Paper Information

Journal:   GEOSCIENCES   Fall-Winter 2004 , Volume 11 , Number 49-50; Page(s) 62 To 77.



The intracotinental Qom- Aran depression basin is located in the central Iran zone and correlated with its tectonic environment. Some of the depression basins such as Qom- Aran, Aredstan- Yazd and Rafsanjan- Zarand basins show NW-SE trend and are located between two subordinate uplifted subzones of the central Iran zone (mid triangle subzone in the north and Urumiyeh-Dokhtar volcanic belt in the south). From Urumiyeh- Dokhtar magmatic subzone toward middle parts of central Iran zone, There are various subordinate trends and morphostructures, Probably due to the affected stress and the reflection of brittle behaviour of the central Iranian crystalline basement, that have produced faulted and rotated blocks with different forms and dimensions as well as the compexity of the morphostructures. Therefore, In the Qom-Aran depression basin, there are three structural trends, NW-SE, SW (Davazdah Emam-Narreh khar kuh fault) NNW- SSE (Qom-Raband Zefreh - fault) and NE-SW (Maranjab fault) .
During the Neogene, spreading of the Red Sea and movement of Arabian Plate to the north produced compressional stress in the Iranian platform. Strike- slip movenents of Central Iranian blocks caused some local extensional movements, such as a long the bended part of Qom- Zefreh fault, and as a result the Qom- Aran pull - a part basin was formed. In the later phases a huge amount of continental facies sediments of the Upper Red Formation and related M1, M2 and M3 members deposited in this basin. The above mentioned deposits are originated by erosion of surrounding uplifted areas. The latter form reliefs which bounded mainly with reverse fault are located in the margin of the Qom-Aran depression basin. In the late Neogene the continuation of the Red Sea spreading and related compressional stress to the north, caused an anticlock rotational movement of the Qom-Aran block. According to this structural evolution some NE-SW trends (Maranjab Fault) are activated so that, the trend of Maranjab Fault shows 75 degree divergence to the Qom-Ravand - Zefreh faults ternd. All structural evidences indicate an extentional movement along the bended parts of the Qom-Ravand - Zefreh strike - slip fault and consequently the formation of the Qom-Aran pull- apart basin. On the other hand, the folding of Upper Red Formation deposits with axial NW-SE (Alborz and Sarajeh anticline) and E-W trends (Qaleh Sadar Anticline) in the border of Qom- Aran depression indicate the limitation of basin dimension due to the oblique convcergence of southern sub- block in eastern part of the depression which has proouced a narrow folded area in the Qaleh Sardar area. The above mentioned rotational movements are in agreement with geophysical and microseismic data, and resulted the structural subdivisions of the area into active (Maranjab) - Passive (Yakhab), captured (Daryacheh-ye -Namak) and isolated (daryacheh-ye - Hozsoltan) blocks.

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