Low Na2O Contents Research Articles

Geochronology and geochemistry characteristics of Neoproterozoic gabbros in Western Yangtze Block and its implication for an injection of mafic magma into the active continental margin

Preserved numerous intermediate to acid igneous rocks with minor basic to ultrabasic rocks, the Western Yangtze Block (WYB) is the window to see the evolutional process of South China Craton during Precambrian era. Here, we report geochronology and geochemistry data from gabbros in the south of Dechang County in SW Sichuan Province. Field investigation and zircon U–Pb age from a gabbro sample suggest that these mafic rocks were emplaced during the early Neoproterozoic era (831.8 ± 2.6 Ma). These gabbros show low contents of SiO2, K2O, and Na2O. They are enriched in Th, and LREEs but depleted in Nb, Ta, Zr, and Ti, showing right-inclined primitive mantle-normalized Rare Earth Elements (REE) patterns with negative to positive weak Eu anomalies. Trace-elemental geochemical features, multiple linear regression, and ratio-ratio plots point to the idea that the primary magma of these gabbros originated from the partial melting of a mantle metasomatized by subduction fluid and contaminated by subducted sediments. The geotectonic discrimination diagrams suggest that these Neoproterozoic gabbros formed at an island arc above a subduction zone in the active continental margin. In addition, we found that the arc-related ~ 830 Ma gabbros in WYB could be divided into two groups. The tholeiite Guandaoshan gabbros showing a flat REE pattern is chemically discerned from the calc-alkaline Dechang and Shimian gabbros having right-inclined REE patterns. We, therefore, thought that a slab window beneath WYB caused Guandaoshan gabbros before it migrated northward to form the Mianning and Shimian A-type granites later.

Effect of alumina on formation mechanism and structure characteristic of sodium calcium silicate compounds with different stoichiometric coefficients

Effect of alumina on formation mechanism and structure characteristic of sodium calcium silicate compounds with different stoichiometric coefficients

Geochemical features of deluvial-lacustrine sedimentogenesis in the basin of lake Chistoye, Northern Priokhotsk area

The results of the geochemical study of loose sediments of the catchment basin and bottom sediments of Lake Chistoye, located in the Northern Priokhotye, showed that the lake was formed at the beginning of the early Holocene about 11200 cal. years ago. Terrigenous sedimentation dominates in it, i. e. the geochemical characteristics of sediments are determined by the particle sizes. Thin grain size sediments have low SiO2, Na2O, K2O, CaO, and Sr contents; and are enriched with Al2O3, TiO2, MgO, Fe2O3, and V. Changes in the nature of sedimentation may be due to climatic reasons and may be associated with cold Bond events. In the Early Holocene, mostly thin silts were deposited in Lake Chistoye. The impulse of “coarse-grained” sediments (140 microns) enriched with silica occurred (9760–9650) and 8810 cal. years ago. A noticeable accumulation of relatively coarse-grained sediments occurred at the very beginning of the Middle Holocene 8540–6920 cal. years ago, as well as 6140 and 4450 cal. years ago. For the Late Holocene, the input of detrital material with increased SiO2 contents was noted in the range of 3470–850 cal. years ago.

Petrogenesis and Tectonic Implications of the Granite Porphyry in the Sinongduo Ag-Pb-Zn Deposit, Central Tibet: Constraints from Geochronology, Geochemistry, and Sr-Nd Isotopes

