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Interaction between tectonics, plutonism and mineralization of the Duna Pb-Ba ore deposit regarding fluid inclusion study (Central Alborz, Iran)

Sadeghi Alireza, Asiabar Saeid Hakimi, Nezafati Nima, Ganji Alireza, Mukherjee Soumyajit

Acta Geologica Polonica

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2023

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Vol. 73, no. 2

201--222

EN

This article discusses the impacts of overprinting of tectonic and plutonic events on the mineralization of the Duna Pb-Ba ore deposit, according to geologic settings and fluid inclusion studies. The Duna carbonate-hosted deposit contains a significant amount of Ag (18.9–264.3 ppm ), Cu (77–41600 ppm), Sb (32.7–11000 ppm), Sr (63.5–15100 ppm), and Fluid inclusions with 7.34–23.65 wt.% NaCl equivalent. The homogenization temperature of about 110–285°C, as well as the paragenesis of the minerals shows a difference compared with other Pb-Zn deposits such as the Irish-type and MVT. The ore mineralization in the Duna mine occurred as stratabound, open space-filling, and along the brecciated fault zones. The concordant (stratabound) type of mineralization, with salinity and homogenization temperature of 18.54 to 23.65 wt.% NaCl equivalent, and 113°C to 165°C respectively, is usually typical of MVT-ore deposits, which in this area evolved during the Early Cimmerian orogeny and was later interrupted by mineralization along younger brecciated fault zones with salinity and homogenization temperature of 7.34 to 23.65 wt.% NaCl equivalent, and 113°C to 285°C respectively. This discordant mineralization, which occurred along the faults, formed by the end of the Late Cretaceous and during the Cenozoic as a result of the intrusion of a plutonic mass, and is comparable to the Irish-type ore deposits.

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Cretaceous magmatic evolution in the Deylaman igneous complex, Alborz zone, Iran : change from extensional to compressional regime

Akmali Sheida, Asiabanha Abbas, Haghnazar Shahrooz

Geological Quarterly

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2019

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Vol. 63, No. 4

757--770

EN

The Deylaman igneous complex, as a part of the Late Cretaceous rock unit that lies behind the Paleogene Alborz magmatic arc, in the northern Alborz zone, is composed of basaltic sheet lavas alternating with the pelagic calcareous sediments, basaltic pillow lavas, felsic lavas and gabbroic-monzodioritic intrusions. The pelagic calcareous deposits contain microfossils representing the Santonian-Maastrichtian ages. Furthermore, petrographic textures such as the hyalomicrolitic texture and swallow-tail plagioclase crystals in the pillow lavas, and also segregation vesicles in the basaltic sheet lavas, imply high external (hydrostatic) pressures as the magma was extruded in a deep-water environment. The rock samples show both compositional bimodality and characteristic trends in the variation diagrams. Also, some geochemical characteristics imply that the basaltic lavas originated from the partial melting of an undepleted deep mantle source containing spinel lherzolite: the enrichment patterns of LREE/HREE ratios of the samples [(La/Yb)n = 3.93-4.16 for basaltic lavas and 10.92 for felsic lavas] lying between those characteristic of OIBs [(La/Yb)n = 12.92] and EMORBs [(La/Yb)n = 1.91]; similarities between the patterns of multi-element spider-diagrams; LILE bulges in the basaltic samples compared with those of OIBs. Moreover, the samples show influence from two geotectonic environments: supra-subduction zone (SSZ) settings and plume-type within-plate magmas. Therefore, because of the deep submarine environment inferred for the effusive volcanic eruptions in Santonian-Maastrichtian time, it seems that the Deylaman igneous complex evolved through two stages: first, a tensional regime in a supra-subduction zone (farther from the Mesozoic magmatic arc) and formation of an embryonic rift-related oceanic basin in the Late Jurassic-Early Cretaceous; secondly, a compressive regime in the Late Cretaceous-Early Paleocene and inland migration of the magmatic arc. Consequently, the Cretaceous magmatism can be interpreted as a prelude to the Eocene magmatic flare-up in the magmatic arcs of Iran.

