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This article focuses on the issues related to the primary nature and metamorphism of gneisses from the Larba block of the Dzhugdzhur–Stanovoy fold area, which are based on the study of the mineralogical composition of supracrustal rocks. The PT-parameters for the highest temperature and pressure metamorphic transformations of rocks of the Larba block are estimated as P = 6.5–8.5 kbar and T > 800°C. Relatively low-temperature garnet–biotite and garnet–biotite–chlorite mineral parageneses were formed at the regressive stage of metamorphism at ~4–6 kbar and temperatures up to 500–600°C. Wide variations in paragneiss compositions indicate that the studied gneisses were derived from protoliths of different composition. Overall, Larba metasedimentary rocks had weakly and moderately weathered source areas. Most of the compositions of paragneisses are located in the field of chlorite–montmorillonite, montmorillonite–kaolinite–hydromica, and chlorite clays formed from the mafic protolith. The low alkalinity in combination with a high MgO content indicates the presence of rock erosion products with a significant admixture of basic volcanic material in the detrital material. Migmatization of the rocks is the most significant factor that distorts the reconstruction of the original rock composition. [ABSTRACT FROM AUTHOR]

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[Display omitted] • The Paleo-Tethys Ocean developed Permian–Triassic ocean islands and submarine fans. • The protoliths of E-MORB-like metabasites have zircon U–Pb ages of ca. 272–241 Ma. • Quartzose schists and South Qiangtang flysch show consistent detrital provenances. Unraveling the protolith origin of high-pressure and low-temperature (HP-LT) metamorphic rocks is the key to understanding the tectonic evolution of active continental margins. A comprehensive study, including field observations, geochemical analyses and zircon U-Pb geochronological dating, was conducted on the Lanling HP-LT terrane to determine its protolith origin and the presubduction paleogeography of the Paleo-Tethys Ocean. The metabasites can be divided into two geochemical groups: Group A samples exhibit low TiO 2 values (1.15–1.81 wt%) and subalkaline basalt affinity with rare earth element (REE) distribution patterns and trace element abundances similar to enriched mid-ocean ridge basalts (E-MORB); Group B samples have higher TiO 2 values (2.75–3.32 wt%) and show alkaline basalt affinity and ocean island basalt (OIB) geochemical signatures. Lanling metabasites are likely derived from a long-depleted mantle source combined with crustal contamination based on the following evidence: (1) positive ε Nd (t) values (+4.8 to +5.6) and a scattered distribution of I sr (t) values (0.704684 to 0.710999), (2) abundant Precambrian zircon grains, and (3) a volcanic arc trend in the tectonic discrimination diagram. Zircon U–Pb dating yields a timing of ca. 272–241 Ma for the protolith age of the Lanling eclogites. The protoliths of the OIB- and E-MORB-type metabasites in Lanling are postulated to be ocean island magmatites and basaltic crust of the Paleo-Tethys Ocean, respectively. Moreover, the Lanling quartzose schists contain only ancient detrital zircons with ages of >500 Ma and show protolith lithostratigraphy and provenance similar to those of the late Paleozoic clastic flysch in the South Qiangtang block (SQB). Based on the above observations and other geological evidence, a hypothetical model of the Permian–Triassic ocean island and adjacent abyssal submarine fan in the Paleo-Tethys Ocean is proposed to explain the protolith origin of the Lanling HP-LT terrane and the presubduction paleogeography in central Qiangtang. [ABSTRACT FROM AUTHOR]

The Dashuigou tellurium deposit is the world's only known independent tellurium deposit. By restoring metamorphic rocks' protolith, we seek to understand not only the development and evolution trajectory of the region but also the origin of the relevant deposits. While there are many ways to restore metamorphic rocks' protolith, we take the host metamorphic rocks of Dashuigou tellurium deposit and leverage various petrochemical eigenvalues and related diagrams previously proposed to reveal the deposit's host metamorphic rocks' protolith. The petrochemical eigenvalues include molecular number, Niggli's value, REE parity ratio, CaO/Al2O3 ratio, Fe3+/(Fe3+ + Fe2+) ratio, chondrite-normalized REE value, logarithmic REE value, various REE eigenvalues including scandium, Eu/Sm ratio, total REE amount, light and heavy REEs, δEu, Eu anomaly, Sm/Nd ratio, and silicon isotope δ30SiNBS−28‰, etc. The petrochemical plots include ACMs, 100 mg-c-(al + alk), SiO2-(Na2O + K2O), (al + fm)-(c + alk) versus Si, (FeO + Fe2O3 + TiO)–Al2O3–MgO, c-mg, Al2O3–(Na2O + K2O), chondrite-normalized REE model, La/Yb-REE, and Sm/Nd ratio, etc. On the basis of these comprehensive analyses, the following conclusions are drawn, starting from the many mantle-derived types of basalt developed in the study area of different geological ages, combined with the previously published research results on the deposit's fluid inclusions and sulfur and lead isotopes. The deposit is formed by mantle degassing in the form of a mantle plume in the late Yanshanian orogeny. The degassed fluids are rich in nano-scale substances including Fe, Te, S, As, Bi, Au, Se, H2, CO2, N2, H2O, and CH4, which are enriched by nano-effect, and then rise to a certain part of the crust in the form of mantle plume along the lithospheric fault to form the deposit. The ultimate power for tellurium mineralization was from H2 flow with high energy, which was produced through radiation from the melted iron of the Earth's outer core. The H2 flow results in the Earth's degassing, as well as the mantle and crust's uplift. [ABSTRACT FROM AUTHOR]

