Search

In the Republic of North Macedonia, the northern marginal part of the Pelagonian Unit comprises several isolated slivers of low-grade blueschist-facies rocks. These rocks were metamorphosed at conditions of the epidote-blueschist facies with rare transitions to the lawsonite-epidote blueschist facies. If present, lawsonite occurs as relic inclusions in albite, suggesting a local metasomatic enrichment of Na. No aragonite or fibrous calcite was detected, suggesting that the rocks were equilibrated at pressures below the aragonite-calcite boundary. When present, calcite + quartz coexist with glaucophane, epidote, and titanite suggesting the presence of a metamorphic H2O-rich fluid phase with very low XCO2 values (< 0.002). Most samples contain chlorite and only some have garnet, which is nearly free of Mg, but contains an andradite component. Albite only occurs in garnet-free rocks. A core-to-rim decrease of Fe3+/(Fe3++Al3++Cr + Mn3+) in epidote, VIFe3+/VI(Fe3++Al) in blue Na-rich amphibole, and Fe3+/(Fe2++Fe3+) in garnet grains suggest a decrease of ƒO2 during metamorphism. The general absence of magnetite and the presence of very small amounts of hematite in some samples suggest that the hematite–magnetite buffer curve was probably not crossed. It is thought that the investigated blueschist-facies rocks were part of the once highly oxidized sedimentary cover of the subducting oceanic plate. The underlying basaltic crust and oceanic mantle, however, were probably relatively reduced. Aqueous fluids which left this part of the lithosphere during subduction (dehydration) partially reduced the overlying oxidized metasediments. Concerning metamorphic P–T conditions, a pressure range of 0.7–0.9 GPa is defined by the presence of glaucophane + epidote + quartz at the lower boundary and the absence of aragonite at the higher boundary. The temperature range of 320–420°C is defined by the absence of Fe-Mg-pumpellyite at the lower side and the presence of lawsonite + albite at the higher side. These conditions can be narrowed down by using calculated equilibrium mineral assemblage diagrams (pseudosections) for three different bulk-rock compositions, resulting in P = 0.74–0.85 GPa and T = 340–370°C. It must, however, be emphasized that many phases (garnet, glaucophane, epidote, and phengite) show significant chemical zonation, which makes the use of pseudosections problematic.

© 2022 Elsevier B.V.This study deals with the age and petrogenesis of mafic-ultramafic intrusions ranging in size from a few meters to 10 km within the Early Carboniferous high-grade gneisses of the Pulur Complex in the Eastern Pontides. The intrusions comprise dunite, wehrlite, gabbronorite, leucogabbro, anorthosite and ilmenite-bearing gabbronorite of cumulus origin, and are crosscut by dikes of ilmenite-bearing gabbronorite, leucogranite and microdiorite. U–Pb dating on zircons from gabbronorite, anorthosite and leucogranite yielded igneous crystallization ages of 322–326 Ma, indicating that the intrusions were emplaced ca. 5–7 Ma after the peak of high-grade metamorphism, and form part of the Late Carboniferous high-volume magmatism in the region. In most cumulate rocks, Cr–Al spinel, olivine and plagioclase were early crystallizing phases, followed by orthopyroxene, clinopyroxene and hornblende. Whole rock geochemical data suggest that wehrlite, gabbronorite, leucogabbro and anorthosite stem from a common magma, and ilmenite-bearing gabbronorite and dikes of leucogranite and microdiorite from different magmas. Application of mineral/melt partition coefficients to trace element compositions of clinopyroxene and hornblende in cumulate rocks suggests that the main cumulate body was derived from middle- to high-K calc-alkaline basic melts, and relatively late ilmenite-bearing gabbronorites from hypersthene-normative Ca-rich melts. All the rock types display radiogenic Sr and Pb isotopic signatures, and unradiogenic Nd isotopic ratios, which are indistinguishable from those of the coeval voluminous high-K calc-alkaline I-type granites in the region; the isotopic ratios are probably related to the metasomatism of the lithospheric mantle by sediment-derived melts. We suggest that the parental melts of the mafic-ultramafic intrusions and those of the high-K calc-alkaline granites were genetically related, and melts of the high-K calc-alkaline granites were probably derived from the melting of newly underplated calc-alkaline basic material at lower crustal depths, that were compositionally comparable to the parental magmas of the mafic-ultramafic intrusions.

We investigated the 53Mn-53Cr isotopic composition of a suite of enstatite chondrites by in situ analyses of various mineral phases with the Cameca IMS 1280-HR ion probe at Heidelberg, Germany, and a Cameca NanoSIMS at Paris, France. Only in sphalerite we found anomalies in 53Cr/52Cr-ratios correlating with 55Mn/52Cr which are due to decay of short-lived 53Mn (t1/2 = 3.7 Ma). A sphalerite in the EH-impact melt LAP 02225 showed the largest excess of 53Cr, with 53Cr/52Cr-ratios ranging up to 2.2. The calculated initial 53Mn/55Mn-ratios are within the range of previous Mn-Cr studies. We observed a spatial variation within a large sphalerite in LAP 02225, translating in distinct initial 53Mn/55Mn values. In case of the EL3 chondrite MAC 88136 the initial 53Mn/55Mn derived for one sphalerite is at the lower end of previously reported values and may reflect a variable influence of alteration-induced exchange of common Cr. This is supported by the total reset of the 53Cr/52Cr-ratio in another sphalerite in contact with an alteration vein irrespective of high Mn/Cr-ratios. Our observed initial 53Mn/55Mn-ratios of Sahara 97158, Indarch and EET 96135 correspond to the I-Xe systematics and hence, show that sphalerites can preserve reasonable age information. For Indarch however, if compared with other initial 53Mn/55Mn values from literature, a considerable scatter is obvious. This clearly demonstrates that the Mn-Cr system in sphalerite can be disturbed by various, still poorly investigated, processes (e.g., by thermal events, weathering, diffusion-controlled remobilization). Future application of Mn-Cr dating to sphalerite in enstatite chondrites thus requires a better understanding of how such processes influence the Mn-Cr systematics and demands for tools to identify the undoubtly present sphalerites carrying a true chronologic information.

In the Variscan Schwarzwald metabasic rocks form small bodies included within anatectic plagioclase-biotite gneisses. Many metabasites first underwent an eclogite-facies metamorphism at about 2.0 GPa and 670–700 °C, resulting in the assemblage garnet + omphacite + rutile + quartz ± epidote ± amphibole ± kyanite. Since these eclogites are nearly free of an OH-bearing phase, they underwent almost complete dehydration during subduction, suggesting formation along an average to warm top-of-the-slab geotherm of 10–13 °C/km. The age of the Variscan high-P/high-T metamorphism is > 333 Ma. After partial exhumation from ~ 65 to ~ 15 km depth, the eclogites were overprinted under increasing activity of H2O by a number of retrograde reactions. The degree of this overprint under amphibolite-facies conditions (0.4–0.5 GPa/675–690 °C) was very different. Up to now, only retrograde eclogites have been found, but some samples still contain omphacite. Kyanite is at least partially transformed to aggregates of plagioclase + spinel ± corundum ± sapphirine. On the other hand, there are amphibolites that are extensively recrystallized and show the assemblage amphibole + plagioclase + ilmenite/titanite ± biotite ± quartz ± sulphides. The last relic phase that can be found in such otherwise completely recrystallized amphibolites is rutile. After the amphibolite-facies metamorphism at ~ 333 Ma, the metabasites underwent a number of low-temperature transformations, such as sericitization of plagioclase, chloritization of amphibole, and formation of prehnite. The intimate association of metabasite bodies with gneisses of dominantly meta-greywacke compositions suggests derivation from an active plate margin. This view is corroborated by bulk-rock geochemical data. Excluding elements that were mobile during metamorphism (Cs, Rb, Ba, K, Pb, Sr, U), the concentrations of the remaining elements in most of the metabasites are compatible with a derivation from island-arc tholeiites, back-arc basin basalts or calc-alkaline basalts. Only some samples have MORB precursor rocks.

The Variscan Rand Granite as defined in this paper is a deformed I-type biotite granite that intruded along the southern-to-southeastern margin of the Central Schwarzwald Gneiss Complex. Former K-feldspar megacrysts (now porphyroclasts) of this K–Mg-rich alkali-calcic granite frequently show zonal crystallographic arrangement of mineral inclusions and are enclosed in a matrix of plagioclase, K-feldspar, quartz, biotite, apatite, zircon, and magnetite. Minor sphene and allanite are mostly altered. K-feldspar is orthoclase with perthitic exsolutions. Myrmekite is common and typically replaces marginal K-feldspar. Both feldspars show cataclastic and incipient ductile deformation that took place within the stability field of biotite (≥ 400 °C) as proven by grey varieties of Rand Granite with stable biotite. At most places, however, the Rand Granite shows a reddish colour, caused by late-stage chloritization of biotite and formation of hematite within K-feldspar. Furthermore, plagioclase became partially altered to sericite. This hydrothermal alteration took place at temperatures below the stability of biotite (

Highlights • Volcanic activity of Harrat Uwayrid (NW Arabia) lasted from 8.2 to 0.3 Ma. • Alkali olivine basalts are followed by basanites, tephrites and tephriphonolites. • Sr-Nd-Pb isotopic ratios of all volcanic rocks suggest a PREMA source. • Different degrees of partial melting of amphibole-garnet-spinel lherzolite • Lithospheric mantle source rather than asthenosphere or plume-type mantle Abstract The volcanic field of Harrat ar Rahah-’Uwayrid (NW Saudi Arabia) consists of an older plateau basalt sequence that overlies Cambrian sandstone and younger cinder cones with smaller flows that are concentrated in the central part of this field. Petrographic and whole rock geochemical data indicate that the older plateau basalts are alkali olivine basalts, while the younger volcanic products are basanites and tephrites with some phonotephrites and tephriphonolites. KAr model ages on 22 bulk-rock samples were obtained for variable grain size fractions (125–250, 250–500 μm). These dates range from 8.2 to 0.34 Ma, whereby three phases of volcanic activity during the Upper Miocene, Pliocene and Quaternary can be distinguished. Sr-Nd-Pb isotopic ratios are similar for all age groups with 87Sr/86Sr = 0.70307–0.70324, 143Nd/144Nd = 0.512912–0.512957, 206Pb/204Pb = 19.360–19.717, 207Pb/204Pb = 15.603–15.633 and 208Pb/204Pb = 39.083–39.521 (present-day ratios are indistinguishable from calculated initial ratios) suggesting that chemical differences among the lavas were probably produced by different degrees of partial melting rather than by different source compositions. Trace element ratios indicate an origin of all volcanics by small degrees of partial melting of amphibole-spinel-garnet peridotite. Geochemical and isotopic data of the Harrat ar Rahah-’Uwayrid are similar to those from the small volcanic fields of Harrat Kura (about 200 km SSE of Harrat al ‘Uwayrid) and of Wadi Jizan in SW Saudi Arabia, but clearly more enriched than those of the volcanic fields that are located in the more central parts of the eastern shoulder of the Red Sea Rift. The lithospheric thickness underneath Harrat ar Rahah-’Uwayrid is estimated to about 60 km based on published results from seismic tomography. Our data support the model that the metasomatized lithospheric mantle was the primary source of the magmas, while the asthenospheric mantle or a plume-type component played an unsignificant role. The composition of the lithospheric mantle source was similar to prevalent mantle (PREMA). There is no need to postulate the participation of a HIMU component and/or enriched mantle components (EM-1, EM-2) in the source of the investigated magmas.

