K2O Contents Research Articles

Petrogenesis and tectonic setting of TTG rocks from the Katoro area, Sukumaland Greenstone Belt, NW Tanzania: Evidence from zircon U-Pb geochronology, Lu-Hf isotopes, whole-rock geochemistry, and Sr-Nd isotopes

The northern part of the Tanzania Craton is mainly comprised of several low-grade metamorphic granite-greenstone belts that are exposed on the east and south shores of Lake Victoria. Due to their gold-endowment, these greenstone belts have been the main focus of research and were interpreted to form in various tectonic settings involving back-arc basin, island arc or continental arc, and oceanic plateau. However, the TTG gneiss, as the dominant component of Archean crust, has received far less attention from the scrutiny of modern analytical methods than its counterpart, the mafic volcanics of the greenstone belts. Here, we present a comprehensive geochemical dataset including zircon U-Pb age, zircon Lu-Hf isotope results, as well as bulk-rock geochemical compositions and Sm-Nd isotopic analyses for TTG suites from the Katoro area in northwestern part of Tanzania. Zircon U-Pb dating for three TTG samples yielded 207Pb/206Pb ages of 2688 ± 19 Ma, 2717 ± 19 Ma and 2695 ± 15 Ma, respectively, and the results fall within the peak crustal growth period in northern part of the Tanzania Craton. The Katoro TTGs have relatively high contents of SiO2 (70.77–74.69 %) and Na2O (4.74–5.16 %), high ratios of Sr/Y (59.49–167.25) and (La/Yb)N (17.27–50.72), but low MgO (0.24–0.70 %) and K2O (1.71–3.26 %) contents, low Nb/Ta ratios (8.50–16.60), and most of them belong to the trondhjemitic series rocks. They are characterized by strong enrichment of LILEs and LREEs with slightly positive Eu anomalies (Eu/Eu*=1.05–1.38), but depleted in Nb-Ta and Ti, as well as heavy REEs and Y. They have positive εHf(t) values (average εHf(t) = +1.90 ± 0.50 or + 2.07 ± 0.33) and εNd(t) values (+1.19 to + 2.40) but lower than the contemporaneous depleted mantle, which is inconsistent with a subducting slab signature, and it is proposed that the Katoro TTGs most likely originated from partial melting of rutile-free, garnet- and amphibole-bearing lower mafic crust of an oceanic plateau. The results presented here suggest that the tectonic evolution in this part of Tanzania Craton needs to invoke a scenario in which crustal growth caused by subduction-related modification of an oceanic plateau.

Fertility Status of Rice Growing Soils of Gadchiroli Tehsil of Maharashtra, India in Relation to Available Macronutrients and Soil Chemical Properties

The present study was undertaken to assess the status of available macronutrients, viz., nitrogen (N), phosphorus (P), potassium (K) and sulphur (S) in relation to soil chemical properties for delineating the fertility status of rice growing soils of Gadchiroli tehsil, Maharashtra. For this, fifteen villages were selected and soil samples were collected from the rice growing fields (0-20 cm depth) after the harvest of crop during the year 2020-21. The soils were found to be slightly acidic to neutral in reaction (pH 5.64 to 6.97), non-saline (EC 0.02 to 0.18 dS m-1) and non-calcareous (CaCO3 0.05 to 1.15 %), with low contents of soil organic carbon (2.1 to 5.4 g kg-1). The available N and S were also low, with ranges varying from 87.81 to 269.70 kg ha-1 for available N and 5.48 to 15.34 mg kg-1 for available S. The available P2O5 content was moderate in the soils, ranging from 23.17 to 41.98 kg ha-1. The available K2O content, however, was found to be very diversified ranging from 123.54 to 465.71 kg ha-1. Correlation studies revealed a highly significant positive correlation between the macronutrients and the soil OC and EC. While, pH and free calcium carbonate showed a negative correlation with the macronutrients, except for potassium, which showed a positive and significant correlation with pH of the soil.

