Eocene-Quaternary magmatic activity in the Aegean: implications for mantle metasomatism and magma genesis in an evolving orogeny

We present a compilation and comparison of geochemical data of Aegean Eocene to Recent magmatic rocks: (1) North Anatolian Eocene magmatic rocks (NAEM), (2) Aegean to west Anatolian Oligocene–Miocene magmatic rocks (AOMM), (3) Pliocene–Quaternary South Aegean volcanic arc (SAVA), (4) Pliocene–Quaternary Denizli–Isparta volcanics (DIV), and (5) Na-alkaline basalts with intra-plate geochemical affinity (IPV). These rocks are also compared with Miocene Galatean volcanics (GVP) from central Anatolia.The NAEM, SAVA and GVP show similar geochemical features indicative of a subduction-related origin in which subducted oceanic plate contaminated the overlying mantle wedge. The distinct geochemical features of the AOMM reflect derivation from an intensely metasomatised mantle source, resulting from partial subduction and accretion of both continental and oceanic assemblages in the fore-arc of a southward migrating subduction system. These features provide an insight into the history of the distinct types of mantle metasomatism in the region and into its geodynamic evolution — an evolution that include complex interaction of subduction roll-back, slab break-off, strike-slip faulting along major transfer zones, block rotations and core complex formation.Thus, the Eocene to recent magmatism in the region was controlled by various tectonic events: (1) the NAEM was most probably related to break-off of the subducted slab in western Anatolia, (2) magmatic activity in the western AOMM was controlled by rotational extension around poles in northern Greece developed in response to rotational roll-back of the Hellenic subduction system, (3) while AOMM magmatism in the east is closely associated with core complex formation and asthenosphere-related thermal input along a ~ N–S-trending slab tear. In contrast, the rocks of the DIV and IPV carry asthenospheric mantle geochemical signatures indicative of roll-back induced asthenospheric upwelling in Rhodope to NW Anatolia, and slab tear-induced asthenospheric upwelling beneath the Menderes Core Complex

Stratigraphic, structural and geochemical features of the NE–SW trending Neogene volcano-sedimentary basins in western Anatolia: Implications for associations of supra-detachment and transtensional strike-slip basin formation in extensional tectonic setting

Western Anatolia has been the focus of many geological studies of the classical extensional tectonics in the region. The NE–SW-trending Neogene volcano-sedimentary basins that characterize western Anatolia, are mainly located on the northern part of the Menderes Massif – a progressively exhumed mid-crustal metamorphic unit that has undergone Neogene extensional tectonics in the area. The NE–SW-trending basins are the Bigadiç, Gördes, Demirci, Selendi, Emet, Güre and U?ak basins. Although many studies have been carried out in these basins, the stratigraphic and tectonic evolution of the NE–SW-trending volcano-sedimentary basins remains controversial, and hence different evolutionary models have been proposed by various authors. Recent studies concluded that there was a close relation in both space and time between the basin formation and the progressive exhumation of the Menderes Massif. In this study, we present new stratigraphic, geochemical and tectonic observations from the Gördes, Demirci and Emet basins, and couple them with data from the other NE–SW-trending basins to produce a tectono-stratigraphic evolutionary model for the area.Gördes basin was opened by strike- to oblique-slip movements on the basin-bounding faults as a result of dextral transtension, such that the transtensional Gördes basin formed where extension is oblique to the margin that bounded the basin. The Demirci, Selendi, Emet, and Güre basins, have similar stratigraphic and tectonic features, and began to develop as supra-detachment extensional basins on an early Miocene corrugated detachment fault (the Simav detachment fault, SDF). In these basins, deposition of a middle Miocene volcano-sedimentary succession was controlled by NE–SW-trending strike- to oblique-slip faults, which developed as accommodation faults in the hanging-wall of a second detachment fault located further south (the Gediz detachment fault, GDF). These data suggest that the Menderes Massif was exhumed through basin formation in the upper plate that arose from successive detachment faulting, accommodated by kinematically-linked dextral strike- to oblique-slip motion to the west. Strike-slip faulting is linked to a previously described crustal-scale zone of weakness on which the Gördes basin was formed (the ?zmir–Bal?kesir transfer zone).The NE–SW-trending basins were also deformed by NE–SW-trending dextral and NW–SE-trending sinistral strike-slip faulting (under pure shear) during the late Miocene, and by E–W-trending dip-slip normal faulting in the Pliocene–Quaternary. The data indicate that the region has been extended in a not, vert, similarN–S-direction since at least the early Miocene, and that this extension occurred episodically in several phases

