Description: High-Mg ultrapotassic volcanic rock occurrences of lamproitic affinity are exposed in southwestern Anatolia, mostly within the Menderes Massif. From north to south the lamproitic volcanism shows increasingly younger ages ranging from 20 to 4 Ma. Volcanism is contemporaneous with more voluminous shoshonitic, high-K calc-alkaline, and ultrapotassic magmatic activity in the Simav–Selendi, Uşak, Kırka, Köroğlu, Afyon and Isparta–Gölcük areas. The southward decrease in the age of the volcanism correlates with changes in geochemical composition, particularly a decrease in 87Sr/86Sr, 207Pb/204Pb, Zr/Nb and Th/Nb, and an increase in 143Nd/144Nd, 176Hf/177Hf, 206Pb/204Pb, 208Pb/204Pb and Ce/Pb, thus delineating a systematic change from orogenic (crust-like) to anorogenic (convecting mantle-like) signatures. Rare earth element compositions of clinopyroxene phenocrysts demonstrate an increasing role for residual garnet for locations in the central parts of the Menderes Massif, indicating a lithosphere thickness greater than 80 km. In contrast, K2O abundances remain nearly constant at around 7%, indicating buffering by phlogopite in the mantle source. Magma genesis in southwestern Anatolia is controlled by post-collisional extensional events initiated after major lithospheric thickening. Geochemical constraints suggest that the mantle source experienced two main geodynamic stages. The first stage caused ultradepletion of the mantle and subsequent metasomatic enrichment, which allowed coupling of the geochemical signatures of ultradepleted harzburgite with those of crust-derived sediments. This happened during the final closure stages of the southern Neotethys Ocean and the accretion of forearc oceanic lithosphere (island-arc type), as shallowly subducted material to the Anatolian lithosphere. The second stage is post-collisional, and is related to the collapse of the orogenic belt and the development of extension-related horst and graben structures. This stage is concurrent with the initiation of a thermal anomaly originating from a gap, identified by seismic tomography, in the subducted slab under western Anatolia. We propose that the lithospheric mantle underwent intense ‘asthenospherization’ owing to lithosphere–asthenosphere interaction, caused by the southward expansion of this gap during slab roll-back. The geochemical resemblance of the lamproites to more voluminous, contemporaneous shoshonitic magmas implies their derivation from a heterogeneous mantle source that had been affected by similar processes. These mantle processes may be closely associated with the major episode of uplift in the Menderes Massif.

Description: The Demir Kapija ophiolitic complex in southern Macedonia–FYROM (Former Yugoslav Republic of Macedonia) represents the southernmost exposure of the Tethyan Eastern Vardar ophiolitic unit in the Eastern Mediterranean. It consists of a mafic volcanic sequence (pillow basalts, sheeted dyke diabases and gabbros) that was subsequently intruded by island arc magmas with and without adakitic affinity. The mafic volcanic sequence is characterized by slightly increased ratios of large ion lithophile elements to high field strength elements (LILE/HFSE), flat rare earth element (REE) patterns, radiogenic 143Nd/144Nd (up to 0·51272) and high TiO2 contents (which reflect Pl + Ol + Cpx fractionation). The relationship between TiO2 and MgO contents indicates that Ti saturation was eventually reached and that Ti-magnetite fractionated. The mafic volcanic sequence of the ophiolite complex formed around 166·4 Ma in a short-lived intra-oceanic back-arc basin by slab roll-back of the Western Vardar Ocean. The rocks with and without adakitic affinity are spatially and temporally closely related. Their crystallization age is around 164 Ma. Our data suggest that two subgroups of arc lavas evolved as discrete volcanic lineages that are not related by fractional crystallization of a common parental magma, and that two different parental magmas are required. The arc lavas with adakitic affinity show some of the typical features of adakites; that is, low heavy REE, elevated Sr/Y, high LILE and high light REE. Major and trace element compositions of clinopyroxene phenocrysts resemble those of typical adakite-derived clinopyroxene. The very high Th/La, Th/Yb and Ba/Yb ratios and the reduced 143Nd/144Nd values (around 0·51245) of the rocks with adakitic affinity are considered to reflect contributions of sedimentary material to their mantle source. By analogy with adakites, these rocks are interpreted as the product of slab + sediment melting in an unusually hot subduction zone (subduction of young oceanic crust). In contrast, the arc lavas without adakitic affinity are related to a different parental melt, similar to common arc magmas. The Demir Kapija ophiolite formed in a short-lived intra-oceanic back-arc basin during subduction initiation within a back-arc. The arc intrusions are related to the change from an extensional to a compressional regime.

