60 years of the Serbo-Macedonian Unit concept: From Cadomian towards Alpine tectonic frameworks

2 Geographical Institute “Jovan Cvijić” of the Serbian Academy of Sciences and Arts, Đure Jakšića 9, 11000 Belgrade, Serbia. Abstract. The study represents a summary of the hitherto tectonic concepts revolving around a peri-Gondwanan fragment referred to as the SerboMacedonian Unit. The Serbo-Macedonian Unit as a gneiss-dominated basement segment is positioned in the proximity of the Baltican craton (peri-Moesian realm). This area represents a repository of the transferred broadly similar thus highly complex, elongated polycrystalline vestiges of the Pan-African inheritance. This peculiar far-travelled composite crustal fragment of north Gondwana is amalgamated on top of the Supragetic unit during the late Variscan peri-Moesian amalgamation. However, the original early Pa leozoic tectonostratigraphic configuration of these three intimate green schistand mediumto high-grade gneiss-amphibolite basement vestiges (Serbo-Ma cedonian/Supragetic and Getic) is further perplexed by the presence of poorly documented pre-Variscan (Ordovician?) lithospheric-scale event. The Pan-African to Lower Paleozoic subduction/magmatic arc stage led to the amalgamation, breakup and dispersal of a cluster of peri-Gondwanan continental and oceanic terranes. Breakup and dispersal from the northern shore of the Gondwanan active margin triggered the development of the Paleozoic deep-marine sedimentary cover (“Kučaj unit” or Getic unit). To make matter more complex, prior the Lower Paleozoic terrane agglomeration and sub sequent dispersal, it appears that a Lower Paleozoic geodynamic linkage is additionally marked by the poorly investigated cross-lithospheric event. This event connects the outboard oceanic Supragetic/“Kučaj” succession with a segment of the former north Gondwanan protobasin (juvenile Serbo-Ma cedonian Unit).

western boundary of the Baltican craton. The Serbo-Mace donian Unit as a highly complex cry stalline basement inlier has documented con trover sies revolving around its polyphase tec to no metamorphic evolution (e.g., GrUBić et al., 1999;POPOVić, 1991;POPOVić & MiLjKOVić, 2000;GerDjiKOV et al., 2014;ZAGOrCHeV et al., 2015;SPAHić & GAUDenyi, 2018, 2019. The following issues pending the answers: (1) is the gneiss-dominating LC SMU also referred to as the "Serbo-Macedonian Massif" discrete or the same geotectonic unit (in both, Variscan and Alpine configuration)? is the LC SMU connected with the adjoining green schist-facies Supragetic base ment/"Vlasina Complex" (concept of DiMi Tri -jeVić, 1959, 1995?; (2) What is the exact continuation of the LC SMU to the north of the Danube river (i.e. is it the Sebeş-Lotru terrane/nappe)?; (3) What was the original depositional-tectonic environment "digesting" such a huge volume of Cambrian clastic detritus (c.f. AViGAD et al., 2017)?; (4) What is the relationship of the latest Cambrian metamorphic imprint (numeric age by BALOGH Fig. 1. Tectonic map of the investigated tectonic units (modified after KoUnoV et al., 2010(modified after KoUnoV et al., , 2017Alpidic tectonic concept after SChMid et al., 2008 andBernoULi et al., 2001). Map clearly exhibits the problem of the Serbo-Macedonian Unit to the east of Belgrade or after the Vršac settlement (question mark and rectangle with the question mark). Map includes the positions of the magmatic bodies of Pan-African and Alpine relevance. Jas Jastrebac tectonic window (MAroVić et al., 2007;erAK et al., 2016erAK et al., ). et al., 1994 with the poorly documented Ordovician event?; (5) in addition to a documented repeated anatexis (ZAGOrCHeV, 2015 and references therein), during which tectonic event widespread Ordovician tectonothermal imprints were produced (472-456 Ma, numeric age by AnTić et al., 2016a;Sebeş-Lotru terrane, ca. 460 Ma;Ograzhden Unit, 462 Ma;ZAGOrCHeV et al., 2012ZAGOrCHeV et al., , 2015MACHeVA et al., 2016)?; (6) What is the LC SMU and Supragetic basement Cadomian to Lower Paleozoic tectonic setting, and what were the circumstances for such atypical late imprints?