Like the Moldanubian parts of the Bohemian Massif and the French Massif Central, the Vosges Mts (NE France) comprise an uppermost tectonic unit that consists of retrograded (U)HP/UHT granulites, eclogites and garnet peridotites, originally metamorphosed at pressures of ≥ 4 GPa and temperatures of ≥ 950 °C. Two amphibole–garnet–spinel-bearing peridotite bodies located near to Col des Bagenelles (CB) and Crebimont (CR) show a pronounced retrograde evolution. Primary garnet was completely transformed to a symplectite of orthopyroxene + clinopyroxene + Cr-poor spinel ± amphibole, partially surrounded by a discontinuous outer zone of coarser grains of pyroxenes ± amphibole. Such symplectites are typical for the sliding reaction garnet + olivine ± Na2O ± K2O ± H2O = orthopyroxene + clinopyroxene + spinel ± amphibole. Both peridotites contain ‘primary’ Cr–Al–spinel. In the sample from CB, such grains occur only within the symplectites after garnet, but never in the matrix, while in the sample from CR, Cr–Al–spinel is present as inclusions within the symplectites and as isolated grains within the surrounding matrix. In the peridotite from CR, that is more depleted than that from CB, these Cr–Al–spinel grains show intense chemical zoning with Cr and Fe2+ decreasing, but Al and Mg increasing from core to rim. This pattern is interpreted as retrograde zoning during decompression. Primary P–T conditions deduced from compositions of matrix pyroxenes under the assumption of equilibration with earlier garnet are ≥ 1.6–1.7 GPa/ ≥ 900 °C for sample CB, but ≥ 2.3 GPa/ ≥ 860 °C for sample CR. Temperature conditions during the breakdown of garnet are indicated by pyroxenes from the symplectites and are 833 ± 18 (CB) and 812 ± 11 °C (CR) using the Ca-in-Opx thermometer at a chosen pressure of 1.3 GPa.

The Eastern Mediterranean region within the Tethyan belt is characterised by two main pulses of suprasubduction-zone ophiolite formation during the Early–Middle Jurassic and Late Cretaceous. Despite vast exposures of the Permo-Triassic accretionary complexes, related suprasubduction-zone ophiolites and the timing of subduction initiation leading to the formation of Permo-Triassic accretionary complexes are unknown so far. Here we report on a ~ 40 km long and 0.3 to 1.8 km wide metaophiolite fragment within transitional greenschist- to blueschist-facies oceanic rocks from NW Turkey. The metaophiolite fragment is made up mainly of serpentinite and minor dykes or stocks of strongly sheared metagabbro with mineral assemblages involving actinolite/winchite, chlorite, epidote, albite, titanite and phengite. The metagabbro displays (i) variable CaO and MgO contents, (ii) anomalously high Mg# (= 100 ∗ molar MgO/(MgO + FeOtot)) of 75–88, and (iii) positive Eu anomalies, together with low contents of incompatible elements such as Ti, P and Zr, suggesting derivation from former plagioclase cumulates. The serpentinites comprise serpentine, ± chlorite, ± talc, ± calcite and relict Cr-Al spinel surrounded by ferrichromite to magnetite. Relict Cr-Al spinels are characterised by (i) Cr/(Cr + Al) ratios of 0.45–0.56 and Mg/(Mg + Fe2 +) ratio of 0.76–0.22, (ii) variable contents of ZnO and MnO, and (iii) extremely low TiO2 contents. Zn and Mn contents are probably introduced into Cr-Al spinels during greenschist- to blueschist metamorphism. Compositional features of the serpentinite such as (i) Ca- and Al-depleted bulk compositions, (ii) concave U-shaped, chondrite-normalised rare earth element patterns (REE) with enrichment of light and heavy REEs, imply that serpentinites were probably derived from depleted peridotites which were refertilised by light rare earth element enriched melts in a suprasubduction-zone mantle wedge. U-Pb dating on igneous zircons from three metagabbro samples indicates igneous crystallisation at 262 Ma (middle Permian). Timing of the metamorphism is constrained by incremental 40Ar/39Ar dating on phengitic white mica at 201 Ma (latest Triassic). We conclude that the metaophiolite represents a fragment of middle Permian suprasubduction-zone oceanic lithosphere, involved in a latest Triassic subduction zone. These data, together with several reports in literature, indicate that the middle Permian was a time of suprasubduction-zone ophiolite formation in the Tethyan belt.

A new occurrence of ardennite near Vitoliste in the southernmost Republic of Macedonia (FYROM) is described. In the westernmost Vardar zone, a high- P / T metamorphic conglomerate contains reddish clasts (up to 20–30 vol% of the rock) that consist of quartz, hematite, ardennite, pyrophyllite, sudoite, cookeite, phengite rimmed by muscovite, epidote/piemontite, lawsonite, tourmaline, titanite, albite, apatite and ±rutile. Epidote may contain inclusions of pumpellyite–(Fe 2+ ) and is partially transformed to piemontite. Ardennite is generally poor in As and its composition essentially follows the T4 exchange vector (Si + Al + P) −1 V, whereby Al and P are relatively low. Three compositional types of ardennite can be distinguished: ardennite-(V), ‘ardennite-(V,Si)’ and ‘ardennite-(Si)’, the latter possibly representing lavoisierite inter- and overgrowths. Metamorphic conditions of 0.65–0.80 GPa and 340–370 °C are deduced. The reddish Fe–Mn–(V–As)-rich detritus may have originated from a hydrothermal Fe–Mn deposit or, more likely, from a nickel–laterite deposit developed from weathered ophiolites. Such laterites and bauxites resulted from re-deposition of ophiolite material in shallow seawater during the Lower Cretaceous.

Trace element compositions of clinopyroxene and oxidation state measurements are both useful parameters for constraining metasomatic interactions within the subcontinental lithospheric mantle (SCLM). Laser ablation inductively coupled plasma mass spectrometry analyses of trace elements in clinopyroxene in combination with oxidation state data from the same samples provide a fuller picture of the metasomatic processes that occurred within the SCLM below the French Massif Central (FMC). A total of 89 spinel peridotite xenoliths from 39 localities across the FMC document variable degrees of partial melting and metasomatism at both regional and local scales. According to the degree of enrichment in light rare earth elements (LREE) and middle rare earth elements (MREE) in clinopyroxene, four main groups (A, B, C and D) are identified. Variations in other trace element concentrations are consistent with these groups. LREE enrichment correlates with a tendency to higher oxygen fugacity (fO2). These characteristics, along with their Ti/Eu–Zr/Hf systematics, are useful in assessing the different metasomatic agents that have interacted with the FMC SCLM. The behaviour of Lu and Hf additionally provides a means for distinguishing secondary clinopyroxene grains from those that have been overprinted. Most samples have been affected by cryptic metasomatism and different signatures indicate interaction with different types of metasomatic agent. Modal metasomatism is apparent by the presence of amphibole or secondary clinopyroxene. The lack of any notable trace element or redox signature related to the occurrence of amphibole suggests that it formed from small amounts of dilute H2O-rich fluids. Most samples from the northern sector of the FMC are fairly refractory and clinopyroxene exhibits a ‘tick-shaped’ REE signature (group D), consistent with metasomatism by subduction-related fluids during Variscan times. Such fluids were oxidizing (Δlog fO2 values > FMQ + 1, where FMQ is the fayalite–magnetite–quartz buffer) and responsible for LREE enrichment in clinopyroxene and low concentrations of the less mobile elements such as Ti, Eu, Zr and Hf. Clinopyroxene in several samples has very low Ti/Eu, elevated (La/Yb)N and suprachondritic Zr/Hf ratios, reflecting local carbonatite metasomatism. These samples also record oxidizing conditions, with Δlog fO2 values > FMQ + 1. Many other samples have clinopyroxenes with higher Ti/Eu and approximately chondritic Zr/Hf ratios, consistent with having undergone silicate melt metasomatism. Their chondrite-normalized REE element patterns vary from LREE-depleted to relatively flat (group A), indicating small but variable metasomatic enrichments in the more mobile elements, which can be attributed to chromatographic effects during reactive flow. The oxidation states of these samples record Δlog fO2 ∼ FMQ + 0·4 ± 0·5. Some samples have clinopyroxene with negative Zr and Hf anomalies and distinctly low Ti/Eu (

