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Title

Incremental growth of mid- to upper-crustal magma bodies during Arabia-Eurasia convergence and collision: A petrological study of the calc-alkaline to shoshonitic Meghri- Ordubad pluton (Southern Armenia and Nakhitchevan, Lesser Caucasus)

Authors
Leuthold, Julien
Tayan, Rodrik
Published in Journal of petrology. 2018, vol. 59, 931–966
Abstract The composite Meghri-Ordubad pluton (MOP) is located in the southernmost Lesser Caucasus and outcrops over ~1000 km2 in southern Armenia and Nakhitchevan. It is characterized by nested intrusions incrementally emplaced over ~30 Myr from the Middle Eocene to Early Miocene, coeval with the closure of the Neotethyan Ocean and the regional Arabia-Eurasia continental collision. We recognize three compositionally distinct intrusive series in the MOP: a medium- to high-K calc-alkaline series 1 dominated by gabbro, quartz diorite and tonalite, a shoshonitic to high-K calc-alkaline series 2 including gabbro, monzogabbro, monzodiorite, monzonite and syenite, and a high-K calc-alkaline adakitic series 3 characterized by the emplacement of lamprophyre dikes followed by porphyritic granodioritic intrusions and dikes. Thermobarometry calculations together with detailed petrography, mineral chemistry and experimental mineral stability P-T diagrams indicate a polybaric crystallization history and magma emplacement at mid- to upper crustal levels (0.1-0.3 GPa). Mineral textures and compositions reveal open-system magmatic processes such as mafic magma replenishment and reactivation of crystal mushes prior to transport towards shallower crustal levels in the MOP. The evolution of magma chemistry (calc-alkaline vs shoshonitic) and mineral assemblages (amphibole-bearing vs amphibole-free) indicate fluctuation in primary melt alkali and water contents over time. Such chemical evolution is ascribed to a decrease in the degree of partial melting of a chemically heterogeneous, but isotopically homogeneous, mantle source. Overall, the MOP is characterized by the successive emplacement of hydrous magma batches in the mid- to upper crust and petrological processes that were dominated by fractional crystallization (± crustal assimilation) upon cooling and, or, decompression (± degassing). We propose a new temporal and spatial petrogenetic model for the MOP, encompassing three long-lived, chemically distinct magmatic series incrementally assembled over 30 Myr within a pre-, syn- and post-collisional geodynamic setting.
Keywords Tethyan orogenic beltIncremental pluton assemblyMagmatic processesMineral chemistryThermobarometry
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Structures
Research group Mineral Resources and Geofluids
Projects
Swiss National Science Foundation: 200020–138130, 200020–155928 and 200020–168996
Autre: SCOPES Joint Research Projects IB7620– 118901 and IZ73Z0–128324
Citation
(ISO format)
REZEAU, Hervé et al. Incremental growth of mid- to upper-crustal magma bodies during Arabia-Eurasia convergence and collision: A petrological study of the calc-alkaline to shoshonitic Meghri- Ordubad pluton (Southern Armenia and Nakhitchevan, Lesser Caucasus). In: Journal of Petrology, 2018, vol. 59, p. 931–966. doi: 10.1093/petrology/egy050 https://archive-ouverte.unige.ch/unige:106907

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Deposited on : 2018-08-07

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