Low TiO2 Contents Research Articles

Metallogeny of the peridotite-hosted magnetite ores of the Nain ophiolite, Central Iran: Implications for Fe concentration processes during multi-episodic serpentinization

Magnetite bodies of the Late Cretaceous Nain ophiolite mélange (Central Iran) are hosted by a small volume of a serpentinized peridotite nappe. These ore bodies and their host peridotites have been studied in detail with respect to their mode of occurrence, petrography and mineral chemistry. The investigated ore deposits consist of m-scale lenses and pods of massive magnetite rocks exposed along a semi-brittle shear zone between pervasively serpentinized harzburgites, upper one with higher-Cr# [=Cr/(Cr + Al), 0.6–0.7] spinel and lower one with lower Cr# (0.5). Silicate mesostasis of the ore bodies is composed of stringy serpentine and chlorite. Cr-spinel grains are occasionally found dispersed within the magnetite rocks. Serpentines of the host serpentinized harzburgites show mesh and bastite textures, and were in part replaced by fibrous serpentine showing an interpenetrating texture. The Cr-spinels show a wide range of Cr# (0.5–0.7) and Mg# [=Mg/(Mg + Fe2+), 0.5–0.7], low TiO2 contents (<0.1 wt%), and relatively high contents of ZnO (0.11–0.26 wt%) and MnO (0.33–0.43 wt%). The magnetites are close in chemistry to the end-member Fe3O4, but some grains show high-SiO2 (up to 1.5 wt%) cores. They strongly resemble accessory Cr-spinels in the host serpentinized harzburgites in chemistry. The magnetite rocks have total precious-metal abundances (ΣPGE + Au = 66–262 ppb) analogous to those of mantle peridotites from other Mesozoic ophiolites. They are poor in PGE (21–67 ppb) relative to Au (45–195 ppb). Our analyses and observations are inconsistent with an igneous origin for the Nain magnetite deposits, but indicate a replacement origin from harzburgite, not from chromitite, via hydrothermal fluids. Overall data indicate that the Nain magnetite bodies were generated by multi-episodic serpentinization of harzburgites. The magnetite ore deformation style itself indicates syn-kinematic emplacement of the ore bodies within the semi-brittle shear zone, where the serpentinization-derived fluid/(altered) peridotite ratio became so high that eventually caused precipitation of magnetite at the ore level.

Geochemistry and U–Pb geochronology of the Wagone and Hermyingyi A-type granites, southern Myanmar: Implications for tectonic setting, magma evolution and Sn–W mineralization

Tin-tungsten-associated granites occur widely in the Dawei region of the Southeast Asian tin belt. In this contribution, we present a detailed study of zircon U–Pb geochronology and whole-rock and zircon elemental geochemistry for the Wagone and Hermyingyi granites in southern Myanmar, with the aim of determining their petrogenesis, mineralization associations, and tectonic setting. These granitic rocks, which belong to the high-K calc-alkaline series A2-type granites, are characterized by high concentrations of SiO2 (75.2–82.5%), Rb (264–927 ppm), Th (18.4–58.3 ppm), U (10.4–18.3 ppm), and Y (33.5–212 ppm), but low contents of TFeO (0.57–3.45%), CaO (0.23–0.86%), MgO (0.02–0.19%), MnO (0.01–0.38%), TiO2 (0.01–0.10%), P2O5 (0.003–0.012%), Ba (3–162 ppm), and Sr (4.3–34.4 ppm). Hydrothermal zircons from the mineralized Wagone pluton show an anomalous lack of zoning and vermicular, spongy internal structures, and they contain high concentrations of Ti, Y, U, and light REEs but low Th/U ratios (mostly < 0.1). These features suggest slow crystallization from a U-enriched and Th-depleted residual magmatic fluid under relatively cool and reducing conditions. LA-ICPMS U–Pb dating of magmatic and hydrothermal zircons from the two granites yielded concordant ages of 61–60 Ma, indicating an Early Paleogene magmatic-mineralization event. Geochemical and geochronological data suggest that these A-type granites have a crustal origin and were produced by partial melting of a felsic clay-rich source in a back-arc extensional setting. The magmas may have ascended relatively slowly in the crust and experienced crystal fractionation and upper crustal contamination, contributing to intensive Sn–W mineralization in the Dawei area.