(7) What was the role of the LC SMU in the neotethyan Permian-Triassic opening (e.g., SPAHić et al., 2020), and an eventual relationship with the Paleotethys (e.g., SPAHić et al., 2019b)? in order to obtain the outline of a Lower Paleozoic geodynamic paleoenvironment, the study incor po rates the recent regional-geological constraints (SPAHić & GAUDenyi, 2018, 2019SPAHić et al., 2018SPAHić et al., , 2019. Study also includes a scarce analytical data repository (HiMMerKUS et al., 2009;MeinHOLD et al., 2010;KOUnOV et al., 2012;ZAGOrCHeV et al., 2012ZAGOrCHeV et al., , 2018AnTić et al., 2016aAnTić et al., , 2017ABBO et al., 2020) focusing almost exclusively on the LC SMU. We tune up the constraints on the regional pre-Alpine i.e. pre-Variscan configuration. By consolidating earlier and recent data, we provide a rejuvenated data platform, ultimately attempting to outline the im portant Lower Paleozoic cross-lithospheric event connecting the pre-Variscan LC SMU with the Supragetic basement.
Depending on the applied tectonic concept (for review see chapter 4.1 of this paper), the LC SMU has ca. 50 to 100 km in width, with its regional analog units, reaches the length of over 1000 km. The western bor derline of the LC SMU striking nnW-SSe is re ferred to as the "Moravsko-Šumadijska dislo kacija" (AnđeLKOVić, 1982). This fault sy stem has the cha racter of a strike-slip fault (KräUTner & KrSTić, 2002). This western border zone of the LC SMU represents a jun ction with the Mesozoic late Alpine neo tethyan suture re ferred to as the Vardar Zone. This tectonic lineament can be traced in Serbia from the river Danube in the north, south wards, near Kragujevac, between Trstenik and Kruševac, conti nuing between jastrebac and Kopaonik Mts., and cros sing near Kumanovo in north Ma cedonia.
The eastern contact zone of the Supragetic unit is the tec tonic lineament locally referred to as the "Moravska dislokacija" (PeTKOVić 1930;AnđeLKOVić, 1982) or the Morava fault system. This nappe system crops out near the town of Golubac, Danube river (east Serbia) (Fig. 2), striking along the Pek and Mlava rivers, east of the sеttlements Alek sinac, niška Banja, passing near Modra Stena farther con tinues in Bulgaria. South wards, this fault system sepa rates the rhodope unit, crossing in north Macedonia and northern Greece. To the east of the LC SMU is the Supragetic unit. The two latter systems are separated by the nappe of Alpine age (KräUTner & KrSTić, 2002;Fig. 1).

Definition of the Serbo-Macedonian Unit
initially, CVijić (1901CVijić ( , 1902 attributed the crustal fragment representing a modern-day Serbo-Macedonian Unit as a segment of the "rhodopean Mass". After the definition of the Serbo-Macedonian Unit, during last 60 years a plethora of local and international geoscientists attempt to describe this crystalline basement. The LC SMU represents a member of essential Alpine-and pre-Alpine relevance exposed within the hitherto Carpathian-Balkan regional geotectonic charts. With a few exceptions, the published studies discussing the Alpine configuration in the frame of Tethyan tectonics describing the South Carpathian/Carpathian-Balkan nappe stack (including LC SMU, so-called "Lower Complex"). The recent studies of the LC SMU segment in Serbia, though scarce, attempt to integrate the knowledge on the Pan-African and Variscan geodynamic evolution of the cluster of displaced basement inliers of oceanic and continental affinity (e.g., AnTić et al., 2016AnTić et al., , 2017SPAHić & GAUDenyi, 2018;SPAHić et al., 2019a).

Historical overview
The Se european tectonics have been more than 150 years in the focus of several generations of geologists, whereas each generation introduced a different interpretation. The ideas about the structural positioning of the rhodope s.l. (or Thracian Massif) аrе in a function of considering the nature and the evolution of the Tethys and subsequent Alpine orogenic belt. Many ideas have been intuitively derived from a "rhodopocentrism" or the first research performed in the 19th century by BOUe (1840), PeTerS (1863), MOjSiSOViCS et al. (1880), SUeSS (1895) and CVijić (1900). The earliest authors assumed that the central parts of the Balkan Peninsula are composed of the oldest (crystalline) mass. CVijić (1901,1903) designates this geologic entity as the rhodope Mass (in Serbian: rodopska masa). The rhodope Mass is described by CVijić (1924) as "the great old core or the oldest mountain around which were formed the smaller mountains later connect to it". CVijić (1901 was the first explorer who recognized that the "Central Crystalline Core" should be a discrete unit relative to the rhodope Mass (in Serbian: Centralno kristalasto jezgro; see Table 1). CVijić, moreover, formulated a generic tectonic chart, describing it as a "chessboard", composed of crystalline blocks displaced by the faults. MiHAiLOVić (1955) pointed out that this crystalline entity has "horst-type" structural fabric. According to MUrATOV (1949), the Macedonian Massif represents the core of a single large, but destroyed anticline, whereas PeTKOVić (1957PeTKOVić ( , 1960 the SMU landform still interprets as the "anticlinorium" or a large-scale anticline. SiKOšeK (1971) and BOnCHeV (1971) independently from each other stated that this mass has features of a single mega anticline (AnDjeLKOVić, 1977;GrUBić, 1999) (Table 1).
