Low CaO Contents Research Articles

The effect of CaO in fly ash on the hydration mechanism and properties of magnesium phosphate cement

Fly ash (FA) is often used to modify MPC, playing a role in delaying setting time, changing color, enhancing mechanical properties, and reducing costs. Current research mainly focuses on higher quality FA, in which the CaO content is low and mainly of F-type. This type is also widely used to modify traditional cement, leading to a shortage in the supply of F-type FA and limiting its engineering applications. Therefore, this study aims to use FA with a higher CaO content and higher stack volume to solve this problem, systematically studying the effect of high CaO content FA on the hydration mechanism and properties of the MPC system, and comparing it with low CaO content FA. The results show that the CaO in FA undergoes a secondary hydration reaction in the MPC, reacting with the phosphate radical to form Ca3(PO4)2. In addition, Ca(OH)2 is only generated at high CaO content and finally reacts to form CaCO3 with the increase of curing age, while CaHPO4 is generated at low CaO content. As the MPC sets and hardens quickly, the newly generated CaCO3 not only enhances compressive strength but also damages the matrix. However, the addition of FA still enhances the compressive strength of MPC, with the highest increase reaching 14.4%.In addition, the incorporation of FA significantly improves the water resistance of MPC, the compressive strength retention rate of the FA/MPC system after 28d of water immersion is significantly higher than that of MPC. This study provides a theoretical basis for the application of high CaO content FA.

Effect of Class F Fly Ash on Strength Properties of Concrete

Reducing the amount of CO2 emissions in the environment is one of the priorities of the EPA and other environmental agencies. A way to reduce CO2 emissions is by using fly ash in the concrete industry. Aside from environmental benefits, fly ash has numerous quality advantages; some of the positive effects were recognized earlier; however, in this research, the objective is to replace cement with a different percentage of class F fly ash with a low CaO content to produce sustainable concrete. Laboratory tests were performed to examine the rational percentage of cement replaced by class F fly ash in ordinary concrete C–25/30 and high-performance concrete C–50/60. In total, twelve different mix designs were prepared to examine consistency, setting time, shrinkage, and compressive strength in different periods of curing for more than 600 days. Using recycled material in new buildings still has some obstacles, but the future of construction must be green, so this research indicates that the objective of producing ordinary and high-performance concrete was achieved by replacing 30% of cement with class F fly ash. Doi: 10.28991/CEJ-2023-09-09-011 Full Text: PDF

Remote Sensing, Petrological and Geochemical Data for Lithological Mapping in Wadi Kid, Southeast Sinai, Egypt

The Wadi Samra–Wadi Kid district in southeastern Sinai, Egypt, has undergone extensive investigation involving remote sensing analysis, field geology studies, petrography, and geochemistry. The main aim of this study is the integration between remote sensing applications, fieldwork, and laboratory studies for accurate lithological mapping for future mineral exploration in the study region. The field relationships between these coincident rocks were studied in the study area. Landsat-8 (OLI) data that cover the investigated area were used in this paper. The different rock units in the study area were studied petrographically using a polarizing microscope, in addition to major and trace analysis using ICP-OES tools. The Operational Land Imager (OLI) images were used with several processing methods, such as false color composite (FCC), band ratio (BR), principal component analysis (PCA), and minimum noise fraction (MNF) techniques for detecting the different types of rock units in the Wadi Kid district. This district mainly consists of a volcano-sedimentary sequence as well as diorite, gabbro, granite, and albitite. Geochemically, the metasediments are classified as pelitic graywackes derived from sedimentary origin (i.e., shales). The Al2O3 and CaO contents are medium–high, while the Fe2O3 and TiO2 contents are very low. Alkaline minerals are relatively low–medium in content. All of the metasediment samples are characterized by high MgO contents and low SiO2, Fe2O3, and CaO contents. The granitic rocks appear to have alkaline and subalkaline affinity, while the subalkaline granites are high-K calc-alkaline to shoshonite series. The alkaline rocks are classified as albitite, while the calc-alkaline series samples vary from monzodiorites to granites. The outcomes of this study can be used for prospecting metallic and industrial mineral exploration in the Wadi Kid district.

