The geochemistry, origin and tectonic setting of the Tozlu metaophiolite in the Kazdağ Massif (Biga Peninsula, NW Anatolia)
Abstract: The Tozlu metaophiolite is composed predominantly of metagabbro, banded amphibolite, metadunite, and serpentinite, which are exposed in the Kazdağ Massif located in the northwestern part of Turkey. The geochemistry (major, trace, and rare earth elements) and petrography of the Tozlu metaophiolite in the Kazdağ Massif provided significant knowledge about protolith, petrogenesis, source characteristics and tectonic setting in northwest Turkey. Trace element geochemistry, Ti/Y (29.95–296.92 ppm) and Nb/Y (0.01–0.17 ppm) ratios suggest that metaophiolitic rocks were derived from a tholeiitic magma and igneous protolith of basaltic composition. The immobile trace element tectono-magmatic discrimination diagrams define a mid-ocean ridge basalt (MORB) to volcanic arc (IAT) affinity for the Tozlu metaophiolite. The metaophiolitic rocks demonstrate flat rare earth element (REE) patterns and enrichment of large ion lithophile elements (LILEs; i.e., Rb, Ba, Th), as well as depletion of high field strength elements (HFSEs; i.e., Nb, Th, Ti, Hf). N-MORB characteristics of the Tozlu metaophiolite on a multi-element diagram suggest that the protolith of metaophiolitic rocks generated in a subduction-related setting. The tholeiitic metaophiolitic rocks resulted from the metamorphism of an island arc-type basaltic protolith and display subduction zone components according to the Th/Yb and Ta/Yb ratios. The Tozlu metaophiolite with MORB/IAT affinity witness for supra-subduction zone originated in island arc/back-arc settings.
Bulk-rock and mineral-scale geochemical evidence of open-system magmatic processes in the felsic rocks of the northern part of the Ditrău Alkaline Massif (Eastern Carpathians, Romania)
Abstract: The felsic suite in the northern part of the Ditrău Alkaline Massif has previously been considered as a homogeneous, uniform unit of the igneous complex. However, these felsic rocks exhibit remarkable diversity on the micro-scale. Petrographic observations were complemented by bulk-rock and mineral-scale geochemical data to further support this hypothesis. Whole-rock composition of the studied rocks validates the presence of two, compositionally-different felsic cumulate piles in the massif (characterised by Eu/Eu* = 2.5–6.7, ΣREE = 125–206 ppm and Eu/Eu* = 1.0–1.1, ΣREE = 358–688 ppm, respectively). Mineral chemical data (amphibole, clinopyroxene, and plagioclase) were acquired from crystals of different textural positions (clot-forming and isolated) to understand which of the ferromagnesian minerals and plagioclase have the highest potential for recognising distinct magmatic environments and open-system magmatic processes. The composition of clinopyroxenes (diopside with mg# = 0.77 and 0.85, respectively) overlaps with the formerly published data. Moreover, a new, cumulus-phase occurrence of the clinopyroxenes with a convex REE pattern has been identified. Abrupt changes of Ba, Sr, TiO2 and ΣREE concentrations in different domains of the zoned amphibole crystals and variations in the MgO, FeO, TiO2, Sr, Ba, La, Ce, and anorthite content in plagioclase crystals, together with the bulk-rock data point to the hybrid nature of the majority of the investigated rocks. Our recent geochemical data support the previous, predominantly petrography-based assumptions that the felsic suite in the northern area of the massif was formed in a dynamic, open-system magmatic environment, wherein crystal settling, magma mixing, crystal/mush transfer, and recycling as well as country rock assimilation, prevailed.