The Thracian Massif (rhodope Mass s.l. according to CVijić, 1901) had often been used for a tectonic entity that occupies the rhodope Massif s.s. of Bulgaria and Greece and the parts of the north Macedonia and Serbia ("Serbo-Macedonian Mass") (at the beginning of the 20 th century, after ZAGOrCHeV, 1998). KOSSMAT (1924 p. 122, 125) concludes that the rhodope Mass for the Balkan Peninsula is the same DARko SPAhIć & TIVADAR GAuDEnyI geologic entity as it is the Central Zone for the eastern Alps. KOCH (1930 p. 3) supported this opinion. ne vertheless, the KOSSMAT'S conclusion was not further developed by other authors of that time (Table 1). BOnCHeV (1936) in his most detailed report introduce the Kraishtides "the youngest orogenic system on the Balkan Peninsula that is accommodated obliquely to South Carpathians and Balkanides, further associating these systems in a form of a Balkan arc" (the tec to nic unit accommodated in the southwest Bul garia). According to BOnCHeV (1936), the Kraish tides "escaped" from the Balkanides. The Kraishtides were depicted as an allochotonous system or as a "thrust land" ("deckenland"). According to the author, "the rocks are considerably folded, having the fold axes trending nnW-SSe, i.e. perpendicular to the principal stress trend... ". ZAGOrCHeV (2006) in the review of the Kraishtides concludes "...only in Paleo gene and neoge ne times, the Strouma (Kraishtid) lineament played the role of a fault belt with con siderable dextral strike-slip movements, and repeated rifting in transtensional conditions" (Table 1). jArA nOFF (1938) points that rhodope Mass entity in the western (and the eastern) parts have own shorten ing fold and thrust episodes, whereas MUrATOV (1949 p. 18-19) indicat ed that the "rhodope Mass has own continuity in the Macedonian Massif". A similar opinion had PeTKOVić & MAKSiMOVić (1976;p. 165). A considerably different perspective on this subject exhibited BOnCHeV (1940BOnCHeV ( , 1943 pointing out that the area between the Kra ištides and Vardar Zone represents an uniform old massif designating as the "Macedonian-Pannonian Mass" (Makedonsko-panonska masa). Later, similar opinions exhibited MiHAiLOVić (1955) and DiMiTrijeVić (1959DiMiTrijeVić ( , 1963 ( Table 1).
For an extended period of time, the prevailing hypothesis between geologists was that the rhodope Mass is an uniform tectonic unit. The results of systematic, decades-long field-geological surveying for the purpose of the Basic Geological Map of yugoslavia in scale 1: 100,000 exhibited that the crystalline rocks of Serbia and Macedonia (north Macedonia) differ in comparison with those in Bulgaria (with an exception of its SW parts). The following key features and discrepancies, DiMiTri -jeVić (1959) emphasized in order to uncouple the "Serbian Macedonian Mass" (Srpsko makedonska masa) from rhodope: a) The marbles, a regular member of the Bulgarian rhodope Mass, is absent in the "Serbian Macedonian Mass" complex with an exception of the "Vidojevica Series". b) Feldspar mica-schists and mica-rich gneisses which are a constituent of the "Lower Complex" (lowermost metamorphic unit) of the "Serbian Macedonian Mass", in the rhodope Mass have rather poor mica content.
c) The "Serbian Macedonian Mass" can be characterized by the often interchange of lithofacies, as horizontally, but also stratigraphically (vertically) whereas the rhodopean Mass has a prominent consistency of the rock formations.
d) The "Serbian Macedonian Mass" can be characterized by the linear folds with gentle b axis rotation, whilst the rhodope Mass is abundant with, so-called "brachi-form structures". Additionally, linear features are restricted to a few structurally unstable zones. e) Another essential argument of diMiTriJeVić (1959) was that the Bulgarian structures of the rhodope Mass do not continue westwards directly into the "Serbian Macedonian Mass".
