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Mars missions and Martian meteorites revealed how complex the Martian crust is. The occurrence of both alkaline and sub-alkaline igneous rocks of Noachian age (>3.7 Ga) in Gale crater indicates diverse magmatic processes, with sub-alkaline rocks likely formed through the partial melting of hydrous mafic rocks, as commonly observed on Earth. The orbital discovery of excavated evolved igneous rocks scattered in Noachian terrains raise questions about the petrology of the ancient Martian crust, long thought to be basaltic. A possibly evolved crust beneath a mafic cover is supported by geophysical and seismic measurements from the Insight lander that indicate the bulk crust has a lower density than expected if it were homogeneously basaltic. If localized magmatic processes could form evolved terrains, the detection of abundant intermediate to felsic Noachian crustal exposures through remote sensing suggest regional- to global-scale processes that produced evolved crustal component(s) that are now buried below mafic materials. Due to the lack of centimetric to millimetric textural imaging and compositional measurements, the petrology of such crust is ambiguous. Future orbiter, rover, and aerial missions should focus on Noachian exposed regions exhibiting evolved crustal characteristics to unfold the petrology of the Martian crust and its formation. [ABSTRACT FROM AUTHOR]

Despite of the relatively rare occurrence of alkaline igneous rocks on Earth, they are the most diverse group of igneous rocks due to variations in their mineral assemblages and geochemical compositions. Alkaline igneous rocks are generally characterized by Si undersaturation, and K-Na (and in some cases C) enrichment. Although there is no unified alkaline igneous rock classification scheme, diagrams such as total alkalis-SiO2 or K2O-SiO2 can be used to classify alkaline igneous rocks. The origins of silica-saturated alkaline rocks (SiO2>52 wt.%) are relatively complex because multiple episodes of magmatism are often involved, therefore most studies have focused on the origins of silica-undersaturated alkaline magmas. Numerous experimental petrological studies have been conducted in the past few decades. Initially, it was considered that enrichment of trace elements was only achieved by low-degree partial melting of mantle peridotite, but the experimental melts could not reproduce the geochemical composition of natural alkaline igneous rocks. Subsequent studies have focused on carbonate-bearing eclogites that represent the average component of subducted oceanic crust. Although experimental studies indicate that silica-undersaturated and alkali-oversaturated melts can be generated from eclogites, some studies have considered that natural silica-undersaturated alkaline igneous rocks are the result of multi-stage source enrichment by incompatible elements. Low-degree partial melts of the mantle can be emplaced in the lithospheric mantle, forming veins consisting of phlogopite, amphibole, and pyroxene. Melting experiments including these components show that the produced melts better reproduce the naturally occurring silica-undersaturated alkaline magmas. Silica-deficient alkaline igneous rocks occur in various tectonic settings. Those in intraplate and divergent settings (i.e., mainly continental rifts) normally involve contributions from recycled components such as subducted slabs at the mantle transition zone (MTZ) or metasomatized lithospheric mantle. At convergent plate boundaries, silica-undersaturated alkaline magmas can be derived by the melting of mélange or the focused breakdown of phlogopite at back-arc depths. We compiled global data for alkaline igneous rocks and discovered that silica-undersaturated alkaline igneous rocks in continental collisional zones are K-rich and differ from those from other tectonic settings. We suggest that subducted continental sediment is an important K-rich end-member, which contributes a large amount of K to the alkaline magmas in the collision zone. Moreover, the solidus of K-rich minerals in the subducted plate implies that K can only participate in magmatism in the subduction zone. Before the plate reaches a depth of ∼300 km, the mica-group minerals, K-feldspar, evaporitic minerals, and other K-rich minerals are gradually consumed and rarely participate in deeper processes. In contrast, relatively Na-rich minerals such as pyroxene can be transported into the deeper mantle with eclogitic oceanic crust, and the resultant melt can enter the lithosphere owing to convective mantle flow. This forms metasomatic minerals, such as amphibole, in the lithospheric mantle, which melt to generate Na-rich and low-Si alkaline magmas. [ABSTRACT FROM AUTHOR]

Giant Nb deposits hosted by alkaline igneous rocks worldwide are characterized by hydrothermal and/or metamorphic modifications after magmatic crystallization. However, the impact of secondary processes on Nb mineralization in alkaline igneous rocks remains controversial. In this study, U–Pb ages, elemental, and Nd isotope compositions of titanite from a series of Nb-rich dyke swarms in the Ziyang region of South Qinling (China) have been investigated to unveil Nb remobilization and enrichment histories during magmatic and hydrothermal processes. Three types of titanite are documented: magmatic, deuteric, and hydrothermal. The magmatic titanite (Ttn I) grains are euhedral wedge-shaped, while the deuteric type (Ttn II) occurs as coronas on magmatic ilmenite. The hydrothermal titanite (Ttn III) occurs as either bead-like clusters within the cleavage planes of chloritized biotite or as anhedral grains (lesser than 200 μm in diameter) coexisting with hydrothermal actinolite, chlorite, fluorite, and/or REE-rich oxides. The magmatic titanite grains from the most primitive igneous rocks have U–Pb ages of 455 ± 25 Ma and are characterized by high levels of Nb2O5 (up to 1.4 wt%) and other high field strength elements (HFSE, up to 1.3 wt% ZrO2), rare earth elements (REE), and V, and high mean crystallization temperatures (880 ± 40 °C), suggesting that they nucleated and crystallized in a high-T and Nb-rich alkaline magma during the Early Paleozoic. The gradual decrease in V, Sr, and Ba in Ttn I from mafic to intermediate dykes exemplifies the role of fractionation on magmatic enrichment of Nb (mean of 170 ppm and 7300 ppm for Ttn I in mafic and intermediate dykes, respectively) and other incompatible elements (e.g., Ta, Zr, Hf, Sn, Y, and REE) in the residual melt. The deuteric and hydrothermal types of titanites in each lithology have lower concentrations of HFSE (e.g., Nb mean of 140 ppm and 860 ppm for Ttn II in mafic and intermediate dykes, respectively), Sn, LREE, and Y but higher Al, F, V, Sr, and HREE contents than their magmatic counterpart. The deuteric and hydrothermal types of titanite have U–Pb ages of 420 ± 25 Ma and 232 ± 49 Ma, respectively, supporting two distinct hydrothermal events at Ziyang. The magmatic and deuteric types of titanite have similar ranges of εNd(t) values (+ 1.4 to + 3.5 and + 2 to + 4.2, respectively), indicative of a common source for these two generations. The hydrothermal titanite also has comparable εNd(t) values (+ 0.8 to + 2.7) to the magmatic and deuteric types, indicating a minimal external contribution to Nd (and by analogy Nb as well) from the late hydrothermal fluids. The deuteric and late hydrothermal F-rich fluids in Ziyang dyke swarms both remobilized the dispersed Nb in magmatic ilmenite, amphibole, and biotite to form secondary titanite (Ttn II, III), which is beneficial to the metallurgical extraction of this critical metal. Therefore, both magmatic fractional crystallization and hydrothermal remobilization contributed to Nb mineralization. [ABSTRACT FROM AUTHOR]

Late Devonian felsic volcanic rocks of the Grand Beach complex (GBC) of Avalonia from the Burin Peninsula, southeastern Newfoundland (northwestern Appalachians) are part of an overstep sequence overlying the Neoproterozoic basement. The volcanic complex is composed of volcanic and volcaniclastic rocks deposited in a post-tectonic extensional setting proximal to the St. Lawrence granite (SLG), a Devonian pluton associated with a prominent vein-type fluorite mineralization. The volcanic rocks are alkali rhyolites, which are weakly peraluminous and exhibit geochemical characteristics of A-type felsic magmas, such as low FeOt, MgO, CaO, and TiO2 but high contents of alkalis, Nb, Y, and Zr and high Ga/Al and FeOt/MgO ratios. They have positive ɛNd(t) values (~ + 2.5) and their Nd-depleted mantle model ages (~ 0.9 Ga) are consistent with derivation of the parental magma from metasomatized dry Avalonian lower crustal basement via partial melting followed by fractional crystallization. The U–Pb zircon age for the volcanic complex (375.6 ± 1.1 Ma) is closely comparable to the age of the SLG, suggesting that they were emplaced during the same magmatic episode. They also have similar chemical and isotopic compositions, suggesting that the GBC represents a volcanic equivalent of the SLG. The compositional differences between the volcanic rocks and the main phase of the granite pluton, including higher oxidation state of the GBC, reflect the interaction of the parental magma with crustal material and fluids. The close proximity of SLG and GBC suggests that the volcanic complex could host fluorite mineralization. [ABSTRACT FROM AUTHOR]

