Enriched Sr Research Articles

Petrogenesis of Jurassic granitic plutons in Liaodong Peninsula, NE China: Insights into the subduction of Paleo − Pacific plate

• Jurassic granites in Liaodong Peninsula formed at 184–179 and 162–151 Ma. • Granite geochemistry reveals the thinning of continental crust from Early to Late Jurassic . • The granites constrain the subduction history of the Paleo–Pacific plate. There is a debate about the subduction of Paleo − Pacific plate in the Jurassic tectonic evolution of the northeastern North China Craton. Here we present new geochronological and geochemical investigations for Early and Late Jurassic granites on Liaodong Peninsula. The Early Jurassic granites (184–179 Ma) show high SiO 2 and low MgO contents, and are classified as I − type granites, with enrichment in large − ion lithophile elements (LILEs) and light rare earth elements (LREEs) and depletion in high − field − strength elements (HFSEs) and heavy REEs (HREEs), and enriched Sr − Nd − Hf − O isotopic compositions. Combined with their typical adakitic properties as high Sr, low Y and Yb contents, and high Sr/Y ratios, we conclude that they originated from thickened lower crust. The spatio − temporal distribution of Early Jurassic intrusive and volcanic rocks and large scale of compressive deformation suggest the onset of flat subduction of Paleo − Pacific plate. In contrast, the Late Jurassic granites (162–151 Ma) are classified as I − type granites, with enrichment in LILEs and LREEs and depletion in HFSEs and HREEs and more enriched Sr − Nd − Hf − O isotopic compositions. Based on Sr and Y contents and Sr/Y ratios, we divided them into two groups. Group 1 show high SiO 2 and low MgO contents and typical adakitic properties, indicating an origin of thickened lower crust. In contrast, group 2 show relatively higher SiO 2 and lower MgO contents, with low Sr and high Y contents and high Nb/U ratios, suggesting an origin of lower crust in normal thickness. The spatio − temporal distribution of Late Jurassic bimodal igneous rocks and continuous volcanic and sedimentary deposition as well as the shifted accretionary complexes, indicate the oblique subduction of Paleo − Pacific plate.

Response of trace elements to partial melting of felsic crust at high to ultrahigh temperatures: Implications for granite geochemistry

It is known that partial melting and melt extraction of crustal rocks result in chemical differentiation of the continental crust. But it is unknown how these two processes have affected the composition of granites due to a limited knowledge of trace element behaviors during crustal anatexis. In order to quantify this issue, a combined study of whole-rock and mineral trace elements and mineral modal proportions was conducted for high-temperature (HT) to ultrahigh-temperature (UHT) felsic granulites from the Tongbai orogen in central China. Reconstruction of LREE budgets suggests that LREE mainly reside in monazite in both HT and UHT granulites. As monazite is predicted to be not stable at UHT conditions in the modelling of previous studies, the presence of monazite in the Tongbai UHT granulites suggest that it was not sufficiently dissolved into anatectic melts. Considering monazite mainly occurs as interstitial grains, fast melt-residue separation may be the dominant factor for impeding its dissolution. Calculation of mineral/mineral trace element ratios indicates that K-feldspar has a higher capacity to accommodate Ba and Sr than biotite and plagioclase, with DBaK-feldspar/biotite of 2.5–3.0 and DSrK-feldspar/plagioclase values of 1.4–1.9, and ilmenite can preserve more Nb and Ta than biotite with DNbbiotite/ilmenite values of 0.07–0.1 and DTabiotite/ilmenite values of 0.04–0.05. In addition, partitioning of first row transition elements (FRTE) was constrained in the felsic granulites, with preference of Sc into garnet, and Co, V, Ni, and Cr into biotite. Modelling based on the presently constrained partition coefficients indicates that trace elements show consistent differentiation trends during anatexis of various felsic rocks, with enrichment of Sr, Ba, Nb, Ta and FRTE but depletion of Rb in anatectic restites. The high DNb/Ta values of biotite and ilmenite cause the residues produced by biotite dehydration melting to be commonly of higher Nb/Ta ratios than protoliths, indicating that the residues are potentially high Nb/Ta reservoirs. In contrast, the change of peritectic minerals due to various protolith compositions and melting conditions results in differential responses of Sr, Ba, and FRTE to partial melting, suggesting that these elements may be useful indicators to trace the petrogenetic process of granites. The correlation between Ba and Sc contents or between Sr/Ba and Sc/Co ratios is demonstrated to be a valid index in discriminating melts from metagreywackes and metapelites due to different modes of garnet, orthopyroxene, and K-feldspar in their anatectic residues. Moreover, as the proportions of garnet and orthopyroxene in the residues are significantly influenced by melting pressures, the Sc/Co ratio and Sc content of granites can be used to trace their anatectic depth.

