High MgO Contents Research Articles

Geochemical and Sr–Nd–Hf–O isotopic constraints on the source and petrogenesis of the Xiangshuigou silicic alkaline igneous complex from the northern margin of the North China Craton

We present eudialyte and zircon U–Pb ages, whole-rock geochemical, and Sr–Nd–Hf and zircon Hf–O isotope data for the Xiangshuigou silicic alkaline igneous complex from the northern margin of the North China Craton (NCC). We use these data to investigate the source and petrogenesis of these alkaline igneous rocks and the lithospheric mantle evolution of the NCC. The Xiangshuigou complex consists of nepheline and porphyritic syenites without associated mafic or intermediate rocks. Zircon and eudialyte U–Pb dating yielded consistent ages of 227–219 Ma for these rocks. All the alkaline igneous rocks from the Xiangshuigou complex have high Na2O, Al2O3, Rb, Th, and Zr, and low MgO, CaO, P2O5, and Ba contents, and are enriched in large-ion lithophile and light rare earth elements. These rocks are not depleted in high-field-strength elements. Whole-rock Nd–Hf isotopic compositions are slightly enriched, with εNd(t) = −3.7 to −3.0 and εHf(t) = −3.1 to +0.6. Zircon Hf–O isotope analyses yielded εHf(t) and δ18O values of −0.6 to −6.0 and +5.1‰ to +6.0‰, respectively. These geochemical and isotopic features suggest that the silicic alkaline igneous rocks were derived by partial melting of an enriched lithospheric mantle source before experiencing protracted two-stage fractional crystallization. The lithospheric mantle source of the Xiangshuigou complex was distinct from the Paleozoic cratonic lithospheric mantle and experienced mantle metasomatism by depleted mantle-derived carbonate-bearing materials prior to the alkaline magmatism. This indicates that, in addition to subducted crustal melts/fluids, asthenosphere-derived materials were also involved in modifying the lithospheric mantle of the northern NCC. As such, our work not only approves the effectivity of using whole-rock geochemistry and Sr–Nd–Hf–O isotopic data to reveal origin of the silicic alkaline igneous rocks, but also argues for a multiple modification for the northern NCC during the late Paleozoic to early Mesozoic.

Early Cretaceous (Albian) intra‐oceanic subduction in northern branch of Neotethys in NW Iran: Zircon U–Pb geochronology and geochemistry of ophiolitic metagabbros from the Chaldoran area

The Chaldoran ophiolite in NW Iran and at the Turkish border is a part of the larger Khoy ophiolite. Serpentinized peridotites, pillow basalt, cumulate and isotropic gabbro, pelagic limestone, and radiolarite along with volcano‐sedimentary units are the main rock types in the area. These rocks are mixed together in some places as tectonic and “coloured” mélanges. The gabbro consituent of this ophiolite is either fresh or is metamorphosed up to upper greenschist facies. These meta‐basic rocks contain relatively large crystals of plagioclase and clinopyroxene, partially changed to amphibole. Metamorphic epidote is formed in some samples. Whole‐rock chemistry of these rocks shows a basaltic magmatic composition. Low SiO2 contents along with relatively high MgO and FeOtotal contents testify for a mantle source for the parental magma of the studied samples, intermediate between tholeiitic and calc‐alkaline series. LREE and HFSE are slightly depleted and LILE show enrichment in the studied samples and Ta, Nb, Ti show negative anomalies with respect to MORBs. All chemical features are compatible with a supra‐subduction zone setting for the rocks. The studied rocks are similar to primitive arc and less evolved rocks, geochemically. Also the samples show both MORB‐like magmas, formed at the initial stage of a subduction and IAT chemical features. U–Pb dating of zircons on the gabbro sample gave 107.5 ± 1.3 Ma (Albian) crystallization age. The metabasites from the Chaldoran ophiolite are similar to intra‐oceanic ophiolite‐related igneous rocks from the Zagros suture zone in Iran and NE Iraq and equivalent rocks from the Neotethyan sutures in east Turkey and Armenia and basic rocks from the Late Cretaceous ophiolites of the outer Zagros and Taurus, which are related to the subduction initiation (SI) stage.

The Characteristics and Significance of Peng Co Peridotites in the Middle Segment of Bangong Co‐Nujiang Suture in Tibet

