Habibollah Ghasemi; Khadijeh Jamshidi; Mahmoud Sadeghian
Volume 5, Issue 17 , April 2014, , Pages 51-68
Some high silica adakitic domes with rhyolite, dacite, trachy-dacite, trachy-andesite and andesite compositions belonging to upper Eocene-Pliocene, trending W-NW, intruded in to the ...
Some high silica adakitic domes with rhyolite, dacite, trachy-dacite, trachy-andesite and andesite compositions belonging to upper Eocene-Pliocene, trending W-NW, intruded in to the Cretaceous-Paleocene ophiolitic complex, the Eocene volcano-sedimentary series and in some cases the Oligocene-Miocene sedimentary rocks, and enclose some fragments of these rocks as xenoliths. The most abundant minerals in these rocks are plagioclase and amphibole with various textures such as felsitic porphyric, microlitic porphyric, sieve, flow and glomeroporphyric. The presence of large volumes of detritic fragments of these adakitic domes in the Pliocene conglomerates and their absence in the Miocene detritus indicate uplifting and exposing of the studied domes in the earth surface in the Miocene-Pliocene interval. The parent magma of these rocks has calc-alkaline and per-aluminous nature which is characteristics of the arc volcanics. These rocks fall into the field of high-silica adakites (HAS) in classification diagrams. Enrichment in light rare earth elements (LREEs) and large ion lithophile elements (LILEs) and depletion in heavy rare earth elements (HREEs) are obvious in their MORB, primitive mantle and chondrite normalized spider diagrams. Strong depletion in HFSEs including Nb, Ti and P which is signature of arc volcanic, can be observed in these rocks. According to the petrogenetic diagrams, the parental magma of the rocks studied generated by partial melting of an eclogitic-garnet amphibolitic source derived from metamorphism of the Sabzevar Neotethyan subducted oceanic slab underneath the southern edge of the eastern Alborz zone. Also, the magma has been subjected to assimilation, fractional crystallization (AFC) and crustal contamination during ascend to higher levels and emplacement into the ophiolitic belt. The presence of the xenoliths, corrosion and chemical disequilibrium of the phenocrysts and their sieve textures and (Sr87/Sr86) i â0.7045 in these rocks support the occurrence of these processes.