The Calzadilla Ophiolite (SW Iberia) and the Ediacaran fore-arc evolution of the African margin of Gondwana

In the Ossa Morena Domain of SW Iberia, the Calzadilla Ophiolite is formed by an ensemble of ultramafic and mafic rocks that seem to represent a fragment of an oceanic Moho transition zone. The ophiolite consists of a main sheet with a minimum thickness of c. 1000m and several ultramafic slices that appear imbricated with Ediacaran siliciclastic rocks of the so called Serie Negra. The mafic rocks of the Calzadilla Ophiolite show an extreme depletion in some HFSE such as Nb, Zr, Th, Hf and Ta, low TiO2 contents and high MgO, which allow identifying them as magmatic types of boninitic affinity, such as those frequently associated with fore-arc settings. U-Pb zircon dating of the gabbroic rocks suggests that the igneous protoliths crystallised at c. 600Ma and were extracted directly from the mantle, according to the juvenile isotopic sources revealed by the Hf isotopic composition of the dated zircons. At c. 540Ma the U-Pb isotopic system was affected by a partial resetting event with moderate generation of new zircon. According to these data, it is considered that the Calzadilla Ophiolite was formed in a supra-subduction zone setting, very likely in a fore-arc domain, during a roll-back episode affecting the peri-Gondwanan subductive slab. The fore-arc domain was probably proximal to the West Africa Craton. It is very likely that the ductile deformation, metamorphism and tectonic imbrication of the Calzadilla Ophiolite and the Serie Negra occurred at c. 540Ma, during an increase in the subduction rate and a significant decrease of the subduction angle of the oceanic slab. The information provided by the Calzadilla Ophiolite allows to better constrain the geodynamic evolution of the African margin of Gondwana.

Identification of ca. 850 Ma high-temperature strongly peraluminous granitoids in southeastern Guizhou Province, South China: A result of early extension along the southern margin of the Yangtze Block

Strongly peraluminous granites are characterized by high A/CNK values (>1.1) and are important for understanding the regional tectonic regime. Here, we present integrated studies of zircon U–Pb ages, trace elements and Lu–Hf isotopes, whole-rock major and trace elements, and Nd isotope compositions for the newly discovered Nage granite porphyry in southeastern Guizhou Province. The porphyry has a crystallization age of 852 ± 5 Ma and shows wide ranges in SiO2 (64.5–72.51 wt%) and Al2O3 (13.08–19.34 wt%) contents, with low TiO2 (0.41–0.84 wt%) and P2O5 (<0.15 wt%) contents. All the samples are strongly peraluminous with A/CNK >1.1, and they have similar trace element patterns with depletion in high field strength elements (HFSE, e.g., Nb and Ta) and enrichment in large-ion lithophile elements (LILE, e.g., Rb, Th and U). Initial zircon Hf isotopes of the porphyry vary from εHf(t) = −7.6 to −0.6, whereas whole-rock Nd isotopes are relatively uniform with εNd(t) = −6.0 to −6.7. They record high zircon saturation temperatures (Tzr) (786–842 °C, mostly >810 °C), but low oxygen fugacity (logfO2 = −16 to −25, corresponding to ΔFMQ −3 to ΔFMQ −7) and emplacement pressure of <0.5 GPa. Major and trace elements, 10,000 Ga/Al ratios and Zr + Nb + Ce + Y values, show good correlations with Tzr, indicating that fractional crystallization may have played an important role. Although these granites show low P2O5 contents that decrease with increasing Rb, the high A/CNK (>1.1), K2O/Na2O (0.7–2.6; average 1.4) and CaO/Na2O (0.2–0.8; mostly >0.5) ratios suggest that clay-poor metasedimentary rock were dominant in the source. Combined with the Nd–Hf isotopes, we suggest that the Nage granite porphyry formed by anatexis of an immature arkose and greywacke source, which was a mixture of weathered juvenile igneous materials and minor recycled ancient crustal components. The ca. 850 Ma strongly peraluminous granites, along with coeval extension-related magmatism along the southwestern margin of the Yangtze Block, indicate an extensional environment started as early as ca. 850 Ma.

Influence of inorganic additives on the photocatalytic removal of nitric oxide and on the charge carrier dynamics of TiO2 powders

Building materials employing TiO2 as photocatalyst usually contain several additives. The interplay of the additives and the photocatalytic NO degradation has been rarely investigated, although it is of utmost importance for the design of new highly active materials. Hence, in the present study the effects of such additives (BaSO4, CaCO3, and Na2CO3) on the photocatalytic activity and on the charge carrier dynamics have been evaluated. The degradation of nitric oxide (NO) was studied employing a standardized photocatalytic activity test (ISO 22197-1) and the charge carrier kinetics were observed by transient absorption spectroscopy. TiO2-additive powder samples were obtained by grinding pure anatase TiO2 with a single additive with varying volume composition. Overall, the obtained apparent quantum yields of the samples correlated well with the charge carrier concentration. Moreover, BaSO4 has proven its chemically inert character. However, the optical properties of the powder samples containing BaSO4 lead to relatively high photonic efficiencies even with low TiO2 content. TiO2-BaSO4 samples with only 25% TiO2 showed nearly the same quantum yield for the NO degradation as the pure photocatalyst. The reason for the high photocatalytic activity is the strong absorption of UV-light caused by the scattering inside the powder samples. The charge carrier kinetics of TiO2 after the addition of Na2CO3 and CaCO3 revealed two different chemical effects of the additives. Na2CO3 reduced the apparent quantum yield of the TiO2 samples due to the fast recombination of charge carriers (identified by a fractal kinetics fit). On the other hand, the presence of CaCO3 had a beneficial influence on the stabilization of trapped charge carriers in TiO2.