AbstractThe Peng Co ophiolite is located to the west of Peng lake in the area of lakes in north Tibet, which belongs to the Baila‐Yilashan sub‐belt of the the middle Bangong Co‐Nujiang ophiolitic belt. The Peng Co ophiolite is mainly composed of mantle peridotites, cumulates, diabase dikes. About 70 percent peridotites are harzburgites and 30 percent are lherzolites. Mineral chemistry of the Peng Co lherzolitesare characterized by low Fo contents (88.85–90.33) of olivine and high Al2O3 content (4.26%–7.25%) in pyroxenes. Compared to the primitive mantle, the Peng Co peridotites have relatively higher MgO contents, lower CaO, Al2O3 and TiO2 contents. The total rare‐earth element (REE) contents of the lherzolites are 1.11–1.53 ppm, which are lower than those of the primitive mantle. The chondrite‐normalized REE patterns of the Peng Co peridotites display slight loss in LREE. In the primitive mantle‐normalized spider diagram, the Peng Co peridotites exhibit negative Rb and Zr anomalies and intensively positive U, Ta, Sr anomalies. The PGE contents of Peng Co lherzolites are between 22.9–27 ppb. The chondrite‐normalized PGE patterns of the Peng Co lherzolites are consistent with that of the primitive mantle. Mineral and whole‐rock geochemistry characteristics of the Peng Co lherzolites show an affinity to abyssal peridotites, indicating that it may have formed in the mid‐ocean ridge setting. Through quantitative modeling, we conclude that the Peng Co lherzolites formed after 5%–10% degree of partial melting of the spinel‐phase lherzolite mantle source. The sharp increase of Cr# (56.74 –60.84) in Spinel of harzburgites and relatively high Pd/Ir and Rh/Ir ratios suggest that they have experienced melt‐rock reaction. The crystallization sequence of Peng Co cumulate is olivine‐clinopyroxene‐plagioclase. The Mg# value of clinopyroxene in cumulate peridotite ranges from 86.92 to 89.93, and the mean value of Fo is 84.45, which is obviously higher than that of MOR‐type ophiolite cumulates. The mineral composition, sequence of magmatic crystallization and mineral components of Peng Co cumulate are similar to those of the cumulate formed by the SSZ‐type ophiolite in the subduction zone. Therefore, we can draw a preliminary conclusion that Peng Co lherzolites were formed in an environment of mid oceanic ridge and were remnants of the spinel lherzolite zone which experienced a partial melting of no more than 10%. In the later period, due to the intra‐oceanic subduction, it experienced the rock‐meltinteraction, and thus formed the SSZ‐type cumulate and harzburgite of high Cr value.

Geochronology and Geochemistry of Gabbros from Moa‐Baracoa Ophiolitic Massif, Eastern Cuba: Implication for Early Cretaceous SSZ Magmatism

AbstractA series ophiolitic massifs in the northeastern part of Cuba are generally considered to be relics of proto‐Caribbean or Caribbean lithosphere, emplaced during Paleogene collision of the NW Caribbean and North American plates (Iturralde‐Vinent et al., 2016). However, neither their age nor their geodynamic settings are well constrained. They are generally considered to be Creataceous in age but they have been interpreted as having formed in a back‐arc basin, forearc basin or plume setting (e.g. Giunta et al., 2009; Marchesi et al., 2016; Kerr et al., 1999). The Moa‐Baracoa ophiolitic massif consists of mantle harzburgite, a Moho transition zone, layered and isotropic gabbro, and pillow basalts. The isotropic gabbros, collected west of Moa (20°35′ 17.99″N, 75°02′56.58″W), are composed mainly of subhedral plagioclase and subhedral to euhedral clinopyroxene with minor primary brown amphibole. The plagioclase grains are fresh, whereas the clinopyroxene very weakly altered and partly replaced by secondary amphibole. Cathodoluminescence (CL) images of zircon grains separated from isotropic gabbro display oscillatory zoning and broad zoning, analogous to typical igneous zircon in gabbro. Ten zircon grains with oscillatory zoning in CL images yielded a mean U‐Pb SHRIMP age of 136.7±1.8 Ma. Isotropic gabbro samples have low SiO2 (47.22 wt%–49.25 wt%), TiO2 (0.13wt%–0.26 wt%) and K2O (0.04 wt%–0.08 wt%) and high MgO (8.22 wt%–16.72 wt%), Cr (1337–2065 μg/g) and Ni (192–507 μg/g) contents. Their CaO, Al2O3 and Na2O contents vary from 13.56 wt% to 15.78 wt%, 14.98 wt% to 21.98 wt%, and 0.71 wt% to 1.87 wt%, respectively. In the SiO2 versus Zr/TiO2∗0.0001 diagram, the samples plot in the sub‐alkaline basalt field but show calc‐alkaline affinities in the FeOT/MgO vs. SiO2 diagram. The gabbros contain low REE contents (ΣREE = 4.71–7.71), and their chondrite normalized REE patterns show very weak depletion in light REE (LREE, (La/Yb)N = 0.34–0.50) and flat heavy REE (HREE, (Gd/Yb)N = 1.02–1.15) profiles, with slightly positive Eu anomalies (Eu/Eu∗ = 1.55–1.76) suggesting magmatic accumulation of plagioclase. Furthermore, all samples are depleted in Nb and Th, and enriched in Ba, Pb and Sr in the primitive mantle‐normalized trace element diagram. Geochemical features, such as high values of Ba/La (30–38) and low Th/Yb (0.02–0.03), medium values of (Ta/La)PM (0.30–0.35) and (Hf/Sm)PM (0.58–0.80), indicate enrichment by slab‐derived fluids and subduction‐related metasomatism. These isotropic gabbros are geochemically comparable with those of the Kermanshah and Neyriz ophiolites of Iran (Monsef et al., 2018) that are thought to have originated in a SSZ environment. Therefore, we suggest that the isotropic gabbros in the Moa‐Baracoa massif crystallized from early Cretaceous SSZ magmas that were most likely derived from a mantle source metasomatized by slab fluids in a suprasubduction zone environment.