A microcosm of modern crust formation: Evidence from zircon ages, Hf[sbnd]O and Nd[sbnd]Sr isotopes and bulk geochemistry of the Menglian Batholith, SE Tibet

Modern continental crust has evolved to a more potassic, granitic composition than early continental crust, which comprises largely sodic TTG-suite magmas. The present paradigm holds that the latter are largely “juvenile” (in the sense that the time from mantle extraction to felsic crust production is comparatively short, of the order 10–100 Ma) while the former represent recycled older crust of igneous or sedimentary composition. The data from high-Mg diorites, tonalites, granodiorites and potassic granites of the 125–115 Ma Menglian Batholith (SE Tibet) exemplify the modern situation and can therefore be used to constrain current crust formation processes. These rocks have higher concentrations of incompatible elements than magmatic rocks from typical continental arc settings, with a continuum of increasing K2O/Na2O ratios, SiO2, K2O, Rb, and Th concentrations juxtaposed with decreasing MgO, CaO, and Sr. They consistently record both higher zircon δ18O values than mantle values and decoupled NdHf isotope systems caused by the interaction of subducted sediments with the mantle wedge. Petrogenetic mechanisms that connect the suite include crystal fractionation within the diorites, melting of the lower crust induced by advection of heat and water by the diorites, and high-level fractionation of the tonalite-granodiorite suite to produce the high-silica granites. Therefore, this example of modern fertile continental crust had a five-stage evolution: (1) subduction-enrichment of the mantle source, (2) mantle melting to produce mafic magmas that pooled in or below the lower crust, (3) mafic magma differentiation to produce the tonalite-granodioritic magmas controlled by crystal-liquid equilibria, (4) crustal melting and admixture to the evolving felsic magmas and (5) final high-level fractionation and melt extraction to produce the silicic extreme, enriched in incompatible elements such as Rb, Th and K. This model could be a general mechanism for how modern mature continental crust evolves. Importantly, it indicates a significant role for mafic magmas and thence a more important role for juvenile additions than is generally accepted.

Synthesis and Characterization of Nanozeolite from Sugarcane Bagasse Ash and Its Nutrient Loading Potential

Sugarcane bagasse, a known agricultural waste product in the Philippines with 88% silica (SiO2) content based on elemental analysis, is a viable starting material for zeolite synthesis. In this study, silica derived from sugarcane bagasse ash (SBA) collected from La Carlota, Negros Occidental, Philippines, was extracted via an alkaline extraction method using 2M NaOH and precipitation with 5 N H2SO4 under constant stirring at elevated temperature. Sodium aluminate was added as aluminum source then subjected to ageing at 80°C for 72 h to form the clinoptilolite-type zeolite crystals. Characterization using Scanning Electron Microscopy – Energy Dispersive X-ray Spectroscopy and X-Ray Diffractometry confirmed the successful synthesis of the SBA silica and clinoptilolite, with an Si/Al ratio of 1.59 and average pore diameter of 85.77 nm. Surface modification was done by adding CTAB, a cationic surfactant. Nutrient loading was performed using synthesized nanozeolite (SNZ) for N and K loading and surface modified synthesized nanozeolite (SMSNZ) for PK loading which was compared with nutrient loading performance of commercial natural zeolite. The nanozeolite was added to 1 M urea for N loading, 1 M potassium chloride (KCl) for K loading, and 1 M potassium dihydrogen phosphate (KH2PO4) for PK loading at 1:10 (solid: liquid) solution ratio for 8 h under constant stirring followed by filtration and air drying. Chemical characterization of the synthesized nanozeolite revealed that it has a total CEC of 199.30 meq 100 g-1, ICEC of 182.51 meq 100 g-1, and ECEC of 16.79 meq 100 g-1. Nutrient loading resulted in a 9.62% N and 17.01% K2O content using SNZ and a 13.35% P2O5 and 16.26% K2O content using SMSNZ, which were relatively higher compared to using a commercial natural zeolite. These can be attributed to the high internal CEC due to the high quantity of nanopores in the zeolite, which can capture and store the K+ and NH4+ ions via geometric fit, then release them to the soil on-demand via ion-exchange or occlusion. The surface modification with a surfactant drastically alters the surface chemistry of zeolite allowing simultaneous adsorption of anions (PO4-) externally and cations (K+) internally. The chemical characterization confirmed successful loading of N, K, and PK to synthesize nanozeolite from SBA-derived silica, and its potential as a controlled release fertilizer can be tested in further studies.

Latest Oligocene adakitic rocks in western Iran: implications for early crustal thickening and tectonic evolution of the Iran Block

