. 5. Summary of K-Ar age determinations clustered according to the occurrence areas shown within the chronostratigraphic scale of
Vass & Balogh (1989). Individual K-Ar ages are displayed with error bars. Rock types are shown by symbols: circles – gabbro-diorites
and basalts/basaltic andesites; squares – diorites and andesites; triangles – granodiorites and dacites; diamonds – rhyolites.
intrusions continued to be emplaced in the PBTTRB until ca.
8 Ma, after the roughly simultaneous interruption of intru-
sive activity in Gutâi and Călimani ca. 9.2 Ma. Intrusive
magmatism resumed for ca. 1 Myr in Gutâi and Călimani
roughly at the time when the youngest intrusions were em-
placed in the PBTTRB ca. 8 Ma (Fig. 6).
K-Ar ages of the main magmatic rock types in the Poiana
Botizei area range between 11.2—10.3 Ma for the intermedi-
ate-basic rocks and 9.7—9.0 Ma for the more acidic rocks.
These data are in agreement with the field evidence: micro-
granodiorites/dacites dated to 9.3 Ma pierce the 11.2 Ma mi-
crodiorites in Runca Peak (Fig. 3A).
Besides the nine age determinations from magmatic rocks
belonging to the two main phases in the ible Mts (Table 1,
Fig. 5) three K-Ar ages were obtained from postmagmatic
minerals (phlogopite from magnesian skarns and illite from
hydrothermal veins; Kovacs et al. 1997). The dacitic rocks of
the larger intrusions are ca. 10 Ma (two determinations).
9.8—9.4 Ma is the age interval of the main monzodioritic in-
trusion and its ring. Small intrusions from the north-western
part of the complex cluster between 11.5—10.2 Ma. These
ages confirm the observed field relationships between the
rocks of the two main phases (the quartz monzodiorites of
the ible -Bran-Măgura Neagră pierce the Tomnatec dacites,
Fig. 3B). The small andesitic-dioritic intrusions emplaced
outside the ring in the north-western part of the mountains
are slightly older than the rocks of the larger intrusions. The
radiometric age of phlogopite from the magnesian skarns
(10.0 ± 0.5 Ma; Kovacs et al. 1997) in the contact area of the
monzodioritic main intrusion, found in a mining gallery,
confirms the age of the generating intrusion. The 7.8 and
8.0 Ma ages obtained from two illite samples from hydro-
thermal veins (Kovacs et al. 1997) near the main monzodior-
itic intrusion are consistent with the ages obtained from the
fresh igneous rocks.
188
PÉCSKAY, SEGHEDI, KOVACS, SZAKÁCS and FÜLÖP
In the Toroiaga Massif only Vertic granodiorites (9.7 and
9.6 Ma) and Toroiaga andesites (9.0 Ma) have been dated.
The ages of the rocks are comparable with the ages of the in-
termediate rocks from ible Mts and Rodna—Bârgău area.
However, the much shorter time interval may reflect rather
the scarcity of radiometric age data than the real age range of
intrusion emplacement.
No obvious relationships could be pointed out between rock
types and intrusion ages in the Rodna and Bârgău areas
(Fig. 5). The K-Ar ages are in agreement with geological ob-
servations on a local scale suggesting the emplacement of dif-
ferent rock compositions in individual bodies at various time
intervals. The obtained ages are relevant for emplacement
times of the small-sized intrusions, while in the case of the
large bodies (Cornii, Heniul and Colibi a) the emplacement
history cannot be resolved yet. However, the data suggest
long-range development of intrusive activity for those bodies
for which multiple datings are available (e.g. 10.6—8.4 Ma for
Heniu, 9.9—8.9 Ma for Cornii).
Discussion
The PBTTRB represents the eastern segment of the arc-type
Carpathian magmatic front which attained its maximum
length (ca. 700 km) in the ca. 12—10 Myr time interval (Sza-
kács et al. 2007). The western segment of the same magmatic
front includes a number of small-sized intrusions in eastern
Moravia and in the Pieniny area in Poland (Pécskay et al.
1995a and Pécskay et al. 2006) with no trace of volcanic activ-
ity, while its central segment is volcanic. The PBTTRB intru-
sive activity is delayed (11.5—8 Ma) compared to that of the
Eastern Moravia-Pieniny intrusions (13.5—10.8 Ma; Pécskay
et al. 1995a, 2006). This evolutionary pattern records a pro-
gressive extension of the magmatic front in the 15—10 Myr
time interval which is, in fact, the only period during which a
clearly defined magmatic front was present along the Car-
pathian arc (Szakács et al. 2007).
Fig. 6. Histogram with K-Ar age distribution of intrusive rocks in the PBTTRB in comparison with the time intervals of volcanic activity
and intrusive magmatism in the neighbouring Oa -Gutâi and Călimani massifs.
