Enrichment Of Cs Research Articles

Lithospheric influences on magma compositions of late Mesozoic and Cenozoic intraplate basalts (the Older Volcanics) of Victoria, south-eastern Australia

Abstract Basaltic volcanism, ranging in age from Late Cretaceous to Holocene and extending across the southern part of the state of Victoria in south-eastern Australia was initiated during the earliest stages of rifting associated with opening of the Tasman Sea and Southern Ocean. Volcanism has continued sporadically since that time with major breaks in activity occurring between 77 and 62 Ma and 18 and 7 Ma. Basaltic rocks with ages in the range 95 to 18 Ma occur in small lava fields scattered across eastern and south-eastern Victoria and they have also been recovered from bore holes in the west of the state. They have been referred to as the “Older Volcanics” to differentiate them from more volumetrically extensive and younger (mainly Older Volcanics vary in composition from SiO 2 -undersaturated nephelinites, basanites, basalts and hawaiites through transitional basalts to hypersthene and quartz normative tholeiites. Strontium, Nd and Pb isotopic compositions lie between depleted (DM) and enriched (EM1 and EM2) end member mantle components in Sr–Nd–Pb isotopic space. Trace element compositions are generally characterised by enrichment of Cs, Ba, Rb, Th, U, Nb, K and light REE over heavy REE, Ti, Zr and Y and the overall patterns of major and trace element behaviour can be explained in general terms by petrogenetic models involving partial melting of a complex spectrum of mantle compositions with subsequent but limited additional modification by fractional crystallisation with or without assimilation of crust. Among basalts with relatively high Mg# [100 ∗ Mol. MgO/(MgO + FeO) > 65], two distinct end member compositions can be differentiated using primitive mantle normalised extended element patterns. Group 1 basalts have convex upward patterns with enrichment of light over heavy REE and depletion of Rb, Ba, Th and U relative to Nb. Group 2 basalts also have distinctive convex upwards patterns but are characterised by strong depletions of K, Rb and Ba relative to Nb. In both groups there is additional subtle variation with some samples having patterns with relative enrichments in Nb, Sr and Eu and/or depletions in Pb. Group 1 basalt compositions can be approximated by quantitative models involving 2 to 10% partial melting of an originally depleted mantle composition that has been metasomatised by the addition of 2 to 3% of an enriched component with a composition similar to EM1 intraplate basalt. The trace element patterns of Group 2 basalts can be modelled by 2 to 10% partial melting of an originally depleted mantle metasomatised by the addition of 1% of a calci-carbonatite composition. When Sr isotope data for Older Volcanics are projected onto an east–west profile across the state of Victoria, they outline distinctive discontinuities in isotopic composition that appear to be related to surface and subsurface structural features within the basement. One such discontinuity has previously been identified using data for the Newer Volcanics of the Western District Province of Victoria. Lithospheric blocks present beneath southern Victoria range in age from NeoProterozoic or Cambrian to Palaeozoic and some of the lowest 87 Sr/ 86 Sr ratios are observed in basalts erupted above an older basement unit (the Selwyn Block). The inference is that there is some form of lithospheric control on basaltic magma chemistry and since a substantial proportion of Older Volcanics have the geochemical characteristics of primary magmas (high Mg# and moderate to high abundances of Ni and Cr), this could indicate that magmas have been sourced from regionally heterogeneous, variably metasomatised, sub-continental lithospheric mantle. Neither the temporal and spatial relationships of the magmatic activity that followed continental breakup nor the uplift history of the south-eastern Australian passive margin are readily explained in terms of deep mantle plume tectonic models. Edge-driven convection across the irregular base of the southern Australian lithosphere, within the asthenosphere offers an elegant explanation for the longevity of the magmatic activity, its distribution, the small magma volumes involved and the uplift history as well as the geochemical variation observed in the eruptives.

Geochemistry and petrogenesis of the Cretaceous A‐type granites in the Laoshan granitic complex, eastern China

AbstractMajor element and trace element compositions, and Sr, Nd and Pb isotopic compositions for postcollisional granites from the Laoshan granitic complex, in the eastern side of the Triassic suture between the South China and North China tectonic blocks were determined. The granites are alkaline, A‐type and can be further classified as A1 granites. The trace element composition of these granites is transitional between those of oceanic island basalt and enriched mid‐oceanic ridge basalt, with depletions in Ba, Sr, P, and Ti that can be ascribed to mineral fractionation and enrichments in Cs, Rb, Th and U possibly resulted from the involvement of slab fluids. The isotopic signature of Laoshan granites represent a mixture between an enriched mantle type 1 (EMI)‐like end‐member and lower continental crust (LCC). We propose that the magmas that formed the Laoshan A1 granites are a mixture between those derived from the EMI‐like delaminated eclogitic rocks (subsequently enriched by fluids released from Mesozoic Pacific subducted slab) and those derived from the LCC, which consists of granulites or metamorphic residues from the prior generation of I‐type granites in the region. The mixed magmas then experienced a strongly alkali feldspar‐dominated fractionation prior to their emplacements as A‐type granites in the Laoshan granitic complex.

