Lithophile Light Elements Research Articles

Geochronology, geochemistry, and petrogenesis of Early Cretaceous highly differentiated I-type granites in the central Great Xing’an Range, northeastern China

In this study, we undertook zircon U–Pb dating and Hf isotopic and whole-rock geochemical analysis of Mesozoic granites from the Zhalantun and Arxan areas of the Great Xing’an Range, northeastern China. Zircon U–Pb dating of four samples indicates they formed in the Early Cretaceous (ca. 140.7–130.0 Ma). Geochemically, the samples have high silica (74.00–77.29 wt.%) and total alkali (8.52–8.90 wt.%) and low CaO (0.21–0.71 wt.%), MgO (0.06–0.48 wt.%), and P2O5 (0.01–0.06 wt.%) contents and exhibit the weakly peraluminous (A/CNK = 0.98–1.06) and high-K calc-alkaline characteristics, with highly differentiated I-type granite affinities (differentiation index = 93.19–96.93). The studied granites are enriched in light rare earth and large ion lithophile elements and depleted in heavy rare earth and high field strength elements. Their zircon εHf(t) values are mainly positive (+2.49 to +11.64) and yield two-stage Hf model ages of 1023–445 Ma. The geochemical and isotopic data indicate they might have been derived from the partial melting of medium- to high-K basaltic crust material during the Mesoproterozoic to Phanerozoic. They underwent fractional crystallization in the magma evolution process, and K-feldspar and plagioclase were the major crystallization phases. Combined with the temporal–spatial migration of the Mesozoic magmatic events in the whole northeastern China, we propose that the generation of Early Cretaceous highly differentiated I-type granites in the central Great Xing’an Range was associated with the delamination effect caused by the roll-back of the Paleo-Pacific plate.

The influence of oxygen fugacity and chlorine on amphibole–liquid trace element partitioning at upper-mantle conditions

Abstract. The recycling of volatile and incompatible elements through the entire Earth's history is one of the most important processes for the chemical evolution of the lithosphere. In this context, amphiboles are important hydrous minerals playing a key role in the chemical differentiation of the crust–mantle system. We carried out amphibole–liquid partitioning (Amph/LD) experiments starting from a hydrous alkali basalt with variable chlorine content and doped in 37 trace elements of geochemical interest. Experiments were conducted with an end-loaded piston cylinder apparatus at a fixed pressure of 1.4 GPa, temperature from 1015 to 1050 ∘C, and at two different oxygen fugacity conditions (fO2; ΔFMQ ≈-2.6 (log fO2 [experiment] − log fO2 [FMQ buffer]) and ΔFMQ ≈+ 1.7). These conditions approach those of the Earth's upper mantle chemically metasomatised by subduction-derived agents that may occur in several geological settings. All runs show Ti-pargasites and kaersutites, either as individual crystals or replacing former clinopyroxenes, in equilibrium with alkali-rich (4 wt %–6 wt %) and silica-intermediate (52 wt %–59 wt %) melts. A comprehensive trace element dataset (LLEs – light lithophile elements, LILEs – light ion lithophile elements, REEs – rare Earth elements, HFSEs – high field strength elements, actinides, transition metals, chalcophiles) has been determined in glass and amphibole with a laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS). Although the melt polymerization has a major influence on Amph/LDs, we provide evidence that changes in the fO2 of both the system and Cl content in amphibole (up to 0.88 wt %) also affect the Amph/LDs of several trace elements and their ratios. In particular, at higher fO2 conditions lower Amph/LD values for U and Mo are observed likely in relation to the low capability of amphibole to incorporate the more oxidized forms of these cations. The Amph/LDTh/Amph/LDU ratio is positively correlated with the Cl content in amphibole, while the opposite behavior is shown by Amph/LD ratios of other elements with the same charge and different ionic radius (e.g., Gd / Yb, Nb / Ta, and Pb / Ba). Dimensional modification of the amphibole structure in relation to the incorporation of Cl in the O(3) site are at the origin of the observed variations. General implications of our results are discussed.