Links between intrusive magmatism and regional geody-
namics
Tischler et al. (2006) invoke sinistral transpression 16 to
12 Ma along the Bogdan Vodă fault that shifts to sinistral tran-
stension 12—10 Ma along the coupled Bogdan-Drago -Vodă
fault system. The coeval inception of intermediate intrusive
activity ca. 11.5 Ma might be explained speculatively as a re-
sponse to the change in the regional tectonic regime from
transpressional to transtensional 12 Ma (Tischler et al. 2006)
allowing magma ascent and shallow intrusion emplacement.
The spatial distribution of intrusive bodies in the PBTTRB
does not show a direct relationship with the main trace of the
Drago Vodă fault. They are rather controlled by secondary
conjugate extensional faults (NW—SE and NE—SW) located
both to the North (Toroiaga) and South (Poiana Botizei,
ible , Rodna—Bârgău) of the main fault trace.
Conclusive petrological studies are missing in this area.
Seghedi et al. (1995) concluded that most of the acidic rocks
in the PBTTRB were derived from crustal melts rather than
from differentiation of a basic parent magma, resulting from
melting in the lithospheric mantle. The recent geochemical
and isotopic studies in the Rodna—Bârgău area (Ni oi et al.
2002; Papp et al. 2005) account for different magma sources
to explain the large diversity of rock types; it is suggested that
each intrusion evolved independently with specific fraction-
ation, crustal assimilation and/or magma mixing processes.
Sinistral transpressional (16—12 Ma) followed by sinistral
transtensional (12—10 Ma) stress regimes along the Bogdan-
Drago -Vodă fault system (Tischler et al. 2006) controlled the
generation and emplacement of intrusive bodies ca. 12—8 Ma
as related to the melting of the local heterogeneous mantle
lithosphere, that was previously fertilized via subduction
processes (e.g. Seghedi et al. 2004). The resulting rocks
show one of the most composite petrographic varieties in the
entire Carpathian-Pannonian region.
The estimation of intrusion depths of the subvolcanic bod-
ies looks very important for the understanding of possible re-
189
GEOCHRONOLOGY OF THE NEOGENE CALC-ALKALINE INTRUSIVE MAGMATISM (ROMANIA)
lationships with volcanism especially related to larger bodies
( ~ 10 km across), but a detailed assessment is missing. Such
bodies may represent magma chambers to feed volcanism on
the surface. Volcanic deposits possibly emplaced on the sur-
face could be eroded away completely due to the strong up-
lift of the study area (e.g. at least 1 km in the Rodna Mts) as
pointed out by exhumation histories according to fission
track studies (e.g. Tischler et al. 2006), but no volcanic prod-
ucts have been identified so far in the PBTTRB area.
Conclusions
The intrusive magmatism located in the internal Eastern
Carpathians of Northern Romania (PBTTRB) developed
over ca. 3.5 Myr during Pannonian times. The inception of
intrusive activity was roughly coeval in the Poiana Botizei,
ible and Rodna—Bârgău areas ca. 11.5 Ma. Most intrusions
were emplaced in the 9—10.5 Myr time interval. The latest
intrusions are obviously older (ca. 9 Ma) in the western part
of the area (Poiana Botizei and ible ) than in the east (ca.
8 Ma in Rodna—Bârgău). There is no obvious relationship
between rock-types and age, but the only rhyolitic rocks be-
long to the youngest age group. The tighter age spectrum of
Toroiaga intrusions probably reflects the very few radiomet-
ric age determinations available as compared to the other oc-
currence areas. In the 8—9 Ma age interval the PBTTRB is
the only area in the Eastern Carpathians where intrusive
magmatism took place, whereas around 11.5—9 Ma intru-
sions were also emplaced in the neighbouring Oa -Gutâi and
Călimani volcanic massifs. It is interesting to note that the
end of intrusive magmatism in the PBTTRB (8 Ma) coin-
cides with the reactivation of intrusion emplacement in both
adjacent areas; the geodynamic significance of these devel-
opments are to be unraveled by future studies. The PBTTRB
area was characterized during Pannonian time by a complex
transpressional-transtensional tectonic regime (Tischler et al.
2006) that gave way to magma emplacement processes dur-
ing continental lithosphere transtension at ~ 12 Ma that con-
trolled all major phases of shallow intrusions.
Acknowledgments: The financial support for this research
work was provided by the Hungarian National Scientific
Fund (OTKA No. K68153). The field-work has been done in
the framework of bilateral agreements between the Roma-
nian Academy and Hungarian Academy of Sciences during
1995—2004. The Institute of Nuclear Research of the Hungari-
an Academy of Sciences (ATOMKI) and the Institute of Geo-
dynamics of Romanian Academy are acknowledged. The
authors wish to thank, Krzysztof Birkenmajer, Vladica Cvet-
ković and the responsible editor Jaroslav Lexa for the critical
reading of the manuscript and for their constructive reviews.
