Wyniki wyszukiwania - Biblioteka Nauki

1

Procesy geomorfologiczne na wybranych wysadach soli w pasie fałdowo-nasuwczym gór Zagros w Iranie

100%

Bukowski K.

Przegląd Geologiczny

|

2020

|

tom Vol. 68, nr 3

167--177

EN

Presently, about 160 salt domes of various sizes exist in the Zagros fold-thrust belt in southern Iran. The salt domes constitute a unique proving ground for research on salt tectonics. In the dry climate that currently dominates in Iran, forms of horizontal salt formations are created, referred to as salt glaciers, in addition to typical steeply falling salt domes. Consequently, it is possible to conduct observations of geomorphological processes developing on the surface of exposed salt rocks and keep a continuous record of their tectonic activity. Salts occurring in that area represent the Hormuz (Hormoz) Formation of the Ediacaran period (Late Neoproterozoic to Early Cambrian). The rocks of the formation usually present a colourful blend of rock salt, anhydrite, black dolomite, shale, and red volcanic tuff, as well as extrusive magmatic and metamorphosed rocks that are interpreted as fragments of deep basement elevated to the land surface by salt domes. The paper describes the geology and geomorphology of the Jashak (Dashti) salt glacier from the Busher Province and two salt domes located on the Persian Gulf Islands: Hormuz (Hormoz Island) and Namakdan (Qeshm Island). The present-day salt dome geomorphology is a result of both climatic effects (precipitation and air temperature) and diapir uplifting forces.

2

Earthquake Potential in the Zagros Region, Iran

100%

Madahizadeh R. , Mostafazadeh M. , Ashkpour-Motlagh S.

Acta Geophysica

|

2016

|

tom Vol. 64, no. 5

1462--1494

EN

Seismic strain and b value are used to quantify seismic potential in the Zagros region (Iran). Small b values (0.69 and 0.69) are related to large seismic moment rates (9.96×1017 and 4.12×1017) in southern zones of the Zagros, indicating more frequent large earthquakes. Medium to large b values (0.72 and 0.92) are related to small seismic moment rates (2.94×1016 and 6.80×1016) in middle zones of the Zagros, indicating less frequent large earthquakes. Small b value (0.64) is related to medium seismic moment rate (1.38×1017) in middle to northern zone of the Zagros, indicating frequent large earthquakes. Large b value (0.87) is related to large seismic moment rate (2.29×1017) in northwestern zone, indicating more frequent large earthquakes. Recurrence intervals of large earthquakes (M > 6) are short in southern (10 and 14 years) and northwestern (13 years) zones, while the recurrence intervals are long in the middle (46 and 114 years) and middle to northern (25 years) zones.

3

The evolution of arc magmatism related to Palaeotethys in the west of Salmas, north of the Sanandaj-Sirjan Zone, Iran

85%

Fazlnia A.

Geological Quarterly

|

2017

|

tom Vol. 61, No. 1

124--137

EN

The Mingol-Mamakan gabbroic-appinitic intrusions are located in northwestern part of Iran and belong to the Sanandaj–Sirjan zone (SSZ). These intrusions have had a significant impact on evolution of the northwestern part of the SSZ during Upper Carboniferous. The rocks typically include layered and massive gabbros-gabbrodiorites. The age of layered gabbros is 303-300 Ma and they mainly consist of leuco-gabbro, mezzo-gabbro, melano-gabbro, anorthosite, and hornblendite (appinite) with gradational or sharp bedding contacts alternatively. Layered gabbros with 314-322 Ma are mostly composed of leuco-gabbro, mezzo-gabbro, melano-gabbro, and hornblendite. Most of these samples are appinite in composition. The intrusions show no obvious deformation. Therefore, mineral composition changes in the rocks have been controlled by crystallization processes, such as fractionation in the magma chamber. Our investigations indicate that different rock types with tholeiitic magma series are probably derived from partial melting of spinel lherzolite upper mantle co-genetic source. Geochemical information and dating from the Mingol-Mamakan intrusive rocks reveal that the intrusions were formed of subduction-related immature or sub-mature island arc tholeiitic basalt which is enriched in Al2O3, FeO, Sr and depleted in K and Nb. Subsequently, primary tholeiitic arc basalt magma underwent fractional crystallization to form intrusive rocks at the lower crust, relatively in high pressures conditions. Geochemical modeling based on the partition coefficient of elements in minerals indicates that trace elements concentrations (large-ion lithophile elements, LILEs, high field strength elements, HFSE, and rare earth elements, REEs) in the Mingol-Mamakan intrusions throughout the crystallization were controlled by variable amounts of common minerals such as amphibole, clinopyroxene (for all trace elements) plagioclase (only for LILE) and probably spinel in the source rock (only for HFSE). Moreover, elements of first transition series of periodic table mainly controlled by orthopyroxene, olivine and possibly by clinopyroxene and amphibole in much smaller amounts.

4

Delineation of potential seismic sources using weighted K means cluster analysis and particle swarm optimization (PSO)

80%

Sheikhhosseini Z. , Mirzaei N. , Heidari R. , Monkaresi H.

Acta Geophysica

|

2021

|

tom Vol. 69, no. 6

2161--2172

EN

Potential seismic sources play an important role in seismic hazard analysis. Identification of seismic sources is generally carried out on the basis of expert judgments, and in most cases, different and controversial results are obtained when several experts are consulted. In fact, the method of source identification is probably an important cause of uncertainty in the seismic hazard analysis. The main objective of this research is to provide an algorithm which combines the weighted K-means clustering analysis and Particle Swarm Optimization in order to automatically identify global optimum clusters by analysing seismic event data. These clusters, together with seismotectonic information, can be used to determine seismic sources. Two validity indexes, Davies–Bouldin's measure and Chou–Su–Lai's measure (CS), are used to determine optimum number of clusters. Study area is located at the longitude of 46°–48° E and latitude of 34°–36° N that is considered as the most seismically active part of Zagros continental collision zone, which has experienced large and destructive earthquakes due to movements of Sahneh and Nahavand segments of Zagros Main Recent Fault. As a result, 7-cluster model which is identified on the basis of DB validity index seems to be suitable for the considered earthquake catalogue, despite some limitations in partitioning.