Geochronological and geochemical characteristics of the Dehzaman intrusive and volcanic rocks (NE Iran): Implication for a Cadomian magmatism

Abstract

Cadomian magmatism is interpreted to indicate fragments of late Neoproterozoic-Early Cambrian continental arcs bordering the northern margin of Gondwana. Cadomian rocks constitute the main elements of the continental crust of central Iranian block (including the Lut block). An example of such Cadomian rocks from NE Iran is studied here: the Dehzaman igneous rocks within the Kashmar- Kerman Tectonic Zone (KKTZ). The Cadomian exposure in NE Iran includes intrusive rocks with a thick sequence of felsic volcanic rocks. Zircon U-Pb dating of syenogranites and ryholites yielded 238U/206Pb crystallization ages of ≈521.3 to ≈524.3 Ma, respectively and the age of 557 Ma to Biosyenogranites already was obtained by Rossetti et al. (2015) (Ediacaran-Early Cambrian). Geochemically, the intrusive rocks are mostly characterized by high-K content and are similar to the I-type granites. These rocks are characterized by enrichment in large ion lithophile elements (LILEs) and light rare earth elements (LREEs) along with depletion in high field strength elements (HFSEs). Their initial εNd (t) ranges from -0.6 to -2.1 at 86Sr/87Sr (i)=0.7045-0.7073. The Cadomian rocks from NE Iran, along with similaraged rocks from Turkey and Iran are suggested to form in an early stage of an active continental margin.