Upper Cretaceous magmatic suites of the Timok Magmatic Complex

The Upper Cretaceous Timok Magmatic Complex (TMC) developed on a continental crust composed of different types of Proterozoic to Lower Cretaceous rocks. The TMC consists of the magmatic suites: Timok andesite (АТ) – Turonian–Santonian, Metovnica epiclastite (ЕМ) – Coniacian–Campanian, Osnić basaltic andesite (АО) and Ježevica andesite (AJ) – Santonian–Campanian, Valja Strž plutonite (PVS) – Campanian and Boljevac latite (LB). The sedimentary processes and volcanic activity of the TMC lasted nearly continuously throughout nearly the whole Late Cretaceous. The sedimentation lasted from the Albian to the Maastrichtian and the magmatism lasted for 10 million years, from the Upper Turonian to the Upper Campanian. The volcanic front migrated from East to West. The volcanic processes were characterized by the domination of extrusive volcanic facies, a great amount of volcanic material, a change in the depositional environment during the volcanic cycle, sharp facial transitions and a huge deposition of synand post-eruptive resedimented volcaniclastics.


Introduction
The Upper Cretaceous volcanо-sedimentary complex of the Carpatho-Balkanides belt spreads discontinuously from the northern parts of the Apuseni Mountains and Banat in Romania, over Timok Krajina in eastern Serbia, down to Srednogorie and the Black Sea in Bulgaria.This zone is 1500 km long and 70 km wide.Further on, this complex continues over the Pontides (Turkey) down to the northern parts of Iran.This is the most important active mining area in Europe, belonging to the Tethyan Eurasian Metallogenic Belt (JANKOVIĆ 1977).More recently, this entire province was named the Banatitic Magmatic and Me-tallogenic Belt (abbreviated as BMMB, BERZA et al. 1998), or Apuseni-Banat-Timok-Srednogorie Magmatic and Metallogenic Belt (abbreviated as ABTS, POPOV et al. 2002).BOCCALETTI et al. (1974) and AIELLO et al. (1977) consider Srednogorie in Bulgaria as a back-arc rift.Geodynamic and tectonic models have also been provided (HSU et al. 1977;DABOVSKI et al. 1991;VLAD 1997;CIOBANU et al. 2002and VON QUADT et al. 2004, 2005).Recent high precision U/Pb, 40 Ar/ 39 Ar, Re/Os and geochemical data have improved and refined the tectonic models of this area and shed more light on its magmatic activity and metallogeny (LILOV & CHIPCHAKOVA 1999;VON QUADT et al. 2002QUADT et al. , 2004QUADT et al. , 2005;;CLARK & ULLRICH 2004;HANDLER et al. 2004;BANJEŠEVIĆ et al. 2006 andZIMMERMAN et al. 2008).
The Upper Cretaceous magmatic activity in eastern Serbia occurred along two subparallel magmatic belts, namely: the Timok Magmatic Complex (TMC) and the Ridanj-Krepoljin belt in the East and West, respectively.The TMC is 85 km long and extends from Majdanpek in the North all the way to the Bučje Village in the South.It developed on a continental crust composed of different types of Proterozoic to Lower Cretaceous rocks (ANTONIJEVIĆ et al. 1974).Geotectonically, it belongs to the Getic Nappe (GRUBIĆ 1983 andKRÄUTNER &KRSTIĆ 2003) or the Kučaj Terrane as part of the complex Carpathian-Balkan Terrane in eastern Serbia (KARAMATA & KRSTIĆ 1996).The Upper Cretaceous rocks of the TMC are overlain by Paleogene, Neogene and Quaternary deposits.Based on continuous geological mapping (ĐORĐEVIĆ & BANJEŠEVIĆ 1997;BANJEŠEVIĆ 2002 andBANJEŠEVIĆ et al. 2003) and new geological data (BANJEŠEVIĆ 2006 andLJU-BOVIĆ-OBRADOVIĆ 2008), the TMC is interpreted as a succession of the following magmatic suites (Fig. 1): Timok andesite (АТ) -Turonian-Santonian, Metovnica epiclastite (ЕМ) -Coniacian-Campanian, Osnić basaltic andesite (АО) and Ježevica andesite (AJ) -Santonian-Campanian, Valja Strž plutonite (PVS) -Campanian and Boljevac latite (LB).This paper will show a synthesis of the data gathered through many years of geological investigations and a modified version of the TMC units.A first version of the formations was published in the Geological Map and Booklet of the southern part of the TMC (ĐORĐEVIĆ & BANJEŠEVIĆ 1997).The definition of the lithodemic hierarchy in this paper is made according to the recommendations of the North American Stratigraphic Code (by North American Commission on Stratigraphic Nomenclature) and International Stratigraphic Guide (SALVADOR 1994).In addition, it will provide a volcanological approach to the study of volcanic facies, including the implementation of modern volcanological terminology (e.g., CAS & WRIGHT 1987;MCPHIE et al. 1993 andSCHMINCKE 2004).