Platinum‐Group Elements Geochemistry and Chromian Spinel Composition in Podiform Chromitites and Associated Peridotites from the Cheshmeh‐Bid Deposit, Neyriz, Southern Iran: Implications for Geotectonic Setting

AbstractDunite and serpentinized harzburgite in the Cheshmeh‐Bid area, northwest of the Neyriz ophiolite in Iran, host podiform chromitite that occur as schlieren‐type, tabular and aligned massive lenses of various sizes. The most important chromitite ore textures in the Cheshmeh‐Bid deposit are massive, nodular and disseminated. Massive chromitite, dunite, and harzburgite host rocks were analyzed for trace and platinum‐group elements geochemistry. Chromian spinel in chromitite is characterized by high Cr#(0.72–0.78), high Mg#(0.62–0.68) and low TiO2 (0.12 wt%–0.2 wt%) content. These data are similar to those of chromitites deposited from high degrees of mantle partial melting. The Cr# of chromian spinel ranges from 0.73 to 0.8 in dunite, similar to the high‐Cr chromitite, whereas it ranges from 0.56 to 0.65 in harzburgite. The calculated melt composition of the high‐Cr chromitites of the Cheshmeh‐Bid is 11.53 wt%–12.94 wt% Al2O3, 0.21 wt%–0.33 wt% TiO2 with FeO/MgO ratios of 0.69–0.97, which are interpreted as more refractory melts akin to boninitic compositions. The total PGE content of the Cheshmeh‐Bid chromitite, dunite and harzburgite are very low (average of 220.4, 34.5 and 47.3 ppb, respectively). The Pd/Ir ratio, which is an indicator of PGE fractionation, is very low (0.05–0.18) in the Cheshmeh‐Bid chromitites and show that these rocks derived from a depleted mantle. The chromitites are characterized by high‐Cr#, low Pd + Pt (4–14 ppb) and high IPGE/PPGE ratios (8.2–22.25), resulting in a general negatively patterns, suggesting a high‐degree of partial melting is responsible for the formation of the Cheshmeh‐Bid chromitites. Therefore parent magma probably experiences a very low fractionation and was derived by an increasing partial melting. These geochemical characteristics show that the Cheshmeh‐Bid chromitites have been probably derived from a boninitic melts in a supra‐subduction setting that reacted with depleted peridotites. The high‐Cr chromitite has relatively uniform mantle‐normalized PGE patterns, with a steep slope, positive Ru and negative Pt, Pd anomalies, and enrichment of PGE relative to the chondrite. The dunite (total PGE = 47.25 ppb) and harzburgite (total PGE = 3 4.5 ppb) are highly depleted in PGE and show slightly positive slopes PGE spidergrams, accompanied by a small positive Ru, Pt and Pd anomalies and their Pdn/Irn ratio ranges between 1.55–1.7 and 1.36–1.94, respectively. Trace element contents of the Cheshmeh‐Bid chromitites, such as Ga, V, Zn, Co, Ni, and Mn, are low and vary between 13–26, 466–842, 22–84, 115–179, 826—‐1210, and 697–1136 ppm, respectively. These contents are compatible with other boninitic chromitites worldwide. The chromian spinel and bulk PGE geochemistry for the Cheshmeh‐Bid chromitites suggest that high‐Cr chromitites were generated from Cr‐rich and, Ti‐ and Al‐poor boninitic melts, most probably in a fore‐arc tectonic setting related with a supra‐subduction zone, similarly to other ophiolites in the outer Zagros ophiolitic belt.

Age, geochemistry, and emplacement of the ~40-Ma Baneh granite–appinite complex in a transpressional tectonic regime, Zagros suture zone, northwest Iran

ABSTRACTThe Baneh plutonic complex is situated in the Zagros suture zone of northwest Iran between the Arabian and Eurasian plates. This complex is divided into granite and appinite groups. Zircon U–Pb dating shows that granites crystallized 41–38 million years ago but appinites experience more protracted magmatic evolution, from at 52 to 38 Ma. Whole-rock chemical compositions show significant major and trace element variations between the two lithologies. Granitic rocks are more evolved, with high contents of SiO2 (62.4–77.0 wt%), low contents of TiO2 (0.25 wt%), MgO (0.05–1.57 wt%), and Fe2O3 (0.40–4.06 wt%) and high contents of Na2O + K2O (≈10 wt%). In contrast, appinites have low contents of SiO2 (51.0–57.0 wt%) and K2O (<2.1 wt%) and high Fe2O3 (6.4–9.35 wt%), MgO (2.0–9.9 wt%), and Mg number (Mg# = 35–76). The concentration of rare earth elements in the appinites is higher than in granitic rocks, making it difficult to form granites solely by fractionation of appinite magma. (87Sr/86Sr)i and εNd(40 Ma) in both groups are similar, from 0.7045 to 0.7061 and −1.2 to +2.6, except for a primitive gabbroic dike with εNd(40 Ma) = +9.9. Appinites show mainly typical I-type characteristics, but granites have some S-type characteristics. The sigmoidal shape of the Baneh pluton and its emplacement into deformed Cretaceous shales and limestone showing kink bands, asymmetric and recumbent folds in a broad contact zone, with pervasive ductile to brittle structures in both host rocks and intrusion, indicate that magma emplacement was controlled by a transpressional tectonic regime, perhaps developed during early stages in the collision of Arabia and Eurasian plates.