The Paleocene ore deposits related to the India–Asia continental collision are widely distributed in the Gangdese metallogenic belt. Among these, Sinongduo is the first discovered epithermal Ag-Pb-Zn deposit in the Lhasa terrane. However, there is still controversy over the ore-forming magma in this deposit. This study mainly reports new zircon U-Pb isotopic ages, whole-rock geochemistry, and Sr-Nd isotopic data for the granite porphyry from the Sinongduo deposit, aiming to discuss the petrogenesis and tectonic setting of the granite porphyry and its genetic link between the Ag-Pb-Zn mineralization. The results show that zircon U-Pb analyses yield ages of 62.9 ± 0.5 Ma and 59.0 ± 0.7 Ma for the granite porphyry, indicating that it formed during the Paleocene period. The timing of the granite porphyry intrusion is contemporaneous with the mineralization, suggesting that it is most likely the ore-forming magma in the Sinongduo deposit. The granite porphyry has high SiO2 and K2O, moderate Al2O3, and low Na2O, CaO, and FeOT contents, and it displays significant enrichments in LREEs and LILEs and depletions in HREEs and HFSEs, with negative Eu anomaly. The granite porphyry is a peraluminous series and can be classified as S-type granite. Moreover, the granite porphyry shows relatively high ratios of (87Sr/86Sr)i and low values of εNd(t). The geochemical and isotopic compositions of the granite porphyry from the Sinongduo area are similar to those of the upper continental crust, which suggests that the granite porphyry was most likely derived from the melting of the upper continental crust in the Lhasa terrane during the India–Asia collisional tectonic setting.

An innovative intelligent design method of alkali-activated foamed geopolymer: Mixture optimization and performance prediction

An innovative intelligent design method of alkali-activated foamed geopolymer: Mixture optimization and performance prediction

Geochemical variations of anatectic melts in response to changes of P–T–H2O conditions: Implication for the relationship between dehydration and hydration melting in the Himalayan orogen

Geochemical variations of anatectic melts in response to changes of P–T–H2O conditions: Implication for the relationship between dehydration and hydration melting in the Himalayan orogen

Lattice-preferred orientation (LPO) of olivine and amphibole in amphibole peridotites and neighboring hornblendites from Gapyeong, South Korea and implications for seismic anisotropy

Amphibole peridotites and neighboring hornblendites are often found in subduction zones. To understand the effect of amphibole-rich rocks on seismic anisotropy in subduction zones, we studied the lattice-preferred orientation (LPO) of olivine and amphibole in amphibole peridotites and neighboring hornblendites in Gapyeong, South Korea. The major minerals of amphibole peridotites were olivine (31–51% in volume), amphibole (28–47%), and orthopyroxene (7–16%). Amphibole in amphibole peridotites showed relatively high SiO2 and low TiO2 and Na2O contents (S-type amphibole), indicating that it was formed under supra-subduction conditions. Amphibole in amphibole peridotites showed the type-I, type-II, and type-IV LPO, whereas amphibole in neighboring hornblendites showed the type-III and type-IV LPO. In the case of olivine, most samples showed a mixture of A- and B-type LPO, and one sample showed a mixture of B- and C-type LPO. Many serpentine inclusions were found in olivines. Fourier-transform infrared (FTIR) analysis of the samples showed that the olivines contained a large amount of water (~29000–45000 ppm H/Si). We also found many dislocations in olivines. These observations indicate that samples showing a mixture of A- and B-type LPO and a mixture of B- and C-type LPO of olivine were deformed under water-rich conditions by dislocation creep. In amphibole peridotites, the P-wave anisotropy of olivine was relatively low (0.9–4.8%), whereas the P-wave anisotropy of amphibole was high (6.5–17.7%). The maximum S-wave anisotropy of olivine was also relatively low (0.87–2.89%), whereas the maximum S-wave anisotropy of amphibole was high (3.81–15.19%). In hornblendites, the P-wave anisotropy and maximum S-wave anisotropy of amphibole were high (6.9–13.6% and 4.27–10.61%, respectively). The P-wave anisotropy and maximum S-wave anisotropy of the amphibole peridotites were in the range of 2.6–8.4% and 1.73–7.30%, respectively. The seismic velocity and anisotropy pattern of amphibole peridotites were more similar to those of amphibole than those of olivine, indicating that the seismic properties of amphibole peridotites were more strongly affected by amphibole than by olivine. Furthermore, the seismic anisotropy of the mixture of amphibole peridotite and hornblendite in subduction zones was also found to be significantly affected by the amphibole LPO in hornblendite.