Petrological, geochemical and geodynamic evolution of the Wadi Al-Baroud granitoids, north Arabian-Nubian shield, Egypt

The Wadi Al-Baroud area, in Egypt's Eastern Desert, exposes Neoproterozoic rocks of the Arabian-Nubian Shield (ANS), including both syntectonic granitoids (granodiorite and tonalite) and post-collisional granites. We present field work, petrographic study, mineral compositions, and whole-rock geochemistry results from these granitoids and discuss their petrogenesis, magmatic sources, evolution, and tectonic significance. The syntectonic granitoids show subduction affinity and an anomalous steep trend of K-enrichment that suggests assimilation of a granitic component during their evolution. The post-collisional granites form two plutons, on opposite sides of Wadi Al-Baroud, named here the Ras Baroud pluton (RBP) and the Abu Hawis pluton (AHP). They intruded the syntectonic granitoids with sharp intrusive contacts. The post-collisional plutons are devoid of mafic enclaves and are cut by very few dikes. They dominantly consist of biotite monzogranite that grades into muscovite monzogranite. The latter lithology hosts Nb-Ta oxide minerals (columbite, tantalite, and wodginite) displaying a variety of textural and compositional features. The cores are primary columbite-(Mn), whereas rims are overgrown or partly replaced by tantalite-(Fe) and wodginite due to late interactions with highly fractionated residual melt. The highly-evolved AHP and RBP granites are typical of the post-collisional granitoids of the ANS, including high concentrations of rare earth elements (REE), Ta, Hf, Nb, Zr, Y, and Rb; elevated ratios of Ga/Al; and low contents of Sr, CaO, and MgO. Their geochemistry suggests that the parental magma of both plutons formed from an I-type tonalitic source rock that underwent partial melting during the thermal disturbance that followed a lithospheric delamination event during the post-collisional stage of the East African Orogeny. The variations in major oxide and trace element contents among individual samples of the AHP and the RBP cannot be explained as a liquid line of descent due to fractional crystallization; rather we interpret them as sampling variable proportions of an evolved liquid and the solid crystals in equilibrium with that liquid.

Characteristics of early Paleozoic granite-pegmatite and associated lithium-beryllium mineralization in the Tugeman area, Altun orogenic system, northwestern China

The Altun Orogenic Belt (AOB) is located on the northern margin of the Tibetan Plateau. We report the petrography, zircon U-Pb ages, Hf isotopic compositions, and whole-rock geochemistry of the Tugeman pegmatitic and granitic rocks from the AOB to constrain their petrogenesis and tectonic setting. Zircon U-Pb dating of the pegmatitic and granitic rocks yielded ages of 500–440 Ma, which we interpret as the emplacement ages of the granites and formation age of pegmatite. The granites are weakly peraluminous to peraluminous (A/CNK = 1.01–1.26), and they have high SiO2 (63.9–74.2 wt%) and Al2O3 (13.7–17.6 wt%) and low CaO (0.72–3.80 wt%) and P2O5 (0.06–0.44 wt%) contents. They show marked depletion in HREEs, enrichment in LREEs, and pronounced negative Eu anomalies, and they are enriched in Th, U, K, Pb, Nd, and Sm and depleted in Ba, Nb, Ce, Sr, P, and Ti. Zircon εHf(t) values vary from − 12.0 to + 3.3, with two-stage Hf model ages of 2.2–1.2 Ga, implying that the granites were derived mainly from ancient crust with a minor contribution from juvenile crust. Weakly peraluminous pegmatitic rocks have geochemistry characters of SiO2 (74.4–79.9 wt%) and Al2O3 (12.3–14.9 wt%) and low CaO (0.08–0.69 wt%) and P2O5 (0.05–0.33 wt%), depletion in HREEs, enrichment in LREEs, depletion in Ba, La, Ce and Ti, enriched in U, K, Pb and P. Granitic pegmatite can be formed at different stages of crystallization differentiation of granitic magma, but the pegmatite associated with highly differentiated granites is favorable to the Li and/or Be mineralization, while the pegmatite associated with low differentiated granites (such as biotite granites) is unfavorable to the Li and/or Be mineralization. Based on our findings, we propose that the Tugeman granitic magmas originated from partial melting of crustal metagreywacke and metabasalt. Furthermore, we suggest that the early Paleozoic magmatism in the Central Altun Block (CAB) can be categorized into three groups, which correspond to different tectonic events. These events include the northward subduction of the Central Altun Ocean (CAO) beneath the CAB around 520 Ma, the closure of CAO at 490–480 Ma, and post-collisional extension at 480–440 Ma induced by slab breakoff and delamination of the subducted CAO.