Shock-induced melt veins in amphibolites from the Nordlinger Ries often have chemical compositions that are similar to bulk rock (i.e., basaltic), but there are other veins that are confined to chlorite-rich cracks that formed before the impact and these are poor in Ca and Na. Majoritic garnets within the shock veins show a broad chemical variation between three endmembers: (1) $${}^{\text{VIII}}{{\text{M}^{2+}}_3} {}^{\text{VI}}{\text{Al}}_{2} ({}^{\text{IV}}{\text{SiO}}_{4} )_{3}$$ (normal garnet, Grt), (2) $${}^{\text{VIII}}{{\text{M}^{2+}}_3} {}^{\text{VI}}[{\text{M}}^{2 + } ({\text{Si,Ti}})]({}^{\text{IV}}{\text{SiO}}_{4} )_{3}$$ (majorite, Maj), and (3) $${}^{\text{VIII}}({{\text {Na} {\text M}^{2+}}_2}) {}^{\text{VI}}[ ({\text{Si,Ti}}){\text {Al}}]({}^{\text{IV}}{\text{SiO}}_{4} )_{3}$$ (Na-majorite50Grt50), whereby M2+ = Mg2+, Fe2+, Mn2+, Ca2+. In particular, we observed a broad variation in VI(Si,Ti) which ranges from 0.12 to 0.58 cations per formula unit (cpfu). All these majoritic garnets crystallized during shock pressure release at different ultrahigh pressures. Those with high VI(Si,Ti) (0.36–0.58 cpfu) formed at high pressures and temperatures from amphibole-rich melts, while majoritic garnets with lower VI(Si,Ti) of 0.12–0.27 cpfu formed at lower pressures and temperatures from chlorite-rich melts. Furthermore, majoritic garnets with intermediate values of VI(Si,Ti) (0.24–0.39) crystallized from melts with intermediate contents of Ca and Na. To the best of our knowledge the ‘MORB-type’ Ca–Na-rich majoritic garnets with maximum contents of 2.99 wt% Na2O and calculated crystallisation pressures of 16–18 GPa are the most extreme representatives ever found in terrestrial shocked materials. At the Ries, the duration of the initial contact and compression stage at the central location of impact is estimated to only ~ 0.1 s. We used a ~ 200-µm-thick shock-induced vein in a moderately shocked amphibolite to model its pressure–temperature–time (P–T–t) path. The graphic model manifests a peak temperature of ~ 2600 °C for the vein, continuum pressure lasting for ~ 0.02 s, a quench duration of ~ 0.02 s and a shock pulse of ~ 0.038 s. The small difference between the continuum pressure and the pressure of majoritic garnet crystallization underlines the usefulness of applying crystallisation pressures of majoritic garnets from metabasites for calculation of dynamic shock pressures of host rocks. Majoritic garnets of chlorite provenance, however, are not suitable for the determination of continuum pressure since they crystallized relatively late during shock release. An extraordinary glass- and majorite-bearing amphibole fragment in a shock-vein of one amphibolite documents the whole unloading path.

Oxidation state is a sensitive indicator of geochemical processes within the upper mantle. Here we report results of a regional study of the oxidation state of spinel peridotite xenoliths from 45 volcanic centers distributed over ∼20 000 km2 in the Massif Central, France. The Δlog fO2 values relative to the fayalite–magnetite–quartz oxygen buffer (FMQ) were determined from the equilibrium between the Fe-bearing components in olivine, orthopyroxene and spinel, with the Fe3+ content of spinel measured either by Mossbauer spectroscopy or by electron microprobe using secondary spinel standards. For the entire suite of samples, Δlog fO2 values range between FMQ – 0·47 and FMQ + 1·66. Our data confirm the presence of two distinct lithospheric mantle domains, previously reported in the literature, lying north and south of 45°30'N, respectively. The northern domain, with its refractory bulk composition, tends to record more oxidized conditions, having Δlog fO2 values mostly at or above FMQ + 1. The Δlog fO2 in the southern domain is more variable, including values below FMQ. Assuming that increasing equilibration temperatures among xenoliths reflect increasing depths of origin, samples from the northern domain suggest that the shallower part of the subcontinental lithospheric mantle (SCLM) is somewhat more oxidized than at deeper levels. On the other hand, such a general observation cannot be made for the southern domain. The high Δlog fO2 values of harzburgites suggest that they are more sensitive to resetting of their oxidation state by metasomatism than lherzolites. In terms of modally metasomatized xenoliths, the ‘melt’ leading to the addition of clinopyroxene apparently had a higher oxidation state (Δlog fO2 > FMQ + 1) than the agent responsible for crystallization of amphibole (Δlog fO2 ∼ FMQ + 0·6). Furthermore, amphibole-bearing and amphibole-free peridotites exhibit the same range in fO2. Cryptic metasomatism can also reset oxidation state, sometimes very effectively. Metasomatic processes are probably the reason why the xenolith suite from the Massif Central records relatively high Δlog fO2 values compared with ‘normal’ non-cratonic SCLM. This study demonstrates the utility of using oxidation state to help characterize and delineate domains in the lithospheric mantle.

Within the Tethyan realm, data for the subduction history of the Permo–Triassic Tethys in the form of accretionary complexes are scarce, coming mainly from northwest Turkey and Tibet. Herein we present field geological, petrological and geochronological data on a Triassic accretionary complex, the Agvanis metamorphic rocks, from northeast Turkey. The Agvanis metamorphic rocks form a SSE–NNW trending lozenge-shaped horst, ∼20 km long and ∼6 km across, bounded by the strands of the active North Anatolian Fault close to the collision zone between the Eastern Pontides and the Menderes–Taurus Block. The rocks consist mainly of greenschist- to epidote-amphibolite-facies metabasite, phyllite, marble and minor metachert and serpentinite, interpreted as a metamorphic accretionary complex based on the oceanic rock types and ocean island basaltic, mid-ocean ridge basaltic and island-arc tholeiitic affinities of the metabasites. This rock assemblage was intruded by stocks and dikes of Early Eocene quartz diorite, leucogranodiorite and dacite porphyry. Metamorphic conditions are estimated to be 470–540°C and ∼0.60–0.90 GPa. Stepwise 40Ar/39Ar dating of phengite–muscovite separates sampled outside the contact metamorphic aureoles yielded steadily increasing age spectra with the highest incremental stage corresponding to age values ranging from ∼180 to 209 Ma, suggesting that the metamorphism occurred at ≥ 209 Ma. Thus, the Agvanis metamorphic rocks represent the vestiges of the Late Triassic or slightly older subduction in northeast Turkey. Estimated P–T conditions indicate higher temperatures than those predicted by steady state thermal models for average subduction zones, and can best be accounted for by a hot subduction zone, similar to the present-day Cascadia. Contact metamorphic mineral assemblages around an Early Eocene quartz diorite stock, on the other hand, suggest that the present-day erosion level was at depths of ∼14 km during the Early Eocene, indicative of reburial of the metamorphic rocks. Partial disturbance of white-mica Ar–Ar age spectra was probably caused by the reburial coupled with heat input by igneous activity, which is probably related to thrusting due to the continental collision between Eastern Pontides and the Menderes–Taurus Block.

A new occurrence of Mn-rich rocks was discovered within the high-pressure/low-temperature metamorphic rocks on the Palos peninsula of Syros (Greece). Near the summit of Mount Prionas, a meta-conglomerate consists of calcite (~63 wt%), pink manganian phengite, blue–purple manganian aegirine–jadeite, microcline, albite and quartz. In addition, it contains abundant braunite-rich aggregates (up to ~1.5 cm in diameter) that include hollandite [(Ba0.98–1.02K

Li, Be, B and δ7Li SIMS analyses of plagioclase phenocrysts from the 1040–1941 Niki dacite lava (Nea Kameni, Santorini, Greece) exhibit varied processes. From their anorthite contents alone, the crystals may be segregated into four main types: type-N shows the normal decline in An during crystallisation (An62–40); type-O has only oscillatory zoning accompanied by resorption surfaces (An58–39); type-C is complex with high-An cores (subtype C1: An64–58, subtype C2: An88–73) and normal rims (An55–42). Type-A plagioclase with high An content (An92–82) is found within mafic enclaves. On the basis of their Li concentrations, type-O crystals may be subdivided into subtype O1 with flat Li concentration profiles and subtype O2 with decreasing Li concentration from core to rim. The concentrations of Be and B of all four types show a negative correlation with anorthite content (An), but Li concentration profiles differ amongst the different plagioclase types. Types N and O1, and the cores of type-C, are equilibrated in Li concentration. Types O2 and A, and the mantles of type-C display an initial enrichment in Li, probably from volatile influx into the melt. Consistent with the propensity towards equilibrium with the melt, these crystals display dramatic rim-ward declines in Li concentration. All analysed plagioclase crystals, except for the xenocrystic type-A, have nearly the same Li, Be and B concentrations at their rims. These coincide with the composition of plagioclase microlites in the groundmass, thereby affording estimates of plagioclase-melt partitioning for the light elements: K Li = 0.19–0.28, K Be = 0.24–0.38 and K B = 0.007–0.009. δ7Li profiles in type-O2 and type-A phenocrysts manifest an unmistakable inverse relation to Li concentration, with variations of up to ~39 ‰, revealing preferential kinetic diffusion. This may have been driven by Li loss from the melt, most likely through degassing during decompression, perhaps in the course of magma ascent to subsequent eruption. Considering the rapid diffusion of Li in plagioclase, in situ phenocryst analyses may yield useful information about processes leading up to, or even causing, eruptions.

We present the first comprehensive noble gas study on eclogites. The four eclogite samples were recovered during the Chinese Continental Scientific Drilling and are from two distinct profile depth sections differing in their degree of interaction with meteoric water, based on their δ 18O-values (surface related and of mantle-type). Hence, noble gas analyses offer the potential to further discriminate between shallow (meteoric) and deep (mantle) fluid sources. Noble gas compositions reveal typical crustal fluid compositions, characterized by a variable mixture of atmospheric gases with significant contributions of nucleogenic neon, radiogenic 4He*, radiogenic 40Ar*, fissiogenic 131–136Xe, and presumably bariogenic 131Xe, but no significant addition of mantle gases. This signature can be also considered to represent one endmember component of eclogitic diamonds. Concentrations of non-radiogenic noble gases are rather low, with depletion of light relative to the heavier noble gases. Eclogites from lower depth which experienced a higher degree of interaction with meteoric water also showed higher contributions of atmospheric gas compared with eclogites recovered from greater depth. This is interpreted to result from interaction with high-salinity fluids during ultrahigh pressure (UHP). It demonstrates that the atmospheric noble gas abundance is a proxy for interaction with surface related fluids. 40Ar/39Ar (inverse) isochron ages of two phengite separates (241.2 ± 0.4 Ma and 275.0 ± 1.8 Ma, 1σ-errors) predate the main phase of UHP metamorphism (ca. 220 Ma). Biotite yields an integrated age of about 1100 Ma. These age values are interpreted to reflect the likely addition of excess 40Ar without any chronological meaning.