Adakitic rocks occur in a variety of tectonic settings and are key to understanding the tectonic evolution and geodynamics of orogenic belts. We investigated latest Oligocene (23.5–22.5 Ma) quartz monzonites and granites from the western segment of the Urumieh–Dokhtar magmatic belt in Iran, which are likely to have formed in response to the early stages of Arabia–Eurasia collision. The studied rocks have the geochemical characteristics of typical adakites, such as high SiO 2 (60.18–68.82 wt%) and Sr (499–793 ppm) contents, low Y (8.90–17.1 ppm) and Yb (0.88–1.58 ppm) contents, and high Sr/Y (26.1‒67.8) and (La/Yb) N (21.9‒32.9) ratios. They have variable K 2 O (3.88–5.09 wt%), MgO (0.44–2.74 wt%; Mg# = 33.7–52.5), Cr (4.27–40.59 ppm), Ni (4.28–35.68 ppm) and Th (9.56–59.59 ppm) contents, and relatively depleted Sr–Nd isotopic compositions [( 87 Sr/ 86 Sr) i = 0.70450–0.70516; ε Nd ( t ) = 2.1–2.7]. These characteristics indicate that the quartz monzonites were derived from the partial melting of delaminated lower crust that interacted with mantle peridotite with high MgO, Cr and Ni contents and depleted Sr–Nd isotopic compositions and suggest that the granites were formed by the fractional crystallization of quartz monzonitic magma. The geochemical features of the studied adakitic rocks could therefore have been affected by magmatic processes (e.g. fractional crystallization), which might be misleading in interpretations of their petrogenesis and related tectonic settings. The geochemical features of the studied rocks indicate that the crust of the western segment of the Urumieh–Dokhtar magmatic belt was thickened to c. 50 ± 4.43 km during the latest Oligocene ( c. 23.5 Ma) as a result of Arabia–Eurasia collision. Supplementary material: Whole rock geochemical and Sr–Nd isotopic compositions, and zircon U–Pb and Lu–Hf isotopic data are available at https://doi.org/10.6084/m9.figshare.c.6188328

Petrogenesis of Alkaline Complex of the Longbaoshan Rare Earth Element Deposit in the Luxi Block, North China Craton, China

The alkaline complex in the southwest region of Luxi Terrane of the North China Craton is spatially correlated with the newly discovered Longbaoshan REE deposit. Its petrogenesis, however, remains ambiguous. In this study, we present an integrated petrology, whole-rock geochemistry, sphene U-Pb and rare earth element data from the Longbaoshan alkaline complex to investigate the petrogenesis, magma source and tectonic evolution. The Longbaoshan alkaline complex consists of mafic to intermediate rocks of hornblende diorite and alkaline hornblende syenite porphyry, biotite monzonite porphyry and aegirine diorite porphyrite. The hornblende diorites show a composition of low SiO2, high MgO, Fe2O3 and moderate Na2O, CaO and are metaluminous and medium-to-high-K calc-alkaline. The hornblende syenite porphyries, biotite monzonites and argirine diorite porphyrites display a relatively higher content of SiO2, Na2O, K2O and Al2O3 and lower contents of MgO, Fe2O3 and CaO and are metaluminous, peralkaline, high-K calcic-alkaline and shoshonite. The sphene U-Pb data shows that the parent magma of the hornblende diorite was emplaced at ca. 120 Ma. All these samples show a common depletion in Th, Nb-Ta and Zr-Hf and enrichment in large ion lithophile elements (e.g., Pb, Ba, Sr) and Light Rare Earth Elements. The magma may have experienced fractionation of pyroxene, amphibole, sphene, apatite and zircon during its evolution. The variable La content, La/Sm, Rb/Sr and (Ta/Th) N ratios indicate that the parent magma may produce by partial melting of a mantle source that was interacted with sediment-derived melts in a subduction setting. Therefore, we propose that the parent magma of the Longbaoshan alkaline complex was derived from a lithospheric mantle which was metasomatized by sediment-derived melt in a prior subduction process. The enriched magma was emplaced through an extension process and experienced subsequent fractionation and assimilation with the continental crust during the rollback of the Paleo Pacific Ocean plate.

Preparation of Ni/SiO2 using silicon-rich-biomass as source for acetic acid steam reforming

In this paper, four kinds of silicon-rich biomass (rice husk, rice straw, peanut shell, corncob) were used as raw materials for SiO2 extraction by heat treatment method. And the extracted SiO2 was applied to prepare Ni/SiO2 catalyst for acetic acid (AcOH) steam reforming. Various characterization methods were used to analyze the purity, structure and specific surface area characteristics of SiO2 extracted from different sources. It was found that the silica prepared by acid washing and calcination (AWC) had larger specific surface area, abundant pore channels and larger pore volume. By water washing and calcination (WWC), K2O impurity would be remained in SiO2, which might dissolve SiO2 during the calcination process, generating an increase in the pore size and a decrease in the specific surface area. While the CaO impurity in SiO2 promoted the dispersion of the active components and enhanced the interaction between the active component and the carrier. A series of reforming catalysts were prepared by using the obtained SiO2 as carriers. It was found that the lifetime of catalyst from low to high was Ni/RS-SiO2 <Ni/PS-SiO2 <Ni/RH-SiO2, which was in the opposite order of K2O content. Acid washing was beneficial for the enhancement of Ni/RH-AC-SiO2 activity, and the increase of Ni/RS-AC-SiO2 stability. Among the four catalysts, the Ni/RH-AC-SiO2 catalyst exhibited the highest carbon conversion (100%) and hydrogen yield at 600 °C, which may be because that the acid washing removed the metal oxide impurity K2O. And its large specific surface area, the concentrated pore size distribution, and the suitable interactions between the support and carrier may also contribute to its high catalyst activity.

