Extension-related Miocene calc-alkaline magmatism in the Apuseni Mountains, Romania

20 Pages·2005·1.01 MB·English

Schweizerische Mineralogische und Petrographische Mitteilungen 84, 153–172, 2004
Extension-related Miocene calc-alkaline magmatism in the
Apuseni Mountains, Romania: Origin of magmas
Emilian Ros¸u 1, Ioan Seghedi 2, Hilary Downes 3, David H. M. Alderton 4, Alexandru Szakács 2,
Zoltan Pécskay 5, Cristian Panaiotu 6, Cristina Emilia Panaiotu 6 and Liviu Nedelcu 1
Abstract
The Miocene magmatism of the Apuseni Mountains in the Carpatho-Pannonian area hosts some of Europe’s largest
porphyry epithermal Cu–Au ore systems associated with shallow subvolcanic intrusions. Detailed field observations
combined with K–Ar ages, geochemical analyses, Sr–Nd isotopes and paleomagnetic data constrain a model for the
geotectonic evolution and processes of melt generation that may account for the exceptional mineralizing potential
of the magmatic activity in this region. The magmatic activity developed mainly between 14.7 and 7.4 Ma and after a
gap ceased at around 1.6 Ma. Geotectonic conditions do not support contemporaneous subduction processes, but
were represented by transtensional and rotational tectonics, which generated horst and graben structures and fa-
voured the generation and ascent of magmas. The “subduction signature” of the magmas emphasizes the significant
involvement of fluids (mantle lithosphere and/or lower crust) inherited during previous geodynamic events. The
mechanism of magmagenesis is considered to be related to decompressional melting (various degrees of) of a hetero-
geneous source situated at the crust-lithosphere mantle boundary. Mixing with asthenospheric melts generated dur-
ing the extension-related attenuation of the lithosphere may also be implied. The evolution from normal to adakitic-
like calc-alkaline and alkaline magmas generally is time-dependent as a consequence of variable fluid-present melt-
ing. Fractional crystallization-assimilation processes in shallow magma chambers are suggested for early magmatism
but were almost absent from later magmatism, which related to an increasingly extensional regime. The youngest
alkalic (shoshonitic) magmatism (1.6 Ma) is asthenosphere-derived, but in a different extensional event, being al-
most coeval with the OIB-like alkali-basaltic magmatism (2.5 Ma) occurring along the South Transylvanian fault. The
fluid-present melting of the source seems to be the critical factor for the presence of the copper-gold-bearing miner-
alizing fluids.
Keywords: Romania, Apuseni Mountains, Miocene, calc-alkaline, alkaline, adakite-like, extension.
Introduction models, which invoke subduction-related process-
es (e.g. Rădulescu and Săndulescu; 1973; Bocaletti
Neogene calc-alkaline and alkaline magmatic et al., 1973; Bleahu, 1974) have so far failed to ex-
rocks in the Apuseni Mountains (Romania) crop plain the unusual position of this volcanism. In
out either in intra-mountain basins such as the ca. contrast, some authors (Roșu et al., 1996; Balin-
100 km long Zarand-Brad-Zlatna Basin, or in a toni and Vlad, 1998; Seghedi et al., 1998) have sug-
cluster of magmatic bodies that are orientated gested that these Neogene calc-alkaline to alka-
roughly NW–SE (Fig. 1). The isolated position of line magmas were generated in response to exten-
these magmatic products with respect to the Car- sion of the lithosphere.
pathian fold-and-thrust belt, some 200-km behind Neogene magmatism is accompanied by sig-
the East Carpathian main volcanic arc, is striking. nificant metallogenetic activity, particularly for
Although a “subduction signature” has been al- Cu–Au (Mo), together with Au–Ag ± Te and base
ready demonstrated for the volcanic rocks (e.g. metal mineralization (Udubașa et al., 2001). How-
Borcoș et al., 1972; Roșu et al., 1996), geotectonic ever, not all the intrusions are accompanied by
1 Geological Institute of Romania, str. Caransebeș, 1, 78344 Bucharest 32, Romania. <[email protected]>
2 Institute of Geodynamics, 19-21, str. J.-L. Calderon, 70201 Bucharest, Romania.
3 Research School of Earth Sciences at UCL/Birkbeck, University of London, Malet St., London WC1E 7HX, UK.
4 Department of Geology, Royal Holloway, London University, Egham, Surrey TW20 OEX, UK.
5 Institute of Nuclear Research of the Hungarian Academy of Sciences, P.O. Box 51, Bem ter 18/c, H-4001 Debrecen,
Hungary.