Geological setting of the TMC
After continuous carbonate sedimentation from the Early Jurassic, a new sedimentation period commenced with the Albian transgression.The new sedimentation processes had clastic character and were related to oscillations of the depositional environment.The sedimentation proceeded with manifestations of Turonian volcanism in the TMC.These Albian-Cenomanian sediments are concentrated along the eastern boundary of the TMC (Fig. 1) and rarely in the central part of the western boundary of the TMC (near Zlot and Boljevac).The Albian clastites transgressively overlie Early Cretaceous rocks (Barremian-Aptian limestones or Aptian carbonate sandstones).
After a hiatus, the Turonian-Senonian evolution commenced with a new sedimentary cycle.The sediments overlie Albian-Cenomanian clastites (Figs. 4  and 6).The lowest part of the sediments contain microfauna (Helvetoglobotruncana helvetica), indicating Lower to Middle Turonian age (LJUBOVIĆ-OB-RADOVIĆ 2008).During the Senonian, the whole TMC area shows a considerable difference in the evolution between the eastern (Bor-Lenovac tectonic block -BLTB) and the western (Crna reka tectonic block -CRTB) part (ĐORĐEVIĆ & BANJEŠEVIĆ 1997, Fig. 1).Until the Maastrichtian, the first sediments and the epiclastites developed in the BLTB, whereas from the Turonian to the Lower Campanian, andesites originated in this block.In the CRTB, the sediments developed until the Middle Santonian when andesitic and basaltic andesitic volcanism also started.When the volcanism ended, in the Early Campanian, plutonic rock was intruded and the sedimentation continued over a wider area.After the Upper Campanian to the Maastrichtian period, in the central part of the TMC, reef sedimentation commenced (Figs. 1 and 6).On the eastern part of the TMC, in the Upper Campanian, coarse-grained and regressive clastites were deposited (Figs. 1 and 2).This was the period when the TMC uplifted and its existence as an area of active volcanism and marine sedimentation terminated.

Timok andesite (AT)
Name: After the Timok River Synonyms: "Timazit" -BREITHAUPT 1860."Andesites or volcanites of the I volcanic phase (Timocite) " -DROVENIK et al. 1962 Type locality (Type section): The Timok River locality from the Gamzigradska Banja to the Zvezdan Village.An a additional outcrops are exposed in the Krivelj Village area.
Location, boundaries, lithology and genesis: The AT occur in the eastern parts of the TMC (Fig. 1), where they overlie Cenomanian and Turonian sediments.They are covered by Senonian sediments (Fig. 2) and the EM.Amphibole andesites and trachyandesites of high potassium character predominate.They are light-grey to green-grey rocks, showing a holo-to hypo-crystalline porphyritic texture, sometimes characterized by cm-sized amphibole phenocrysts -Timazit (BREITHAUPT 1860).Andesine plagioclase, tschermakite amphibole (rarely Mg-hornblende), biotite and clinopyroxene are the main phenocryst phases (in decreasing order of abundance), whereas quartz phenocrysts are very rare.The amount of phenocrysts is usually around 50 % (rarely more than 60 %).
Upper Cretaceous magmatic suites of the Timok Magmatic Complex According to their lithological, volcanological and petrofabric characteristics, the andesites are distinguished into the following facies: lava flows (coherent and autoclastic), lava domes (Fig. 3), shallow intrusions and various volcaniclastic rocks.Completely or partially autobrecciated lava flow facies are predominant, while hyaloclastites are very rare.They have high aspect ratios having thicknesses that sometimes reach several tens of meters and a rather small aerial distribution, commonly < 100 m 2 .The autobrecciated lava flows show a clast-supported volcaniclastic texture with subangular to angular clasts up to 30 cm in size, which show almost the same fabric and compo-sition.The matrix is usually subordinated (up to a few vol.%).Lava dome or cryptodome facies are usually exposed on the surface in the range of several square kilometers.At several locations, the central parts of the lava domes are exposed as columnar and rectangular jointed volcanic rocks (Fig. 3).Dykes are usually up to 10 m wide and up to 50 m long.Syn-eruptive and post-eruptive redeposited volcaniclastic rocks   have a great prevalence (here described as Metovnica epiclastite, see below).
Age: According to high precision U/Pb, 40 Ar/ 39 Ar age (VON QUADT et al. 2002 andCLARK &ULLRICH 2004), the AT ranged from 89.0±0.6 to 84.26±0.67Ma (Upper Turonian to Upper Santonian).Location, boundaries, lithology and genesis: The EM developed in the eastern part of the TMC (Fig. 1) in a shallow marine environment, infilling sharp volcanic bedrocks (ĐORĐEVIĆ & BANJEŠEVIĆ 1997).The rocks are coarse-to fine-grained, massive, coarsely banded, sometimes even laminated (Fig. 5).They are composed of texturally and structurally different fragments deriving from different volcanic facies of the AT.The EM are often interlayed with the sediments (Figs. 2, 5 and 6).