A new occurrence of epidote-(Sr) CaSr(Al2Fe3+)[Si2O7][SiO4]O(OH), Sr-REE-rich epidote and Sr-rich allanite-(Ce) is located in Lower Cretaceous, Sr-rich hydrothermally altered leucocratic dykes penetrating alkaline igneous rocks (teschenites) near the Nový Jičín town (the Silesian Unit, Outer Western Carpathians). The dykes contain phenocrysts of pyroxene, amphibole, biotite, fluorapatite and dominant felsic groundmass consisting mostly of alkali feldspars and zeolites (analcime, natrolite and thomsonite-Ca). Accessory minerals include Ti-rich magnetite, prehnite, chamosite, pyrite, calcite, (OH, F)-rich grossular, epidote-group minerals, HFSE-, REE-rich minerals, Sr-rich baryte and slawsonite. The Sr-rich epidote forms columnar crystals or irregular aggregates, which are mostly spatially related to chamosite-titanite pseudomorphs; it contains 0.15–0.81 apfu Sr, ≤ 0.55 apfu REE; Fe3+/(Fe3+ + Al) = 0.16–0.48. The Sr2+ substitutes Ca2+ in the A2 site by a coupled substitution involving other A2 (REE3+, Th4+) or M (Al3+, Fe3+, Fe2+) cations. The Sr-rich epidote crystallized from hydrothermal solutions, probably at temperatures between ~ 250–430 °C, during cooling of the host rock. The dykes show higher Sr contents (5680–7830 ppm) and 87Sr/86Sri(120 Ma) ratios (~ 0.7046–0.7047) compared to host mesocratic teschenites (1310–1470 ppm Sr and ~ 0.7038–0.7045, respectively). The Sr isotopes indicate origin of most Sr from primary magmatic plagioclase in parent teschenite. Nevertheless, there also participated external fluids, derived from the Lower Cretaceous seawater or diagenetic waters related to associated siliciclastic sediments with 87Sr/86Sri(120 Ma) = ~ 0.7073–0.7083. These more radiogenic sources contributed at least 6–21% of the bulk Sr budget of the studied Sr-rich epidote-bearing leucocratic dykes. [ABSTRACT FROM AUTHOR]

Northwest Africa (NWA) 7611/10480 are lunar regolith breccia meteorites, composed of mineral fragments and various clasts including mare basalts, volcanic glasses, gabbroic lithologies, and a diverse variety of highland materials (ferroan anorthosite, Mg‐suite, magnesian anorthosite, and alkali suite rocks) as well as different subvarieties of impact melt breccia. The Apollo two‐component mixing model calculation reveals that the NWA 7611 source region contains 58 wt% mare materials and 42 wt% highland components, but the estimated mare components in NWA 10480 have a higher abundance (66 wt%). The predominantly very low‐Ti (VLT) composition in both fine‐grained basaltic and coarse‐grained gabbroic lithologies indicates a provenance associated with a thick lava flow or a single magmatic system. The co‐occurrence of zoning patterns and fine‐scale exsolution lamellae in pyroxene debris supports a cryptomare deposit as the best candidate source. Phosphate Pb–Pb ages in matrix fragments, impact melt breccia, and basaltic clast indicate that the breccia NWA 7611 records geological events spanning approximately 4305–3769 Ma, which is consistent with the ages of ancient lunar VLT volcanism and the products of basin‐forming impacts on the lunar nearside. The youngest reset age at ~3.2 Ga is potentially related to the strong shock lithification process of breccia NWA 7611. Moreover, the similar petrology, texture, geochemistry, cosmic‐ray exposure data, and crystallization ages support that basaltic component in Yamato (Y)‐793274, and Queen Alexandra Range (QUE) 94281, NWA 4884, and NWA 7611 clan came from the same basalt flow. [ABSTRACT FROM AUTHOR]

In eastern Anatolia, the Divriği-Hekimhan Magmatic Province (DHMP) includes ~77–69 Ma alkaline rock units which are located to the NW of the Baskil Arc of ~85–74 Ma. The magmatic rocks are composed of nepheline (Ne)–to quartz (Q)–normative alkaline basaltic to trachytic/syenitic units. Among them, the basaltic rocks are composed of plagioclase (Or2–11Ab32–51An39–64) + clinopyroxene (Wo47–51En35–42Fs9–16) + Fe-Ti oxide ± alkali feldspar (Or57–98Ab2–42An1) ± biotite ± olivine. Their 87Sr/86Sr(I) ratios and ɛNd(I) values vary in the ranges of 0.70591–0.70871 and−3.2–1.6, respectively. The subvolcanic trachytic rocks are composed of perthitic alkali feldspar phenocryst in a matrix of feldspar (Or45–61Ab38–54An0–2), biotite, and Fe-Ti oxides. The trachytic volcanic rocks are made up of feldspar (Or38–63Ab34–59An1–4) in a fine-grained matrix. Their 87Sr/86Sr(I) ratios and ɛNd(I) values vary in the ranges of 0.70532–0.70952 and−3.2–0.7, respectively. The syenitic rocks in the region contain both quartz- and nepheline-sodalite-bearing syenites. Geochemical features reveal that the Ne-normative basaltic magmas have undergone mafic mineral fractionation coupled with crustal contamination to produce the Q-normative derivatives. Enhanced differentiation of the Ne- and Q-normative fractionated magmas via feldspar-dominated fractionation created the silica-undersaturated and -oversaturated trachytic magmas, respectively. During the feldspar-dominated differentiation, the re-melting of accumulated alkali feldspars in the magma chamber likely gave rise to the formation of trachytic rocks with alkali feldspar-like whole rock compositions. The final products of the Ne-normative magmas are represented by the phonolites and foid-syenites with silica-undersaturated eutectic compositions. A geochemical evaluation of the basaltic rocks revealed that the alkaline magmatism mainly originated from a shallow asthenospheric mantle source which had previously been metasomatized by oceanic to continental subduction. We suggest that the DHMP was formed in response to STEP fault-controlled rolling back of the northward subducting slab of the Baskil Arc, which created a localized gap for asthenospheric upwelling. [ABSTRACT FROM AUTHOR]

Alkaline igneous rocks have become a potentially important source of Nb, except for the carbonatites. The metallogenetic mechanism of Nb during the magmatic-hydrothermal evolution of alkaline rocks remains ambiguous. From the perspective of Nb minerals, the mineral chemistry of pyrochlore supergroup minerals provides the mineralogical evidence for indicating the respective contributions of magma and hydrothermal fluids to Nb mineralization. In the Miyi County of the Panzhihua-Xichang (Pan-Xi) area, the central zone of the Permian Emeishan large igneous province (ELIP) in SW China, hundreds of Nb-Y-F mineralized pegmatites (NYF-type) are exposed. This study conducted in situ mineral chemistry analyses on four types of pyrochlores to elucidate the Nb mineralization process. Both Pcl-I and Pcl-II exhibit well-developed oscillatory zoning (OZ), representing magmatic pyrochlore formed through disequilibrium crystallization in an oscillatory environment. Pcl-III, with a homogeneous and less variable composition, is also considered of magmatic origin due to its coherent chemical evolution with Pcl-II. Pcl-IV is considered of hydrothermal origin based on its irregular zoning texture, extremely high Na2O contents, and compositional gap compared with magmatic types. The decrease in TiO2 contents, coupled with the increase in Na2O, F, and Nb2O5 contents from Pcl-I to Pcl-III and from the core to the rim of zoned Pcl-II, indicates that fractional crystallization facilitates the crystallization of albite and the enrichment of volatiles, as well as the precipitation of Nb from the early to late stages. During the magmatic-hydrothermal transition stage, the reductive, Na- and F-enriched fluid transports Nb more effectively, leading to further Nb enrichment in pyrochlore. Consequently, there are two-stage Nb mineralization processes associated with the magmatic-hydrothermal evolution in the Miyi pegmatite, with the primary magmatic ore assemblages being the dominant Nb mineralization, which may be a general model for the mineralization of NYF-type pegmatites. [ABSTRACT FROM AUTHOR]

Characterization of microstructures and perlitic textures may be carried out by combining volcanological and glass technical concepts, with supporting evidence from image analysis. These methods enable investigation of the mechanisms of protracted fracture formation, propagation, and characterization of fracture networks in silica-rich volcanic glass. Here we present analyses of rhyolitic lava and ignimbrites from different locations and geological ages. Our results allow characterization of the relationship between primary sublinear quench fractures and secondary rounded perlitic fractures, which together form a three-dimensional fracture network. Completely hydrated samples from the pre-Cenozoic show no variations in volatile fluid content within fractured glass but do show differential depletion in alkali contents, suggesting significant fluid-mediated alteration. In contrast, younger samples are incompletely hydrated and may demonstrate a connection between alkali mobility and rock hydration. Formation of primary fractures and a first generation of secondary fractures is caused by thermal shock close to the glass transition temperature. Formation and propagation of subsequent fracture generations is related to intrinsic stresses induced by the continued hydration of volcanic glass. We find that the pore space in rhyolitic rocks is not only influenced by fracture porosity or initial vitric porosity but may increase or decrease during post-emplacement, low-temperature alteration processes. [ABSTRACT FROM AUTHOR]