Petrogenesis and tectonic implications of the Early Carboniferous high‐K granites with enriched isotope signatures in the northern North China Craton

Although an extensive continental arc magmatism was recorded in the northern North China Craton (NCC) during the Carboniferous, a general geodynamic model has not been constructed, and associated crust–mantle processes are not fully understood. Here, we carried out systematic geochronological and geochemical investigations on the alkali‐feldspar granite pluton in the Zhaojinggou area, northern NCC. U–Pb dating of high‐U–Th zircons failed to obtain concordant ages due to severe metamictization, while apatite U–Pb dating yielded a perfect age of 327.6 ± 4.1 Ma, indicating the emplacement of granites in the Early Carboniferous. The granites have high SiO2 (74.99–76.88 wt%) and K2O (5.73–6.43 wt%) contents and exhibit enriched LREEs, K, Rb, Th, U, and Pb, and depleted Nb, Ta, P, and Ti contents, which are typical of highly fractionated, I‐type high‐K granites formed under a continental arc setting. Moreover, the high‐K granites show highly enriched Nd isotopic compositions (with whole‐rock and apatite εNd(t) of −33.6 to −16.3) that are distinctly lower than other Carboniferous continental arc rocks in the northern NCC (εNd(t) from −18.5 to −9.9). These geochemical characteristics indicate that the high‐K granites possibly originated by partial melting of the Archean TTG gneisses and mafic rocks in the lower crust. Involvement of mantle‐derived fluids is crucial to induce the low‐temperature melting, and sufficient fractional crystallization was reached during subsequent magmatic evolution. Previous studies suggest that the Carboniferous continental arc rocks in the northern NCC have mantle‐derived or crust–mantle mixed sources. Our study, however, indicates that there also exist coeval crust‐derived magmatic rocks in this area. In combination with previous work and this study, we support the hypothesis that the widespread Carboniferous continental arc magmatism in the northern NCC is related to the southward subduction of the Palaeo‐Asian Ocean (PAO), and the different magma sources and extensive crust–mantle interactions are responsible for the formation of diverse types of magmatic rocks with contrasting isotopic compositions. We also draw attention to the fact that phosphate minerals such as apatite may be a preferable chronometer relative to high‐U–Th zircon in a highly fractionated igneous system.

Effect of coffee husk ash as alkaline activator in one-part alkali-activated binder

Coffee husk ash (CHA) was utilized as the alkaline activator with blast-furnace slag (BFS) as the solid precursor to produce a one-part alkali-activated binder (OP-AAB). CHA was prepared in the laboratory to achieve the best alkaline activator properties. The ash was physicochemically characterized. Physical/mechanical properties of mortars and microstructural analysis of pastes were performed to evaluate CHA influence in OP-AAB. Results showed that CHA presented high K2O content (as potassium carbonate), adequate solubility, and pH. Mortars’ compressive strength revealed that CHA-based samples achieved over 40 MPa after 28 days. Microstructural studies showed that CHA completely reacted with BFS and generated a dense structure of (K,C)-ASH reaction product.

Geochronology and geochemistry of the granitoids in the Diancangshan-Ailaoshan fold belt: Implications on the Neoproterozoic subduction and crustal melting along the southwestern Yangtze Block, South China