Immature intra-oceanic arc-type volcanism on the Izanagi Plate revealed by the geochemistry of the Daimaruyama greenstones in the Hiroo Complex, southern Hidaka Belt, central Hokkaido, Japan

The Izanagi Plate is assumed to have underlain the western Panthalassa Ocean to the east of Eurasia, and to have been subducting under the Eurasian continent. Although the Izanagi Plate has been lost to subduction, the subduction complexes of the circum-Panthalassa continental margins provide evidence that subduction-related volcanism occurred within the Panthalassa Ocean, and not just along its margins. The Daimaruyama mass is a kilometer-sized allochthonous greenstone body in the Hiroo Complex in the southeastern part of the Nakanogawa Group in the southern Hidaka Belt, northern Japan. The Hiroo Complex is a subduction complex that formed within the Paleo-Kuril arc–trench system at 57–48 Ma. The Daimaruyama greenstones consist mainly of coarse volcaniclastic rocks with lesser amount of lava. Red bedded chert, red shale, and micritic limestone are also observed as blocks associated with the greenstones. The presence of Early Cretaceous (Aptian–Albian) radiolaria in red bedded cherts within the greenstones indicates that the Daimaruyama greenstones formed after this time. An integrated major and trace element geochemical dataset for whole-rocks and clinopyroxenes of the greenstones indicates a calc-alkaline magmatic trend with low TiO2 contents and increases in SiO2 and decreases in FeO* with increasing differentiation. Negative anomalies of Nb, Ta, and Ti in normal mid-ocean-ridge basalt type normalized patterns are interpreted as “arc-signatures”. Using “rhyolite-MELTS”, we conducted a numerical simulation of magmatic differentiation under conditions of 1.5 kbar and H2O = 3 wt% to reproduce the liquid line of descent of the Daimaruyama greenstones. Back-calculations of the equilibrium melt compositions from the trace element chemistry of the clinopyroxenes generally agree with the whole-rock rare earth element compositions of the Daimaruyama greenstones, therefore providing support for the conditions used for the rhyolite-MELTS calculations as well as the actual results. Clinopyroxene trace element compositions indicate substantial enrichment of Ba in the magma, reflecting the participation of shallow subduction components such as aqueous fluids. Geochemical investigations reveal that the Daimaruyama greenstones were probably submarine volcanic rocks that formed as a result of the subduction of the Izanagi Plate within the Thalassa Ocean (the Thalassa Ocean was the eastern realm of Panthalassa, and represents the proto-Pacific Ocean) after the Early Cretaceous (Aptian–Albian; 125–101 Ma), and they were eventually accreted onto the Paleo-Kuril arc–trench system at 57–48 Ma to form an allochthonous block as part of the mélange facies of the Hiroo Complex on the landward slope of the trench.

Influence of Al2O3 Content on the Melting and Fluidity of Blast Furnace Type Slag with Low TiO2 Content

The increasing usage of iron ores with high Al2O3 content significantly increases the amount of Al2O3 in blast furnace slag and consequently affects its performance. This work uses slag sampled on site to study the effects of changes in Al2O3 content on the fluidity of the CaO–SiO2–Al2O3–MgO–TiO2 slag system that is characterized by high Al2O3 and low TiO2 contents, as well as on the phase transition law during the cooling process. Slag viscosity exhibits a rising trend with an increase in Al2O3 content, and Al2O3 in the tested slag is alkaline. The viscous flow activation energy of molten slag rises from 157 kJ/mol to 172 kJ/mol with an increase in Al2O3 content, and the viscous flow units in the slag become large and complicated. When slag is cooled, the main precipitated phase is melilitite. Spinel, perovskite, and olivine are also observed. The crystallization amount of the melilitite phase decreases constantly with an increase in Al2O3 content.

Geochronology and petrogenesis of the Early Cretaceous A-type granite from the Feie'shan W-Sn deposit in the eastern Guangdong Province, SE China: Implications for W-Sn mineralization and geodynamic setting