Petrogenesis and tectonic setting of Late Devonian high-Mg andesites in the Beishan orogen, NW China

AbstractHigh-Mg andesites (HMAs) are crucial for the reconstruction of plate tectonics, continental margin formation and lithospheric evolution. In this study, we present new fossil age, whole-rock geochemical and Sr–Nd isotope data on the newly discovered Dundunshan Group HMAs in the Dundunshan area of the Beishan orogen (central-southern Central Asian Orogenic Belt). The Dundunshan HMA samples are characterized by high MgO (6.47–7.02 wt%) contents and high Mg# values (67.27–68.77), with SiO2 (58.57–62.13 wt%), Al2O3 (14.49–16.07 wt%) and CaO (5.05–6.24 wt%) resembling typical HMAs. The Dundunshan HMA samples are calc-alkaline and strongly enriched in light rare earth elements (LREEs) and large-ion lithophile elements (LILEs), with slightly negative Eu anomaly and high-field-strength element (HFSE) depletions. Their (87Sr/86Sr)i ratios (0.7041–0.7057) and ϵNd(t) (3.73–5.59) indicate that the Dundunshan HMAs were mainly formed by the interactions between subducted oceanic sediment-derived melts and mantle peridotites. Fossil evidence and published radiometric age data constrain the formation of the Dundunshan HMAs to early Late Devonian time. Sedimentological features of the Middle Devonian Sangejing Formation and regional tectonic correlation suggest that the Hongliuhe–Niujuanzi–Xichangjing Ocean in the Dundunshan area was likely closed during late Middle Devonian time, and that the Dundunshan HMAs were formed in a post-collision extensional setting.

Early Cretaceous crust–mantle interaction linked to rollback of the Palaeo-Pacific flat-subducting slab: constraints from the intermediate–felsic volcanic rocks of the northern Great Xing’an Range, NE China

AbstractLate Mesozoic igneous rocks are important for deciphering the Mesozoic tectonic setting of NE China. In this paper, we present whole-rock geochemical data, zircon U–Pb ages and Lu–Hf isotope data for Early Cretaceous volcanic rocks from the Tulihe area of the northern Great Xing’an Range (GXR), with the aim of evaluating the petrogenesis and genetic relationships of these rocks, inferring crust–mantle interactions and better constraining extension-related geodynamic processes in the GXR. Zircon U–Pb ages indicate that the rhyolites and trachytic volcanic rocks formed during late Early Cretaceous time (c. 130–126 Ma). Geochemically, the highly fractionated I-type rhyolites exhibit high-K calc-alkaline, metaluminous to weakly peraluminous characteristics. They are enriched in light rare earth elements (LREEs) and large-ion lithophile elements (LILEs) but depleted in high-field-strength elements (HFSEs), with their magmatic zircons ϵHf(t) values ranging from +4.1 to +9.0. These features suggest that the rhyolites were derived from the partial melting of a dominantly juvenile, K-rich basaltic lower crust. The trachytic volcanic rocks are high-K calc-alkaline series and exhibit metaluminous characteristics. They have a wide range of zircon ϵHf(t) values (−17.8 to +12.9), indicating that these trachytic volcanic rocks originated from a dominantly lithospheric-mantle source with the involvement of asthenospheric mantle materials, and subsequently underwent extensive assimilation and fractional crystallization processes. Combining our results and the spatiotemporal migration of the late Early Cretaceous magmatic events, we propose that intense Early Cretaceous crust–mantle interaction took place within the northern GXR, and possibly the whole of NE China, and that it was related to the upwelling of asthenospheric mantle induced by rollback of the Palaeo-Pacific flat-subducting slab.

Geochemistry and zircon ages of the Yushigou diabase in the Longshoushan area, Alxa Block: implications for crust–mantle interaction and tectonic evolution

AbstractThe North Qilian orogenic belt in North China has been defined as a subduction–collision zone between the Alxa Block and the Qilian Block. We present petrography, zircon U–Pb geochronology, major- and trace-element geochemistry, and Sr–Nd–Pb–Hf isotope analysis for the Yushigou diabase from the Longshoushan area, which is located SW of the Alxa Block, aiming to understand its petrogenetic link to subduction processes. The Yushigou diabase belongs to the tholeiite series, and shows enrichment in light rare earth and large-ion lithophile elements, and a depletion in heavy rare earth and high-field-strength elements. Laser ablation – inductively coupled plasma – mass spectrometry U–Pb zircon dating yielded an emplacement age of 414 ± 9 Ma, with an ϵHf(t) value in the range of −10.3 to 1.8. The whole-rock initial 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios of the diabase range over 16.811–17.157, 15.331–15.422 and 37.768–37.895, respectively. The (87Sr/86Sr)i ratios vary between 0.7086 and 0.7106, and ϵNd(t) values vary between −14.4 and −13.4, which are significantly higher than the ϵHf(t) value (Nd–Hf decoupling). An interpretation of the elemental and isotopic data suggests that the Yushigou diabase was derived from partial melting of an enriched mantle I (EM-I) -type lithospheric mantle in the spinel–garnet transitional zone. Based on the geochemical features and previous regional geological data, we propose that the Silurian magmatism was most likely triggered by slab break-off after the closure of the North Qilian Ocean, and ancient continental materials from the subduction slab metasomatized the overlying lithospheric mantle during exhumation.