Genesis of Cretaceous igneous rocks and its related large scale porphyry Cu-Au mineralization in Chating, the Middle-Lower Yangtze River Metallogenic Belt: The geochemical constrains

The newly discovered large Chating porphyry Cu–Au deposit is associated with early Cretaceous intrusive rocks in the Middle-Lower Yangtze River Belt (MLYRB), eastern China. Two types of intrusive rocks in the Chating area have been identified, i.e., the quartz-diorite porphyry, related to the Cu–Au mineralization, and the diorite porphyry that is ore-barren. Zircon LA–ICP–MS U–Pb dating yields 145–136 Ma for the Chating intrusions. They both belong to High-K calc-alkaline series, with enrichments of large-ion lithophile elements (LILEs) and light rare earth elements (LREEs), depletions of high field-strength elements (HFSEs) and heavy rare earth elements (HREEs), and no or slightly negative Eu anomalies. The quartz-diorite porphyry shows high Sr contents and Sr/Y ratios; low MgO, Cr and Ni contents; medium (La/Yb)N and Mg# (34.6–54.6) and low K2O/Na2O (<1) values; decoupling of Sr/Y and (La/Yb)N; and low Th/U (3.49–6.08) values, thus exhibiting characteristics of slab-derived adakitic rocks. In addition, it has slightly enriched Sr–Nd–Hf isotopes ((87Sr/86Sr)i = 0.70655–0.70717, εNd(t) = −6.9 to −8.8, and εHf(t) = −7.6 to −10.6) and high radiogenic Pb isotopes ((206Pb/204Pb)i = 18.22–18.70, (207Pb/204Pb)i = 15.63–15.66 and (208Pb/204Pb)i = 38.49–38.97), reflecting the involvement of subducted sediments in the magma source. Therefore, the fertile quartz-diorite porphyry was most likely generated by the partial melting of the slab-derived, subducted sediments and a partial degree of metasomatized mantle-derived magma with crustal assimilation. As to the barren diorite porphyry, it has similar Sr–Nd–Pb isotope and trace element features as the fertile adakitic samples. However, it shows relatively lower SiO2 contents; high contents of MgO (3.89–4.06 wt%), Cr and Ni (avg. 47.6 ppm and avg. 15.01 ppm); high Mg# (51.2–69.8); and more enriched Hf isotope characteristics (−8.5 to −12.9), which imply that this barren diorite porphyry could be generated from the partial melting of enriched metasomatised lithospheric mantle assimilated with old continental crust materials. The δ34S values of the pyrite and chalcopyrite of the ores in Chating indicate a magmatic-derived source, resembling other porphyry-skarn Cu–Au deposits in the MLYRB. The fertile Qtz-diorite porphyry adakitic rocks are characterized by higher oxygen fugacities than the barren diorite porphyry, which are closely related with the partial melting of the subducted oceanic slab in an oxidizing environment, thus making them favorable for Cu–Au mineralization.

The Tapes Complex (Nico Pérez Terrane, Uruguay): Constraining the Mesoproterozoic evolution of the Río de la Plata Craton

The Tapes Complex crops out in the southeastern Nico Pérez Terrane (NPT) of the Río de la Plata Craton and forms part of a NE-trending Mesoproterozoic belt together with the Calymmian (1.48–1.43 Ga) Parque UTE and Mina Verdún groups. The complex is characterized by interbedded/tectonically interleaved metasedimentary (mainly siliciclastic) and metaultramafic rocks, with subordinate intercalations of metabasites, carbonate and chert, all metamorphosed in the greenschist facies. The age of the Tapes Complex is constrained by: (i) a U–Pb SIMS age of 1360 ± 12 Ma for the youngest detrital zircon, (ii) the K–Ar age of 1253 ± 32 Ma for synkinematic muscovite of the Zapicán thrust, which affects the unit, and (iii) an Sm–Nd isochronic age of 1403 ± 150 Ma for ultramafic and mafic rocks. The intruding Tapes Chico Syenite yielded a much younger U–Pb SIMS age of 601 ± 5 Ma, associated with Brasiliano-Pan African tectonism, negative εHf values (mean = −31), δ18O zircon ratios ranging between 5.45 and 6.68‰ V-SMOW and inherited zircons dated at 1774-1756 Ma. The best preserved mafic and ultramafic samples yielded Nd model ages (TDM) between 1.55 and 1.68 Ga, close to the assumed crystallization age, and positive εNd(t). Nd model ages of metasedimentary rocks vary between 1.8 and 3.1 Ga, which is interpreted as reflecting two contrasting sources: Archean units of the NPT and Mesoproterozoic mafic and ultramafic rocks, including fragments of oceanic crust. Chondrite-normalized REE patterns of metasedimentary rocks are characterized by LREE enrichment and lack of an Eu anomaly, similar to REE patterns of co-occurring metabasalts. High MgO concentrations, high Cr/V and low Y/Ni and Th/Sc ratios imply the involvement of ultramafic rocks in the source area, which is also supported by whole-rock Pb isotope data. A geodynamic evolution is envisaged, from an extensional tectonic setting between 1.48–1.43 Ga (rift or retroarc basin) into a compressional, retroarc foreland basin at ca. 1.25–1.20 Ga, the latter being probably related to the Kibaran Orogeny in the Namaqua-Natal Belt. It is proposed that the corresponding arc granites and high-grade metamorphic rocks are likely to be found in one of the several terranes in the Namaqua sector of the belt. The Apiaí Terrane (Ribeira Belt, Brazil) shows a similar geological record and evolution as the NPT, and maybe a fragment of the latter displaced to the NW by the Ibaré Shear Zone. The Tapes Complex is a key unit for understanding the assembly of the Río de la Plata and Kalahari cratons, and their incorporation into the Rodinia supercontinent.

