The emplacement mode of Upper Cretaceous plutons from the southwestern part of the Sredna Gora Zone (Bulgaria): structural and AMS study

Abstract

Several plutons located in the southwestern part of the Sredna Gora Zone -Bulgaria are examples of the Apuseni-Banat-Timok-Sredna Gora type of granites emplaced during Late Cretaceous (86-75 Ma) times. The studied intrusive bodies are spatially related to and deformed by the dextral Iskar-Yavoritsa shear zone. The deformation along the shear zone ceased at the time of emplacement of the undeformed Upper Cretaceous Gutsal pluton, which has intruded the Iskar-Yavoritsa mylonites. A clear transition from magmatic foliation to high-, moderate-and low-temperature superimposed foliation and lineation in the vicinity of the Iskar-Yavoritsa and related shear zones gives evidence for simultaneous tectonics and plutonism. Away from the shear zones, the granitoids appear macroscopically isotropic and were investigated using measurements of anisotropy of magnetic susceptibility at 113 stations. The studied samples show magnetic lineation and foliation, in agreement with the magmatic structures observed at a few sites. Typical features of the internal structure of the plutons are several sheet-like mafic bodies accompanied by swarms of mafic microgranular enclaves. Field observations indicate spatial relationships between mafic bodies and shear zones as well as mingling processes in the magma chamber which suggest simultaneous shearing and magma emplacement. Structural investigations as well as anisotropy of magnetic susceptibility (AMS) data attest to the controlling role of the NW-SE trending Iskar-Yavoritsa shear zone and to the syntectonic emplacement of the plutons with deformation in both igneous rocks and their hosts. The tectonic situation may be explained by partitioning of oblique plate convergence into plate-boundary-normal thrusting in the Rhodopes and plate-boundary-parallel transcurrent shearing in the hinterland (Sredna Gora).

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

“…Although the origin of the Strandzha, Circum‐Rhodope, and the Rhodope Units is somewhat ambiguous, they certainly have been part of the European continental margin since at least Cretaceous times [ Okay et al , ; Schmid et al , ; Burg , ]. The Rhodope Unit is separated from the Dacia Mega‐Unit along the right‐lateral Maritsa fault system that comprises several NW‐SE trending shear zones, among others the Iskar‐Yavoritsa shear zone, which became active in the Late Cretaceous [ N. Georgiev et al , ; Naydenov et al , ].…”

The exposed base of a collapsing wedge: The Nestos Shear Zone (Rhodope Metamorphic Province, Greece)

“…This process is associated with ∼500 km retreat of the Hellenic slab in Cenozoic times [ Jolivet and Brun , 2010]. The scenario of post‐Early Cretaceous nappe stacking in the Rhodope Mountains at a “proto‐Hellenic” active margin is supported by widely observed synmetamorphic top‐southwest shearing and by the existence of Late Cretaceous arc volcanism in the Sredna Gora Mountains north of the Rhodopes in central Bulgaria [ Boccaletti et al , 1978; von Quadt et al , 2005; Georgiev et al , 2009].…”

Structural and geochronological evidence for Paleogene thrusting in the western Rhodopes, SW Bulgaria: Elements for a new tectonic model of the Rhodope Metamorphic Province

“…[e.g., Boccaletti et al, 1978;Georgiev et al, 2009], which is part of the extensive Apuseni-Banat-Timok-Srednogorie belt. Geochronological studies in the Sredna Gora revealed a general southward younging of the magmatism, from circa 92 Ma in the north to circa 78 Ma in the south [von Quadt et al, 2005].…”