Tectonics
Ebrahim Gholami; Asghar Ahmadi; mohammadmahdi Khatib; Saeed Madanipour
Abstract
Located at the Arabia-Eurasia collision zone, the E-W trending Bozgoosh Mountain aligned perpendicularly to N-S trending Chehel-Nour Mountain in the northwest of the Iranian Plateau. There is not any thermochronometry study has been performed to determine the initial time of their uplift and exhumation. ...
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Located at the Arabia-Eurasia collision zone, the E-W trending Bozgoosh Mountain aligned perpendicularly to N-S trending Chehel-Nour Mountain in the northwest of the Iranian Plateau. There is not any thermochronometry study has been performed to determine the initial time of their uplift and exhumation. Our low-temperature Thermochronometry analysis in the apatite U-Th/He (AHe) system in combined with previously unpublished data set at central Bozghush Mountains and structural data show that the onset of the Late Cenozoic uplift and exhumation of the Bozgoosh Mountain (~19-25 Ma) is a bit older than Chehel-Nour - Gaflankuh Mountain (~15 Ma). It seems that deformation of the Bozgoosh Mountains started at with respect to middle Miocene unset time of deformation at Chehl-Nour and Gaflankuh Mountain. Then it can be concluded that these two perpendicular maountain ranges have not been formed in a single phase of partitioned deformation. On the other hand N-S trending Chehel-Nour and Ghaflankuh Mountains have similarly deformedsynchronous with the N-S trending part of the southern Talesh Mountains in its eastern border. Our results have also document that the Bozgoosh and Chehl-Nour mountains intersection is actually a part of Bozgoosh mountain.
Petrology
Nargess Shirdashtzadeh; Ghodrat Torabi
Abstract
In this study, some mantle lherzolites of Ashin ophiolite are investigated which contain evidence of a geotectonic/metamorphism during exhumation and obduction of oceanic lithosphere on the continental crust, after closure of Neo-Tethys Ocean. Based on petrography, their primary rock-forming minerals ...
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In this study, some mantle lherzolites of Ashin ophiolite are investigated which contain evidence of a geotectonic/metamorphism during exhumation and obduction of oceanic lithosphere on the continental crust, after closure of Neo-Tethys Ocean. Based on petrography, their primary rock-forming minerals are orthopyroxene, clinopyroxene, olivine, and chromian spinel. Mineralogy and geothermobarometry indicate that these 4-phase lherzolites were formed in the lithospheric mantle (at pressures ~ 21.6 to 8.6 kbar) by melt/wall rock reactions (at temperatures ~ 1012-1183 °C). Then, they were emplaced and obducted on the continental crust along the fault zone of this region, and consequently deformed. The first ductile deformation event occurred in the depth of lithosphere and resulted in high-temperature mylonitization at temperatures higher than 600 to 800 °C. Mineralogical features confirm pressure decreasing of this stage by subsolidus reaction of pyroxene and spinel and substitution of plagioclase and olivine. Therefore, petrography and thermobarometry data are indicative of the spinel to plagioclase lherzolite facies for these rocks. Finally, they partially underwent brittle and cataclastic deformation at temperatures below 600°C and lower pressures and depth during exhumation. However, most of plagioclases were replaced by with prehnite, pumpellyite, chlorite, hydrogrossular and xonotlite minerals by further alterations.