article i nfo Concentrations of boron in whole rocks and minerals of the peralkaline, 1.16 Ga Ilimaussaq intrusion and its granitic country rocks (South Greenland) were analysed using secondary ion mass spectrometry (SIMS) and prompt gamma neutron activation (PGNAA) analysis. The intrusion consists of an early augite-syenite shell, a later alkali-granite sheet and still later nepheline syenites, which dominate the Complex. Boron concentrations are high (250-280 μg/g) in all rocks containing fresh sodalite, whereas boron is constantly low in the sodalite-free augite syenites (4-6 μg/g) and in the alkali granites (7-22 μg/g). Rocks with sodalite altered to analcime contain only low amounts of boron (2-7 μg/g), which records boron extraction by late- magmatic fluids. Concentration profiles of B in the analysed minerals (olivine, amphibole, clinopyroxene, aenigmatite, eudialyte, biotite, feldspar, nepheline and sodalite) record magmatic fractionation to various extents, late- magmatic to hydrothermal fluid/rock interaction, and sub-solidus diffusion. Whole-rock concentration data cannot be directly translated into the geochemical evolution of the peralkaline melts, since they are largely affected by cumulate fractionation of sodalite and amphibole and furthermore by late-stage hydrothermal alteration processes resulting in B loss. However, trace-element concentrations of mineral zones representing equilibrium fractionation from magmatic liquids can be used in combination with mineral-melt partition coefficients to unravel the enrichment processes of elements in the melt. Boron isotope values of minerals from the intrusion and the country rocks resemble the trend observed for Li isotopes in an earlier study. Amphibole and feldspar display a clear trend from light boron in the inner nepheline syenitic part of the intrusion (δ 11 B=−20‰ and −17‰ for amphibole and feldspar, respectively)

To investigate the geochemical behaviour of argon isotopes during mantle metasomatism and to obtain chronological information on the age of metasomatic events under the Arabian Shield, we analyzed mantle xenoliths and hornblende megacrysts from Saudi Arabian volcanic fields (Uwayrid, Al Birk) applying the 40Ar-39Ar dating technique. Two hornblende megacrysts yield plateau ages indicating formation or total resetting of the K/Ar system 1-2 Myr ago. The ultramafic xenoliths trapped mantle-derived and atmospheric argon in different proportions, resulting in variable isotopic compositions: 40Ar/36Ar ratios range from 296 (i.e. atmospheric) to 10 500, reflecting interactions with isotopically and genetically different fluids and/or melts during recent mantle metasomatism. One such episode of metasomatism led to the formation of Ba-rich phlogopite, which yielded a saddle-shaped age spectrum with a maximum age estimate of 18 Ma. Another episode, inducing formation of secondary pargasite in the lithospheric mantle, was dated to 4 Ma. In the mantle xenoliths the concentration of mantle argon is clearly related to the intensity of metasomatism. Argon extraction by high-resolution stepwise heating allowed us to deconvolve various argon components distributed heterogeneously within single xenoliths and ascribe them to specific carrier phases. Pyroxenes generally preserve much higher 40Ar/36Ar ratios than olivine, as they contain up to 100 times higher concentrations of mantle argon, which also correlates with a higher fluid inclusion content in pyroxenes. Hydrous phases (phlogopite/amphibole) have more variable 40Ar/36Ar ratios. K and Cl concentrations and the argon isotope compositions of the Uwayrid xenoliths indicate distinct metasomatic agents, causing elemental and isotopic disequilibrium on a local scale. On the basis of correlations between Ar isotope composition and K and Cl concentration in the samples most strongly affected by the late metasomatic fluids, we suggest that metasomatic processes in the local mantle occurring simultaneously with the opening of the Red Sea were accompanied by the introduction of saline-water saturated fluids into deep lithospheric zones.

Shock veins up to 1.1 mm thick were found within non-porous lithic clasts from suevite breccia of the Nordlinger Ries impact structure. These veins were studied by optical microscopy in transmitted and reflected light and by scanning electron microscopy. In shocked amphibolites, two types of Ca-rich majorite occur within and adjacent to the veins. The first type crystallized from shock-induced melts within the veins. Si contents of these majorites suggest dynamic pressure of ~15–17 GPa, implying minimum temperatures in the range of ~2,150–2,230°C. The second type of majorite was formed adjacent to the shock veins within pargasitic hornblende. This majorite contains significant amounts of H2O (0.7–0.9 wt%). Based on the textural setting, the shrinkage cracks and the chemical compositions of both phases, a solid-state mechanism is deduced for the hornblende to majorite phase transition. Both genetic types of Ca-rich majorite are described for the first time from a terrestrial impact crater. Along with stishovite, majorite constitutes the second silicate mineral displaying sixfold coordination of Si at Ries. Using micro-Raman spectroscopy, jadeite + coesite and jadeite + grossular were identified within local melt glasses of alkali feldspar and plagioclase composition, respectively. Stishovite aggregates, produced by solid-state reaction, along with shock-induced high-pressure melt glasses of almandine composition were also detected in shock veins of a garnet-cordierite-sillimanite restite. The quenched, homogeneous almandine glasses point to melting temperatures of more than ~2,500°C for the veins. Our findings demonstrate that terrestrial shock veins can give valuable information on shock-induced mineral transformations and transient high pressures of host rocks during a natural impact event.

The Gumushane pluton, a high-K calc-alkaline I-type granodionte/granite complex, forms an important component of the pre-Liassic basement of the Eastern Pontides (NE Turkey) In its eastern part, the pluton shows a compositional zonation ranging from biotite-hornblende granodiorite in the NW through biotite-hornblende granite to leucogranite/granophyre in the SE Numerous mafic microgranular enclaves (up to similar to 40 cm in diameter) suggest the former presence of globules of mafic melt during crystallization Emplacement of the pluton occurred during the latest Early Carboniferous, as shown by the 320 +/- 4 Ma Ar-40-Ar-39 bionte/homblende and 324 +/- 6 Ma LA-ICP-MS U-Pb zircon ages. In Harker diagrams, samples of the different rock types exhibit well-defined data trends. With increasing SiO2, the abundances of TiO2, Al2O3, Fe2O3tot, MnO, MgO, CaO, P2O5 and Sc decrease, but those of K2O and Rb increase However, the variations of Sr, Ba, (La/Yb)(cn) Sr/Y and Sigma REEs vs SiO2 form distinctive groupings, which cannot be explained by a simple fractional crystallization Chondrite-normalized (cn) REE patterns of granodionte/granite samples show concave-upward shapes with (La/Yb)(cn) ranging from 5.2 to 124 and Eu/Eu* from 084 to 0.47, while there is almost no fractionation of the middle REE relative to the heavy REE In primitive mantle-normalized element concentration diagrams, all rocks display marked negative anomalies in Ba, Nb/Ta, Sr, P and Ti. but positive anomalies in K and Pb. These geochemical features imply a fractionating mineral assemblage of clinopyroxene, amphibole and plagioclase without significant involvement of garnet. The granophyres are, on the other hand, characterized by higher K2O/Na2O and Rb/Sr ratios, lower (La/Yb)(cn), ratios (1 3 to 4 8) and more pronounced negative anomalies in Ba, Nb/Ta, Sr, Eu, P and Ti Initial epsilon(Nd) values range from -3 78 to -5.30 and Nd model ages from 1 38 to 163 Ga The magmas of the granite/granodiorite portion were probably generated by partial melting of high-potassic amphibolitic rocks, and those of the granophyres by a relatively felsic micaceous crustal source. The Gumushane pluton was emplaced at the wake of the lowpressure-high-temperature metamorphism, and is regarded as a late phase of Hercynian orogeny in the Eastern Pontides (C) 2010 Elsevier B.V All rights reserved

An eclogite barometer has profound importance in the study of upper mantle processes and potential application to diamond prospecting. Studies on the partitioning of Li between clinopyroxene (cpx) and garnet (grt) in natural samples have shown that this particular element is very sensitive to changes in pressure and could be calibrated as the barometer demanded for bimineralic eclogites. Experiments were performed from 4 to 13 GPa and 1,100–1,400°C in the CMAS (CaO, MgO, Al2O3, SiO2) system with Li added as Li3PO4 to quantify this pressure dependence into a barometer expressed in the following equation: P = (0.00255T – ln K d)/0.2351 where P is in GPa, T is in °C and K d is defined as the partition coefficient of Li (in ppm) between clinopyroxene and garnet. The experimental pressures are reproduced to ±0.38 GPa (1σ) by this equation. This barometer is strictly applicable only to CMAS. Experiments at 1,300°C, 8–12 GPa showed that Henry’s Law is fulfilled for Li partitioning between cpx and grt in the concentration range of approximately 0.01–1 wt% Li. Direct application of the equation to experiments in natural systems performed at 1,300°C from 4 to 13 GPa consistently overestimates pressures by approximately 2 GPa.

Concentrations of Li, Be and B and the isotopic composition of lithium have been measured in minerals from a suite of dry and metasomatised spinel peridotite and pyroxenite xenoliths from Harrat Uwayrid, a Pliocene–Quaternary volcanic field in the NW part of the Arabian peninsula, developed during formation of the Red Sea. In most peridotites, Li concentrations in pyroxene and olivine grains show significant systematic zoning, with a core-to-rim decrease in pyroxene but a minor increase in olivine. δ 7 Li tends to show a rim-ward increase in clinopyroxene, while it is constant or decreases slightly in olivine. These variations indicate a diffusive transfer of Li from clinopyroxene to olivine during cooling, implying that the partition coefficients K Li Ol/Cpx and K Li Ol/Opx are temperature-dependent and increase with falling temperature. K Li Cpx/Opx , stays nearly constant at ∼ 1. δ 7 Li values measured in virtually unmodified cores of olivine, orthopyroxene and clinopyroxene from three peridotites are similar within individual xenoliths but vary among the xenoliths, with individual values ranging from + 1.1 to + 9.7‰. In marked contrast to Li, the concentrations of Be and B are nearly constant in mineral grains, and apparent inter-mineral partition coefficients for these elements are independent of concentrations and xenolith equilibration temperature. Concentrations of Li, Be and B in minerals of un-metasomatized peridotites are relatively low and are similar to values reported previously. Relative abundances of the three light elements in minerals of xenoliths affected by metasomatism have been used to constrain the nature of metasomatic agents. A preferential enrichment of both Li and B relative to Be that is observed in some xenoliths suggests metasomatism by a hydrous fluid, well below the critical point of the solvus between hydrous fluid and silicate melt. A uniform enrichment of all three light elements shown by other xenoliths points to either a silicate melt at subcritical conditions or a supercritical liquid as metasomatic agent.

