Tectonic, magmatic, and metallogenic evolution of the Late Cretaceous arc in the Carpathian‐Balkan orogen

Abstract

The Apuseni-Banat-Timok-Srednogorie Late Cretaceous magmatic arc in the Carpathian-Balkan orogen formed on the European margin during closure of the Neotethys Ocean. It was subsequently deformed into a complex orocline by continental collisions. The Cu-Au mineralized arc consists of geologically distinct segments: the Apuseni, Banat, Timok, Panagyurishte, and Eastern Srednogorie segments. New U-Pb zircon ages and geochemical whole rock data for the Banat and Apuseni segments are combined with previously published data to reconstruct the original arc geometry and better constrain its tectonic evolution. Trace element and isotopic signatures of the arc magmas indicate a subduction-enriched source in all segments and variable contamination by continental crust. The magmatic arc was active for 25 Myr (~92-67 Ma). Across-arc age trends of progressively younger ages toward the inferred paleo-trench indicate gradual steepening of the subducting slab away from the upper plate European margin. This leads to asthenospheric corner flow in the overriding plate, which is recorded by decreasing Nd (0.51234 to 0.51264) ratios over time in some segments. The close spatial relationship between arc magmatism, large-scale shear zones, and related strike-slip sedimentary basins in the Timok and Pangyurishte segments indicates mild transtension in these central segments of the restored arc. In contrast, the Eastern Srednogorie segment underwent strong orthogonal intraarc extension. Segmental distribution of tectonic stress may account for the concentration of rich porphyry Cu deposits in the transtensional segments, where lower crustal magma storage and fractionation favored the evolution of volatile-rich magmas.

U‐PB Detrital Zircon Geochronology of the Lower Danube and Its Tributaries: Implications for the Geology of the Carpathians

“…Gallhofer et al (2015Gallhofer et al ( , 2017 have contributed to the U-Pb geochronology knowledge of the Jurassic and Cretaceous Carpathian magmatic arc rocks of South Apuseni and Banat, respectively. Instead, as we will show below, they are dominated by Neoproterozoic U-Pb ages (560-610 Ma) and a distinctive array of less abundant 1-2-Ga zircons that are rather similar to the Danubian unit in the South Carpathians but very different from the higher Alpine structural units found toward the Carpathians interior.…”

“…A few early extension-related rocks in Dobrogea and the East Carpathians are known to be of Triassic age; the Ditrau alkaline massif of the East Carpathians (Ar-Ar age of 230 Ma; Dallmeyer et al, 1997) with a diameter of about 20 km is sizable but unlikely to be a major source of DZs. A belt of intermediate calc-alkaline rocks extending into the South Carpathians to the Apuseni Mountains, sometimes referred to as banatites , formed in response to the Sava ocean subduction to the south over a short period between 75 and 82 Ma in the Romanian segment (Gallhofer et al, 2015;Zimmerman et al, 2008). These rocks occupy a sizable portion of the southern Apuseni Mountains but are probably zircon poor due to their relatively mafic average composition.…”

Polycyclic alpine orogeny in the Rhodope metamorphic complex: the record in migmatites from the Nestos shear zone (N. Greece)

“…1), the RMC is characterized by an almost complete lack of radiometric ages in the time interval between ∼115 and ∼70 Ma. Ages around 70 Ma are found along the northern margin of the RMC where several intrusions were emplaced at ∼67-72 Ma, representing a southern extension of the adjacent Srednogorie magmatic arc (von Quadt and Peytcheva, 2005;Gallhofer et al, 2015). As suggested in Section 1, the existence of a large time gap (≥ 45 Myr) in the geochronological record seems to support the hypothesis of a polycyclic orogenic evolution for the largest part of the RMC.…”

“…Judging from the ∼115 to ∼70 Ma "geochronological gap" on the regional scale, renewed underthrusting of the SU rocks is unlikely to have started before 70 Ma. From ∼90 to ∼78 Ma, syn-kinematic plutons associated with the Srednogorie magmatic arc were emplaced along the Maritsa Shear Zone, a major NW-SE strike-slip shear zone forming the northern boundary of the RMC (e.g., Georgiev et al, 2009;Naydenov et al, 2013;Gallhofer et al, 2015). At the northwestern tip of the RMC, top-to-SE oblique thrusting within higher levels of the metamorphic pile has recently been dated at ∼76 Ma (Gorinova et al, 2015).…”

“…In Figure 18, we have taken 17°/km for the mean geothermal gradient in a stable continental crust, which yields 600°C at the base of a crust 35 km thick. During the period from ≥ 100 to ∼70 Ma, the RMC was in a supra-subduction setting (except possibly the PU and UPU; e.g., Froitzheim et al, 2014) and evolved from fore-arc to "near-arc" conditions as a result of the southward migration of arc magmatism in the Srednogorie domain north of the RMC (e.g., Gallhofer et al, 2015). Consequently, the geothermal gradient within the RMC may have progressively increased, but no attempt is made to display this feature in Figure 18.…”