Document Type : Original Research Paper
Authors
1 Assistant Professor, Research Institute for Earth Sciences, Geological Survey of Iran, Tehran, Iran
2 M.Sc., Research Institute for Earth Sciences, Geological Survey of Iran, Tehran, Iran
Abstract
Lava-dome shallow massive bodies located right around Nodeh Engelab, SE Jogatay in Khorasan Razavi province, cutting Eocene volcanic rocks in northern part of Sabzevar ophiolitic belt, are covered by Pliocene-Quaternary deposits. The margin of bodies comprise of lavas of basalt, phyric andesite basalt, fluidal andesitic compositions but the medial parts and roof of masses composed of phyric andesite-trachy andesite, phyric-aphyric dacites and quartz monzodiorite. No impacts of pyroclastic deposits have been observed around these masses. The sieve texture, oscillatory zoning in plagioclase crystals could be attributed to disequilibrium in magma chamber. The lava from margins of shallow massive bodies has calc alkaline and the rocks from middle parts of the bodies show calc alkaline to high-K calc alkaline affinities. The spider diagrams of margin lavas have substantial compliance with those middle parts of bodies and show enrichment in Rb, Ba, Th, La, Sr, and clear depletion in Nb and Ti. Despite some samples plot in adakitic domain, but they do not display chemical characteristic of index adakites. It seems that the parental magma of the studied shallow intrusions produced from partial melting of mantle wedge which have different enrichment and probably influenced by the components released from subducted slab. The other scenario could be attributed to the partial melting of metamorphosed mafic rocks at the top of subducted slab.
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