The crystalline base has asymmetric structures which are composed of numerous rather complex synforms and antiforms (according to DiMiTrijeVić, 1995;MArOVić, 2001). After that time, the "Serbian Macedonian Mass" was established and accepted within a scientific community as a tectonic unit crosscutting Southeast europe (Table 1). Some early rese archers, e.g. KOBer (1952), "the crystalline belt between the Carpatho-Balkanides and the Vardar Zone does not represent any kind of "mass" even is not an "old" and a "middle" mass. Kober this unit entitled to "Moravides thrust over the Carpatho-Balkanides". Later, a similar perspective had CODArCeA (1964), AnDjeLKOVić (1963AnDjeLKOVić ( , 1965AnDjeLKOVić ( , 1976    Mass" is an individual part of the rhodope Mass, Di -MiTrijeVić (1974, 1995 and GrUBić (1980) described the "Serbian Macedonian Mass" as an independent tectonic unit. ZAGOrCHeV (1976) introduced the polycyclic Ograzhden complex in a SW Bulgarian part of the "Serbian Macedonian Mass". Later in 1996 (ZA - GOrCHeV, 1996) gives more details about the Ograzhdean Supergroup ( Table 1).
The term "Serbian Macedonian Mass" coined by DiMiTrijeVić (e.g., DiMiTrijeVić 1959, describes a discrete unit in the classical subdivision of the geology of northern Greece (e.g., jACOBSHAGen, 1986). Later it was recognized as Pirgadikia-, Kerdilion-and Vertiskos Units that belong to the "Serbian Macedonian Massif" (after HiMMerKUS et al., 2006) (Table  1). HAyDOUTOV (HAyDOUTOV, 1989(HAyDOUTOV, , 1991HAy DOUTOV & yAneV, 1997) from the Thracian Massif ("Serbian Macedonian Massif" and rhodopean Mass) differentiate the Balkan Terrane or its westernmost parts as a segment of the "Serbian Macedonian Massif" (def. after DiMiTrijeVić, 1959). The easternmost parts in Serbia are later referred to as the "ranovac-Vlasina-Osogovo Terrane" (Table 1). POPOVić (1991) use lithostratigraphical and metallogenic reasons to subdivide the "Serbian Macedonian Massif" into the two units: Morava Massif in the north and Pelagonia rhodope on the south. ćirić (1996 p. 17) in his monography, criti cized the "Serbian Macedonian Massif" as a "mass" because "it can be characterized by a series of different mophostructures, horsts and faults, having differentiated geological formations", The author underlines that the "Serbian Mace donian Massif" cannot be described as a "uniform mass" (Table 1). KrSTić & KArAMATA (1992) subdivided the SMU (defined by DiMiTrijeVić, 1959 of "Serbian Macedonian Mass" s.l.) into "Serbian Macedonian Massif" s.s. and "ranovac-Vlasina Terrane". The "ranovac-Vlasina Terrane" was incorporated into the Carpatho-Balkanides. Same year, similarly, KArAMATA & KrSTić (1996) subdivided the Serbian Macedonian Massif" s.l. into "Serbian Macedonian Massif" s.s. and "Vlasina Unit", according to the mentioned subdivisi on the "Vlasina Unit" belongs to the Carpatho-Balkanides. One year later, KArAMATA (1997) subdivided the "Serbian Macedonian Massif" (coined by Dimitrijević, 1959) into the two subunits: "the west composite terrane of "Serbian Macedonian Massif" and "ranovac-Vlasina-osogovo terrane". The west composite terrane kept its original name ("Serbian Macedonian Massif" s.s.), whereas the "ranovac-Vlasina-Osogovo terrane" was assigned to the Carpatho-Balkanides. Similar attempts were in the past ALeKSić et al. (1974) and BOGDAnOVić (1976) pointing out that the eastern parts of the "Serbian Macedonian Massif" belong to a system of the inner napes of the Carpatho-Balkanides. Following the "Serbian Macedonian Massif" concept of KArAMATA (1997), in the paper of KräUTner & KrSTić (2002) for the "Serbian Macedonian Massif" s.s. and Supragetic units has been introduced: "both units derived from the same Bucovino-Getic microplate, the western, Serbo-Macedonian part overthrust towards the west the ophiolitic Vardar zone, whereas the eastern, Supragetic part obviously belongs to the east-vergent Carpathian nappe system". The two units are dif ferentiated by a prominent (probably dextral) shear zone, extending a few hundreds of meters in width. The zone is of post-Upper Cretaceous age being mostly covered by younger sediments. The shear zone is exposed at Vršac, between