Interface Properties and Physicochemical Characterization of the Low-Temperature Molten Salt Li/K/Cs Acetate

The surface of macroscopic films of the ternary molten salt mixture Li0.2K0.275Cs0.525[OAc] has been investigated by angle-resolved X-ray photoelectron spectroscopy (XPS) as a function of temperature. With increasing temperature a preferential depletion of K+ is observed by ∼40%. From temperature programmed desorption we find that the onset for the cation desorption follows the order Cs+, K+, and Li+, with activation energies of 125, 148, and 157 kJ mol–1, respectively; the corresponding value for the [OAc] anion is 147 kJ mol–1, which is, within the margin of error, identical to the average of the value found for the cations. Ultrathin films of the molten salt deposited on a Au(111) surface by physical vapor deposition show preferential enrichment of Cs+, in line with the lower activation energy and thus higher desorption rate of Cs[OAc] from the ternary mixture. Angle-resolved XPS of the molten salt/gold interface demonstrates that the first molten salt monolayer grows in a layer-by-layer growth, follow...

Petrology, Geochemistry and Tectonic Significance of the Metamorphic Peridotites from Longmuco–Shuanghu Ophiolitic Melange Belt, Tibet

Abstract:Taoxinghu metamorphic peridotite is a firstly reported mantle sequence of ophiolite since Longmuco‐Shuanghu‐Lancangjiang suture zone (LSLSZ) was proposed, and it is also an important discovered for ophiolite studying in central Qiangtang. Based on detailed analyses of whole–rock geochemistry of Taoxinghu metamorphic peridotites and contrast to metamorphic peridotites in typical ophiolites worldwide, the paper investigates their petrogenesis and geological implication. The petrologic results show that the protolith of Taoxinghu metamorphic perdotites have the mineral assemblage and texture characteristic of mantle peridotite. Most metamorphic peridotites hav near global abyssal peridotites major elements contents, while the few is similar to SSZ‐type peridotites. They exhibit typically U‐shaped REE patterns, characterized by slight enrichment of LREE and HREE relative to MREE and a low fractionated LREE to HREE segment. Trace elements contents are low and all samples are strong enrichment in Cs, U, Pb, weak enrichment in Ba and depletion in Th, but negative Nb anomalies are only observed in few samples. That suggests Taoxinghu metamorphic peridotites have depletion mantle and suprasubduction affinities. A two‐stage evolution history is considered: Taoxinghu metamorphic peridotites originated as the residue from melting at a ridge with 7%‐20% degree of fraction melting and were subsequently modified by interaction with mafic melt and aqueous fluid within mantle wedge on subducted zone. Combined with previous studies, we preliminarily propose Taoxinghu metamorphic peridotites may be the Products of initial rifting of palo–Tethys, forming at middle Ordivician‐upper Cambrian, and they may be the direct evidences for spreading of palo–Tethys.

The blueschist-associated perovskite-andradite-bearing serpentinized harzburgite from Dobšiná (the Meliata Unit), Slovakia

*Corresponding author Unique, perovskite(Prv)–andradite(Adr)-bearing serpentinized harzburgite fragments occur in Late Jurassic–Early Cretaceous subduction–accretionary wedge complex of the Meliata tectonic Unit (Slovakia, Western Carpathians). These rocks reflect magmatic (E1) and partial melting (E2) mantle events followed by metamorphic blueschist-facies (E3) and fluid–rock interaction (E4) events accompanied by crystallization of Prv and/or Adr. The incompletely solidified slightly depleted (residual) harzburgite composed of early-magmatic assemblage of Ol, Opx 1 , Cr-Spl ± Cpx 1 (E1 event) underwent partial melting (E2 event) under subsolidus mantle conditions. The late-magmatic aggregates of Cpx 2 , Cr-Spl, scarce Opx 2 , due to this batch melting, occur around the Opx 1 (±Cpx 1 ) porphyroclasts. The fractures and cleavage planes of the kinked Opx 1 porphyroclasts are filled by Cpx 3 as a result of subsolidus recrystallization of the Opx 1 . Cloudy lower Al Cpx 4 associated with pargasite in reaction rims between the Opx 1 and Cpx 2 , or antigorite replacing Ol, could represent the E3 high-pressure metamorphic event (dated at 160 to 150 Ma, according to published 40 Ar– 39 Ar data for “phengitic” white mica from blueschists) in serpentinites. Serpentinized zones of harzburgite contain Prv, which occurs in serpentinized Opx 1 porphyroclasts. Orthopyroxene (Opx 1 ) breakdown and formation of Prv, (Ti-rich) Adr and chrysotile appears to be postdating the closure of the Meliata back-arc basin (c. 200 to 160 Ma) and HP metamorphism. Perovskite genesis can therefore be bound to the exhumation-related serpentinization in subduction channel and emplacement of serpentinites into subduction–accretionary wedge (E4 event at 300–500 oC/5–15 kbar, at 150 to 130 Ma?). The bulk-rock trace-element patterns suggest enrichment in LREE, Ba, Cs, U, Pb, Sb and Li in comparison with HREE, HFSE, Rb and Sr. Such element mobility indicates fluid–rock interaction. Pervading aqueous fluids rich in CO 2 were transporting Ca, Ti, Fe, LREE partitioned into Prv grown along the Cpx exsolution lamellae in Opx 1 . The sources of such fluids might have been the blueschist- to greenschist-facies rocks from the Meliata melange type subduction–accretionary wedge. The late-metamorphic H 2 O–CO 2 /Si–Fe–Mn-rich fluids caused partial replacement of Prv by pyrophanite and crystallization of (Ti-rich) Adr at the expense of Cpx and Prv.