6 University of Bucharest, Paleomagnetism Laboratory, Bălcescu 1, 70111 Bucharest, Romania.
0036-7699/04/0084/153 ©2004 Schweiz. Mineral. Petrogr. Ges.
154 E. Ros¸u et al.
1
g.
Fi
Extension-related Miocene magmatism in the Apuseni Mountains, Romania 155
mineralization. A variety of mineral deposit types low lava and sheeted dykes (Savu, 1996; Nicolae,
are present including porphyry copper, low-sulfi- 1995) and Jurassic calc-alkaline volcanics (Nico-
dation and rarer high-sulfidation epithermal lae, 1995), as well as Lower to Upper Jurassic
veins, breccia pipes and replacement bodies. ocean-floor and continental shelf sediments, and
The purpose of this paper is to describe and Lower Cretaceous flysch and wildflysch (Lupu,
interpret the nature and origin of calc-alkaline 1976). Calc-alkaline intrusive rocks pierced the
and alkaline Neogene magmas in the Apuseni ophiolitic basement during Late Jurassic–Early
Mountains. The presence of adakite-like charac- Cretaceous times (Ștefan, 1986; Nicolae, 1995).
teristics as pointed out by Roșu et al (2001) re- During the Late Cretaceous–Paleogene times,
quires reconciling the “subduction signature” of “banatitic” magmatism developed along a N–S
the magmatic rocks with their unusual tectonic alignment crossing through both the Apuseni
setting. This contribution provides a new insight Mountains and the western part of the South Car-
into the generation of calc-alkaline magmatism in pathians and Dinarides (Ștefan et al., 1992; Berza
a tectonic setting, which was not subjected to sub- et al., 1998), and was partly coeval with Maastrich-
duction, on the basis of a review of existing and tian–Paleocene molasse deposition. Post-Paleo-
new geochemical and isotopic data. cene tectonic uplift of the whole area interrupted
sedimentation until it resumed in Early–Middle
Miocene times. The post-suture (i.e. post-Lara-
Geologic and tectonic setting mian) evolution of the Apuseni Mountains is relat-
ed to brittle tectonics (Royden, 1988; Săndulescu,
In recent geotectonic models of the Carpathian- 1988) during the Paleogene–Neogene interval as
Pannonian region (e.g. Csontos, 1995), the Apuse- a consequence of its behaviour as a single rigid
ni Mountains are part of the Tisia (Tisza-Dacia) block (Tisia block). This tectonic style, mainly
lithospheric block, whose eastward translation, marked by horst and graben structures, which are
along with the Alcapa block, constituted the ac- visible mostly along the northern and western
tive driving force of the Carpathian collision and edges of the Apuseni Mountains (Fig. 1), is a con-
consequent orogenesis during Cretaceous to Mio- sequence of the Neogene extensional develop-
cene times (Royden, 1988; Săndulescu, 1988; ment of the neighbouring Transylvanian and Pan-
Royden and Burchfiel, 1989; Csontos et al., 1992; nonian Basins (Fodor et al., 1999), as well as of the
Csontos, 1995). Paleomagnetic data demonstrate translational and rotational movements of the Ti-
that during Eocene-Early Miocene times, the Ti- sia block (Pătrașcu et al., 1994; Csontos, 1995; Pa-
sia block experienced a 20° clockwise rotation at naiotu, 1998; Seghedi et al., 1998; Roșu et al.,
the same time as the Alcapa block underwent 2000). From Badenian times the Apuseni Moun-
counterclockwise rotation. The Apuseni Moun- tains formed the high-relief part of the Tisia block,
tains underwent a further 60° clockwise rotation left upstanding after the general subsidence of the
after cessation of the counterclockwise rotation Pannonian and early Transylvanian basins. Devel-
of the Alcapa block. This rotation started around opment of the Neogene volcanism was closely re-
14 Ma, diminished at 13 Ma to around 28° and lated to this extensional evolutionary stage of the
ceased at around 12 Ma (Panaiotu, 1998, 1999). Apuseni Mountains, as part of the Tisia block.
