229-9 Multi-Stage Magmatic Evolution in the Central Urumieh–Dokhtar Magmatic Arc (NE Saveh, Iran): Evidence from Zircon U-Pb Dating, Lu-Hf Isotopes, and Whole-Rock Geochemistry

Session: Crustal Petrology (Posters)

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Abstract:

Cenozoic plutonic rocks in northeast Saveh, part of the central Urumieh-Dokhtar Magmatic Arc (UDMA) in Iran, comprise monzonite, monzodiorite, gabbro, and gabbro-diorite. Detailed investigations involving whole-rock major and trace elements, mineral chemistry, zircon Hf isotopes, and U-Pb zircon geochronology provide valuable insights into mantle dynamics and magmatic processes from the Paleocene to the Pliocene. These rocks define a medium-K, calc-alkaline, metaluminous series with trace element signatures characteristic of arc-related magmatism. Zircon U-Pb ages from monzonitic to gabbroic rocks range from ~60 to 3 Ma, indicating prolonged magmatic activity from the Middle Paleocene through the Middle Pliocene. In contrast to earlier studies suggesting a magmatic hiatus of ~15 million years (ca. 72–57 Ma), our data show zircon ages between 55 and 63 Ma (mean age 60.4±0.8 Ma), pointing to a shorter quiescent period of about 10–12 million years in the UDMA. Distinct magmatic pulses are recorded in the Late Eocene (40–47 Ma), Early Miocene (23–18 Ma), and Late Miocene to Pliocene (11–5.2 Ma), reflecting ongoing subduction-related magmatic processes well into the Pliocene. Zircon ages from gabbroic rocks (11–2.5 Ma) document the latest stages of magmatism, continuing to the Pliocene-Pleistocene boundary, marking the youngest magmatic events in the central UDMA. These late-stage magmatic episodes are linked to evolving subduction dynamics and have significant implications for the geodynamic evolution of the Zagros orogen. Zircon εHf(t) values from monzonitic (−11.43 to +12.5) and gabbroic (−7.4 to +11.9) rocks, along with geochemical data, indicate processes such as fractional crystallization, crustal assimilation, and mantle-derived melt contributions. Clinopyroxene crystallization temperatures range between 1150°C and 1200°C. Rare earth element patterns and elevated La, Sm, and Yb concentrations point to partial melting of metasomatized mantle sources within the spinel-lherzolite stability field at depths less than 80 km. Geochemical evidence, including negative Nb anomalies and high water content in pyroxenes, supports the involvement of (meta-)sedimentary components (>4%). These data collectively suggest magma generation through partial melting of the lithospheric mantle triggered by asthenospheric upwelling and slab rollback associated with the subduction of the Arabian plate beneath the Iranian block.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9703

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