Geochemistry of arc alkaline magmatism of Java Island, Sunda Arc: a statistical review

Alkaline magmatism develops in the rear arc area of Java, Sunda Arc, at different range of slab depth; ~270-580 km in central section and ~150 km in the east. We collate published geochemical data of volcanic rocks from four alkaline volcanoes (Muria, Lasem, Bawean, and Ringgit-Beser) and perform statistical analysis to evaluate geochemical characteristics of each suite. A set of major and trace elements is scaled and transformed using principal component analysis (PCA) and then followed by implementation of k-means algorithm to cluster the data points based on Euclidian distances. K-means clustering of the dataset suggests that Central Java alkalines are most elevated in K2O and total alkali. The algorithm further suggests that Muria samples can be clustered into two, owing to these components. These two clusters, however, are not well reflected on trace element-based clustering. Lasem volcanics show distinct cluster high in Na2O/K2O and SiO2, while Bawean samples are mixed into both Muria clusters. Ringgit-Beser alkalines show two distinct clusters tied to MgO and enrichment in Ba, Rb, and Sr. Our findings suggest that the potassium and LILE enrichment in these alkaline rocks is independent of slab depth and is most likely regulated by tectonic-related arc segmentation in Java subduction zone.

Late Jurassic Wenjiaping high Sr/Y granite: A product of partial melting of the Precambrian basement rocks trigged by lithospheric extension in the Songpan–Garzê fold belt, SW China

The Wenjiaping granite, as one of the few Late Jurassic granites in the Songpan–Garzê fold belt (SGFB), can provide an important clue for comprehensively recognizing the tectonic evolution and mineralization of this belt. In this contribution, we present new age and geochemical data for this pluton to better constrain its petrogenesis and discuss the tectonic and metallogenic implications. LA‐ICP‐MS zircon U–Pb dating shows that the Wenjiaping pluton was emplaced at ~159 Ma. The granite contains minor amphibole, and exhibits slightly peraluminous characteristics (A/CNK = 1.03–1.10) and lower initial Sr–Pb isotope ratios than those of the Liwu Group, which excludes the possibility that the Wenjiaping granite was derived from partial melting of the metasedimentary rock‐dominated Liwu Group as previously suggested. Significantly, high Sr/Y (40.93–54.30), LaN/YbN (39.64–56.64), and K2O/NaO (0.77–1.11) ratios, low MgO (0.47%–0.86%) and Cr (25.1–41.3 ppm) contents, and relatively enriched Sr–Nd–Pb–Hf isotope compositions of the Wenjiaping granite are comparable to those of the Late Triassic adakitic rocks in the SGFB, indicating that they probably share a similar source. Combined with previous researches, we propose that large‐scale detachment of the Jianglang dome caused by post‐collisional lithospheric extension in the SGFB‐induced decompressional partial melting of the Precambrian basement rocks can account for the generation of the Late Jurassic Wenjiaping pluton. In addition, our results also suggest that the Wenjiaping pluton probably cannot supply abundant metal elements for the Liwu‐type Cu‐polymetallic deposits in the Jianglang dome, SGFB.

Geochemistry, Zircon U–Pb Ages, and Hf Isotopes of the Devonian Mafic and Acidic Dykes of the Jinba Gold Deposit, NW China: Petrogenesis and Tectonic Implications

The Jinba deposit is an orogenic gold deposit located in the Markakuli shear zone, in the southern part of the Altay orogenic belt, northwestern China. Several granite and diorite dykes are present in the area of the mine, with ore bodies occurring in the diorite dykes. However, the diagenetic age, genesis, and evolution of these magmas, and the tectonic setting of the dyke emplacement process, remain unclear. The present study is based on a detailed geological survey, zircon U–Pb dating, Lu–Hf isotopes, and geochemical analysis of the granitic and diorite dykes. The crystallization ages of the granitic and diorite dykes are 384.5 ± 1.2 Ma and 393.9 ± 3.5 Ma, respectively, which indicates formation in the Early to Middle Devonian. Zircon εHf(t) values of the granitic and diorite dykes are 1.43 to 5.2 and −4.47 to −1.18, respectively, with a corresponding two-stage model of depleted mantle (TDM2) ages of 1046 to 1285 Ma and 1242 to 2623 Ma, respectively. This indicates that the granitic and diorite dykes were formed by the mixing of mantle magma and crustal materials to varying degrees, and diorite dykes are more obviously contaminated by the lower crust. Geochemical analysis shows that the granite dykes have a high SiO2 (72.51%–74.87%) and moderate Al2O3 (12.88%–14.04%) content, a total alkali of (K2O + Na2O = 5.51%–6.44%), and aluminous (A/CNK = 1.0–1.02). Granite dykes are enriched in LREE and Th, U, and Pb, and depleted in P, Sr, and Nb elements, with clear Eu negative anomalies (δEu = 0.62~0.66). The SiO2 content of diorite dykes is 51.48%–53.71%, Al2O3 contents are high (14.70%–15.99%), K2O is 1.94%–2.54%, Na2O is 2.97%–3.96%, MgO contents are high (5.15%–6.46%), and TFe2O3 is (13.42%–15.13%), enriched Sr, U, Pb, deficient Th elements, rare earth fractionation is not obvious, and Eu anomaly is not obvious (δEu = 0.93~1.1). We conclude that the Early to Middle Devonian magmatism in the southern margin of Altay (which corresponds to the Jinba gold deposit) may have formed in an island arc-related subduction environment.