The northern Apuseni Mountains have a base-
ment of metamorphic rocks and associated anatec-
tic Hercynian granites, belonging to the Inner Spatial distribution of Neogene volcanic rocks
Dacides (Ianovici et al., 1969, 1976; Săndulescu,
1984; Balintoni, 1994, 1997), with a Permian post- The overall spatial distribution of Neogene mag-
tectonic sedimentary and volcanic cover (Stan, matic rocks in the southern Apuseni Mountains
1987). The southern Apuseni Mountains are dom- (Fig. 1) strongly suggests a NW–SE oriented de-
inated by the Tethyan ophiolitic suture zone velopment of the igneous activity and a connec-
(Săndulescu, 1984), including Lower-Jurassic pil- tion with coeval Miocene sedimentation in exten-
Fig. 1 Sketch map of Neogene volcanic rocks in the Apuseni Mountains and location of analyzed samples: open
squares—K–Ar ages and geochemical data; open triangles—K–Ar ages only; open circles—geochemical data only.
All ages are in Ma (boxed), samples numbers in brackets refer to Table 1. Light grey background shading: grouping
of volcanic centres as in Fig. 2. Inset: geological sketch of Carpathian-Pannonian realm showing Apuseni Mountains
and Moigrad occurrence (boxed). Regional map with schematic deformation structures during Middle Miocene
after Maţenco (1997). Symbols: 1a —internal basement; 1b—ophiolite belt; 2—Neogene magmatic rocks; 3—thin-
skinned belt; 4—autochthonous foreland and intra/inter-mountain depressions; 5—dextral/sinistral fault; 6—normal
fault; 7—thrust fault.
156 E. Ros¸u et al.
sion-controlled small basins (Roșu et al., 1997; Petrography
Ciulavu, 1999). However, closer examination of
the spatial occurrence of the outcrops reveals a The Neogene magmatic rocks in the Apuseni
more complicated pattern (Fig. 1). Most magma- Mountains range from basaltic-andesites to da-
tic rocks are distributed along a WNW–ESE cites, with subordinate occurrences of alkaline af-
trend, especially between Miniș in the west and finity. However, andesite is the most common and
Zlatna in the east, within a ca. 100 km long area. volumetrically the prevalent rock-type (Fig. 1).
Many of the igneous rocks are concentrated in the Basaltic andesites are present as two small-scale
eastern half of the area and apparently follow a occurrences in the Detunata hills, but also occur
NNE–SSW trend, ca. 60 km long, between Baia de in the Zarand area. These rocks are slightly por-
Arieș in the north and Deva in the south (Fig. 1). phyritic, with plagioclase, augite, olivine and re-
These two “alignments” (we use the term “align- sorbed amphibole microphenocrysts in a ground-
ment” without any genetic or tectonic connota- mass of plagioclase microlites and augite, magne-
tion) cross each other at the south-eastern end of tite, ilmenite, olivine, resorbed amphibole and
the WNW–ESE “alignment”. glass (Savu et al., 1993).
Along the NNE–SSW “alignment” magmatic Andesites display a large spectrum of varie-
rocks occur in several volcano-intrusive struc- ties. Two-pyroxene andesites are abundant in the
tures (Roșu et al., 1997). From north to south they Zarand Mountains. They contain abundant clino-
are: (1) Baia de Arieș, Roșia Montană-Bucium; and orthopyroxene phenocrysts, generally show-
(2) Zarand, Brad, Zlatna; (3) Săcărâmb and (4) ing corroded and opaque rims. Amphibole ± py-
Deva, where we include also the youngest activity roxene andesites are present mostly in the eastern
at Uroi (Fig. 2). There is an additional, isolated, half of the region. They are largely porphyritic
small-scale occurrence at the northernmost edge and have plagioclase, amphibole, clino-orthopy-
of the Apuseni Mountains at Moigrad, located roxene, and sometimes, corroded quartz and ac-
about halfway between the Southern Apuseni cessory Fe–Ti oxides, apatite, zircon, sulphides
and the Oaș-Gutâi Neogene volcanic areas (Fig. and Cr-spinels. Rare garnet-bearing varieties can
1) (Ștefan et al., 1986). be found at Zlatna, Bucium and in the Brad areas.
Fig. 2 Time evolution of volcanic activity in the Southern Apuseni Mountains. Symbols for rock types (black sym-
bols are normal calc-alkaline rocks, open symbols are adakite-like calc-alkaline rocks): squares—dacites; circles—
andesites; diamond—basalts andesites; triangle—alkaline rocks. (see Fig. 1 for area locations). K–Ar ages from
Pécskay at al. (1995), Roșu et al. (1997) and this study.