Petrogenesis, tectonic setting and geodynamic implications of keziergayin granites in the kelan basin (Chinese Altai): constraints from geochemistry, zircon U-Pb geochronology and Nd‒Hf‒Pb‒O isotopes

The Chinese Altai is characterized by abundant granitoids, which not only are indicators of the interaction between crust and mantle but also provide critical constraints on the tectonic evolution of the orogen. This study presents zircon U‒Pb‒O isotopes, whole-rock major and trace element and Nd‒Hf‒Pb isotopes data for granite porphyries from the Keziergayin region in the Kelan Basin. The granite porphyries intrude in the Kangbutiebao Formation with zircon U‒Pb dating of 394 ± 3 Ma. They have the characteristics of subalkaline and metaluminous to weakly peraluminous and show geochemical affinity with I-type granite. The granite porphyry samples display negative εNd(t) (−1.9 to −1.4), positive εHf(t) (+4.3 to +11.4) values, with Nd–Hf decoupling; low Pb isotope compositions; δ18OV-SMOW (6.38‰–8.45‰) is less than 10‰, within the range of O isotopes of medium-basic igneous rocks. These geochemical signatures indicate that the granite porphyries originated from lower crust medium−basic igneous rocks extracted from the lithospheric mantle metasomatized by subducted melt. They are characterized by high SiO2 contents and Rb/Sr ratios; low CaO contents and K/Rb ratios, hinting that they were formed by highly evolved magmas, with fractionation crystallization of feldspar, apatite, garnet, allanite and/or monazite. The granite porphyries possess positive Rb, Th, U, Nd, Zr, Pb and light rare Earth elements (LREEs) anomalies with strong negative Ba, Nb, Ta, Sr, P, Ti and Eu anomalies, implying that their formation were related to an island arc. Combined with previous studies, it is suggested that the existence of the Early Devonian arc-basin system associated with subducting slab rollback in the Chinese Altai, which belongs to the Siberian active continental margin system.

Revealing the Individual Effects of Firing Temperature and Chemical Composition on Raman Parameters of Celadon Glaze

The Raman polymerization index (or IP value) is often used as a positive indicator of the firing temperature of the glazes of ancient ceramics. Previous studies have also reported that the IP value was negatively correlated with the chemical composition of the glaze. However, these findings were derived from data on the potential integrative effects of temperature and composition. To explore their individual effects, we prepared celadon glaze samples with controlled composition and firing temperatures. Particularly, according to the typical content of K2O and CaO in celadon glaze, four categories, or, in total, fifteen compositional formulations, were designed, and each formulation was fired at multiple temperatures (from 1180 to 1250 °C by 10 °C). The chemical compositions and the glassy matrix of samples were analyzed by an energy-dispersive X-ray fluorescence spectrometer and Raman spectroscopy, respectively. A positive correlation between firing temperature and IP value (correlation coefficient = 0.56) was detected only in the samples with low contents of K2O and CaO. However, no significant correlation was found when combining the samples with broad variation in chemical composition. Additionally, both the K2O content and CaO content were negatively related to the IP value, with regression coefficients of −9.645 and −5.332, respectively. Our results help to clarify the technology of ancient ceramic production and to improve its preservation.

Geochemical and remote sensing integrated with satellite gravity data of Darhib and Atshan talc deposits, South Eastern Desert, Egypt

The current contribution conducted new geochemical, remote sensing integrated with gravity detailed studies of talc deposits to identify the talc protolith as well as its extension, depth, and structures. There are two examined areas, distributed from north to south, Atshan and Darhib and both belong to the southern sector of the Egyptian Eastern Desert. They occur as individual lenses or pocket bodies in ultramafic-metavolcanics following NNW-SSE and E-W shear zones. Geochemically, among the investigated talc, Atshan samples have high contents of SiO2 (av. 60.73 wt.%), and higher concentrations of transition elements such as Co (av. 53.92 ppm), Cr (781 ppm), Ni (av. 1303.6 ppm), V (av. 16.67 ppm), and Zn (av. 55.7 ppm). Notably, the examined talc deposits contain low contents of CaO (av. 0.32 wt.%), TiO2 (av. 0.04 wt.%), SiO2/MgO (av. 2.15), and Al2O3 (av. 0.72 wt.%), which is comparable with ophiolitic peridotite and forearc setting. False color composite (FCC), principal component analysis (PCA), minimum noise fraction (MNF), and band ratio (BR) have been used to distinguish talc deposits in the investigated areas. Two new proposed band ratios were created to separate talc deposits. FCC band ratios (2/4, 4/7, 6/5) and (4 + 3/5, 5/7, 2 + 1/3) have been derived to focus on talc deposits in two case studies, Atshan and Darhib areas. The application of regional, residual, horizontal gradient (HG), and analytical signal (AS) techniques to gravity data are used in interpreting the structural directions of the study area. The analysis of this technique displays several notable faults trending in NW–SE, NE–SW, NNW–SSE, and E–W directions. Two techniques of gravity depth calculation were applied in the study areas, namely source parameter image (SPI), and Euler deconvolution (EU). The analysis of these techniques reflects that the depth of subsurface sources ranges between 383 and 3560 m. Talc deposits may be attributed to greenschist facies metamorphism or to a magmatic solution that is (associated with granitic intrusions) interacted with the surrounding volcanic rocks forming metasomatic minerals.