Geochronology, geochemistry and Sr–Nd–Pb–Hf isotopes of the alkaline–carbonatite complex in the Weishan REE deposit, Luxi Block: Constraints on the genesis and tectonic setting of the REE mineralization

The Weishan rare earth element (REE) deposit at the southeastern margin of the North China Craton (NCC) is one of the three largest carbonatite-associated REE deposits (CARDs) in China. The REE-bearing carbonatite veins formed within quartz syenite and were controlled by NW- and NE-trending faults. The laser ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS) U–Pb ages of zircons from the quartz syenite and postmineralization granite porphyry dyke samples of the Weishan REE deposit yield weighted mean 206Pb/238U ages of 124.6 ± 1.5 Ma (n = 10, mean squared weighted deviation (MSWD) = 1.7) and 123.3 ± 1 Ma (n = 13, MSWD = 1.7), respectively. The quartz syenite and REE-bearing carbonatite in the Weishan REE deposit have similar Sr–Nd–Pb isotope compositions, and their diagenetic and metallogenetic ages are the same within error, indicating that they have a very close genetic relationship and originate from identical material sources. The Sr–Nd–Pb–Hf isotope compositions of both the quartz syenite and REE-bearing carbonatite are within the range of those of the Mesozoic isotopically enriched subcontinental lithospheric mantle (SCLM) beneath the southeastern margin of the NCC. The Weishan REE-bearing carbonatite is extremely enriched in REEs, Sr, and Ba and has a high Ba/Th ratio. A positive correlation between the REE and Ba contents and a negative correlation between the REE content and Sr/Ba ratio are observed in the Weishan carbonatite, indicating that the excessive enrichment of Sr, Ba, and REEs in the Weishan REE deposit might be related to the involvement of CO2-rich fluids from recycled marine sediments. Taking previous results on the Mesozoic tectonic evolution of the NCC into consideration, we infer that the parent metallogenic magma of the Weishan REE deposit formed by the partial melting of the REE-refertilized and isotopically enriched SCLM, which had been previously metasomatized by melts derived from the subducted South China Block (SCB) during continental collision and by high-flux REE- and CO2-rich fluids derived from subducted marine sediments and oceanic crust during the subduction of the Paleo-Pacific Plate.

Hydrochemical Characteristics and Formation Mechanism of Strontium-Rich Groundwater in Tianjiazhai, Fugu, China

Strontium-rich groundwater exists in the underlying carbonate rocks of the Tianjiazhai Shimachuan River basin, Fugu, China. In this study, the hydrochemical characteristics and formation mechanisms of Sr-rich groundwater were assessed using mathematical statistics and traditional water chemistry, combining geological and hydrogeological conditions, as well as hydrogeochemical theory. The results showed that the Sr2+ content range in Sr-rich groundwater was 0.85~2.99 mg·L−1, which is weakly alkaline fresh water. HCO3− Ca·Mg·Na was the main facies type of Sr-rich groundwater. Sr-rich groundwater has relatively stable contents of chemical elements. The water–rock interaction was the main factor controlling the hydrochemical characteristics of Sr-rich groundwater, particularly carbonate dissolution, influenced by some degree of cation exchange. The Sr element in groundwater mainly comes from the dissolution of the sandstone of the Yanchang Formation. The higher the degree of weathering and the longer the water–rock reaction time, the more favorable the dissolution and enrichment of Sr in groundwater. Moreover, the large weathering thickness and fracture development of the rocks in the Tianjiazhai area provide favorable conditions for the formation of Sr-rich groundwater. The results of this study provide a scientific basis for developing effective policies to protect Sr-rich groundwater resources.

Generation of REE-rich syenite-(carbonatite) complex through lithosphere-asthenosphere interaction: An in-situ Sr–Nd–O isotopic study of the Mesozoic Weishan pluton, Northern China

Carbonatite-alkaline complexes are commonly derived from the mantle. However, whether the source is lithospheric or asthenospheric mantle remains debated. In order to better understand this issue, this paper conducts a Sr-Nd-O isotopic study on the Early Cretaceous, Weishan REE-rich syenite-(carbonatite) complex, Northern China. Two types of apatite are identified from the Weishan complex, namely magmatic and xenocrystic apatite. In-situ Sr-Nd isotopic analyses on magmatic apatite yielded (87Sr/86Sr)i from 0.70690 to 0.70719, and εNd(t) from −7.6 to −8.8. The pristine calcite from carbonatite has similar (87Sr/86Sr)i (0.70727–0.70739) with magmatic apatite. In-situ oxygen isotopic analyses on zircon yielded δ18OVSMOW(‰) from 5.9 to 6.7 ‰. Previous studies reveal that coeval, mantle lithosphere-derived rocks in the region have more enriched Sr (87Sr/86Sri greater than 0.709) and Nd [εNd(t) 〈 −1 2] isotopes than the Weishan complex; whereas the asthenosphere-derived rocks in the region are characterized by depleted Sr-Nd isotopes (87Sr/86Sri < 0.706; εNd(t) greater than 0) and low δ18OVSMOW values (mostly < 5.4 ‰). It is well known that Northern China experienced destruction in the Early Mesozoic, which was accompanied with asthenosphere upwelling along trans-lithosphere faults. Considering that the Weishan complex locates adjacent to the trans-lithosphere Tanlu fault, generation of the complex may be related to asthenosphere-lithosphere interaction. Notably, the Weishan complex differs from coeval REE-barren carbonatites in that its source involved asthenosphere-derived components; hence, involvement of asthenosphere-derived components may be important for the formation of such a REE-rich complex. In general, this study highlights the importance of lithosphere-asthenosphere interaction in supplying necessary heat and materials for the generation of the Weishan complex.