Element mobility from seafloor serpentinization to high-pressure dehydration of antigorite in subducted serpentinite: Insights from the Cerro del Almirez ultramafic massif (southern Spain)

The Cerro del Almirez ultramafic massif is composed of antigorite serpentinite and chlorite harzburgite separated by a narrow transitional zone that marks the front of prograde serpentinite-dehydration at high pressure in a paleo-subduction setting. Concentrations of Sc and V indicate that the peridotite precursor of serpentinite experienced up to 20% partial melting in the spinel stability field at −2<Δlog fO2FMQ<0. Peridotites underwent intense seafloor serpentinization in a fluid-dominated system. Olivine hydrolysis at ~200°C and pyroxene serpentinization at >350–400°C remobilized Ca and REE (especially LREE and Eu) and caused the progressive enrichment of Cs, Rb, Ba, U and Pb and locally the crystallization of talc by silica fluid addition. Transformation to antigorite serpentinite upon subduction led to Sr depletion, and Ti, Tm, Yb and Lu were remobilized at the sample scale during fluid-assisted crystallization of titanian clinohumite. The high-pressure prograde breakdown of antigorite to chlorite harzburgite preserved the REE fractionations and the characteristic negative Eu anomaly of precursor serpentinites. Relative enrichment of Th–U–Nb–Ta–Pb–Sr in chlorite harzburgite cannot be balanced by closed-system dehydration of serpentinite indicating that dehydration occurred in an open system involving external fluids equilibrated with crustal sources, such as rodingites and/or metasediments. Prograde chlorite harzburgite acts as a sink of these elements during open-system fluid flux along pathways of fluid discharge in the subducted slab. This process results in the recycling into the deep convective asthenospheric mantle of prograde harzburgite enriched in Th, U, HFSE and Pb relatively to oceanic depleted peridotite. This signature and the preservation in dehydrated subducted serpentinite of negative Eu anomaly and C–O–H–S crustal-like isotopic compositions make prograde serpentinite a potential reservoir for the balance of the Earth's HFSE budget and a potential source for diamonds with a low-pressure inherited geochemical signature.

BERYL FROM MIAROLITIC POCKETS OF GRANITIC PEGMATITES, ELBA, ITALY: CHARACTERIZATION OF CRYSTAL CHEMISTRY BY MEANS OF EMP AND SIMS ANALYSES

Crystals of beryl from miarolitic pockets, hosted in pegmatitic dikes on the Island of Elba, in Italy, were analyzed for the major and minor elements, including the light elements, by EMPA and SIMS techniques. Back-scattered electron (BSE) images and X-ray maps were used to define the complex textures of these crystals and to highlight the pattern of element distribution in each sample. The majority of the analyzed crystals exhibit a complex pattern of zoning caused by changes in the chemical composition, which follow the main mechanisms of substitution defined for the crystal chemistry of beryl. The following main features are illustrated: (1) the occurrence of crystals with octahedral-site or tetrahedral-site substitutions in different domains of the same crystal, (2) the occurrence of crystals with exclusively tetrahedral or exclusively octahedral substitutions, and (3) the occurrence of crystals or crystal domains having a limited extent of octahedral-site and tetrahedral-site substitutions. However, the analytical data confirm the presence of a gap between the two series, having octahedral-site or tetrahedral-site substitutions. The observed enrichment in Cs and Li is strictly related to the geochemical and petrological features of the LCT host pegmatites. The presence of Ca in some beryl crystals in pegmatites emplaced in carbonate rocks suggests an interaction of the late hydrothermal fluids with country rocks. An enrichment in Fe could also be ascribed to the circulation of fluids having such a contaminant element attributed to the contribution of country rocks or the destabilization of early-crystallized Fe-rich minerals.

A Cretaceous forearc ophiolite in the Shyok suture zone, Ladakh, NW India: Implications for the tectonic evolution of the Northwest Himalaya

The northwestern Himalaya in India contains critical evidence of the convergent margin and collision tectonics between the Ladakh arc and the Karakoram block. Here we present new petrochemical and geochronological data from a forearc ophiolite at the Shyok‐Nubra river confluence. Whole-rock geochemical data show relatively high large-ion lithophile elements (LILE), light rare earth elements (LREE), and Ba, U and Pb anomalies, and depletions in La, Ce and Zr, particularly, the high-field strength elements (e.g. Nb, Ta); these geochemical characteristics are similar to those in modern ophiolites that formed in arc-related environments. Meta-volcanic greenschists that contain spinel layers have high MgO, Ni, Co, and Cr contents. In contrast, they have low contents of TiO2, very low Nb and Zr that are diagnostic of high‐Ca boninitic magmas in modern forearc settings, as in Izu–Bonin–Mariana (IBM) and Tonga. The spinels have high Cr# [Cr/(Cr+Al)] and Mg#[Mg/(Mg+Fe2+)], which are characteristic of spinels in forearc boninite‐type of melts. The spinel-free meta-volcanic samples have incompatible trace element abundance patterns similar to those of MORB. However, their enrichments in Cs, Rb, Pb, U and depletion in HFSE may reflect an input of subduction fluids that are different from MORB; these MORB-like basalts are suggestive of a forearc complex that erupted prior to the formation of boninitic rocks.Our data from the Shyok ophiolite indicate the existence of supra-subduction rocks on the southern Karakoram margin. Albite porphyroblasts in greenschists yield a K–Ar age of 104.4±5.6Ma that represents the time of early exhumation of the greenschists. The boninite‐type melts formed prior to 104Ma, thereby indicating that the time of initiation of subduction on the southern margin of the Karakoram block was before 104Ma. These geochemical signatures together with the spatial and temporal distribution of the arc rocks on the southern margin of Karakoram block suggest northward subduction of NeoTethys in the Early Cretaceous. The subsequent collision between the Ladakh arc and the Karakoram block thrusted/obducted the forearc ophiolite onto the southern edge of the Karakoram block probably between 74Ma and 97Ma.