Nanoscale hydrous silicate melt inclusions at the clinopyroxene-amphibole interface in a mantle xenolith from the Perșani Mountains Volcanic Field

We studied amphibole lamellae and associated hydrous nano-silicate melt inclusions (NSMI) in upper mantle xenoliths from the Perșani Mountains Volcanic Field, southeastern Transylvania (Romania). Transmission Electron Microscope (TEM) results revealed submicron-scale pieces of evidence of escaped fluids in the form of nano-silicate melt inclusions along clinopyroxene-amphibole interfaces. These NSMIs consist of ∼80 vol% silicate glass and ∼ 20 vol% volatile bubble from which the former has a high SiO2 (>60 wt%) and Al2O3 (>20 wt%) and low CaO, FeO and MgO (<8 wt%) content determined by SDD-EDS analyses. We calculated the original bulk composition of the nano-silicate melt inclusions with Monte Carlo simulation, using hydrated fluid molecules and suggest that originally the nano-silicate melt inclusions had most probably low SiO2 (∼ 43.6 wt%) and high Al2O3 (∼ 15.5 wt%), Na2O (∼11.9 wt%) and H2O (∼ 30.3 wt%) contents. Using petrographic evidence, we propose that the amphibole lamellae formed as a result of post-entrapment reaction between clinopyroxene and the trapped fluid of the fluid inclusion. The presence of the hydrous nano-silicate melt inclusions suggest fluid migration along the clinopyroxene-amphibole interface, supporting the continuous growth of the studied amphibole. The association of the studied amphibole with hydrous nano-silicate melt inclusions suggests that H2O consumption from the fluid found in the micrometer-scale fluid inclusion continued at the nanoscale after a metasomatic event in the lithospheric mantle. This nanoscale process may also give information about the behavior of H2O globally in the lithospheric mantle where amphibole is stable, and along the lithosphere-asthenosphere boundary in younger oceanic and continental plates.

The Petrogenesis of the Gaohushan A-Type Granite from the Northeastern Jiangxi Province and Its Metallogenic Implication

The Taqian–Zhuxi–Fuchun metallogenic belt in northeastern Jiangxi Province contains significant ore deposits that are closely associated with the Gaohushan granites. The Gaohushan granites predominantly consist of two-mica granites and have been dated using zircon U-Pb isotopic dating to be 129.4 ± 1.9 Ma (MSWD = 3.8). These granites have high SiO2, ranging from 73.79% to 76.04% and low CaO and MgO contents (ranging from 0.24% to 0.59% and from 0.03% to 0.1%, respectively). The Gaohushan granites also exhibit high FeOT/MgO ratios from 9.00 to 27.55 with an average of 17.55. The total alkali contents (Na2O + K2O) range from 7.08% to 8.43%, and the K2O/Na2O ratios range from 1.07 to 2.00 with an average of 1.47. These rocks are peraluminous series with A/CNK ratios (or ASI index) ranging from 1.19 to 1.47 and an average of 1.30. The Gaohushan granites have low rare earth element (REE) contents (∑REE = 2.33~23.50) with strongly negative Eu anomalies (δEu from 0.02 to 0.32) and a distinctive differentiation between heavy rare earth elements (HREEs) and light rare earth elements (LREEs) (LREE/HREE = 1.99~7.79). The normalized distribution pattern of REE in Gaohushan granite exhibits a right-dipping feature classified A-type; these rocks range from 1.06 to 2.71. The spider diagram shows that these rocks are characterized by depletion of Ba, Th, La, Sr, Nd, and Ti and enrichment of Rb, U, Ta, Nb, and P. The Gaohushan granites are classified as A-type granite and were emplaced during an anorogenic extensional event that occurred in the late Yanshannian period, driven by mantle-derived magma underplating. It is these granites or their analogues that have the potential for hosting tungsten, tin, niobium, and tantalum deposits, making them a promising target for mineral exploration.

Mixing of magmas from multiple sources in the petrogenesis of multi‐stage Early Cretaceous syenites in the Wulingshan alkaline complex, northern North China Craton: Evidence from enclaves