Mineralogy, geochemistry, and 40Ar/39Ar dating of hornblendite/amphibolite pods in Penjween Ophiolite of northeastern Iraq: Implications for petrogenesis and tectonics

Penjween ophiolite is one of the ophiolitic complexes of northeastern Iraq. The serpentinites within the Penjween Ophiolite hosts many pods of hornblendite and amphibolite, and dikes of diorite among many other igneous bodies. These pods have very sharp contacts with the surrounding mantle serpentinized harzburgites. The hornblendites and amphibolites are usually intimately intergrown together as extremely hard, dark green to black colored, fine-to medium-grained pods with ∼2 x ∼2 x ∼(0.5–1) m dimensions. This study presents petrography, mineral chemistry, whole-rock major and trace element geochemistry, and electron probe microanalyses (EPMA) for the major minerals in the studied rocks. The hornblendite is composed entirely of amphiboles (>99% vol.), meanwhile the amphibolite consists of comparable amounts of amphibole and plagioclase which occasionally occurs as layered rocks with banded texture. The diorite dikes are white in color and consist dominantly of coarse-grained plagioclase and less amphiboles. The amphiboles of these rocks belong to pargasite (Mg# 0.69–0.77) ─ edenite (Mg# 0.74–0.79) endmembers where pargasite is by far the predominant mineral; meanwhile the plagioclase is albite (Ab93.4An6.4Or0.2). The amphiboles are replacement products of pyroxenes indicated from the relict pyroxene within their crystals. The amphiboles are abnormally rich in various dust-like inclusions of transparent minerals like REE-rich epidote, rutile, zircon, apatite, titanite, and ore minerals like ilmenite, and pyrrhotite, oriented along the crystallographic axes and form distinct zones in the core of amphibole crystals. The geochemical characteristics of the studied hornblendite (MgO = 13.07%, Ni = 260 ppm, Mg# = 66.57) as well as the high Sc (33 ppm) and V (254 ppm) concentrations are collectively consistent with a mantle-derived, igneous origin. The primitive-mantle normalized trace elements spidergram showed enrichment (hump) in Ba, Th, U, La, Ce, Pb, and Sr, and depletion (trough) in Nb, Ta, K, and Ti. The chondrite-normalized REE diagram showed enrichment of LREE relative to HREE, indicated from the smooth and steady decrease in the negative slope from LREE towards HREE with a negligible Eu-anomaly. Various tectonic discriminating diagrams showed that the studied hornblendite, amphibolite pods and diorite dikes are of igneous fore-arc origin, formed from calc-alkaline and/or tholeiitic magma within an active continental margin setting. The 40Ar/39Ar laser age of hornblendite is late Paleocene (Thanetian) (57.8 ± 5.1 Ma) which might represent an event during the obduction between the oceanic fore-arc Island and the Arabian Plate during the Late Cretaceous/Paleocene period.

Geochronology and geochemistry of 2.3 Ga mafic intrusions in the Dengfeng area: Evidence for early Paleoproterozoic subduction in the southern North China Craton

The time of 2.45–2.2 Ga in the early Paleoproterozoic era is called as ‘Quiet Interval’ because of the decreased magmatic activity worldwide. However, tectonic evolution of old continents during this time interval is still in dispute due to the rare geological records, especially for magmatism. In the southern North China Craton (NCC), the Jingwan mafic intrusions intruded into the Songshan Group and its zircon U-Pb dating yielded a weighted mean 207Pb/206Pb age of 2301 ± 16 Ma, and thus they are the only ca. 2.3 Ga mafic magmatic records founded in this region. These diabases belong to low-K tholeiitic series with relatively low K2O (0.1–0.7 wt%) and total alkalis (Na2O + K2O) (2.4–4.7 wt%). They have low SiO2 (44.8–54.1 wt%), slightly variable Fe2O3T (10.1–14.4 wt%), Al2O3 (14.8–17.0 wt%), CaO (5.5–10.6 wt%), and medium to high MgO (6.1–10.8 wt%) and Mg# values (58–65). The rocks display LREE enrichment ((La/Yb)N = 3.02–3.58) without obvious Eu anomaly (Eu/Eu* = 0.87–1.18). They are characterized by obvious depletion in Nb, Zr and Ti, and enrichment of Sr, Ba and Pb, indicative of geochemical features of island arc magmas. The rocks have experienced crystallization from clinopyroxene to orthopyroxene, then plagioclase, suggesting the hydrous fractionation order. They also exhibit variable εNd(t) values ranging from − 0.2 to + 0.8 and zircon εHf(t) values from − 3.0 to + 6.6. These features suggest that the mafic intrusions are formed by partial melting of a garnet-spinel lherzolite and derived from an enriched mantle source metasomatized by slab-derived fluids at a shallow depth. Combined with the previous reported magmatic records, the ca. 2.3 Ga magmatic activity may be a result of the oceanic slab subduction beneath the Eastern Block of the NCC, and the subduction probably continue throughout the early Paleoproterozoic from ca. 2.5 Ga to ca. 2.3 Ga, at least 200 Ma. Therefore, the prevalence of early Paleoproterozoic magmatic activities in the southern NCC indicate that the tectonic activity did not shutdown globally during the interval of the ‘tectono-magmatic lull’.