Systematics of clinopyroxene phenocrysts, megacrysts, and cumulates in Tertiary basalts of southern Slovakia with implications in the structure of lithospheric mantle
Abstract: Tertiary alkali basalts in the South-Slovakian Basin contain homogeneous clinopyroxene megacrysts, composite phenocrysts with chemically and optically homogeneous olive-green cores overgrown by oscillatory zoned rims, and fragments of clinopyroxene-rich igneous cumulates. Discrimination based on Ca, Na, Ti and Cr concentrations defined clinopyroxenes with alkalic, tholeiitic and transitional affinities. Single-pyroxene thermobarometry revealed that the incipient clinopyroxene crystallization occurred at 1300–1350 °C and 2.0–2.2 GPa, thus identifying the zone of mantle melting in a depth of >70 km. The highest frequency of pressure data from clinopyroxene-rich mafic cumulates, betwen 0.7 and 1.2 GPa, indicate stagnant basaltic reservoirs located beneath the Moho discontinuity, 30–43 km deep. Late fractionation products of alkali basalt derivatives may have occurred as laccoliths and dykes in the lower crust. Thermodynamic modelling of mineral assemblages of cumulate xenoliths revealed that parental melts for both alkalic and tholeiitic affinities were silica-undersaturated 46–46.5 wt. % SiO2) and moderately alkalic (index of alkalinity 2.0–3.8, Mg# ~50) basalt to basanite, with pre-eruptive water contents between 1 and 2 wt. %. Amphibole–biotite–titanite–ilmenite–plagioclase cumulates recorded the advanced stage of fractionation of more calcic basalt at 900–920 °C and 0.65 GPa. Deep-seated basalt reservoirs have been less alkalic than erupted lavas, the latter showing a Mg depletion and an increasing aluminium saturation index diagnostic of the extensive crystal separation on the way to the surface. Olive-green megacrysts and cores of zoned phenocrysts originated at lower temperatures and higher pressures than their autocrystic rims. The megacrystic assemblage of Fe-diopside–Al-augite, Mg-calcite, apatite, ulvöspinel, and disintegrated amphibole crystallized from evolved, relatively cold (~950–1100 °C), Fe-rich carbonatite–alkalic silicate melt within the depth interval of 26–53 km, corresponding to a lithostatic pressure of 0.7–1.5 GPa. The silicate–carbonate–phosphate melt fraction probably originated in the subducting slab of oceanic crust.
An updated generic status of Ammogloborotalia aff. subvesicularis (Hanzlíková) from the Middle Eocene deposits of the Fore-Magura Unit (Polish Outer Carpathians)
Abstract: The Middle Eocene microfauna of the Fore-Magura Unit contains rich foraminiferal assemblages with numerous trochospiral, agglutinated species originally described as Trochammina subvesicularis Hanzlíková. The paper provides a reconsideration of this taxon due to its inconclusive generic status. A new insight into the systematics of trochamminid species is also discussed. A total of 25 samples from Middle Eocene slope marl deposits of the Fore-Magura Unit (from the western part of the Polish Outer Carpathians) were taken for examination. Based on the analysis of 183 specimens recovered from deep-sea mixed foraminiferal assemblages the species is assigned to the genus Ammogloborotalia (Zheng & Fu). The Eocene specimens, named under different generic names and in open nomenclature, similar to the description of Trochammina subvesicularis Hanzlíková, should be referred to the taxonomic name Ammogloborotalia aff. subvesicularis. Similar to modern species of Ammogloborotalia (Zheng & Fu), their Middle Eocene representatives imply a bathyal water depth and good connection of the flysch-type Fore-Magura zone basin with the World Ocean.
Variation of seismicity parameters and its link to tectonic features of the central portion of the Zagros Fold-Thrust Belt, Iran
Abstract: The Zagros Fold-Thrust Belt is one of the most tectonically active regions in the world. The seismicity of this belt is affected by various factors and has certain complexities. This paper provides the results of assessment of temporal and spatial seismicity variations of the central portion of the belt in Fars and Bushehr provinces and their link to regional tectonic properties. Relatively, everywhere in the belt, the geometry of the folds has been mainly affected by thrusts and basement faults. There is a meaningful link between seismic activity and folding in the belt. The most abundant types of folds are detachment folds, fault bend and fault propagation folds. They play an important role in the spatial seismicity of the area. The maximum number of seismic events have medium magnitude which ranges between 2.5 and 3. There is a decreasing trend of a and b parameters from south-west to north and north-east where the occurrence of higher magnitude earthquakes is expected. Temporal analysis of seismicity shows that earthquakes with magnitude ≥ 6.5 have a ten-year return period in the region. The occurrence of several earthquake groups in the belt was in the form of swarms showing point or linear spatial distribution. Some of these possible swarms are around transverse faults, salt domes and some are related to blind faults, which indicate the complexity of the seismicity in this belt. Spatial distribution of low magnitude seismic clusters is also influenced by two other factors (1) existence of frequent salt domes many of which might be active and their spatial links to major faults and (2) human-related activities, especially hydrocarbon extraction.