GEOCHEMISTRY AND PETROLOGY OF LAVAS IN THE UPPER ONVERWACHT SUITE, BARBERTON MOUNTAIN LAND, SOUTH AFRICA

The basis of this study comprises 540 geochemically analysed samples collected systematically from eighteen stratigraphic sections (2257 m in total length) through the submarine volcanic rocks of the tectonically separated Hooggenoeg, Kromberg and Mendon Complexes in the southwestern part of the Paleoarchean Barberton Greenstone Belt. The lavas are predominantly high- to low-MgO tholeiitic basalts but include minor komatiite and komatiitic basalt. They are non-deformed and preserve delicate igneous textures, but have been allochemically altered and regionally metamorphosed. Comparison of pillow cores and rims, samples from massive flows and interelement correlations demonstrate that Ti, Al, Cr, V, Nb, Ta, Zr, Hf, Y, Pb, Th and the REE were relatively immobile during alteration and hence preserve geochemical evidence bearing on the origin and tectonic setting of the lavas. Chondrite-normalized REE patterns are slightly LREE depleted in komatiite to slightly LREE enriched in basalts. MORB-normalized values of non-conservative elements (Cs, Ba, Pb, Th) are high relative to conservative elements (Ta, Nb, Zr, Hf, Y, HREE) in all of the volcanic rocks, particularly those of the Hooggenoeg Complex. Most of the samples exhibit enrichment of Cs and Ba, Pb anomalies and depletion in Nb and Ta, consistent with a subduction-related oceanic environment. With the exception of the lavas of the Hooggenoeg Complex, using primordial mantle (PM) values for normalisation generally subdues the enrichments of the non-conservative elements seen in MORB-normalised multi-element diagrams. However, negative Nb and Ta anomalies relative to La remain significant. High Ba/Th ratios indicate relatively shallow level enrichment of the magma source in large ion lithophile elements by aqueous fluids, whilst enhanced Th concentrations reflect deeper partial melting. Estimated subduction related contributions to Th vary in the ca. 2700 m thick section of the Hooggenoeg Complex and suggest changes in the depth to the subducting slab, which may relate to variation in the subduction angle in the course of ca. 10 million years. ɛ Nd(T) values suggest earlier melt extraction and possible incorporation of older crustal material, probably subducted clastic sediments. Our inferred model for the formation of the Upper Onverwacht Suite, based on the lithological and structural development of the lavas and their geochemistry invokes eruption in intra-oceanic back-arc basins and volcanic island arcs. Magmas were generated by variable degrees of partial melting at different depths and temperatures of metasomatised mantle above subducting and dehydrating oceanic lithosphere, and were subsequently modified by fractional crystallization and hybridization. In terms of MORB-and PM-normalised multi-element patterns, as well as Nd-isotope ratios, the volcanic rocks of the Onverwacht Suite are comparable with the west Pacific-Indonesian arc systems.

Geochemistry of Ocean Floor and Fore-arc Serpentinites: Constraints on the Ultramafic Input to Subduction Zones