Late Permian orogenic gold mineralization at Haoyaoerhudong, northern China: Constraints from hydrothermal titanite and apatite chemistry

The giant Haoyaoerhudong gold deposit is located on the north margin of the North China Craton. This deposit takes the form of lenticular orebodies hosted by the Mesoproterozoic carbonaceous schist, phyllite, and slate. Gold-related hydrothermal alteration types recognized at Haoyaoerhudong are silicification, sulfidation, biotitization, and graphitization. In addition, titanite and apatite were recorded in hydrothermal system. There are four types of hydrothermal apatite, namely, rounded Ap-S in altered schist, fractured Ap-V1 in quartz–biotite–sulfide veins, anhedral Ap-V2 in quartz–sulfide stringers, and Ap-V3 with abundant fluid inclusions in quartz–sulfide veinlets. As for different titanite types, Ttn-S is found to replace ilmenite in altered schist. Clustered Ttn-V1 is associated with graphite and gold in quartz–biotite–sulfide veins. Anhedral Ttn-V2 generally coexists with pyrrhotite and chalcopyrite in quartz–sulfide stringers. Euhedral Ttn-V3 is intergrown with Ap-V3 in quartz–sulfide veinlets. A U–Pb age of 255.6 ± 2.5 Ma (MSWD = 4.2, n = 27) was obtained for Ttn-V3 via in situ U–Pb analyses, which is younger than the nearby biotite granite (272.9 ± 1.5 Ma MSWD = 2.1, N = 25). The Haoyaoerhudong deposit can therefore be considered the product of a postmagmatic mineralization event at around 256 Ma. Apatite and titanite trace elements are robust tools for tracking fluid pathways in orogenic gold deposits. The enrichment of Mn, Fe, Y, and rare earth elements (REE) is observed in Ap-S but is progressively depleted from Ap-V1 through Ap-V2 to Ap-V3. There are also higher concentrations of Mn, Fe, Mo, Bi, Nb, Ta, Zr, Hf, and REE for Ttn-S than other titanites. Nevertheless, the K, Ba, Sr, and V concentrations are enriched in Ttn-V3, similar to the enrichment of Sr in Ap-V3. The apatite and titanite compositions measured here indicate the low salinity but Sr and alkali metals -enriched ore-forming fluids, typical for orogenic gold systems. Systematic geochemical variations in Eu, Mn, and V concentrations may imply that the ore-forming fluids were slightly oxidized compared to altered schist. The interaction between the carbonaceous schist and hydrothermal fluids would have led to CO2 consumption and apatite, titanite, and graphite formation. We further concluded that Sn vs. Mo, V vs. Th/U, and Zr + Hf vs. Th/U diagrams help to distinguish hydrothermal titanite in orogenic gold deposits from those in porphyry, skarn, and iron oxide–copper–gold deposits.

Revealing the interplay between “intelligent behavior” and surface reconstruction of non-precious metal doped SrTiO3 catalysts during methane combustion

The impact of surface reconstruction of a model perovskite, SrTiO3 (STO), on CH4 activation for combustion and oxidative coupling was previously revealed that the reaction rate was proportional to the creation of Sr-terminated step sites. Doped perovskites (SrTi1−xMxO3, M=metal dopant) present yet another form of reconstruction throughout the surface and the bulk, where the metal dopant can migrate in and out of the perovskite lattice, also known as “intelligent behavior”. In this work, understanding the interplay between perovskite surface reconstruction (surface termination) and the “intelligent behavior” is tackled for the first time, and the catalytic consequences are probed with CH4 combustion as a model reaction. A set of experimental techniques, including XRD, Raman spectroscopy, X-ray adsorption spectroscopy, kinetic measurements, as well as DFT calculations were used to understand the catalytic behavior of the reconstructed surfaces of Ni and Cu-doped STO for methane combustion. We found that during methane oxidation, the diffusion of Ni and Cu into the lattice due to the “intelligent behavior” is accompanied by Sr enrichment on the surface of the perovskite. This Sr-enrichment process is reversible when Cu or Ni species exsolute as clusters/nanoparticles upon H2 treatment. Such a surface reconstruction is found to greatly impact the catalytic activity of doped perovskites towards methane combustion.

Genesis of alunite-bearing kaolin deposit in Mudamköy member of the Miocene Göbel Formation, Mustafakemalpaşa (Bursa), Turkey

