Akademik Veri Yönetim Sistemi
Lithos, cilt.516-517, 2025 (SCI-Expanded, Scopus)
Across-arc geochemical variations in igneous rocks are common in magmatic belts that form at convergent margins, but the geological processes responsible are unclear. To investigate this, we acquired new whole-rock major and trace element data, coupled with Sr–Nd–Pb isotopic ratios, zircon Hf isotopes, and U[sbnd]Pb geochronology for three intermediate and felsic intrusions in the Baghu, Chalu and Gandi regions of the Moallemen magmatic complex, NE Alborz rear-arc. These were compared to data from well-exposed Early Cenozoic Alborz rear-arc igneous rocks in northeastern and northwestern Iran. The Chalu intrusions are mainly monzonite, quartz-monzonite, whereas the Baghu and Gandi intrusions are granodiorite and granite, respectively. U[sbnd]Pb zircon crystallization ages of 49.9 ± 0.74 and 46.3 ± 0.82 Ma for the Chalu intrusions indicate that they are slightly older than the Baghu granodiorite (41.2 ± 2.3 Ma) and Gandi granite (42.2 ± 0.99 Ma). The Chalu monzonite and quartz-monzonite rocks display relatively higher LILE/HFSE (Ba/Th: 60–167) but similar LILE/LREE (Ba/La: 17–21) values to those of the Baghu and Gandi intrusions (Ba/Th: 27–54; Ba/La: up to 25). All three units show the same Sr–Nd–Pb isotopic compositions, having same radiogenic Sr (87Sr/86Sr, 0.70400–0.70425) and Pb (206Pb/204Pb, 18.50–18.53; 207Pb/204Pb, 15.58–15.59; 208Pb/204Pb, 38.56–38.63), Nd (143Nd/144Nd, 0.51272–0.51295) and zircon Hf (+7.2 to +11.4) isotopic compositions. Modeling of Sr[sbnd]Nd isotopes suggests that these magmas were generated by the interaction of mantle-derived melts with lower continental crust through a series of assimilation-fractional crystallization (AFC) processes during ascent in the NE Alborz rear-arc. Published major and trace element data, bulk rock εNd(t) and zircon εHf(t) isotope data across the Alborz rear-arc show that melts of enriched lithospheric mantle and subducted slab-derived experienced less crustal interaction in the central and NW Alborz rear-arc than in the NE Alborz rear-arc. This variation reflects differences in subduction dynamics, crustal thickness, and mantle wedge processes along the Alborz rear-arc, indicating the utility of magmatic complexes for deciphering ancient tectonic processes. This work also settles a long-standing debate about the geodynamic evolution of the Alborz rear-arc, showing that a compressive to extensional tectonic regime existed during the Arabia–Eurasia collision.