A blueschist facies tectonic sliver, 9 km long and 1 km wide, crops out within the Miocene clastic rocks bounded by the strands of the North Anatolian Fault zone in southern Thrace, NW Turkey. Two types of blueschist facies rock assemblages occur in the sliver: (i) A serpentinite body with numerous dykes of incipient blueschist facies metadiabase (ii) a well-foliated and thoroughly recrystallized rock assemblage consisting of blueschist, marble and metachert. Both are partially enveloped by an Upper Eocene wildflysch, which includes olistoliths of serpentinite-metadiabase, Upper Cretaceous and Palaeogene pelagic limestone, Upper Eocene reefal limestone, radiolarian chert, quartzite and minor greenschist. Field relations in combination with the bore core data suggest that the tectonic sliver forms a positive flower structure within the Miocene clastic rocks in a transpressional strike-slip setting, and represents an uplifted part of the pre-Eocene basement. The blueschists are represented by lawsonite-glaucophane-bearing assemblages equilibrated at 270-310 degrees C and similar to 0.8 GPa. The metadiabase dykes in the serpentinite, on the other hand, are represented by pumpellyite-glaucophane-lawsonite-assemblages that most probably equilibrated below 290 degrees C and at 0.75 GPa. One metadiabase olistolith in the Upper Eocene flysch sequence contains the mineral assemblage epidote + pumpellyite + glaucophane, recording P-T conditions of 290-350 degrees C and 0.65-0.78 GPa, indicative of slightly lower depths and different thermal setting. Timing of the blueschist facies metamorphism is constrained to c. 86 Ma (Coniacian/Santonian) by Rb-Sr phengite-whole rock and incremental Ar-40-Ar-39 phengite dating on blueschists. The activity of the strike-slip fault post-dates the blueschist facies metamorphism and exhumation, and is only responsible for the present outcrop pattern and post-Miocene exhumation (similar to 2 km). The high-P/T metamorphic rocks of southern Thrace and the Biga Peninsula are located to the southeast of the Circum Rhodope Belt and indicate Late Cretaceous subduction and accretion under the northern continent, i.e. the Rhodope Massif, enveloped by the Circum Rhodope Belt. The Late Cretaceous is therefore a time of continued accretionary growth of this continental domain.

High-pressure metamorphic (HPM) rocks (derived from igneous protoliths) and their metasomatised rinds from the island of Syros (Greece) were analysed for their B and Cl whole-rock abundances and their H2O content by prompt-gamma neutron-activation analysis (PGNAA) and for their Li and Be whole-rock abundances by ICP-OES. In the HPM rocks, B /Be and Cl /Be ratios correlate with H2O contents and appear to be controlled by extraction of B and Cl during dehydration and prograde metamorphism. In contrast, samples of the metasomatised rinds show no such correlation. B /Be ratios in the rinds are solely governed by the presence or absence of tourmaline, and Cl /Be ratios vary significantly, possibly related to fluid inclusions. Li/Be ratios do not correlate with H2O contents in the HPM rocks, which may in part be explained by a conservative behaviour of Li during dehydration. However, Li abundances exceed the vast majority of published values for Li abundances in fresh, altered, or differentiated oceanic igneous rocks and presumably result from metasomatic enrichment of Li. High Li concentrations and highly elevated Li/Be ratios in most metasomatised samples demonstrate an enrichment of Li in the Syros HP melange during fluid infiltration. This study suggests that B and Cl abundances of HPM meta-igneous rocks can be used to trace prograde dehydration, while Li concentrations seem to be more sensitive for retrograde metasomatic processes in such lithologies.

Two large pegmatitic crystals of sodic pyroxene (aegirine) and sodic amphibole (arfvedsonite) from the agpaitic igneous Ilimaussaq Complex, south Greenland were found to be suitable as reference materials for in situ Li isotope determinations. Lithium concentrations determined by SIMS and micro-drilled material analysed by MC-ICP-MS generally agreed within analytical uncertainty. The arfvedsonite crystal was homogeneous with [Li] = 639 ± 51 μg g−1 (2s, n = 69, MC-ICP-MS and SIMS results). The aegirine crystal shows strongly developed sector zoning, which is a common feature of aegirines. Using qualitative element mapping techniques (EPMA), the homogeneous core of the crystal was easily distinguished from the outermost sectors of the crystals. The core had a mean [Li] of 47.6 ± 3.6 μg g−1 (2s, n = 33) as determined by SIMS. The seven micro-drilled regions measured by solution MC-ICP-MS returned slightly lower concentrations (41–46 μg g−1), but still overlap with the SIMS data within uncertainty. Based on MC-ICP-MS and SIMS analyses, the variation in δ7Li was about 1‰ in each of the two crystals, which is smaller than that in widely used glass reference materials, making these two samples suitable to serve as reference materials. There was, however, a significant offset between the results of MC-ICP-MS and SIMS. The latter deviated from the MC-ICP-MS results by −6.0 ± 1.9‰ (2s) for the amphibole and by −3.9 ± 1.9‰ (2s) for the aegirine. This indicates the presence of a significant matrix effect in SIMS determinations of Li isotopes for amphibole and pyroxene relative to the basalt glasses used for calibration. Based on the MC-ICP-MS results, mean δ7Li values of +0.7 ± 1.2‰ (2s, n = 10) for the arfvedsonite crystal and of −3.7 ± 1.2‰ (2s, n = 7) for the core of the aegirine crystal were calculated. Adopting these values, SIMS users can correct for the specific IMF (instrumental mass fractionation) of the ion probe used. We propose that these two crystals serve as reference materials for in situ Li isotope determinations by SIMS and pieces of these two crystals are available from the first author upon request. Deux grands cristaux pegmatitiques, un pyroxene sodique (aegerine) et une amphibole sodique (arfvedsonite) provenant du complexe agpaitique Ilimaussaq (sud du Groenland) ont ete selectionnes pour etre des materiaux de reference lors d'analyses in situ des isotopes de Li. Les concentrations en lithium ont ete determinees par SIMS et par MC-ICP-MS sur du materiel preleve par micro-forage. Les deux determinations sont en accord aux erreurs analytiques pres. Le cristal de arfvedsonite est homogene avec [Li] = 639 ± 51 μg g−1 (2s, n = 69, donnees MC-ICP-MS et SIMS). Le cristal d'aegerine presente des zonations tres franches, comme il est classique dans les aegerines. En utilisant les techniques de cartographie chimique qualitative des elements (EMPA) il a ete possible de clairement distinguer le cœur du cristal, homogene, de ses bordures zonees. Le cœur a un [Li] moyen de 47.6 ± 3.6 μg g−1 (2s, n = 33) d'apres l'analyse par SIMS. Les sept regions micro forees et analysees par MC-ICP-MS en solution presentent des concentrations legerement inferieures (41–46 μg g−1) mais qui neanmoins sont dans la meme gamme, aux erreurs analytiques pres, que celles determinees par SIMS. Les donnees obtenues par MC-ICP-MS et SIMS montrent que la variation de δ7Li dans chaque cristal est de 1‰, ce qui est bien inferieur a celle mesuree dans les verres de reference generalement utilises. Ces deux echantillons sont donc tres adaptes a une utilisation comme materiaux de reference. Il y a neanmoins un decalage significatif entre les donnees de MC-ICP-MS et les donnees obtenues par SIMS, ces dernieres different des premieres de −6.0 ± 1.9‰ (2s) pour l'amphibole et de −3.9 ± 1.9‰ (2s) pour l'aegerine. Ceci demontre l'existence d'un effet de matrice non negligeable lors de l'analyse par SIMS des isotopes de Li dans des amphiboles et des pyroxenes, par rapport au verre basaltique utilise pour la calibration. Les valeurs moyennes de δ7Li de +0.7 ± 1.2‰ (2s, n = 10) pour le cristal d'arfvedsonite et de −3.7 ± 1.2‰ (2s, n = 7) pour le cœur du cristal d'aegerine ont ete calculees a partir des donnees obtenues par MC-ICP-MS. Les utilisateurs de SIMS peuvent utiliser ces valeurs pour corriger leurs resultats du fractionnement de masse instrumental (IMF) specifique a la sonde ionique utilisee. Nous proposons d'utiliser ces deux cristaux comme materiaux de reference lors de determinations in situ des isotopes de Li par SIMS et des fragments de ces deux cristaux peuvent etre demandes au premier auteur.

In the southern zone of the Eastern Pontides, an isolated small (~ 1.5 km 2 ) outcrop of plagioleucitites occurs in the Asutka thrust sheet. Field relations constrain the timing of volcanism between Maastrichtian and late Paleocene. The plagioleucitites consist of clinopyroxene, analcime (former leucite), Ti-magnetite, plagioclase, sanidine, apatite and accessory biotite. The rocks are represented by three geochemical and petrographic varieties: Types I and II are mostly blocks within epiclastic debris and type III are lava flows. All the rocks are considerably altered, whereby leucite is almost totally analcimized, apart from leucite inclusions within clinopyroxene that are remote from cracks. Furthermore, calcite and chlorite/smectite have been formed. Chemical effects of alteration are primarily reflected in an unsystematic variation of whole-rock K 2 O/Na 2 O ratios (0.12 to 1.71) and of the abundances of large-ion lithophile elements, such as Cs and K, and perhaps also Rb. Both the high modal abundance of (former) leucite and the composition of clinopyroxene indicate an ultrapotassic nature of the primary rocks. In primitive mantle-normalized element concentration diagrams, all samples are characterized by negative anomalies of Nb–Ta, Zr–Hf and Ti and a positive anomaly in Pb, testifying the orogenic nature of the volcanics. The rocks cover restricted ranges in all initial isotope ratios with 87 Sr/ 86 Sr(i) (60 Ma) ranging from 0.70537 to 0.70568, 143 Nd/ 144 Nd(i) from 0.512529 to 0.512585, 206 Pb/ 204 Pb(i) from 18.65 to 18.83, 207 Pb/ 204 Pb(i) from 15.65 to 15.66 and 208 Pb/ 204 Pb from 38.64 to 38.88. There is no obvious relationship between the degree of analcimization and the isotopic composition. In Pb–Pb variation diagrams, the rocks plot above the Northern Hemisphere Reference Line (NHRL). Chondrite-normalized rare earth element (REE) patterns show no significant Eu anomaly, but a strong enrichment of the LREE over the HREE with (La/Yb) cn = 11.6–14.2, whereby normalized concentrations of Er to Lu are nearly similar. The Everek Hanlari plagioleucitites represent the youngest products of Cretaceous to Paleocene arc magmatism of the Eastern Pontides, thus documenting the last stages of the Neotethyan subduction.