Tectonic-controlled hydrothermal alteration of Lower Miocene volcanic rocks in the Mustafakemalpaşa (Bursa) region resulted in the development of kaolin deposit, which have an economical potential. This study will be important for the mineralogical, geochemical, and genetic contributions to the ongoing mining operation of this kaolin deposit and its possible application fields. The upward mineralogical and geochemical zonation of the kaolin deposit is as follows: kaolin, alunite-bearing kaolin, silicified kaolin, and silcrete; associated with Fe-oxide bearing veins and silicification. The characteristics of the kaolinized and alunitized units and their parent rocks were examined using polarized-light microscopy, X-ray powder diffractometry (XRD), scanning electron microscopy (SEM–EDX), chemical (ICP–AES and –MS), and isotopic (H–O, S–O) methods. Kaolinite and alunite are abundant and generally associated with quartz, feldspar, volcanic glass, and mica, locally smectite, accessory halloysite, and goethite. The kaolinite content increases up to 75% in the kaolin zone. Kaolinite shows both ideal hexagonal book-like and non-idiomorphic (initial stage) crystal forms associated with rhombohedral blocky alunite are formed authigenically on altered volcanic materials and locally covered by accessory star-like goethite and tube-like halloysite crystals. Under the open hydrological system and acidic conditions, the Al ± Fe/Si ratio and Al + K + S values increased compared to the parent rocks, favoring the formation of kaolinite and alunite, respectively. The enrichment of Sr, Ba, and depletion of Fe, Rb, Ce, Y, and La, and the negative Eu anomaly shows that the fractionation of feldspar and mica originated from Miocene volcano-sedimentary components during the magmatic and hydrothermal alteration process(es) were the main sources for the formation of kaolinite and alunite. The δD and δ18O composition and formation temperatures of kaolinite are 106–167 °C, suggesting an epithermal alteration process(es). The negative δ34S and positive δ18O values for alunite exhibit local contribution of meteoric water mixed with magmatic fluid during hydrothermal activity.

Self-stabilized hybrid cathode for solid oxide fuel cell: A-site deficient perovskite coating as solid solution for strontium diffusion

Challenged by the surface strontium (Sr) enrichment, long-term stability of the La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) cathode remains to be the most intractable problem hindering its further development and application in solid oxide fuel cells (SOFCs). To enhance the durability and performance of LSCF-based electrodes, we propose a novel approach by introducing a highly active A-site deficient La0.95CoO3-δ (LC95) thin film onto the surface of the porous LSCF scaffold, simultaneously working as the accepter for Sr diffusion and conformal collector for electrons conduction. Besides the inhibiting effect from the dense coating, the A-site deficiencies reserved in coating lattice enable promising stabilization for Sr diffusion and segregation. At 700 °C, the La0.6Sr0.4Co0.2Fe0.8O3-δ@La0.95CoO3-δ (LSCF@LC95) hybrid cathode shows a polarization resistance of 0.28 Ωcm2, much lower than that for pristine LSCF cathode (0.36 Ωcm2). In addition to the higher electrochemical activity, single cell with LSCF@LC95 cathode exhibits remarkable long-term stability without detectable degradation over 120 h.

New ages of Early Cretaceous magmatic rocks in the Yanbian area (NE China): implications for the subduction and slab rollback of the Paleo-Pacific Plate beneath eastern China during Early Cretaceous

ABSTRACT The precise age of slab rollback of the Paleo-Pacific Plate during Early Cretaceous has been contentious. In this study, we have conducted LA-ICP-MS zircon U-Pb dating, major and trace elements, and Sr-Nd isotopes analyses on the late Early Cretaceous diabase porphyries, andesitic basalts and basanites in the Yanbian area (NE China). Zircon U-Pb dating of basanites, andesitic basalts, and diabase porphyries yielded weighted average ages of 104 ± 1.9 Ma (MSWD = 0.55, n = 5), 106 ± 1.6 Ma (MSWD = 0.68, n = 6), and 111 ± 2 Ma (MSWD = 16, n = 3), respectively. The whole-rock geochemical results indicate that the late Early Cretaceous rocks predominantly belong to the low-K tholeiitic and medium-K calc-alkaline series. The diabase porphyries and andesitic basalts are characterized by large ion lithophile elements (e.g. Ba, K, and Sr) enrichment and high field strength elements (e.g. Nb and Zr) depletion with weak positive Eu anomalies, low initial 87Sr/86Sr ratios (0.70361–0.70394) and high ε Nd (t) values (5.96–7.87). The tectonic discrimination diagrams show that the diabase porphyries and andesitic basalts formed in the continental Island arc environment related to subduction of the Paleo-Pacific Plate in the late Early Cretaceous. In contrast, the basanites are enriched in Ba, Th, and U and depleted in K, Sr, and Ti, with weak negative Eu anomalies. The basanites display high magnesium values (Mg# = 0.79), which are approaching the primary magma. They have low Ti values (TiO2 = 1.45%) and Al values (A12O3 = 9.98–10.15%) and high Co values (78.1–80.2 ppm) and Ni values (549.5–585.5 ppm). The basanites formed in the intraplate extensional tectonic setting and were the products of lithospheric thinning and mantle upwelling during the late Early Cretaceous. The spatial-temporal relationship of late Early Cretaceous magmatic rocks in NE China suggests a slab rollback from high-angle subduction to low-angle subduction of the Paleo-Pacific Plate at ca. 106 Ma.