We provide new insights into the geochemistry of serpentinites from mid-ocean ridges (Mid-Atlantic Ridge and Hess Deep), passive margins (Iberia Abyssal Plain and Newfoundland) and fore-arcs (Mariana and Guatemala) based on bulk-rock and in situ mineral major and trace element compositional data collected on drill cores from the Deep Sea Drilling Project and Ocean Drilling Program. These data are important for constraining the serpentinite-hosted trace element inventory of subduction zones. Bulk serpentinites show up to several orders of magnitude enrichments in Cl, B, Sr, U, Sb, Pb, Rb, Cs and Li relative to elements of similar compatibility during mantle melting, which correspond to the highest primitive mantle-normalized B/Nb, B/Th, U/Th, Sb/Ce, Sr/Nd and Li/Y among subducted lithologies of the oceanic lithosphere (serpentinites, sediments and altered igneous oceanic crust). Among the elements showing relative enrichment, Cl and B are by far the most abundant with bulk concentrations mostly above 1000 µg g−1 and 30 µg g−1, respectively. All other trace elements showing relative enrichments are generally present in low concentrations (µg g−1 level), except Sr in carbonate-bearing serpentinites (thousands of µg g−1). In situ data indicate that concentrations of Cl, B, Sr, U, Sb, Rb and Cs are, and that of Li can be, increased by serpentinization. These elements are largely hosted in serpentine (lizardite and chrysotile, but not antigorite). Aragonite precipitation leads to significant enrichments in Sr, U and B, whereas calcite is important only as an Sr host. Commonly observed brucite is trace element-poor. The overall enrichment patterns are comparable among serpentinites from mid-ocean ridges, passive margins and fore-arcs, whereas the extents of enrichments are often specific to the geodynamic setting. Variability in relative trace element enrichments within a specific setting (and locality) can be several orders of magnitude. Mid-ocean ridge serpentinites often show pronounced bulk-rock U enrichment in addition to ubiquitous Cl, B and Sr enrichment. They also exhibit positive Eu anomalies on chondrite-normalized rare earth element plots. Passive margin serpentinites tend to have higher overall incompatible trace element contents than mid-ocean ridge and fore-arc serpentinites and show the highest B enrichment among all the studied serpentinites. Fore-arc serpentinites are characterized by low overall trace element contents and show the lowest Cl, but the highest Rb, Cs and Sr enrichments. Based on our data, subducted dehydrating serpentinites are likely to release fluids with high B/Nb, B/Th, U/Th, Sb/Ce and Sr/Nd, rendering them one of the potential sources of some of the characteristic trace element fingerprints of arc magmas (e.g. high B/Nb, high Sr/Nd, high Sb/Ce). However, although serpentinites are a substantial part of global subduction zone chemical cycling, owing to their low overall trace element contents (except for B and Cl) their geochemical imprint on arc magma sources (apart from addition of H2O, B and Cl) can be masked considerably by the trace element signal from subducted crustal components.

Molecular investigations of comets C/2002 X5 (Kudo-Fujikawa), C/2002 V1 (NEAT), and C/2006 P1 (McNaught) at small heliocentric distances

We present unique spectroscopic radio observations of comets C/2002 X5 (Kudo-Fujikawa), C/2002 V1 (NEAT), and C/2006 P1 (McNaught), which came within $r_h ~ 0.2 AU of the Sun in 2003 and 2007. The molecules OH, HCN, HNC, CS, and CH3OH were detected in each of these comets when they were exposed to strong heating from the Sun. Both HC3N and HCO+ were detected in comets C/2002 X5 and C/2006 P1, respectively. We show that in these very productive comets close to the Sun screening of the photodissociation by the Sun UV radiation plays a non-negligible role. Acceleration of the gas expansion velocity and day-night asymmetry is also measured and modeled. The CS photodissociation lifetime was constrained to be about 2.5 x 10**-5 s-1 at r_h = 1 AU. The relative abundances are compared to values determined from more distant observations of C/2002 X5 or other comets. A high HNC/HCN production-rate ratio, in the range 10 to 30 % between 0.5 and 0.1 AU from the Sun, is measured. The trend for a significant enrichment in CS in cometary comae (CS/HCN proportional to r_h**-0.8) is confirmed in all three comets. The CH3OH/HCN production rate ratio decreases at low r_h. The HC3N/HCN production rate ratio in comet C/2002 X5 is four times higher than measured in any other comet.

Geochemistry of garnetiferous Ti–clinohumite rock and talc–kyanite–phengite–almandine schist from the Kokchetav UHP terrane, Kazakhstan: An insight to possible origins of some chemically unusual UHP rocks

Major-element, trace-element and O-isotope analyses were carried out for garnetiferous Ti–clinohumite rocks and eclogites from the Kumdy Kol area, as well as talc–kyanite–phengite–almandine schists (previously named as whiteschists) and eclogites from the Kulet area of the Kokchetav ultrahigh-pressure (UHP) terrane, to explore their possible origins. Both garnetiferous Ti–clinohumite rocks and talc–kyanite–phengite–almandine schists are possibly genetically related to eclogites, as they occur in close association with eclogites enclosed within gneiss/metapelite in these two areas. Most eclogites from the Kumdy Kol and the Kulet areas exhibit chemical characteristics similar to that of ocean floor basalt, although a few show arc affinity with slight Ta and Nb depletions. Garnetiferous Ti–clinohumite rocks from the Kumdy Kol region are characterized by very high Mg, low Si, Ca, Na, and K contents compared with eclogites. They also exhibit LREE depleted patterns with negative Eu anomalies. Their O-isotope compositions are less than + 5.6‰. On the other hand, the rocks show comparable Al, Ni, Cr, Co and HREE contents as eclogites. The Mg enrichment of these garnetiferous Ti–clinohumite rocks is suggested to have originated from their mafic protoliths that had been subjected to mafic rock–ultramafic rock–fluid interactions. Talc–kyanite–phengite–almandine schists from the Kulet area are typically low in Ca and Na, but high in Mg, K, Rb, Ba, Cs, Th, U and O-isotope compositions (+ 6 to + 10‰) relative to eclogites. This peculiar chemical composition can be accounted for if the basaltic protoliths had been subjected to sequential high-temperature (enrichment of Mg) and low-temperature (enrichment of K, Rb, Ba, Cs, Th, U and O-isotope compositions) seawater–basalt interactions. One talc–kyanite–phengite–almandine schist sample KLW 7 is distinctly high in Si and K, but low in Mg and Fe, which can be attributed to more severe low-temperature hydrothermal alterations. However, except for Mg, the enrichment of Rb, Ba, Cs, Th, U and O-isotope compositions in these schist samples could also be enhanced by, or otherwise be interpreted as a result of, fluid influx sourced from enclosing metapelite during subduction.