Field and geochemical studies of the Bunu area, SW Nigeria, were carried out on gneiss-metasedimentary rocks that consist of migmatised gneiss, quartz-mica schist, and foliated and massive quartzites. These gneiss-metasedimentary rocks are interbedded with meta-igneous rock (amphibolite), all of which are intruded by granitoid and cut by basic and felsic dykes. Geochemical data on major, trace, and rare Earth elements of these rocks from the area were used to speculate on the petrogenetic and geodynamic evolution of the rocks in the area. Compositionally, the metasedimentary rocks in the area have a restricted range of major oxides such as SiO2 and Al2O3 with low average values of Fe2O3, MnO, CaO, and P2O5. Concentrations of average values of HSFE such as Zr, Nb, and Y are moderately high in migmatitic gneiss, quartz-mica schist, and low in both massive and foliated quartzite. ∑LREE average values are 124.25, 132.41, and 18.64 ppm respectively for migmatite gneiss, quartz-mica schist, and low in both massive and foliated quartzite. These rocks are also generally enriched in Ba, Cs, Pb, U, Cr, Rb, and Zr and depleted in Be, Sr, Ti, Mo, Th, and W. This enrichment–depletion in major oxides and trace elements of the rocks in this area is probably a consequence of the movement of metamorphic remobilized fluids within the rocks in the area during the Pan-African or earlier events as noted in the adjacent Egbe-Isanlu Schist belt. A further geochemical characterisation of the rocks in the area using Log (Na2O/K2O) vs Log (SiO2/Al2O3 indicates that while the protolith of migmatised gneiss and quartz-mica schist are greywackes to litharenite in compositions that of quartzites are sublitharenite to quartz arenite. On the ternary plot of Al2O3-(CaO + Na2O)-K2O for metasedimentary rocks in the area, most migmatitic gneiss and quartz-mica schist rocks plot close to average shale while quartzites mostly tend to illite compositions and almost toward the Al2O3-apex of the diagram attesting to depletion of CaO and NaO with the removal of K2O. CIA vs PIA plot of the rocks in the area shows that while migmatitic-gneiss and quartz-mica schist are moderately weathered, both massive and foliated quartzites are high to extremely weathered. They are all derived mostly from predominantly felsic igneous to quartzose sedimentary provenance and mostly emplaced in passive continental margins. These nature of the protoliths suggests gradual subsidence of the basin during its genesis, and/or tectonic stable or inactive environment from which the sediments were derived. [ABSTRACT FROM AUTHOR]

Situated at the central part of the Central African Fold Belt in Cameroon, the Shissa pluton consists of two-mica granites and biotite granites. All the granites are shoshonitic in nature and present high K2O/Na2O ratios (1.50–2.42). The biotite granites are subaluminous and present I-type character (A/CNK ranges 1.0–1.1). The two-mica granites are typically two-mica alkali granites with S-type signature (A/CNK ranges 1.1–1.21) and Al2O3-rich (Al2O3 = 12.86–13.40 wt.%) than the biotite granites (Al2O3 11.24–13.26 wt.%). The Shissa granites multi-element patterns show enrichment in LILE such as Rb, Th, U, and Pb and are depleted in HFSE such as Ti, Ba, and P, suggesting the crustal source with an inherited arc signature. All the granites present the Nb/Th ratio (0.2–1.2) significantly lower than that of the mantle (> 15), indicating the crustal source for the granites. The chemistry of the biotites suggests that the biotite granites are generated from the partial melting of already differentiated metabasite to metatonalitic source under high oxidizing conditions at the temperature between 908 and 1009 °C, while the two-mica granites were formed under moderated oxidizing conditions between 836 and 917 °C from the assimilation of felsic crustal component by the biotite granite magma during its ascent. The Shissa granites formed at a relatively hydrous environment (4 wt.% of the water content). The upwelling of the asthenosphere through slab break-off may have favored the partial melting of the meta-igneous lower crust by supplying the thermal anomaly as it is the case in the Central African Fold Belt in Cameroon. The whole-rock geochemistry and the biotite mineral chemistry suggest the collisional tectonic setting for the Shissa granite as several granitoid plutons in the CAFBC. [ABSTRACT FROM AUTHOR]