Petrogenesis of the Neogene volcanic units in the NE–SW-trending basins in western Anatolia, Turkey

The western Anatolian volcanic province formed during Eocene to Recent times is one of the major volcanic belts in the Aegean–western Anatolian region. We present new chemical (whole-rock major and trace elements, and Sr, Nd, Pb and O isotopes) and new Ar/Ar age data from the Miocene volcanic rocks in the NE–SW-trending Neogene basins that formed on the northern part of the Menderes Massif during its exhumation as a core complex. The early-middle Miocene volcanic rocks are classified as high-K calc-alkaline (HKVR), shoshonitic (SHVR) and ultrapotassic (UKVR), with the Late Miocene basalts being transitional between the early-middle Miocene volcanics and the Na-alkaline Quaternary Kula volcanics (QKV). The early-middle Miocene volcanic rocks are strongly enriched in large ion lithophile elements (LILE), have high 87Sr/86Sr(i) (0.70631–0.71001), low 143Nd/144Nd(i) (0.512145–0.512488) and high Pb isotope ratios (206Pb/204Pb = 18.838–19.148; 207Pb/204Pb = 15.672–15.725; 208Pb/204Pb = 38.904–39.172). The high field strength element (HFSE) ratios of the most primitive early-middle Miocene volcanic rocks indicate that they were derived from a mantle source with a primitive mantle (PM)-like composition. The HFSE ratios of the late Miocene basalts and QKV, on the other hand, indicate an OIB-like mantle origin—a hypothesis that is supported by their trace element patterns and isotopic compositions. The HFSE ratios of the early-middle Miocene volcanic rocks also indicate that their mantle source was distinct from those of the Eocene volcanic rocks located further north, and of the other volcanic provinces in the region. The mantle source of the SHVR and UKVR was influenced by (1) trace element and isotopic enrichment by subduction-related metasomatic events and (2) trace element enrichment by “multi-stage melting and melt percolation” processes in the lithospheric mantle. The contemporaneous SHVR and UKVR show little effect of upper crustal contamination. Trace element ratios of the HKVR indicate that they were derived mainly from lower continental crustal melts which then mixed with mantle-derived lavas (~20–40%). The HKVR then underwent differentiation from andesites to rhyolites via nearly pure fractional crystallization processes in the upper crust, such that have undergone a two-stage petrogenetic evolution

Geochemistry and petrology of the Early Miocene lamproites and related volcanic rocks in the Thrace Basin, NW Anatolia

The extensional Thrace basin (NW Anatolia) contains an association of early Miocene diopside–leucite–phlogopite (Do?anca) and diopside–phlogopite (Korucuköy) lamproites with Oligocene medium-K calc-alkaline andesites (Ke?an volcanics), early Miocene shoshonitic rocks (Alt?nyaz? trachyte) and middle Miocene Na-alkaline basalts (Be?endik basalts). The Do?anca lamproite (K2O = 5.1–5.5 wt.%; K/Na = 2.78–2.89; MgO = 11.4–11.8 wt.%) consists of olivine (Fo71–86), diopside (Al2O3 = 1.0–5.0, Na2O = 0.2–0.6), phlogopite (TiO2 = 1.1–9.4, Al2O3 = 11.1–13.9), spinel (Mg# = 22.9–32.6; Cr# = 64–83.4), leucite, apatite, zircon, Fe–Ti-oxides and magnetite in a poikilitic sanidine matrix. The potassic volcanic units (lamproites and trachytes) in the region have similarly high Sr and low Nd isotopic compositions (87Sr/86Sr(i) = 0.70835–0.70873 and 143Nd/144Nd(i) = 0.51227–0.51232). The major and trace element compositions and Sr–Nd–Pb isotopic ratios of the shoshonitic, ultrapotassic and lamproitic units closely resemble those of other Mediterranean ultrapotassic lamproites (i.e., orogenic lamproites) from Italia, Serbia, Macedonia and western Anatolia. The Be?endik basalts show intraplate geochemical signatures with an Na-alkaline composition, an absence of Nb negative anomalies on primitive mantle-normalized multi-element diagrams, as well as low Sr (~ 0.70416) and high Nd (0.51293) isotopic ratios; and include olivine (Fo72–84), diopside, spinel, Fe–Ti-oxides and magnetite.The Oligocene Ke?an volcanics were emplaced in the earlier stages of extension in Thrace, and represent the typical volcanic products of post-collisional volcanism. The continental crust-like trace element abundances and isotopic compositions of the most primitive early Miocene ultrapotassic rocks (Mg# up to 74) indicate that their mantle sources were intensely contaminated by the continental material. By considering the geodynamic evolution of the region, including oceanic subduction, crustal accretion, crustal subduction and post-collisional extension, it is suggested that the mantle sources of the potassic volcanic units were most likely metasomatized by direct subduction of continental blocks during accretion and assemblage of various Alpine tectono-stratigraphic units. Overall, the magma production occurred in an extensional tectonic setting that controlled the core-complex formation and related basin development, with the middle Miocene Be?endik basalts being derived from asthenospheric sources during the late stages of extension