The effects of K-metasomatism in the Bahía Laura Volcanic Complex, Deseado Massif, Argentina: Petrologic and metallogenic consequences

Abstract The Deseado Massif is a 60 000 km2 geological region located in southern Argentinean Patagonia. The most important geological feature of this area is an extensive plateau characterized by complex and long-lived Middle to Upper Jurassic volcanism, composed of intermediate to acid volcanic rocks of the Bahia Laura Volcanic Complex. This voluminous volcanism originated in a widespread extensional environment that affected all of Patagonia, related to the opening of the Atlantic Ocean. The volcanic rocks are genetically related to Jurassic epithermal deposits. Consequently the region is an important gold and silver producer with four operational mines (Cerro Vanguardia, Mina Martha, Manantial Espejo and San Jose) and more than 50 epithermal occurrences undergoing different levels of exploration. Potassic metasomatism identified in the Bahia Laura Volcanic Complex is difficult to recognize in hand specimen, but is characterized by K2O/Na2O ratios higher than 2.5 and L.O.I. values lower than 3 wt.%, and affects only rocks with silica contents over 68 wt.%. The metasomatism produced an intense geochemical change in the affected rocks, with significant additions of K2O, Rb, Au, Sb, W and a minor enrichment in Cs, Cu, As, and probably Ag and Hg. Strongly depleted elements are MgO, CaO, Na2O, P2O5, MnO, Sr and U, whereas FeOt, TiO2, L.O.I., Pb and Zn are moderately depleted. Finally, SiO2, Al2O3, Mo and most trace elements and REE remained almost invariant during increasing metasomatism. Strong similarities in lithologies and geochemical signatures observed in K-metasomatized areas around the world, regardless of their geological settings and fluid origins, suggest that volcanic glass probably played an important role as an ion exchanger during alteration. Due to the high mobility of elements that occurs during K-metasomatism, no classification or discrimination diagram based on major elements, TiO2 or Rb are considered to be valid for the chemical characterization of volcanic rocks based on metasomatized samples. The precious and base metals enrichment/depletion pattern of K-metasomatized rocks is identical to the geochemical signature observed in the upper parts of low sulfidation environments from the Deseado Massif. This geochemical signature, along with spatial relations observed between K-metasomatized rocks and epithermal manifestations, implies that hydrothermal fluids were responsible for the metasomatism observed in the Bahia Laura Volcanic Complex.

Burning of coal waste piles from Douro Coalfield (Portugal): Petrological, geochemical and mineralogical characterization

Abstract In the Douro Coalfield anthracites were exploited for decades (1795–1994). Besides many small mines Douro Coalfield had two principal mining areas (S. Pedro da Cova and Pejao). Coal mining activities cause several impacts on the environment, one of which is the amount of discard or waste which was disposed of all over Douro Coalfield resulting in one of the most significant and severe impacts on the environment. Over 20 waste piles exist in the old mining areas, geographically dispersed, and three of them are presently burning. Their ignition was caused by forest fires during the summer of 2005. Samples from the burning and unburned zones of the waste piles were studied as were the gas from vents and the minerals resulting after combustion. Geochemical processes and mineralogical transformations in the burning coal waste pile were investigated. Microscopic analyses of the samples identified some particular aspects related with combustion: oxidation of pyrite, the presence of iron oxides, organic particles with cracks and rims with lowered (suppressed) Rr, devolatilization vacuoles and some char structures. The occurrence of vitreous (glassy) material as well as Fe–Al spinels in the burning coal waste provide evidences that the combustion temperature could have reached values above 1000 °C. Due to combustion, and as expected, the samples studied reported high ash yields. Samples taken from the burning zones reported an increase of As, Cr, Li, Nb, Ni, Pb, Rb, Sr and LREE concentrations and a decrease in Zr and HREE concentrations. Enrichment in Cs, Li and Rb was noted when comparing with the geochemical composition of black shales and world coals composition that is related with the contribution of granitic rocks in the sediments that originated the main lithologies of the Douro Coalfield (carbonaceous shale and lithic arenites). Cluster analyses (R-type and Q-type) were performed to understand the trend between the unburned and burning samples and it seems that some chemical variations are responsible for this separation. Elemental sulphur and salammoniac (ammonium salt) are the coal fire gas minerals neoformed on the surface of piles, near the burning zones. They were identified by different techniques, mainly SEM-EDX, XRD and FTIR. Relatively high concentrations of several aromatic compounds were detected in the gas collected at the studied areas, as well as aliphatic hydrocarbons. The highest concentrations of aromatic hydrocarbons were measured in gas samples from S. Pedro da Cova waste pile. The exposure to hazardous compounds present in the gas is a serious risk to human health and the environment.

