3/12/2018 1564

Education: Geological Background

Geologically, Iranian Plateau can be divided into some geological zones. Each of these zones has a different history. Knowing that each area belong to what zone, can help us to detecting geological events in the past. Main geological zones in Iran are Kopet-dag, Central Iran and Zagros, and Aras Geopark is located in Central Iran.

Geologically, Iranian Plateau can be divided into some geological zones. Each of these zones has a different history. Knowing that each area belong to what zone, can help us to detecting geological events in the past. Main geological zones in Iran are Kopet-dag, Central Iran and Zagros, and Aras Geopark is located in Central Iran.

From a structural geology point of view, the Geopark is a fold and thrust system and thrust faults (a reverse fault with low dip) and folded structures are dominant tectonic structures in the area. The predominant fold’s trend is east-west to northwest-southeast, which is coincident with regional scale fold’s trend.

Central Iran Zone is micro-continent between Zagros Zone in the south and Kopet-dag in the north, and stretched beyond the eastern and western Iranian borders. This micro-continent itself, is a part of micro-continental belt named Cimmeria extended form Turkey to China. The micro-continent Cimmeria was a part of super-continent Gondwana in the southern hemisphere near the Equator until late Paleozoic and early Permian (about 300 Ma). In that time, with intra-continent rifting caused by convection currents in mantle, the micro-continent separated from Gondwanaland, and moved toward super-continent Laurasia in the north. In the Late Triassic Period, the micro-continent Cimmeria collide with super-continent Laurasia, leading to folding seabed sedimentary layers and uplifting the area. Since then, continues compression has resulted in folding and thrusting in the area.

Aras Geopark has significant geological and geomorphological features, including extended outcrops of well-bedded sedimentary rocks with distinctive colors, Middle Paleozoic to Early Mesozoic rich fossil beds, Cretaceous and Eocene clastic deposits, Eocene and Miocene red clastic sediments, and Oligocene intrusive and extrusive igneous rock.

In the Geopark, sedimentary rock outcrops are dominant, and the oldest sedimentary rocks date to 400 Ma, namely Devonian Period. Paleozoic to Mesozoic Limestone has deposited in a vast platform basin with low tectonic activities, leading to Jeirood formation Devonian limestone and dolostone, Dorood formation sandstone and Ruteh limestone date to Permian Period, and Elika formatin Triassic limestone and dolostone. Flysch deposits are extended well too in the area. These deposits resulted from depositing alternate sandstone and shale in the deep marine basins, near a continental active orogeny. In these basins, with progressing the orogeny, erosion exacerbates, which lead to transporting a huge mass of sediments, from sand to mud, into the sea, via rivers and deposit in deep marine basin. Outcropping Miocene clastic deposits with massive conglomerate, red sandstone and green marl, formed amazing landscapes from colored slopes. These landscapes usually are seen around Siahrood and Eiry village in the Geopark. These sedimentary rocks often contain fossil, forming a diverse assemblage of brachiopods, pelecypoda, ammonites, echinoids and corals. Placing plutons in the eastern part of Geopark, around Ushtabin and Kordasht villages and volcanic eruptions date to Oligocene, plays and important role in forming the Geopark topography and its highlands.