Plate-Tectonic Setting of Ab-e-Haji Sandstones, Tabas Block, Central Iran

Mahdi Shadan¹ and Mahboubeh Hosseini-Barzi²

1Corporation of Engineering, Zamin Rizkavan, Tehran, Iran; 2Shahid Beheshti University, Tehran, Iran

shadangeo@gmail.com, m_hosseini@sbu.ac.ir

Plate-tectonic setting have been investigated by using modal analysis of 20 samples from sandstones of Ab-e-Haji Formation (consisted of 1100m shale and sandstone), in Dar-e-Bidkhoon section, located at the east of the Kuh-Banan basement fault in Tabas Block.

Central Iran, including Tabas Block was separated from Gondwana during Permian and collided to Eurasia in the Late Triassic (e.g. [8]) and onset of Eo-Cimmerian deformation caused a dramatic change from Middle Triassic platform carbonates to dominantly upper Triassic-Jurassic siliciclastic sediments. Therefore, study of Lower Jurassic Ab-e-Haji Formation is beneficial to understanding of evolution of the Iranian plate during Mesozoic time.

Tectonic provenance determination of ancient terrigenous deposits, using detrital composition of sandstones, follows a classical approach base on petrographic modal analysis (e.g. [5,6]). Ab-e-Haji sandstones mainly composed of quartz grains and labile lithic fragments, implying compositional immature characteristic. Monocrystalline and polycrystalline quartz grains show extremely undulose extinction which point to derivation from metamorphic sources (e.g. [1,4]). Moreover, quart grains bearing individual fibers with apparent bends were observed as evidence of deformed parent rock for these sandstones [7]. The abundance of feldspars is low and comprises rarely microcline and weathered orthoclase. The sandstones contain a considerable amount of rock fragments including meta-sedimentary (slate and phyllitic quartzite lithics) and sedimentary types (shale, chert and sandstone).

Plotting the modal analysis data in the ternary QmFLt and QtFL diagram [2], shows transitional recycled and the recycled orogen tectonic provenance respectively. However, sediments which originate from recycled orogens include various proportions of materials whose compositions reflect ultimate derivation from different sources. Therefore, based on sands classification of Dickinson [3], Ab-e-Haji sandstones show quartzolithic nature (Qm₃₈-F₂-Lt₆₀, Qt₅₈-F₂-L₄₀) representing sand grains derivation from napes and thrust sheets of metamorphic and sedimentary rocks and eventually transport to adjacent foreland basin. This conclusion can be conformed to exposure of supra-crustal successions during collision event between Iran and Eurasia plates in Late Triaasic. In addition, according to considerable amount of labile rock fragments in the sandstones, it is most probably that tectonic movements along the basement Kuh-Banan fault played an important role for local availability of sediment source in southern part of Tabas Block.

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