Veliki-and Mali-jastrebac, north of Leskovac (Dušanovo mylonite zone). The aforementioned report introduced a new structural framework of the Carpatho-Balkanides (Ora viţa, niš, and Sofia), whereas the Serbo-Macedonian Unit and the Vardar Zone were introduced as a segment of Carpatho-Balkanides. A few recent authors (e.g., VOZárOVá et al., 2009) mentioned that the "ranovac-Vlasina-Osogovo Terrane" and the Supragetic are synonymous ( Table  1). The authors published in the colored tectonic sketch of the Carpatho-Balkanides within the geological map of Carpatho-Balkanides (KräUTner & KrSTić, 2006). However, this new map is more-less the same as it is the version published previously by KräUTner & KrSTić (2002). The aforementioned map along with the earlier map ("harta geneto-tectonicâ a europei Alpine central şi de sud-est") introduced by SAn DULeSCU (1984) seems to be a groundwork for the paper and associated map "The major tectonic units Alps, Car pathians and dinarides" introduced a bit later by SCHMiD et al. (2008). This paper contains rather ambiguous observations of the "Serbian Macedonian Massif": "…the south, in Serbia and western Bulgaria, we also included the structurally highest unit, referred to as Serbo-Macedonian "Massif" (e.g. DARko SPAhIć & TIVADAR GAuDEnyI diMiTriJeVić 1959, 1997, into this nappe sequence. however, we do not imply that this also applies to a unit that carries the same name in Greece and which experienced a severe Alpine metamorphic overprint (Kilias et al., 1999)". The authors am biguously proposed that the northern parts of the same tectonic unit ("Serbian Macedonian Massif") are incorporated into the Carpatho-Balkanides as the part of the "Dacia Mega-Unit", whereas for its southern limb authors provide no comment considering the tectonic configuration. On the basis of this paper of SCHMiD et al. (2008), CVeTKOVić et al. (2015) introduced the Serbo-Mace donian Massif as the structural up permost part of "Dacia terrane" and a more internal unit relative to the above-described Car patho-Balkanides (compa rable to the Supragetic nappe of romania). GrUBić et al. (1999) stated that the "Serbian Macedonian Massif" is "neither unique, nor old nor middle unit". This system, according to the authors, is comprised of the two tectonic layers: the "Upper Complex" -Moravicum, and the "Lower Complex"jastrebicum (jastrebac tectonic window, western margin of the LC SMU). The Moravicum is consisting of the juhor-jablanica composite terrane and the "ranovac-Vlasina-Osogovo terrane" (terranes defined after KArAMATA & KrSTić, 1996). The most recent paper of GrUBić et al. (1999GrUBić et al. ( , 2005 suggests that the Moravicum and jastrebicum should be a part of the Carpatho-Balkanides denominated as the "inner Carpatho-Balkanides" ( Table 1).
With regards to the southern extension of the LC SMU in Bulgaria, north Macedonia and Greece, there is a separate ongoing discussion. riCOU et al. (1998) according to the analysis of the metamorphism and some rather unclear observations classified the "Serbian Macedonian Massif" as a part of the rhodope Massif (Table 1). ZAGOrCHeV (in CArMinATi et al., 2004) concluded that the "Serbian Macedonian Massif" was initially a discrete entity -a peri-Gondwanan fragment "Dardania". A bit later (ZAGOrCHeV & MiLOVAnOVić, 2006) still kept the "Serbian Macedonian Massif" as an open question because the "Serbian Macedonian Massif" is a peri-Gon dwanan fragment or the relict of the pre-Cadomian continent. The latest analytics of PeyTCHeVA et al. (2015) corroborates that the "Serbian Macedonian Massif" is a peri-Gondwanan fragment (Table 1). iAnCU et al. (2005) recognized the tectonic similarities in the Banat Mts. (Suprageticum) and the SMU (Table 1). AnTić et al. (2016a,b) defined a Paleozoic "Galatian supra-terrane" whereas the author incorporated the 'eastern Veles Series' and the "Serbian Macedonian Massif" s.s. suggested earlier by DiMiTrijeVić (1995, 1997), rOBerTSOn et al., (2013 (Table 1). ABBO et al. (2020) just recently indicated an orthobasic origin of the Greek segment indicating a pre-Silurian age instead Silurian that was pointed out by some earlier authors (HiMMerKUS et al., 2009).