Early Cretaceous continent basalts in the Alxa Block, NW China: geochronology, geochemistry, and tectonic implications

ABSTRACT NE Asia has experienced Significant extensional events in the Early Cretaceous, including related volcanic rocks, extensional basins, metamorphic core complexes (MCCs), and low-angle detachment faults. Previous studies primarily focused on the eastern North China Craton (NCC); however, the extensional manifestations in the western NCC are poorly studied and the mechanism is still controversial. This study reports Wuliji volcanic clusters in northern Alxa Block, westmost NCC. Geologic mapping shows that the volcanic cluster is mainly composed of dark grey basalts with interlayered pyroclastic rocks showing columnar joints. The youngest LA-ICP-MS zircon U-Pb age is 103 Ma, consistent with the age constrained by fossils in the interlayered sandstones. Though the Wuliji basalts have amounts of captured zircons, the high MgO, TFe2O3 and low SiO2, along with Nb/U, Nb/Ta, Zr/Hf ratios and positive Nb, Ta anomalies, indicating no contamination of continental crustal materials. These alkaline basalts are characterized by enrichment in light rare earth elements (LREEs) and large ion lithophile elements (LILEs), slightly positive Eu anomalies and no Nb and Ta depletions similar to other volcanic rocks in Alxa Block, implying an affinity with ocean island basalts (OIB). These volcanic rocks could have been derived from the partial melting of spinel lherzolite in an intracontinental rift setting. The basalts in the Alxa Block are slightly younger than basalts in the eastern NCC in the Early Cretaceous. The occurrence of Early Cretaceous basalts and coeval rift basins with various extensional faults in the westmost NCC may have resulted from the eastward movement of mantle materials due to the rollback of the Paleo-Pacific Plate to the east.

Geochronology, geochemistry, and Sr–Nd–Hf isotopes of the Late Permian–Early Triassic granitoids in Eastern Kunlun Orogen, Northwest China: petrogenesis and implications for geodynamic setting

ABSTRACT The Eastern Kunlun Orogenic Belt (EKOB) in Northwest China, is an ideal area for understanding the tectonic evolution of the Palaeo-Tethys Ocean. The EKOB is marked by widespread Palaeozoic to Early Mesozoic magmatism. However, the Late Permian–Early Mesozoic tectonic evolution of the Palaeo-Tethys Ocean tectonic regime is poorly understood. Here, we report new zircon LA-ICP-MS U–Pb dating and geochemical analyses of Late Permian–Early Triassic intrusive rocks in the Xiangyanggouxi and Dageledong areas in the EKOB, Northwest China, to discuss their petrogenesis and geodynamic setting and reconstruct the tectonic evolution of Palaeo-Tethys oceanic tectonic regime. Zircon U-Pb dating results indicate that these granitoids crystallized during ca. 256–248 Ma, i.e. the Late Permian to Early Triassic. These granitoids are mainly comprised of granodiorites and monzonitic granites that possess high concentrations of SiO2 (66.81–75.98 wt.%), K2O+Na2O (6.21–7.92 wt.%), and low contents of MgO, CaO, Cr, Ni, and Mg# (<0.44). They are classified as medium- to high-K calc-alkaline and metaluminous I-type granitoids. These granitoids are rich in light rare earth elements (LREEs) and large ion lithophile elements (LILEs) and are depleted in heavy rare earth elements (HREEs) and high field strength elements (HFSEs) with arc affinity. In addition, combined with the εHf(t) values of −2.4 to +2.4 with two-stage model ages ranging from 1409 Ma to 1027 Ma, and the εNd(t) values from −3.73 to −2.95, it is suggested that the primary magma of these granitoids was derived from the partial melting of the Late Meso–Proterozoic mafic lower crust. These findings, combined with spatio-temporal distributions of regional magmatism, reveal that the Late Permian and Early Triassic granitoids formed in a continental magmatic arc setting related to the northward subduction of the Palaeo-Tethys Ocean plate beneath the EKOB-Qaidam terrane.

Zircon U-Pb-Hf isotopes and geochemistry of Jurassic igneous rocks from the southern Zhangguangcai Range, NE China: constraints on magmatism, petrogenesis and tectonic implications