Extension-related Miocene magmatism in the Apuseni Mountains, Romania 157
Amphibole-biotite ± pyroxene andesites occur in Besides the above-mentioned lithologies,
the Săcărâmb, Deva and Baia de Arieș areas. The which are characterized by normal calc-alkaline
main phenocrysts are plagioclase, amphibole, bi- compositions, there are a few small-scale occur-
otite, two pyroxenes and the same accessory min- rences of alkaline rocks in the south-eastern part
erals as for the amphibole ± pyroxene andesites. of the region. Two of them occur in the Săcărâmb
These rock types also often contain quartz pheno- area (trachyandesite and microdiorite plotted in
crysts. The spatial distribution of different types of the basaltic trachyandesite field in Fig. 3) and the
andesites seems to follow a systematic trend, with third, a trachyandesite body, at Uroi in the south-
the more basic pyroxene-bearing varieties in the eastern extremity of the region (Fig. 3). Trachy-
west, and more acidic, amphibole and biotite- andesite from Zâmbriţa is slightly porphyritic,
bearing varieties in the east and towards the ex- dark, and contains plagioclase, amphibole, two
tremities of the NNE–SSW “alignment”. Interme- pyroxenes, biotite and quartz as micropheno-
diate-type, amphibole-pyroxene andesites occur crysts in a microgranular groundmass of the same
in between. Andesites and porphyritic microdio- composition, as well as apatite, zircon, magnetite,
rites also occur as a cluster of small intrusive bod- ilmenite and Cr-spinels as accessories. The micro-
ies at Moigrad. Their phenocryst assemblage in- diorites from Pârâul lui Toader contain several
cludes plagioclase, clinopyroxene and sporadic generations of plagioclase, amphibole substituted
orthopyroxene and amphibole, and sometimes bi- either by clinopyroxene or an aggregate of
otite (Ștefan et al., 1986). clinopyroxene, plagioclase, quartz and biotite,
Altered dacites are present as clasts in ~15 Ma fresh amphibole, clinopyroxene along apatite, zir-
intra-basinal volcaniclastic and sedimentary de- con, magnetite, ilmenite and sulphides as accesso-
posits (Cioflica et al., 1966; Roșu et al., 1997). They ries. The Uroi trachyandesites (according to a
display a phenocryst assemblage of plagioclase, TAS diagram) or shoshonites (according to a KO
2
quartz, biotite and minor amphibole. Dacite intru- vs. SiO diagram) closely resemble the sho-
2
sions are mostly found in the Roșia Montană area, shonites, which occur at the southeastern end of
showing porphyritic textures with plagioclase, the East Carpathian volcanic range (Seghedi et
quartz, amphibole and biotite as phenocrysts, and al., 1986, 1987; Mason et al., 1996). They display a
magnetite, ilmenite, apatite and zircon as acces- disequilibrium mineral assemblage containing Ti-
sory minerals in a microgranular groundmass. augite, hypersthene, amphibole and biotite
Fig. 3 SiO vs. KO+NaO diagram for Neogene Apuseni magmatic rocks (classification after Le Bas et al., 1986).
2 2 2
Legend: Rocks in the age interval: 14.7-13.5 Ma — open circles; 13.5-12 Ma — open squares; 12-10 Ma — filled
triangles; 10-7.4 Ma — open triangles; ~1.6 Ma — open diamonds.
158 E. Ros¸u et al.
Table 1
Extension-related Miocene magmatism in the Apuseni Mountains, Romania 159
Table1 Sample location, rock type, lithology and K–Ar ages (whole rocks) for Neogene magmatic rocks in Apuseni
Mountains. Abbreviation: (cid:1)—andesite, (cid:1)(cid:2)—basaltic andesite, (cid:3)(cid:1)—trachyandesite, m(cid:4)—microdiorite, (cid:5)—dacite:
am— amphibole, bi—biotite, px—pyroxene, q—quartz. Sources of K–Ar ages are from: (1) Pécskay at al., 1995; (2)
Roșu et al., 1997; (4) this study. Geochemical data are from: (3) Alderton et al., 1998 and Alderton and Fallick, 2000;
(5) this study.
phenocrysts and accidental quartz xenocrysts, and Nd have also been analyzed using this tech-
many with reaction rims (Savu et al., 1994). nique for all the samples.
REE concentrations (Table 3) were deter-
mined for selected samples by Inductively Cou-
Sampling and analytical techniques pled Plasma Atomic Emission Spectrometry
(ICP-AES) at Royal Holloway, using the meth-
We used 40 samples for the geochemical and iso- od described by Walsh et al. (1981). Powdered
topic study (Table 2), some of which are already samples (0.5 g) were dissolved in HF and HClO .