Proterozoic high‐grade marbles cover a significant portion of the Highland Complex (HC) of Sri Lanka. Although many studies on metamorphic silicate rocks of the country have been carried out, marbles, which can be used as a tool to interpret the evolution history of the crust, has been paid little attention. The present study aims to understand the genesis and characteristics of protolith of these marbles by investigating their mineralogy and geochemistry. The studied marbles occur as bands intercalated with pelitic gneisses and quartzites of the HC, indicating the pre‐existing sandstone‐shale‐carbonate sedimentary sequence. Except along the lithological contacts, the studied marbles contain low amounts of silicate minerals (<5%) and are dominated by dolomites (>90%) with minor calcites. Calcites occur as inclusions within dolomites or as fine grains along the grain boundaries of dolomites. Silicate minerals always occur as lensoid or layered aggregations. Dolomites are related to the protolith composition, while most of the calcites are metamorphic products formed due to the reaction of silicate minerals with dolomite. Silicate mineralogical zones suggest the inherited compositional variations of the protolith. Although the marbles have undergone granulite‐grade metamorphism, their trace elemental contents have been well preserved. Concentrations of Fe, Mn, Sr, Na, and K as well as rare earth element (REE) contents of the marbles are comparable to those of marine origin carbonates. Hence, marine dolostone can be proposed as the protolith for Sri Lankan marbles. The distinct mineralogy as well as elevated trace element and REE concentrations of marble in the lithological contact zones are evidenced for prevailed syn‐ to post‐metamorphic fluid activities in the HC. Mineralogical and trace elemental composition of Sri Lankan marbles are correlated well with the marbles from other East‐Gondwanaland crustal units. [ABSTRACT FROM AUTHOR]

Detrital zircon U–Pb ages are reported from the Haast Schist in western Otago and Marlborough, South Island, New Zealand. The majority are from the Aspiring Lithological Association in Otago, which intervenes between Caples Terrane and Rakaia Terrane protoliths. These indicate provenances similar to those in established Jurassic and Late Triassic sandstones of the Waipapa Composite Terrane in the North Island. The populations are dominated (>60%) by Early Jurassic, Triassic and Permian zircons with only small proportions of pre-Permian zircons. In contrast, schists east of the Aspiring Lithological Association have substantial proportions (>20%) of early Paleozoic–Precambrian zircons and are thus assigned to the Triassic–Permian, Rakaia Terrane (Torlesse Composite Terrane), which is extensive across eastern Otago. However, three small areas of anomalous schist, with dominantly (80%) Carboniferous zircons, are considered the oldest level of the Rakaia Terrane protolith. Similar datasets from western Marlborough Schist confirm the correlation with western Otago Schist and are also assigned to the Waipapa Composite Terrane. The new Haast Schist datasets support a suspect terrane model in which both Rakaia and Waipapa Composite terrane protoliths have sediment provenances in eastern Australia and Au–W sources at their subsequent mineralisation sites. Original protoliths are recognisable within the Haast Schist of New Zealand on the basis of distinctive detrital zircon age patterns. The Aspiring Lithological Association (Otago Schist) of western Otago, is correlated with a similar belt of schistose rocks (Marlborough Schist) in western Marlborough, and both are assigned to a Waipapa Composite Terrane protolith of Jurassic to Late Triassic age. The Jurassic-Late Triassic sandstones within Waipapa Composite Terrane are dominantly of granitoid provenance in eastern Australia. Detrital zircons of Carboniferous age in the Waipapa Composite Terrane support a possible New England Orogen provenance in northeastern NSW and southeastern Queensland, and also indicate possible primary sources for the gold and tungsten in the western Otago Schist and western Marlborough Schist. This result is in marked contrast to eastern Otago Schist where the protolith is Rakaia Terrane of Late Triassic age and whose provenance is in central-eastern Queensland. [ABSTRACT FROM AUTHOR]