Mixed ionic-electronic transport in Na2O doped glassy electrolytes: Promising candidate for new generation sodium ion battery electrolytes

In the present communication, newly developed glassy electrolytes, Na2O–ZnO–CdO, have been considered to discuss their electrical transport behavior at ambient temperature. The AC conductivity and relaxation behavior of them have been studied in the light of Almond-West formalism. The electrical conductivity (mixed conduction) is found to be a function of frequency as well as temperature. In the low-frequency range, it shows a flat conductivity owing to the diffusional motion of Na+ ions, whereas at high frequency, the conductivity shows dispersion. The DC conductivity ( σ dc ) and hopping frequency have been computed from the best fitted plots of experimental data. The AC conductivity at different concentrations and a constant temperature has been reported. The variation in the conductivity data with reciprocal temperatures indicates the dynamical behavior of charge carriers via hopping conduction in sodium oxide glassy systems. Mixed conduction in the present system may be dominated by polaron hopping in the samples with a lower Na2O content with a percolation type of motion of the electron/polaron. On the other hand, three-dimensional Na+ motion is the dominating charge carrier for the samples with a higher Na2O content. A negligible small difference in pathways in the I–V characteristics in both the directions should make the present system a promising candidate for the new generation battery electrolyte.

A clean two-stage Bayer process for achieving near-zero waste discharge from high-iron gibbsitic bauxite

A clean two-stage Bayer process for achieving near-zero waste discharge from high-iron gibbsitic bauxite

Reappraisal of the petrogenetic processes of Neoproterozoic granitoids in the Altyn Tagh, NW China: Implications for reconstruction of the Qaidam block in Rodinia

• The early Neoproterozoic granitoids in the Qaidam block show typical S-type properties, generating via partial melting of Mesoproterozoic metasedimentary rocks. • These granitoids were formed under high-temperature and low-pressure conditions in a late syn- to post-collision setting. • Qaidam block was located at the core of the Rodinia supercontinent, adjacent to Laurentia, Baltica and Amazonia during the Neoproterozoic. Neoproterozoic granitoids are widely distributed in the Altyn Tagh, and provide indispensable information on the pre-Cenozoic tectonics and evolutionary history at the northeastern margin of Tibetan Plateau. In this study, zircon U-Pb geochronological results show that the granitoids were emplaced during the interval between 997 Ma and 901 Ma. Petrological studies reveal that these granitoids have high Al 2 O 3 and K 2 O, low CaO and Na 2 O contents with Al-rich minerals, such as muscovite, which show typical S-type properties. These Neoproterozoic granitoids contain abundant inherited cores of Mesoproterozoic age with ε Hf (t) values between 9.43 to 4.60. We interpret this to indicate magma generation via partial melting of Mesoproterozoic metasedimentary rocks. Based on a comparison to similar Neoproterozoic magmatic and metamorphic events described in the East Kunlun and North Qaidam, we suggest that the Altyn Tagh, East Kunlun and North Qaidam were part of the same terrane (Qadiam block) during the early Neoproterozoic. Petrogenetic data when combined with other geological and tectonic information suggest a late syn- to post-collisional setting rather than a syn -collisional setting. The Qaidam block was probably located adjacent to Laurentia, Baltica and Amazonia, during Neoproterozoic time.

Significance of Granulometric Composition and Physicochemical Properties for Interpreting the Lake Grand Sedimentation