The island of Kos at the eastern end of the South Aegean Volcanic Arc hosts numerous late Neogene amphibole- and mica-bearing lamprophyres. The Sr and Nd isotope compositions of these mantle-derived magmatic rocks correlate negatively, extending from the undepleted end of the mantle array towards values typical for continental crust. The crust-like signature is linked to the addition of subducted Mediterranean sediments, which dominate the Pb isotopic composition of all lamprophyres. The mantle endmember of the Sr–Nd isotope mixing array is strongly enriched in incompatible trace elements and shows anorogenic affinities. Whole-rock geochemistry indicates that the lamprophyres originate from depleted lithospheric mantle above the Hellenic subduction zone that was modified by (1) K-rich silicic partial melts or supercritical fluids from subducted metasediments and (2) melts that originate from the asthenosphere below the subducting slab. The first metasomatic component formed phlogopite–orthopyroxene-rich veins, whereas the second component formed amphibole-bearing clinopyroxenites. Subsequent melting preferentially affected these enriched domains. Variable dilution by contributions from ambient peridotite and mixing between the two components caused the large chemical variation observed in the lamprophyres. The asthenosphere-derived component represents an incipient melt with a carbonatite-like trace element signature (e.g. superchondritic Nb/Ta and Zr/Hf; low Ti/Eu). This metasomatic agent probably was introduced into the mantle wedge along ruptures in the slab of the retreating Hellenic subduction zone. Lamprophyres dominated by the sediment signature have isotopic and chemical similarities to basaltic rocks erupted along the South Aegean Volcanic Arc. The much stronger enrichment in incompatible trace elements of the lamprophyres is related to only minor dilution by melts from the ambient mantle. Partial melting in the lithospheric mantle is attributed to extensional tectonics, probably during a stage of rapid slab rollback, with a limited availability of fluid as a fluxing agent. Lamprophyre emplacement occurred along sinistral en echelon structures in a crustal-scale shear zone, which separates Anatolia from the faster extending Aegean back-arc basin.

The boron isotopic composition of zoned tourmaline in two metasediments from the island of Syros, determined by secondary-ion mass spectrometry (SIMS), reflects the sedimentary and metamorphic record of the rocks. Tourmaline from a silicate-bearing marble contains small (≤20 μm) detrital cores with highly variable δ11B values (−10.7 to +3.6‰), pointing to a heterogeneous protolith derived from multiple sources. The sedimentary B isotopic record survived the entire metamorphic cycle with peak temperatures of ∼500°C. Prograde to peak metamorphic rims are homogeneous and similar among all analysed grains (δ11B ≈ +0.9‰). The varying δ11B values of detrital cores in the siliceous marble demonstrate that in situ B isotope analysis of tourmaline by SIMS is a potentially powerful tool for provenance studies not only in sediments but also in metasediments. A meta-tuffitic blueschist bears abundant tourmaline with dravitic cores of detrital or authigenic origin (δ11B ≈ −3.3‰), and prograde to peak metamorphic overgrowth zones (−1.6‰). Fe-rich rims, formed during influx of B-bearing fluids under retrograde conditions, show strongly increasing δ11B values (up to +7.7‰) towards the margins of the grains. The δ11B values of metamorphic tourmaline from Syros, formed in mixed terrigenous–marine sediments, reflect the B signal blended from these two different sources, and was probably not altered by dehydration during subduction.

Harrat Uwayrid is one of several volcanic fields that developed along the western margin of the Arabian plate during opening of the Red Sea rift. Volcanic activity started in the late Miocene and Pliocene with the eruption of alkaline flood basalts. After a period of extensional faulting, numerous cinder cones formed in the central part of the volcanic field during the Quaternary. Xenoliths of both mantle and crustal origin are abundant. The mantle-derived suite is dominated by spinel lherzolite with XMg of olivine and XCr of spinel ranging from 0.868 to 0.911 and from 0.074 to 0.636, respectively. In addition to lherzolite, various types of pyroxenites and wehrlites occur. Most xenoliths contain primary and/or secondary amphibole (pargasite/kaersutite), indicating at least two enrichment events, both related to the formation of the Red Sea. Chemical zonation profiles of mineral grains constrain the thermal evolution of the xenoliths and their source regions in the shallow upper mantle. Ca contents in olivine are constant in the inner parts of the grains, but increase in the outermost zones (< 35 μm). XMg values of spinel grains adjacent to olivine often show a rimward increase in their outer zones (< 150 μm). Both types of zonation patterns are interpreted to result from heating by the host magma during transport. Zonation patterns of Al and Ca/(1 - Na) in pyroxene grains record different thermal evolutions, such as (i) simple cooling, whereby a ’near-equilibrium’ state was rarely achieved, (ii) cooling followed by heating, and (iii) simple heating. Diffusion modelling on measured zoning profiles suggests that cooling lasted for no more than ∼ 10 Myr. Temperature estimates for pyroxene core and rim compositions, calculated by using various pyroxene geothermometers range from ∼ 800 to 1140 °C (at an assumed pressure of 1.5 GPa). In conjunction with upper pressure limits derived from the composition of spinel, these values imply relatively high temperatures for the shallow upper mantle. This is corroborated by P-T estimates for spinel lherzolites obtained by combination of the two-pyroxene thermometer based on the solvus between enstatite and diopside and the Ca-in-olivine geothermobarometer. While the high-T state that preceded cooling was probably a regional phenomenon, renewed heating was of local nature, most probably related to advective heat transport by ascending and stagnating magmas.

The microtextures of stishovite and coesite in shocked non-porous lithic clasts from suevite of the Ries impact structure were studied in transmitted light and under the scanning electron microscope. Both high-pressure silica phases were identified in situ by laser-Raman spectroscopy. They formed from silica melt as well as by solid-state transformation. In weakly shocked rocks (stage I), fine-grained stishovite (≤1.8 μm) occurs in thin pseudotachylite veins of quartz-rich rocks, where it obviously nucleated from high-pressure frictional melts. Generally no stishovite was found in planar deformation features (PDFs) within grains of rock-forming quartz. The single exception is a highly shocked quartz grain, trapped between a pseudotachylite vein and a large ilmenite grain, in which stishovite occurs within two sets of lamellae. It is assumed that in this case the small stishovite grains formed by the interplay of conductive heating and shock reverberation. In strongly shocked rocks (stages Ib–III, above ∼30 GPa), grains of former quartz typically contain abundant and variably sized stishovite (

We performed a noble gas isotope study on mantle xenoliths from the Quaternary volcanic field of Chyulu Hills, S Kenya, c. 100 km east of the Kenya rift graben. 4He/3He ratios were in the range of 100 000–120 000 and indistinguishable from other subcontinental lithospheric mantle compositions worldwide and similar to most results of the East African rift system. 21Ne/22Ne ratios corrected for atmospheric contributions displayed less nucleogenic values compared to mid ocean ridge basalts. This requires addition of Ne from a more primitive mantle source, that could be assigned to the postulated Kenyan mantle ‘plume’ or alternatively might be attributed to the ‘high 3He/4He’ Afar hotspot c. 2000 km distant. Whereas He and Ne isotopes reflect a rather homogeneous source composition, we observe a variable air corrected Ar isotopic composition. This might mirror additional contributions of atmospheric fluids strongly enriched in Ar. Nevertheless, in the least contaminated xenolith we were able to calculate a maximum 40Ar/36Ar ratio of 34,800 ± 500 assuming a mantle 20Ne/22Ne = 12.5. This is regarded as best approximation of the real 40Ar/36Ar ratio of the investigated mantle source. The same sample showed the highest observed 129Xe/130Xe and 136Xe/130Xe ratios of 7.01 ± 0.12 and 2.37 ± 0.05, respectively. The correlation of 129Xe/130Xe–136Xe/130Xe ratios is in broad agreement with mantle Xe in OIB and MORB sources. Within uncertainties a minor contribution of crustally derived xenon is possible, though not compelling.

We performed argon measurements on rocks of the subcontinental lithospheric mantle (SCLM) from the Red Sea region applying stepwise crushing extractions, and argon analyses using high-resolution stepwise heating techniques, the latter combined with 40 Ar/ 39 Ar dating. Maximum 40 Ar/ 36 Ar ratios of individual samples range from 4190 ± 240 to 25,590 ± 620, the latter (sample SA 87-2/12) being the highest measured value of any mantle peridotite or pyroxenite sample so far. For five samples, reasonably defined binary mixing correlations between atmospheric and mantle-derived argon and neon resulted in calculated sample-specific mantle- 40 Ar/ 36 Ar ratios of 5040 ± 50, 7500 ± 70, 9510 ± 220, 29,600 ± 2700, and 39,000 ± 2500 at an assumed mantle- 20 Ne/ 22 Ne value of 12.5. These observations indicate a highly heterogeneous argon isotopic composition of the trapped mantle fluids. Furthermore, most samples exhibit mantle- 36 Ar/ 22 Ne ratios higher than considered to represent an unfractionated mantle source. These characteristics could be explained by mixing of plume-related (low 40 Ar/ 36 Ar) and lithospheric (high 40 Ar/ 36 Ar) melts or fluids following elemental fractionation between Ar and Ne. Alternatively, we propose the presence of a severely fractionated atmospheric component highly enriched in argon, admixed to the mantle fluids before trapped by the ultramafic rocks. This primary, seriously fractionated atmospheric component cannot be monitored by Ne isotopes. Incorporation of such a primary atmospheric component could occur either during magma ascent at relatively shallow, upper crustal levels, or by mobilization of atmospheric fluids in a subduction-related metasomatized lithospheric mantle during Pan African times (c. 600–800 Ma ago).

A model for the release of Li, Be and B from progressively dehydrating altered oceanic crust during subduction is presented. Combining clinopyroxene/fluid partition coefficients determined experimentally in an earlier study Brenan et al. [Brenan, J.M., Ryerson, F.J., Shaw, H.F., 1998. The role of aqueous fluids in the slab-to-mantle transfer of boron, beryllium, and lithium during subduction: Experiments and models. Geochim. Cosmochim. Acta 62, 3337–3347] with apparent mineral/clinopyroxene partition coefficients as observed in natural high-pressure metamorphic rocks Marschall et al. [Marschall, H.R., Altherr, R., Ludwig, T., Kalt, A., Gmeling, K., Kasztovszky, Zs., 2006a. Partitioning and budget of Li, Be and B in high-pressure metamorphic rocks. Geochim. Cosmochim. Acta 70, 4750–4769] results in a set of mineral/fluid partition coefficients for high-pressure metamorphic minerals. Mineral modes of altered oceanic crust as a function of pressure and temperature along a given subduction path can be derived from thermodynamic calculations using the program PerpleX. Combination of these modes with mineral/fluid partition coefficients results in whole rock/fluid partition coefficients at any stage of the P–T path including information on the amount of fluid released at any depth. Based on these data, the concentrations of Li, Be and B in subducting rocks and released fluids along a given P–T path can be modelled. The derived information on B concentrations in rocks and fluids are combined with the temperature-dependent fractionation of B isotopes in order to model the B isotopic evolution of subducting rocks and released fluids. Model calculations are performed for two slightly different chemical compositions (hydrous MORB without K and with 0.5 wt.% K2O), in order to demonstrate the impact of phengite on the boron budget. Provided the necessary input data are available, the concept of such a model could be employed to quantify the trace element release from the slab from any lithology along any reasonable P–T path.