The Golgohar iron mine is located at 55 km southwest of Sirjan in the Sanandaj-Sirjan structural zone. The host rocks of the ore deposit include metamorphosed rocks in green schist and amphibolite facies. The mineralization is massive or disseminated in adjacent rocks. The metabasic rocks are classified into amphibolite, epidote amphibolite, epidote-biotite amphibolite and biotite amphibolite types. Base on major, trace, and rare earth elements, the protolithsof these rocks are basic igneous rocks varying from basalt, basaltic andesite, trachy basalt, basaltic trachy andesite compositions. The trace elements pattern shows enrichment in large-ion lithophileelements and depletion in high field strength elements, suggesting their island arc signatures. LREEs enrichment and relatively flat HREEs patterns further support this interpretation. According to geochemical data these rocks were derived from depleted mantle that was contaminated by the melts of subducted sediments. The relative age of these rocks does not match with the tectonic setting. It seems that the Neo-Tethyan subduction along the northern subduction zone caused the emplacement of the study rocks in the Upper Triassic time. In this case, geochronological data may be helpful.

Lunar mare regolith is traditionally thought to have formed by impact bombardment of newly emplaced coherent solidified basaltic lava. We use new models for initial emplacement of basalt magma to predict and map out thicknesses, surface topographies and internal structures of the fresh lava flows, and pyroclastic deposits that form the lunar mare regolith parent rock, or protolith. The range of basaltic eruption types produce widely varying initial conditions for regolith protolith, including (1) autoregolith, a fragmental meter‐thick surface deposit that forms upon eruption and mimics impact‐generated regolith in physical properties, (2) lava flows with significant near‐surface vesicularity and macroporosity, (3) magmatic foams, and (4) dense, vesicle‐poor flows. Each protolith has important implications for the subsequent growth, maturation, and regional variability of regolith deposits, suggesting wide spatial variations in the properties and thickness of regolith of similar age. Regolith may thus provide key insights into mare basalt protolith and its mode of emplacement. Plain Language Summary: Following recent studies of how lava eruptions are emplaced on the lunar surface, we show that solid basalt is only one of a wide range of starting conditions in the process of forming lunar soil (regolith). Gas present in the lavas during eruption also produced bubbles, foams, and explosive products, disrupting the lava and forming other starting conditions for mare soil parent material. Key Points: New basalt magma emplacement models explore fresh lava flows that form the lunar mare regolith parent rock, or protolithSome conditions predict immediate formation of a fragmental meter‐thick "autoregolith" that mimics impact‐generated regolithLava flows with significant near‐surface vesicularity, macroporosity, and magmatic foams will create nontraditional regolith growth rates [ABSTRACT FROM AUTHOR]

The Early Paleozoic age of the protolith for gneisses in the East Uralian megazone (South Urals) is proved by zircon dating. Two metamorphic complexes have been identified in the eastern framing of the Middle–Late Paleozoic Suunduk granitoid pluton. The Zelenodolsk complex is represented by granitic gneisses, while the Kusakan complex (Kusakan Formation) is represented by metavolcanic gneisses, crystalline schists, and quartzites. U–Th–Pb analyses (SHRIMP II) of accessory magmatic zircons from the Zelenodolsk granitic gneiss yielded dates of 478 ± 5 Ma. The protolith age of the Kusakan gneiss (andesitic metatuff) is 529 ± 6 Ma. The origin of volcanic, volcanosedimentary rocks, and granitoids in the East Uralian megazone is associated with the evolution of the volcanoplutonic belt in the active continental margin. [ABSTRACT FROM AUTHOR]

This work presents the results of a study of metamorphic rocks of the Bekturgan and Balazhezdy groups of the Precambrian Ulutau massif (Central Kazakhstan), which have been traditionally identified with the most ancient Early Precambrian complexes, comprising the massif's basement. The protoliths of the metamorphic rocks, represented by lavas and tuffs of basalt and rhyolite–trachyrhyolite composition, sandstones, and tuffaceous sandstones, comprise a contrasted volcanic-sedimentary sequence. The obtained U‒Th–Pb zircon ages (LA–ICP MS, SHRIMP II) demonstrate that the formation of this sequence occurred during a narrow (762–788 Ma) interval during the second half of Tonian (Neoproterozoic). The metamorphic transformations of the rocks were completed before an intrusion of the alkaline syenites of the Karsakpai complex (673 ± 2 Ma), which were not subject to metamorphism. The whole-rock Nd isotopic compositions of the metamorphic rocks indicate the origin of their protoliths due to erosion and partial melting of the more ancient complexes of the Precambrian continental crust of the Ulutau massif. The Hf isotopic compositions of zircons indicate that the main stages of formation and transformation of the Ulutau continental crust occurred during the Neoarchean–Neoproterozoic and coincided with the main stages of the Precambrian magmatism in the western part of the Central Asian Orogenic Belt. [ABSTRACT FROM AUTHOR]