Abstract —The paper is concerned with a study of the slope deposits being weathering products of rhyolites and their tuffs in the vicinity of Lake Grand (northern Okhotsk area). The samples were divided into grain size fractions of 2500, 250, 140, 100, 63, 40, 20, and 1 μm. Analysis for major and trace elements and mineralogical and petrophysical studies were performed for each fraction. It is shown that a decrease in the fraction size is accompanied by the enrichment of the sediments with Al2O3, Fe2O3, TiO2, MgO, Y, Rb, Ni, and paramagnetic minerals and by an increase in LOI. The fine fractions are characterized by low contents of SiO2 and Na2O and high values of CIA, PIA, and Rb/Sr. The maximum magnetic susceptibility, saturation magnetization, and contents of CaO, Sr, and Zr are established in the fractions of 40 μm. The values of magnetic susceptibility, Js, and Jrs decrease in passing from the fractions of 40 μm to the fractions of 1 μm, whereas the values of Bc and Bcr increase. A specific feature of these fractions is high paramagnetic susceptibility and the presence of lepidocrocite. The qualitative composition of ferrimagnetic minerals is the same for the slope deposits and lacustrine sediments. In passing from coarse fractions to fine ones, the contents of quartz and K-feldspar decrease, and the contents of muscovite, biotite, chlorite, and kaolinite increase. The distribution of petromagnetic and geochemical characteristics in the Lake Grand sediments of varying grain size is similar to that in the slope deposits. The complex characteristics of the lacustrine sediments that formed in cold and warm periods are consistent with the distribution of these parameters in various fractions of deluvium and colluvium. Moreover, the fine-grained material acquired specific geochemical, mineralogical, and petrophysical properties when being on the slopes. Comparison of the SiO2/TiO2 and Fe2O3/TiO2 ratios of the slope deposits and lacustrine sediments makes it possible to identify the intervals of biogenic and chemogenic sedimentation in water basins.

Decoupled Trace Element and Isotope Compositions Recorded in Orthopyroxene and Clinopyroxene in Composite Pyroxenite Veins from the Xiugugabu Ophiolite (SW Tibet)

Abstract Pyroxenite veins and dikes are commonly observed in the mantle section of ophiolites. Because of their mantle occurrence, these pyroxenites are free from crustal contamination and offer a unique opportunity for studying mantle compositions and melt–rock interaction processes. We conducted an integrated petrological and geochemical study of a suite of composite orthopyroxenite, websterite, and pyroxene-bearing dunite veins from the Xiugugabu ophiolite located on the western segment of Yarlung–Zangbo Suture Zone. The dunite is separated from the host peridotite by a layer of pyroxenite, forming a composite vein system. Systematic variations in major, minor, and trace element compositions in minerals across the composite veins are observed. Two generations of orthopyroxenes in the pyroxenites are characterized by high Mg#, low TiO2 concentrations, and depleted patterns of incompatible trace elements. Clinopyroxenes in the pyroxenites are characterized by high Mg#, low contents of TiO2 and Na2O, spooned shaped REE patterns, and a negative Zr anomaly. Through major and trace element modeling, we showed that both orthopyroxene and clinopyroxene were in equilibrium with melts with different compositions. This hypothesis is further confirmed by distinct initial Nd and Hf isotope ratios in the two pyroxenes. A model for the formation of composite pyroxenite veins is developed, whereby hydrous and silica-rich melts percolate along the margins of a dunite channel. The orthopyroxenite was formed by the reaction between a hydrous, silica-rich melt and the surrounding peridotite. The websterite is formed by reactive crystallization of a hybrid melt produced by mixing silica-rich melt and the melt formed by remelting of previously depleted peridotite in the deeper part of the mantle column. The extremely enriched Nd–Hf isotope compositions of the pyroxenite veins (εNd = −20.3 to +11.5 and εHf = −13.2 to +25.3, 125 million years ago) can be explained by the addition of ancient, recycled sediments to the mantle source in a supra-subduction setting. Based on the low-Cr# spinel in the Xiugugabu dunites (Cr# = 19–50) and the depleted nature of the parental melt of the Xiugugabu pyroxenites, we deduced that the formation of pyroxenites postdate the formation of the Xiugugabu ophiolite at ~125–130 Ma. Collectively, results from this study have provided support to the hypothesis that the Xiugugabu ophiolite experience a two-stage evolution, i.e., firstly formed in a mid-ocean ridge setting and subsequently modified in a supra subduction zone.

