R Kohansal; M Ghorbani; S.M Pourmafi; M Khalatbari Jafari; J Omrani
Abstract
The Forumad ophiolite pillow lavas crop out at west of Sabzevar and at the periphery of north central Iran microcontinent. These lavas include Upper Cretaceous pelagic limestone with microfossils and are classified in two Late Turonian- Santonian and Coniacian- Late Campanian groups. These basaltic ...
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The Forumad ophiolite pillow lavas crop out at west of Sabzevar and at the periphery of north central Iran microcontinent. These lavas include Upper Cretaceous pelagic limestone with microfossils and are classified in two Late Turonian- Santonian and Coniacian- Late Campanian groups. These basaltic pillow lavas have tubular and flattened forms, with external (vitrified), medial (variolite) and internal (intergranuler) parts. Each part has its own texture with mineral composition of clinopyroxene ± plagioclase ± olivine. The medial part is characterized by formation of skeletal crystals of olivine and lesser extend of plagioclase, indicating high nucleation rate. The nature of Late Turonian- Santonian lavas is tholeiitic and Coniacian- Late Campanian lavas are tholeiitic and calc-alkaline. Despite of enrichment in LILE, relative depletion of HFSE, different enrichment in LREE and various linear trends of HREE which suggest the formation of pillow lavas in the arc environment and the heterogeneous mantle with varying degrees of partial melting, but low ratios of Th/ Yb, La/ Nb, Ce/ Nb and Ce/ Th indicate that they are more inclined to intermediate between IAB and MORB environments. Unlike Late Turonian – Santonian lavas, high ratios of La/Yb, Nb/ Yb in Late Coniacian – Late Campanian lavas represent mantle fertility and decrease of Nb/ Ta ratios as well as relative increase of Th exhibit the effect of partial melting of subducted slab in genesis of these lavas. The depth of partial melting was 40 to 70 km in the spinel lherzolite stability zone. It seems that the formation of Forumad ophiolitic pillow lavas is accrued in a marginal basin to a back arc basin of a supra-subduction zone.
F Mesbahi; M Mohajjel; M Moazzen; L Namaki
Abstract
In the east of Tabriz city, south of Eskandar village, Upper Cretaceous rock units are exposed. The structures in these rock units include meso-scale folds inclined towards NNE, and a thrust system which has transported Upper Cretaceous units in three thrust sheets towards NW. This thrust system has ...
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In the east of Tabriz city, south of Eskandar village, Upper Cretaceous rock units are exposed. The structures in these rock units include meso-scale folds inclined towards NNE, and a thrust system which has transported Upper Cretaceous units in three thrust sheets towards NW. This thrust system has cut the NNE-verging folds in Upper Cretaceous units. These deformed rock units are unconformably overlain by the Miocene beds. The vergence of folds in the Miocene units is toward SSW. There are SW-verging thrust faults and right-lateral strike-slip faults parallel to the North Tabriz fault in the study area. We conclude that the N-verging structures in Upper Cretaceous rock units has been formed in the time interval between Upper Cretaceous and Miocene and were cut by the North Tabriz fault. The structural characteristics of the Upper Cretaceous rocks as the remnants of the Upper Cretaceous oceanic crust in the Neotethyan marginal basin indicate that the probable subduction direction of this basin was towards south.
