Migration of Arc Magmatism Above Mantle Wedge Diapirs With Variable Sediment Contribution in the Aegean. (17th June 2021)

• Record Type: Journal Article
• Authors: Schaarschmidt, A.; Haase, K. M.; Voudouris, P. C.; Melfos, V.; Klemd, R.
• Is Part Of: Geochemistry, geophysics, geosystems. Volume 22:Number 6(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-06-17
• Subjects: arc migration -- shoshonitic magmatism -- sediment subduction -- diapirs -- Hellenic subduction zone; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 550.5
• DOI: 10.1029/2020GC009565
• Languages: English
• ISSNs: 1525-2027

Abstract

Abstract: Compiled data show the age progression of magmatic centers along the two approximately linear profiles from NE Greece and NW Turkey to the South Aegean Volcanic Arc. The age progression reveals the southwestward migration of arc magmatic activity from Oligocene to present, perpendicular to the Hellenic Trench. This is in accordance with the migration of the Aegean subduction zone due to the collision of oceanic and continental blocks, trench retreat, mantle flow, and coeval extension. We suggest that the subduction of large volumes of sediments and their contribution to the sub‐arc magma source controlled the composition of calc‐alkaline to high‐K calc‐alkaline and shoshonitic arc magmas during the past 30 Ma. The magma geochemistry and the approximately linear age‐progressive migration of magmatic activity suggest focused ascent of mixed material from the subducted slab into the mantle wedge, most likely in the form of mélange diapirs. Geochemical data along the profile reveals increasing Sr and decreasing Nd isotopes during Upper Miocene in agreement with the ongoing subduction of continental blocks, low subduction rates, and development of an accretionary wedge. The different K‐rich arc magmas reflect the variable subduction of sediments, whereas crustal assimilation often plays a minor role. Magmas with variable 87 Sr/ 86 Sr, P/Nd, and Ba/La indicate a variable contribution of clastic, phosphate‐bearing, and barite‐bearing sediments. Low‐degree partial melting in sediment‐dominated mélange diapirs causes the formation of shoshonitic magmas with high Sr and P2 O5 contents and high La/Yb in the northern Aegean. Plain Language Summary: The volcanic rocks of the South Aegean Islands were formed due to the subduction of the African plate below the Eurasian plate during the past 4 million years. Thirty million years ago, this subduction was situated further north and generated magmatic activity in northeast Greece and northwest Turkey. We present two profiles from the Northern Aegean to the South Aegean Islands across magmatic centers that document the temporal and spatial migration of the subduction zone from 30 million years ago to the present. A compilation of geochemical data of these magmatic rocks indicates that they were all generated by partial melting of the mantle above the descending plate, but this mantle source shows different compositions along the profile. Variable Sr isotope ratios as well as trace element concentrations of the magmas indicate that different sediments of the descending plate with variable amounts of clay, phosphate, or barite affected the mantle source of the magmas. The variable potassium and trace element concentrations of the magmas can be explained by the ascent of sediment and mantle material in heterogeneous balloon‐like structures, so‐called diapirs, above the descending plate. Key Points: Age‐progression of magmatic centers reveals the linear migration of Aegean arc magmatism Subduction of heterogeneous continental lithosphere controls K‐rich magma formation Sediment‐rich mélange diapirs trigger arc magmatism at localized magmatic centers