Overview of the hitherto geodynamic concepts
The LC SMU and Supragetic basement as the metamorphic inliers have been considered within several, rather contrasting tectonic concepts with an abundance of discrepancies (see also discussion in SPAHić et al., 2019a): (1) The tectonic concept of DiMiTrijeVić (1959,1963,1992,1997,1999) which configured the SMU (LC SMU and Supragetic/"Upper Complex") as a discrete first-order tectonic unit. SMU is comprised of the two subunits: the low-grade metamorphic complex ("Upper Complex"), and the medium-to high-grade metamorphic complex (LC SMU); (2) The tectonic concept of the Moravides which explains a set of the four nappes within the firstorder entity (interpreting also as the southern extension of the romanian Supragetic) introduced by AnđeLKOVić (1982); (3) Milestone of the Alpine concept in the Southern Carpathians portrayed the SMU as a segment of the Getic/Supragetic Unit (sensu SAnDULeSCU, 1984). This configuration is comprised of several basement ter ranes interfingered by a network of Variscan and Alpine thrusts (see also iAnCU et al., 2005 and references therein); (4) The concept of the SMU s.s. which is exclusively the LC SMU which means a discrete first-order terrane, accommodated to the west of the con temporary "ranovac-Vlasina-Osogovo Terrane" or the 60 years of the Serbo-Macedonian Unit concept: From Cadomian towards Alpine tectonic frameworks Supragetic in Serbia (sensu KrSTić & KArAMATA, 1992;KArAMATA & KrSTić, 1996;KräUTner & KrSTić, 2002;Fig. 3a). The authors divided the Supragetic base ment into the "Upper Supragetic" ("Bosca-Bu kovik Vlasina nappe") and the "Lower Supragetic" ("Locva-ra novac-Poružnica nappe") excluding a non-dif ferentiated Serbo-Macedonian Unit or the LC SMU. Despite a significant contribution to the Alpine configuration (KräUTner & KrSTić, 2002, 2006, it remains unclear which unit or terrane makes the northern extension of the LC SMU in romania; (5) The recent tectonic synthesis enclosing the central part of See (including the LC SMU and Supragetic), excludes the correlation with its basement analogs in north Macedonia and Greece (SCHMiD et al., 2008(SCHMiD et al., , 2020. This attempt synthesizes a regional Mesozoic configuration favoring the interpretation of the Alpine-Carpathian-Balkan fold-and-thrust belt as an aggregation of the lithotectonic units referred to as of Mesozoic aggregated "terranes" -"Major tectonic units" (SCHMiD et al., 2008). Accordingly, to the Alpine basement "terranes" (Supragetic basement and LC SMU) are the members of the "Dacia Mega-Unit". This terrane represents an ag glomerated terrane (probably depicted by the similar exhumation times) connecting the pre-Mesozoic exotic-and local Alpine allochthones; (6) The pioneering pre-Alpine or the Variscanbased reconstruction explaining the Variscan or "Thracian suture" (HAyDOUTOV, 1989)

ment) and Thracian terrane (includes the LC SMU)
of Pan-African inheritance (e.g., HAyDOUTOV, 1989;HAyDOUTOV & yAneV, 1997;yAneV et al., 2005;Win -CHeSTer et al., 2002, 2006); (7) A recent attempt of the reconstruction of early Paleozoic tectonics based on the detrital zircon analyses of the LC SMU and Supragetic basement (AnTić et al., 2016b) was driven by a Paleozoic paleogeographic reconstruction favoring the "Galatian Superterrane" proposed by STAMPFLi et al. (2013 and referenced therein). A set of samples (with sedimentary protolith) collected from the Supragetic basement, LC SMU and its regional analogs (Ograzhden unit). The diagrams exhibited the two main source systems of the recycled grains. The dominant ages are: (i) Supragetic basement has distinctive peak of 540 Ma (lowermost Cambrian), (ii) within the LC SMU there are two peaks -560 Ma and the distinctive peak of 460 Ma.
Despite a significant effort of regional authors (iAnCU et al., 2005;KräUTner & KrSTić, 2002;BALin -TOni et al., 2010, 2012, 2014AnTić et al., 2016bAnTić et al., , 2017ZAGOrCHeV, 2015 and references therein;KyDOnAKiS et al., 2016;iAnCU & SeGHeDi, 2017;SPAHić & GAUDenyi, 2018;SPAHić et al., 2019a), it is still difficult to even infer the complete Alpine architecture and displaced Variscan imprints. Thus, a proper definition and outlining the original LC SMU in cludes the con nection with the Supragetic Unit and its basement is of vital importance (Fig. 1, 3a). To make matters more complex, the southern continuation of the LC SMU (north Ma ce donia, Greece) has indeed another set of peculiarities: a presence of the "eastern Veles Series" (DiMiTrijeVić, 1997;AnTić et al., 2016b;SPAHić et al., 2019b;position in Fig. 1); the Vertiskos unit of northern Greece (southern extension of the LC SMU) is of Silurian-(HiMMerKUS et al., 2009) or still of pre-Silurian age , whereas the Supragetic basement is absent in Greece.