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Temporal variations of seismicity parameters in the Central Alborz, Iran

Agh-Atabai M., Mirabedini M.S.

Acta Geophysica

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2014

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Vol. 62, no. 3

486--504

EN

Temporal changes of b-value, fractal (correlation) dimensions of epicenters (De) and occurrence time of earthquakes (Dt) and relations between these parameters were calculated to investigate precursory changes before 28May 2004, Baladeh-Kojour earthquake (Mw = 6.3) of Central Alborz, Iran. 2086 events with MN ≥ 1.7 were selected for our analyses. A wide range of variation was seen in these parameters: b-value ~ 0.61.11, De ~ 0.97-1.64, and Dt ~ 0.13-0.93. The results showed decreases in all fractal parameters several months before the main shock. This decrease, which might have arisen due to clusters of events occurred between 2002-2003, was followed by a systematic increase, corresponding to the increased level of low-magnitude seismicity. It seems that changes in fractal parameters may be precursors of Baladeh-Kojour earthquake which was caused by seismic activation and quiescence. Furthermore, a positive correlation between b-value and De was detected before the main shock (De = 0.87 + 0.7b) and during aftershock sequences (De = 2b ± 0.09), which was further on changed to a negative one (De = 2.56 – 1.32b).

4

Early Carboniferous chondrichthyans from the Mobarak Formation, Central Alborz Mountains, Iran

Habibi T., Ginter M.

Acta Geologica Polonica

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2011

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Vol. 61, no. 1

27-34

EN

Well exposed Tournaisian, mainly carbonate, rocks of the Mobarak Formation in the area of Shahmirzad village, Central Alborz, Iran, yielded almost 200 chondrichthyan teeth and scales, associated with numerous actinopterygian microremains. Ten different taxa were recognised among the chondrichthyan teeth, of which the most abundant are those representing Euselachii (Protacrodus and Lissodus), Symmoriiformes (Denaea), and Phoebodontiformes (Thrinacodus). The high relative abundance of protacrodont crushing teeth, but lack of holocephalian dental elements suggest that the sediments forming the Shahmirzad section were deposited in a shallow shelf environment, but probably not on a carbonate platform.

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Biostratigraphy (ammonites) of the Shemshak Formation (Norian – Lower Bajocian) in eastern Alborz (North Iran)

Seyed-Emami K.

Volumina Jurassica

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2006

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Vol. 4, no. 1

214-215

EN

The Shemshak Formation is a thick, siliciclastic and carbonaceous sequence, being widely distributed along Central and North Iran. It is bounded at the base and on the top, by two major orogenic events in early Late Triassic (Early Cimmerian) and early Middle Jurassic (Mid-Cimmerian). The molassic composition of these strata, with thicknesses up to 4000 m and lateral and vertical facies changes, indicate sedimentation in several foreland basins, in front of tectonically active and uplifted areas, created by Late Triassic movements. The sedimentary environment changes from continental foreland basins to deltaic, swampy and paralic environments to shallow marine and even deeper shelf environments. Three undisturbed and well-exposed sections in southeastern Alborz (Jajarm, Tazareh and Shahmirzad) have been studied in detail [Seyed-Emami et al. 2005; Fursich et al. 2005; Seyed-Emami et al. (in press) and Seyed-Emami et al. (in preparation)]. Apart from several short-term marine transgressions in Norian, Late Sinemurian, Late Pliensbachian, the most extensive and long-lasting transgression within the Shemshak Formation occurred during Toarcian and Aalenian stages, being well-documented by ammonites. Hitherto more than 70 ammonite taxa have been described, belonging to the following families: Phylloceratidae, Cymbitidae, Echioceratidae, Amaltheidae, Dactylioceratidae, Hildoceratidae, Graphoceratidae, Hammatoceratidae, Erycitidae and Stephanoceratidae. The fauna is closely related to northwest and central Europe, allowing a similar biozonation. On the contrary, the relations to the Mediterranean Realm are minimal. Of great interest is the nearly total absence of Lytoceratidae and very few Phylloceratidae (<1%).