ABSTRACT In this study, we present new zircon U-Pb and Hf isotope data and geochemical analyses for Jurassic igneous rocks from the southern Zhangguangcai Range, NE China. In the context of our new U/Pb data together with other published data (n = 165), we recognize three major magmatic pulses in the eastern Songnen Block during the Jurassic: earliest Jurassic (200–195 Ma), late Early Jurassic (183–175 Ma) and early Late Jurassic (ca. 163 Ma). According to the petrological classification scheme, rocks are divided into two categories of andesite and I-type granitoids. Generally, Early Jurassic monzogranites have more evolved compositions with SiO2, Al2O3, and K2O+Na2O concentrations of 67–74 wt.%, 13.28–17.04 wt.% and 7.25–9.31 wt.%, respectively than Late Jurassic granodiorite. Early Jurassic andesite has SiO2, Al2O3, Na2O+K2O contents of 54.64–56 wt.%, 17.27–17.44 wt.% and 3.47–4.06 wt.%, respectively with low Mg# values of 0.18–0.26. In addition, all samples show enrichment in light rare earth elements (LREEs) and large-ion lithophile elements (LILEs) but depletion in high strength field elements (HSFEs, such as Nb, Ta, P and Ti) and low Sr/Y and (La/Yb)N ratios, all of which are characteristic of arc-type magmatic signatures. In view of the Hf isotope signatures, these rocks show high initial 176Hf/177Hf ratios (0.282711–0.283069) corresponding to positive εHf(t) values (+0.39 to +13.66) and Neoproterozoic two-stage model ages (1154–550 Ma). In summary, the geochemical results suggest that the primary magmas of Jurassic granitoids were derived from variable degrees of partial melting of juvenile lower crust, whereas Early Jurassic andesite was derived from the partial melting of mantle wedge peridotite metasomatized by hydrous melts from subducting sediments and/or oceanic crust. The Jurassic arc-type magmatism in the eastern Songnen Block indicates that the Mudanjiang oceanic plate was still subducting in the Jurassic.

Late Cretaceous magmatic activity in the southern Lhasa terrane: insights from the Dazhuqu hornblende gabbro and the Xietongmen granite porphyry

ABSTRACTThe mechanisms triggering the emplacement of Cretaceous magmatic rocks related to Neo-Tethyan subduction in the southern Lhasa subterrane (SLT) remain controversial because geochronological, geochemical, and isotopic data from the Cretaceous magmatic rocks in the western portion of the SLT are lacking. This paper provides the first report indicating that the Dazhuqu hornblende gabbro and Xietongmen granite porphyry were generated in the Late Cretaceous (ca. 100 Ma and ca. 68 Ma, respectively) in the western portion of the SLT. The Dazhuqu hornblende gabbro is characterized by high MgO, Na2O, Cr, Co, and Mg# values, enrichment in light rare earth elements (LREEs) and large ion lithophile elements (LILEs), and depletion in high field strength elements with no Eu anomalies. The Xietongmen granite porphyry displays high SiO2, low MgO, Mg#, Cr, Co, and Ni, enrichment in LREEs and LILEs, flat heavy rare earth element (HREE) patterns and negative Eu anomalies. Zircons from the Dazhuqu hornblende gabbro and Xietongmen granite porphyry display high positive εHf(t) ranges from 11.79 to 14.91 and from 9.05 to 12.38, respectively. The Dazhuqu hornblende gabbro was produced by the partial melting of 12–15% garnet peridotite in the depleted mantle that was metasomatized by fluids released from the dehydrating subducted Neo-Tethyan oceanic slab. This magma was then emplaced at an upper crustal depth of 5.3–7.0 km. The Xietongmen granite porphyry was generated by the partial melting of underplated basaltic crust during the subduction of the Neo-Tethyan oceanic crust and formed in the presence of pyroxene, plagioclase, and minor hornblende in its magmatic source. In combination with previously published data from Cretaceous magmatic rocks in the SLT, our data suggest that the petrogenesis of the Dazhuqu hornblende gabbro was related to flat or low-angle slab subduction of the Neo-Tethyan oceanic crust during 109–97 Ma and that the formation of the Xietongmen granite porphyry was related to lithospheric delamination in the western portion of the SLT after ca. 68 Ma.

Volatile and light lithophile elements in high-anorthite plagioclase-hosted melt inclusions from Iceland