Ca. 815 Ma intra-plate granitoids and mafic dykes from Emeishan pluton in the western Yangtze Block, SW China: A record of rifting during the breakup of Rodinia

• Monzogranite from the Emeishan pluton (ca. 815 Ma) is the A-type granites affinity. • The Emeishan diabase dyke (ca. 815 Ma) have WPB geochemical characteristic. • The igneous assemblage provides an important record of within plate rifting. • A-type affinity granites discovered from margin to interior of Yangtze Block. • The plutons from the intra-plate and margin suggesting in the same tectonic setting. The western Yangtze Block, South China is characterized by voluminous Neoproterozoic extension-related volcano-sedimentary sequences and intrusions (e.g. Emeishan granitoid intrusion) and spatially associated mafic dykes. The origin and tectonic setting of Emeishan granitoid intrusion and mafic dykes in the Yangtze Block is poorly study. Understanding the origin and geodynamic setting of dykes and granitoid intrusion are significant in deciphering thermal structure and composition of mantle, tectonic evolution as well as crustal growth processes in the Yangtze Block. SIMS Zircon U–Pb dating of Emeishan granitoid intrusion and mafic dykes suggests that the granitoids (ca. 818 Ma) and mafic dykes (ca. 814 Ma) are contemporaneous. Compositionally, the Emeishan granitoids are restricted and characterized by high SiO 2 (69.11–70.50 wt%), Na 2 O + K 2 O (3.52–4.13%) and Al 2 O 3 (14.16–14.47%), but low CaO (1.78–2.03%), MgO (0.72–0.91%) contents. They feature strong LREE-enrichment (La/Yb N = 7.2–12.3) in conjunction with negative Eu anomalies. The mafic dykes have low SiO 2 (48.09–48.65 wt%), K 2 O (1.94–2.12 wt%) and Na 2 O (1.64–1.75 wt%) contents, and high Mg # (61.67–62.26). On primitive mantle-normalized trace element plot, they are characterized by enrichment of LILEs and depletion of HFSEs. Both the mafic dykes and granitoids record similar zircon ε Hf (t) values (+2.2 to +12.1, +1.4 to +6.8), and zircon δ 18 O values (4.47‰ and 10.41‰, 4.49‰ and 12.05‰, respectively). The rifting-related geochemical signature of the Emeishan pluton and contemporaneous margin and intra-plate plume-related magmatism suggest that they were derived from mantle melting in extensional tectonic setting during mid-Neoproterozoic.

Mineralogical and Re-Os isotope constraints on fluid– and melt–rock interactions and the origin of mantle peridotites from the Amdo ophiolite, northern Tibet

Ophiolites from the Bangong–Nujiang Suture Zone in the central part of the Tibetan Plateau represent relics of Neo-Tethyan oceanic lithosphere. Here we present the results of a detailed mineralogical and Os isotopic study of mantle peridotites of the Amdo ophiolite, which provide new insights into the origin of the peridotites and their diverse melt/fluid–peridotite reactions. The Amdo ophiolite comprises mantle peridotites, mafic–ultramafic cumulates, massive gabbros, diabases, and pillow basalts. The mantle peridotites are mainly refractory harzburgites, composed of olivine (Ol, 65%–85%), orthopyroxene (Opx, 12%–35%), clinopyroxene (Cpx, <4%), and Cr-spinel (Cr-Spl, ~2%). Most olivine grains (Ol-I) are protogranular, locally enclosed in orthopyroxene and Cr-spinel, and have high Fo values (91.1–92.9) and NiO contents (0.29–0.44 wt%), typical of residual origin. In contrast, interstitial olivines (Ol-II) have low Fo values (67.2–84.7) and NiO contents (<0.05 wt%), but extremely high MnO contents (0.28–1.65 wt%), suggesting metasomatism by carbonate-bearing fluids. Hypidiomorphic-granular clinopyroxene grains (Cpx-I) have high Mg# values (~94.5) and low Al 2 O 3 (average 1.26 wt%) and Na 2 O (<0.19 wt%) contents, typical of residual phases after melting. However, clinopyroxene coronas (Cpx-II) around orthopyroxene have higher Na 2 O contents (0.24–1.06 wt%), indicative of mantle metasomatism by melts. Osmium isotopic compositions in the harzburgites vary from subchondritic to suprachondritic ( 187 Os/ 188 Os ratios: 0.11716–0.13284). The subchondritic Os isotopic compositions (0.11716–0.12367) correspond to T RD model ages of 0.76–1.56 Ga, suggesting Mesoproterozoic mantle depletion events. On the other hand, several harzburgites with low Os (0.29–0.86 ppb) and suprachondritic 187 Os/ 188 Os ratios (0.12823–0.13284) reflect the overprinting of original Os budgets and Os isotopic compositions by percolating melts or fluids. The combined mineralogical and Os isotopic compositions suggest that the Amdo peridotites represent a mixture of ancient subcontinental lithospheric mantle (SCLM) and Mesozoic oceanic lithosphere, which were subsequently infiltrated by carbonate-bearing fluids and silicate melts in a supra-subduction zone. • Multiple generations of mineral assemblages are present in the Amdo harzburgite. • Some of the Amdo mantle peridotites may have originated from ancient SCLM. • The Amdo ophiolite formed in a forearc environment.