The modern ultra-thin slivered crustal configuration of the LC SMU is largely depicted by the deep-crustal geophysical data beneath the investigated basement inlier (MiLiVOjeVić, 1993 ; Fig. 3b). With regards, the Alpine structural configuration or boundaries of the inlier, the overprinted interface between the Supragetic and Getic is in the form of the east-vergent nappe (Serbia; Fig. 3a). The LC SMU is positioned to the west, on top of the documented Mesozoic suture referred to as the (east) Vardar Zone (SPAHić & GAUDenyi, 2019 and references therein; Fig.  1). Towards the eastern boundary i.e. towards the Supragetic Unit, the interface is re presented by an east-verging nappe (Fig. 3a). nevertheless, the very character of the boundary varies along the strike. in the vicinity of Mali jastrebac Mt. (see Fig. 1 for position) interface is in the form of the shear zone (erAK et al., 2016;SPAHić & GAUDenyi, 2019). The apatite fission track ages derived from the samples collected across the central-southern LC SMU (Serbia) point to the Late Cretaceous cooling (97±21 and 73±13 Ma;AnTić et al., 2016a). Similar age and the low-tem perature thermochronology (zircon and apatite fission-track from gneisses and mica schists of the "Morava unit" or the LC SMU (chlorite-sericite schists of the "Boljevac-Vukanja sub-unit") indicated the late early to early late Cretaceous exhumation times (~110-90Ma;erAK et al., 2016). Similar eocene to the Oligocene exten sional core-complex event exhumed the Osogovo-Lisets Metamorphic Complex (AnTić et al., 2016a; Fig. 4). However, the Alpine criteria (nappe stacking architecture and its vergence), does not provide a satisfactory correlation level between these basement units tectonically displaced within the region. One of the prominent examples is the greenshist-facies Miniş unit in romania (iAnCU et al., 2005). At the first glance, this unit which requires further correlation with the "Lužnica Unit" in eastern Serbia (Fig. 3a).
The LC SMU and the ana log Ograzhden Unit (sensu ZAGOrCHeV, 1967;KOUnOV et al. 2012;Fig. 4) have the two prominent synoptic density peaking of the ma gmatic and metamorphic zircon spectra of 480 Ma to 550 Ma. The age of the Ograzhden Unit is reported as ~462-451 Ma (ortho-and para metamor phic rocks are dated with a combination of LA-iCP-MS and iD-TiMS U/Pb zircon methods, ZAGOrCHeV et al., 2012ZAGOrCHeV et al., , 2015MACHeVA et al., 2016) whereas PeyTCHeVA et al. (2015) in the Ograzhden and Belasitsa Mountains use iD-TiMS with the in-situ LA-iCP-MS U-Pb zircon dating suggesting the 450-455 Ma age of the Ograzhden orthogneisses. A segment with the Silurian age of LC SMU is documented within the augengneisses (orthogneisses) of the Vertiskos Unit in Greece (HiMMerKUS et al., 2009).
The peculiar mediumgrade Variscan metamorphism of the LC SMU was recently dated according to the overprint of the Silurian igneous rocks (AnTić et al., 2016b). The earlier results indicated the early Paleozoic or late Cambrian event (BALOGH et al., 1994;ZAGOrCHeV & MiLOVAnOVić, 2006), whereas the am phibolite facies overprint is attributed to a Variscan orogenic event (DiMiTrijeVić et al., 1967;MeDAriS et al., 2003). However, as the LC SMU is positioned far from the Variscan Carpathian-Balkan front (location of the late Paleozoic suture at SPAHić et al., 2019), it remains unclear in which manner the LC SMU was over printed reaching the medium-to high-grade level (similar to some of the basement units of the Getic basement; Fig. 3a) whereas the more internal pro ximate Supragetic basement has a greenschist-facies imprint. Thus, the original tecto nostratigraphic relationship between the LC SMU and the Supragetic basement is the vital criterion for successful de ciphering of the modern tectonic framework.

