دکتر عبدالله یزدی

The Plio-quaternary sub-volcanic domes are the products of magmatism in the Turkish-Iranian plateau in the collision zone between Eurasia and Arabia. Intermediate-felsic volcanic rocks are found 50 km west of Ardabil. These volcanic domes make a significant part of the Sabalan volcanic, a Plio-quaternary stratovolcano in northwest Iran. The igneous rocks (adakitic) include dacite, trachyte, andesite, trachy-andesite, and trachydacite, associated with ignimbrite and pyroclastic equivalents. They mainly comprise phenocrysts and a microcrystalline groundmass of pyroxene, amphibole, and plagioclase, with biotite and titanomagnetite. These rocks are enriched in Light Rare Earth Elements (LRREs) and Large Ion Lithophile Elements (LILEs) and depleted from Heavy Rare Earth Elements (HRREs) and High-Field Strength Elements (HFSEs). In these rocks, the SiO2 content is 56-66 wt%, Na2O is > 3.5 wt%, Al2O3  > 15 wt%, Yb < 0.2 ppm, and Y < 7 ppm, which are typical of high silica adakitic rocks. The initial ratios of the 143Nd/144Nd range from 0.5127 to 0.5129 and the initial ratios of 87Sr/86Sr for the adakites range from 0.7035 to 0.7060, reflecting the heterogeneity of the mantle and different degrees of crystallization. These geological, geochemical, and Sr, and Nd isotopic data indicate that these rocks belong to the post-collisional adakite type, and are derived from low-degree partial melting of a subduction-metasomatized continental lithospheric mantle (eclogite or amphibolite garnet). In the studied area, mineralization related to Plio-quaternary adakitic rocks has not been observed.

Fudge dikes of diorite and microdiorite are penetrated in the Mio-Pliocene sedimentary-volcanic series in the northeast of Bam. In terms of lithology, these dikes are placed in two categories: gabbro-diorite. The primary minerals of the dikes are plagioclase, amphibole (hornblende), and augite, and secondary minerals such as chlorite, biotite, and sericite. Also, their textures are granular, ophitic, and microgranular. From the geochemical point of view, gabbro-diorites have sub-alkaline and met aluminum with enrichment of LILE and HREE and depletion of Nb and Ta elements. The parental magma of the gabbro-diorites is obtained from the melting of a part of the subcontinental lithospheric mantle affected by the subduction producers and in equilibrium with lherzolite spinel. The characteristics of incompatible element patterns include LILE enrichment and HFSE depletion compared to REE similar to subduction zone igneous rocks. These rocks show the intermediate geochemical characteristics of the volcanic arc magmatism of arc islands and margins, consistent with the formation of these rocks in active continents. Geochemical evidence, as well as the association of igneous rocks with green tuffites and other shallow sea sediments, indicate the occurrence of an extensional basin behind the continental arc.

Stability analysis is essential to ensure the stability of rock slopes. There are various methods for stability analysis of slopes, especially rock slopes. According to the geological studies, the considered slope which is in the spillway area of Gabric dam (south of Iran), is located in marl-sandstone layers’ question, with Eocene Oligocene age. Considering the height of this terrace and the gradual process of changing the nature of the layers from marl to sandstone, the considered parameters are equivalent parameters. In the analysis of the overall stability of a rock slope, the parameters of shear strength have been used based on the Hoek-Brown failure criterion. After the analysis of the overall stability and the design of the support system, the stability of the stone wedges has been analyzed and the adequacy of the support system for the stability of the wedges that have the potential to slip. has been investigated and also to consider the loading related to the earthquake, in addition to static analyses, quasi-static analyzes have been performed by applying horizontal acceleration corresponding to the design and use level of the roof to reach the appropriate reliability coefficients. According to the analysis, it shows that in the spillway of Gabric Dam, there is a planar rupture and a pit, which reduces the reliability factor due to saturation and earthquake.

Geosites and their contents including minerals, fossils, etc. can strongly represent the history of a region. They greatly help our understanding of the evolution of Earth, volcanic activities, plate tectonics, and the characteristics of different environments. These are some of the vital information about 4500 million years of the Earth's life, and are our common international heritage. Geoconservation’s main purpose is the protection of geosites as major units of geoheritage, and this principle is achieved through the application of specific methods such as indexing geological phenomena, assessment, preservation, valuation, and estimating the importance of each geosite, as well as monitoring (or watching these phenomena). In this paper, geoconservation is introduced as a specialized and essential branch of geological science, which is currently under development. Therefore, geoconservation principles are presented here, and their relation to other geosciences is discussed. In addition, through scientific and cultural education related to sustainable development (in regard to the geoscience), citizens can be informed that lack of conserving natural resources would reduce geo-resources, and on the other hand, is a serious threat to geoheritage of the planet Earth. This crucial subject can be achieved by making information available and by teaching skills by which making prospective and correct decisions is possible.