Part VII of the evolutionary system of mineralogy catalogs, analyzes, and visualizes relationships among 919 natural kinds of primary igneous minerals, corresponding to 1665 mineral species approved by the International Mineralogical Association—minerals that are associated with the wide range of igneous rock types through 4.566 billion years of Earth history. A systematic survey of the mineral modes of 1850 varied igneous rocks from around the world reveals that 115 of these mineral kinds are frequent major and/or accessory phases. Of these most common primary igneous minerals, 69 are silicates, 19 are oxides, 13 are carbonates, and 6 are sulfides. Collectively, these 115 minerals incorporate at least 33 different essential chemical elements. Patterns of coexistence among these minerals, revealed by network, Louvain community detection, and agglomerative hierarchical clustering analyses, point to four major communities of igneous primary phases, corresponding in large part to different compositional regimes: (1) silica-saturated, quartz- and/or alkali feldspar-dominant rocks, including rare-element granite pegmatites; (2) mafic/ultramafic rock series with major calcic plagioclase and/or mafic minerals; (3) silica-undersaturated rocks with major feldspathoids and/or analcime, including agpaitic rocks and their distinctive rare-element pegmatites; and (4) carbonatites and related carbonate-bearing rocks. Igneous rocks display characteristics of an evolving chemical system, with significant increases in their minerals' diversity and chemical complexity over the first two billion years of Earth history. Earth's earliest igneous rocks (>4.56 Ga) were ultramafic in composition with 122 diferent minerals, followed closely by mafic rocks that were generated in large measure by decompression melting of those ultramafic lithologies (4.56 Ga). Quartz-normative granitic rocks and their extrusive equivalents (>4.4 Ga), formed primarily by partial melting of wet basalt, were added to the mineral inventory, which reached 246 diferent mineral kinds. Subsequently, four groups of igneous rocks with diagnostic concentrations of rare element minerals—layered igneous intrusions, complex granite pegmatites, alkaline igneous complexes, and carbonatites—all first appeared ~3 billion years ago. These more recent varied kinds of igneous rocks hold more than 700 diferent minerals, 500 of which are unique to these lithologies. Network representations and heatmaps of primary igneous minerals illustrate Bowen's reaction series of igneous mineral evolution, as well as his concepts of mineral associations and antipathies. Furthermore, phase relationships and reaction series associated with the minerals of a dozen major elements (H, Na, K, Mg, Ca, Fe, Al, Si, Ti, C, O, and S), as well as minor elements (notably Li, Be, Sr, Ba, Mn, B, Cr, Y, REE, Ti, Zr, Nb, Ta, P, and F), are embedded in these multi-dimensional visualizations. [ABSTRACT FROM AUTHOR]

Trachyrhyolite and comendite of the Pechalninskii ore field contain high potentially commercial concentrations of a number of rare metals and REEs. The enrichment coefficients vary from several (Zn, Ga, and LREEs) to tens (Be, Y, Zr, Nb, Rb, and HREEs) of times. The REE distribution is indicative of uniform enrichment in HREEs relative to LREEs at (La/Yb)N in the range of 0.16–1.01. All samples are distinguished by highly negative Eu anomalies with Eu/Eu* = 0.13. Based on a comparative analysis with similar world-known fields in alkali volcanic rocks, the Pechalninskii ore field could become an unconventional large-volume HREE source. [ABSTRACT FROM AUTHOR]

This study revises the early-magmatic, late-magmatic, and hydrothermal mineral assemblages occurring in rocks of agpaitic affinity, mainly represented by nepheline syenites and phonolites, from the Poços de Caldas alkaline massif. Mostly composed of different types of silicates, these rocks include rare minerals of of distinct groups, such as sulfides, oxides, carbonates, phosphates, sulfates, niobates, and notably halides, with villiaumite (NaF) as an important phase indicative of extreme alkali enrichment. Hydrothermal alteration products of nepheline and alkali feldspar typically consist of feldspathoids and zeolites. The rare minerals are of varied origin, from magmatic crystallization to hydrothermal and weathering processes. In general, they tend to occur interstitially or form euhedral crystals, especially when filling cavities or growing out from their walls. Petrological conditions involving the formation of the agpaitic rocks and their mineral assemblages are discussed. [ABSTRACT FROM AUTHOR]

West Kalimantan has very large bauxite resources, reaching 2.07 billion tons, equivalent to 57.32% of the total bauxite resources in Indonesia with bauxite reserves of 0.84 billion tons or equivalent to 66.77% of the total national mineral reserves. The researched area covers Sompak District and surrounding areas, Landak Regency, West Kalimantan. This research aims to determine geological conditions, laterization, and characteristics of laterite bauxite in the studied area. Methods used in this research are geological mapping, lateritic mapping, and petrographic and geochemical analyses. The lithology of the researched area is composed of granodiorite, porphyry quartz diorite, granite, porphyry andesite, porphyry basalt, alluvial, and swamp deposits. Laterite profiles in the researched area generally consist of topsoil, latosol, bauxite, and clay zone. The laterite bauxite derived from granodiorite is classified as a medium grade, laterite bauxite from porphyry quartz diorite is classified as high-grade bauxite, laterite bauxite from andesite porphyry is classified as low-medium grade bauxite, and laterite bauxite from porphyry basalt in the studied area is classified as high grade bauxite. Laterite bauxites in the researched area were formed from weathered parent rocks which were intermediate - alkaline igneous rock. [ABSTRACT FROM AUTHOR]

Magmatic and metasomatic zircon occurs in many alkaline igneous rocks and both are potential economic reservoirs of Zr, and in some places, rare-earth elements. The Baerzhe deposit in China is an example of a system where both types of zircon occur. Previous studies recognized deuteric and variably altered magmatic zircon in a transsolvus miaskitic granite, as well as four types of metasomatic zircon in a transsolvus agpaitic granite. In this study, the relationships among, and origins of, zircon and how these relate to models for rare-metal mineralization are assessed. In situ backscattered electron (BSE) and cathodoluminescence (CL) imaging, Raman spectroscopy (including mapping), and chemistry of zircon from the agpaitic granite were conducted, combined with evaluation of published data on zircon from Baerzhe. Their textural, spectroscopic, and chemical characteristics suggest that the four types of metasomatic zircon in the agpaitic granite were not subjected to metamictization or intense alteration, with trace-element accommodation largely following a xenotime substitution mechanism. The most abundant type of metasomatic zircon in the agpaitic granite occurs in zircon-quartz pseudomorphs and exhibits comparable CL, Raman spectral, and chemical features to rare zircon that has partially replaced elpidite. This confirms that the pseudomorphs formed by complete replacement of elpidite. The pseudomorph zircon occurs in association with snowball quartz that contains inclusions of zircon, aegirine, and albite, and with secondary quartz containing aegirine. This is consistent with their coeval formation during Na metasomatism. The restriction of Na metasomatism to the agpaitic granite indicates that this event and the associated zircon formation resulted from early autometasomatism of the agpaitic phase. REE- and Be-rich zircon that replaced magmatic amphibole crystallized as a result of reaction with a REE- and Be-rich fluid that most likely was responsible for the later REE-Nb-Be mineralization that affected both the miaskitic and agpaitic granites. The miaskitic granite contains deuteric and altered magmatic zircon with diferent chemical characteristics to the four types of metasomatic zircon in the agpaitic granite. This suggests that secondary Zr mineralization in the miaskitic granite formed from diferent fluids to those that metasomatized the agpaitic granite and may also have resulted from autometasomatism. This study reveals a complex picture for the formation of zircon at Baerzhe, the character of which can vary significantly, both temporally and spatially. Such variable chemistry of the various types of zircon resulted not only from their diferent origins (magmatic vs. metasomatic), but also from localized water-rock interaction that involved multiple stages of fluids. Zircon in both the miaskitic and agpaitic phases was mainly the product of autometasomatism that was constrained to their parental granites. [ABSTRACT FROM AUTHOR]

Sun et al. [[44]] performed a highly accurate mineral chemistry investigation and found an unusual mechanism of substitution in these pyrochlore supergroup minerals involving Nb and REE. This Special Issue aims to highlight the pivotal role of the minerals found in alkaline igneous rocks in tracing magmatic processes. The detailed mineral chemistry characterization carried out by D'Antonio et al. [[33]] instead highlighted that the clinopyroxene present in the MEGT products collected near the vent area on Ischia, which is still variable, never reached the aegirine composition. Hence, the chemical composition of minerals coexisting in an igneous rock can yield estimates of the pressure-temperature-oxygen fugacity (P-T-fO SB 2 sb ) conditions established during specific stages of magma crystallization (e.g., [[1]]). [Extracted from the article]