Melt inclusions formed during the early stages of magmatic evolution trap primitive melt compositions and enable the volatile contents of primary melts and the mantle to be estimated. However, the syn- and post-entrapment behaviour of volatiles in primitive high-anorthite plagioclase-hosted melt inclusions from oceanic basalts remains poorly constrained. To address this deficit, we present volatile and light lithophile element analyses from a well-characterised suite of nine matrix glasses and 102 melt inclusions from the 10ka Grímsvötn tephra series (i.e., Saksunarvatn ash) of Iceland’s Eastern Volcanic Zone (EVZ). High matrix glass H2O and S contents indicate that eruption-related exsolution was arrested by quenching in a phreatomagmatic setting; Li, B, F and Cl did not exsolve during eruption. The almost uniformly low CO2 content of plagioclase-hosted melt inclusions cannot be explained by either shallow entrapment or the sequestration of CO2 into shrinkage bubbles, suggesting that inclusion CO2 contents were controlled by decrepitation instead. High H2O/Ce values in primitive plagioclase-hosted inclusions (182–823) generally exceed values expected for EVZ primary melts (∼180), and can be accounted for by diffusive H2O gain following the entrainment of primitive macrocrysts into evolved and H2O-rich melts a few days before eruption. A strong positive correlation between H2O and Li in plagioclase-hosted inclusions suggests that diffusive Li gain may also have occurred. Extreme F enrichments in primitive plagioclase-hosted inclusions (F/Nd=51–216 versus ∼15 in matrix glasses) possibly reflect the entrapment of inclusions from high-Al/(Al+Si) melt pools formed by dissolution-crystallisation processes (as indicated by HFSE depletions in some inclusions), and into which F was concentrated by uphill diffusion since F is highly soluble in Al-rich melts. The high S/Dy of primitive inclusions (∼300) indicates that primary melts were S-rich in comparison with most oceanic basalts. Cl and B are unfractionated from similarly compatible trace elements, and preserve records of primary melt heterogeneity. Although primitive plagioclase-hosted melt inclusions from the 10ka Grímsvötn tephra series record few primary signals in their volatile contents, they nevertheless record information about crustal magma processing that is not captured in olivine-hosted melt inclusions suites.

Lithium isotopes and light lithophile element abundances in shergottites: Evidence for both magmatic degassing and subsolidus diffusion

AbstractDegassed magmatic water was potentially the major source of surficial water on Mars. We measured Li, B, and Be abundances and Li isotope profiles in pyroxenes, olivines, and maskelynite from four compositionally different shergottites—Shergotty, QUE 94201, LAR 06319, and Tissint—using secondary ion mass spectrometry (SIMS). All three light lithophile elements (LLE) are incompatible: Li and B are soluble in H2O‐rich fluids, whereas Be is insoluble. In the analyzed shergottites, Li concentration decreases and Be concentration increases from cores to rims in pyroxenes. However, B concentrations do not vary consistently with Li and Be abundances, except in QUE 94201 pyroxenes. Additionally, abundances of these three elements in olivines show a normal igneous‐fractionation trend consistent with the crystallization of olivine before magma ascent and degassing. We expect that kinetic effects would lead to fractionation of 6Li in the vapor phase compared to 7Li during degassing. The Li isotope profiles, with increasing δ7Li from cores to rims, as well as Li and B profiles indicate possible degassing of hydrous fluids only for the depleted shergottite QUE 94201, as also supported by degassing models. Conversely, Shergotty, LAR 06319, and Tissint appear to have been affected by postcrystallization diffusion, based on their LLE and Li isotope profiles, accompanied by diffusion models. This process may represent an overlay on a degassing pattern. The LLE profiles and isotope profiles in QUE 94201 support the hypothesis that degassing of some basaltic shergottite magmas provided water to the Martian surface, although evidence may be obscured by subsolidus diffusion processes.

Partitioning of light lithophile elements during basalt eruptions on Earth and application to Martian shergottites

An enigmatic record of light lithophile element (LLE) zoning in pyroxenes in basaltic shergottite meteorites, whereby LLE concentrations decrease dramatically from the cores to the rims, has been interpreted as being due to partitioning of LLE into a hydrous vapor during magma ascent to the surface on Mars. These trends are used as evidence that Martian basaltic melts are water-rich (McSween et al., 2001). Lithium and boron are light lithophile elements (LLE) that partition into volcanic minerals and into vapor from silicate melts, making them potential tracers of degassing processes during magma ascent to the surface of Earth and of other planets. While LLE degassing behavior is relatively well understood for silica-rich melts, where water and LLE concentrations are relatively high, very little data exists for LLE abundance, heterogeneity and degassing in basaltic melts. The lack of data hampers interpretation of the trends in the shergottite meteorites. Through a geochemical study of LLE, volatile and trace elements in olivine-hosted melt inclusions from Kilauea Volcano, Hawaii, it can be demonstrated that lithium behaves similarly to the light to middle rare Earth elements during melting, magma mixing and fractionation. Considerable heterogeneity in lithium and boron is inherited from mantle-derived primary melts, which is dominant over the fractionation and degassing signal. Lithium and boron are only very weakly volatile in basaltic melt erupted from Kilauea Volcano, with vapor-melt partition coefficients <0.1. Degassing of LLE is further inhibited at high temperatures. Pyroxene and associated melt inclusion LLE concentrations from a range of volcanoes are used to quantify lithium pyroxene-melt partition coefficients, which correlate negatively with melt H2O content, ranging from 0.13 at low water contents to <0.08 at H2O contents >4 wt%. The observed terrestrial LLE partitioning behavior is extrapolated to Martian primitive melts through modeling. The zoning observed in the shergottite pyroxenes is only consistent with degassing of LLE from a Martian melt near its liquidus temperature if the vapor-melt partition coefficient was an order of magnitude larger than observed on Earth. The range in LLE and trace elements observed in shergottite pyroxenes are instead consistent with concurrent mixing and fractionation of heterogeneous melts from the mantle.