Eocene volcanic are exposed in southeast of Zanjan in the Tarom magmatic zone that located in the Central Iran structural zone. The Abhar Eosen pyroclastic with andesite, trachy-andesite, dacite and rhyolite along with tuff compositions is located 120 km southeast of Zanjan. Mineralogically point of view, the studied volcanic rocks have low quartz, negligible alkaline feldspar, abundant plagioclase, and pyroxene contents. Textureally, Porphyritic, microlithic porphyritic, glomeroporphyritic, and poikilitic are predominant in these rocks. All of the studied samples display REE patterns characterized by LREE-enriched (Rb and Ba) and HREE-depleted segments typical of arc lavas which is one of the characteristics of subduction zone. The geochemical characteristics of the studied samples indicated that fractional crystallization is the primary cause of the diversity and differentiation of these rocks compared to crustal contamination. The rocks of the study area are composed of a similar origin to the OIB (mantle components) and partial melting of subcontinental lithospheric mantles. Of course, this mantle source has been modified by recycled sediments and melt released from the edge of the subducting oceanic crust.

Middle-Upper Eocene volcanic and volcano-sedimentary rocks of the Torud region have been formed by the sequences of basic-intermediate lavas, pyroclastic rocks, and sedimentary layers (e.g., siltstone, sandstone, and nummulite-bearing limestone) within a shallow marine basin. According to microscopic studies, the volcanic rocks of the region include basalt, basaltic andesite, trachyandesite, andesite, and dacite. These rocks have originated from the differential crystallization processes and occasionally calc-alkaline contamination geochemical properties. Generally, they contain olivine, clinopyroxene, and plagioclase ± amphibole minerals. Porphyritic to megaporphyritic textures with microlithic and flow matrixes are observed in these rocks. Studying the main and rare elements of these rocks indicates that reducing MgO content is accompanied by an increase in Al2O3, K2O, Na2O, and SiO2 and a decrease in Fe2O3 and CaO concentrations. These rocks are mainly enriched in LIL and LREE elements but depleted of HFS elements. The prominent features of these rocks are the presence of positive anomalies in the K, Sr, Rb, and Ba elements, the depletion of some samples of Nb and Ta, and their depletion of Ti and P. This result reveals the crustal contamination of the mantle mafic magma constructing these rocks. According to the geochemical data, magmatic pollution has not been an effective process in the formation of these rocks. In addition, the relatively higher levels of Cr, Ni, and MgO in the alkali basalts of the region indicate that these rocks are originated from partial melting (5 to 10%) of a spinel-garnet peridotite. Overall, they have no subduction-dependent rock characteristics and mainly represent characteristics of alkali basaltic magmas of the preliminary back-arc basin (BAB). These features, attributed to their calc-alkaline nature, represent the formation of these rocks in a tectonic back-arc setting in the Middle-Upper Eocene.

The Cretaceous Moro Formation from the Rakhi Nala section Dera Ghazi Khan has been studied in detail to investigate the Sedimentology and provenance. This paper describes the litho-facies changes, depositional environment, and provenance analysis of the Cretaceous Moro Formation from the Rakhi Nala section, eastern Sulaiman Range. The studied Formation is 110-140 meters thick and consists mainly of fine to coarse-grained sandstone,  with minor-siltstone, mudstone (claystone, shale), and limestone. The uppermost beds of the Moro Formation are consist of sandstone with iron types of cement. Twelve lithofacies have been identified based on a petrographic investigation related to the depositional environment of the Moro Formation ranging from deltaic to marine setting (Delta Plain-Delta front). Petrographic analysis of sandstone reveals the presence of quartz both, mono-crystalline and poly-crystalline, less feldspar; heavy minerals like hematite and magnetite, and glauconite were found in negligible amounts. Detrital mineral composition shows that in Moro Formation, the sandstone shows a litharenite. Modal composition of the sandstone from the QFL diagram was Q 66% F 0.3% L 33.7% and that of the QmFLt diagram was QM, 57% F 0.23% L 43.77%. The overall average composition is Q 61.5% F 0.27% L 38.7%. A total of 37 thin-sections are studied for provenance analysis, out of which twenty-seven samples are considered as Litharenite (this shows recycled, or craton interior origin), eight Quartz arenite categories are identified and two samples are fall in the sublitharenites category (Quarts recycled source area).

In the southeast of Iran (SE Bam), there is a collection of volcanic rocks with andesite, basalt and trachyandesite composition. The textures of these rocks are often porphyritic with microlithic, porphyric cavity, and sometimes glomeroporphyritic, sore throat trachytic. Main minerals include olivine, clinopyroxene, plagioclase and secondary minerals including opaque minerals, Iddingsite, secondary biotite, chlorite and calcite. The analysis of magma textures gives us valuable information about magmatic processes.   Micro textures in plagioclase of volcanic rocks in the region are divided into two groups: a) texture-linked to crystalline growth including: sieve texture, oscillatory zoning and degraded surfaces and b) Morphological textures such as glomerular crystals. Sieve texture and zoning in crystal represent processes such as magmatic mixing and abrupt reduction of pressure and, in general, unbalanced conditions in magmatic reservoirs. Based on electron microscope studies, plagioclase of igneous rocks of the region is within the boundaries of labradorite and bytownite.  

In the southeast of bam, there is a collection of volcanic rocks with andesite, basalt and trachy andesite composition. The texture of these rocks are often porphyritic with microlithic, porphyric cavity, and sometimes glomerulophorphuri, sore throat trachytic. Main minerals include Olivine, Clinopyroxene, Plagioclase and secondary minerals including opaque minerals, Iodenzyte, secondary Biotite, Chlorite and Calcite. Sieve texture and zoning in crystal represent processes such as magmatic mixing and abrupt reduction of pressure and, in general, unbalanced conditions in magmatic reservoirs.