There are several different models for the origin of syenites, but the role of magma mixing in the formation of syenites remains unclear. The Wulingshan alkaline complex in the northern North China Craton consists mainly of porphyritic syenite and syenite with abundant enclaves. These enclaves may provide new insights into the petrogenesis of syenites. We obtained zircon U–Pb age, mineral chemistry, whole‐rock major and trace elements, and Sr–Nd isotopic data for the enclaves and their host rocks to constrain the petrogenesis and identify the role of magma mixing during the formation of the different syenites in the Wulingshan alkaline complex. The results of zircon U–Pb dating indicate that the enclaves and host rocks crystallized contemporaneously at ca. 133 Ma. The enclaves contain abundant clinopyroxene, amphibole, and biotite, and their average Nb/Ta (18.46) and Th/Ce (0.04) ratios are similar to those of the mantle. The enclaves have relatively high Fe2O3T, MgO, and CaO contents, and their SiO2contents are equivalent to those of intermediate rocks, indicating that they formed by mixing the mafic and felsic magmas to some extent. The different mineral assemblages, major and trace elements and isotopic compositions of the enclaves in the porphyritic syenite and syenite indicate that they are two batches of parental magma with different properties derived from the mantle. The porphyritic syenite and syenite have high SiO2and low Fe2O3T, MgO, and CaO contents, as well as low V, Cr, Co, and Ni contents. These major and trace element characteristics of the host rocks require the involvement of crustal components. The Sr–Nd isotopic compositions of the enclaves and the host syenitoids plot on a mixing curve between enriched lithospheric mantle and lower crust, indicating that these rocks are the products of magma mixing and crust–mantle interaction. Considering the contact relationships, the geochemistry data, and the mixing model presented in the paper, we propose that the upwelling of the hot asthenosphere heated the overlying enriched lithospheric mantle and triggered low‐degree partial melting. The alkalic mafic magmas derived from enriched mantle sources were mixed with felsic magmas generated by partial melting of the lower (or upper) crust to form the different syenites.

Petrogenesis and Tectonic Evolution of Kab Amiri Ophiolites and Island-Arc Assemblages, Central Eastern Desert, Egypt: Petrological and Geochemical Constraints

The Kab Amiri area in the Central Eastern Desert (CED) of Egypt comprises ophiolitic rocks, island arc metasediments, and granitic rocks. This study deals with the petrography and geochemistry of the ophiolitic and island arc rocks to understand their petrogenesis and geodynamic evolution of the CED ophiolitic belt. The Kab Amiri ophiolite is dismembered, comprising serpentinites and metabasalt (spilite). Serpentinites have low contents of Al2O3 (1.14 wt%) and CaO (0.65 wt%), suggesting they are depleted peridotite protoliths (e.g., depleted harzburgites to dunites). The high L.O.I. value (13.7 wt%) of serpentinite rocks indicates intense hydration and serpentinization during alteration processes. Petrographic and geochemical studies suggest that serpentinites were likely formed after depleted peridotites in a supra-subduction zone (SSZ) setting (e.g., a fore-arc setting). Spilitic basalt shows a tholeiitic affinity of the depleted mantle source. The arc-related metasediments are represented mainly by schists and slate. Many samples of metasediments are relatively low in alumina (Al2O3 &lt; 15%), suggesting a low clay content and formation in an island arc setting. In contrast, protoliths of island-arc metabasalts and meta-andesites crystallized from calc-alkaline magmas in the immature oceanic arcs.

The earliest known artificial synthesized ε-Fe2O3 in the Deqing Kiln ceramic ware of Tang Dynasty

Metastable ε-Fe2O3 was discovered on a ceramic ware of Deqing kiln of the Tang Dynasty, which coexists with α-Fe2O3 in the brown area between adjacent black glaze areas, and it is the earliest known artificially synthesized ε-Fe2O3. Based on the composition analysis of α-Fe2O3, ε-Fe2O3 and the glass phase around them, it is speculated that some Fe3+ ions were replaced by Al3+ ions during the formation of ε-Fe2O3, and a relatively low CaO content may be required for its crystallization. This work may promote researchers' understanding of ε-Fe2O3 crystals, and provide clues for the artificial synthesis of large ε-Fe2O3 crystals.

Experimental Modeling of the Interaction between Garnets of Mantle Parageneses and CO2 Fluid at 6.3 GPa and 950–1550 °C

Abstract —Experimental modeling of the interaction of eclogitic and lherzolitic garnets with CO2 fluid was carried out on a multianvil high-pressure apparatus of the “split-sphere” type (BARS) in platinum ampoules with inner graphite capsules, using a buffered high-pressure cell with a hematite container, at a pressure of 6.3 GPa and in the temperature range 950–1550 °C. It has been established that the main interaction processes at 6.3 GPa and 950–1250 °C are partial dissolution, recrystallization, and carbonation of garnet which lead to the formation of magnesian carbonate, kyanite, and coesite, a decrease in Mg contents in the recrystallized garnet, and the formation of carbonate, silicate, and oxide inclusions in it. Under these conditions, crystallization of metastable graphite and growth of diamond on the seed at ≥1250 °C were observed. In the temperature range 1350–1550 °C, the garnet underwent partial dissolution and recrystallization in CO2 fluid; no carbonation took place. These processes were accompanied by a decrease in the portion of the grossular component in the garnet and by the enrichment of the fluid phase with calcium. We have established the indicative characteristics of garnet that interacted with CO2 fluid: zoning, with low contents of CaO and MgO in the rims of crystals relative to the cores, and the presence of carbonate, kyanite, coesite, and CO2 inclusions. The compositions of the produced garnet and carbonates are consistent with the data on these minerals in mantle peridotite and eclogite parageneses and in inclusions in diamonds, which suggests a significant role of metasomatism with the participation of CO2 fluid in the evolution of deep-seated rocks and in the diamond formation. In this experimental research, we have first studied the processes of diamond crystallization and determined the boundary conditions for diamond growth in the system silicate–carbonate–CO2, which simulates natural diamond formation media. In general, the established regularities can be regarded as potential indicators of mantle metasomatism and mineral formation with the participation of CO2 fluid.