4
published in Roșu et al. (2001), Alderton et al. The residue was ignited and fused with NaOH,
(1998) and Alderton and Fallick (2000). Most of and the solution was passed through ion ex-
the samples have been dated by the K–Ar method change columns, which separated and concen-
(Roșu et al., 1997; Pécskay et al., 1995a); results trated the REE before analysis. In-house stand-
for some are presented for the first time here ards were also analyzed to check the accuracy of
(Table 1). Sample selection took account of fresh- the method.
ness (limited amount of hydrothermal alteration) Sr–Nd isotope ratios were determined using
spatial coverage, and lithological representation the VG-354 5-collector mass spectrometer at the
of Neogene magmatism in the Apuseni Moun- University of London radiogenic isotope facility,
tains, plus Moigrad at its northern periphery. Thus, with Nd analyzed as oxide (Thirlwall, 1991).
the data set can be considered as being represent- Measured Sr and Nd isotope standard ratios for
ative for the Miocene igneous activity in the 87Sr/86Sr on SRM987 and 143Nd/144Nd on an in-
Apuseni Mountains. house “Aldrich” standard were 0.710248 and
For K–Ar age determination approximately 0.511420 (equivalent to La Jolla of 0.511857;
500 mg was used for Ar analysis. An Ar extraction Thirlwall, 1991). Results are shown in Table 2. No
line and a mass spectrometer were used for the Ar age corrections were made since they are not sig-
measurement. Approximately, 100 mg of the pul- nificant for 87Sr/86Sr at ~10 Ma.
verized material was digested in HF with the ad-
dition of some sulphuric and perchloric acids for
the K measurements. 100 ppm of Na and Li were Age and time-space evolution
added as buffer and internal standard. K concen-
tration was measured with a digitalized flame Neogene magmatic rocks in the Apuseni Moun-
photometer of OE-85 type manufactured in Hun- tains range in age from 14.7 to 7.4 Ma, except for
gary. The inter-laboratory standards HD-B1, GL- one occurrence (Uroi), which is 1.6 Ma old (Péc-
O, LP-6 and Asia 1/65 were used for calibration. skay et al., 1995a; Roșu et al., 1997, 1998, 2000).
Details of the instruments, the applied methods The general time-space evolution of volcanism is
and results of calibration have been described presented in Figs. 1 and 2. Compared with other
elsewhere (Balogh, 1985). The results of the K–Ar Neogene volcanic areas of the Carpathians, the
age determination are summarized in Table 1. magmatic rocks in the Apuseni Mountains are
Analytical ages were calculated according to the roughly coeval with those from the Tokaj-Slanske
constants of Steiger and Jäger (1977). All analyti- area and Vihorlat-Beregovo-Oaș-Gutâi-Ţibleș
cal errors represent one standard deviation (i.e. arc segment (Pécskay et al., 1995b, 2000; Roșu et
68% analytical confidence level). al., 1997).
Major and trace element data (Table 2) were The earliest volcanic rocks are Lower Bade-
obtained on a Philips PW1480 X-ray fluorescence nian (ca. 15 Ma old) dacitic tuffs, the age of which
(XRF) spectrometer at the University of London is inferred from stratigraphic relationships with
XRF facility at Royal Holloway. Major element paleontologically dated Miocene sediments
oxides were determined on fused glass discs and (Roșu et al., 1997). Intermediate calc-alkaline
trace elements on pressed powder pellets, with magmatic activity has produced complex volca-
matrix correction calculated from major element no-intrusive structures. Except for lava flows and
compositions. Analytical reproducibility for most associated volcaniclastic deposits in the Zarand
trace elements is ± 1 ppm (2SD), but is about ± 0.3 Mountains, most of the porphyritic andesites oc-
ppm for Nb, Y and Rb. The REE elements La, Ce cur as small intrusive bodies (Roșu et al., 1997).
160 E. Ros¸u et al.
8333403998 497 0893 4
1 55952544813 03 88 61958 6 133965 65 0
40 63.0.17.4.0.1.5.3.1.0.99. 1.0. 5.12.0615.14.67.17.10.2162.55068.5.29.24.38.22. 705512 11.
6 1 3 41 0.0.
72984235819 95 1
7 26511640223 94 23 23943 2231 94 8
38 61.0.17.6.0.2.7.3.1.0.00. 1.0. 7.16.6323.39.71.17.7.85370396.7.4.20.1429.14. 00 12.
1 1 3 3
6
34964 34698 96
7 16531870410 84 4 9116 5 2527 6 4
11 61.0.17.6.0.2.6.3.1.0.00. 1.0. 818.3919.33.67.16.71240.78086.4.22.13.2814. 00 13.