Chemical, mineralogical, and physicochemical features of surface saline muds from Southwestern sub-basin of the East Vietnam Sea: Implication for new peloids

This study presents the chemical, mineralogical and physicochemical features of 8 saline mud samples from 8 gravity cores located in the southwestern sub-basin of the East Vietnam Sea. The grain-size analysis of mud samples reveals the amount of clay and silt particles in the ranges of 65.1-89.2% and 9.5-34.2%, respectively and a very low fraction of sand. The analytical results showed that mud samples have high contents of SiO2 (32.79-48.09%), Al2O3 (11.26-13.63%), CaO (3.10-13.93%), Fe2O3 (4.15-9.45%), and low contents of TiO2, MnO, MgO, Na2O, K2O and P2O5. The XRD analysis of mud samples indicated mineral compositions with major minerals of quartz, illite, calcite, chlorite, feldspar, kaolinite, and other minor minerals like halite, smectite, fluorapatite, pyroxene, amphibole. The organic and physicochemical parameters of mud samples were also measured. Potentially toxic elements in mud samples were determined and compared with reference values and the technical standard. This study proposes that saline mud samples from the studied area are potential peloids.

Decoupling of Sr-Nd Isotopic Composition Induced by Potassic Alteration in the Shapinggou Porphyry Mo Deposit of the Qinling–Dabie Orogenic Belt, China

In our previous study on petrogenesis of quartz syenite and granite porphyry, the host rocks of the Late Mesozoic Shapinggou Mo deposit in the Qinling–Dabie orogenic belt, we found that the initial Sr isotopic composition of the host rocks is strongly affected by the degree of K-alteration. Here, we provide further isotopic evidence of the host rocks and their minerals to investigate the geochemical behaviour of trace elements and isotopes during the alteration and to explain the phenomenon of decoupling of Sr–Nd isotopic composition. The quartz syenite and granite porphyry are altered by K-alteration in varying degrees and have high K2O and Rb contents and low Na2O, CaO, Sr, and Ba contents. Rock samples of both quartz syenite and granite porphyry have variable Rb/Sr ratios and initial 87Sr/86Sr values (even &lt; 0.70) but contain quite homogeneous εNd(t) values (−12.8 to −14.8). Minerals from the rocks of moderate to intense K-alteration have very low initial 87Sr/86Sr values (even &lt; −17), while those from the weakly altered rocks have 87Sr/86Sr(t) values of 0.7044 to 0.7084. The same phenomenon of the decoupling in Sr–Nd isotopic composition can be observed from several Mo deposits within the eastern Qinling–Dabie orogenic belt. This fact suggests similar hydrothermal features and a comparable origin for both the magmatic rocks and hydrothermal fluids in this belt. A comparison between porphyry Mo and porphyry Cu deposits shows that elements and the Rb–Sr isotope system have different behaviours during the K-alteration, implying distinct material sources and igneous rocks for porphyry Mo and porphyry Cu deposits, respectively.

