eocene-oligocene volcanic units of momen abad, east of iran: petrogenesis and magmatic evolution

This study investigates petrology and major, minor, and rare earth elements geochemistry of east iranian eocene–oligocene volcanic rocks in sistan suture zone, to examine their petrogenesis and magma evolution. the volcanic rocks include andesite, trachy-andesite, dacite and rhyolite. these calc-alkaline rocks of high-k series are enriched in large ion lithophile elements of rb and ba and depleted in high field strength elements (e.g. ti and nb). the ree pattern shows eu negative anomaly. these features are comparable with rocks in subduction zone of continental margin setting. the petrographic features and the geochemical variation of major oxides and trace elements against sio2 can be related to fractional crystallization in parent magma. the trace element ratios, e.g. nb/la, nb/u, ba/rb, nb/y and rb/y, verify crustal contamination with a remarkable upper crustal contamination as the main process in the formation of volcanic series. the ratios of nb/ba and nb/zr indicate that magmatic activity in momen abad had resulted from sub-continental lithospheric mantle. in addition, nb/y and zr/yb versus ta/yb reveals an e-morb like mantle source. a spinel lherzolite composition with significant role of the afc processes are deduced from the concentrations of yb and y, and the ratios of th/yb and la/yb. the ba/nb, ba/th and th/nb ratios presume a metasomatized mantle source resulted from the melting of upper crust sediments inherited from the subduction of neotethys ocean beneath the lut block.