International Geological Journal - Official Journal of the Carpathian-Balkan Geological Association

Volume 70 no. 3 / June 2019

Volume 70 no. 3 / June 2019

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Articles in this issue

  • Deformation patterns in the Van region (Eastern Turkey) and their significance for the tectonic framework

    Abstract: The area of investigation is located on the south-eastern shore of Lake Van in Eastern Turkey where a destructive earthquake took place on 23rd October, 2011 (Mw = 7.1). Following the earthquake, different source mechanisms, deformations, and types of faulting have been suggested by different scientists. In this research, Edremit district and vicinities located on the southern side of Van have been investigated to understand the deformation pattern in a travertine (400 ka) formation on the surface, and its structural and stratigraphic relationships with the main faults under the surface by using two-dimensional (2D) Electrical Resistivity Tomography (ERT) profiles. The results were used to document the deformation pattern of rocks with the Miocene and the Holocene (400 ka travertine) in ages. By means of the investigations, deformation patterns implying the tectonic regimes during the Oligocene–Miocene–Pliocene, and Quaternary time have been determined. According to detailed field work, the local principal stress direction has been defined as approximately N 35° W. This is also supported by the joint set and slip-plane data. Moreover, Oligocene–Miocene units provide a similar principal stress direction. Our data suggest that the southern part of the Elmalık fault is characteristic of reverse faults rather than of the normal fault system that has been previously reported. In addition, the Gürpınar fault controlling the deformation patterns of the region is a reverse fault with dextral component.
  • Graptolite turnover and δ13Corg excursion in the upper Wenlock shales (Silurian) of the Holy Cross Mountains (Poland)

    Abstract: The mid–late Homerian Age of the Silurian Period was a time of intense changes in biota, oceanic chemistry, and sea level and is known as the lundgreni extinction (for the graptolite extinctions), the Mulde bioevent (for the conodont turnover event) or the Homerian carbon isotope excursion (CIE) probably related to glacially influenced climate perturbation. New information on this interval from the deep water sedimentary and graptolite succession of the Kielce Region (Holy Cross Mountains, Poland) of the northern margin of the Małopolska Block is presented here based on analysis of the Prągowiec Ravine section. The lundgreni–nilssoni graptolite biozones interval have been recognized there. This interval is composed by dark shales with very rare benthic fauna, which indicate the deep open-marine (pelagic) paleoenvironment. Ten samples were taken for the δ13Corg analysis from the lundgreni (2 samples), parvus (2 samples), praedeubeli (2 samples), praedeubeli–deubeli (1 sample), ludensis (2 samples) and nilssoni (1 sample) biozones. According to the δ13Corg results, the first positive δ13Corg excursion of the Mulde Bioevent is well recognized. The δ13Corg values rise from −30.7 – −30.1 ‰ in the lundgreni Biozone to −29.3 – −28.7 ‰ in the parvus Biozone and fall below −30 ‰ in the praedeubeli–deubeli interval. The second positive δ13Corg peak of the Mulde Event was not recognized in the Prągowiec Ravine. Based on the numerical comparisons using Raup-Crick metric of co-occurrences of graptolite species, the upper Homerian was characterized by significant between-biozone turnover of these taxa at the given locality.
  • Geochronology and Sr–Nd–Hf isotope constraints on the petrogenesis of teschenites from the type-locality in the Outer Western Carpathians

