Alkaline magmas in zones of continental convergence
- Alkaline igneous rocks are relatively rare in settings of tectonic convergence and little is known about their petrogenesis in these settings. This study aims to contribute to a better understanding of the formation of alkaline igneous rocks by an investigation of the Tezhsar volcano-intrusive alkaline ring complex (TAC) in the Armenian Lesser Caucasus, which is located between the converging Eurasian and Arabian plates. We present new petrological, geochemical and Sr Nd isotope data for the TAC to constrain magma genesis and magma source characteristics. Moreover, we provide a new Ar-40/Ar-39 age of 41.0 +/- 0.5 Ma on amphibole from a nepheline syenite that is integrated into the regional context of ongoing regional convergence and widespread magmatism. The TAC is spatially concentric and measures similar to 10 km in diameter representing the relatively shallow plumbing system of a major stratovolcano juxtaposed by ring faulting with its extrusive products. The plutonic units comprise syenites and nepheline syenites, whereas theAlkaline igneous rocks are relatively rare in settings of tectonic convergence and little is known about their petrogenesis in these settings. This study aims to contribute to a better understanding of the formation of alkaline igneous rocks by an investigation of the Tezhsar volcano-intrusive alkaline ring complex (TAC) in the Armenian Lesser Caucasus, which is located between the converging Eurasian and Arabian plates. We present new petrological, geochemical and Sr Nd isotope data for the TAC to constrain magma genesis and magma source characteristics. Moreover, we provide a new Ar-40/Ar-39 age of 41.0 +/- 0.5 Ma on amphibole from a nepheline syenite that is integrated into the regional context of ongoing regional convergence and widespread magmatism. The TAC is spatially concentric and measures similar to 10 km in diameter representing the relatively shallow plumbing system of a major stratovolcano juxtaposed by ring faulting with its extrusive products. The plutonic units comprise syenites and nepheline syenites, whereas the extrusive units are dominated by trachytic-phonolitic rocks. The characteristic feature of the TAC is the development of pseudomorphs after leucite in all types of the volcanic, subvolcanic and intrusive alkaline rocks. Whole-rock major element data show a metaluminous (Alkalinity Index = 0-0.1), alkalic and silica-undersaturated (Feldspathoid Silica-Saturation Index <0) character of the TAC. The general trace element enrichment and strong fractionation of REEs (La-N/Yb-N up to 70) indicate a relatively enriched magma source and small degrees of partial melting. All TAC rocks show a negative Nb Ta anomalies typical of subduction zone settings. The initial 87Sr/85Sr ratios (0.704-0.705) and positive sNd values (+3 to +5) indicate an isotopically depleted upper mantle and lack of significant crustal influence, which in turn suggests the TAC magma has formed via differentiation from lithospheric mantle melts.…
Author details: | Krzysztof SokolORCiD, Ralf HalamaORCiDGND, Khachatur Meliksetian, Ivan P. Savov, Gevorg Navasardyan, Masafumi SudoORCiDGND |
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DOI: | https://doi.org/10.1016/j.lithos.2018.08.028 |
ISSN: | 0024-4937 |
ISSN: | 1872-6143 |
Title of parent work (English): | Lithos : an international journal of mineralogy, petrology, and geochemistry |
Subtitle (English): | the Tezhsar volcano-intrusive ring complex, Armenia |
Publisher: | Elsevier |
Place of publishing: | Amsterdam |
Publication type: | Article |
Language: | English |
Year of first publication: | 2018 |
Publication year: | 2018 |
Release date: | 2021/07/08 |
Tag: | Alkaline igneous rocks; Ar-40/Ar-39 dating; Armenia; Geochemistry; Pseudoleucite; Ring complex |
Volume: | 320 |
Number of pages: | 20 |
First page: | 172 |
Last Page: | 191 |
Funding institution: | Santander Travel Bursaries |
Organizational units: | Mathematisch-Naturwissenschaftliche Fakultät / Institut für Geowissenschaften |
DDC classification: | 5 Naturwissenschaften und Mathematik / 55 Geowissenschaften, Geologie / 550 Geowissenschaften |
Peer review: | Referiert |
Publishing method: | Open Access / Green Open-Access |