Crustal Contamination and Hybridization of an Embryonic Oceanic Crust during the Red Sea Rifting (Tihama Asir Igneous Complex, Saudi Arabia)

AbstractThe Red Sea rift system represents a key case study of the transition from a continental to an oceanic rift. The Red Sea rifting initiated in Late Oligocene to Early Miocene (24–23 Ma) and was accompanied by extensive magmatism throughout the rifted basin, from Afar and Yemen to northern Egypt. Here, we present a petrological and geochemical study of two gabbro bodies and associated basalts from the Tihama Asir igneous complex, which formed at 24–20 Ma within the rifted Arabian-Nubian Shield (ANS). The Tihama Asir is therefore an ideal location to study the initial phase of syn-rift magmatism and its influence on the geodynamic evolution of the Red Sea rift system. The most primitive olivine gabbros present modal, bulk and mineral compositions consistent with formation from Mid-Ocean Ridge Basalt (MORB)-type parental melts, whereas the evolved olivine-free gabbros and oxide-bearing gabbros show saturation of phlogopite and a crystal line of descent diverging from fractional crystallization trends. In detail, whole-rock and mineral compositions in the most evolved lithologies show high Light over Middle Rare Earth Elements (LREE/MREE) ratios (LaN/SmN = 0.89–1.31) and selective enrichments in Sr, K and highly incompatible elements (Rb, Ba, U, Th). We relate these geochemical characteristics to a process of progressive assimilation of host continental crust during the emplacement of the gabbroic plutons. Interestingly, high LREE/MREE ratios (LaN/SmN = 1.45–4.58) and high Rb, Ba, Th and U contents also characterize the basaltic dike swarms associated to the gabbros. Incompatible trace element compositions of these basalts approach those of the melts that formed the most hybridized gabbros. Therefore, we propose that the dike swarms represent melts partially contaminated by assimilation of continental crust material, extracted from the underlying gabbroic crystal mush. Our results suggest that early syn-rift magmatism led to the partial replacement of the thinned continental crust by MORB-type gabbroic bodies, in turn suggesting that oceanic magmatism started prior to continental break-up. Extensive syn-rift magmatism is consistent with the interpretation of the southern Red Sea rift system as a volcanic rifted margin. One possible implication of this study is that extensive but diffuse syn-rift magmatism possibly hampered continental break-up, leading to a protracted rifting stage.

Late Summer Water Sources in Rivers and Lakes of the Upper Yana River Basin, Northern Eurasia, Inferred from Hydrological Tracer Data

Major ions, stable isotopes, and trace elements, including rare earth elements (REEs), are used as natural tracers in the qualitative assessment of potential water sources in lakes and rivers of the upper Yana River basin, between Verkhoyansk and Chersky Ranges, during the late summer period. Three distinct regions were sampled, and a dominant water source in each region was qualitatively inferred from water chemistry data. The REE distribution pattern was found to be highly regional and controlled by pH and carbonate contents. Mountain headwater stream at the Verkhoyansk Range north slope, the Dulgalakh River, shows an input from a mixture of shallow groundwater and icing meltwater, with a depleted isotopic signature (δ18O below –21‰), d-excess (dex = δ2H − 8·δ18O) above 18, enrichment in Mg and Sr, and depletion in heavy REEs. The Derbeke Depression lakes and streams are fed by rainfall having ultra-low total dissolved solids (TDS) content, below 25 mg/L, and a convex-up REE pattern. In a medium mountainous river at the Chersky Range flank, the Dogdo River, leaching through fissured Jurassic carbonates is a dominant runoff pathway. Riverine water is heavily depleted in light REEs, but enriched in Mo, Rb, Sb, W and U. In the Dulgalakh River water, high positive Sm and Gd anomalies were observed, attributed either to local geology (greenshists), historical mining legacy, or contemporary winter road operations.

Thermally Controlled Activation and Passivation of Surface Chemistry and Oxygen-Exchange Kinetics on a Perovskite Oxide

The state-of-the-art oxygen electrode materials used in solid oxide cells at 600–800 °C can deteriorate by gradual passivation of their surfaces related to changes in the surface chemistry. We have recently observed the unexpected recovery of the oxygen-exchange activity on La0.6Sr0.4FeO3 after short-term exposure to high temperatures; a 10 h-long thermal treatment at above 800 °C resulted in a 40-fold increase in the oxygen-exchange coefficient, kchem, from 1 × 10–5 to 4 × 10–4 cm/s. The present work addresses the underlying mechanism of this improvement by investigating the chemical and morphological changes at the surface with respect to thermal history. Using repeated sequences of 10 h-long thermal treatments at 1000 °C over weeks-long aging at around 650 °C, we have probed the oxygen-exchange kinetics and surface chemistry concurrently by electrical conductivity relaxation and X-ray photoelectron spectroscopy (XPS). The oxygen-exchange coefficient decreases with aging at 650 °C following Avrami-type kinetics but sharply increases after each high-temperature treatment. An increased amount of strontium [40% cation fraction; XSr/(XLa + XSr + XFe)] is found on the surface of all thermally treated samples (compared to the bulk nominal 20%). Hence, the passivation/reactivation is not due to the total Sr enrichment as such. By XPS, two different states of Sr are observed on the surface (labeled “lattice-bound” and “secondary phase”). The relative amounts in these two phases vary with time, differently at 650 °C versus 1000 °C. The amount of “lattice-bound Sr” decreases and the amount of “secondary phase Sr” increases with aging at 650 °C and the opposite at 1000 °C. We show that it is the Sr in the secondary phases, rather than the total amount, which is the main culprit for performance degradation. The findings are further supported by the observations of morphological changes on the surface in the form of SrO, SrCO3, and SrSO4 precipitates and layers. Decomposition of secondary Sr phases at 1000 °C and simultaneous dissolution of Sr back in a perovskite lattice rejuvenate the surface and lead to a significant increase in exchange kinetics.