Osnić basaltic andesite (AO) and Ježevica andesite (AJ)
Name: After the Osnić Village.Synonyms: "Basaltic andesites or volcanites of the II volcanic phase" -DROVENIK et al.Type locality (Type section): A section northern of the Osnić Village, from the Metovnica Village to the Šarbanovac Village.An a additional localities are in the area of the Ježevica Mt. and the Brestovačka Banja.
Location, boundaries, lithology and genesis: The rock suite corresponding to andesite -basaltic andesite of calc-alkaline to tholeiitic character can be distinguished among the Senonian volcanic rocks of the TMC.The first subsuite includes pyroxene basaltic andesite (AO), while the second subsuite comprises amphibole andesite (AJ).Both rock subsuites are located in the central and western parts of the TMC (Fig. 1) and are sometimes closely associated.The AO are predominant.These volcanic rocks are both underlain and overlain by sedimentary rocks (Fig. 6).Field and laboratory studies on several profiles showed that the underlying sediments contain Turonian-Santonian microfauna (Fig. 6), while the overlying sediments are composed of resedimented volcaniclastites, clastitic or reef sediments of Campanian-Maastrichtian age (ĐORĐEVIĆ & BANJEŠEVIĆ 1997).
The pyroxene basaltic andesites are dark grey rocks (Fig. 7) of porphyritic texture, characterized by mmsized phenocrysts.The structure is most commonly massive and sometimes vesicular.Plagioclase and clinopyroxene are the most abundant phenocrysts, while orthopyroxene and amphibole occur in small amounts or are completely subordinate.The plagioclase contains 42-93 % of An components, therefore these plagioclases are more basic than those occurring in the amphibole andesites and the AT.The amphiboles correspond to tschermakites, rarely to Mg hornblende, and show very primitive, more basic character than the amphiboles in the AT.The clinopyroxene corresponds to augites (Wo 40.3-50.2-En 36.3-45.2-Fs 11.1-18.1 ), while the rhombic pyroxene is enstatitic in character.The amount of phenocrysts in these rocks rarely reaches 50 vol.%.The groundmass is most often hypocrystalline, but rare holocrystalline varieties also occur.
The amphibole andesites are most frequently massive rocks, rarely with vesicular or banded structure, sometimes with very well exposed tabular or rectan- gular jointing.Their color varies from grey, palegreen to green-grey.The texture is hypo-to holocrystalline porphyritic, often with a fluidal groundmass.Amphibole and plagioclase phenocrysts are always present, clinopyroxene is subordinate, while orthopyroxene and biotite occur only rarely.The chemical composition of the minerals is very similar to the pyroxene-bearing varieties, except that the plagioclases are more basic in the latter.
The volcanic rocks predominantly occur as lava flow facies (autobreccias and hyaloclastic breccias) and resedimented volcaniclastic deposits.Lava flow facies are up to several meters thick, while their length reaches several hundred meters.The transitions from coherent to autobrecciated parts are usually very sharp (Fig. 7).The fragments are most often angular, rarely subangular, and have a very uniform composition and dimensions.They are rarely coarser than 10 cm in diameter.The hyaloclastites show gradual transitions to-ward coherent lava flow facies.They are unstratified, poorly sorted rocks, composed of semi-angular to angular fragments of different size -from 1 cm to up to 20 cm.The rock fragments show typical hyaloclastic characteristics, such as chilled margins, tiny normal joints and jig-saw-fit puzzle textures (YAMAGISHI 1991).In addition, there are numerous occurrences of lava lobes and pseudo-pillows (KANO et al. 1991).Shallow intrusion facies are represented by necks and dykes.Remnants of the pyroclastic rock deposits are very rare and exposed at only a few localities.
The resedimented volcanoclastites are mostly stratified volcaniclastic rocks, psamitic to psephitic in grain-size of different origin and type of transport.The sedimentological and lithological characteristics of some deposits are very well exposed, clearly referring to sedimentary types of transportation (mostly debris flow or grain flow).However, for the other deposits, neither transportation type nor material source can be determined.The rock composition is heterogeneous, although there are some layers showing very similar fragment composition.The fragments are semi angular to rounded.The rocks are mostly semi-or well-sorted, but sometimes they can be very poorly sorted, showing typical sedimentary structures: normal and inversed gradation, parallel lamination, rarely also crossed or wave-like lamination.
Age: According U/Pb age zircon analysis, between 82.27±0.35 and 81.79±0.54Ma.The age of the AO of the dyke from the Brestovac Village to the Brestovačka Banja area was confirmed as Santonian-Lower Campanian (BANJEŠEVIĆ et al. 2006).
Age: According to U/Pb age zircon analysis, the age of the Valja Strž plutonite is 78.62±0.44Ma, Upper Campanian age of the PVS was confirmed (VON QUADT et al. 2002).

