Mehdi Rezaei-Kahkhaei; Ayoub Taheri; Habibollah Ghasemi; Sara Gardideh
Abstract
The Chekneh subvolcanic domes with dacite and trachydacite compositions from the Miocene is located 110 km NE of Sabzevar, and are parts of the North Sabzevar-South Ghochan magmatic ...
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The Chekneh subvolcanic domes with dacite and trachydacite compositions from the Miocene is located 110 km NE of Sabzevar, and are parts of the North Sabzevar-South Ghochan magmatic belt. The dome rocks have porphyry, sieve, trachytic and glomeroporphyritic textures, consisting of plagioclase and amphibole. Primitive mantle normalized spider diagram and chondrite-normalized REE patterns of the study domes suggest that they are enriched in LREE and LILE and are depleted in HREE and HFSE. They are calc-alkaline with significant negative HFSE (e.g., P, Nb and Ti) anomalies and (La/Yb)N>12 which are characteristics of magmas formed in active continental margin. Based on SiO2, high Sr/Y, low K2O/Na2O and low Y, Yb, Cr and Mg# contents, the study rocks are similar to high-silica adakites (HSA). Thus, it seems that the parent magma of the study domes was originated from amphibole eclogite or garnet amphibolite rocks of metamorphosed Neotethys oceanic lithosphere during its subduction beneath the southern part of eastern Alborz in the Miocene. The initial 87Sr/86Sr (0.7039-0.7043) and ɛNd10Ma (2.9-4.98) of the Chekaneh domes is similar to MORB composition, which are coincided with those adakites originated from the partial melting of the Cenozoic oceanic lithosphere.