Petrogenesis of late Campanian alkaline igneous rocks in Eastern Anatolia: magmatism related to a subduction transform edge propagator (STEP) fault?

In eastern Anatolia, the Divriği-Hekimhan Magmatic Province (DHMP) includes ~77–69 Ma alkaline rock units which are located to the NW of the Baskil Arc of ~85–74 Ma. The magmatic rocks are composed of nepheline (Ne)–to quartz (Q)–normative alkaline basaltic to trachytic/syenitic units. Among them, the basaltic rocks are composed of plagioclase (Or 2–11Ab 32–51An 39–64) + clinopyroxene (Wo 47–51En 35–42Fs 9–16) + Fe-Ti oxide ± alkali feldspar (Or 57–98Ab 2–42An 1) ± biotite ± olivine. Their 87Sr/ 86Sr (I) ratios and ɛNd (I) values vary in the ranges of 0.70591–0.70871 and−3.2–1.6, respectively. The subvolcanic trachytic rocks are composed of perthitic alkali feldspar phenocryst in a matrix of feldspar (Or 45–61Ab 38–54An 0–2), biotite, and Fe-Ti oxides. The trachytic volcanic rocks are made up of feldspar (Or 38–63Ab 34–59An 1–4) in a fine-grained matrix. Their 87Sr/ 86Sr (I) ratios and ɛNd (I) values vary in the ranges of 0.70532–0.70952 and−3.2–0.7, respectively. The syenitic rocks in the region contain both quartz- and nepheline-sodalite-bearing syenites. Geochemical features reveal that the Ne-normative basaltic magmas have undergone mafic mineral fractionation coupled with crustal contamination to produce the Q-normative derivatives. Enhanced differentiation of the Ne- and Q-normative fractionated magmas via feldspar-dominated fractionation created the silica-undersaturated and -oversaturated trachytic magmas, respectively. During the feldspar-dominated differentiation, the re-melting of accumulated alkali feldspars in the magma chamber likely gave rise to the formation of trachytic rocks with alkali feldspar-like whole rock compositions. The final products of the Ne-normative magmas are represented by the phonolites and foid-syenites with silica-undersaturated eutectic compositions. A geochemical evaluation of the basaltic rocks revealed that the alkaline magmatism mainly originated from a shallow asthenospheric mantle source which had previously been metasomatized by oceanic to continental subduction. We suggest that the DHMP was formed in response to STEP fault-controlled rolling back of the northward subducting slab of the Baskil Arc, which created a localized gap for asthenospheric upwelling. </p

Origin and significance of tourmalinites and tourmaline-bearing rocks of Menderes Massif, western Anatolia, Turkey

In the western central portion of Anatolia lies the Menderes Massif — a large metamorphic crystalline complex made of Neoproterozoic to Precambrian basement rocks overlain by Palaeozoic to early Tertiary metasedimentary rocks, and with a multistage metamorphic evolution developed from the late Neo-Proterozoic to Eocene. We have undertaken a study of the petrology, geochemistry and boron isotope composition of these tourmaline occurrences aiming to constrain the processes responsible for the enrichment of boron and other fluid mobile elements in the Menderes Massif. The dispersed tourmaline has chemical and boron isotope compositions typical of a continental crust setting, but while some of the tourmalinites display similar signatures, others have heavier boron isotope compositions (up to + 7.5‰). We suggest that the tourmalinites with continental characteristics formed part of the original Pan African basement rocks, whereas those with heavier ?11B signatures formed by later metamorphism during the Alpine orogeny, possibly through interaction with subduction-like fluids. This proposed process may also have been coincident with metasomatism of the lithospheric mantle beneath the massif, which is known to have experienced multistage metasomatism and enrichment history up to Neogene time

