Tectonics
Ali Bandegani; Ali Yassaghi; Mohsen Eliassi
Abstract
In this paper, the structural evolution of Bamu fault zone located in the Zagros folded belt zone is presented as an example of northeast-trending fault zone in the Zagros, using the kinematic and dynamic analysis of accompanied structures. Based on structural and paleostress analyzes two phases of shortening ...
Read More
In this paper, the structural evolution of Bamu fault zone located in the Zagros folded belt zone is presented as an example of northeast-trending fault zone in the Zagros, using the kinematic and dynamic analysis of accompanied structures. Based on structural and paleostress analyzes two phases of shortening were determined as NE and NNE. In order to define the chronology of the deformation stages in the region, the relationship between fault structures and folds in the folded rock formations has been utilized. The result showed that the first compression stress trend in the area was NE that caused formation of the Bamu transverse Fault with left-lateral strike-slip mechanism and its accompanied structures. Since this stage of deformation has affected the Oligocene- early Miocene formations, more likely occurred at this time. During the next phase the shortening direction, due to change in the collision zone direction of the Arabian-central Iran in the Miocene-Pliocene, has changed to NNE which causes development of younger structures in the form of folding and reverse faulting in the fault zone. This shows that the NE-trending fault zones, like other major NW-faults, in Zagros affected by the change in the convergence of Zagros collision.
Petrology
Z. Gharamohammadi; A. Kananian; M. Eliassi
Abstract
The Dehe Bala pluton is exposed approximately 45 km south-west of Boein Zahra town, Qazvin province. This pluton includes several mafic microgranular enclaves (MMES) with ellipsoidal and rounded shapes and varying sizes (from a few centimeters up to 30 cm). The MMEs are composed of diorite, monzodiorite ...
Read More
The Dehe Bala pluton is exposed approximately 45 km south-west of Boein Zahra town, Qazvin province. This pluton includes several mafic microgranular enclaves (MMES) with ellipsoidal and rounded shapes and varying sizes (from a few centimeters up to 30 cm). The MMEs are composed of diorite, monzodiorite and diorite-gabbro while the host rocks comprise mainly granodiorite. The presence of disequilibrium textures in enclaves, such as plagioclase phenocrysts with repeated resorption surfaces and sieve texture, quartz ocelli and acicular apatite, suggest a varity of magma mixing processes affecting the Dehe Bala pluton. The distribution of major, trace and rare earth elements apparently reflect exchange between the MMEs and the felsic host rocks. Unusual REE enrichment of the enclaves compared to the country rocks can be attributed to significant differences in their parent magma compositions. The complexity of the morphology of the enclaves (fractal dimension) caused by magma mixing processes. Fractal dimensions of the enclaves vary between 1.14 to 1.29. The frequencies of Dbox = 1.29 is the highest frequency in histogram. According to the fractal dimensions of enclaves, the logarithm of the viscosity ratio between the host granodiorite and the enclave ranges between 0.56 to0.96 with most values clustering around 0.96. The most of enclaves in the Dehe Bala pluton characterized by silica content around 56 w% and a high fractal dimension. These evidence confirmed the occurrence of slight hybridization between the mafic enclave magma and surrounding felsic magma, causing increasing of viscosity difference between the host granodiorite and the enclave magmas.
S. Rajabi; M. Eliassi; A. Saidi; A. Shahidi
Abstract
In this research, heterogeneous fault slip data are used as the main data for doing paleostress analysis in North-Tehran tectonic wedge, which is restricted between Mosha and North-Tehran faults. Using these data and paleostress methods, the studied area is divided into 15 smaller stable stress regions ...
Read More
In this research, heterogeneous fault slip data are used as the main data for doing paleostress analysis in North-Tehran tectonic wedge, which is restricted between Mosha and North-Tehran faults. Using these data and paleostress methods, the studied area is divided into 15 smaller stable stress regions and the mean stress tensor related to each region is determined. Then, stress events are separated using Multiple Inverse Method. Based on mean stress tensors -obtained from stress regions- and rotation of fault data orientation -based on Anderson’s theory in compressional tectonic regimes-, the stress trajectory map is sketched for mean stress tensors acting in the regions during geological time. Configurations of trajectories show that they seem to obey the overall tectonic regime in Iran. This result refutes that the North-Tehran tectonic wedge could be a dynamic wedge.
K. Kalantari; A. Kananian; A. Asiabanha; M. Eliassi
Abstract
Paleogene basic to intermediate lava flows of Central Alborz, in the northeast of Qazvin city (Zarjebostan), include trachy-andesite, basaltic trachy-andesite and basaltic andesite. These volcanic rocks are high-K calc-alkaline rocks. Based on the high LILE/HFSE and LREE/HREE ratios ...
Read More
Paleogene basic to intermediate lava flows of Central Alborz, in the northeast of Qazvin city (Zarjebostan), include trachy-andesite, basaltic trachy-andesite and basaltic andesite. These volcanic rocks are high-K calc-alkaline rocks. Based on the high LILE/HFSE and LREE/HREE ratios and their similar composition to subduction volcanic rock suites; it seems that they have formed in a subduction zone. The subduction process has little effect on the concentration of Zr, Ta, Hf, Sm, Tb, Nd, Eu and Y elements, while it has strong influence on concentration of Th, U and La elements. Due to high Ba/La, Ba/Ta and La/Ta ratios and low TiO2 content of lavas, they could be attributed to magmatic arc setting. Th/Yb vs. Ta/Yb diagrams and association of study suite with extensive volume of acidic tuffs, indicate that these rocks have been formed in an active continental margin.
M. Eliassi; S. Ahmadian
Abstract
Analysis of paleostress history in Kan_Karaj Area is the main object of this research. Paleostress phases were determined and categorized by numerous mesoscale faults containing slickenside lineations .The results were controlled and supported by some other geological features such as orientation of ...
Read More
Analysis of paleostress history in Kan_Karaj Area is the main object of this research. Paleostress phases were determined and categorized by numerous mesoscale faults containing slickenside lineations .The results were controlled and supported by some other geological features such as orientation of axial plane of folds, intrusion and stylolitic planes. The orientation of finite principal stress axes and geometrical shape of stress ellipsoid in a 4-D stress space were analyzed by determination of rotational axis of each sub-area, according to Anderson Theory. Two different stress phases were separated and geometrical configuration of the maximum compressional stress trajectory were illustrating on the structural map. The resulting trajectory shows north- south trend with an outstanding convergence to the north which reflects incremental intensity of stress in that direction during the fault system activities.