The Neoproterozoic magmatic and tectonic history of the South China Craton (SCC) is critical for the reconstruction of Rodinia break-up and subsequent Gondwana assembly. Nonetheless, the tectonic attribution of the Neoproterozoic igneous rocks in the southwestern Yangtze is contentious, and the mechanism for crustal anatexis remains unclear. Here, we report mineralogical, whole-rock geochemical and Sr-Nd isotope data, and zircon U-Pb-Hf-O isotope data from the newly found Neoproterozoic trondhjemites and granites in the Diancangshan-Ailaoshan (DCS-ALS) fold belt along the southwestern Yangtze. Both the trondhjemites (ca. 771–762 Ma) and granites (ca. 767 Ma) have high SiO2 and low MgO contents. The trondhjemites have relatively high CaO, Na2O and Sr contents, but low K2O contents and Rb/Sr ratios, and show positive to slightly negative Eu anomalies and heavy rare earth elements (HREEs) depletions, resulting in high Sr/Y and La/Yb ratios. In contrast, the granites have lower CaO, Na2O, and Sr contents, but higher K2O and Rb/Sr, and display negative Eu anomalies and flat HREEs patterns. The trondhjemites have negative εNd(t) (-4.12 to −3.85), positive to negative εHf(t) (-2.50 to + 5.28) and low δ18O (4.37 ‰–7.27 ‰) values. In comparison, the granites have positive εNd(t) (0.09 to 0.26), εHf(t) (+1.24 to + 9.86) and higher δ18O (6.50 ‰–7.24 ‰) values. The distinct elemental and isotopic compositions between the trondhjemite and granite samples reflect two different types of crustal anataxis within different crustal levels. The trondhjemites were formed by water-fluxed melting of the juvenile mafic lower continental arc crust (with addition of ancient Yangtze basement). The granites were derived from dehydration melting of juvenile felsic middle crust. Our results imply that the trondhjemites and granites were formed in a continental arc setting. The melting processes revealed here should be applicable to decipher the widespread Neoproterozoic crustal melting along the southwestern Yangtze, which was most likely fluid-controlled via subduction-induced asthenosphere upwelling. Combined with available regional geological data, we suggest that a long-lived Neoproterozoic (∼880–730 Ma) subduction zone may have extended from the Panxi-Hanna region in the northern/western Yangtze Block to the DCS-ALS fold belt in the southwestern Yangtze. Thus, the SCC may have located on the northwestern margin of Rodinia.

Ca. 800 Ma I-type granites from the Hong’an Terrane, central China: New constraints on the mid-Neoproterozoic tectonic transition from convergence to extension in the northern margin of the Yangtze Block

The northern margin of the Yangtze Block was thought to have witnessed the tectonic shift from a compressional setting to an extensional setting at ca. 820 Ma, or to have remained as a subduction-related setting until ca. 700 Ma. Our new geochronological, isotopic, and geochemical data for the Daleishan granitic Pluton, which is the largest batholith in the Hong’an Terrane of the Qinling-Tongbai-Dabie Orogen, central China, provide new constraints on the Neoproterozoic magmatic and tectonic evolution of the Yangtze Block. Four representative samples from the Daleishan Pluton yield consistent zircon U–Pb ages within analytical errors of ca. 800 Ma. Samples from the pluton exhibit evolved compositions, including high SiO2 (71.53–77.05 wt%) and K2O (3.93–5.00 wt%) contents, low Zr/Hf (22–37) and Nb/Ta (7.9–16.4) ratios, enrichment in Rb, Th and U, and depletion in Ba, Sr, Eu, and Ti, with rare earth element tetrad effects in the chondrite-normalized element patterns. The studied samples have slightly elevated zircon δ18O values (+5.64 ‰ to + 7.11 ‰) relative to the mantle value but negative zircon εHf(t) (mostly of −12.0 to −5.5) and bulk rock εNd(t) (−9.6 to −7.9) values. Our new geochemical data classify the rocks as moderately to highly-fractionated I-type granite, rather than A-type granite as previously thought. These rocks may have been derived from the partial melting of mafic rocks in the region and the magma underwent fractional crystallization. Integrating the new and published data, we propose that the emplacement of the Daleishan Pluton was associated with the final stage of early Neoproterozoic oceanic-crust subduction along the northern margin of the Yangtze Block. Accordingly, a mid-Neoproterozoic tectonic transition from convergence to extension in response to the breakup of the Rodinia supercontinent may have occurred at 800–780 Ma.

Geochronology and geochemistry of Early Cretaceous granitic plutons in northern Great Xing’an Range, NE China, and implications for geodynamic setting

AbstractEarly Cretaceous granitic rocks are widely distributed in the Great Xing’an Range, northeast China. However, their precise age and tectonic evolution remain controversial. This study presents new zircon U–Pb, Lu–Hf, and whole-rock geochemical data for the granitic plutons in the Yili area, Xing’an Massif, northern Great Xing’an Range. The aim of this study was to decipher the tectono-thermal history and obtain further understanding of the geodynamic setting of the large-scale Late Mesozoic magmatism in the Great Xing’an Range. Zircon U–Pb age dating indicated that the plutons were emplaced during the Early Cretaceous, with ages of 132.2–130.1 Ma. The plutons showed similar geochemical features, characterized by high concentrations of SiO2and Na2O + K2O and low concentrations of P2O5, CaO, MgO, and TFe2O3. The plutons were enriched in light rare earth elements and large ion lithophile elements and depleted in heavy earth elements and high-field-strength elements. Such features indicate that the plutons are highly fractionated with I-type granite affinity. These findings, combined with plutonεHf(t) values of + 5.25 to + 8.28 and two-stage model ages (tDM2) of 661–855 Ma, indicate that the primary magmas originated from partial melting of juvenile basaltic crustal material accreted during the Neoproterozoic. These results combined with regional geological evolution indicated that the generation of Early Cretaceous plutons in the northern Great Xing’an Range might be closely related to the post-collisional gravitational collapse and subsequent extension resulting from the closure of the Mongolia-Okhotsk Ocean. Their generation also superimposed the back-arc extension resulting from retraction of the Paleo-Pacific subduction plate.