Late Mesozoic Tectono-stratigraphic evolution of the Hekimhan Basin and the environs (central eastern Anatolia): implications for the eastern Taurides and Gürün Curl

The east-west trending Taurides form a curved area in central eastern Anatolia known as the Gürün Curl. In order to understand the origin of the Gürün Curl and Tauride evolution in general, the results of a new field study of this region have been synthesized together with previously published data. We suggest that the geodynamic evolution of the area began with the likely presence of a Tethys Ocean transform fault. This fault separated the Taurides into the Akdere Sector in the west and the Munzur Sector in the east in the Late Cretaceous. During the late Santonian–early Campanian, ophiolites obducted onto the Munzur Sector, while platform sediments continued to accumulate in the Akdere Sector. This was followed by the development of an Andean-type arc-type magmatism (the Baskil Arc) during the early–middle Campanian in the Munzur Sector. Continued closure of the Tethys led to the collision of the Bitlis Massif in the south of the Munzur Sector in the Campanian. This, in turn, resulted in continental subduction and slab roll-back that was controlled by a Subduction Transform Edge Propagator (STEP) Fault that lay on the original transform fault between the Akdere and Munzur sectors. Because the subducted slab was free at its western corner, the western edge rolled back faster than in the east, leading to an asymmetrical extensional regime on the upper plate that created the late Campanian Hekimhan Basin. While these geodynamic events were taking place in the Munzur Sector, the Akdere Sector was in a platform setting. During the Palaeocene, the Late Mesozoic units of the Akdere Sector began to overthrust on the Hekimhan Basin and the ophiolites. Following the Palaeocene, all these tectonostratigraphic units were covered by Eocene sediments around the Gürün Curl of which the modern appearance was completed by the Miocene to Recent movements along the strike-slip faults.</p

40Ar/39Ar geochronology, geochemistry and petrology of volcanic rocks from the Simav Graben, western Turkey

Major and trace element compositions with Sr–Nd isotopic ratios, as well as Ar–Ar radiometric ages of the Miocene volcanic rocks from the Neogene units around Simav region (western Anatolia), are used to discuss the genetic relationship between (1) high-voluminous Lower–Middle Miocene high-potassic, calc-alkaline (HKCA) and (2) Middle Miocene small-voluminous high-MgO shoshonitic–ultrapotassic (SHO–UK) magmatic units in the region. All the HKCA rocks, including basaltic to rhyolitic (and granitic) samples, share similar trace element characteristics (enrichments of LILE and LREE and depletions in HFSE as a common feature of orogenic magmatic rocks), with subtle differences in their 87Sr/86Sr(i) ratios (basalts and rhyolites ~0.708, dacites ~0.710). Most of the samples of the high-MgO SHO–UK group are classified as shoshonite and latite, with some lamproites, sharing similar geochemical features with the other ultrapotassic rocks of the Mediterranean. All the rock groups have similar and high abundances of incompatible trace elements, and radiogenic Sr. Geochemical modeling of the trace element and isotopic ratios of the samples reveals that both the SHO–UK and HKCA groups were derived from a common mantle source which had been highly metasomatized and enriched by continental materials during partial subduction of the crustal metamorphic slices in a continental collision setting. The geochemical variations of these rocks were mainly controlled by source characteristics (such as heterogeneity) and variable degrees of partial melting and subsequent effects of fractional crystallization, with low degrees of crustal contamination. The HKCA series were derived by higher degrees of partial melting of the lithospheric mantle source than the SHO–UK rocks. The HKCA rocks then underwent two-stage fractional crystallization (clinopyroxene-dominated followed by feldspar-dominated fractionating mineral assemblages) to form the high-K calc-alkaline basalt to rhyolite series, whereas the SHO–UK rocks experienced comparatively little fractional crystallization. A tectonic scenario involving the rapidly extending and thinning of orogenic crust is compatible with the time-dependent compositional variation of the magmatic rocks

Chemo-probe into the mantle origin of the NW Anatolia Eocene to Miocene volcanic rocks: implications for the role of, crustal accretion, subduction, slab roll-back and slab break-off processes in genesis of post-collisional magmatism