Western metamorphic belt in Thailand elongated in North-South direction has been grouped into the Chiang Mai-Lincang belt. As part of this metamorphic belt, the Lan Sang National Park located in the west of Tak Province is an affected area from northwest-southeast striking Mae Ping fault. Along the fault zone, rock formations have been strongly deformed, yielding steep foliation and lineation. Based on petrographic study, these rocks are mainly characterized by gneisses showing very fine- to coarse-grained textures which consist of quartz, plagioclase, K-feldspar, biotite, pyroxene, and chlorite. Calc-silicate and impure marble are partly interlayered in these gneisses; they are composed of calcite, quartz, feldspar, pyroxene, and garnet. Moreover, granitic gneiss, which cuts into the host gneisses and calc-silicate, appears to have a similar composition of gneiss. Based on geothermobarometry, these rocks should have undertaken high-grade metamorphism of lower amphibolite facies with P-T (pressure-temperature) ranges of 570-590 °C and 5.8-8.1 Kbar for gneiss. These rocks appear to have several evolution stages. Sedimentary protoliths of gneisses and calc-silicate may have situated in the area prior to regional metamorphism. Subsequently, dikes and veins crosscut into these gneissic and calc-silicate rocks before later metamorphism appears to have continued and reached the ductile-brittle stage. [ABSTRACT FROM AUTHOR]

The results of geological, geochemical, Sm–Nd isotopic geochemical studies of metamorphic rocks of the Djagdagle Formation and U–Pb geochronological studies of its zircons are presented. In correlation schemes of geological complexes of the Bureya Terrane, this formation is the oldest (conditionally, Late Archean) amid other formations of the terrane; thus, it is considered its basement. The biotite and two-mica garnet-bearing gneisses of the formation formed owing to transformation of primary sedimentary rocks. The maxima on the relative probability curve of zircon age correspond to 487, 541, 690, 778, and 896 Ma. Thus, the Djagdagle Formation is Paleozoic rather than Early Precambrian, as was considered before. The lower age boundary of the accumulation of the protolith is identified by the age of the youngest zircon population of ~487 Ma. Similar ages of some cores and rims of zircons indicate that the rocks of the protolith underwent structural metamorphic transformations under PT conditions of amphibolite facies. The results of Sm–Nd and Lu–Hf isotopic studies indicate that the geological complexes which originated by means of reworking of the Mesoproterozoic crust could have been the source of primary sedimentary rocks. Taking into account the lack of Mesoproterozoic (and older) rocks in the structure of the Bureya Terrane, it can be suggested that the sources included some amount of ancient recycled material. Similar geological evolution of the Bureya and Jiamusi terranes is suggested on the basis of similar age ranges of metasedimentary rocks of the Djagdagle Formation and Turan Group of the Bureya Terrane and the Kimkan Formation of the Jiamusi Terrane. This is also evident from their synchronous Neoproterozoic magmatism. [ABSTRACT FROM AUTHOR]

In this work, the calc-silicate rocks affiliated to the ‘Kadana Formation’, a youngest formation of the Lunavada Group have been investigated. These rocks are found to be embedded within associated rock types, viz., quartzites and metapelites in the form of isolated lensoidal bodies. Contact metamorphic textures and the typical mineral assemblage, viz., Act +Di + Cal + Qtz + Ttn ± Mc ± Pl ± Bt ± Ep ± Scp ± Chl with minor proportion of apatite, zircon and opaques can be observed in these calc-silicates. Major oxides, trace and rare earth elements were analysed to investigate the protolith type, provenance and tectonic setting of these rocks. Protolith must be calcareous sandstone with varied proportion of clay and deposited in shallow water environment as revealed by CaO, Al2O3 and FeO+MgO and Al–Zr–Ti ternary diagram, respectively. Low to moderate weathering of source rocks has been indicated by A–CN–K ternary diagram. Th/Sc vs. Zr/Sc and Th/Co vs. La/Sc plots confirm the continental source with felsic nature for these rocks and the calc-silicate samples fall within the active continental margin region of Sc–Th–Zr/10 diagram which also justify the kind of provenance for primary sediments. Highlights: The calc-silicate rocks show major oxides, trace and rare earth element compositions which are very similar to those of their post-archean counterparts. Similarly, in the REEs vs. sample/REE chondrite normalized pattern, a moderate negative Eu anomaly is observed; these observations suggest that the chemical composition of the continental crust of the study area was similar to that of the post-archean continental crust. Data plotted in Al2O3, CaO and FeO + MgO diagram of Barton et al. (1991) indicated that the protolith of calc-silicate rocks of the study area is calcareous sandstone with small and varied amounts of clay within it, as most of the samples fall within or very close to the greywacke zone. CIA studies are pointing towards the low to moderate weathering of the source under the cold and arid conditions. The Th–Sc characteristics (Th/Sc > 1) support a predominantly continental source for these rocks; similarly, values of Zr/Sc indicate a moderate amount of sediment recycling. Higher abundances of incompatible elements imply predominantly felsic rocks in the source, which is also supported by LREE-enriched patterns. As per the Th/Co vs. La/Sc plot, mostly of granitic (felsic) composition is inferred for primary sediments for these calc-silicate rocks. The study concludes that the primary sediments for the calc-silicates of the Lunavada Group were deposited in an active continental margin setting. [ABSTRACT FROM AUTHOR]