The Kurtoglu metamorphic complex, that forms part of the pre-Liassic basement of the Sakarya zone in northern Turkey, consists of at least two tectonic units. Blueschist-facies rocks of unknown metamorphic age in the southern part of the complex are tectonically overlain by Variscan low-pressure high-temperature metamorphic rocks. The latter comprise mica schists and fine-grained gneisses, cut by metaleucogranitic dikes, as well as migmatitic biotite gneisses and subordinate amphibolite intercalations. Structural data indicate that metamorphism and penetrative deformation occurred after dyke intrusion. Peak metamorphic conditions of the mica schists, fine-grained gneisses and metaleucogranites are estimated to ∼650°C and ∼0.4 GPa, based on phase relationships in the system NCKFMASH, Fe–Mg partitioning between garnet and biotite as well as garnet-aluminosilicate-quartz-plagioclase (GASP) and garnet-plagioclase-biotite-quartz (GBPQ) barometry. Peak temperatures of the migmatitic biotite gneisses and amphibolite intercalations are not well constrained but might have been significantly higher (690–740°C), as suggested from hornblende-plagioclase thermometry. 40Ar–39Ar incremental dating on muscovite and biotite fractions from the mica schists and fine-grained gneisses yielded plateau ages of ∼323 Ma. Significantly older model ages of ∼329 and ∼337 Ma were obtained on muscovite fractions from two metaleucogranite samples. These fractions contain both relict igneous and newly formed metamorphic muscovite.

Pelagic micritic limestones within an upper Cretaceous accretionary complex in the Tavsanli Zone, NW Turkey, preserve textures indicating incomplete prograde transformation of micritic calcite to aragonite, representing the only known example of this type. Aragonitization starts at the central parts of the micritic limestone beds and advances towards the lower and upper parts of the layers at the expense of micrite. Micrite is very fine grained (

Plio-Pleistocene volcanism in the Golan and Galilee (northeastern Israel) shows systematic variability with time and location: alkali basalts were erupted in the south during the Early Pliocene, whereas enriched basanitic lavas erupted in the north during the Late Pliocene (Galilee) and Pleistocene (Golan). The basalts show positive correlations in plots of ratios of highly to moderately incompatible elements versus the concentration of the highly incompatible element (e.g. Nb/Zr vs Nb, La/Sm vs La) and in diagrams of REE/HFSE (rare earth elements/high field strength elements) vs REE concentration (e.g. La/Nb vs La). Some of these correlations are not linear but upward convex. 87 Sr/ 86 Sr ratios vary between 0� 7031 and 0� 7034 and correlate negatively with incompatible element concentrations and positively with Rb/Sr ratios. We interpret these observations as an indication that the main control on magma composition is binary mixing of melts derived from two end-member mantle source components. Based on the high Sr/Ba ratios and negative Rb anomalies in primitive mantle normalized trace element diagrams and the moderate slopes of MREE–HREE (middle REE–heavy REE) in chondrite-normalized diagrams, we suggest that the source for the alkali basaltic end-member was a garnet-bearing amphibole peridotite that had experienced partial dehydration. The very high incompatible element concentrations, low K content, very low Rb contents and steep MREE–HREE patterns in the basanites are attributed to derivation from amphibole- and garnet-bearing pyroxenite veins. It is suggested that the veins were produced via partial melting of amphibole peridotites, followed by complete solidification and dehydration that effectively removed Rb and K. The requirement for the presence of amphibole limits both sources to lithospheric depths. The spatial geochemical variability of the basalts indicates that the lithosphere beneath the region is heterogeneous, composed of vein-rich and vein-poor domains. The relatively uniform 143 Nd/ 144 Nd («Nd ¼ 4� 0–5� 2) suggests that the two mantle sources were formed by dehydration and partial melting of an originally isotopically uniform reservoir, probably as a result of a Paleozoic thermal event.

The post-collisional Saraycik granodiorite intruded into a late Paleocene to early Eocene nappe pile that formed during collision of the Pontides in the North and the Anatolide-Tauride platform in the South, leading to the formation of the Izmir-Ankara-Erzincan suture. A relatively shallow pluton intrusion depth (∼5 to 8 km) was estimated from Al-in-hornblende geobarometry and contact metamorphic assemblages. The emplacement age is tightly constrained to ∼52 Ma by two Ar–Ar plateau and total fusion ages on biotite. The main mass of the pluton consists of metaluminous to peraluminous biotite granodiorite and hornblende-biotite granodiorite. In addition, up to 10-m thick dacitic and

High-pressure metamorphic rocks showing a large range of chemical compositions were analyzed by PGNAA, XRF and solution ICP-MS for major components and a variety of trace elements. The large data set allowed a comparison of results from PGNAA to the established methods and revealed good agreement for most major elements and for Sc and Gd. For V, Cr, Co and Ni, PGNAA data are satisfactory only at high concentration levels. B, Cl and H were analyzed by PGNAA with very good precision, even at low concentrations.

Solar-type helium (He) and neon (Ne) in the Earth’s mantle were suggested to be the result of solar-wind loaded extraterrestrial dust that accumulated in deep-sea sediments and was subducted into the Earth’s mantle. To obtain additional constraints on this hypothesis, we analysed He, Ne and argon (Ar) in high pressure–low temperature metamorphic rocks representing equivalents of former pelagic clays and cherts from Andros (Cyclades, Greece) and Laytonville (California, USA). While the metasediments contain significant amounts of 4He, 21Ne and 40Ar due to U, Th and K decay, no solar-type primordial noble gases were observed. Most of these were obviously lost during metamorphism preceding 30 km subduction depth. We also analysed magnetic fines from two Pacific ODP drillcore samples, which contain solar-type He and Ne dominated by solar energetic particles (SEP). The existing noble gas isotope data of deep-sea floor magnetic fines and interplanetary dust particles demonstrate that a considerable fraction of the extraterrestrial dust reaching the Earth has lost solar wind (SW) ions implanted at low energies, leading to a preferential occurrence of deeply implanted SEP He and Ne, fractionated He/Ne ratios and measurable traces of spallogenic isotopes. This effect is most probably caused by larger particles, as these suffer more severe atmospheric entry heating and surface ablation. Only sufficiently fine-grained dust may retain the original unfractionated solar composition that is characteristic for the Earth’s mantle He and Ne. Hence, in addition to the problem of metamorphic loss of solar noble gases during subduction, the isotopic and elemental fractionation during atmospheric entry heating is a further restriction for possible subduction hypotheses.

Noble gas isotopes are widely used to elucidate the history of the rocks in which they have been trapped, either from distinct reservoirs or by accumulation following radioactive decay. To extract noble gases from their host rocks, stepwise heating is the most commonly used technique to deconvolve isotopically different components, e.g., atmospheric, in situ radiogenic, or excess radiogenic from mantle or crustal reservoirs. The accurate determination of the isotopic composition of these different components is of crucial importance, e.g., for ages obtained by 40 Ar- 39 Ar stepheating plateaus. However, diffusion theory-based model calculations predict that the stepwise thermal extraction process from mineral phases induces isotope fractionation and, hence, adulterates the original composition. Such effects are largely unconsidered, as they are small and a compelling experimental observation is lacking. We report the first unequivocal evidence for significant mass fractionation of argon isotopes during thermal extraction, observed on shungite, a carbon-rich Precambrian sedimentary rock. The degree of fractionation, as monitored by 38 Ar/ 36 Ar and 40 Ar/ 36 Ar ratios, very well agrees with theoretical predictions assuming an inverse square root dependence of diffusion coefficient and atomic mass, resulting in easier extraction of lighter isotopes. Hence, subatmospheric 40 Ar/ 36 Ar ratios obtained for argon extracted at low temperatures may not represent paleoatmospheric argon. Shungite argon resembles modern atmospheric composition, but constraints on the timing of trapping appear difficult to obtain, as shungites are multicomponent systems. In 40 Ar- 39 Ar stepwise heating, the isotope fractionation effect could cause systematic underestimations of plateau ages, between 0.15 and 0.4% depending on age, or considerably higher if samples contain appreciable atmospheric Ar. The magnitude of this effect is similar to the presently achieved uncertainties of this increasingly precise dating technique. Our results also indicate the importance of thermally activated diffusion as a possible fractionation mechanism, e.g., for hydrothermal gas exhalations, or for carbonaceous carrier phases such as “Q” in meteorites that have been suggested as carriers of highly fractionated noble gas residues from the early solar nebula.

Late Cenozoic mafic alkaline volcanism associated with lithospheric thinning is a widespread phenomenon in Europe. However, there is no consensus about its geodynamical causes, e.g., if active shallow or deep mantle-derived plume upwelling has driven this activity. Seismic tomography demonstrated 400–500 km deep plume-like structures under the Massif Central and Eifel volcanic fields, but cannot prove compellingly a lower mantle root. Here, we present high-precision helium, neon and argon isotope data on ultramafic xenoliths from mafic alkaline volcanic formations from the Pannonian basin and the Eifel region. Noble gas extraction by stepwise crushing allowed a successful separation of variably fractionated atmosphere- and mantle-derived components, and the detailed evaluation of helium–neon and neon–argon isotope mixing relationships. The mantle xenoliths trapped mantle fluids with two distinct noble gas components: one component is derived from the local lithospheric and/or a HIMU mantle source with 21 Ne/ 22 Ne mantle =0.07 and 4 He/ 3 He of about 120,000, and dominates helium and part of the neon. The second component is similar to hot spot-type noble gases, e.g., Hawaii or Reunion. It is clearly resolvable in neon isotopes and dominates the argon budget. Its isotopic structure is determined to 40 Ar/ 36 Ar=15,000±1200, 21 Ne/ 22 Ne mantle =0.042±0.005 and 4 He/ 3 He of about 36,000. Our results are consistent with previous suggestions that a deep mantle component is involved in European intraplate volcanism.