Post-collisional Cenozoic magmatic activity in NW Anatolia produced widespread volcanism across the region. In the Biga Peninsula, in the west, medium-K calc-alkaline to ultra-K rocks with orogenic geochemical signature were emplaced at ~ 43–15 Ma (Biga orogenic volcanic rocks; BOVR). Volcanic activity in the Central Sakarya region, to the east, is mainly restricted to ~ 53–38 Ma, but also continued during the Early Miocene with small basaltic extrusives (Sakarya orogenic volcanic rocks; SOVR). This study presents a new set of geochemical data (whole rock major and trace elements and Sr–Nd–Pb isotopic compositions), obtained from the Cenozoic calc-alkaline volcanic rocks from these two regions. While there is considerable overlap in the emplacement time of volcanism in the two areas, the post-collisional volcanic rocks of these two regions differ in terms of their geochemical compositions: (1) the BOVR show an age-dependent increase in K and other large-ion lithophile elements (LILE), coupled with an increase in radiogenic Sr and Pb compositions from the Eocene to Miocene; whereas (2) the SOVR are characterized by more sodic compositions with lower K and less radiogenic Sr contents with respect to the BOVR, which were unchanged in Eocene and Miocene. We conclude that these geochemical features were principally related to the distinct modes of subduction-related mantle enrichment processes. We suggest that the Eocene to Miocene progressive enrichment in the BOVR mantle was related to successive subduction of oceanic and crustal materials in the western Aegean, while the SOVR mantle was dominantly enriched during the pre-collisional events. Magma generation in the western region was related to subduction roll-back processes associated with post-collisional extension. In the east, thermal perturbation of the mantle in response to asthenospheric upwelling due to slab break-off process was responsible for the magma generation. The time-dependent increase of K (and other LILE and radiogenic Sr) in the Cenozoic orogenic lavas from the Rhodope to Biga region emphasizes the importance of crustal imbrication and subduction in the genesis of orogenic K-rich lavas of the Alpine–Himalayan orogenic belt

The petrology of Paleogene volcanism in the Central Sakarya, Nallihan Region: Implications for the initiation and evolution of post-collisional, slab break-off-related magmatic activity

Zircon ages, mineral chemistry, whole-rock major and trace element compositions, as well as Sr–Nd isotopic ratios of basaltic (basanite, basalt, and hawaiite with MgO = 3.90–10.06 and SiO2 = 43.18–48.16) to andesitic (SiO2 = 50.86–61.27) and rhyolitic (SiO2 = 71.11–71.13) volcanic rocks (E-W emplaced Nallıhan volcanics) in the Lower Eocene terrestrial sedimentary units in the Central Sakarya Zone were studied and compared with those of the northerly located E-W-trending Eocene volcanic rocks (the Kızderbent Volcanics with 52.7–38.1 Ma radiometric ages) that are thought to be related to slab break-off process following the continental collision in the NW Anatolia. Zircon U–Pb ages of the Nallıhan volcanics vary from 51.7 ± 4.7 to 47.8 ± 2.4 Ma.Clinopyroxene from the basaltic and andesitic rocks record crystallization conditions from ~ 7–8 kbars (~ 23 km) and ~ 1210 °C, to 4.5–1.5 kbars (~ 14–1.5 km) and 1110–1010 °C crystallization conditions, respectively. The olivine-bearing, high-MgO (up to 10 wt%) basaltic rocks of the Nallıhan volcanics have nepheline-normative and Na-alkaline compositions, while the andesitic to rhyolitic rocks show calc-alkaline affinity with mainly sodic character. This is the first time this type of volcanic rock has been described in this region. The initial Sr isotopic ratios of both basaltic and andesitic–rhyolitic samples from the Nallıhan volcanics are similar (~ 0.7040–0.7045), indicating that fractional crystallization processes were not accompanied by crustal contamination and that the magma chambers were likely stored within ophiolitic units. Trace element ratios suggest that the Nallıhan volcanics were derived from E-MORB- or OIB-like enriched mantle sources, while the Kızderbent volcanics had N-MORB-like depleted mantle sources. Both volcanic units were produced by partial melting of spinel-bearing (shallow) mantle sources that had undergone subduction-related enrichment processes, with the degree of enrichment having been greater for the Kızderbent volcanics.The geochemical features of both the Nallıhan and Kızderbent volcanics are best explained as the result of slab break-off, in which the Nallıhan volcanics (located closer to the original subduction front) were produced mainly by the melting of upwelling asthenospheric mantle. Further back from the subduction front, the upwelling interacted with more highly metasomatized sub-arc mantle that underwent partial melting to produce the Kızderbent volcanics. This geodynamic scenario can be used for understanding other post-collisional slab break-off-related magmatic activities