The anomalous enrichment of clay minerals in fault zones is considered a key factor affecting the seismic behavior of faults, fault permeability, and mineralization. This process also weakens the rock strength and triggers deformation, instability, and geological disasters. Nevertheless, the geological factors affecting the growth and anomalous enrichment patterns of clay minerals in fault zones are not systematically understood. In this study, the anomalous enrichment patterns of clay minerals within 220 natural faults are investigated (detailed information can be found in Appendix A). The main geological factors and processes affecting the anomalous enrichment of clay minerals in fault zones are revealed. The main formation modes and occurrence forms of the clay minerals in fault zones are investigated. The anomalous patterns of clay minerals in fault zones are classified into four categories and eight types, i.e., the felsic anomaly category (illite type and kaolinite type), mafic anomaly category (chlorite type), ultramafic anomaly category (smectite type, serpentine + talc type, vermiculite type, and palygorskite + sepiolite type), and argillaceous anomaly category (mixed-layer type). The 220 case studies include different types of faults and fault rocks. Thus, the results are promising for a wide range of engineering geological applications, e.g., analysis of fault activity and permeability changes and studying the genetic mechanisms of geological disasters near faults. • Four categories and eight types of clay mineral anomalous patterns are proposed. • The main occurrence forms and formation modes of clay minerals are investigated. • The main geological factors and processes affecting clay minerals anomalies are revealed. [ABSTRACT FROM AUTHOR]

The article gives a detailed mineralogical, petrographic and petrogeochemical characteristics of eclogites of the Beloretsk metamorphic complex (BMK). It was found that the most likely the eclogite protoliths were Early-Middle Riphean basites of the Bashkir meganticlinorium. The calculations show that the maximum thermobaric parameters of eclogites formation in BMK reached: P - ≈13 kbar, T - ≈650°C. At the same time, widespread in rocks with symplectic structures who formed at P = 4.4-5.5 kbar, T = 480-500°C indicate a relatively rapid exhumation of the complex on the surface. It is concluded that the formation of para- and ortho- rocks of the Beloretsk metamorphic complex with a certain degree of conditionality can be divided into two main stages. The first stage is due to local(?) rifting, manifested at ≈730-710 million years ago. The second stage - the basic - happened during orogeny in fold area of Timanides under stress load (or stress + lithostatic pressure), which makes BMK as typical representative of metamorphic complexes collision type.

The paper presents geochemical and isotopic characteristics of gneyss-granite of the Chechek dome structure that located in Irtysh Shear Zone. It shows that all “granitoid” of Chechek structure have a similar composition. Reconstruction of primary substrate is based on this data. It was found that gneyss-granite protolith is silty-sandy sediments Kalba-Narym basin from D2 to C1. Nd model age of the protolith responds meso- and neoproterozoic (1.0-1.1 GA), which is consistent with the model ages of high metamorphic and sedimentary rocks that are located in the Irtysh Shear Zone.