Description: The Demir Kapija ophiolitic complex in southern Macedonia–FYROM (Former Yugoslav Republic of Macedonia) represents the southernmost exposure of the Tethyan Eastern Vardar ophiolitic unit in the Eastern Mediterranean. It consists of a mafic volcanic sequence (pillow basalts, sheeted dyke diabases and gabbros) that was subsequently intruded by island arc magmas with and without adakitic affinity. The mafic volcanic sequence is characterized by slightly increased ratios of large ion lithophile elements to high field strength elements (LILE/HFSE), flat rare earth element (REE) patterns, radiogenic 143 Nd/ 144 Nd (up to 0·51272) and high TiO 2 contents (which reflect Pl + Ol + Cpx fractionation). The relationship between TiO 2 and MgO contents indicates that Ti saturation was eventually reached and that Ti-magnetite fractionated. The mafic volcanic sequence of the ophiolite complex formed around 166·4 Ma in a short-lived intra-oceanic back-arc basin by slab roll-back of the Western Vardar Ocean. The rocks with and without adakitic affinity are spatially and temporally closely related. Their crystallization age is around 164 Ma. Our data suggest that two subgroups of arc lavas evolved as discrete volcanic lineages that are not related by fractional crystallization of a common parental magma, and that two different parental magmas are required. The arc lavas with adakitic affinity show some of the typical features of adakites; that is, low heavy REE, elevated Sr/Y, high LILE and high light REE. Major and trace element compositions of clinopyroxene phenocrysts resemble those of typical adakite-derived clinopyroxene. The very high Th/La, Th/Yb and Ba/Yb ratios and the reduced 143 Nd/ 144 Nd values (around 0·51245) of the rocks with adakitic affinity are considered to reflect contributions of sedimentary material to their mantle source. By analogy with adakites, these rocks are interpreted as the product of slab + sediment melting in an unusually hot subduction zone (subduction of young oceanic crust). In contrast, the arc lavas without adakitic affinity are related to a different parental melt, similar to common arc magmas. The Demir Kapija ophiolite formed in a short-lived intra-oceanic back-arc basin during subduction initiation within a back-arc. The arc intrusions are related to the change from an extensional to a compressional regime.

