What do the arc magmatism trace element patterns and Sr-Nd-Pb isotopic data reflect: Insight from the Urumieh-Dokhtar magmatic arc of Iran

Abstract. Mafic volcanic rocks from the Cenozoic Urumieh-Dokhtar Magmatic Arc (UDMA) of Iran, a segment of the Alpine-Himalayan orogenic belt, provide rather restricted ranges of trace element abundances and patterns and Sr-Nd-Pb isotopic signatures that are distinct enough to help characterize the geochemical signatures inherited from their arc system components. The volcanic rocks are classified into three series; the LILE-rich, LILE-poor, and incompatible trace elements-rich series (ITE-rich series; that include samples with OIB-like patterns). The LILE-rich series is derived from a mantle source metasomatized by wet-slab partial melts whereas the LILE-poor series, high in immobile, highly incompatible elements that include La, Ce, is derived from a mantle source metasomatized by dry-slab partial melts. The ITE-rich series bear the signatures of mantle metasomatized by slab partial melts that was induced by and reacted with asthenospheric mantle ascended through a slab window or rupture. Given almost primitive geochemical signatures of the mafic rocks, the Sr-Nd isotopic modeling indicate a mantle wedge:slab melt:sediment melt contribution of 45:27.5:27.5 and 55:09:36 for the LILE-rich and LILE-poor series respectively. The mafic volcanic rocks stretching from mantle array (i.e., NHRL) towards enriched mantle on the Pb-Pb isotopic plots support this finding. High Sr and low Nd isotopic ratios of two mafic volcanic rocks from the LILE-poor series stand in sharp contrast to the other mafic rocks from LILE-poor series that plot near mantle array. Less differentiated signature of these two samples along with their older Nd model ages indicate derivation from older metasomatized mantle segments implying that the source mantle of the UDMA is heterogeneous. Eocene to Early Miocene ages for these three series favor intermittent volcanisms of the three rock series over an extended period of time rather than single episodic magmatism for each geochemically distinct magma series.