Alkaline intrusions of the Sakju Complex distributed in the western area, DPR Korea were formed in mid-Proterozoic era. The REE and fluorite mineralization occurs in Ryongpho alkaline intrusion of the Sakju Complex. In general, the most important REE resources are associated with alkaline igneous rocks and carbonatites, although REE deposits are also known from a range of other geological settings. REE deposits associated with alkaline igneous rocks are typically lower grade but with larger tonnage and a higher content of the most critical HREE. The Sakju Complex mostly consists of alkaline pyroxenite, alkaline gabbro, alkaline amphibole syenite and alkaline feldspar syenite which reflect well the magmatic differentiation, and their metasomatic rocks. The contents of REEs in intrusions of the Sakju Complex are much higher than the average contents of the earth's crust and those in alkaline rocks. The study of the REE and fluorite mineralization characteristic of Ryongpho alkaline intrusion indicates that the contents of REEs and fluorite gradually decrease in the order from alkaline pyroxenite, alkaline gabbro, alkaline amphibole syenite to alkaline feldspar syenite. The constituent rocks have the similar chondrite-normalized REE distribution patterns, i.e., rich in LREE and deficient in HREE, and no or weak negative anomaly of Eu. The REE distribution curves are rightward inclined, indicating LREE > HREE as a whole. REEs are concentrated in the fluorite zone experienced Ca-F metasomatism in alkaline pyroxenite and alkaline gabbro to form a medium-high grade REE ore body. Fluid inclusion data of fluorites in the constituent rocks indicates that the metasomatic temperature is 250–450°C. Also, the total of rare earth element contents in the fluorites range from 1807 to 5201 ppm. The Tb/Ca and Tb/La ratios of fluorites in the constituent rocks varies respectively between 5.68 × 10–6 and 0.277 × 10–6, and between 0.0491 and 0.0074, and these ratios indicate a formation from a hydrothermal and less pegmatite stage. Also, the results suggest that the darker the fluorite color becomes, the stronger the intensity of REE mineralization and fluorite mineralization, and the higher the total REE contents in the rocks become. [ABSTRACT FROM AUTHOR]

Orogenic gold deposits associated with metamorphic orogenic fold belts are the major sources of gold currently being mined in the world. The role of metamorphic and magmatic processes and crustal and mantle sources in the gold mineralization genesis are of much debate. The formation of orogenic gold deposit in Precambrian metamorphic belts is usually described by а metamorphic devolatilization model. Some of the orogenic deposits, however, are proved to be much younger than the peak of regional metamorphism. Geological features of these deposits suggest close relation of their gold-forming systems with deeper lithospheric processes. The Baikal-Muya Belt (BMB) of the Central Asian Orogenic Belt is an example of such a region. The BMB comprises ca. 20 orogenic gold deposits and occurrences of Permian age. Gold mineralization at the deposits is usually located in quartz lodes situated in the vicinity of fault zones in association with Late Paleozoic sub-alkaline and alkaline basic and acid intrusions. Using high-precision (0.02–0.03%, 2SD) MC-ICP-MS method, we studied in detail Pb isotopic composition of the Permian gold-bearing mineralization at six BMB deposits, as well as metamorphic and igneous rocks of Tonian to Permian age. The 46 studied sulfide samples representing BMB gold-bearing lodes are highly variable regarding their Pb isotopic composition: 206Pb/204Pb from 16.628 to 18.293, 207Pb/204Pb from 15.325 to 15.614, and 208Pb/204Pb 36.742 to 38.384. Individual Permian orogenic gold deposits and occurrences differ in Pb isotope ratios and degree of their Pb isotopic composition heterogeneity. The Pb isotope features weakly correlate with the geological setting of the deposits. Age-corrected Pb–Pb data for the 41 samples of the BMB metamorphic and igneous rocks are similar to those of the gold mineralization: 206Pb/204Pb from 16.89 to 18.57, 207Pb/204Pb from 15.34 to 15.65, and 208Pb/204Pb 36.67 to 38.4. The high variability of model parameters (µ2 = 9.02–9.78, ω2 = 35.2–42.5, Th/U = 3.84–4.46) and Pb-isotope mixing trends for the ore lead suggest different sources of the metal. One of the sources was the BMB Neoproterozoic metamorphic and magmatic rocks hosting the gold deposits. The obtained data also suggest a common source for these deposits which is identical in its Pb-isotope characteristics to the Permian alkaline and sub-alkaline igneous rocks. We propose that the metasomatized subcontinental lithospheric mantle (SCLM) as well as the SCLM derived alkaline mafic magmas could be the important source of metals (including gold) for the Permian orogenic gold mineralization of the BMB. [ABSTRACT FROM AUTHOR]

Corundum is rarely found in situ within alkali syenites. A corundum-bearing syenite was found in the Yushishan rare metal deposits of the eastern section of the Altyn Tagh fault in the northeastern Tibetan Plateau, but the characteristics and formation of corundum remain unknown. We describe a corundum-bearing syenite dike emplaced in biotite plagioclase gneiss that suffered overprinted deformation with characteristics of mylonitization. The corundum crystals have variable grain sizes, and the largest ones are megacrystic with growth zoning. The corundum crystals contain a variety of mineral inclusions that are divided into primary and secondary. The primary mineral inclusions within the corundum include variable contents of Fe-Ti oxide needles, ilmenite, zircon, monazite-(Ce), potassium feldspar, pyrochlore, columbite-(Fe), magnetite, samarskite-(Y), and pyrite that indicate corundum crystallized in peraluminous Zr-rich and Si-poor alkali rock with variable TiO2 contents. Secondary mineral inclusions include Zn-rich hercynite, ilmenite, magnetite, annite, fluorapatite, and intergrowths of ilmenite with columbite-(Fe) and goethite that reveal late-stage influx of Zn-, Ti-, Fe-, and F-bearing fluids into corundum that caused metasomatism and element migration and mineral precipitation. The trace element analysis of corundum shows high-Fe and -Ga contents and low-Mg and -Cr contents that are consistent with the characteristics of corundum of magmatic origin. The trace element characteristics and the oxygen isotopes (6.2–8.2‰) results indicate that corundum crystallized in melts with the involvement of Al-rich and Si-poor crustal material. [ABSTRACT FROM AUTHOR]

The levels of CO2 emissions generated by the cement industry and the growth in demand for its products have led to a search for ways to reduce these emissions. The use of supplementary cementitious materials has become one of the solutions proposed for this problem. Illite, which is found all over the world, is a possible supplementary cementitious material. Before illite can be used, it must be milled and treated thermally in order to activate it, so that the alkalis (Na+ and K+) are free and available to react. Alkalis in cement participate in deleterious reactions (alkali-silica reaction) or have a beneficial effect (alkaline activation). The alkalis present in the rocks can play an active role in these phenomena, however. In addition, the material could be influenced by the alkaline environment produced by the cement. The current study was aimed at analyzing whether an alkali release occurs and if so, how it is affected when a milled and thermally treated illitic rock is in contact with water or an alkaline solution. The material was characterized by X-ray fluorescence, polarizing microscopy, and X-ray diffraction (XRD). The sample was treated thermally at 300, 600, and 900°C, and the thermal activation was evaluated through XRD, density, and Atterberg limits. The evolution of alkali release was studied by determining the sodium and potassium concentration of contact water obtained by mixing the samples with different pH solutions for various lengths of time. In addition, the calcium concentration was determined. The concentrations of sodium and potassium in the contact water were determined by flame photometry, and of calcium by EDTA (ethylenediaminetetraacetic acid) titration. The results showed that with increasing age, increasing solution pH, and higher treatment temperatures, alkali release occurred and increased, whereas Ca2+ concentration decreased. [ABSTRACT FROM AUTHOR]

Alkaline-silicate complexes host some of the world's largest resources of rare-earth elements and high-field-strength elements (REE & HFSE) and represent the most fractionated magmatic systems on our planet. Geochemical evidence indicates that they are mantle melts, but while various studies highlight a role for lithospheric mantle, we do not know the precise origin of their contained REE and HFSE, and whether enrichment of the mantle source for these magmas can be attributed to specific geodynamic processes or events. We present new Nd-Hf isotope measurements (▪/▪ &▪/▪) made by LA-MC-ICP-MS, as well as a compilation of existing isotopic data for a suite of alkaline igneous rocks from the Gardar Province, a Mesoproterozoic continental rift in southern Greenland. Neodymium and hafnium isotopes are unaffected by crystal fractionation and can directly fingerprint the source of REE and HFSE. The dataset covers both phases of Gardar magmatism (1325–1261 and 1184–1140 Ma) and incorporates mafic dyke swarms and km-scale intrusive complexes, including Ilimmaasaq (Ilímaussaq) and Motzfeldt, which host some of the world's largest REE and HFSE deposits. The majority of Gardar complexes have a narrow range of positive median initial ε Nd (0 to +3.3) and ε Hf values (+0.2 to +6.0). Only two granite intrusions and the Eriksfjord basaltic lavas have crustally contaminated Nd-Hf isotope compositions, with the vast majority of Gardar igneous rocks preserving the isotope signature of their mantle source. Considering the diversity of rock types in the Gardar Province, initial ε Nd - ε Hf compositions are remarkably homogeneous, indicating a derivation of the Gardar's REE and HFSE from a laterally-extensive mantle melt source. Several Gardar systems have low initial ε Hf for a given ε Nd (▪ ε Hf to -9.7), a distinctive signature as few geological processes decouple the Nd and Hf isotope systems. The decoupled Nd-Hf isotope signatures are consistent with contributions from isotopically-matured phlogopite-bearing metasomatic veins (commonly known as PIC: phlogopite-ilmenite-clinopyroxene) in the lithospheric mantle. The metasomatising fluids that formed these source rocks were introduced via Palaeoproterozoic subduction, but the Gardar isotopic signatures indicate that REE and HFSE enrichment of these metasomes was not derived from subducted sediment; instead it is likely that metals were scavenged from the mantle wedge overlying the ancient subduction zone. The Gardar Nd-Hf isotope evolution trends overlap with a global compilation of kimberlites through time and allow us to tie the origin of the PIC metasomes to the regional geodynamic history of South Greenland. We identify PIC metasomes as a key metal source for the Gardar and by extension perhaps other REE-mineralised igneous provinces globally. • Nd Hf isotopes reported for alkaline rocks from REE rich Gardar continental rift. • Negative ▪ ε Hf discounts enrichment of mantle source by subducted sediment. • REE & HFSE derive from isotopically matured metasomatic veins in lithospheric mantle. • Origin of enriched source tied to regional geodynamic history. • Provides conceptual basis for distribution of REE HFSE provinces globally. [ABSTRACT FROM AUTHOR]