Petrogenesis of the Triassic Sihaiping granite in the South Qinling orogen, central China: Implications for Mo-W mineralization

Late Triassic granites and related magmatic-hydrothermal Mo-W mineralization are common in the South Qinling orogen of central China, for which the Sihaiping granite pluton is a typical example. However, the petrogenesis of the Sihaiping granite remains enigmatic. Unraveling its petrogenesis can aid in our understanding of the Mo-W metallogeny in the South Qinling orogen. In this study, we present in situ zircon U-Pb ages, whole-rock geochemistry, and Sr-Nd-Hf isotopes of the Sihaiping granite. Zircon U-Pb dating by laser ablation inductively coupled plasma mass spectroscopy yielded Late Triassic ages of 206.6 ± 0.94, 206.5 ± 0.96, and 205.9 ± 0.75 Ma. The granite displayed high SiO2, K2O, and Rb contents, but low MgO, P2O5, TiO2, Sr, Ba, and Eu contents, indicating highly fractionated I-type granite affinity. The magma was interpreted to have been derived from Proterozoic crystalline basement in the South Qinling given its relatively low (87Sr/86Sr)i (0.704006 to 0.705039), negative εNd(t) (–4.9 to –3.5), and zircon εHf(t) (–6.2 to +1.6) values, with Nd model ages ranging from 1.39 to 1.27 Ga and two-stage Hf model ages ranging from 1.36 to 1.04 Ga. The strong fractional crystallization and suitable oxygen fugacity (ΔFMQ values mainly concentrated between +2 to +8) in the magmatic system played a major role in the Mo-W mineralization, indicating that the pluton has significant Mo(-W) metallogenic potential. Overall, the findings suggest that the Triassic Sihaiping granite and its related Mo-W mineralization likely formed in the transitional stage from syn- to post-collision between the South China Block and South Qinling along the Mianlue suture.

The Carboniferous shoshonitic (s.l.) gabbro–monzonitic stocks of Veiros and Vale de Maceira, Ossa-Morena Zone (SW Iberian Massif): Evidence for diverse subduction-related lithospheric metasomatism

Post-collisional potassium-rich rocks are a critical petrogenetic and geodynamic marker across the European Variscan Belt. We present a detailed characterization of the only potassium-rich mafic intrusions identified so far in the Ossa-Morena Zone (Iberian Massif). Using new major, trace and SmNd isotopic whole-rock analyses, as well as mineral chemistry analyses, we discussed the petrogenesis of the early Carboniferous potassium-rich Veiros and Vale de Maceira (Portugal) stocks in the geotectonic framework of the southern Iberia, marked by the collision of the Ossa-Morena Zone, a Gondwanan terrane, with the South Portuguese Zone, a Laurussian terrane. The Veiros and Vale de Maceira shoshonites (s.l.) range from gabbros to syenites, with a predominance of monzonites and monzogabbros, characterized by different proportions of olivine, clinopyroxene, orthopyroxene, plagioclase, alkali feldspar, phlogopite and brown hornblende. The Veiros stock is mainly composed of fine-grained ultrapotassic rocks, and the Vale de Maceira stock is composed chiefly of medium-grained shoshonite rocks. A small group of hornblende-bearing medium-grained calk-alkaline rocks was also identified. The stocks have high contents of K2O, MgO, total alkalis, Th and other LILE, high ratios of LREE/HREE and LREE /HFSE, and show a Nb-Ta-Ti negative anomaly, typical of orogenic settings. Sr and Nd isotopes yielded moderate radiogenic Sr and unradiogenic Nd, that might suggest the involvement of a crustal component. However, the combined use of isotopic and elemental compositions rules out significant contamination by crustal materials upon ascent and emplacement. Instead, a source metasomatised by subduction-related fluids and hydrous melts from the slab is proposed. This diversely metasomatised source was a phlogopite-amphibole-bearing and (phlogopite-free) amphibole-bearing lherzolite at the upper part of the garnet stability field in the sub-continental lithospheric mantle. The Devonian mafic volcanic rocks point to a northward dipping (present coordinates) subduction of the Rheic oceanic plate underneath the Ossa-Morena Zone during the Variscan Orogeny. However, the Veiros and Vale de Maceira magmas originated during the post-collisional stage from the partial melting of the supra-subduction metasomatized lithosphere. The melting occurred during a period of enhanced heat due to asthenospheric upwelling related to the slab break-off of the Rheic's slab. The stocks are concomitant with the profusion of granitoid intrusions, which is compatible with a post-collisional tectonic setting. They are also coeval with the opening of the Beja-Acebuches back-arc, likely related to slab roll-back of a segment of the Rheic oceanic crust, implying polyphasic subduction and a complex geodynamic setting for the late stages of oceanic closure in southern Iberia.