Pre- and syn-eruptive degassing and crystallisation processes of the 2010 and 2006 eruptions of Merapi volcano, Indonesia

The 2010 eruption of Merapi (VEI 4) was the volcano’s largest since 1872. In contrast to the prolonged and effusive dome-forming eruptions typical of Merapi’s recent activity, the 2010 eruption began explosively, before a new dome was rapidly emplaced. This new dome was subsequently destroyed by explosions, generating pyroclastic density currents (PDCs), predominantly consisting of dark coloured, dense blocks of basaltic andesite dome lava. A shift towards open-vent conditions in the later stages of the eruption culminated in multiple explosions and the generation of PDCs with conspicuous grey scoria and white pumice clasts resulting from sub-plinian convective column collapse. This paper presents geochemical data for melt inclusions and their clinopyroxene hosts extracted from dense dome lava, grey scoria and white pumice generated during the peak of the 2010 eruption. These are compared with clinopyroxene-hosted melt inclusions from scoriaceous dome fragments from the prolonged dome-forming 2006 eruption, to elucidate any relationship between pre-eruptive degassing and crystallisation processes and eruptive style. Secondary ion mass spectrometry analysis of volatiles (H2O, CO2) and light lithophile elements (Li, B, Be) is augmented by electron microprobe analysis of major elements and volatiles (Cl, S, F) in melt inclusions and groundmass glass. Geobarometric analysis shows that the clinopyroxene phenocrysts crystallised at depths of up to 20 km, with the greatest calculated depths associated with phenocrysts from the white pumice. Based on their volatile contents, melt inclusions have re-equilibrated during shallower storage and/or ascent, at depths of ~0.6–9.7 km, where the Merapi magma system is interpreted to be highly interconnected and not formed of discrete magma reservoirs. Melt inclusions enriched in Li show uniform “buffered” Cl concentrations, indicating the presence of an exsolved brine phase. Boron-enriched inclusions also support the presence of a brine phase, which helped to stabilise B in the melt. Calculations based on S concentrations in melt inclusions and groundmass glass require a degassing melt volume of 0.36 km3 in order to produce the mass of SO2 emitted during the 2010 eruption. This volume is approximately an order of magnitude higher than the erupted magma (DRE) volume. The transition between the contrasting eruptive styles in 2010 and 2006 is linked to changes in magmatic flux and changes in degassing style, with the explosive activity in 2010 driven by an influx of deep magma, which overwhelmed the shallower magma system and ascended rapidly, accompanied by closed-system degassing.

Multi-methodological investigation of kunzite, hiddenite, alexandrite, elbaite and topaz, based on laser-induced breakdown spectroscopy and conventional analytical techniques for supporting mineralogical characterization

Gem-quality alexandrite, hiddenite and kunzite, elbaite and topaz minerals were characterized through a multi-methodological investigation based on EMPA-WDS, LA-ICP-MS, and laser-induced breakdown spectroscopy (LIBS). With respect to the others, the latter technique enables a simultaneous multi-elemental composition without any sample preparation and the detection of light elements, such as Li, Be and B. The criteria for the choice of minerals were: (a) the presence of chromophore elements in minor contents and/or as traces; (b) the presence of light lithophile elements (Li, Be and B); (c) different crystal chemistry complexity. The results show that LIBS can be employed in mineralogical studies for the identification and characterization of minerals, and as a fast screening method to determine the chemical composition, including the chromophore and light lithophile elements.

Petrogenesis of the Bao'anzhai granite and associated Mo mineralization, western Dabie orogen, east-central China: Constraints from zircon U–Pb and molybdenite Re–Os dating, whole-rock geochemistry, and Sr–Nd–Pb–Hf isotopes