Abstract Whole rock major and trace element compositions of seven eclogites from the Tso Morari ultra-high pressure (UHP) complex, Ladakh were determined with the aim of constraining the protolith origins of the subducted crust. The eclogites have major element compositions corresponding to sub-alkaline basalts. Trace element characteristics of the samples show enrichment in LILE's over HFSEs (Rb, Th, K except Ba) with LREE enrichments ((La/Lu) n = 1.28–5.96). Absence of Eu anomaly on the Primitive Mantle normalized diagram suggests the absence of plagioclase fractionation. Positive correlation between Mg# with Ni and Cr suggests olivine fractionation of mantle melts. Narrow range of (La/Yb) n (2.1–9.4) and Ce/Yb (6.2–16.2) along with Ti/Y (435–735) ratios calculated for the Tso Morari samples is consistent with generation of melts by partial melting of a garnet free mantle source within the spinel peridotite field. Ternary diagrams (viz. Ti–Zr–Y and Nb–Zr–Y) using immobile and incompatible elements show that the samples range from depleted to enriched and span from within plate basalts (WPB) to enriched MORB (E-MORB) indicating that the eclogite protoliths originated from basaltic magmas. Primitive Mantle normalized multi element plots showing significant Th and LREE enrichment marked by negative Nb anomalies are characteristic of continental flood basalts. Positive Pb, negative Nb, high Th/Ta, a narrow range of Nb/La and the observed wide variation for Ti/Y indicate that the Tso Morari samples have undergone some level of crustal contamination. Observed geochemical characteristics of the Tso Morari samples indicate tholeiitic compositions originated from enriched MORB (E-MORB) type magmas which underwent a limited magmatic evolution through the process of fractional crystallization and probably more by crustal contamination. Observed geochemical similarities (viz. Zr, Nb, La/Yb, La/Gd, La/Nb, Th/Ta ratios and REE) between Tso Morari eclogites and the Group I Panjal Traps make the trap basalt the most likely protoliths for the Tso Morari eclogites. Graphical abstract Image 1 Highlights • Eclogites are characterized by major and transition element compositions typical of tholeiitic basalts. • Trace element enrichment in LILE's over HFSEs with LREE enrichments (La/Lu n = 1.28–5.96) is observed. • Geochemically the eclogites originate from E-MORB type magmas showing limited magmatic evolution and crustal contamination. • Trace and REE compare well with Group I Panjal Traps basalts and are the most likely protoliths for the studied eclogites. [ABSTRACT FROM AUTHOR]

Abstract Geochemical, Sr Nd isotopic and geochronological methods were used to reveal the protoliths and geodynamic implications of the newly discovered Triassic Baqing eclogites, eastern Qiangtang terrane, central Tibet. We assessed the mobility of trace elements, and it turned out that high field strength elements (HFSEs) and rare earth elements (REEs) were immobile in the high-pressure (HP) metamorphic process and reliably employed to discriminate the protoliths of the Baqing eclogites. Whole-rock geochemical data (especially immobile elements) suggested both arc-related (negative Nb Ta anomalies, high light (L) REEs/heavy (H) REEs ratios) and mid-oceanic ridge basalt (MORB)-related (without negative Nb Ta anomalies, relatively low REEs contents) characteristics, indicating the contribution of different proportions of subduction material with a backarc basin origin. According to the Sr Nd isotopic ratios (initial 87Sr/86Sr ratios: 0.7078–0.7086; ε Nd (t) values: −0.58 to +1.96), the protoliths of the Baqing eclogites originated from mantle which experienced continental crustal contamination in the subduction zone. Compared with nearby subduction-related magmatic rocks from eastern Qiangtang terrane, backarc basin was the most likely tectonic environment for the Baqing eclogite protoliths. The Jinsha Paleo-Tethyan Ocean southward subduction underneath East Qiangtang block (EQB) and rollback led to the formation of this backarc basin between the Late Permian and Early Triassic, and subsequent northward subduction of the backarc basin formed the Baqing eclogites in early Late Triassic (227–221 Ma). Graphical abstract Unlabelled Image Highlights • Late Triassic (227–221 Ma) Baqing eclogites from eastern Qiangtang, Tibet, are reported. • Protoliths of Baqing eclogites originated from Late Permian–Early Triassic backarc basin. • The Jinsha Paleo-Tethys southward subduction and rollback accounted for the formation of the Baqing backarc basin. • The CQMB eclogites constrained the boundary of East and West Qiangtang. [ABSTRACT FROM AUTHOR]