Syenites are highly valued for economic and strategic exploration programs worldwide, along with associated rocks (e.g., carbonatites), as a primary source for several industrial minerals and strategic elements, such as phosphate, potash, rare earth elements (REE), and Nb. Rapid identification and mapping of syenite outcrops and their major geochemical signatures (i.e. potassic and sodic) over vast areas are crucial for exploration programs aimed at identifying new economic deposits. For this, remote sensing provides an interesting way to delineate these alkaline igneous rocks and predicts their mineralogical and geochemical characteristics. In the literature, few remote sensing studies have been devoted to syenite outcrops, and an effective predictive tool for their mapping and mineralogical-geochemical classification remains to be done. Accordingly, we explore in the present study the potential of using ASTER thermal emissivity data for prospectivity mapping and predicting the main alkaline mineralogical and geochemical affinities of syenite rocks. This approach was applied to the Moroccan High-Atlas Mountains (area ∼ 42,000 km2), known for the presence of several alkaline intrusions hosting different alkali-syenites. Hence, a spectral syenite index [SyI = (B10/B11 * B10/B13 * B14/B13)] without the use of in-situ field data, was suggested in the first stage to quickly highlight potential areas, reducing the initial exploration zone to only ∼1000 km2/42000 km2 that include all well-known syenites in the studied area. Subsequently, several in-situ field missions were conducted in the identified zones to sample and obtain precise GPS points of well-exposed syenitic outcrops. For discrimination of mineralogical and geochemical endmembers (Na vs. K) of syenites, two new spectral indices were proposed [SpI-A = (B14-B12)/(B14 + B12) for K syenite signature and SpI-B = (B10-B11)/(B10 + B11) for Na syenite signature]. These indices highlight the two major geochemical affinities in the High-Atlas Mountains: the potassic syenite character (K-feldspar- and nepheline-rich) in the Midelt-Tamazeght Cenozoic complex and the sodic syenite character (albite-rich) in the Imilchil Mesozoic massifs. The results have significant implications for early exploration programs, aiming to cost-effectively discover favorable areas of alkali syenites, potassic against sodic affinities, and optimize fieldwork as well as preliminarily mineralogical and geochemical characterization. • ASTER thermal data were used to assess the syenite mineralogical signatures. • High prospective areas were delineated using the concentration-area fractal model. • To reduce the investigated area by 99 %, the Only-Presence Modelling was deployed. • Using spectral features of alkali-minerals, Na- and K-syenites were differentiated. [ABSTRACT FROM AUTHOR]

Windhoekite, Graph HT ht , is a rare hydrated silicate of calcium and iron. Windhoekite, C a 2 F e 3 - x 3 + (S i 8 O 20) (O H) 4 - 10 H 2 O, a new palygorskite-group mineral from the Aris phonolite, Namibia. The palygorskite-group minerals (including windhoekite) are among the last to crystallize in the miarolitic cavities; Chukanov et al. ([2]) suggest the following general order of crystallization: microcline -> aegirine -> fluorapophyllite -> palygorskite-group minerals -> arisite. [Extracted from the article]

In the MRC, helvine-group minerals occur in pegmatite miarolitic cavities and are represented by the minerals genthelvite [Be SB 3 sb Zn SB 4 sb (SiO SB 4 sb ) SB 3 sb S] and danalite [Be SB 3 sb Fe SB 4 sb SP 2+ sp (SiO SB 4 sb ) SB 3 sb S]. These pegmatites are often macroscopically indistinguishable because they are composed of the same major mineral assemblages: quartz and microcline ± albite, with a notable absence of mica minerals. In all these units, beryl, the most common beryllium mineral, was never a crystallizing phase; instead, a suite of less-common late-stage primary and secondary Be-bearing minerals are present. Most notably, beryl was never a crystallizing phase; instead, other Be-minerals including bertrandite, phenakite, bazzite, gadolinite, hingganite, and helvine-group minerals are the primary Be-bearing minerals. [Extracted from the article]

Dolostone is widely distributed and commonly used as concrete aggregates. A large number of studies have shown that there are significant differences in the expansibility of different dolostones, and the key factors determining the expansibility of alkali carbonate rocks have not been clarified. In this paper, rocks were selected from five different geological ages: Jixianian, Cambrian, Ordovician, Devonian, and Triassic ages. The ordering degree and the content of MgCO3 of dolomites in rocks of different geological ages were determined by X-ray diffraction (XRD). The degree of dedolomitization reaction in rocks cured in 80 °C, 1 mol/L NaOH solution was determined by quantitative X-ray diffraction (QXRD). The morphology of dolomites in rocks was determined by a polarizing microscope. The products of the dedolomitization reaction were determined by field emission electron microscopy (FESEM-EDS). According to the test results, the following conclusions are drawn. There is a good positive correlation between ordering degree and the molar fraction of MgCO3 of dolomites. When the MgCO3 mole fraction of dolomites varies from 47.17% to 49.60%, the higher the MgCO3 mole fraction, the greater the ordering degree of dolomite. By analyzing the degree of the dedolomitization reaction of different dolostone powders cured at 80 °C in 1 mol/L NaOH solution, it is found that the older the geological age of dolostone, the slower the dedolomitization reaction rate and the lower the degree of dedolomitization reaction. The lower the ordering degree of dolomite crystal in the same geological age, the faster the rate of dedolomitization reaction and the higher the degree of dedolomitization reaction. [ABSTRACT FROM AUTHOR]

Luku alkali syenite is distributed throughout the southern end of the Hongge basic‐ultrabasic intrusion in Panzhihua, Sichuan, SW China. Using LA‐ICP‐MS, the alkali syenite intrusion yielded a zircon U‐Pb age of 264.5 ± 1.6 Ma, concordant with the ages of the E'meishan large igneous province (260 Ma). The intrusion displayed silica‐saturated, Al‐adequate and alkali‐rich signatures, with SiO2 62.07%–64.04%, Al2O3 16.26%–16.79% and Na2O + K2O 9.17%–9.91% (averaging 9.31%). The rock falls into the alkaline zone on the SiO2‐A.R. diagram, as well as in the potassium zone on the K2O‐Na2O diagram, indicating a potassium alkaline rock. The rock has a low total REE concentration and showed enrichment in LREE (LREE/HREE = 7.06–7.95), typical negative Eu anomalies (δEu = 0.73–0.80), trace element deficiencies in LILEs (Ba, K, Sr, Zr) and enrichment in HFSEs (Th, U, Nd, Sm, Ta and Nb), displaying crust and mantle element information. Zircons show a strong positive Ce anomaly and negative Eu anomaly, similar to the characteristics of crustal source magmatic zircon, however the (Lu/Gd)N ratio ranges from 1.48 to 3.17, and the (Yb/Sm)N ratio ranges from 38.49 to 77.15, which are similar to the characteristics of mantle‐derived magmatic zircon. In the La/Yb‐δEu correlation diagram, the data plots near the boundary between crust type and crust‐mantle type. From the combined 'trinity' spatiotemporal relationship of Indosinian intermediate‐acid alkali intrusive rocks in the Panxi area with E'meishan basalt and basic‐ultrabasic intrusive rocks, the regional tectonic evolution and the partial melting model of the most intraplate magma sources, we believe that the Luku alkali syenite in Sichuan was formed from the partial melting of a crust‐mantle source material, due to underplating of the mantle plume basic magma. [ABSTRACT FROM AUTHOR]

Large reserves of feldspar ore deposits are found in the alkali granite rocks at Al-Madinah province, Saudi Arabia. Magnetic separation and flotation tests were used in order to achieve the aims of this study which are: reduce the iron and titanium contents of Medina feldspar ore, which impart color and decrease the feldspar quality, as well as produce a high-quality feldspar concentrate, which meets the commercial grade of the raw material specifications for the ceramics and glass industry. The obtained results from this study showed that the efficient separation of Fe- and Ti-bearing minerals could be achieved by a combination of the dry high-intensity magnetic separator at 14.000 gauss and the direct cationic flotations under 500 g/ton dosage of Aero 801 + Aero 825 + Aero 830 mixture in an acidic medium at pH 3. The feldspar concentrate was produced with 65.18 wt.% SiO2, 19.02 wt.% Al2O3, 0.06 wt.% Fe2O3, 0.09 wt.% TiO2 9.09 wt.% K2O and 6.01 wt.% Na2O grades, which meet the commercial scale of feldspar. [ABSTRACT FROM AUTHOR]