The Feie'shan greisen–type W–Sn deposit in the eastern Guangdong Province forms part of the Southeastern Coastal Metallogenic Belt (SCMB) in South China. Here we present zircon LA–ICP–MS U–Pb geochronology of the biotite granite which shows a weighted mean 206Pb/238U age of 134.7±2.0Ma, consistent with the zircon U–Pb, biotite 40Ar–39Ar and molybdenite Re–Os ages in the previous study. The biotite granite is peraluminous and belongs to high–K calc–alkaline type. It is characterized by high SiO2, K2O, F, K2O+Na2O and FeOt/(FeOt+MgO), and low CaO, MgO, TiO2 and P2O5 contents, enrichment in Rb, Cs, Th and U, and depletion in Ba, Sr, Zr, Ti and P, with flat REE patterns and distinctly negative Eu anomalies, showing an A2–type affinity. The rocks also display extremely low Ba, Sr and Ti concentrations and high Rb/Sr, Rb/Ba and low CaO/(Na2O+K2O) ratios, indicating high degree of fractionation. Zircon grains from the granite have low Eu/Eu⁎ and Ce4+/Ce3+ ratios, suggesting low oxygen fugacity. The highly fractionated and reduced features imply that the Feie'shan mineralization is genetically related to the biotite granite. The εNd(t) values and zircon εHf(t) values of the biotite granite range from −2.96 to −1.95 and −5.69 to 0.62, with two–stage Nd and Hf model ages (TDM2) of 1083 to 1164Ma and 1150 to 1552Ma, indicating that they were derived from magma hybridization between anatectic granitic and mantle–derived mafic magmas. In combination with previous studies, we propose a geodynamic model for the 145―135Ma W–Sn mineral system and related magmatism in the southwestern domain of the SCMB. After ca. 145Ma, the subduction orientation of the Izanagi plate changed from oblique to parallel with respect to the continental margin resulting in large–scale lithosphere extension and thinning, which led to the upwelling of asthenosphere. The ascending mantle–derived mafic magmas provided not only supplied the heat for crustal remelting but also added juvenile mantle–derived melts resulting in the formation of mafic dikes, and I– or A–type granitic intrusions related to the W–Sn ore mineral systems.

The Guleman ophiolitic chromitites (SE Turkey) and their link to a compositionally evolving mantle source during subduction initiation

Economically viable chrome ore bodies are hosted within a unit of pervasively serpentinized harzburgite in the Guleman mine of the homonymous ophiolite in SE Turkey. Chrome ores consist of m- to tens of m-scale tectonically imprinted chromitite bodies, showing semi-massive to massive texture and podiform to lenticular morphology. They are hosted in dunite envelopes of variable thickness and are composed of chromian spinel [Cr-spinel] with high Cr# [Cr/(Cr + Al) = 0.61–0.81] and Mg# [(Mg/Mg + Fe2+) = 0.56–0.72], and low TiO2 (0.06–0.33 wt%) content. Compositionally, they are divided into intermediate-Cr (CrSp#: 0.61–0.69) and high-Cr chromitites (Cr#Sp: 0.71–0.81). Chromian spinel from the intermediate-Cr chromitites is richer in Ni, Ti, Zn and Ga compared to that from the high-Cr chromitites. Both chromitite types show a general enrichment in IPGE (Os, Ir and Ru) over PPGE (Rh, Pt and Pd). The PGM assemblages of these chromitites are dominated by small (≤6 μm), idiomorphic inclusions of Ru-Os bisulfides and subordinate Os-Ir-Ru alloy in Cr-spinel. Bisulfides within the intermediate-Cr chromitites show a wider range of Os-for-Ru substitution than those hosted in the Cr-rich chromitites [Ru/(Ru + Os): 0.15–0.86 vs. 0.71–0.86, respectively].Geochemical calculations and PGE-mineralogical data demonstrate that the parental melts of the investigated chromitites had variable Al2O3 (10.62–14.58 wt%) and S contents. This implies a range of magma compositions generated at different degrees of partial melting of a common depleted mantle source. The calculated range of compositions is not consistent with a typical mid-ocean ridge or mature suprasubduction zone setting, but is thought to be representative of the evolving composition of a deep-seated, heterogeneous mantle source during subduction initiation beneath a forearc basin.

Magmatic history during late Carboniferous to early Permian in the North of the central Xing’an-Mongolia Orogenic Belt: a case study of the Houtoumiao pluton, Inner Mongolia

ABSTRACTWe undertake zircon U–Pb dating, Hf isotopes, and geochemical analyses of the Houtoumiao pluton in the Xilinhot microcontinent (XLMC) in the central Inner Mongolia with an aim of determining their ages, petrogenesis, and sources, which are important for understanding the late Palaeozoic tectonic evolution of the Xing’an-Mongolia Orogenic Belt. The Houtoumiao pluton consists of medium-grained granodiorite, coarse- and medium-grained syenogranite. Mafic microgranular enclaves (MMEs) are common in the Houtoumiao pluton. Zircon U–Pb dating has yielded ages of 303 ± 2 and 301 ± 2 Ma for the granodiorite, 295 ± 2 Ma for the syenogranite, and 292 ± 1 Ma for the MMEs. The granodiorite and syenogranite have features of high-K high silica content, rich in Rb, U, and Th, but low content of HFSE, belong to calc-alkaline series. The P2O5 concentration decreases with the increasing SiO2 content, suggesting I-type affinity. The MMEs, which are characterized by low SiO2, relatively high and variable TiO2, Al2O3, FeOT, MgO, CaO, Ni, and Cr contents, also have much higher total rare earth element concentrations that the REE patterns are subparallel to those of the host rocks. Zircons from the host rocks have εHf(t) values from +3.91 to +7.73 and TDM2 values of 820–1067 Ma, suggesting that the granitoids were probably dominated by remelting of juvenile crust materials. The MMEs are of εHf(t) value ranging from +6.23 to +11.04 and TDM1 values from 490 to 693 Ma, suggesting that the primary magma probably was derived from partial melting of a depleted lithospheric mantle, the mafic mineral fractional crystallization and crustal contamination occurred during the magma evolution. Combined with previous studies on the contemporaneous magma-tectonic activities in the Uliastai Continental Margin and XLMC, we suggest that the Houtoumiao pluton formed in a post-orogenic setting.