Stabilization of hazardous lead glass sludge using reactive magnesia via the fabrication of lightweight building bricks

This study focused on the stabilization of lead glass sludge (LGS) using reactive magnesia (MgO) via the fabrication of lightweight building bricks. Two types of MgO with different reactivities were prepared by the thermal treatment of magnesium carbonate at 800 °C and 1200 °C (MgO-800 and MgO-1200, respectively). The fabrication of bricks and Pb stabilization were performed by wet mixing LGS with MgO followed by humidity incubation. Results showed that the Pb immobilization and performance of the produced bricks were strongly affected by MgO reactivity, curing time, and LGS–MgO weight ratios. Pb immobilization was performed by the transformation of soluble lead into an insoluble hydrocerussite phase, particularly in hydrated mixtures with high MgO content (> 25 wt%). Pb immobilization inside a magnesium silicate hydrate skeleton is the main mechanism in the hydrated samples containing 25 wt% MgO. To achieve “sustainability,” we recommend the use of a hydrated mixture containing 75 wt% of LGS and 25 wt% of MgO-800 in the production of building bricks because this mixture exhibits high compressive strength, high Pb immobilization, low energy demand, and low environmental pollution.

The Ryonchon podiform chromitite from the Chongjin ophiolite, northern Korea Peninsula

Ryonchon chromitite is located structurally in the Chongjin area, the northern part of the Korean Peninsula, which crops out at Chongjin terrane, the eastern end of the Jilin-Yanbian-Hambuk Fold Belt. We made on-site geological survey of this deposit and conducted the analyses on the investigated chromitite by means of microscopes, single crystal X-ray diffraction (SXRD) and electron probe micro-analysis (EPMA) to elucidate the phase composition, the chemical composition and the texture and structure of the chromitite. The chromian spinels from the study area are separated into four groups according to chemical composition of spinel as ordinary spinel-group minerals are. The studied chromites have different compositions according to their occurrences, which is not owing to the precipitation of different pararental melts but the subsolidus re-equilibration during the hydrous alternation.The massive/semi-massive unaltered chromite in chromitite from dunite have consistently low Cr (Cr# < 0.6) and low Al (Al2O3 23–26 wt%), whereas Al2O3melt and (FeO/MgO)melt values range 14.58–15.43, 0.40–0.52, respectively, which have been contrasted with that of the typical podiform chromitite. By comparing present analyses with previous works, the parental melt of the Ryonchon chromitite from the Chongjin ophiolite is similar in chemical compostion to Island arc tholeiitic melts rather than boninitic melt, whose tectonic setting corresponds to a forearc environment of a suprasubduction zone. In addition, both cumulus texture and euhedral crystal shapes of the chromite grains in massive/semimassive chromitite from dunite support their magmatic origin. We found that the chromitite from this area have undergone the hydrothermal alteration as appearance of fluidal ferritchromit, Cr# of ferritchromites higher than 0.8, the high MgO content of the ferritchromit, occurrence of typical hydrothermal minerals such as heazlewoodite and the differences in the products formed during several metamorphic processes.

Subduction initiation of Proto-Tethys Ocean and back-arc extension in the northern Altun Mountains, northwestern China: Evidence from high-Mg diorites and A-type rhyolites

Subduction initiation and sequent evolution of oceanic lithosphere at convergent plate boundaries have important implications for our understanding of plate tectonics. Using zircon U-Pb and Lu-Hf isotopic and whole-rock geochemical data of newly identified Baijianshan diorites and Dawanbei and Dabanxi rhyolites from the center of the North Altun Orogenic Belt, we provide the time constraint for the initial subduction of the Proto-Tethys Ocean lithosphere and back-arc extension in the northern Altun Mountains. Zircon U-Pb ages show that the Baijianshan diorites emplaced at ~535 Ma and the Dawanbei and Dabanxi rhyolites erupted at ~495 Ma. The Baijianshan diorites share most features of high-K calc-alkaline high-Mg andesites, characterized by moderate SiO2 contents (56.34-57.65 wt.%), high MgO contents (4.72-5.26 wt.%) and Mg# (57-65) values, and LREE and LILE enrichment relative to HREE and HFSE (Nb/La = 0.46-0.78). Their elemental geochemistry and coupled negative whole-rock ɛNd(t) (-9.1 to -8.5) and zircon ɛHf(t) (-15.4 to -10.9) values suggest that the diorites were formed by interaction between the subducted sediment-derived melts and peridotites in the mantle wedge. The Dawanbei and Dabanxi rhyolites are metaluminous to weakly peraluminous, and have high SiO2 (70.07-78.65 wt.%) and Na2O (2.27-5.97 wt.%) contents, and low K2O (0.95-4.72 wt.%) contents. The rhyolites are enriched in most incompatible trace elements (e.g. Rb, Th, Zr, Hf and REE), and show affinity with A2-type granites. Isotopically, they have whole-rock ɛNd(t) values of -0.7 to -0.2 and zircon ɛHf(t) values of -2.3 to 6.4. Geochemical and isotopic compositions suggest that these rhyolites were derived through shallow (1-3 kbar) dehydration melting of basaltic rocks. Our analysis together with the regional geology of the northern Altun Mountains indicates that subduction of the Proto-Tethys Ocean lithosphere began started at ~535 Ma in the northern Altun Mountains. The juvenile A-type rhyolites (~495 Ma) are spatially and temporally associated with the Dawan high-Mg andesites and diorites (480-495 Ma), indicating that they were likely formed in a back-arc basin that was extending due to rollback of subducted oceanic lithosphere. The subduction process most likely continued until ~460 Ma and the Proto-Tethys Ocean finally closed at ~440 Ma. As a result, the central Altun terrane, as well as Tianshuihai-Mazar, Central Qilian, and North Qinling docked to the northern margin of Eastern Gondwana at ~440 Ma.