This paper mainly takes Zhacun goldmine as the research object and carries out research on the metallogenic system and genesis of the deposit in the area. The research methods are as follows: according to the geological characteristics of the metallogenic mining area in the Zhacun goldmine, combined with the comparative analysis of the metallogenic age, alteration characteristics and lithology between the Zhacun goldmine and the Lianhuashan alkali rich rock mass, and the analysis of the isotopic data in the Zhacun goldmine, this paper demonstrates that the magmatic activity of the Lianhuashan quartz monzonite porphyry plays an important role in the mineralization of this area, which is both an important ore source and fluid source. It is also the main heat source driving the circulation of ore-forming fluid. On this basis, through the analysis of the metallogenic elements in the area, the metallogenic system model of Zhacun goldmine is constructed. It is considered that under the action of long-term horizontal compressive stress, the atmospheric precipitation infiltrated into the formation continued to penetrate along the fractures and fissures to deep crust and finally mixed with the magmatic water sealed in the thick formation. During this period, a series of shallow and ultrashallow porphyry mass intruded, providing heat source and part of the ore-forming materials and resulting in incomplete homogenization under high temperature and high pressure, which formed highly mineralized mixed water. Under the combined action of long-term compressive stress and various deep thermal dynamics, these mineral fluids migrated along the buried deep faults near the core of the duplex anticline to the upper part of the crust. When the metal elements in these ore fluids migrated over long distances to the nappe fault zone of the gold-bearing fracture zone, the gold began to precipitate, and the native gold and the coarse-grained pyrite and quartz formed at the same time or earlier started to fill the fracture zone along the fissures and accumulate into minerals. Then, through the analysis of metallogenic conditions, gold mineralization process, and genetic mechanism of the deposit, it is proposed that the genetic type of the ore deposit in this area is magmatic mesothermal-epithermal gold deposit. The establishment of metallogenic system model in Zhacun goldmine will provide theoretical and practical guidance for deep and peripheral prospecting prediction in the area, carry out targeted and reasonable prediction, and improve prospecting effectiveness. [ABSTRACT FROM AUTHOR]

Natural nepheline usually contains very small amounts of MgO (<0.1 wt.%), although these examples are mainly from Mg-poor alkaline igneous rocks such as nepheline syenites. However, this work shows that nepheline and kalsilite with much higher MgO concentrations can occur in the groundmass of strongly SiO2-undersaturated, feldspar-free, mafic volcanic rocks (i.e. olivine-rich foidites). Furthermore, a strong positive correlation is evident between their Mg and Fe contents. The occurrence of Mg-rich nepheline and kalsilite seems to be related to their derivation from Mg-rich magmas when compared to most of the host rocks investigated to date. Additionally, the physicochemical conditions of crystallisation seem to have an important role in the incorporation of 'small' divalent cations by these minerals. The prevalence of Mg-rich nepheline and kalsilite as late magmatic phases and the divergent Mg and Fe relationships for phenocrysts and 'quenched' groundmass crystals support this hypothesis. The positive correlation between Mg and Fe contents reflects their strong geochemical affinity and the entrance of Fe3+, Fe2+ and Mg2+ cations into the same crystallographic site of nepheline and kalsilite structures. The calculation of atomic formulae and stoichiometry parameters for nepheline-group minerals where data for the T2+ cations (e.g. Mg2+) are incorporated gives more reliable compositional parameters (see Paper 1). Calculated excess silica values (Si′) are affected significantly when the coupled substitution 2Al3+ = Mg2+ + Si4+ is considered. Thus, specific analyses of 'small' divalent cations are essential to obtain more realistic values of excess Si′, in particular, for nepheline and kalsilite that crystallised from Mg-rich, Si-poor, mafic–ultramafic alkaline lavas. [ABSTRACT FROM AUTHOR]

The Bashisuogong alkaline igneous intrusion is located between the South Tianshan Orogenic Belt and the Kepingtage foreland thrust belt at the northern margin of the Tarim Craton and hosts economically significant Nb–Ta–Zr–rare earth element mineralization. Eudialyte has recently been discovered in the syenite unit of this intrusion, which is the primary host mineral for high-field-strength and rare earth elements. Based on detailed petrographic investigations, this study investigated the behavior of trace elements during magma evolution and the enrichment of ore-forming elements using whole-rock geochemical analyses of eudialyte-bearing syenite and compositional analyses of aegirine–augite and different types of eudialyte. We also undertook in situ titanite U-Pb dating. The Bashisuogong syenite comprises aegirine–augite and aegirine–augite–eudialyte syenite, the latter of which have higher total rare earth element contents. Both types of syenite exhibit slight enrichments in light rare earth elements, significant enrichments in high-field-strength elements (Nb, Ta, Zr, Hf, and Th), depletions in large-ion lithophile elements (Ba and Sr), and large negative Eu anomalies. There are two types (I and II) of eudialyte. Eudialyte I has higher Mn/Fe, Zr/Hf, and Nb/Ta ratios but lower Th/U ratios compared with eudialyte II but similar Y/Ho ratios. Eudialyte II crystallized earlier than eudialyte I, and aegirine–augite, titanite, and apatite crystallized earlier than eudialyte I. Both aegirine–augite and eudialyte have similar trace element characteristics to the host rocks, exhibiting enrichments in highly incompatible high-field-strength and rare earth elements, as well as marked negative Eu anomalies and depletions in Sr. These characteristics suggest that the Bashisuogong alkaline rocks formed by low-degree partial melting of geochemically enriched, metasomatized lithospheric mantle, which formed an alkaline basaltic parental melt that then underwent protracted magma evolution and fractionation in the shallow crust. The eudialyte syenite yield a titanite U-Pb age of 277.3 ± 1.2 Ma, which is consistent with the ages of different types of alkaline igneous rocks in the study area, indicating they were the products of the same magmatic event. Temporally and spatially, the Bashisuogong ore-bearing alkaline rocks were associated with the Tarim mantle plume, and the mantle plume provided the heat for their formation. [Display omitted] • Eudialyte-bearing syenite unit was discovered in the Bashisuogong alkaline complex. • Variation Zr/Hf, Nb/Ta, Th/U of Eud I and II are due to fractional crystallization. • Eudialyte geochemistry suggests syenite derives from alkali basaltic parent melt. • Titanite U-Pb dating reveals that eudialyte syenite is emplaced at ca. 277 Ma. [ABSTRACT FROM AUTHOR]

This study presents a geochemical and Sm Nd isotopic study on pyrochlore from the Ririwai alkaline complex in north-central Nigeria, aiming to reconstruct the magmatic-hydrothermal history and provide insights into the formation of niobium deposit hosted in alkaline igneous rocks. Three texturally and compositionally distinct types of pyrochlore (Pcl I, II, and III) are identified. Primary Pcl I grains are enriched in Nb 2 O 5 (mean of 60.5 wt%) and other high field strength elements (HFSE), rare earth elements (mean of 17.2 wt% REE 2 O 3), Ca, Na, and F, suggesting that they crystallized in a Nb-rich peralkaline magma. The occurrence of patchy zoning as well as the development of microfractures and pores within these pyrochlore grains indicate two stages of hydrothermal alteration responsible for the formation of Pcl II and Pcl III. The first stage of alteration from Pcl I to Pcl II was induced by high-temperature, alkali-rich, and F-moderate fluids, leading to the removal of Na, Ca, and F while filling the vacant A- and Y-sites with K, Rb, Y, and Zn. The Nb and REE contents in Pcl III (mean of 41.3 wt% and 9.4 wt%, respectively) are lower than those in Pcl I and Pcl II (mean of 58.1 wt% and 17.3 wt%, respectively). Thereby, the second stage of alteration from Pcl II to Pcl III was related to low-temperature, Si- and Al-rich alkaline fluids, which resulted in the leaching of Nb, Ti, Th, U, and REE (mainly LREE) from the A- and B-sites, compensated by the incorporation of Si, Pb, K, Al, Fe, and Mn. The leached elements either precipitated into Nb-bearing minerals such as rutile, thorite, and zircon in alteration assemblages as an in-situ replacement of Pcl II or remobilized locally to form hydrothermal veins of Si, Al, Nb, and CO 2 -bearing oxides. The comparable εNd(t) values between hydrothermal Pcl II and III (−1.9 to −2.8 and − 1.5 to −3.2, respectively) and magmatic Pcl I (−2.0 to −2.6) indicate that there was only a minimal external contribution to Nd (and by analogy Nb as well) from fluids. Two-stage hydrothermal fluids in the Ririwai alkaline complex have limited effects on Nb mobilization, without significantly enhancing or reducing the Nb grade. [ABSTRACT FROM AUTHOR]