Petrogenesis of Mediterranean lamproites and associated rocks: The role of overprinted metasomatic events in the post-collisional lithospheric upper mantle

Abstract High-MgO lamproite and lamproite-like (i.e. lamprophyric) ultrapotassic rocks are recurrent in the Mediterranean and surrounding regions. They are associated in space and time with ultrapotassic shoshonites and high-K calc-alkaline rocks. This magmatism is linked with the geodynamic evolution of the westernmost sector of the Alpine–Himalayan collisional margin, which followed the closure of the Tethys Ocean. Subduction-related lamproites, lamprophyres, shoshonites and high-K calc-alkaline suites were emplaced in the Mediterranean region in the form of shallow level intrusions (e.g. plugs, dykes and laccoliths) and small volume lava flows, with very subordinate pyroclastic rocks, starting from the Oligocene, in the Western Alps (northern Italy), through the Late Miocene in Corsica (southern France) and in Murcia-Almeria (southeastern Spain), to the Plio-Pleistocene in Southern Tuscany and Northern Latium (central Italy), in the Balkan peninsula (Serbia and Macedonia) and in the Western Anatolia (Turkey). The ultrapotassic rocks are mostly lamprophyric, but olivine latitic lavas with a clear lamproitic affinity are also found, as well as dacitic to trachytic differentiated products. Lamproite-like rocks range from slightly silica under-saturated to silica over-saturated composition, have relatively low Al 2 O 3 , CaO and Na 2 O contents, resulting in plagioclase-free parageneses, and consist of abundant K-feldspar, phlogopite, diopsidic clinopyroxene and highly forsteritic olivine. Leucite is generally absent, and it is rarely found only in the groundmasses of Spanish lamproites. Mediterranean lamproites and associated rocks share an extreme enrichment in many incompatible trace elements and depletion in High Field Strength Elements and high, and positively correlated Th/La and Sm/La ratios. They have radiogenic Sr and unradiogenic Nd isotope compositions, high 207 Pb over 206 Pb and high time-integrated 232 Th/ 238 U. Their composition requires an originally depleted lithospheric mantle source metasomatized by at least two different agents: (1) a high Th/La and Sm/La (i.e. SALATHO) component deriving from lawsonite-bearing, ancient crustal domains likely hosted in mélanges formed during the diachronous collision of the northward drifting continental slivers from Gondwana; (2) a K-rich component derived from a recent subduction and recycling of siliciclastic sediments. These metasomatic melts produced a lithospheric mantle source characterized by network of felsic and phlogopite-rich veins, respectively. Geothermal readjustment during post-collisional events induced progressive melting of the different types of veins and the surrounding peridotite generating the entire compositional spectrum of the observed magmas. In this complex scenario, orogenic Mediterranean lamproites represent rocks that characterize areas that were affected by multiple Wilson cycles, as observed in the Alpine–Himalayan Realm.

Early Paleozoic high-temperature metamorphism of garnet amphibolite in the Longyou area, Cathaysia Block of South China: P–T path and tectonic implications