Amalgamation between the Yangtze and Cathaysia blocks in South China: Evidence from the ophiolite geochemistry

Neoproterozoic ophiolites in the southeastern margin of the Yangtze Block record tectonic evolution of South China. The ∼1.0 Ga Xiwan ophiolite and the ca. 830 Ma Fuchuan ophiolite indicate a long-term assembly of the Yangtze and Cathaysia blocks during the Neoproterozoic time. Peridotites from the Xiwan ophiolite show high Al2O3 (1.24–2.67 wt%) and low MgO contents (39.61–44.26 wt%), similar to the abyssal and back-arc peridotites that experienced low degrees of partial melting. Their U-shaped REE patterns and HFSE enrichment indicate weak melt metasomatism. Whole rock 187Re/188Os (0.09–0.29) and 187Os/188Os ratios (0.11526–0.12193) yield a melt-extraction age of 1.8–2.1 Ga. However, peridotites from the Fuchuan ophiolite are more refractory and have low Al2O3 (0.51–0.95 wt%) and high MgO contents (43.99–48.24 wt%), similar to the forearc peridotites that underwent high degrees of melt extraction. Their 187Re/188Os (0.01–1.08) and 187Os/188Os (0.11852–0.12867) variations may have resulted from fluxed melting induced by the subduction-related fluids. The peridotites, in combination with the overlying mafic oceanic crustal rocks, suggest that the Xiwan and Fuchuan ophiolites are SSZ-type ophiolites which were formed in back-arc and forearc settings, respectively, followed by the collision between the Yangtze and Cathaysia blocks at ca. 830 Ma.

Late Miocene to Pliocene crustal extension and lithospheric delamination revealed from the ~5 Ma Palopo granodioritic intrusion in Western Sulawesi, Indonesia

Recent studies have revealed that following collision between the Western Sulawesi and Sula Spur microcontinents during the early to middle Miocene, the Western Sulawesi microcontinent subsequently underwent extension. However, the geodynamic process that resulted in extension is unknown. The petrogenesis of late Miocene to Pliocene granitoids in the region provides insights to the mechanism of extension. To achieve this goal, we studied the Palopo granodioritic intrusion, a well-exposed representative pluton that crops out along the Palu–Koro Fault. Zircon U–Pb dating indicates a 4.8–4.7 ± 0.1 Ma crystallization age for the pluton. Compared with arc igneous rocks, the pluton has high Sr contents and low Y and Yb contents, with relatively high Sr/Y and LaN/YbN ratios. These geochemical signatures are similar to those of typical adakites. The samples exhibit high MgO (1.60–2.54 wt%), Cr (46–65 ppm), and Ni (14.1–19.0 ppm) contents relative to adakitic rocks derived from thickened lower crust. In addition, negative εHf(t) (−9.7 to −5.5) and εNd(t) (−8.5 to −11.1) values, together with relatively low 143Nd/144Nd and high initial 87Sr/86Sr ratios, reflect an origin through recycling of ancient crustal materials, which is clearly different from adakites derived from melting of a subducting slab. The most plausible mechanism for generation of the late Miocene–Pliocene adakitic granodiorites in the Western Sulawesi microcontinent is partial melting of delaminated lower crust that interacted with the mantle. We propose that the late Miocene to Pliocene crustal extension in the Western Sulawesi microcontinent was triggered by delamination of pre-existing thickened lithosphere.

Sintering properties of olivine and its utilization potential as a refractory raw material: Mineralogical and microstructural investigations

In this study, an olivine sample obtained as final tailing from a chromite enrichment plant was examined for its sintering properties and utilization potential as a refractory raw material. For this purpose, cylindrical specimens were first prepared and then sintered at the temperatures of 1300, 1400, 1450 and 1500 °C for 2 h in a laboratory furnace. Quality of the products was evaluated in terms of some physical and mechanical refractory specifications such as bulk density, water absorption, porosity, shrinkage and cold crushing strength. Furthermore, phase developments and microstructural changes due to the sintering were determined in detail with X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis, respectively. According to the experimental results, with increasing temperature, the bulk density and shrinkage values increased while the porosity and water absorption values decreased. Specifically, the bulk density and shrinkage values varied in the ranges of 2.33–2.60 g/cm3 and 1–5%, respectively. The porosity values of 24.10 and 15.68% were obtained after sintering at 1300 and 1500 °C, respectively. The cold crushing strengths slowly increased from 46.90 to 55.86 MPa after sintering between 1300 and 1450 °C. A sudden rise to 93.44 MPa was then observed at 1500 °C. Accordingly, the thermo-optical analysis indicates that the olivine exhibited a sintering point of 1478 °C and no softening up to 1500 °C. However, the formation of undesirable low-melting enstatite was detected by the XRD and SEM analysis which also specified the increasing amorphous phase and crystallizations of forsterite and spinels with rising temperature. Overall results have shown that the olivine sample used has a promising potential as a refractory raw material mainly due to its high MgO content, low loss on ignition (LOI) value and appropriate particle size.