Effects of Methanol on the Seeded Precipitation of Al(OH)3 from Potassium Aluminate Solution

AbstractThe effects of methanol on the seeded precipitation of Al(OH)3 from potassium aluminate solution are investigated. The solubility of Al(OH)3 decreases in the presence of methanol, leading to a faster crystallization and a higher precipitation ratio than the normal seeded precipitation process. Under the optional precipitation conditions of temperature 323.15 K, K2O concentration 170 g L−1, and addition of an equal volume of methanol to potassium aluminate solution, the precipitation ratio can exceed 85% within 7 h. Characterization of the Al(OH)3 products using X‐ray diffraction, scanning electron microscopy, and particle size distribution shows a typical gibbsite crystal phase composed of sheet‐like agglomerates with an average particle size of 74 µm. An interaction model between methanol molecules and Al(OH)3 crystal face is established and calculated by using the molecular dynamics method, which indicates the morphology transition mechanism of the Al(OH)3 crystal. The result indicates that methanol molecules would hinder the growth of the (002) crystal face, so that the (002) crystal face is eventually retained and becomes the main crystal face for the Al(OH)3 product. Infrared radiation and Raman spectra analyses suggest that the added methanol captures water molecules from the aluminate ion hydration sphere and thus catalyzes the crystallization process.

Paleoproterozoic (ca. 2.1–1.9 Ga) dioritic-granitic magmatism in the Dunhuang Terrane, Northwestern China: Implications for petrogenesis and tectonic evolution

The implications of petrogenesis and tectonics of Paleoproterozoic (ca. 2.1–1.9 Ga) granitoid rocks in Dunhuang Terrane have hitherto received less attention. According to data from zircon UPb dating, the ages of dioritic gneiss, granodioritic gneiss and potassic granite are 2045 ± 44 Ma, 1998 ± 15 Ma and 1950 ± 38 Ma, respectively. The dioritic gneiss has MgO = 1.87–2.93 wt% (Mg# = 46.8–50.9), Yb ≤ 1.9 ppm and Y ≤ 18 ppm, with variable εHf(t) (−2.8 − +5.5) and εNd(t) (−5.6 − +1.3) values, indicating that the mantle wedge source above the subducted slab contributed with subduction fluids and ocean sediment melt in an arc setting. The granodioritic gneiss has relatively high MgO (3.00–1.83 wt%), variable Cr (13.5–106 ppm) and Ni (12.2–72.9 ppm), negative εHf(t) (−20.4 to −10.1) and εNd(t) (−15.2 to −12.8) values, and high P2O5 and TiO2 saturation temperatures (∼800 °C). These data indicate magma source of late Paleo- to early Mesoarchean (∼3.2–3.1 Ga) continental crust rocks. The potassic granite has high K2O (5.52–6.79 wt%) and low MgO (0.10–0.19 wt%) concentrations, low Mg# (37.7–44.6) values, and negative εHf(t) (−12.8 to −2.5) and εNd(t) (−10.6 to −4.8) values. These results suggest that pre-existing Neoarchean crustal rocks were partially melted possibly under transitional stage from syn- to post-collision. Compared with the adjacent areas, Paleoproterozoic (ca. 2.1–1.8 Ga) evolutionary period related to assembly of Columbia supercontinent in Dunhuang Terrane is comparable with that in northeastern Tarim Craton and southwestern Alxa Block, but terminated ∼100 Ma later than that in southeastern Tarim Craton (Aketashtage Terrane).