Alkaline igneous rocks host many global high-field-strength element (HFSE) and rare-earth element (REE) deposits. While HFSEs are commonly assumed to be immobile in hydrothermal systems, transport by late-stage hydrothermal fluids associated with alkaline magmas is reported. However, the magnitude of the flux and the conditions are poorly constrained and yet essential to understanding the formation of REE-HFSE ores. We examined the alteration of country rocks ("fenitization") accompanying the emplacement of a syenite magma at Illerfissalik in Greenland, through analysis of changes in rock chemistry, mineralogy, and texture. Our novel geochemical maps show a 400-m-wide intrusion aureole, within which we observed typically tenfold increases in the concentrations of many elements, including HFSEs. Textures suggest both pervasive and structurally hosted fluid flow, with initial reaction occurring with the protolith's quartz cement, leading to increased permeability and enhancing chemical interaction with a mixed Ca-K-Na fenitizing fluid. We estimated the HFSE masses transferred from the syenite to the fenite by this fluid and found ~43 Mt of REEs were mobilized (~12% of the syenite-fenite system total rare-earth-oxide [TREO] budget), a mass comparable to the tonnages of some of the world's largest HFSE resources. We argue that fenite can yield crucial information about the tipping points in magma evolution because retention and/or loss of volatile-bonded alkali and HFSEs are key factors in the development of magmatic zirconosilicate-hosted HFSE ores (e.g., Kringlerne, at Ilímaussaq), or the formation of the syenite-hosted Nb-Ta-REE (Motzfeldt-type) roof-zone deposits. [ABSTRACT FROM AUTHOR]

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Mafic-ultramafic subvolcanic intrusive complexes, at the 1–10-km scale, constitute favorable environments for the formation of orthomagmatic Ni-Cu-PGE sulfide deposits. Within 100–1000-km scale large igneous provinces (LIPs), the most favorable economic target areas may be difficult to identify using a traditional regional exploration approach. We report results of field and laboratory studies focused on an integrated geochemical-architectural model for the Ni-Cu-PGE sulfide potential of the High Arctic large igneous province (HALIP) of Canada, the largest and best-exposed portion of this circum-arctic LIP. Previous lithogeochemical studies of the Canadian HALIP (130–80 Ma) concluded that subalkaline mafic units located on Axel Heiberg Island were more prospective than younger, alkalic igneous rocks (alkaline basalts to basanites) exposed on northern Ellesmere Island. Mapping carried out for this study revealed the presence of abundant subalkaline igneous rocks on western Ellesmere Island. We interpret these units as an extension of the Schei Sills, a stratigraphically bound sequence of intrusions exposed along a ~ N-S belt on eastern Axel Heiberg Island. Samples from the Schei Sills and from the Middle Fiord Intrusive Complex (~ 20 km2, central Axel Heiberg Island) show Cu/Zr values above and below unity, consistent with complementary sulfide enrichment and removal, respectively, within these intrusive systems. The spatial association of the Schei Sills with the post-emplacement Eocene Stolz Thrust is noteworthy, as later thrusting associated with the Paleogene Eurekan Orogeny caused the uplift of deeper parts of the HALIP subvolcanic feeder system and associated wall-rock stratigraphy. Absolute Ir-group PGE contents are low throughout the HALIP; however, Pt-group PGE contents range widely among analyzed tholeiitic intrusive rocks. For example, relatively elevated Pt + Pd values of 10–30 ppb in samples from the Middle Fiord Intrusive Complex and the Schei Sills suggest heightened prospectivity in these two areas. In contrast, tholeiitic flood basalts in the Strand Fiord Formation and associated intrusions exposed in western Axel Heiberg Island (~ 95 Ma) exhibit Cu/Zr < 1 and low Pt + Pd contents (below 10 ppb). The ca. 120 Ma magmatic event associated with the Schei Sills and Middle Fiord Intrusive Complex appears to have generated magmas that are more prospective than those of the younger (ca. 95 Ma) magmatic pulse associated with the flood basalts of the Strand Fiord Formation. This work demonstrates that not all architectural elements of a LIP are equal in terms of metallogenic potential, and that nested zones of higher prospectivity can be identified through the integration of several geological constraints. [ABSTRACT FROM AUTHOR]

The rare earth elements (REE) are critical raw materials for much of modern technology, particularly renewable energy infrastructure and electric vehicles that are vital for the energy transition. Many of the world's largest REE deposits occur in alkaline rocks and carbonatites, which are found in intracontinental, rift-related settings, and also in syn- to post-collisional settings. Post-collisional settings host significant REE deposits, such as those of the Mianning-Dechang belt in China. This paper reviews REE mineralization in syn- to post-collisional alkaline-carbonatite complexes worldwide, in order to demonstrate some of the key physical and chemical features of these deposits. We use three examples, in Scotland, Namibia, and Turkey, to illustrate the structure of these systems. We review published geochemical data and use these to build up a broad model for the REE mineral system in post-collisional alkaline-carbonatite complexes. It is evident that immiscibility of carbonate-rich magmas and fluids plays an important part in generating mineralization in these settings, with REE, Ba and F partitioning into the carbonate-rich phase. The most significant REE mineralization in post-collisional alkaline-carbonatite complexes occurs in shallow-level, carbothermal or carbonatite intrusions, but deeper carbonatite bodies and associated alteration zones may also have REE enrichment. [ABSTRACT FROM AUTHOR]

Thick-crusted (>45 km) Cordilleran arcs exhibit cyclic processes including periods of magmatic quiescence interspersed with pulses of high-flux magmatism. Most models assume that during high-flux events, fractional crystallization and partial melting within the deep crustal hot zone generate a dense (>3.4 g/cm3) arclogitic subarc root that can readily founder into the mantle. Yet these models do not consider that: (1) the retention of low-density melt within the subarc root, and (2) the protolith lithology of the restitic portion of the subarc root may greatly impact the density evolution of the root and its susceptibility to foundering. In this article, we first address the effect of retained melt on the foundering ability of the subarc root by calculating the density and time for foundering of melt-bearing arclogitic residue at 1.5, 2, and 2.5 GPa. We find that melt volumes >10–18% are required to stabilize the root within the lower crust; melt volumes below this threshold lower the viscosity of the residue so much so as to decrease the time for foundering by an order of magnitude. We then constrain through phase equilibria modeling the effect of partial melting of different lower crustal protoliths on the density of the restitic subarc root. To do this, we model the density and mineralogical evolution of restites in equilibrium with their derivative melts during open-system, isobaric partial melting of typical crustal assemblages from 600–1100°C at 1.5 (~50 km) and 2 GPa (~65 km). In our models, typical end-member assemblages in a lower crustal hot zone include basalt, metapelite, and metagraywacke. We find that melt-depleted restites derived from basaltic compositions are amphibole-bearing arclogites with densities conducive to foundering, which at 2 GPa can occur even in the presence of the coexisting hydrous felsic residual melt. Foundering of the amphibole ± melt-bearing root may refertilize the mantle wedge and induce melting of the surrounding asthenosphere as well as the arclogitic mass. However, if temperatures in a 50-km deep subarc hot zone are not sufficient to drive melt depletion of basaltic restites, these dense (3.1–3.3 g/cm3) residues are gravitationally stable, increasing the density of the lower crust and lowering the elevation of the arc. In comparison, partial melting of metasedimentary country rock produces alkali feldspar-rich residues that never achieve densities conducive to foundering. Thus, if high-flux events are driven by the influx of melt-fertile lithosphere beneath the arc as envisioned by the Cordilleran cycle model, then partial melting of the metasedimentary portion will generate low-density residues that remain in the lower crust and contribute to the thickness, geochemistry, and seismic structure of the bulk arc. [ABSTRACT FROM AUTHOR]