A middle Permian ophiolite fragment in Late Triassic greenschist- to blueschist-facies rocks in NW Turkey: An earlier pulse of suprasubduction-zone ophiolite formation in the Tethyan belt

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

The Wenquan ultramafic rocks in the Central East Kunlun Fault zone, Qinghai-Tibet Plateau—crustal relics of the Paleo-Tethys ocean

The Wenquan ultramafic rocks, located in the East Kunlun Orogenic belt in the northeastern part of the Qinghai-Tibet Plateau, consist of dunite, wehrlite, olivine-clinopyroxenite and clinopyroxenite, and exhibit cumulate textures. Olivine from dunite has high Fo (forsterite, 90.0–91.8 wt%) and NiO content (0.15–0.42 wt%). Cr-spinels from all of the rocks in this suite are characterized by high Cr# (100×[Cr/(Cr + Al)], 67–91), low Mg# (100×[Mg/(Mg + Fe2+)], 17–35) and low TiO2 contents (mostly 80) and low-CaO (< 0.08 wt%) olivine, high-Cr# (up to 91) spinel, and low Ti contents of clinopyroxene and Cr-spinel indicate that the Wenquan cumulates were generated by high-degree partial melting of a depleted oceanic lithosphere mantle. The ultramafic intrusion most likely evolved from high-Mg basaltic magmas (Mg# = 77.5) that underwent fractional crystallization and crustal contamination. Zircon grains from clinopyroxenites yield a U–Pb weighted mean age of 331 ± 2 Ma, which is nearly coeval with the formation age of the A’nyemaqen ophiolites. The Wenquan Carboniferous ophiolites are confirmed to exist in the Central East Kunlun Fault zone, whereas previous studies have considered them to be the Proterozoic ophiolites. The Wenquan ophiolite might be a relict of the Paleotethyan ocean, indicating that there were two cycles of oceanic–continental evolution along the Central East Kunlun Fault zone.

Compositional fingerprints of chromian spinel from the refractory chrome ores of Metalleion, Othris (Greece): Implications for metallogeny and deformation of chromitites within a “hot” oceanic fault zone

The chrome ores of the retired Metalleion mine of the Othris ophiolite are hosted in a small volume of a pervasively serpentinized, tabular harzburgite body. These ores have been studied to determine their geological mode of occurrence, mineralogy and chromian spinel (Cr-spinel) chemistry. The ores consist of massive chromitite (85–95% modal Cr-spinel) with mylonitic fabric in imbricate-shaped pods. Chromian spinel displays a limited range in Cr# [Cr/(Cr+Al)×100=53–63] and Mg# [Mg/(Mg+Fe2+)×100=59–73] and low TiO2 content (≤0.11wt%). Minor- (Ti, Ni, V, Mn and Zn) and trace-element (Sc, Co and Ga) concentrations do not show any significant variations from Cr-spinel cores to boundaries and were not considerably modified by post-magmatic processes. However, Cr-spinel compositions show slight enrichments in Zn and V, and depletions in Ti and Sc when compared to the composition of chromite from the East Pacific Rise mid-ocean ridge (MOR) basalts. The composition of Cr-spinel from the Metalleion chromitites is quite anomalous on a global perspective as these ores are not clearly associated to a suprasubduction zone (SSZ) or MOR chemistry.Field data indicate that the Metalleion chromitites lack remnant dunite envelopes due to prolonged shearing within the deforming harzburgite host and are constrained in location to a ductile-brittle shear zone that correlates with the transforming direction of the Domokos oceanic fault. Compositional data indicate that chromitites equilibrated with ambient harzburgite via a melt-peridotite interaction process followed by melt mixing. Geochemical calculations demonstrate that the parental magmas of the Metalleion chromitites had intermediate affinity between typical mid-ocean ridge basalts (MORB), island arc tholeiites (IAT) and boninites. We conclude that these melts originated within a hydrated and oxidized mantle wedge beneath an infant forearc basin connected by a transform fault to an active MOR.