Recently, many Mo deposits genetically related to emplacement of Early Cretaceous granites have been found in the Dabie–Qinling belt. A typical intrusion that combines magmatism and metallogenesis, the Bao'anzhai granite, yields a zircon 238U–206Pb age of 123.2 ± 1.1 Ma and a molybdenite Re–Os isochron age of 122.5 ± 2.7 Ma. This granite is characterized by high silica and alkali, but low Mg, Fe, and Ca. It is enriched with light rare earth elements (REEs) and large-ion lithophile elements (LILEs, Rb, K, Th, U) but depleted of heavy REEs, high field strength elements (HFSEs, Nb, Ta, Ti, and Y), and Sr. This high-K granite has medium initial 87Sr/86Sr ratios (0.706518–0.707116) and low initial Pb isotopic ratios [(206Pb/204Pb)i, 16.423–16.699; (207Pb/204Pb)i, 15.285–15.345; (208Pb/204Pb)i, 37.335–37.633], and is characterized by low ϵNd(t) and ϵHf(t) values (−14.92 to −14.22 and −21.67 to −19.19, respectively). These data indicate that this pluton is a high-K calc-alkaline fractionated I-type granitite. It was generated by partial melting of the Yangtze lower crust, which is probably similar to Neoproterozoic TTG-like magmatic rocks at the north Yangtze Block under a non-thickened lower crust environment (<35 km). The ores also have low radiogenic Pb isotopes (206Pb/204Pb, 16.592–17.674; 207Pb/204Pb, 15.300–15.476; 208Pb/204Pb, 37.419–37.911) and low Re content in molybdenite (5.693–10.970 ppm), suggesting a crustal magmatic source for the metallogenic minerals in the Mo deposit.

Sr-rich apatite from the Dangzishan leucitite-ijolite xenoliths (Heilongjiang Province): Mineralogy and mantle-fluid metasomatism

Abundant apatite grains with elevated SrO content were found in leucitite-ijolite xenoliths in the Dangzi Mountain, Heilongjiang Province. Morphological and mineralogical associations, and compositional analysis of the Sr-rich apatite, were carried out using an electron microprobe. Two principal types of apatite were distinguished. One type occurs as short-prismatic crystals with Sr-rich rims, while another type with acicular or finely columnar shapes constitutes Sr-rich apatite element maps and systematic quantitative analysis of apatite revealed great variations in SrO content (0.42%–26.79%). The calculated structural formula of the measured Sr-rich apatite is: (Ca3.15–4.963Sr0.019–1.510Ba0.00–0.030Na0.006–0.108REE0.106–0.153) (P2.84–3.028Si0.009–0.094)O12(F0.675–1.079, Cl0.000–0.256, OH0.084–0.297). Mineralogical textures of apatite implied a replacement mechanism for the Sr-rich apatite. Sr-rich rims of apatite are suggested to have formed after metasomatism (isomorphic replacement) of early fluorapatite in a Sr-, light rare-earth elements (LREE), lithophile light elements (LILE)- and volatile-rich residual melt during late magmatism. However, the acicular apatite probably directly crystallized from a Sr-rich residual melt. The Sr-Nd isotopic composition of the apatite was distinctive from that of leucitite-ijolite and its host rock. These differences, combined with mineralogical features of apatite, imply that Sr-LREE-LILE-volatile-rich components in the residual melt were derived from deep in the asthenosphere, and subsequently were enriched at a late stage in magma evolution.

Trace and rare-earth element behaviors during alteration and mineralization in the Attepe iron deposits (Feke-Adana, southern Turkey)

Hydrothermal-metasomatic iron ores consisting mainly of siderite, ankerite and hematite are located in the Lower–Middle Cambrian limestone marbles of the Eastern Taurus Belt. The siderite, ankerite, hematite and host rock samples from the deposits have been investigated for major, trace, and rare-earth elements (REE) to evaluate the element mobility and mass transfer during fluid–rock interactions. Geochemical data show that the (Fe + Mn) concentrations regularly increase, and the (Ca + Mg + TC) contents progressively decrease from the host rock through ankerite, siderite, and hematite ores with increasing chemical index of metasomatism (CIM) values. The host limestone exhibits a pronounced positive Eu anomaly (2 to 3.45) and negative Ce anomalies (0.59 to 0.96). This limestone has much lower REE contents (3.92 ppm) than the Post-Archean Australian Shale (PAAS, 184.77 ppm). The elements of Cr, Y, Tb, Ho, and Lu are immobile and effectively conserved during hydrothermal processes. Compared with the host rock (precursor rock), the altered (ankerite) and mineralized rocks (siderite and hematite) were enriched in Fe, Mn, Ba and depleted in Ca, Mg, Si, Al, K, Na, Ti, and P during alteration and mineralization. The average REE contents of the ore samples (9.13 to 12.01 ppm, mean = 10.44 ppm) are higher than those of the host rock (3.92 ppm), but significantly lower than in the PAAS. Most of the REE were mobilized and fractionated during the hydrothermal processes that may have resulted mainly from low Eh and pH, plentiful complexing ligands, variable high temperature, changing ionic radius of REE and composition of the mineralizing fluids. The middle rare-earth elements (MREE) show diverse behaviors in different sample groups. The light rare-earth elements (LREE) were strongly leached out of the system, and the heavy rare-earth elements (HREE) were preferentially retained as REE-Cl and/or –SO 4 complexes. The (La/Lu) N ratios show a decreasing trend from the host rock to siderite, ankerite, and hematite with increasing HREE and decreasing LREE contents. The ore samples show pronounced positive Eu (1.61 to 8.86) anomalies and weak to moderate negative Ce anomalies (0.34 and 0.98). Three samples display slightly positive Ce (1.06–1.09) anomalies. In the ore samples, the high field strength elements (HFSE) such as Ti, Zr, and P were depleted, as were the light lithophile (LIL, e.g., K, Th, U, Pb, La, and Ce) and trans-transition (TRT, e.g., Cu, Ni, and Zn) elements. The Ba and Sr demonstrate dissimilar behavior during the fluid–rock interaction. Ba was enriched, while Sr was depleted.