Lead isotope and trace element composition of K-feldspars from peraluminous granitoids of the Late Devonian South Mountain Batholith (Nova Scotia, Canada): implications for petrogenesis and tectonic reconstruction

The South Mountain Batholith (SMB) of southwestern Nova Scotia (Canada) is a Late Devonian (~375 Ma) composite intrusion, which crops over an area of about 7,300 km2. This peraluminous granitoid body consists of rocks ranging from granodiorite through monzogranite and leucomonzogranite to leucogranite that locally host greisen tin-base metal mineralization. K-feldspar displays large compositional variations of trace elements and Pb isotopic ratios, particularly in the highly fractionated rocks. Many variations are consistent with processes of fractional crystallization, but a distinct enrichment of Rb, Li and Cs accompanied by low K/Rb, Ba/Rb, Eu/Eu* and K/Cs ratios point to the role of fluids during the late stages of magmatic evolution. The correlation of Pb isotopic ratios with the enriched elements and their ratios implies that the isotopic variations are an integral part of the evolution of the SMB. Together with well-defined isochronal relationships of Pb systems in the feldspars, the correlation suggests that fractional crystallization accompanied in the late stages by fluid fractionation led to the formation of Li–F-rich leucogranites. Internally derived U-rich fluids fractionated U/Pb ratios, which in turn produced distinct variations of 206Pb/204Pb and 238U/204Pb ratios in K-feldspars. This implies that the Pb isotopic values of K-feldspar, which have traditionally been used for tectonic reconstructions, might have been modified in many granitic rocks. Thus, only early magmatic K-feldspars, which show no discernible effects of fluid fractionation yield the initial Pb isotopic compositions of the parental granitic magmas and their sources. The data also show that the geochemical characteristics of the leucogranites are the results of magmatic evolution rather than a distinctive source.

Trace element geochemistry of K-rich impact spherules from howardites

The howardite–eucrite–diogenite (HED) achondrites are a group of meteorites that probably originate from the asteroid Vesta. Howardites are complex polymict breccias that sometimes contain, in addition to various rock debris, impact melt glasses which show an impressive range of compositions. In this paper we report on the geochemistry and O isotopes of a series of 6 Saharan polymict breccias (4 howardites and 2 polymict eucrites), and on the trace element abundances of high-K impact spherules found in two of them, Northwest Africa (NWA) 1664 and 1769, which are likely paired. The high-K impact spherules found in the howardites NWA 1664 and NWA 1769 display remarkable trace element patterns. Compared to eucrites or howardites, they all show prominent enrichments in Cs, Rb, K, Li and Ba, strong depletion in Na, while the REE and other refractory elements are unfractionated. These features could not have been generated during impact melting of their host howardites, nor other normal HED target materials. The involvement of Na-poor rocks, and possibly rocks of granitic composition, appears likely. Although these lithologies cannot be well constrained at present, our results demonstrate that the surface of Vesta is certainly more diverse than previously thought. Indeed, despite the large number of available HED meteorites (about 1000 different meteorites), the latter are probably not sufficient to describe the whole surface of their parent body.

Oxidized multiwalled carbon nanotubes for quantitative determination of cationic surfactants in water samples using atmospheric pressure matrix-assisted laser desorption/ionization mass spectrometry

Oxidized multiwalled carbon nanotubes (O-MWCNT) are used as preconcentrating probes for the quantitative determination of cationic surfactants (CS +) in water samples using atmospheric pressure matrix-assisted laser desorption/ionization mass spectrometry (AP-MALDI-MS). The method is based on the electrostatic interactions of positively charged CS + with the negatively charged O-MWCNT for the preconcentration and isolation of analytes from sample solutions. The O-MWCNT/AP-MALDI-MS is performed for the determination of CS + in river- and waste-water samples. The optimum extraction efficiency of CS + is observed for 7 min of contact time at 1.0 mg dosage of O-MWCNT at pH 7.0. The acceptable relative recovery percentage in water sample is obtained in the range 90.5–97.8% with relative standard deviation (R.S.D.) < 14.5%. The results suggested that the newly proposed method is rapid, accurate and effective and could be successfully applied for the enrichment and quantitative determination of CS + in water samples.

Process research of macroporous resin chromotography for separation of N-( p-coumaroyl)serotonin and N-feruloylserotonin from Chinese safflower seed extracts

N-( p-Coumaroyl)serotonin (CS) and N-feruloylserotonin (FS) are two bioactive serotonin derivatives in safflower ( Carthamus tinctorius L.) seeds with many biological effects. In the present study, the sorption and desorption characteristics of six widely used macroporous resins, coded D312, 860021, DM131, HZ801, AB-8 and XDA-1, respectively, is critically evaluated and compared for enrichment and preparative separation of CS and FS. Static adsorption and desorption experiments on these resins showed that XDA-1 had the best adsorption and desorption equilibrium for CS and FS, and its adsorption equilibrium fits the best to the Langmuir isotherm. Dynamic adsorption and desorption experiments on XDA-1 resin packed column were conducted to establish the optimum parameters as: CS and FS concentration in sample solution 0.346 and 0.276 mg/mL, respectively, sample size 5-bed volumes (BV), sample flow rate 2 mL/min, temperature 25 °C (for adsorption); eluent 80% ethanol, 11 BV, flow rate 1 mL/min (for desorption). After one run of adsorption and desorption, the contents of CS and FS were increased from 2.01%, 1.67% to 24.1% and 22.4%, and the recoveries were 77.2% and 68.5%, respectively. The chromatographic process optimized in the present work is a promising basis for large scale preparation of CS and FS upon further scaling up tests.

