Age, clinopyroxene geochemistry and petrogenesis of post-collisional magmatic rocks in the Jonob-e-Sechangi area, Lut block, eastern Iran

Author(s): Seyed Ali Mazhari, Kwan Nang Pang, Urs Klötzli, Huichuan Liu
Abstract: The Lut-Sistan region, eastern Iran has an extensive record of Eocene-Oligocene magmatism the origin of which is not fully understood. In this study, we analyze a set of volcanic rocks in the Jonob-e-Sechangi area of the Lut block. U-Pb zircon analyses demonstrate that magmatism can be divided into two age groups. Group 1 formed at ∼45 Ma and involved different felsic (calc-alkaline rhyolitic to dacitic) and intermediate (high-K calc-alkaline andesitic) rocks. All samples from Group 1 display nearly identical initial 87Sr/86Sr values (⁸⁷Sr/⁸⁶Sri = 0.7045-0.7056). However, the felsic rocks show higher ԐNd_t (+2.21 to +2.73) and lower T_DM (0.51-0.61 Ga). In contrast, intermediate rocks have ԐNd_t values of +1.27 to +2.23 and T_DM values between 0.63 and 0.74 Ga. Additional geochemical variations suggest that the felsic and intermediate rocks of Group 1 are not co-genetic. The felsic extrusive rocks in the Jonob-e-Sechangi area likely formed from the partial melting of the amphibolitic arc crust. In contrast, the high-K calc-alkaline andesitic rocks of Group 1 may have originated from low-degree partial melting of a spinel-peridotite mantle source. Group 2 formed basaltic andesite to andesitic rocks at37-40 Ma, showing high-K calc-alkaline to shoshonitic compositions, relatively high ⁸⁷Sr/⁸⁶Sri (0.7047- 0.7076) and relatively low ԐNd_t (0.48 to-5.86). These geochemical features require magma derivation from a mantle source that is not only elementally but also isotopically enriched, followed by variable fractionation and crustal contamination. The enriched mantle source was most likely resided in the lithosphere and formed by metasomatism by continental crust-derived materials. Clinopyroxene trace elements compositions display marked variations between different magmatic rocks. Clinopyroxene in dacitic samples of Group 1 shows relatively high contents of Sr, Rb, and Ba whereas that in Group 2 rocks has relatively high contents of Sc, V, Ga, Nb, Zr, Hf, Y and rare earth elements (REE). The findings of this study show that the intricate interactions between the lithosphere and asthenosphere, stemming from post-collisional delamination processes following the closure of the Sistan Ocean and the collision of the Lut-Afghan blocks, led to differing levels of partial melting in the region's heterogeneous metasomatized mantle. This phenomenon explains the diverse range of volcanic rocks found not just in the Jonob-e-Sechangi area but also in other regions of the Lut Block.
Organisation(s): Department of Lithospheric Research
External organisation(s): Hakim Sabzevari University, China University of Petroleum, Academia Sinica Institute of Astronomy and Astrophysics (ASIAA), No. 1, Section 4, Roosevelt Road
Journal: Lithos
Volume: 468-469
ISSN: 0024-4937
DOI: https://doi.org/10.1016/j.lithos.2024.107493
Publication date: 03-2024
Peer reviewed: Yes
Austrian Fields of Science 2012: 105105 Geochemistry, 105120 Petrology, 105127 Geochronology
Keywords
ASJC Scopus subject areas: Geology, Geochemistry and Petrology
Portal url: https://ucrisportal.univie.ac.at/en/publications/e432727b-d681-4f7d-8ffd-2baf8deee009

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