Iranian Journal of Earth Sciences
Volume:15 Issue: 2, Apr 2023

Among several distribution characteristics, temporal distribution characteristics of earthquakes provide the most crucial information on the temporal patterns of past seismicity. Identification of such patterns is required for seismic hazard, forecast studies and also simulation of future seismicity. The confusion of how to model the past temporal patterns does limit further development:. Though the Poisson model is routinely used in hazard modelling, its validity is often questioned. Furthermore, the question as to which model best represent past temporal patterns of earthquake occurrence is not answered yet. Within this context, in this study, to investigate the interevent time (IET) distribution, two seismically active regions in Turkey are selected where the seismic activity never diminishes and the hazard remains high. These regions, namely the western end of the North Anatolian Fault Zone and East Anatolian Fault Zone are known to produce moderate or large magnitude earthquakes. Four distributions, namely, exponential, gamma, Weibull and lognormal models are tested for how well they fit the earthquake records of the two faults, and importantly, the hazard functions that is instantaneous rate of occurrence of events, and conditional probabilities are also developed for performance evaluation. In the end, it is observed that, each model has flaws in identification of temporal pattern of earthquake occurrences and forecasting earthquakes.

The concentrations of heavy metals (inorganics) and poly aromatic hydrocarbons (organics) were determined in soils around fueling stations and automobile workshops. Mean concentrations of nickel, lead, cadmium and vanadium were 636, 1379, 12.0 and 18.0 µg/kg, respectively. Flourene, benzo (a) pyrene, benzo (b) fluoranthene and benzo (ghi) pyrelene recorded means of 2.01, 2.014, 1.14 and 1.12 µg/kg, respectively, but other poly aromatic hydrocarbons recorded means <1. Heavy metals levels were higher at sites of activities than the control site. Phenanthrene, naphthalene and benzo (k) fluoranthene were present at control site but absent in some locations of activity. These showed they were not only from petroleum products handling facilities. Mean levels of both inorganics and organics were below world standards for agricultural soil quality. Principal component analysis of heavy metals produced two principal components that explained 40.72% and 36.90% of the total variance. These reflect geological weathering, automobile exhaust and petroleum combustion sources. Analysis of poly aromatic hydrocarbons data produced four principal components, which explained 36.30%, 19.96%, 15.19% and 12.81% of total variance. The sources of these organics are internal combustion of gasoline, kerosene and rock weathering. Diagnostic ratios ranged from 0.3-0.94 showing that poly aromatic hydrocarbons are of pyrogenic and petroleum combustion origin. Single pollution index means ranged from 0.0002-0.02 and Numerov composite pollution index attained a mean of 0.028. Therefore, the soil is unpolluted and heavy metals levels are not toxic to human health. The study provides information on sources of soil pollutants and their environmental and health risks.

The investigation of lithostratigraphy, biostratigraphy and the microfacies analysis of the Gadvan Formation as an oil reservoir of Lower Cretaceous in the Zagros Basin is crucial. In this study Naser Abad section (Coastal Fars region, SW of Iran), consists of 170 meters thin to medium-bedded limestone with interbeds shale and marly limestone. According to stratigraphic distribution of identified foraminifers, two biozones are established which are: Paleorbitolina lenticularis zone and Hedbergella infracretacea Zone. Based on the investigated faunal assemblage, the age of Gadvan Formation is assigned to late Barremian-early Aptian. Microfacies studies led to the identification of five microfacies types which include: Algal-intraclast- bioclast wackestone, Intraclast- bioclast wackestone, Planktonic- bioclast wackestone, Radiolarian packstone and Orbitolina- bioclast wackestone. These microfacies show that the Gadvan Formation was deposited in both shallow water ramp and hemipelagic paleoenvironments. According to microfacies, carbonate platform of Gadvan Formation in the studied area corresponds to a moclinal platform which was affected by basement of Kazerun Fault zone.