Origin of the Bashierxi monzogranite, Qiman Tagh, East Kunlun Orogen, NW China: A magmatic response to the evolution of the Proto-Tethys Ocean

The Qiman Tagh of the East Kunlun Orogen, NW China, lies within the Tethysides and hosts a large W–Sn belt associated with the Bashierxi monzogranite. To constrain the origin of the granitic magmatism and its relationship with W–Sn mineralization and the tectonic evolution of the East Kunlun Orogen and the Tethys, we present zircon U–Pb ages and Hf isotopic data, and whole-rock compositional and Sr–Nd–Pb isotopic data of the Bashierxi monzogranite. The granite comprises quartz, K-feldspar, plagioclase, and minor muscovite, tourmaline, biotite, and garnet. It contains high concentrations of SiO2, K2O, and Al2O3, and low concentrations of TiO2 and MgO, indicating a peraluminous high-K calc-alkaline affinity. The rocks are enriched in Rb, U, Pb, and light rare earth elements, and relatively depleted in Eu, Ba, Nb, Sr, P, and Ti, and are classified as S-type granites. Twenty zircon grains yield a weighted mean 238U/206Pb age of 432±2.6Ma (mean square weighted deviation=1.3), indicating the occurrence of a middle Silurian magmatic event in the region. Magmatic zircons yield εHf(t) values of −6.7 to 0.7 and corresponding two-stage Hf model ages of 1663–1250Ma, suggesting that the granite was derived from Mesoproterozoic crust, as also indicated by 207Pb/206Pb ages of 1621–1609Ma obtained from inherited zircon cores. The inherited zircon cores yield εHf(t) values of 8.3–9.6, which indicate the generation of juvenile crust in the late Paleoproterozoic. Samples of the Bashierxi granite yield high initial 87Sr/86Sr ratios and radiogenic Pb concentrations, and negative εNd(t) values. Isotopic data from the Bashierxi granite indicate that it was derived from partial melting of ancient (early Paleozoic to Mesoproterozoic) sediments, possibly representing recycled Proterozoic juvenile crust. Middle Silurian granitic magmatism resulted from continental collision following closure of the Proto-Tethys Ocean. The Qiman Tagh represents a Caledonian orogenic belt containing S-type granites and associated W–Sn deposits.

Solidification Behavior of CaO–SiO2–Al2O3 Mold Fluxes Containing MgO and Low TiO2 Content Using Single Hot Thermocouple Technique (SHTT): Continuous‐Cooling‐Transformation (CCT) and Viscosity Analysis

The effect of MgO and low TiO2 content on the solidification of CaO–SiO2–Al2O3 based mold fluxes is investigated. The crystallization and viscosity behaviors are analyzed using single hot thermocouple technique (SHTT) and rotating viscometer, respectively. Continuous‐cooling‐transformation (CCT) results point to an increase of critical cooling rate (CCR) with increasing MgO content. Conversely, the presence of TiO2 seems to mitigate the effect of MgO on the crystallization due to the strong glass former characteristic of titanium dioxide. Viscosity measurements show an increase with increasing MgO content in slags containing TiO2. Break temperatures (Tbr) are compared to the onset crystallization temperatures from CCT experiments. Scanning electron microscopy (SEM) and X‐ray diffraction (XRD) analysis results indicate the presence of melilite (Al2Ca2Mg0.5O7Si1.5) for all samples of mold flux containing both MgO and TiO2.

Diverse lamprophyres origins corresponding to lithospheric thinning: a case study in the Jiurui district of Middle-Lower Yangtze River Belt, South China Craton

Late Mesozoic magmatic rocks that range in composition from mafic to felsic are widespread in the Jiurui district of the Middle-Lower Yangtze River belt in eastern Yangtze Craton of southeastern China. Among which the lamprophyre dikes represent mantle-derived magma and record deep mantle magmatic processes in the region. In this paper, we report a detailed study of geochronology, mineral chemistry, petrochemistry and Sr-Nd-Pb isotopes on the lamprophyres from the Nangang area in the Jiurui district, in an attempt to provide a comprehensive understanding in their petrogenesis, as well as the Mesozoic lithospheric mantle characteristics, and geodynamical control of the extensive Mesozoic magmatism in the Jiurui district. The Nangang lamprophyres belong to alkaline lamprophyre. They are characterized by low contents of SiO2 and TiO2, high Mg# values and high contents of compatible elements, and are enriched in LREE and LILE but depleted in HFSE (with Nb-Ta-Ti negative anomalies). They show moderate enriched Sr-Nd isotopic compositions with initial 87Sr/86Sr values of 0.70598 to 0.70715 and εNd(t) values of −2.2 to −1.6. They also show radiogenic Pb isotopic compositions with (206Pb/204Pb)i values of 17.678 to 18.558, (207Pb/204Pb)i values of 15.544 to 15.591 and (208Pb/204Pb)i values of 38.349 to 38.664. Combining new data from the Nangang lamprophyres with those of previously published data for lamprophyres in the Jiurui (i.e. Wushan I and II lamprophyres) and Edong districts (i.e. Ruanjiawan lamprophyres), we suggest that the Jiurui lamprophyres were likely derived from partial melting of the enriched lithospheric mantle characterized by phlogopite-bearing lherzolite in spinel-garnet transition zone at 75–85km depth. The feature of enriched-mantle source region was formed by metasomatism of subducted slab-derived fluids and melts, which is likely related to the Mesozoic subduction of the paleo-Pacific plate underneath the eastern China continent and the Neoproterozoic subduction of Cathaysia Block towards the Yangtze Craton. In contrast, the Ruanjiawan lamprophyres from the Edong district have the geochemical characteristics (such as the Nb-Ta positive anomalies) which are obviously different from the Jiurui lamprophyres, and we conclude that the Ruanjiawan lamprophyres, which are located more inland than the Jiurui district, were likely derived from the depleted asthenospheric mantle that show no significant influence by the subduction-related metasomatism. Furthermore, interpretation of the Sr-Nd-Pb isotope data for the Jiurui lamprophyres suggests slightly different petrogenesis for the various lamprophyre dikes, namely, the Nangang and Wushan–I lamprophyres were derived mainly from the enriched lithospheric mantle, but with addition of depleted asthenospheric mantle materials, whereas the Wushan–II lamprophyre dikes were product of the enriched lithospheric mantle without any signature for addition of depleted asthenospheric mantle materials. Given that these lamprophyres with distinct different isotopic compositions are sympatric and coeval, we consider that in the Late Jurassic to Early Cretaceous period (ca. 155–125Ma), the lithosphere was thinned to about 75–85km depth. The enriched lithospheric mantle was heated by the underlying convective asthenosphere and underwent partial melting to generate the Wushan–II lamprophyres. Subsequently, the enriched lithospheric mantle delaminated into depleted asthenospheric mantle, followed by partial melting coupled with an intensive interaction with the asthenospheric mantle to generate the Nangang and Wushan–I lamprophyres, respectively. Towards more inland, the Ruanjiawan lamprophyres were derived from the depleted asthenospheric mantle.