Description: High-Mg ultrapotassic volcanic rock occurrences of lamproitic affinity are exposed in southwestern Anatolia, mostly within the Menderes Massif. From north to south the lamproitic volcanism shows increasingly younger ages ranging from 20 to 4 Ma. Volcanism is contemporaneous with more voluminous shoshonitic, high-K calc-alkaline, and ultrapotassic magmatic activity in the Simav–Selendi, Usak, Kirka, Köroglu, Afyon and Isparta–Gölcük areas. The southward decrease in the age of the volcanism correlates with changes in geochemical composition, particularly a decrease in 87 Sr/ 86 Sr, 207 Pb/ 204 Pb, Zr/Nb and Th/Nb, and an increase in 143 Nd/ 144 Nd, 176 Hf/ 177 Hf, 206 Pb/ 204 Pb, 208 Pb/ 204 Pb and Ce/Pb, thus delineating a systematic change from orogenic (crust-like) to anorogenic (convecting mantle-like) signatures. Rare earth element compositions of clinopyroxene phenocrysts demonstrate an increasing role for residual garnet for locations in the central parts of the Menderes Massif, indicating a lithosphere thickness greater than 80 km. In contrast, K 2 O abundances remain nearly constant at around 7%, indicating buffering by phlogopite in the mantle source. Magma genesis in southwestern Anatolia is controlled by post-collisional extensional events initiated after major lithospheric thickening. Geochemical constraints suggest that the mantle source experienced two main geodynamic stages. The first stage caused ultradepletion of the mantle and subsequent metasomatic enrichment, which allowed coupling of the geochemical signatures of ultradepleted harzburgite with those of crust-derived sediments. This happened during the final closure stages of the southern Neotethys Ocean and the accretion of forearc oceanic lithosphere (island-arc type), as shallowly subducted material to the Anatolian lithosphere. The second stage is post-collisional, and is related to the collapse of the orogenic belt and the development of extension-related horst and graben structures. This stage is concurrent with the initiation of a thermal anomaly originating from a gap, identified by seismic tomography, in the subducted slab under western Anatolia. We propose that the lithospheric mantle underwent intense ‘asthenospherization’ owing to lithosphere–asthenosphere interaction, caused by the southward expansion of this gap during slab roll-back. The geochemical resemblance of the lamproites to more voluminous, contemporaneous shoshonitic magmas implies their derivation from a heterogeneous mantle source that had been affected by similar processes. These mantle processes may be closely associated with the major episode of uplift in the Menderes Massif.

Description: Western Anatolian lithosphere comprises several sutures and major continental fragments with Laurasian and Gondwanan affinities, assembled prior the Oligocene. One of the major tectonic features shaping its structure is the Menderes metamorphic massif, which consists of several assembled and imbricated terrains exhumed by the Late Miocene during the extension that affected the entire Aegean province. A predominant opinion is that the Menderes is a core complex delineated by low-angle detachment faults. An alternative explanation associates it with shallow subduction of Neotethyan oceanic lithosphere that was later delaminated. To distinguish between these possibilities, direct evidence from the Western Anatolian mantle lithosphere would be ideal, because of the compositional differences of the continental and oceanic mantle lithosphere. In the absence of mantle xenoliths, mantle-derived volcanics and their macrocrystal populations, offer the only information about the composition of the mantle-lithosphere under the Menderes.

Description: Continental and oceanic mafic alkaline magmas have comparable major and trace element compositions that point towards similar P-T and volatile conditions during partial melting of their upper mantle source regions. While it is now widely accepted that OIB source regions must contain small amounts of recycled mafic components that contribute disproportionately to the magmatism, the geochemical and isotopic heterogeneity of equivalent magmas beneath continental interiors are more commonly explained by the contribution of partial melts of ultramafic veins at the base of the lithosphere. Vein-style metasomatism has also been suggested to explain the isotopic heterogeneity observed in OIBs formed on thick oceanic lithosphere, such that recycling of oceanic crust may not be the dominant source of mantle heterogeneity [1]. We analysed a suite of Mesozoic primitive mafic alkaline basalts and Permian alkaline lamprophyres from southern Sweden (Baltic Shield) for their major and trace element, and Sr-Nd-Hf-Pb isotope compositions. Although the Mesozoic alkaline basalts exhibit trace element features typically ascribed to melting of hydrous potassic phases within the mantle lithosphere, relatively homogeneous, moderately depleted radiogenic isotope compositions argue against derivation from old vein-metasomatized lithosphere. Isotopic modelling of hydrous metasomatic veins (represented by the Permian lamprophyres) potentially introduced to the lithospheric mantle beneath the Baltic Shield during Permo-Carboniferous plume magmatism suggests that such vein material, if it persisted to the Mesozoic, did not play a role in later mafic alkaline magmatism. In contrast, our data show that low-volume alkaline basaltic magmas beneath a thick continental lid ‘oversampled’ recycled oceanic crust from an otherwise highly depleted convecting upper mantle, similar to OIBs and E-MORBs.