The Cenozoic Arabia-Iran continental collision was associated with emplacement of a large variety of magmatic rock types. Thisaspect is particularly evident in the Bijar-Qorveh area of NW Iran, where Miocene andesitic to rhyolitic rocks and Quaternary basicalkaline rocks crop out. The Miocene intermediate to acid products show radiogenic Sr and Pb isotopic compositions (87Sr/86Sri0.70531-0.71109, 206Pb/204Pb 18.71-19.01, 207Pb/204Pb 15.66-15.73, 208Pb/204Pb 38.76-39.14), coupled with unradiogenic Nd isotopic ratios(143Nd/144Ndi 0.51223-0.51265). These characteristics, together with primitive mantle-normalised multielemental patterns resembling'subduction-related' geochemical fingerprints, are considered ultimately derived from the Iranian plate mantle wedge,metasomatisedduring previous NE-directed Neothetyan Ocean subduction. The alkali-rich andesitic and dacitic rocks evidence both closed- and open system differentiation, as typically observed for collisional settings in general. Both rock types display a high Sr/Y (37-100) and La/Yb(29-74) 'adakitic' signature that it is interpreted here with plagioclase (± amphibole) accumulation or melting of local mafic crustalrocks. Open-system processes involve recycling of crustal cumulates for pyroxene-rich andesite and biotite-rich dacite varieties andlow-degree partial melting of the local crust for rhyolites. A radical change occurred during the Quaternary, when SiO2-understaturatedto SiO2-saturated poorly evolved rocks (basanites, tephrites, alkaline and subalkaline basalts) were emplaced. The complete change ofmantle sources suggests a phase of local extensional tectonics related with WNW-ESE right-transcurrent faults. The major oxide, aswell as incompatible trace element and Sr-Nd-Pb isotopic fingerprint of these younger rocks is more akin to that of intraplate magmas,but still bearing some evidences for a variable contribution from a 'subduction-modified' mantle source. The NW-trend of increasinginvolvement of this subduction component is indicative of the strong tectonic control on magmatism. Additional lithotypes indicatethe presence of open-system differentiation and remelting processes in the youngest phase of magmatic activity
A showcase of igneous processes in the Urumieh-Dokhtar Magmatic Arc: the Miocene-Quaternary collisional magmatism of the Bijar-Qorveh area, northwest Iran Get access Arrow
Agostini S;Lustrino M
2022
Abstract
The Cenozoic Arabia-Iran continental collision was associated with emplacement of a large variety of magmatic rock types. Thisaspect is particularly evident in the Bijar-Qorveh area of NW Iran, where Miocene andesitic to rhyolitic rocks and Quaternary basicalkaline rocks crop out. The Miocene intermediate to acid products show radiogenic Sr and Pb isotopic compositions (87Sr/86Sri0.70531-0.71109, 206Pb/204Pb 18.71-19.01, 207Pb/204Pb 15.66-15.73, 208Pb/204Pb 38.76-39.14), coupled with unradiogenic Nd isotopic ratios(143Nd/144Ndi 0.51223-0.51265). These characteristics, together with primitive mantle-normalised multielemental patterns resembling'subduction-related' geochemical fingerprints, are considered ultimately derived from the Iranian plate mantle wedge,metasomatisedduring previous NE-directed Neothetyan Ocean subduction. The alkali-rich andesitic and dacitic rocks evidence both closed- and open system differentiation, as typically observed for collisional settings in general. Both rock types display a high Sr/Y (37-100) and La/Yb(29-74) 'adakitic' signature that it is interpreted here with plagioclase (± amphibole) accumulation or melting of local mafic crustalrocks. Open-system processes involve recycling of crustal cumulates for pyroxene-rich andesite and biotite-rich dacite varieties andlow-degree partial melting of the local crust for rhyolites. A radical change occurred during the Quaternary, when SiO2-understaturatedto SiO2-saturated poorly evolved rocks (basanites, tephrites, alkaline and subalkaline basalts) were emplaced. The complete change ofmantle sources suggests a phase of local extensional tectonics related with WNW-ESE right-transcurrent faults. The major oxide, aswell as incompatible trace element and Sr-Nd-Pb isotopic fingerprint of these younger rocks is more akin to that of intraplate magmas,but still bearing some evidences for a variable contribution from a 'subduction-modified' mantle source. The NW-trend of increasinginvolvement of this subduction component is indicative of the strong tectonic control on magmatism. Additional lithotypes indicatethe presence of open-system differentiation and remelting processes in the youngest phase of magmatic activityFile | Dimensione | Formato | |
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Descrizione: A showcase of igneous processes in the Urumieh-Dokhtar Magmatic Arc: the Miocene-Quaternary ...
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