Subduction and Collision of the Jinsha River Paleo‐Tethys: Constraints from Zircon U‐Pb Dating and Geochemistry of the Ludian Batholith in the Jiangda–Deqen–Weixi Continental Margin Arc

AbstractThe Jiangda–Deqen–Weixi continental margin arc (DWCA) developed along the base of the Changdu–Simao Block and was formed as a result of the subduction of the Jinsha River Ocean Slab and the subsequent collision. The Ludian batholith is located in the southern part of the DWCA and is the largest batholith in northwest Yunnan. Granite samples from the Ludian batholith yield an early Middle Permian age of 271.0 ± 2.8 Ma. The geochemical data of the early Middle Permian granitoids show high Si2O, low P2O5 and MgO contents that belong to calc‐alkaline series and peraluminous I‐type rocks. Their ∊Hf(t) values range from –5.01 to +0.58, indicating that they were formed by hybrid magmas related to the subduction of the Jinsha River Tethys Ocean. The monzonite and monzogranite samples yield Late Permian ages of 250.6 ± 1.8 Ma and 252.1 ± 1.3 Ma, respectively. The Late Permian granitoids are high‐K calc alkaline and shoshonite series metaluminous I‐type rocks. Their ∊Hf(t) values range from –4.12 to –1.68 and from –7.88 to –6.64, respectively. The mixing of crustal and mantle melts formed the parental magma of the Late Permian granitoids. This study, combined with previous work, demonstrates the process from subduction to collision of the Jinsha River Paleo‐Tethys Ocean.

Sinterability and mechanical properties of glass-ceramics in the system SiO2-Al2O3-MgO/ZnO

The sintering, crystallization and mechanical behavior of three glass compositions in the SiO2-Al2O3-MgO/ZnO system were investigated. Partial substitution of MgO by ZnO causes a decrease in Tg, a slight increase in the crystallization temperature and improves sinterability. Cordierite and enstatite were crystallized in bulk glasses heat treated at 1000 °C. Addition of ZnO resulted in the crystallization of cordierite, willemite and gahnite for the heat treated bulk glasses and cristobalite, enstatite, gahnite and willemite for the sintered glass powders. The first phase to crystallize is the β-quartz solid solution at 850−900 °C for all compositions. The glass and glass-ceramic with ZnO had the lowest hardness and elastic modulus. There was no variation of fracture strength with composition. The glass-ceramic with ZnO had a similar wear resistance in comparison to the composition with higher MgO content.

Early Cretaceous Xiuyan adakitic granitoids in the Liaodong Peninsula, eastern China: petrogenesis and implications for lithospheric thinning of the North China Craton

Mesozoic magmatic rocks are widely distributed in the North China Craton (NCC) and are crucial to understanding the timing, location, and geodynamic mechanisms of lithospheric thinning of the NCC. In this study, we report geochronological, petrogeochemical, and Lu–Hf isotopic data for adakitic granitoids from different parts of Xiuyan pluton in the Liaodong Peninsula, aiming to constrain their magma sources, petrogenesis, and tectonic implications. The adakites are metaluminous to weakly peraluminous and are classified as high-K calc-alkaline I-type granite with Early Cretaceous zircon U–Pb ages of 129–126 Ma. They exhibit adakite-like geochemical characteristics, such as high Sr content and low Yb and Y contents, coupled with high Sr/Y and no pronounced Eu anomalies. They are enriched in Rb, U, and light rare-earth elements and are depleted in Ta, Nb, P, and Ti. The adakites from the eastern part of the pluton have low εHf(t) values (–8.5 to –4.0) with old TDM2ages (1.57–1.31 Ga), indicating they were derived from the lower crust containing juvenile mantle-derived materials. In contrast, adakites from the northern part of the pluton have lower εHf(t) values (–19.7 to –16.6) with older TDM2ages (2.21–2.03 Ga), indicating that they were derived mainly from an ancient crust. Our results show that both adakitic magmas were derived from partial melting of delaminated lower crust. Their relatively high MgO and Ni contents and Mg# values indicate that the melts interacted with mantle peridotites. The lower crust delamination beneath the Liaodong Peninsula resulted from paleo-Pacific plate subduction during the Early Cretaceous, which resulted in thinning of Mesozoic crust in the Xiuyan area.

Mesozoic continental crustal rejuvenation of South China: Insights from zircon Hf[sbnd]O isotopes of early Jurassic gabbros, syenites and A-type granites

Whole rock geochemistry and Sr-Nd-Hf isotope, zircon UPb and HfO isotope data are reported for the early Jurassic gabbro-syenite-alkali-feldspar granite in the inland of South China, in order to investigate their sources, petrogenesis and tectonic implication, and to further trace the rejuvenation of continental crust of South China. The zircon UPb dating constrains the crystallization ages of 198–195 Ma for syenites, and of about 190 Ma for alkali-feldspar granites and gabbros, respectively. The early Jurassic gabbros have low SiO2 contents and high MgO, TiO2, Cr, V and Ni concentrations, with weak negative Nb and Ta anomalies, variable whole rock initial 87Sr/86Sr ratios (0.7064–0.7117), εNd(t) values (−1.5 to +0.6), εHf(t) values (−1.6 to +5.7) and zircon εHf(t) values (+3.4 to +6.4) and mantle-like δ18O values (+4.9 to +6.2‰). They are inferred to be derived from partial melting of a fertile lithospheric mantle that had been metasomatized by subduction-related fluids/melts, with subsequent limited crustal assimilation and fractional crystallization. The early Jurassic syenites are high-K to shoshonitic rocks with weakly negative Nb and Ta anomalies, strongly negative Sr, P and Ti anomalies, unradiogenic Sr and radiogenic Nd and Hf isotopic compositions (εNd(t) up to +5.3 and εHf(t) up to +11.5), indicating that they were generated by low-percentage partial melting of an amphibole-bearing lithospheric mantle, with subsequent crustal assimilation and extensive crystal fractionation and/or accumulation. The geochemical features of the early Jurassic K-feldspar granites suggest that they were mainly generated by mixing between mantle-derived mafic magma and crustal-derived felsic magma with extensive feldspar-dominant fractional crystallization. The early Jurassic magmatism was possibly triggered by asthenospheric upwelling following delamination of the flat-subducted Paleo-Pacific plate beneath South China, which provided heat to partial melting of above lithospheric mantle and continental crust. The underplating of depleted mantle-derived magmas changed the ancient crustal structures and modified the components of continental crust, indicating lithospheric rejuvenation during early Jurassic in South China.