Petrochemistry and mineralogy of pumice from the Sarychev Peak Volcano, Matua Island, Central Kuril Island

Background. The article presents the first results of a mineralogical and petrographic study of the pumice of the Sarychev Peak volcano, Matua island, the Central Kuril islands.Aim. To reconstruct the compositions of magmatic melts of a caldera-forming eruption of the proto-Matua volcano.Materials and methods. The main research methods included an X-ray fluorescence spectral analysis to determine the content of petrogenic, rare and trace elements, as well as an electron-probe microanalysis to study variations in the chemical composition of mineral inclusions of pumice.Results and conclusion. According to the content of SiO2 and the sum of alkalis, the composition of pumice varies from andesibasaltes (SiO2 = 55.94 wt.%) to dacites (SiO2 = 67.70 wt.%). According to the content of K2O, pumice can be classified as a moderate-potassium series of rocks. The inclusion minerals represented by plagioclase, amphibole, apatite and Fe-Ti oxides were crystallized at the same time from a water-saturated magmatic melt at a pressure of about 1.5–2.2 kbar. The igneous melt was enriched with volatile components of H2O, CO2, S, F and Cl.

Nutritional survey of kinnow orchards soil series at Rawatsar and Fatehgarh of Hanumangarh district of arid Rajasthan

The present study was conducted to evaluate the fertility status of kinnow orchards at Rawatsar and Fatehgarh soil series of Hanumangarh district in irrigated area of arid Rajasthan. All kinnow orchards soils were found saline in nature, EC2 of all the orchard soil samples was normal. The calcium carbonate content in soils showed increasing trend with depth, low in organic carbon and available N, low to medium in available P2 O5, medium to high in available K2O content, majority of samples were found high in available Fe, available Mn and low to sufficient in available Cu and low in available Zn content. Leaf N content were found low in kinnow orchards, majority of leaf samples found medium to optimum in leaf P, Fe, and Mn content, whereas leaf K content and Zn content were found low to medium in kinnow orchards. The leaves Cu content were found optimum range in kinnow orchards. Fruit juice N, Fe and Mn content were found low to optimum, whereas fruit juice P, K and Cu content were found optimum and Zn content low at Rawatsar and Fatehgarh soil series of Hanumangarh district.

Source controls on mineralisation: Regional geology and magmatic evolution of Fiji

There is a well-established link between world-class gold telluride mineral deposits and alkalic magmatic host rocks, often emplaced post-subduction in arc terranes. Fiji is home to two such deposits, and provides an ideal location to study the relationship between the alkalic (shoshonitic) host rocks, their geodynamic context, and potential roles in metal enrichment. A total of 93 new geochemical analyses of magmatic rocks from across Fiji are presented, alongside detailed petrography and mineralogy and a new compilation of literature data. Despite relatively similar mineralogy across syn- and post-subduction samples, there are geochemical differences between them, with the latter displaying elevated concentrations of Ba (<2137 ppm), Rb (<218 ppm), Sr (<2648 ppm) and K2O (<10.18 wt%), and depletions in Nb and Ta. Multi-element trends suggest exaggerations of ‘typical’ arc patterns in post-subduction shoshonites. Geochemical data suggest that whilst the fluxing of fluids and sediment melts from a subducted slab may play a role in producing the distinctive post-subduction magmas, they are likely insufficient to drive such strong trends. Instead, biotite or possibly phlogopite in the lithosphere are suggested as being a key ‘ingredient’. Earlier subduction can modify the lithosphere through the addition of hydrous phases, both by metasomatism of the lithospheric mantle, or by the formation of residual minerals during fractional crystallisation. Remelting of these phases could liberate trace elements and metals. Biotite in particular could facilitate some of the observed large ion lithophile elements (LILE) enrichments and the alkali-rich (potassic) nature of the magmas.

Türkiye'deki Muskovit Ocaklarının Elementel Bileşimlerinin Dağılımı

In this study, the contents of thirty-five elements (nine major-minor oxides, twenty-one heavy metals, and five other elements) in eighty-four muscovite samples collected from three commercially operated quarries in Manisa province of Turkey were determined using an energy dispersive X-ray fluorescence (EDXRF) spectrometer. The mean concentrations of SiO2, Al2O3, K2O, MgO, Na2O, Fe2O3, P2O5, TiO2 and CaO analyzed in mica samples were determined as 57.1, 32.8, 8.7, 2.9, 1.4, 0.8, 0.3, 0.3 and 0.3%, respectively. The mean concentrations of Cr, Zr, Mn, Zn, Ni, Co, Pb, Cu, Cd and Hg analyzed as primary toxic trace heavy metals in mica samples were found as 136.2, 124.6, 58.7, 19.2, 14.8, 6.8, 6.3, 2.6, 2.0 and 1.2 mg kg-1, respectively.