Garnet amphibolite can provide crucial information on tectonic processes. Recent progresses on garnet amphibolite in the Longyou area of the Cathaysia Block, South China have attracted geologists’ wide concerns and discussions about the regional metamorphic history and geodynamic setting. The Longyou garnet amphibolite shows a prominent porphyroblastic texture involving garnet (~40 vol%), hornblende, clinopyroxene, quartz and ilmenite, with minor plagioclase (<5 vol%), sphene, rutile, pyrite and apatite. Garnet presents as aggregations with double-/multi-nuclear structure and has embayed rims surrounded by quartz and plagioclase. Clinopyroxene is partially replaced by late hornblende and plagioclase. A clockwise high-temperature P–T evolution involving four stages has been determined. The generalized prograde stage shows increases of P–T conditions. The Pmax and Tmax stages lie in P–T conditions of 13 ± 0.6 kbar/808 ± 13 °C and 10 ± 0.9 kbar/840 ± 10 °C, reflecting apparent thermal gradients of ~17 °C/km and 22–23 °C/km, respectively. Both stages match medium-pressure facies series metamorphism. The late retrograde stage shows decompression and cooling. A P–XMg [=Mg/(Mg + Fe) in mole] pseudosection drawn at T = 840 °C suggests that low bulk-rock XMg contents (=0.29–0.33) in the Longyou garnet amphibolite are responsible for the high content of garnet in the rock. A P–M(Na2O) pseudosection at T = 840 °C reveals that the low content of plagioclase in the rock is caused by low bulk-rock Na2O contents (=0.44–1.18 mol.%). The integrated P–T–t data from the Cathaysia Block indicate that the early Paleozoic metamorphism can be connected to an intraplate orogenic setting.

Geochemistry, geochronology, and zircon Hf isotopic compositions of felsite porphyry in Xiangshan uranium orefield and its geological implication

Recently, a new kind of volcanic rock, felsite porphyry, has been revealed by drilling in Xiangshan area, Jiangxi Province, China. To better understand petrogenesis and magmatic evolution sequence of the Xiangshan volcanic-intrusive complex, we studied systematic petrology, geochemistry, LA-ICP-MS zircon U–Pb dating, and Hf isotope results of the felsite porphyry. Results show that the felsite porphyry has similar geochemical characteristics to the porphyroclastic rhyolite, which is the predominant lithology of Xiangshan uranium orefield. Felsite porphyry and porphyroclastic rhyolite have high SiO2, Al2O3, and K2O contents, low Na2O, and MgO contents, and slightly negative Eu anomalies. Moreover, these rocks are relatively depleted in large ion lithophile elements (K, Ba, and Sr) and are enriched in high field strength elements (Th, Zr, and Hf). LA-ICP-MS zircon U–Pb dating of the felsite porphyry yielded a crystallization age of 132.2 ± 0.9 Ma, which is coeval to that of the porphyroclastic rhyolite. These ages signified that Xiangshan volcanic-intrusive complex formed in the Early Cretaceous, during which the entire South China was in the back-arc extension tectonic setting related to the subduction of the Pacific Plate under the Euroasian Plate. In-situ zircon Hf isotope data on a felsite porphyry sample show eHf(t) values from − 8.82 to − 5.11, while the Hf isotope two-stage model age (TDM2-Hf) ranges from 1513 to 1747 Ma. Combined with petrological, mineralogical, geochemistry, and geochronology results of the felsite porphyry, it is concluded that the felsite porphyry in Xiangshan might be originated from the partial melting of the Mesoproterozoic ancient metamorphic rocks, with possible input of small amounts of mantle materials.

Geochemistry of Granites from Chail Group of Garhwal Region, Lesser Himalaya, NW India

Paleoproterozoic granites are well exposed in the Chail group of Garhwal region, Lesser Himalaya crystalline sequences (LCHS). These granites are less studied in terms of geochemical classification and tectonic settings. In the present work, we carried out the geochemical analysis of granites of the Chail group from the Chirbatiya-Khal and Ghuttu areas. All the samples have high SiO2 (73.24 ̶79.1 wt %), Al2O3 (11.2 ̶12.95 wt %), K2O (3.8 ̶5.9 wt %) and low P2O5 (0.11 ̶0.24 wt %), CaO (0.21 ̶1.02 wt %), and Na2O (2.2-3.03 wt %; exceptionally low in one sample, that is 0.009 wt %) contents. The A/CNK values for the samples are range from 1.19 to 2.91, characteristic of S-type granites. REE patterns for these granites are moderately fractionated with an average (La/Yb)N ̴8.21 and europium anomaly (Eu/Eu*) ̴0.15. The tectonic settings of the studied granite suggest that they are formed in syn-collision tectonic environments.