Kharazmi Journal of Earth Sciences

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The Hojdek Formation in the Kale-shur area consists of alternation of fine quartz arenitic-arkosic sandstones with dark gray to green shales and coal seams. This formation includes relatively well-preserved plant macrofossils which are studied here for the first time. 15 species of 9 genera belong to different orders such as Equisetales, Filicales, Sycadales and Pinales have been determined in this study. Based on these species, one biozone called Nilssonia bozorga - Coniopteris hymenophylloides Assemblage zone and two subzones in ascending order called Klukia exilis Taxon Range zone (I) and Ferizianopteris undulata-Equisetites sp. cf.E. columnaris  Interval zone (II) were recognized in this section. These biozones in the study area are comparable with the correspondent biozones of the Middle Jurassic interval in the Tabas area. Thus, the Coniopteris hymenophylloides-Klukia exilis Assemblage zone is proposed as a widespread biozone for the Tabas area during the Middle Jurassic. According to occurrence of the index fossils such as Coniopteris hymenophylloides and Klukia exilix the age of Aalenian-Bajocian is considered for this assemblage.  Analytical studies reveals the Filicales, Cycadales, Pinales and Equisetales respectively with relative abundance of 48.08%, 32.69%, 15.38% and 3.85% were the most plentiful orders in the Middle Jurassic succession of the Kale-shur area. In addition, Nilssonia, Podozamites, Ferizianopteris and Lobifolia were the most abundant genera with 32.69%, 15.38%, 11.54% and 11.54% abundance in the region. The relative abundance of Filicales and Cycadales established a humid sub-tropical climate for this region.
 

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Soltanabad metamorphic complex cropped out in the ophiolitic range of NE Sabzevar. There is a distinct gneissic body exposed in this complex which is associated with metabasite, serpentinite and adakitic intrusions. Quartz, albite, epidote, amphibole, garnet and chlorite are the rock forming minerals of gneissic samples. Based on abundances of light and dark minerals, different types of felsic, intermediate and mafic gneisses are distinguishable. Metamorphic conditions of the Soltanabad complex gneisses is estimated as 462 (±39)^°C at pressure of 12.4 (±2.15) kb indicating a hot thermal regime of a subduction setting. Based on the whole rock geochemistry gneisses have plagiogranitic composition and formed by partial melting of mafic sequence in oceanic crust. Isotopic ratio of zircon’s Hf and REE pattern confirm a MORB affinity of these gneisses. The Soltanabad metamorphic complex gneissesdisplay considerable compositional similarity with plagiogranite of Iran and Cyprus ophiolitic zones and thier geochemical characteristics are comparable with plagiogranites of supra-subduction zone setting. Probably gneisses and blueschists of the Soltanabad metamorphic complex are plagiogranites and mafic rocks of the Sabzevar oceanic lithosphere that experienced subduction zone metamorphism.  

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