1 1 3 21
2 26
TNA 6922 60.670.6317.727.190.182.546.733.381.490.1400.67 1.250.41 6.29.84618.470.854.817.234.39145.68688.97320.31227.213 7062551242 12.6
A 1 1 3 3 0.0.
D-BRAD-ZL 135199 59.9460.560.690.7118.4916.916.867.140.10.111.833.195.897.092.83.191.181.30.220.1800.02100.38 2.040.440.3460.469 814.51124.8281762423.93457.37061.21916.4106.6512492444.2151999911876.344.52128.51914.43226.31915.1 00.7046400.512778 a11.912.8
N 1 1 3 4
RA 1061394806237271131754 96461 a6
a. ZA 8 59.0.17.7.0.3.5.3.1.0.100. 1.0. 65167229907817736231183887324112513 00 12.
Romani 2048 58.190.8118.486.860.122.617.723.131.310.2199.44 0.440.43 15.818.720922.395.366.717.76.627644.419412784.73111.427.615.6 00 13
Mountains, 5186 6158.52570.74517.97927.12140.13553.18217.29683.38271.18140.192399.7 640.275040.47 10.921.914917.738.871.1183.927434.22301275.84.625.311.929.915.5 00 a513.4
ni 9 58.0.17.6.0.3.7.2.1.0.00. 1.0. 927542245951710852878937419132712 00 12.
e 1 1 1 2 3
Apus 529 7.480.87.647.920.163.637.83.131.120.239.91 0.210.476 0.70.836.50.48.67.25.343.6805.13.94.12.67.65.4 00 2.43
atic rocks from the E ARIES 7903636 61.4361.750.640.6718.6316.5516.055.620.130.142.452.937.065.872.883.291.391.990.140.28100.899.049 0.950.3690.4450.508 3.97.3115.925.331401502020.220.4211.531.8459.864.3617.417.817.719.72126653550.1603262121123101156117.817.44.68.822.821.2216.329.7134.457216.8251 0.7083120.7047040.5124210.512667 14.69.311
m D 7 504531959 12
e mag AIA 799 60.40.718.25.20.12.96.33.71.60.299.6 0.70.5 8.713.218727.527.663.818.31973343.3124511818.610.920.835.364.526.2 00 7.6
eogen UM-B 6913 60.060.818.886.780.172.197.442.931.10.19100.54 1.130.39 8.422.496.214.88.391.420.76.922536.42251498.54.132.115.235.520.3 00 14.7
entative N NA-BUCI 11 59.830.5517.6494.8440.1592.0416.6223.2861.7250.26199.76 92.89880.455 55122168641912659597391108619213918 00 a9.4
res TA 84 9.40.68.65.50.12.67.33.21.80.29.7 0.90.4 5.82.49.539.18.58.25.186.4297.25.10.39.72.36.2 00 9.3
ep N 5 1 9 11623511676608 2131
of r MO 5 0473675912551972513648 31557 5 13332 4 499 69 8
Chemical analyses ROSIA 7881278 55.2058.9159.0.90.620.16.0017.9418.6.836.815.0.150.150.6.363.083.9.717.747.2.842.733.1.450.741.0.260.120.99.799.78100. 0.260.940.0.6490.4730. 26.1718.22495520516915438.42519.61.333249.59.18859.23.41819.11.6315.596207141240.61631.5682128831087714616.8617.4.647.19.12117.20.51133402459.19.21225. 0.7044000.51268900 a7.414.27.