Геохімічні особливості нагромадження і міграції Стронцію в торфах Львівської області

The article is devoted to the study of geochemical characteristics of the distribution, accumulation and migration of Strontium in the lowland peats of the Lviv region, both laterally and vertically, and to identify the main factors influencing the formation of its concentrations. A significant uneven distribution of concentration, high dispersion and variability (coefficient of variation – 116.61, standard deviation – 564.11) of Sr in peats within deposits, districts and regions both with depth and area of distribution and high content indicators were established Sr relative to clarks of the lithosphere, soils, plant ash (CC relative to the lithosphere = 1.42; CC relative to soil clarks = 1.94; Сs relative to background values in the soils of Ukraine = 4.56; CK relative to clarks of terrestrial plants = 1.61). The content of Sr in the peat of the Lviv region ranges from 40–3190 mg/kg (average content 483.75 mg/kg, median content (background content) – 250 mg/kg), which is due to natural-climatic, geological, lithological, hydrogeochemical and anthropogenic factors. The features of the distribution and the degree of concentration of Sr in the peatlands of the Lvіv region are mainly influenced by the chemical-mineralogical-petrographic composition of the bedrocks of the wear area during their weathering; terrain, climatic, geomorphological, tectonic and hydrogeological conditions of the area, which determine the of the weathering processes of the rocks in the wear areas, the degree of transformation of terrigenous material in the weathering processes, the rate of accumulation of biomass and the rate of its decomposition; features of water and mineral nutrition of the peatland. High concentrations of Strontium in the peat of the Lviv region reflect the local regional processes of the concentration of the element in the mass of peat and may indicate the accumulation of Sr of both natural and anthropogenic origin in the upper layers of peat profiles.There is an enrichment of Sr in the upper intervals of deposits (0–1 m) of deposits in the northeastern part of the Lviv region (Malopoliska peat region) is observed.

NEW TYPES OF BASIC ROCKS IN THE KORSUN-NOVOMYRHOROD ANORTHOSITE-RAPAKIVI GRANITE PLUTON AS AN INDICATOR OF ITS PETROGENESIS

Two species types of basic rocks contrasting in chemical and mineral composition were investigated within the Korsun-Novomyrhorod anorthosite-rapakivigranite pluton (KNP) of the Proterozoic age. In comparison to more typical basic rocks of KNP, the investigated rocks are presented by the extremely Fe-rich fayalite gabbroids and the most MgO enriched biotite gabbronorite. The first of them occupy a deeper level of the Horodishche massif in the central part of KNP. According to a high-Fe association of minerals and reduced or low An content in plagioclase they may represent the crystallization of a highly evolved basic melt (after anorthosite and gabbronorites separation), which were crystallized under abyssal conditions and low oxygen fugacity. Preliminary geochemical data indicate that trace elements concentration and negligible negative Eu-anomalies (0.72-0.95) are similar to most distributed basic rocks but unlike the last it is slightly differed by decreasing La/Yb and enriched in Sc (up to 118 ppm). Thus, we suppose those rocks might be crystallized as a result of mixing highly differentiated (iron and alkali enriched) melt with the early generation of anorthitic plagioclase, with subsequent dissolution of the last. Enrichment in iron of the mafic minerals and increasing of alkalinity of plagioclase in the basic rocks is consistent with the appearance of ferrodioritic melts as a product of prolonged crystalline differentiation of the initial melt. In contrast to fayalitic gabbroids, the pyroxene-biotite gabbronorites from the border zone in according to increased Mg# of the mafic minerals and rocks are obviously the least differentiated varieties of the anorthosite-gabbronorite series. The regularities in chemical composition in such type of rocks are consistent with the liquid line of dissent for basic rocks in KNP, which implies their crystallization at an earlier stage of magma ascending. By composition, such melt can be formed at an intermediate stage from slightly differentiated melt. This is indicated by enrichment in Sr (453-881 ppm) and Ba (910-930 ppm), Eu/Eu* (0.85-1.10), increased content MgO (up to 8 wt. %), Cr and V (59-193 and 169-350 ppm respectively). At the same time these rocks are enriched in Zr and Hf (378-478 and 10.3-12.02 ppm respectively), highly enriched in Rb (169-192 ppm), with moderate Nb and Ta content (14.6-18.1 and 0.91-2.84 ppm respectively) that point out to interaction and partial assimilation by crust material. Summarizing geological data of the deep drill-holes, it is possible to reveal a general direction of the mafic minerals evolution in the basic rocks and the evidences of cryptic layering. The last are quite clearly manifested both in the large gabbro-anorthosite massifs and individual intrusive bodies. We suppose that the evolution trend of mafic mineral composition are consistent with the tholeiitic trend differentiation of the primary melt with gradual increasing of iron content (under low oxygen fugacity) during differentiation and ascending in the upper crust. According to this interpretation of the inner structure of gabbro-anorthositic massifs, on the modern erosional level of KNP are often exposed the fragments of the upper (or lateral) layered series (Fe-enriched), less often the drill-holes reach up to the heads of the lower layered series.