An undated high-pressure low-temperature tectonic melange in the Elekdag area (central Pontides, N Turkey) comprises blocks of MORB-derived lawsonite eclogite within a sheared serpentinite matrix. In their outer shells, some of the eclogite blocks contain large (up to 6 cm) tourmaline crystals. ‘Prograde’ inclusions in poikiloblastic garnet from a well-preserved eclogite block are lawsonite, epidote/clinozoisite, omphacite, rutile, glaucophane, chlorite, Ba-bearing phengite, minor actinolite, winchite and quartz. In addition, glaucophane, lawsonite and rutile occur as inclusions in omphacite. These inclusion assemblages document the transition from a garnet-lawsonite-epidote-bearing blueschist to a lawsonite eclogite with the peak assemblage garnet + omphacite I + lawsonite + rutile. Peak metamorphic conditions are not well-constrained but are estimated approximately 400–430°C and >1.35 GPa, based on Fe–Mg exchange between garnet and omphacite and the coexistence of lawsonite + omphacite + rutile. During exhumation of the eclogite–serpentinite melange in the hanging wall of a subduction system, infiltration of B-rich aqueous fluids into the rims of eclogite blocks caused retrogressive formation of abundant chlorite, titanite and albite, followed by growth of tourmaline at the expense of chlorite. At the same time, omphacite I (XJd=0.24–0.44) became unstable and partially replaced by omphacite II characterized by higher XJd (0.35–0.48), suggesting a relatively low silica activity in the infiltrating fluid. Apart from Fe-rich rims developed at the contact to chlorite, tourmaline crystals are nearly homogeneous. Their compositions correspond to Na-rich dravite, perhaps with a small amount of excess (tetrahedral) boron (~5.90 Si and 3.10 B cations per 31 anions). δ11 B values range from −2.2 to +1.7‰. The infiltrating fluids were most probably derived from subducting altered oceanic crust and sediments.

Summary High-grade gneisses from the Pulur complex in NE Turkey bear evidence for biotitedehydration melting at � 820 � C and 0.7–0.8 GPa, melt segregation and nearisothermal decompression to 0.4–0.5 GPa. During further exhumation, the rocks underwent secondary pervasive rehydration at temperatures between � 400 and 230 � C and fluid pressures between � 0.3 and 0.1 GPa. Metamorphic peak conditions are dated at 331–327 Ma, while hydrothermal retrogression occurred significantly later at 315– 310 Ma under static conditions. During the rehydration event, primary high-grade mineral assemblages including garnet, cordierite, sillimanite, spinel, biotite, plagioclase and ilmenite were extensively replaced by muscovite, paragonite, margarite, corundum, diaspore, chlorite, kaolinite, pumpellyite, prehnite, epidote, titanite, anatase, pyrite and chalcopyrite. Secondary mineral assemblages indicate that the infiltrating fluids were characterized by low f O2, very low XCO2 (

In the East European Alpine belt, leucite-sanidine-phlogopite-olivine-bearing volcanic rocks of Late Cenozoic age occur at eight localities within the Vardar suture zone and at one locality in the Southern Carpathian fold-and-thrust belt. Most of these volcanics are characterized by high Mg# (66.6–78.6), high abundances of Ni (117–373 ppm) and Cr (144–445 ppm) as well as high primary K2O contents (5.63–7.01 %) and K2O/Na2O values (1.93–4.91). Rocks with more differentiated compositions are rare. A lamproite affinity of these rocks is apparent from their relatively low contents of Al2O3 (9.9–14.3 wt%) and CaO (6.2–8.3 wt%) in combination with high abundances of Rb (85–967 ppm), Ba (1,027–4,189 ppm), Th (18.9–76.5 ppm), Pb (19–54 ppm), Sr (774–1,712 ppm) and F (0.16–0.52 wt%), and the general lack of plagioclase. Although eruption of the magmas took place in post-collisional extensional settings, significant depletions of Nb and Ta relative to Th and La, low TiO2 contents (0.92–2.17 %), low ratios of Rb/Cs, K/Rb and Ce/Pb as well as high ratios of Ba/La and Ba/Th suggest close genetic relationships to subduction zone processes. Whereas Sr and Nd isotope ratios show relatively large variations (87Sr/86Sr = 0.7078–0.7105, 143Nd/144Nd = 0.51242–0.51215), Pb isotope ratios display a very restricted range with 206Pb/204Pb = 18.68–18.88 and variable but generally high Δ7/4 (11–18) and Δ8/4 (65–95) values. The observed petrographic, geochemical and isotopic characteristics are best explained by a genetic model involving preferential melting of phlogopite-rich veins in an originally depleted lithospheric mantle source, whereby the metasomatic enrichment of the mantle source is tentatively related to the addition of components from subducted sediments during consumption of Tethyan oceanic lithosphere.

In the Pulur complex (Sakarya Zone, Eastern Pontides, Turkey) a low-grade tectonometamorphic unit (Dogankavak) is exposed in three tectonic windows beneath a complex medium-pressure high-temperature metamorphic unit of late Carboniferous age. The thrust plane between both units is transgressively covered by Liassic conglomerates. The Dogankavak unit comprises a sequence of metabasites with MORB-type chemical compositions and phyllites, with subordinate calcareous phyllites, marbles, quarzofeldspathic schists and metacherts. This sequence is interpreted as a former accretionary complex related to the consumption of the Palaeotethys. Mineral parageneses in the metabasites allow for the distinction of two domains with slightly different peak metamorphic conditions, i.e. 375–425 °C/0.5–0.8 GPa (greenschist facies) and 400–470 °C/0.6–1.1 GPa (albite-epidote amphibolite facies). The age of metamorphism is constrained at ~ 260 Ma (early Late Permian) by two Rb-Sr mineral-whole rock ages (hornblende, phengite) and one 40Ar/39Ar single step total fusion age (phengite). In conjunction with previous data on other accretionary complexes in the Sakarya zone in Northern Turkey, the data presented in this study suggest a continuous subduction of the Palaeotethys at least from Early/Late Permian to Late Triassic and a discontinuous preservation of accretion complexes in both space and time.

The abundances of lithium, beryllium and boron in mineral grains from the ultrahigh-pressure garnet peridotite of Alpe Arami were studied by secondary ion mass spectrometry. In order to eliminate the ubiquitous B contamination problem, polished thin sections were cleaned twice in an ultrasonic cleaner using ultrapure water from a Milli-Q water purification system (Millipore®). Furthermore, a small aperture was used during instrumental analysis so that only the secondary ion beam from the center of the sputtered crater was sampled. Boron abundances measured with the new techniques are generally very low and increase from garnet (10–28 ng/g) via orthopyroxene (25–82 ng/g) and clinopyroxene (26–301 ng/g) to olivine (57–260 ng/g). From these values and the modal composition of the peridotite, a bulk-rock boron content of ∼110 ng/g can be estimated. Beryllium abundances are also very low and increase from olivine (∼0.1–1.0 ng, in rare cases up to 3.4 ng/g) via garnet (

In the Pulur complex, NE Turkey, a heterogeneous rock sequence ranging from quartz-rich mesocratic gneisses to silica- and alkali-deficient, Fe-, Mg- and Al-rich melanocratic rocks is characterized by granulite-facies assemblages involving garnet, cordierite, sillimanite, ilmenite, ±spinel, ±plagioclase, ±quartz, ±biotite, ±corundum, rutile and monazite. Textural evidence for partial melting in the aluminous granulites, particularly leucosomes, is largely absent or strongly obliterated by a late-stage hydrothermal overprint. However, inclusion relations, high peak P–T conditions, the refractory modes, bulk and biotite compositions of the melanocratic rocks strongly support a model of partial melting. The melt was almost completely removed from the melanocratic rocks and crystallised within the adjacent mesocratic gneisses which are silica-rich, bear evidence of former feldspar and show a large range in major element concentrations as well as a negative correlation of most elements with SiO2. Peak conditions are estimated to be ≥800 °C and 0.7–0.8 GPa. Subsequent near-isothermal decompression to ~0.4–0.5 GPa at 800–730 °C is suggested by the formation of cordierite coronas and cordierite–spinel symplectites around garnet and in the matrix. Sm–Nd, Rb–Sr and 40Ar/39Ar isotope data indicate peak conditions at ~330 Ma and cooling below 300 °C at ~310 Ma.

Helium and neon isotopes are ideal tracers to quantify contributions of primitive mantle plumes, which are characterized by a higher proportion of primordial solar-type noble gases compared to lithospheric or asthenospheric mantle sources. This property was used to investigate the role of the Afar mantle plume (a high 3 He/ 4 He plume of up to 20 R A ; 1 R A =atmospheric composition) during continental breakup of the Red Sea rift. We analyzed ultramafic rocks from Zabargad Island and mantle xenoliths from the Quaternary volcanic fields of Al Birk and Jizan (Saudi Arabia) that are representative of the local subcontinental lithospheric mantle. 3 He/ 4 He ratios range from 6.1 to 8.3 R A , similar to results of worldwide lithospheric and asthenospheric mantle, and therefore are not indicative of a plume component. In contrast, we observe significant contributions of plume-derived neon, which is characterized by a higher proportion of primordial solar-type neon than typical mid-ocean ridge basalts (MORB). Considering both helium and neon isotope systematics reveals mixing of a deep mantle plume, a pre-rift MORB-like, and a more radiogenic pre-rift lithospheric mantle component. As the deep mantle plume component has a higher Ne/He ratio when compared to the shallow mantle components, it is more prominent in Ne than in He, with up to 57% plume-derived neon and 11% plume-derived helium present in the investigated samples. This further underlines the importance of high-precision neon measurements. It demonstrates that the Afar plume source contributed primordial noble gases to an intrinsically more radiogenic and nucleogenic lithospheric and asthenospheric component up to a distance of >1800 km (Zabargad), even in the early stages of continental rifting, ∼20 Ma ago. These results present the first unambiguous geochemical evidence suggesting an active role for the Afar mantle plume during the evolution of the Red Sea rift, supporting geochronological and geodynamic evidence.

Previous studies suggest that the metamorphic evolution of the ultrahigh-pressure garnet peridotite from Alpe Arami was characterized by rapid subduction to a depth of c. 180 km with partial chemical equilibration at c. 5.9 Gpa/1180 °C and an initial stage of near-isothermal decompression followed by enhanced cooling. In this study, average cooling rates were constrained by diffusion modelling on retrograde Fe–Mg zonation profiles across garnet porphyroclasts. Considering the effects of temperature, pressure and garnet bulk composition on the Fe–Mg interdiffusion coefficient, cooling rates of 380–1600 °C Myr−1 for the interval from 1180 to 800 °C were obtained. Similar or even higher average cooling rates resulted from thermal modelling, whereby the characteristics of the calculated temperature-time path depend on the shape and size of the hot peridotite body and the boundary conditions of the cooling process. The very high cooling rates obtained from both geospeedometry and thermal modelling imply extremely fast exhumation rates of c. 15 mm yr−1 or more. These results agree with the range of exhumation rates (16–50 mm yr−1) deduced from geochronological results. It is suggested that the Alpe Arami peridotite passively returned towards the surface as part of a buoyant sliver, caused as a consequence of slab breakoff.