Tracing arclogites in the Paleoproterozoic Era – A shift from 1.88 Ga calc-alkaline to 1.86 Ga high-Nb and adakite-like magmatism in central Fennoscandian Shield

Arclogites, i.e., lower crustal garnet-pyroxenite cumulates, are suggested to play an important role in controlling magma differentiation in modern continental arcs. Until now, arclogite-related magmatism has only been described from the Phanerozoic Era. The Svecofennian orogen in the central Fennoscandian Shield hosts a rare association of 1.86 Ga igneous rocks geochemically distinct from the surrounding and much more abundant 1.90–1.87 Ga subduction-related calc-alkaline magmatism. The 1.86 Ga magmatic rocks are divided into three groups: 1) high-Nb gabbros (HNB) which are enriched in Fe2O3T, TiO2, P2O5, F, LILE, and HFSE (especially Nb; 18.9–44 ppm), show positive initial εNd value, and near-chondritic but variable initial zircon εHf values; 2) high-Mg gabbros (HMG) which are characterised by high MgO, CaO, Cr and Ni contents, slight enrichment in LILE, positive εNd, and positive but variable zircon εHf values; 3) adakite-like rocks showing high Al2O3 and Na2O contents, slight enrichment in LILE, relative depletion in some HFSE, positive εNd value, and chondritic to negative zircon εHf values. The three groups yield zircon U-Pb ages of ~1.86 Ga and exhibit undeformed textures in contrast to the surrounding supracrustal rocks metamorphosed at ~1.88 Ga. The ages and compositions are clearly different from the adjacent 1.90–1.87 Ga arc-related igneous rocks suggesting a distinct origin. Despite similar ages and close spatial relationship, separate sources are required for each of the different 1.86 Ga rock groups. Trace element modelling of partial melting suggests that arclogites, with compositions similar to pyroxenite xenoliths found in the kimberlite pipes of eastern Finland, are the source for the HNB rocks. In contrast, subduction-modified mantle peridotite is the source for the HMG rocks, and a mafic lower crustal source is suggested for the adakite-like rocks. The following geodynamic model is suggested: (rutile-bearing) arclogite formation at 1.90–1.87 Ga followed by arclogite delamination and partial melting during extension of the thickened Svecofennian crust at 1.86 Ga.

Amphibole and whole-rock geochemistry of early Late Jurassic diorites, Central Tibet: Implications for petrogenesis and geodynamic processes

Arc magmas are generated by complex geological processes in subduction settings. Due to the complexity of source materials and geological processes, the genesis of arc magmatic rocks can be difficult to disentangle. Here, we report on diorites from the Kenama area of the middle-eastern part of the Bangong–Nujiang suture zone in central Tibet. New SIMS and LA–ICP–MS zircon UPb dating for three diorite samples indicates that they crystallized during the early Late Jurassic (ca. 161 Ma). The diorites can be divided into two groups based on whole-rock major element compositions and mineralogical characteristics: Group I diorites with relatively low SiO2 (47.6–53.4 wt%), and high MgO (4.97–9.10 wt%) and amphibole contents (50–54 vol%); and Group II diorites with slightly higher SiO2 (56.9–59.5 wt%), and low MgO (2.9–3.8 wt%) and amphibole contents (25–30 vol%). The Group I diorites exhibit relative enrichment in light rare earth element (LREE) ((La/Yb)N = 5.7–10.5) with slightly negative Eu anomalies, and are characterized by enrichment of large ion lithophile elements (LILEs; K, Rb, Ba, Th, and U), the depletion of high field strength elements (HFSEs; Nb, Ta, Zr, Hf, and Ti). The Group I diorites have relatively high initial 87Sr/86Sr ratios (0.7073–0.7094), variably negative εNd(t) values(−10.3 to −5.9), negative zircon εHf(t) values (−14.8 to–4.4), and slightly elevated δ18O values (6.5‰–7.3‰). The Group II diorites show similar trace element characteristics to Group I. They also have high initial 87Sr/86Sr ratios (0.7083–0.7087), uniformly negative εNd(t) values (−9.5 to −9.0), negative zircon εHf(t) values (−10.3 to −4.2), and elevated δ18O values (6.6‰–7.5‰). Amphiboles from Group I and Group II diorites have low Al2O3 contents (3.6–9.9 wt% and 5.6–8.5 wt%, respectively), and formed at similar P–T conditions (751–871 °C and 69–226 MPa and 745–832 °C and 77–162 MPa, respectively). On primitive mantle-normalized spider diagrams, these low-Al amphibole grains have slightly convex upward REE patterns with distinctly negative anomalies in Pb, Sr, Eu, Zr, Hf, and Ti, suggesting that amphiboles from both groups crystallized from the similar arc magmas after plagioclase and magnetite crystallization. These mineralogical, geochemical and isotopic characteristics suggest that both groups of Kenama diorites probably originated from an enriched lithospheric mantle metasomatized by subducted oceanic sediment-derived melts. Their parental magmas may have similar geochemical characteristics and underwent varying degrees of accumulation and fractional crystallization. The Group I diorites were likely generated by accumulation of amphibole and fractional crystallization of olivine, clinopyroxene, and plagioclase from mafic magmas, and the Group II diorites were formed by the fractional crystallization of clinopyroxene and plagioclase from mafic magmas that were geochemically similar to the Group I diorites. In combination with regional geology, in particular adjacent ophiolites, high-magnesian andesitic rocks and Cretaceous sedimentary rocks, we conclude that all of the Kenama diorites were probably generated in an early Late Jurassic arc setting related to the subduction of the Bangong–Nujiang Tethys oceanic lithosphere.