The chemical composition of rocks of the Murzinka-Adui metamorphic complex and the Murzinka granite pluton, a reference interformational granite pluton in the Urals, is considered. A detailed comparative analysis of ancient gneisses and related granite veins included an isotope-geochemical study of zircons from both groups of rocks. Zircons are subdivided into seven age groups (I, 1588 ± 20 Ma; II, 1060 ± 28 Ma; III, 530 ± 11 Ma; IV, 380 ± 6 Ma; V, 330 ± 9 Ma; VI, 276 ± 3 Ma; and VII, 260 ± 3 Ma). The first four groups are apparently zircons from gneisses, reworked to different extents, and the other three groups are zircons crystallized during granite genesis. The gneisses and most of the granite samples contain zircons of all the above age populations, which is evidence of trapping zircons from gneisses by granite melts, on the one hand, and the occurrence of "granite-derived" zircons in gneisses, on the other. The granitoids and gneisses of all types differ considerably in geochemical features. The behavior of trace elements and the Rb-Sr ages indicate that the formation of granites of the Murzinka massif was a discrete episode of magmatic activity. The Sr isotope ratios in the granites and gneisses indicate different degrees of the mantle-crust interaction and the participation of the material of the crystalline basement and newly formed crust in their formation. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Western Henan bauxites are characterized by diaspore-illite-anatase assemblage. • Illites occurred as detrital minerals and authigenic minerals during diagenesis. • Boron was extracted during diagenesis by illites and inherited from protoliths. • Provenance analysis reveals a multiple source of western Henan bauxites. • Karst bauxites are the result of the terrestrial deposition and marine modification. Abstract The Poci bauxite deposits in western Henan, China, are hosted in the lower member of Upper Carboniferous Benxi Formation, unconformably overlying upon the paleokarst surface of the Ordovician Majiagou Formation. The orebodies comprise a high-grade bauxite horizon (characterized by the association of diaspore-illite-anatase) and a basal iron-rich horizon (diaspore-goethite-hematite-illite-anatase), sandwiched between the overlying clayey layer (illite-diaspore-goethite-anatase) and the underlying clayey layer (illite-diaspore-microcline-goethite). Geochemical investigations reveal that Rb, Cs, Ba, Cu, Zn are depleted, while B, Ga, Bi, V, Sc, Zr, Hf, Nb, Ta, W, U and Th are enriched in bauxite horizons. B is highly enriched in bauxite ores and clays (contents 176–1061 ppm) and positively associated with SiO 2 , indicating B is mainly hosted in clay components, e.g. dominantly illite, which are considered a mixture of authigenic minerals transformed from kaolinites during diagenesis and unaltered detrital minerals. Mass change calculations reveal that Hf, Zr, Nb, Ta, U, Th, Sc, Cr, and Ga are stable relative to TiO 2 during the bauxitization process, indicating these elements are mainly associated with anatase and diaspore. The bauxite horizons and the underlying clays are more enriched in total REE contents (ΣREEs) and display more intense LREE/HREE fractionation than the overlying clays. Provenance analysis shows that parental materials of Poci bauxites were mainly derived from felsic-dominated igneous rocks along the southern margins of the North China Craton, with minor contribution from siliciclastic sedimentary rocks and argillaceous components of underlying carbonates. A conceptual model is proposed for the formation and evolution of Poci bauxites. Uplift caused by the North Qinling orogenesis along the southwestern margin of NCC led to the formation of karstic topography, allowing aluminum-rich source materials to be transported to the low karst plain and transformed into incipient bauxites under hot and humid tropical conditions. When the platform was submerged, Fe2+ ions were released from Fe/Al oxides/hydroxides under the reducing conditions associated with bacteria activity in an organic-rich environment, and redeposited as pyrites and siderites, generating a high-grade bauxite horizon and an iron-rich bauxite horizon. This marine modification resulted in further aluminum enrichment of bauxite ores. [ABSTRACT FROM AUTHOR]

At least two outcrops of igneous rocks have been reported from the watershed of the Bodrak and Alma Rivers (southwestern Crimea). Previous studies suggested that these outcrops are composed of pre-Middle Jurassic intermediate and acidic tuffs and lavas. We compared the rocks from one of these outcrops with those from the near-contact area of the Middle Jurassic Dzhidair intrusion, which is exposed proximally, near the Trudolyubovka village. The Dzhidair intrusion is mostly composed of altered dolerites. We show that the rocks from both locations were significantly altered to quartz—carbonate—dickite metasomatites due to acidic metasomatism. The pattern of alterations and the appearance of the least altered samples of dolerites are similar across both locations. [ABSTRACT FROM AUTHOR]

The Golgohar iron mine is located at 55 km southwest of Sirjan in the Sanandaj-Sirjan structural zone. The host rocks of the ore deposit include metamorphosed rocks in green schist and amphibolite facies. The mineralization is massive or disseminated in adjacent rocks. The metabasic rocks are classified into amphibolite, epidote amphibolite, epidote-biotite amphibolite and biotite amphibolite types. Base on major, trace, and rare earth elements, the protoliths of these rocks are basic igneous rocks varying from basalt, basaltic andesite, trachy basalt, basaltic trachy andesite compositions. The trace elements pattern shows enrichment in large-ion lithophile elements and depletion in high field strength elements, suggesting their island arc signatures. LREEs enrichment and relatively flat HREEs patterns further support this interpretation. According to geochemical data these rocks were derived from depleted mantle that was contaminated by the melts of subducted sediments. The relative age of these rocks does not match with the tectonic setting. It seems that the Neo-Tethyan subduction along the northern subduction zone caused the emplacement of the study rocks in the Upper Triassic time. In this case, geochronological data may be helpful. [ABSTRACT FROM AUTHOR]