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Poiana Botizei:
Diorites/quartz diorites: Pl–62—78 %, Px–18—30 %, Q–2—7 %;
Porphyritic texture: phenocrysts (Pl–35—55 %, Px–15—25 %);
groundmass–holocrystalline (25—50 %);
Porphyry quartz monzodiorites: phenocrysts (Pl–26—45 %,
Px–10—25 %); groundmass–holocrystalline (35—60 %) with graphic
intergrowths;
Porphyry microgranodiorites/dacites: phenocrysts (Pl–23—30 %,
Px–2—8 %, Am–1—5.5 %, Bi–0.5—3 %, Q–0.5—2.2 %); ground-
mass (56—63 %), holocrystalline, equigranular or microlithic;
Andesites: phenocrysts (Pl–13—30 %, Px–6—17 %, Am–0—3 %,
Bi–0—2 %); groundmass (53—82 %), microlithic to microgranular.
ibles:
Diorites/quartz diorites: phenocrysts (Pl–40—60 %, Px–3—
15 %, Am–0.5—6 %, Bi–1—7 %, Q–2—10 %); groundmass (20—
43 %) equigranular to porphyric microgranular (Hudie and Stegioara);
Quartz monzodiorites: phenocrysts (Pl–18—48 %, Px–2.5—
10 %, Am–2—9 %); groundmass (20—50 %), holocrystalline with
graphic intergrowths, or Pl–40—68 %, K-feldspar–5—20 %, Q–6—
15 %, Px + Am–15—25 % (Arcer gallery);
Microgranodiorites: phenocrysts (Pl–20—30 %, Bi–2—10 %,
Px–2—7 %); groundmass (58—70 %), microgranular with quartz and
K-feldspar (Hudin);
Andesites: phenocrysts (Pl–36—50 %, Px–2—12 %); ground-
mass (46—65 %), microgranular to cryptocrystalline (Arcer);
Dacites: phenocrysts (Pl–20—35 %, Px–4—12 %, Am–1—3 %,
Bi–0—4 %); groundmass (62—70 %), microgranular to pilotaxitic
(Tomnatec).
Toroiaga:
The petrography and the modal data of the main rock types are ac-
cording to Berza et al. (1982 and 1984), as follows:
Diorites and andesites show similar composition but contrasting
Appendix
Main petrographic types together with the modal data
grain-size: phenocrysts (Pl–55 %, Px–1.5—5 %, Am–7.5 %, Bi–
7.5 %, Q–1.5 %); microgranular, cryptocrystalline or granophyric
groundmass ~ 25—30 %; (Secu-Nova and Toroiaga);
Andesites: phenocrysts (Pl–25 %, Am–2.5 %, Bi–3 %, Q–
2.5 %); microlithic to cryptocrystalline groundmass ~ 67 % (Piciorul
Caprei);
Andesites-dacites: phenocrysts (Pl–35 %, Am–3.5 %, Bi–
7 %, Q–3 %); microgranular to cryptocrystalline groundmass
~
45 % (Vertic);
Quartz adesites-dacites: phenocrysts (Pl–35 %, Am–3 %, Bi–
7 %, Q–2.5 %); microgranular to cryptocrystalline groundmass
~
52.5 % (Novicior).
Rodna—Bârgău:
Microdiorites, diorites or gabbrodiorites: phenocrysts (Pl–55—
59 %, Px–1.5—9 %, Am–5—7.5 %, Bi–0—3 %, Q–0—2 %);
groundmass ~ 20—35 % – medium—microgranular or granophyric;
Amphibole-garnet-bearing microdiorites/microgranodiorites or
andesites and dacites: phenocrysts (Pl–20—28 %, Am–4—7 %, Q–
1—3 %, Gn–1—3 %), groundmass–microgranular (75—65 %);
Basaltic andesites and basalts: phenocrysts (Pl–2—3 %, Am–0—
5 %, Cpx–2—3 %), groundmass–microgranular (90—75 %);
Amphibole pyroxene andesites: phenocrysts (Pl–16—24 %,
Am–7—10 %, Cpx–5—8 %, Opx–1—2 %), groundmass–micro-
granular (70—60 %);
Amphibole andesites: phenocrysts (Pl–18—26 %, Am–10—
14 %), groundmass–microgranular (70—60 %);
Amphibole-biotite andesites: phenocrysts (Pl–20—28 %,
Am–3—6 %, Bi–1—4 %, Q–1—3 %), groundmass–microgranular
(75—60 %);
Dacites: phenocrysts (Pl–10—24 %, Q–2—4 %, Am–5—8 %, Bi–
1—3 %), groundmass–microgranular to cryptocrystalline (80—65 %);
Rhyolites: phenocrysts (Pl–5—12 %, Q–2—4 %, Bi–1—4 %),
groundmass–cryptocrystalline (90—80 %).