An attempt to reconstruct central and eastern Iranian ophiolite puzzle

<p>Iran is a mosaic of continental blocks that are surrounded by Palaeo-Tethyan and Neo-Tethyan oceanic relics. Remnants of the ophiolitic rock assemblages are exposed around the Central Iranian Microcontinent (CIM), discretely along the Sanandaj-Sirjan Zone and in Jaz-Murian. The Present-day “ring” distribution of the Iranian ophiolites is not straightforwardly explained by a simple subduction zone architecture. One of the key features to solve the Iranian puzzle is the CIM which is surrounded by Sabzevar ophiolites in the north (99-77 Ma), Birjand-Nehbandan ophiolites in the east (~110 Ma) and Inner Zagros ophiolites in south-southwest (~103-94 Ma). The CIM consists of three major fault bounded sub-blocks, from east to west, Lut, Tabas, and Yazd. They represent an Atlantic-type continental margin that began rifting in Permo-Triassic as a result of opening of Neotethys Ocean. Subsequent convergence in Cretaceous to Paleogene time close the ocean basins around the CIM and emplaced the ophiolites onto the passive margins. Neogene Arabia-Eurasia collision induced replacement structures e.g., strike‐slip reactivation of normal faults that were associated with major block rotations.</p><p>We aim to kinematically restore the opening and closure history of the ocean basins found as ophiolitic relics around the CIM. Key in our analysis is the Doruneh and Great Kavir faults of Central Iran that continues into northern Afghanistan as the Herat Fault. Present-day GPS velocity vector measurements and deformation pattern show a NE-SW orientated shortening in Iran. Structural analysis of the Doruneh Fault indicates slip sense inversion before ~5 Ma. This observation is consistent with the deactivation of the dextral Herat Fault. Pre-Pliocene dextral movement in excess of 500 km along the Doruneh and Great Kavir faults may kinematically accommodate a major counter-clockwise rotation (~65<span>o</span>) of the CIM since the late Jurassic that has been inferred based on previous palaeomagnetic studies. This enables the transport of the Jandaq ophiolite from Aghdarband in the north to Anarak region of Central Iran and, duplication of curved Birjand-Nehbandan ophiolites in Sistan suture. If correct, this may imply that the closure history of the Central Iranian basins is directly connected to the large-scale Cretaceous to Paleogene extrusion tectonics in western Tibet and Hindu Kush regions. This preliminary study shows restoration of the post-Mesozoic deformation is essential to reconstruct the suture zones and pre-collisional setting in Iran, Afghanistan, and Pakistan.</p>

Response of Yakal-yamban (Shorea falciferoides Foxw.), an endangered dipterocap tree species to nutrient addition in a problematic soil

The successful establishment of dipterocarp tree species especially in problematic lands is a challenge since it is still poorly understood. The study was conducted to evaluate the effects of the addition of N, P, and K to Yakal-yamban (Shorea falciferoides Foxw.), a critically endangered dipterocarp tree species, grown in a soil derived from an ophiolitic rock. The seedlings were grown in pots inside a screenhouse and then subjected to the following treatments: control, NPK, NP, PK, and NK. Results revealed that NPK addition generally enhanced the growth of Yakal-yamban in the problematic soil, six (6) months after transplanting, particularly in terms of leaf area, biomass increment and allocation in the leaves. The allocation was enhanced in treatments that receive P, in addition to N, NK, or K suggesting that P was the most limiting nutrient in the problematic soil used. The study also revealed the occurrence of ectomycorrhiza in Yakal-yamban where P was not applied. The results imply that NPK addition is a potential nutrient management strategy for the seedling establishment of Yakal-yamban in problematic soils.

CHROMITITE PROSPECTING USING LANDSAT TM AND ASTER REMOTE SENSING DATA

Studying the ophiolite complexes using multispectral remote sensing satellite data are interesting because of high diversity of minerals and the source of podiform chromitites. This research developed an approach to discriminate lithological units and detecting host rock of chromitite bodies within ophiolitic complexes using the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and Landsat Thematic Mapper (TM) satellite data. Three main ophiolite complexes located in south of Iran have been selected for the study. Spectral transform techniques, including minimum noise fraction (MNF) and specialized band ratio were employed to detect different rock units and the identification of high-potential areas of chromite ore deposits within ophiolitic complexes. A specialized band ratio (4/1, 4/5, 4/7) of ASTER, MNF components and Spectral Angle Mapper (SAM) on ASTER and Landsat TM data were used to distinguish ophiolitic rock units. Results show that the specialized band ratio was able to identify different rock units and serpentinized dunite as host rock of chromitites within ophiolitic complexes, appropriately. MNF components of ASTER and Landsat TM data were suitable to distinguish ophiolitic rock complexes at a regional scale. The integration of SAM and Feature Level Fusion (FLF) used in this investigation discriminated the ophiolitic rock units and prepared detailed geological map for the study area. Accordingly, high potential areas (serpentinite dunite) were identified in the study area for chromite exploration targets.The approach used in this research offers the image processing techniques as a robust, reliable, fast and cost-effective method for detecting serpentinized dunite as host rock of chromitite bodies within vast ophiolite complexes using ASTER and Landsat TM satellite data.

Igneous Activity at the Birth of an Ocean Basin in Eastern Greece

A sequence of varied igneous rocks, of Triassic age, occurs in a complex stack of thrust sheets in the Othris Mountains of eastern Greece. The igneous rocks, which are picritic basalts, diabases, keratophyric tuffs, and pillow lavas, are conformably overlain by marine sediments typical of continental margins, and tectonically overlain by several thrust sheets of ophiolitic rock. The igneous rocks are undersaturated with silica. They are similar in chemistry to igneous rocks erupted on the margins of the Red Sea, which are located on a young, accreting plate margin. The igneous rocks of the Othris Mountains are interpreted as evidence of the development of an accreting plate margin in eastern Greece in Triassic time. The ophiolites overlying them probably came from an ocean basin created at that margin.In contrast to the rocks on the margins of the Red Sea, igneous rocks on many other modern oceanic margins are saturated with silica. This contrast is tentatively related to the speed with which an accreting plate margin develops. Silica-saturated igneous rocks are probably erupted at rapidly separating continental margins, whereas silica-undersaturated igneous rocks are probably erupted in the early stages of activity at plate boundaries which begin to spread only slowly.