Boljevac latite (LB)
Name: After Boljevac.Location, boundaries, lithology and genesis: Numerous latitic dykes occur along the western border of the TMC.These rocks crosscut the AO and the AJ.They appear in the form of shallow intrusions (dykes, sills and veins), seldom as lava flows.They are usually small masses, up to several tens of meters long and 3 to 4 meters thick.The rocks are dark-grey, showing very distinctive textures characterized by large, elongated phenocrysts of plagioclase and potassium feldspar, which sometimes exhibit fluidal orientations (Fig. 9).The texture is fine-grained, very fine-grained or hypocrystalline porphyrithic with a microcrystalline, intersertal and pilotaxitic groundmass.The latites consist of plagioclase (53-67 % An), potassium feldspar (61-69 % Or), clinopyroxene and various accessory minerals (MILOVANOVIĆ et al. 2005).
Age: The latite crosscut the AO and AJ, however their age is poorly constrained.

Conclusions
Through long-term multidisciplinary and continuous geological investigations, as well as the employment of the volcanic facies concept in the textural and  genetic classification of volcanic deposits, new geological data regarding the petrography and volcanic characteristics of the TMC magmatic and sedimentary rocks are available.The TMC consists of magmatic suites and sedimentary formations.After the Albian-Cenomanian sedimentary cycle, sedimentations lasted continuously from the Lower Turonian to the Maastrichtian.The available lithostratigraphic, paleontological and radiometric data indicate that the Upper Cretaceous magmatism in the TMC lasted more than 10 million years, from the Upper Turonian to the Upper Campanian.In this period, the volcanic front moved from East to West.The volcanic processes were subaerial to marine effusive, hypoabyssal and very rarely explosive in character.It commenced with andesitic to trachyandesitic volcanism (Timok andesite) in the present easternmost parts of the TMC.The volcanic rocks overlay Cenomanian or Lower Turonian sediments.When the volcanic processes ceased in the eastern parts, a new volcanic front opened in the central and western parts of the TMC.The Osnić basaltic andesite and Ježevica andesite overlay sediments containing Turonian-Coniacian microfauna and are overlain by Upper Campanian clastic and reef sediments.The magmatic activity finished with plutonic rocks (Valja Strž plutonite) and latitic dykes (Boljevac latite) in the western parts of the TMC.The termination of volcanic activity in the TMC was followed by subvolcanic processes in the Ridanj-Krepoljin Zone, which is situated more to the west.Deposition of reef sediments and coarse-grained sediments (conglomerates and sandstones) of Upper Campanian-Maastrichtian age certainly represent the end of continual marine development in the TMC area.

Fig. 3 .
Fig. 3.The central parts of the coherent andesitic lava dome near the Krivelj Village, with columnar jointing.

Fig. 7 .
Fig. 7.The coherent pyroxene basaltic andesite lava flow (L) and autobreccia (B) in the upper part.The transitions from coherent to autobrecciated parts are very sharp.The dashed line marks the boundary lava flow and autobreccia.

Fig. 8 .
Fig. 8. Grey to dark-grey plutonic rock from Valja Strž with a hypidiomorphic granular texture and a massive structure.

Fig. 9 .
Fig. 9.The dark-grey latite south of Boljevac shows very distinctive textures characterized by large, elongated phenocrysts of plagioclase and potassium feldspar, which exhibit fluidal orientation.