Table 2 SiO2TiO2AlO23FeO23MnOMgOCaONaO2KO2PO25Total LOIMg# NiCrVScCuZnGaPbSrRbBaZrNbThYLaCeNd 8786/Sr143144/Nd Age
Extension-related Miocene magmatism in the Apuseni Mountains, Romania 161
kd
cr
OI 6UR-3 7561.18860.871515.64444.04080.07412.9654.79554.21385.32570.616999.69 270.236040.592 94138.5784.327820.4161.3323.4637.12353358.61878317624.9220.1416.5106184863 0.7044410.51268 61.6 on and Fallidrich standa
UR 76 58.0.17.4.0.3.5.4.4.0.99. 0.0. 44.6175.9.25.58.22.26.20149.75125223.17.16.10117757. 00 1. dertd Al
2 2 1 AlN
DEVAMOIGRAD 56539469204003922479765 262.0462.3356.8758.9460.0356.5157.7920.580.530.580.520.440.870.98117.8416.9718.319.1817.5918.315.5715.355.25.695.514.27.625.510.170.130.110.110.110.120.1122.423.322.942.762.023.183.8716.55.958.086.766.517.566.4473.573.273.893.873.753.444.4411.571.881.321.882.261.153.9310.230.20.220.210.170.290.719100.2799.789899.7497.0899.0499.34 70.931.621.390.432.130.80.57890.4730.5580.5060.4980.4880.4530.58 6.414.334.234.942.612.483.51011.91011.863.613813336019015014611617.62034191219.210.72529.19030.2148.946.780.655.85347.24035.565.318.3171617.819.518.922.710.3171430332.530.2654635219017421800557235530.154.63537.34034.6488561274260018972300181178093.995.512470.1110130239910.3127.9166.929.86.57.510.811.7203.219.320.619.61517.8182422.123.325.54748.86320.112144.145.88084.21204220517.819.94230.26120.766.7 00.70474400.70398200.705713000.51265600.51267800.512580 511.5411.1712.812.611.8512.41.6 OI=loss on ignition. m Alderton et al. (1988); c— Chemical analysesfrom ge for the Sr standard SRM 987 is 0.710239 ± 10 and for
Table 2(continued). SACARAMB ccccc395739677615347672399 55.25S5i7.O8159.8258.0958.4658.5459.0161.1561.4161.762.02TiO0.840.60.610.710.70.590.590.540.560.550.52AlO17.618.4619.3915.7917.1818.3617.0217.2317.4917.1916.823FeO7.845.745.625.825.995.165.725.275.235.234.323MnO0.140.120.110.10.160.130.110.160.120.140.1MgO3.71.562.194.852.432.372.82.493.692.463.1CaO8.717.817.296.937.276.536.355.167.056.055.2NaO3.653.423.633.743.133.373.293.533.513.494.02KO2.011.471.662.921.861.241.762.291.471.852.62PO0.20.170.170.340.350.190.210.250.180.210.325Total99.9499.81100.4999.2999.6399.3498.0399.29100.7199.799.0 LOI1.232.662.690.572.12.851.181.230.80.841.0Mg#0.4830.3500.4360.6230.4450.4760.4920.4830.5830.4820.5 Ni7.287.25696109221134.6Cr11.11119.889.9236192883.42454.8V290142142149147141169152131141111Sc33.22021.718.82118221917.71714Cu1582415.125.3335574633.44619.9Zn55.77063.565.87866626360.66359.6Ga18.91817.919.71818171717.81719.4Pb61.9109.751.12214181921.92136.1Sr2044615568277090953379975610058021737Rb40.54154.653.74540477939.55255.2Ba2038525491216511435061356150694514411763Zr79.410010317114610496104101104162Nb7.377.516.3118101191115Th9.932.621.6105895.7919.7Y212021.222.22921201919.61718.6La42.71515.192.737162828252776.3Ce85.33030.1169.8713353514351141Nd37.91515.267.22916222120.12155 8786bbbbb/Sr00.70514300.7042500.7053160.7045260.704670.7045020.7046060143144/Nd0000.51260900000.51263400 aaaaaAge10.610.7710.7710.51114.0111111.710.8910.3 Major element in weight percent and trace elements in parts per million; all iron as FeO;L2 38786a— inferred age based on the relationship with already known ages; bS— r/Sr values fro(2000). Errors quoted are the internal precision at 2 S.E. for Sr and Nd isotope analyses. Averais 0.511414 ± 4.
162 E. Ros¸u et al.
Table 3 REE for selected samples.