Abyssal and forearc features of mantle peridotites in the Guleman ophiolite in SE Turkey

The mantle section of the Guleman ophiolite consists mainly of depleted harzburgite and dunite with some less depleted harzburgite, all of which contain economically significant chromitite. The depleted harzburgite and dunite are characterized by low average bulk Al2O3 (<0.85 wt%) and CaO (0.14–0.94 wt%) contents, high-Mg olivine (Fo = 90.8–93.8) and orthopyroxene (Mg# = 91.3–92.1) together with moderately high-Cr spinel (Cr# = 54.1–67.6). The less depleted harzburgite (sample EG30) contains higher bulk Al2O3 (1.84 wt%) and CaO (2.15 wt%) contents, slightly lower-Mg olivine (Fo = 90.4) and orthopyroxene (Mg# = 90.4) together with lower-Cr spinel (Cr# = 17.9) and clinopyroxene with high Al2O3 (2.79 wt%) and similar TiO2 (0.05 wt%) contents. The 187Os/188Os isotopic ratios of the Guleman peridotites are 0.12589, 0.12736 and 0.13352, coupled with 187Re/188Os ratios of 0.32822, 0.90743, and 1.48804, respectively, for the dunite and depleted harzburgite These data suggest that the Guleman peridotites were modified by melt metasomatism and/or Re addition. Petrographical and geochemical results reveal that mantle peridotites experienced multi-stage melting and refertilization. In the first stage, abyssal peridotites were formed by ∼15% partial melting of an upwelling mantle at a mid-ocean ridge under anhydrous conditions, which was followed by the second stage of partial melting in a supra-subduction zone environment under hydrous conditions. In this later stage, forearc peridotites were formed with a total of 25–43% partial melting for the two episodes and then refertilized. However, some of the peridotites were unaffected (or less affected) by these later events. As a result, abyssal and forearc peridotites are both observed in the Guleman ophiolite.

Chronological and geochemical characteristics of metavolcanic rocks in the Nanping‐Ninghua tectonic belt: Constraints on the formation of the Cathaysia block

AbstractThe tectonic properties of the Nanping‐Ninghua tectonic belt (NNTB) play a crucial role in understanding the tectonic evolution of the Wuyi orogenic belt, which is related to the Neoproterozoic‐Paleozoic tectonic evolution of the Cathaysian Block. In this study, We present comprehensive petrological, geochronological, and geochemical data on the metavolcanic rocks from the Louqian Formation in Changting, Fujian Province. Our results show that volcanism in Changting occurred between 740.4 and 723.5 Ma, based on zircon U–Pb data for the metavolcanic rocks. The metavolcanic rocks have SiO2 contents ranging from 68.22 to 71.56 wt %, high Al2O3 and Na2O + K2O contents (13.30–15.19 wt % and 7.56–8.25 wt %, respectively), and low CaO, MgO, and FeOT contents (0.09–1.25 wt %, 0.72–0.96 wt %, and 1.57–3.16 wt %, respectively). These samples are enriched in large‐ion lithophile elements (LILEs) such as Ba and Rb, and depleted in high‐field‐strength elements (HFSEs) including Nb, Ta, and Ti, with significant negative Eu anomalies, indicating an affinity for arc igneous rocks. Based on previous geological studies, we suggest that the NNTB formed in an active continental margin environment during the Nanhua Period. The subduction of oceanic crust led to the formation of the volcanic belt along the Nanping‐Ninghua continental margin, which was active until 696 Ma. During the Neoproterozoic, the North and South Wuyi terranes did not merge to form a single Wuyi terrane, and the Cathaysia Block was composed of several terranes.