Multistage metasomatism in ultrahigh-pressure mafic rocks from the North Dabie Complex (China)

Release of metamorphic fluids within the slab and/or from the slab to the mantle wedge in subduction environments can produce important metasomatic effects. Ultrahigh-pressure (UHP) metasomatised rocks represent ideal materials to study the element exchange at pressures corresponding to sub-arc depths in subduction zones. We present a petrologic and geochemical study of eclogites (s.l.) from the Dabie Mountains (China). The investigated samples were collected in the North Dabie Complex, where eclogite-facies rocks are significantly overprinted by granulite-facies metamorphism and partial melting. The studied eclogites are included in meta-lherzolitic bodies, which are in turn hosted by leucocratic gneisses. The textural relations among the various rock-forming minerals enabled us to identify several re-crystallisation stages. The peak (UHP) paragenesis consists of garnet, clinopyroxene and rutile. UHP garnet and clinopyroxene display oriented inclusions of polycrystalline rods of rutile + ilmenite and of albite, K–Ba-feldspar and quartz, respectively. Garnet and clinopyroxene are both rimmed by an inclusion free zone that formed after the peak, still at high-pressure conditions. Such optical zoning does not correspond to a difference in major element concentrations between garnet core and rim. This observation provides evidence that the major element composition of garnet was reset during exhumation, thus preventing thermobarometric determination of peak metamorphic conditions. Further decompression is documented by the formation of limited ilmenite + amphibole and granulite-facies coronas consisting of clinopyroxene, orthopyroxene, plagioclase and amphibole around garnet. In order to investigate the stability of observed mineral parageneses, a series of reconnaissance piston cylinder synthesis experiments were carried out in an identical bulk composition. The experimental study indicates that the peak metamorphic paragenesis is stable at P∼3.5 GPa and T ≥ 750–800 °C. The petrological study, combined with bulk-rock and mineral trace element analyses, provides evidence of intense metasomatism affecting these eclogites. The bulk-rock major and trace element compositions indicate that the eclogites derive from basaltic protoliths with MORB and E-MORB affinity. Compared with such basalts, the studied rocks show strong depletion in SiO 2 and alkalis and enrichment in MgO and FeO. These features likely derive from element exchange with ultramafic rocks prior to subduction, possibly related with the influx of Si-depleted and Mg-enriched fluids produced during the serpentinisation of the associated lherzolitic rocks. On the other hand, the trace element bulk-rock compositions show strong enrichment in Cs, Ba and Pb. The same characteristic enrichment and fractionation is recorded by peak metamorphic clinopyroxene but not in retrograde amphibole. Therefore, influx of crustal fluids transporting LILE and light elements must have occurred during subduction at UHP conditions. This stage likely records the tectonic coupling of the mafic–ultramafic rocks with the associated crustal rock units and provides evidence of LILE mobility between different slab components.

Subduction‐related metasomatism in the thinning lithosphere: Evidence from a composite dunite‐orthopyroxenite xenolith entrained in Mesozoic Laiwu high‐Mg diorite, North China Craton

The North China Craton (NCC) lost its Archean keels in the Phanerozoic. Prevalent and intensive magmatism, mineralization, and development of extensional basins in the late Mesozoic NCC imply that the late Mesozoic could be the key stage for this transformation. Ultramafic xenoliths in the Early Cretaceous high‐Mg diorites of Shandong province might provide key information about the transformation of subcontinental lithospheric mantle (SCLM) beneath the NCC. Here we present a unique composite dunite‐orthopyroxenite xenolith from Tietonggou, one of the high‐Mg diorite‐dominated plutons in Laiwu, Shandong province. The petrography and mineral chemistry of the xenolith suggest complicated metasomatic processes, which occurred before its entrainment in the host magma. Early stage metasomatism includes the growth of intergranular phlogopite and clinopyroxene and the development of a phlogopite‐ and amphibole‐bearing clinopyroxenite veinlet. Late‐stage metasomatism (termed Si (Na) metasomatism) is characterized by the growth of secondary orthopyroxene, Na‐rich plagioclase and amphibole with resorption of olivine and clinopyroxene, and the decomposition of phlogopite. The xenolith has exceptionally high concentrations of Na2O and Al2O3 and shows enrichments in Cs, Rb, Th, U, K, and the light rare earth elements. It also shows positive Pb and Sr anomalies and negative Nb, Ta, P, and Ti anomalies in a primitive mantle normalized spider gram. The geochemistry, as well as the elevated δ18O, suggests that this Si (Na) metasomatism is associated with subduction. The secondary orthopyroxene in the orthopyroxenite portion of the xenolith has exceptionally low Mg# values, which may be the result of reaction between silica‐rich melts and olivine with high melt:rock ratios. Mg‐Fe disequilibrium of the minerals in the orthopyroxenite indicates that Si (Na) metasomatism may have been introduced shortly before entrainment of the xenolith in the host magma. Correlation of the Sr‐Nd‐Pb isotopic compositions of ultramafic xenoliths, high‐Mg diorites, and adakitic granites of the Tietonggou indicates there may be a genetic relationship between these rocks. Thus we propose that the SCLM beneath Shandong may have been metasomatized by a slab‐derived melt. Since Si (Na) metasomatism occurred at the key stage of lithospheric thinning, oceanic subduction might have been involved in the thinning process.