Sample 790 5199 6922 400 2479 767 401 394 776 363 788 UR-3
La 15.70 11.50 13.90 46.50 20.70 23.40 23.30 25.20 91.70 30.60 20.4 111.30
Ce 35.10 27.80 30.60 85.20 45.50 45.80 41.10 47.37 178.8 62.59 43.00 205.70
Pr 4.10 3.56 3.57 9.17 5.27 5.46 6.02 5.58 20.44 7.34 5.06 21.50
Nd 15.80 14.60 13.80 27.50 20.70 19.10 21.70 15.40 66.40 21.00 19.40 67.3
Sm 3.28 3.38 2.94 4.20 3.98 3.29 4.16 3.33 9.43 4.62 3.76 8.76
Eu 0.97 0.94 0.87 1.21 1.28 1.05 1.25 1.02 2.51 1.27 1.22 2.32
Gd 3.48 4.13 3.23 3.30 4.00 3.40 4.66 3.05 6.50 3.95 3.79 5.53
Dy 3.68 4.59 3.32 2.65 3.85 2.99 4.41 2.80 4.02 3.42 3.40 3.26
Ho 0.73 0.93 0.65 0.55 0.76 0.59 0.88 0.56 0.75 0.67 0.66 0.57
Er 2.15 2.87 1.91 1.57 2.18 1.66 2.57 1.78 1.56 2.06 1.88 1.05
Yb 2.13 2.74 1.75 1.57 2.11 1.71 2.48 1.66 1.64 1.90 1.73 1.02
Lu 0.32 0.43 0.26 0.26 0.32 0.27 0.39 0.28 0.25 0.32 0.27 0.15
Eu/Eu* 0.88 0.77 0.87 0.99 0.98 0.97 0.86 0.98 0.98 0.91 1 1.02
(Ce/Yb)N 4.19 2.57 4.41 13.9 5.48 6.78 4.21 7.31 27.56 8.42 6.29 51.72
(Gd/Yb)N 1.31 1.2 1.46 1.69 1.51 1.58 1.5 1.48 3.15 1.67 1.75 4.37
(Yb/Lu)N 1.02 1 1.03 0.92 1.01 0.97 0.98 0.93 1 0.91 0.98 1.05
Basins development in the central part and west- site field and the Zâmbriţa (766) sample in the
ern half of the region (in the Zarand Mountains) trachyandesite field, as do the Uroi trachyande-
preserved the volcanic deposits in depressions. site and trachydacite (UR3). Two of them belong
The oldest rocks (>14 Ma) dated by radiometric to the 7.4–10 Ma age group of the Săcărâmb area
methods occur in the Roșia Montană-Bucium and (Figs. 1, 2, Table 2). The Moigrad andesite plots
Brad areas (Fig. 2). Volcanic activity then started within the medium-K andesite field together with
in the west, in the Zarand basin, where K–Ar ages most of the Apuseni Mountains Neogene rocks.
of 13.4–12.4 Ma have been obtained. From 13 to Major element variations are typical for calc-
11 Ma, volcanic activity shifted towards the east, alkaline rocks, with MgO, FeO*, CaO and TiO
2
occurring mostly in the eastern part of the WNW– decreasing with increasing SiO.NaO and PO
2 2 2 5
ESE “alignment” and in the southern half of the remain roughly constant as no significant plagio-
NNE–SSW “alignment” (Fig. 1). At 11–9 Ma mag- clase and apatite fractionation occurred during
matic activity continued in the eastern part of the magma evolution. When compared with Neogene
WNW–ESE “alignment”, but shifted again into volcanics in the East Carpathian arc, the Apuseni
the northern half of the NNE–SSW “alignment” Mountains samples plot in a similar field to those
where it remained focused for the next 2 Ma (9–7 in the Gutâi Mountains (Kovacs et al., 1998), ex-
Ma) (Fig. 1). The only magmatic occurrence cept for the trachyandesites. Generally, they are
younger than 7.4 Ma is at Uroi (1.6 Ma) at the very similar to Neogene volcanics of any of the
south-eastern most edge of the Apuseni Moun- East Carpathian arc segments, such as the Ukraini-
tains, after a gap in activity of about 6 Ma. The an Trans-Carpathian region (Seghedi et al., 2001),
andesites at Moigrad are 12.4 ± 1.3 Ma old, well or the Călimani-Gurghiu-Harghita chain (Seghedi
within the range of the rest of the Apuseni Moun- et al., 1995; Mason et al., 1996), but without large
tains volcanic rocks. major element variations.
Trace elements
Geochemistry
Trace element contents are given in Table 2. Ni
Major elements and Cr contents show a large variation. Ni ranges
from 3.9 to 56 ppm, but most of the samples con-
Major element compositions of the studied sam- tain <20 ppm. Seven samples have >20 ppm,
ples are given in Table 2. With few exceptions, among them the Detunata basaltic andesite. Cr
most of them plot in the andesite field (Fig. 3). Be- contents vary from 5 to 90 ppm with the excep-
sides the alkaline rocks of Uroi, which plot in the tion of the Detunata basaltic andesite (224 ppm).
trachyandesitic and trachydacitic field, there are Seven samples have >50 ppm Cr, among them
other three rocks displaying high-K calc-alkaline most are trachyandesites. The relatively high Ni
features. These are “Pârâul lui Toader microdior- and Cr, along with high Mg# of the high-K rocks
ite” (765), which plots in the basaltic-trachyande- is striking, as compared with the rest of the rocks.