Neoproterozoic lithospheric extension related to break-up of the Rodinia supercontinent: Constraints from a newly-identified granite porphyry in southeastern Yunnan, China

Although the southeastern Yunnan region preserves an important record of the evolution of the South China block (SCB), its Precambrian geology is not well understood due to poor exposure. The newly-discovered Laojunshan granite porphyry (LNGP) is the only Precambrian unmetamorphosed granitoid unit exposed in the southwestern SCB. Here, we present integrated studies of the LNGP including whole-rock major and trace-element geochemistry and Nd isotopes, together with zircon U-Pb chronology and Lu-Hf isotopes by LA-ICP-MS. Zircon U-Pb dating results for two granite porphyry dykes yielded ages of 811.2 ± 7.0 Ma and 830.3 ± 5.2 Ma. The studied samples have high total alkalis (6.46–9.68 wt%), SiO2 (69.44–75.6 wt%), P2O5 (0.11–0.33 wt%) and Al2O3 (10.44–14.39 wt%) but low CaO (0.09–1.29 wt%) contents; these characteristics together with high Al saturation indices (1.1–1.7), indicate the LNGP is of strongly peraluminous S-type granite affinity. The LNGP is characterized by Rb-Th-U-K enrichments and Ba-Sr-Nb-Ti-Ta depletions, and right-sloping REE patterns with obvious negative Eu anomalies (Eu/Eu* = 0.2–0.4). Major and trace elements show good correlations with SiO2. Diagrams of Th vs Th/Nd, La vs La/Sm and Zr vs Zr/Sm indicate that fractional crystallization was an important process in the genesis of the LNGP. The Ba vs Eu, Sr vs Eu and Ba vs Sr correlations and high Rb/Sr (8.2–74) and Ca/Sr (12–614) ratios demonstrate that magmatic evolution involved extensive fractionation of plagioclase and K-feldspar. The initial zircon Hf isotopic composition of the porphyry varies widely (εHf(t) = −10.1 to +6.7), with corresponding two-stage Hf model ages of 1291–2331 Ma; whereas whole-rock Nd isotopes are relatively uniform (εNd(t) = −5.8 to −4.6), with two-stage Nd model ages of 1886–2130 Ma. The variable zircon Hf isotopic compositions suggest a heterogenous source for the LNGP, containing juvenile components (with higher εHf(t) values) and ancient reworked crustal materials (with lower εHf(t) values). Geochemical data, including Rb/Sr, Rb/Ba, Al2O3/(MgO + Fe2O3T), CaO/(MgO + Fe2O3T) and (Na2O + K2O)/(Fe2O3T + MgO + TiO2) ratios and (Na2O + K2O + Fe2O3T + MgO + TiO2) content suggests a meta-pelite/greywacke source. Early arc-continent or continent–continent collision may produce mixtures of juvenile sediments formed by erosion of with ancient crustal materials that were strongly folded and deeply buried in the studied area. The LNGP has medium to high magmatic temperatures (761–875 °C) and low oxygen fugacity (ΔFMQ −5.4 to ΔFMQ −2.8). The LNGP was emplaced at middle-upper crustal levels (pressure < 5kbar) in an extensional setting analogous to granitoid associated with the Neoproterozoic age rift-related Nanhua and Kangdian magmatic belts that bound the periphery of the Yangtze block. These belts are interpreted to be the result of the break-up of the Rodinia supercontinent during the period 850 to 700 Ma. We similarly interpret the emplacement of the LNGP, which occurred within an extensional setting, to be a response to the break-up of the Rodinia supercontinent.

Constraints on Diagenetic Fluid Source and Genesis in Tight Dolostone Reservoir of Submember Ma55 of Ordovician Majiagou Formation in Northwestern Ordos Basin, China: Evidence from Petrology and Geochemistry

Diagenetic fluids is one of the most important reservoir modifiers, their differences can result in various petrography, storage capacity, and geochemical characteristics, so clarifying the diagenetic fluids is vital for understanding dolostone origin. Dolomitization is an important genetic type of dolostone reservoir, the fluid properties differ in different dolomitization, which may lead to reservoir storage capacity changes. Therefore, the identification of dolomitization fluid properties is critical for deeply understanding of dolomitization process and predicting storage capacity. Two types of dolostone are developed in submember Ma55 of Majiagou Formation in northwestern Ordos Basin, with obviously different petrological characteristics and reservoir properties. On the basis of petrological studies such as core and casting thin section observation and cathodoluminescence analysis, the diagenetic fluid properties of these two dolostone are characterized by geochemical analytical methods such as major and trace element tests. The results show that Type-1 dolostone is mainly composed of micritic dolomite, showing micritic structure and algae-rich lamina structure, and accompanied by evaporite minerals and moldic pores. This type of dolostone has a various Mn content, weak to medium cathodoluminescence intensity, high contents of TiO2, Al2O3, K2O+Na2O, Li, and U, and lower content of TFe2O3. The type-2 dolostone is composed of fine-grained dolomite with obvious residual texture of primary limestone, clear brim, and cloudy center structure, accompanied by the existence of intergranular pores. Most of this kind of dolostone have medium-strong cathodoluminescence, higher TFe2O3 content and lower TiO2, Al2O3, K2O+Na2O, Li, and U contents. Moreover, both the two types of dolostone have similar Fe/Ca and Mn/Ca ratios, and a low and concentrated CaO content, whose composition is similar to that of stoichiometric dolomite. The comprehensive analysis shows that the diagenetic fluid of Type-1 dolostone is mainly a high salinity fluid existed in plaster and calcareous sediments in a near surface environment with low temperature. The diagenetic fluid of Type-2 dolostone may be a high salinity brine formed by evaporation and concentration of seawater with normal salinity. The research results will provide a significant theoretical basis for the evaluation of dolostone reservoir quality and the prediction of favorable areas of reservoir distribution.