Scarce Variscan and pre-Variscan early Paleozoic imprints
As a segment of Alpine orogeny, it is obvious that the Variscan, pre-Variscan imprints or original tectono-stratigraphic relationship between the LC SMU and Supragetic suffered from the repeated tectonic reworking (ALeKSić et al., 1988;also in DiMiTrijeVić, 1997). However, the pre-Alpine kinematic markers or tectonic indicators of the neoproterozoic-Lower Paleozoic magmatic episodes (AnTić et al., 2016b) imprinted into the Carpatho-Balkanides/South Carpathian "terrane" assemblage are: Late Paleozoic suture ("Thracian suture"; sensu HAyDOUTOV, 1989;PLiSSArT et al., 2018). The late Paleozoic suture connecting the "Protomoesian", "Balkan Terrane" and the "Thracian microcontinents" (the "Thracian suture") placing the obducted ophiolite-bearing volcanic arc (Struma Diorite/Frolosh assembly of the neoproterozoic age; HAyDOUTOV, 1989) (Fig. 4). The zone is later characterized as a pre-Mesozoic west-verging thrust, positioning the Supragetic basement over the LC SMU (KrSTić & KArAMATA., 1996). in terms of paleogeography, the presence of the major Carpathian-Balkan Paleozoic suture just recently was proposed at the expense of closing rheic Ocean (BOnCHeVA et al., 2010;SPAHić et al., 2019). Moreover, the back-arc ophiolites of the Devonian age accommodated within the opposed Danubian basement (ZAKAriADZe et al., 2012;PLiSSArT et al., 2017 recently, in a more external position (near the interface of the LC SMU, Sebeş-Lotru terrane and Supragetic basement) another still enigmatic pre-Variscan suture is depicted (iAnCU & SeGHeDi, 2017). in this context, as pointed in the previous chapters, there is a high likelihood that the majority of the neo proterozoic -Lower Cambrian to Lower Ordovician depositional or tectonic structures underwent several deformational events. More precisely, exactly in the case of the LC SMU and the Supragetic basement (exhumed) crustal contact or the shearzone of the Mali jastrebac Mt. (Central Serbia, see it appears that juvenile LC SMU was a kind of neoproterozoic marginal basin associated with the north Gondwanan foredeep (including the Ava lonian-Cadomian magmatic arc stage; AnTić et al., 2016). The neoproterozoic relationship with the Supragetic basement is still ambiguous, despite a widespread neoproterozoic to early Cambrian magmatism (AnTić et al., 2016) connecting these two basement units. The perplexing relationship is further marked by the presence of Lower Ordo vician brachiopods (PAVLOVić, 1977). To make mat ters more complex, the presence of a wi despread Middle Ordovician magmatic event 60 years of the Serbo-Macedonian Unit concept: From Cadomian towards Alpine tectonic frameworks (472-456 Ma, emplacement of mafic dykes; AnTić et al., 2016) with almost identical age is docu mented within the Sebeş-Lotru terrane, ca. 460 Ma;BALin TOni et al., 2010;Ograzhden unit;ZAGOrCHeV et al., 2012ZAGOrCHeV et al., , 2015MACHeVA et al., 2016). Such early Paleozoic imprint pattern suggests a more complex "intra-Ordovician" lithospheric-scale episode (see STePHAn et al., 2019, for a discussion). extension and the onset of the Paleozoic latitudinal drift of these peri-Gondwanan terranes begun after this peculiar stage. This stage can tentatively be marked by the contact between latter terranes (Fig.4). The se paration from the northern Gondwana mainland enabled the oceanic spreading and drift that pro duced deepmarine conditions and the formation of the sedimentary cover belonging to the "Kučaj/Getic Unit" (latest Ordovician -Silurian; sensu KrSTić et al., 2005; c.f. SPAHić et al., 2019a and references therein).

Conclusions
A short summary after 60 years of working in the complex Serbo-Macedonian basement entity is as follows: -The LC SMU represents a segment of wider continental margin of neoproterozoic-Lower Ordovician age imprinted with a set of Cadomian and early Paleozoic isotopic characteristics. This setting reflects a protracted Pan-African to Lower Paleozoic setting of peri-Gondwanan nappes; -LC SMU is a highly complex crustal amalgamation (no evidence of cratonic crust; Fig. 5) with the documented repeated anatexis (ZAGOrCHeV, 2015). The Supragetic basement is an ocean floor assembly of the similar age (AnTić et al., 2016b; SPAHić et al., 2019 and references therein); -in a broader tectonic context, we suggest that these peri-Gondwanan systems (in the configuration of Alpine nappes) with distinctly different basements were under direct control of the southward sub duction of an early Paleozoic ocean. This terrane assembly LC SMU-Supragetic initially amalgamated along the north Gondwanan -Cadomian continental margin involving an unknown event that occurred sometime during post-Cambrian. in paleogeogra phical terms, both peri-Gondwanan systems (the LC SMU and the Supragetic/Getic) were situated in an outer flank of the Pan-African margin; -Post-Lower Paleozoic events significantly disrupted the original configuration of the two ad joining systems: LC SMU and Supragetic basement. Despite significant tectonodepositional discrepancies, both systems can be regarded as discrete entities in the Alpine structural plan as suggested by the KArAMATA & KrSTić (1996). profit sectors. The paper benefited from the constructive review of Prof. Dr iVAn ZAGOrCHeV from Bulgarian Academy of Sciences. eastern Mediterranean region. Geological Soci -истражи вања, као и кроз анализу аналитичких података, указано је на постојање пре-Варисцијског литосферног догађаја највероватније ордовицијумске старости. Искључиво када се буде утврдио директан оригинални однос између Српско-македонске јединице и уп ра гетика биће омогућено решавање проблема како варисцијске конфигурације тако алпске и ко релације ових бејсментских јединица.