Phanerozoic magma underplating associated with remelting of the lower crust beneath the Cathaysia Block: Evidence from zircon U[sbnd]Pb ages and Hf[sbnd]O isotopes of granulite xenoliths from Daoxian, South China

Widespread Mesozoic granitoids in the Cathaysia Block of South China are associated with intensive reworking of the lower crust as a result of magma underplating. This inference is based mainly on studies of mafic igneous rocks, whereas there is little evidence from lower-crustal rocks. Lower-crustal xenoliths in Mesozoic basalts in the Daoxian region within the Cathaysia Block might record information on the relationship between magma underplating and remelting of the pre-existing crust beneath the block. The xenoliths are mainly mafic granulites, with minor felsic granulites. The mafic granulites have low SiO2 contents (47.22–49.46 wt%) and high Mg# values (77.8–82.4), suggesting that their protoliths were derived from a mantle source. The felsic granulite xenoliths have high SiO2 (69.56–70.27 wt%) and low MgO (1.63–2.50 wt%) contents, and zircons in these xenoliths yield negative εHf(t) values (−6.1 to −12.6) and high δ18O values (6.8–7.6‰), consistent with a crustal source. Both mafic and felsic granulite xenoliths record magmatic (226–218 Ma) and metamorphic (218–193 Ma) events, suggesting a genetic link between mafic and felsic rocks in the lower crust. We propose that the magma underplating was responsible for the origin of the mafic granulites and partial melting of pre-existing lower crust, as recorded by the felsic xenoliths. The granulite xenoliths also contain abundant inherited zircons that formed during the Archean–Neoproterozoic (2584–659 Ma), early Paleozoic (peaking at ca. 425 Ma), and late Paleozoic (peaking at ca. 261 Ma). Zircons from the Daoxian granulite xenoliths have distinct HfO isotopic compositions that record the multistage evolution of the lower crust beneath the Cathaysia Block. This evolution involved the accretion of juvenile crust during the late Archean (εHf(t) = +4.2 to +4.6) and late Paleozoic (εHf(t) = +1.3 to +5.3; δ18O = 5.8–6.2‰), crustal reworking during the Neoproterozoic (εHf(t) = −7.5 to −11.8; δ18O = 5.1–9.5‰) and early Paleozoic (εHf(t) = −0.5 to −2.2; δ18O = 7.3–7.5‰), and crustal accretion with significant reworking during the early Mesozoic (εHf(t) = −19.2 to +5.9; δ18O = 6.8–7.6‰). The UPb ages and HfO isotopic data of zircons from the Daoxian granulite xenoliths are consistent with the distribution of Phanerozoic igneous rocks in the Cathaysia Block. These data support the inference that Mesozoic magma underplating triggered the remelting of pre-existing crustal materials and produced extensive granitoid magmatism.

Chalcophile elements track the fate of sulfur at Kīlauea Volcano, Hawai’i

Chalcophile element concentrations in melt inclusions and matrix glasses may be used to investigate low pressure degassing processes, as well as sulfide saturation during crustal fractionation, and mantle melting. Erupted products from Kīlauea Volcano, Hawaiʻi, record three stages of sulfide saturation (in the mantle, crust, and within lava lakes), separated by episodes of sulfide resorption (i.e., sulfide undersaturation) during ascent through the thick Hawaiian lithosphere, and during syn-eruptive degassing. The presence of residual sulfides in the mantle source throughout the melting interval accounts for the high S concentrations of Kīlauean primary melts (1387–1600 ppm). Residual sulfides retain chalcophile elements during melting, decoupling the variability of these elements in high MgO melts from that of lithophile elements. Decompression associated with magma ascent through the thick Hawaiian lithosphere drives an increase in the sulfide concentration at sulfide saturation (SCSS2−), resulting in shallow storage reservoirs (∼1–5 km depth) being supplied with sulfide-undersaturated melts. A drop in temperature, coupled with major element changes during the fractionation of olivine, causes the SCSS2− to decrease. Combined with an increase in melt S contents during fractionation, this initiates a second stage of sulfide saturation at relatively high MgO contents (∼12 wt%). Syn-eruptive degassing of S drives the resorption of sulfides in contact with the carrier liquid. The covariance structure of Cu, MgO and Ni contents in melt inclusions and matrix glasses indicates that the dissolution of sulfides effectively liberates sulfide-hosted Cu and Ni back into the melt, rather than the vapour phase. The contrasting behaviour of Cu, Ni, Se and S during sulfide resorption indicates that the chalcophile element signature of the Kīlauean plume is largely controlled by silicate melt-vapour partitioning, rather than sulfide-vapour partitioning. The participation of dense sulfide liquids in shallow degassing processes may result from their direct attachment to buoyant vapour bubbles, or olivine crystals which were remobilized prior to eruption. Sulfide resorption obscures the textural and chemical record of sulfide saturation in matrix glasses, but not in melt inclusions, which are isolated from this late-stage release of chalcophile elements. The partitioning of S between the dissolving sulfide, melt and the vapour phase accounts for approximately 20% of the total S release into the atmosphere.