An investigation of trace and isotope light elements in mineral phases from well RN-17 (Reykjanes Peninsula, SW Iceland)

The light lithophile (Li, Be and B) and halogen (F, Cl) elements are powerful tracers of fluid transfer due to their mobility during high temperature hydrothermal processes and metamorphic devolatilisation. Moreover, although a great deal of studies have been carried out on these elements in whole rock and minerals of altered rocks from divergent and convergent plate margins, an inventory for mineral phases from the altered Icelandic oceanic crust is still incomplete.In the present paper we report the results of in situ EPMA and SIMS investigations on variously altered magmatic (plagioclase and clinopyroxene) and hydrothermal phases (amphibole and epidote) from selected cuttings drilled at different depths (400 – 3000 m) of the well RN-17, Reykjanes geothermal system (SW Iceland). Our study has benefited from the use of high-magnification SEM investigations; from ICP-MS on Li, P-TIMS determinations of boron isotope composition (δ11B) and ID analyses of B contents on the whole rock.Particularly, SIMS data on epidote have shown that alteration beneath Reykjanes has been more efficient in the shallow and intermediate cuttings, while whole rock data on boron isotope composition have revealed that the alteration has been caused firstly by δ11B-poor fluids and successively by δ11B-rich seawater-hydrothermal fluids.

Late Neoproterozoic passive margin of East Gondwana: Geochemical constraints from the Anakie Inlier, central Queensland, Australia

Development of the East Gondwana passive margin and when it occurred are constrained by the composition of low-grade mafic schists and U–Pb ages of detrital zircons in psammitic schists from the Bathampton Metamorphics in the Anakie Inlier of central Queensland. These rocks show considerable variation in light lithophile elements due to post-magmatic processes. They have flat heavy rare earth element patterns, low-TiO 2 (<2 wt.%) contents and their immobile element Ti, V, Y, La, Nb, Th and Zr values, indicate that they have an N-MORB-like magmatic affinity. However, they differ from N-MORB in that they show light rare earth depleted patterns and lower incompatible trace element contents. Their relative low abundance and association with metasediments suggest they formed in a magma-poor rifted margin setting. They are associated with psammitic rocks with detrital zircon ages indicating probable deposition in the late Neoproterozoic at ca 600 Ma. A magma-poor rifted margin in northeastern Australia differs from the volcanic passive setting that occurred in southeastern Australia at this time. These findings support development of the East Gondwana margin at 600 Ma that may have been related to rifting of a microcontinent off East Gondwana well after the breakup of Rodinia at ca 750 Ma.

A SIMS study of lithium, boron and chlorine in basalts from Reykjanes (southwestern Iceland)

Iceland is one of the few places on earth where it is possible to study on land the effects of hydrothermal alteration on basaltic rocks from oceanic crust. In this frame, we have carried out a micro-analytic study on determining the concentrations of some of the so-called hydrothermal markers, such as the light lithophile (Li, B) and halogen (Cl) elements. They were investigated by the ion microprobe on magmatic phases (plagioclase and clinopyroxene) in three drill-cutting samples, selected on the basis of different depths (400–3000 m), in one unaltered lava from the well RN-17, and one core sample (dolerite dyke) from well RN-19, all of them located within the Reykjanes geothermal fields in SW Iceland. Additionally, B and Li on whole rock were then utilized to better constrain the hydrothermal processes. Whole rock Li and B data have shown that the samples investigated were affected mainly by seawater hydrothermal alteration. On the contrary, the discrepancy between the B concentrations in the whole rock and mineral phases (plagioclase and clinopyroxene) as well as that for Cl between single minerals could be ascribed to the occurrence of secondary phases (such as epidote and amphibole) related to hydrothermal alteration, along with the effects of fluid circulation in fracture zones.