Zircon Geochronology (U-Pb), Petrography, Geochemistry and Radioisotopes of Bornaward Metarhyolites (Central Taknar Zone-Northwest of Bardaskan)

The calc-alkaline compositions of samples BKCh- 12, BKCh-103 and BKCh-177, the high K- calc alkaline of samples BKCh-138 and BKCh-198 of the Bornaward metarhyolites and the higher temperature overgrowth of plagioclase on lower temperature microcline phenocrysts can be a reason for entrance lavas with different generations. The distinct isotopic characteristics of the two groups of rhyolitic samples are the reasons for two different sources for the production of these lavas: 1) partial melting of an enriched mantle reservoir or lower continental crust, and 2) sialic continental crust with high contamination. With respect to the Bornaward metarhyolite- rhyodacites with (¹⁴³Nd/¹⁴⁴Nd)_i ratios from 0.511701 to 0.511855, geochemical characteristics and the high volume of volcanic rocks in the area, their formation can be attributed to a continental rift environment. This rift system can be formed by initiation of a plume in the upper mantle beneath East Iran during Neoproterozoic time.