Zircon U-Pb ages and Hf isotope characteristics of granitic rocks from the Shapinggou molybdenum deposit, Dabie Shan, China

The giant Shapinggou porphyry molybdenum deposit in Jinzhai county, Anhui province is located in eastern Dabie Shan, but its genesis, genetic type and tectonic setting are still debated. New zircon U − Pb age data presented in this contribution show that the granitic rocks at Shapinggou area have been episodically formed at ∼ 135 Ma, ∼127 Ma, ∼117 Ma and ∼ 113 Ma in Early Cretaceous, and can be classified into the early-stage (135–127 Ma) granodiorite and monzogranite plutons, and the late-stage (117–113 Ma) quartz-orthophyre stock and cryptoexplosive breccia pipes. Mo mineralization is closely associated with the late-stage shallow-seated granitic stock or pipes. Granitic rocks of both stages have high contents of SiO2, K2O + Na2O and Al2O3, low contents of TiO2, CaO and MgO, showing a metaluminous to peraluminous, high-K calc-alkaline to shoshonite affinity. They are generally featured by enrichments of LILE (Rb, U, Th) and LREE, and depletions of HFSE (Nb, Ta, Ti) and HREE, with high (La/Yb)N ratios. The early-stage granitic plutons show trace element geochemical signatures of partial melting of over-thickened continental crust (>50 km), whereas element geochemistry of the late-stage small-sized granitic intrusions suggests a shallow source depth (ca. 35 km) under post-collisional extension setting. The Hf isotope data indicate that the Shapinggou granitic rocks are originated from a crustal source predominated by the Kuanping Group mixed with other components such as the mantle. The southward subduction and partial melting of the southern North China Block (including Kuanping Group) beneath the Dabie Shan lead to the generation of the Shapinggou porphyry Mo system in the post-collisional extension setting. Hence the Shapinggou Mo system distinguishes for its crustal source and post-collisional tectonic setting from the porphyry Mo deposits of Climax- or Endako-types, and should belong to collision-type or Dabie-type porphyry Mo deposit.

Petrogenesis of Eocene high-silica granites in the Maliaoshan area, northern Tibet: Implications for the Eocene magmatic flare-up in the Northern Qiangtang Block

The Eocene magmatic flare-up in the Northern Qiangtiang Block is a key event that was genetically related to the uplift of the Tibetan Plateau. This uplift has been considered to have an important impact on the global cooling and oceanic isotopic compositions. Here, we report zircon ages and bulk rock elemental and isotopic compositions for high-silica porphyritic granites in the Maliaoshan area of the Northern Qiangtang Block. Zircon U–Pb dating shows that the porphyritic granites were generated at ca. 41.02 Ma. The porphyritic granites are characterized by uniformly high SiO2 contents (74.3–75.0 wt%), high contents of total alkalis, metaluminous compositions, and low contents of TiO2, Fe2O3T, MgO, CaO, and P2O5. Moreover, the Maliaoshan porphyritic granites have Nd–Hf isotopic compositions similar to those of coeval metaluminous magmatic rocks in the Northern Qiangtang Block. These data together with geochemical modeling results suggest that the Maliaoshan porphyritic granites were formed by the fractional crystallization of 43.06% major minerals and 0.76% accessory minerals from the assumed starting composition (average Eocene metaluminous igneous rock). Based on our new data and Eocene magmatic flare-up event in the Northern Qiangtiang Block, we propose a new geodynamic model to explain such a magmatic flare-up event. The stress produced by the collision of India and Eurasia gradually transferred northward, prompting the Songpan–Garzê Block to subduct southward beneath the Northern Qiangtang Block at ca. 55 Ma, accompanied by minor magmatic activity. Subsequently, the break-off of the Songpan–Garzê Block at ca. 46 Ma resulted in the Eocene magmatic flare-up.