The Sahand volcano (Kuh-e-Sahand) is located in NW Iran, about 60 km E of Lake Urumieh and 40 Km SSE of Tabriz. The volcano is a stratovolcano and is dominated by pyroclastic materials and lava flows in the Miocene-Quaternary. The Mio-Pliocene volcanic rocks are exposed in the Southwest of Bostanabad (Arvanehkuh, Biukdagh, and Ghapandagh masses) East-Azerbaijan province. These rocks formed a part of the Urumieh-Dokhtar Magmatic Belt (UDMB) and consist of andesites and dacites. The rocks display a porphyritic texture and contain phenocrysts of plagioclase, sanidine, amphibole, biotite, and quartz. Based on the geochemical data and multi-elemental pattern, these rocks are medium to high-K calc-alkaline suite and show Large-Ion Lithophile Elements (LILE) and Light Rare-Earth Elements (LREE) enriched normalized multi-elemental patterns, and Nb and Ti depleted. Chondrite-normalized REE patterns of the volcanic rocks display a decrease from LREE to Heavy Rare-Earth Elements (HREE) without any Eu anomaly, indicating their formation in a subduction zone in an active continental margin. They have higher SiO2, Sr content, Sr/Y, and La/Yb ratios and lower MgO, Y, and Yb contents compared to those of normal calc-alkaline volcanic rocks and show high SiO2 adakites (HSA). Based on geochemical data, the origin of these rocks is garnet-amphibolite with the residual phase of garnet and amphibole with a titanium phase. HREE and Y depleted patterns suggest the existence of garnet and amphibole as a residue in the source. The source of these rocks was probably garnet-amphibolite possibly generated during subduction of the Neo-Tethyan oceanic slab beneath the Central Iran zone and in fact, can be termed as classic adakite. Therefore, considering the importance of adakites in inferring continental geodynamic processes, it is recommended to pay attention to their discovery and identification with the help of various petrological and geochemical methods.

The magmatic evidence of the Neotethys opening in Iran, such as the Late Paleozoic A-type granitoids, was mainly discovered along the Sanandaj-Sirjan Zone and parallel to the Neotethys suture. Therefore, they may provide important clues about the geodynamic evolution of the Sanandaj-Sirjan Zone. The South of Lake Urmia (SLU) granite is situated near the Khalifan A-type pluton (315±2 Ma) with a cover of the Permian sediments. The rock-forming minerals of the SLU granite consist of quartz, alkali-feldspars (K-rich and microperthitic), sodic plagioclases, biotite (Fe-rich), zircon, apatite, and Fe-Ti oxides. The chemical composition of the SLU granite is characterized by high FeOt/MgO and (Na2O+K2O)/CaO ratios, which are typical features of A-type granites. Furthermore, the studied rocks exhibit the chemical characters of the A1 subgroup of A-type granites with peraluminous and K2O-rich affinities. On the multi-element spider plot, the SLU granite shows distinct negative Ba, Sr, P, and Ti anomalies and positive Pb anomalies. Moreover, the Chondrite-normalized rare earth elements (REE) patterns display slope downwards from LREE to HREE, with flattening at the HREE end and distinct negative Eu anomalies. The ratios of trace elements provide evidence for the contribution of the OIB-like mafic melts with crustal interactions to generate the granitic magmas of the SLU pluton. The compositional and stratigraphic features of the SLU granite are also consistent with an extensional setting during the Late Paleozoic in Iran. Therefore, the genesis of the SLU granite can be attributed to the syn-rift magmatism of the Cimmerian terranes. A comprehensive review of the Late Paleozoic rocks occurrence shows that they mainly are emerged in the northeast margin of the Sanandaj-Sirjan Zone and around the structural depressions such as Lake Urmia (so-called Tertiary fore-arc or Mesozoic back-arc).

Based on the relation of radioactive and rare earth elements (REEs) in some of prospecting projects (particularly uranium prospecting) in central Iran, in current study, sampling from the Baghak anomaly in Sangan iron ore mine has been done according to radioactivity for the first time. The purpose of this research is to survey such a relation in a different case study (skarn mine) with central Iran. Optical microscopic and scanning electronic microscopic (SEM) studies along with geochemical and statistical analyses (based on the spider diagrams) are employed. The significant amount of uranium, cerium, lanthanum and high a concentration of REEs in results, along with high amount of iron, is one of the reasons why Baghak anomaly is considered very important. Results show the accumulation of cerium in the allanite lattice (as the solid solution).