Effect of TiO2 content on the crystallization behavior and properties of CaO-Al2O3-SiO2 glass ceramic fillers for high temperature joining application

The effects of TiO2 content on the crystallization behavior, microstructure, microhardness, coefficient of thermal expansion (CTE) and softening temperature of CaO-Al2O3-SiO2 glass ceramic fillers were investigated. The results show that the crystallization activation energy (E) firstly decreases and then increases with the TiO2 addition from 10 wt% to 20 wt%. The microstructure and phase composition of glass ceramics importantly depend on the content of TiO2. Low TiO2 content results in formation of Ti-contained crystals (CaTiSiO5) due to phase separation. In contrast, high TiO2 concentrations lead to precipitation of small titanium oxide crystals that act as nuclei, facilitating the development of CaAl2Si2O8. Furthermore, the formation of crystalline phases is beneficial for improving the microhardness and refractoriness of glass ceramics. The CaO-Al2O3-SiO2 glass with 15 wt% TiO2 addition exhibits the highest crystalline volume fraction possibly due to the lowest activation energy of crystallization. As a result, its microhardness and softening temperature can reach as high as 898.2 HV and 1027 °C, respectively. However, its CTE slightly decreases from 7.44 × 10−6/°C to 6.35 × 10−6/°C after crystallization treatment because of the formation of CaTiSiO5.

Geochemistry, 40Ar/39Ar geochronology, and geodynamic implications of Early Cretaceous basalts from the western Qinling orogenic belt, China

The Qinling-Dabie orogenic belt was formed by the collision of the North and South China Cratons during the Early Mesozoic and subsequently developed into an intracontinental tectonic process during late Mesozoic. Field investigations identified the presence of late Mesozoic basalts in the Duofutun and Hongqiang areas in the western Qinling orogenic belt. The petrogenesis of these basalts provides an important constraint on the late Mesozoic geodynamics of the orogen. The representative basaltic samples yield the 40Ar/39Ar plateau age of about 112 Ma. These samples belong to the alkaline series and have SiO2 ranging from 44.98 wt.% to 48.19 wt.%, Na2O + K2O from 3.44 wt% to 5.44 wt%, and MgO from 7.25 wt.% to 12.19 wt.%. They demonstrate the right-sloping chondrite-normalized REE patterns with negligible Eu anomalies (1.00–1.10) and PM-normalized patterns enriched in light rare earth element, large ion lithophile element and high field strength element, similar to those of OIB rocks. These samples additionally show an OIB-like Sr-Nd isotopic signature with εNd(t) values ranging from +6.13 to +10.15 and initial 87Sr/86Sr ratios from 0.7028 to 0.7039, respectively. These samples are geochemically subdivided into two groups. Group 1 is characterized by low Al2O3 and high TiO2 and P2O5 contents, as well as high La/Yb ratios (>20), being the product of the high-pressure garnet fractionation from the OIB-derived magma. Group 2 shows higher Al2O3 but lower P2O5 contents and La/Yb ratios (<20) than Group 1, originating from asthenospheric mantle with input of delaminated lithospheric component. In combination with available data, it is proposed for the petrogenetic model of the Early Cretaceous thickened lithospheric delamination in response to the asthenospheric upwelling along the western Qinling orogenic belt.