Role of magma mixing in generating of the Gheshlagh–Aftabrow intrusions, SW Buin Zahra, Iran: Evidence for a juvenile origin from geochemical and Sr–Nd isotopic data

Abstract

In this paper, we investigate host granodiorites and associated mafic microgranular enclaves (MMEs), including gabbroic to quartz diorite enclaves from the Middle Eocene Gheshlagh-Aftabrow granitoid, to assess magma mixing and crust-mantle interaction in the Urumieh-Dokhtar magmatic arc. The host granodiorites yield zircon U-Pb ages of ca. 40 Ma. Geochemical and bulk rock Nd-Sr isotopic modelling, together with the widespread occurrence of mafic microgranular enclaves with ellipsoidal and spherical shapes and chilled margins, K-feldspar and plagioclase megacrysts in the enclaves, and the presence of acicular apatite, ocellar quartz, plagioclase with oscillatory zoning and resorption surfaces, suggests that the mafic microgranular enclaves are globules of a more mafic magma derived from the mantle that was injected into and mixed/mingled with the magma derived from partial melting of a lower crust. Geochemically, the granitoid rocks are high-K calc-alkaline and metaluminous (A/CNK = 0.87-0.92) and belong to I-type suite. These granitoid host rocks have much higher SiO 2 (65.4-67.3 wt%) and relatively low Fe 2 O 3 (1.8-2.1 wt%) and MgO (1-1.58 wt%), so compared with the host rocks, the mafic microgranular enclaves have much lower SiO 2 contents (50.5-55 wt%), considerably higher Fe 2 O 3 (3.4-4.2 wt%) and MgO (3.9-4.8 wt%). Both the host intrusion and enclaves are enriched in LREE relative to HREEs (LREE/HREE = 3.1-4.1; (La/Yb) N = 2.1-4.1) and show slightly negative Eu anomalies (δEu = 0.75-0.90) and nearly flat HREE patterns ((Gd/Yb) N = 0.86-1.26). Analyses of Sr-Nd isotopes in the host granodiorites and associated enclaves show ( 87 Sr/ 86 Sr) i host = 0.705070-0.705174, εNd (t) host = 0.21-2.31, T DM1 host = 782-983 Ma, ( 87 Sr/ 86 Sr) i enclave = 0.704997-0.705170, εNd (t) enclave = 2.15-2.17, and T DM1 enclave = 874-980 Ma, indicating of juvenile nature for these granites. This characteristic together with similar trace-element compositions indicates intense magma mixing and a high degree of geochemical equilibration between the host granodiorites and their enclaves.A binary mixing model based on Sr-Nd isotopic compositions of the GAG indicates that rocks were mostly generated by mixing of 7-12% melts produced by partial melting of meta-igneous old lower crust rocks with 88-93% contribution of mantlederived juvenile basaltic magmas.The Gheshlagh-Aftabrow granodiorites (GAG) in central Urumieh-Dokhtar magmatic arc (UDMA) are characterized by the presence of mafic-intermediate microgranular enclaves (MMEs). In this paper, we present field relationships, petrographic descriptions, major-and trace-element compositional and textural disequilibrium features of some minerals (e.g., plagioclase), with geochemical and Rb-Sr isotopic data for the granodiorite hosts and associated MMEs of the Gheshlagh-Aftabrow intrusive rocks in order to unravel their respective source characteristics and petrogenesis and to contribute to a better understanding of magma mixing/mingling processes.

Juvenile crust and mantle sources for the Nasrand intrusive rocks, the central Urumieh–Dokhtar magmatic arc, Iran: Insights from elemental and isotopic geochemistry

“…Wholly, the geochemical characteristics indicate that the studied samples over the UDMA show a mixed origin composed of juvenile crust and mantle material as major components and lower old crustal material as a minor component (Figure 9e), resulting from basaltic underplating related to the Neo‐Tethys subduction (see Deng et al, 2018; Kazemi et al, 2020; Sarjoughian et al, 2018, 2019, 2020; Sepidbar et al, 2019). It is interesting that the UDMA intrusive rocks from north‐west to south‐east show more interactions with continental crust; it is supported by Figure 9e too.…”

“…The study area is located in the central part of the UDMA. Other intrusive rocks in UDMA that have been compared with the other area include: North‐west of UDMA (NW): (1) Haji Abad granitoids from Kazemi, Kananian, Xiao, and Sarjoughian (2019); (2) Gheshlaghe‐Aftabrow intrusions from Kazemi, Kananian, Xiao, and Sarjoughian (2020); (3) Saveh magmatic complex from Nouri et al (2018). Center of UDMA: (4) Niyasar plutonic complex from Honarmand et al (2014); (5) Kuh‐e Dom granitoids from Kananian, Sarjoughian, Nadimi, Ahmadian, and Ling (2014); (6) Kajan subvolcanic rocks from Golkaram et al (2016); (7) Zafarghand complex from Sarjoughian, Lentz, Kananian, Ao, and Xiao (2018); (8) Marshenan granitoids from Sarjoughian, Azizi, Lentz, and Ling (2019); (9) Soheyle‐PaKuh granitoids from Sarjoughian et al (2020); (10) Nadoushan granitoids from Shahsavari Alavijeh, Rashidnejad‐Omran, Toksoy‐Koksal, Xu, and Ghalamghash (2019).…”

Mineral Chemistry, Trace Elements, Isotopic Analysis and Zircon U‐Pb Dating in the Hesar Pluton, Northern UDMA, Iran: Implications for Pre‐Collisional Magma Mixing

“…Except for volcanic rocks, the area comprises several intrusive bodies (e.g., Haji Abad, Deh Bala, Gheshlagh, Selijerd) predominantly intruded within the Eocene volcano-sedimentary units (Rezaei-Kahkhaei et al, 2011;Kazemi et al, 2019). The intrusive bodies consist of granodiorite, monzonite, diorite and gabbro with associated aplitic dykes (Kazemi et al, 2018(Kazemi et al, , 2019(Kazemi et al, , 2020, host a large volume of MMEs and were attributed to the mid-Eocene (K-Ar age of ~39 Ma: Caillat et al, 1978; U- Pb Zr age of ~40 Ma: Kazemi et al, 2019;Rb-Sr isotopic data of ~38 Ma: Rezaei-Kahkhaei et al, 2011).…”