    Abstract: The Teschenite Association Rocks (TAR) in the Outer Western Carpathian (OWC) flysch form a classic suite of alkaline intrusions where teschenite and picrite were first defined. They represent continental intraplate volcanism that produced a wide range of melano- to mesocratic rocks emplaced during the Early Cretaceous rifting within the southern margin of the European Plate. Geochemical modelling indicates that they may be a product of ~2–5 % partial melting of the metasomatised, asthenospheric mantle. The variations in REE (low / heavy REE content, LaN/YbN = 11–34) are consistent with deep melting of garnet peridotite. Initial ε(Nd)i = 5.0–6.3 and ε(Hf)i = 4.9–10.0 preclude the significant mature crust involvement. Instead, a linear array formed by the 143Nd/144Nd and 176Hf/177Hf isotopic ratios points to a genesis from the mixed, HIMU–OIB source with the more depleted, MORB-type component. Mantle metasomatism was most likely caused by the Variscan subduction–collision processes as indicated by the depleted mantle Nd model ages. The isotope and trace element ratios of the TAR resemble the European Asthenospheric Reservoir (EAR) — the common mantle end-member for the widespread Cenozoic volcanic rocks in Europe. This confirms a long-term existence of the EAR mantle component beneath the Central Europe, at least since the Early Cretaceous. In situ laser-ablation ICP-MS U–Pb dating of titanite indicates short duration of mafic alkaline magmatism in the OWC, lasting from 123.7 ± 2.1 to 117.9 ± 1.8 Ma. Emplacement of the TAR is correlated with the maximum lithospheric thinning that triggered adiabatic decompression and partial melting of the upwelling asthenospheric mantle. Magmatism ceased most likely due to transition to the dominantly compressive regime associated with the major stress field reorganization directly preceding the Carpathian–Alpine Orogeny.
  • The foreland state at the onset of the flexurally induced transgression: data from provenance analysis at the peripheral Carpathian Foredeep (Czech Republic)

    Abstract: The Žerotice Formation recognised in a confined area NE–SE of Znojmo represents a basal member of the sedimentary succession of the southwestern margin of the Carpathian Foredeep in Moravia (Czech Republic). Two facies associations were recognised within the formation. The first one mantles the pre-Neogene basement with an irregular unconformity, reflects arid climatic conditions and deposition of episodic shallow, high-energy stream flows and/or mass flows (alluvial to fluvial deposits). The second facies association is interpreted as lagoonal to distal flood plain deposits. The barren unfossiliferous deposits of the Žerotice Formation are covered by nearshore marine Eggenburgian deposits. The boundary between these deposits represents a sequence boundary (i.e. the basal forebulge unconformity). Detailed provenance studies of successive beds below and above this sequence boundary showed differences in the source area and paleodrainage. Both the local primary crystalline rocks (Moravian and Moldanubian Unit, Thaya Batholith) and older sedimentary cover (especially Permo–Carboniferous sedimentary rocks) form the source of the Žerotice Formation. All these geological units are located only a few km away from the preserved areal extent of the deposits of the Žerotice Formation (short transport and a local source). The source areas of the overlying marine Eggenburgian beds are located far more to the W and NW in the Moldanubian and Moravian Units (longer transport, extended source area). Local confined preservation of the Žerotice Formation is preliminarily explained as connected with a tectonically predisposed paleovalley.
  • The Upper Cretaceous intrusive rocks with extensive crustal contribution in Hacımahmutuşağı Area (Aksaray/Turkey)

    Abstract: The Hacımahmutuşağı area (Aksaray/Turkey) is located in the western part of the Central Anatolian Crystalline Complex (CACC). Gneiss and marble compose the basement units, while intrusive rocks are gabbros and granitoids. The pegmatitic hornblende gabbros contain pegmatitic to fine-grained hornblendes, plagioclase, clinopyroxene, and accessory opaque minerals. The fine-grained gabbros, on the other hand, are composed of plagioclase, hornblende, and biotite as major components whereas the apatite and opaque minerals are present in accessory content. Granitic–granodioritic rocks are the common intrusive rock types in the area, and constitute quartz, orthoclase, plagioclase and biotite, and accessory zircon and opaque minerals. Leucogranites, comprising quartz, orthoclase, plagioclase with minor biotite, hornblende, and with accessory apatite and opaque minerals, are found as dykes intruding the marble and the granitic–granodioritic rocks. Strontium–neodymium isotope data of gabbros and granitoids have high 87Sr/86Sr(i) ratios (0.7076 to 0.7117) and low ɛNd(i) values (−5.0 to −9.8) point out enriched source and pronounced crustal contribution in their genesis. In the Hacımahmutuşağı area, it is plausible that the heat increase caused by the hot zone, which was generated by underplating mafic magma along with the hydrous mafic sills in the lower crust, might have resulted in partial melts from crystallized mafic sills and older crustal rocks. It can be suggested that these hybrid melts adiabatically rose to the shallow crust, ponded and crystallized there and formed the magma source of the intrusive rocks within the Hacımahmutuşağı area and the other hybrid granitic rocks with crustal signatures in the CACC. Geochemical data indicate that granitoids and gabbros are collision to post-collision related sub-alkaline rocks derived from an enriched source with extensive crustal inputs.