Copyright of Karaelmas Science & Engineering Journal / Karaelmas Fen ve Mühendislik Dergisi is the property of Karaelmas Science & Engineering Journal and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The Cretaceous High Arctic Large Igneous Province (HALIP) in Canada, although dominated by tholeiites (135–90 Ma), contains two main groups of alkaline igneous rocks. The older alkaline rocks (∼96 Ma) scatter around major fault and basement structures. They are represented by the newly defined Fulmar Suite alkaline basalt dykes and sills, and include Hassel Formation volcanic rocks. The younger alkaline group is represented by the Wootton Intrusive Complex (92·2–92·7 Ma), and the Audhild Bay Suite (83–73 Ma), both emplaced near the northern coast of Ellesmere Island. Fulmar Suite rocks resemble EM-type ocean island basalts (OIB) and most show limited crustal contamination. The Fulmar Suite shows increases of P2O5 at near-constant Ba–K–Zr–Ti that are nearly orthogonal to predicted fractionation- or melting-related variations, which we interpret as the result of melting composite mantle sources containing a regionally widespread apatite-bearing enriched component (P1). Low-P2O5 Fulmar Suite variants overlap compositionally with enriched HALIP tholeiites, and fall on common garnet lherzolite trace element melting trajectories, suggesting variable degrees of melting of a geochemically similar source. High-P2O5 Hassel Formation basalts are unusual among Fulmar rocks, because they are strongly contaminated with depleted lower crust; and because they involve a high-P2O5–Ba–Eu mantle component (P2), similar to that seen in alkali basalt dykes from Greenland. The P2 component may have contained Ba–Eu-rich hawthorneite and/or carbonate minerals as well as apatite, and may typify parts of the Greenlandic sub-continental lithospheric mantle (SCLM). Mafic alkaline Audhild Bay Suite (ABS) rocks are volcanic and hypabyssal basanites, alkaline basalts and trachy-andesites, and resemble HIMU ocean island basalts in having high Nb, low Zr/Nb and low 87Sr/86Sri. These mafic alkaline rocks are associated with felsic alkaline lavas and syenitic intrusions, but crustally derived rhyodacites and rhyolites also exist. The Wootton Intrusive Complex (WIC) contains geochemically similar plutonic rocks (alkali gabbros, diorites and anatectic granites), and may represent a more deeply eroded, slightly older equivalent of the ABS. Low-P2O5 ABS and WIC alkaline mafic rocks have flat heavy rare earth element (HREE) profiles suggesting shallow mantle melting; whereas High-P2O5 variants have steep HREE profiles indicating deeper separation from garnet-bearing residues. Some High-P2O5 mafic ABS rocks seem to contain the P1 and P2 components identified in Fulmar–Hassel rocks, whereas other samples trend towards possible High-P2O5 + Zr (PZr) and High-P2O5 + K2O (PK) components. We argue that the strongly alkaline northern Ellesmere Island magmas sampled mineralogically heterogeneous veins or metasomes in Greenlandic-type SCLM, which contained trace phases such as apatite, carbonates, hawthorneite, zircon, mica or richterite. The geographically more widespread apatite-bearing component (P1) could have formed part of a heterogeneous plume or upwelling mantle current that also generated HALIP tholeiites when melted more extensively, but may also have resided in the SCLM as relics of older events. Rare HALIP alkaline rocks with high K–Rb–U–Th fall on mixing paths implying strong local contamination from either Sverdrup Basin sedimentary rocks or granitic upper crust. However, the scarcity of potassic alkaline HALIP facies, together with the other trace element and isotopic signatures, provides little support for a ubiquitous fossil sedimentary subduction-zone component in the HALIP mantle source. [ABSTRACT FROM AUTHOR]

Nepheline (and its rarer potassium analogue: kalsilite) is a sodium‐rich, rock‐forming mineral belonging (like the feldspars and quartz) to the tectosilicates, which are 3‐dimensional structures made up of SiO44−tetrahedra. Relatively rare compared to the feldspars, nepheline is an important mineral in the alkaline igneous rocks, such as nepheline syenites, phonolites and nephelinites. In silica‐deficient magmas, the natural endpoint of crystal fractionation is nepheline syenite just as silica‐rich magmas end at the granite minimum. Nepheline has commercial uses in the glass and ceramic industries and even as a raw material for aluminium production. [ABSTRACT FROM AUTHOR]

The Yangibana rare earth element (REE) district consists of multiple mineral deposits/prospects hosted within the Mesoproterozoic Gifford Creek Carbonatite Complex (GCCC), Western Australia, which comprises a range of rock types including calcite carbonatite, dolomite carbonatite, ankerite–siderite carbonatite, magnetite–biotite dykes, silica-rich alkaline veins, fenite, glimmerites and what have historically been called "ironstones". The dykes/sills were emplaced during a period of extension and/or transtension, likely utilising existing structures. The Yangibana REE deposits/prospects are located along many of these structures, particularly along the prominent Bald Hill Lineament. The primary ore mineral at Yangibana is monazite, which is contained within ankerite–siderite carbonatite, magnetite–biotite dykes and ironstone units. The ironstones comprise boxwork-textured Fe oxides/hydroxides, quartz, chalcedony and minor monazite and subordinate rhabdophane. Carbonate mineral-shaped cavities in ironstone, fenite and glimmerite alteration mantling the ironstone units, and ankerite–siderite carbonatite dykes altering to ironstone-like assemblages in drill core indicate that the ironstones are derived from ankerite–siderite carbonatite. This premise is further supported by similar bulk–rock Nd isotope composition of ironstone and other alkaline igneous rocks of the GCCC. Mass balance evaluation shows that the ironstones can be derived from the ankerite–siderite carbonatites via significant mass removal, which has resulted in passive REE concentration by ~ 2 to ~ 10 times. This mass removal and ore tenor upgrade is attributed to extensive carbonate breakdown and weathering of ankerite–siderite carbonatite by near-surface meteoric water. Monazite from the ironstones has strong positive and negative correlations between Pr and Nd, and Nd and La, respectively. These relationships are reflected in the bulk–rock drill assays, which display substantial variation in the La/Nd throughout the GCCC. The changes in La/Nd are attributed to variations in primary magmatic composition, shifts in the magmatic-hydrothermal systems related to CO2 versus water-dominated fluid phases, and changes in temperature. [ABSTRACT FROM AUTHOR]

Syn-subduction arc magmatism is absent above continental subduction zones, providing important constraints on the nature of petrogenetic processes during continental collision. Nevertheless, we have identified syn-exhumation mafic igneous rocks in an active continental margin above a continental subduction zone, where the South China Block (SCB) was deeply subducted beneath the North China Block (NCB) for collisional orogeny in the Triassic. These mafic igneous rocks occur in the southeastern margin of the NCB, showing consistent Late Triassic zircon U-Pb ages of ca. 219-218 Ma, coeval with exhumation of the deeply subducted continental crust. These rocks are categorized into two series of sub-alkaline and alkaline, all exhibiting arc-like trace element distribution patterns, highly enriched radiogenic Sr-Nd- Hf and high zircon O isotope compositions. In particular, they exhibit two-stage wholerock Nd and Hf model ages and zircon Hf model ages of Paleoproterozoic, which are comparable to those of ultrahigh-pressure metamorphic rocks with the SCB affinity in the Dabie-Sulu orogenic belt. Such geochemical features indicate that these mafic igneous rocks were derived from partial melting of ultramafic metasomatites generated by reaction of felsic melts from the subducted SCB with the mantle wedge peridotite beneath the NCB. The geochemical differences in element and isotope compositions between the two series igneous rocks can be mainly ascribed to different proportions of the crustal component in the metasomatites, which is verified by quantitative modellings of the geochemical transfer in the continental subduction zone. The systematic variations in some geochemical variables such as Fe/Mn, Zn/Fe, and Nb/ Ta ratios indicate pyroxenite-rich and hornblendite- rich lithologies, respectively, for the sub-alkaline and alkaline series igneous rocks. With the tectonic extension for exhumation of the deeply subducted continental crust in the Late Triassic, the fertile and enriched metasomatites in the mantle wedge underwent partial melting for the syn-exhumation mafic magmatism in the southeastern NCB. Therefore, the mafic igneous rocks in the active continental margin not only record the crust-mantle interaction in the continental subduction zone, but also witness the generation of syn-exhumation magmatism in the late stage of continental collision. [ABSTRACT FROM AUTHOR]

The amphibole-plagioclase NaSi-CaAl exchange thermometer by Holland and Blundy (1994) (expression B) has been extensively applied to calcic amphibole-bearing assemblages from metamorphic and igneous rocks, whereas the more recent calibrations of the amphibole-only thermometer by Ridolfi and Renzulli (2012) (expression 2) and Putirka (2016) (expressions 5 and 6) are employed for determining amphibole-saturation temperatures in hydrous magmas. However, a test of these expressions performed on experimental data compiled from the literature reveals significant inaccuracies, tending expression B to underestimate temperatures in high-Mg amphibole, and the amphibole-only expressions to overestimate temperatures in amphibole with either low Mg or high AlVI occupancies. Amphibole NaM4 and Fe3+ occupancies can also affect significantly the accuracy of expression B. In this work, we present three new accurate calibrations (expressions A1, A2, and B2) of the amphibole-plagioclase NaSi-CaAl exchange thermometer calculated by robust regression methods based on multiple maximum-likelihood estimators (MM-estimators; Yohai 1987), considering various calibration and test data subsets to evaluate the robustness of the derived parameters in the thermo-dynamic models, and the accuracy and precision of the expressions. Non-ideality in plagioclase was corrected using the ternary feldspar solution model of Elkins and Grove (1990) in expressions A1 and A2, whereas the simplified version of the Darken's Quadratic Formalism (DQF) approach of Holland and Powell (1992) was used in expression B2. The formulation of the multisite macroscopic solution model of Powell and Holland (1993) was used for deriving the mixing parameters of amphibole in the three calibrations. Expression B2 is strictly pressure-independent, while the two others show a negligible dependence on pressure for plagioclase with low orthoclase component (<11 mol%). The three calibrations yield an overall precision close to those reported for the tested amphibole-based thermometers but are significantly more accurate, a requisite for an unambiguous interpretation of precision. The new expressions can be used in a wide range of igneous and high-grade metamorphic rocks that bear subcalcic to calcic amphibole and oligoclase or more calcic plagioclase. However, they must be applied only to amphibole-plagioclase pairs whose compositions lie in the optimal region of use prescribed in the work. [ABSTRACT FROM AUTHOR]

Seek for new Rare Earth Elements (REE) sources encourage looking for easily available sources located in Europe. REE in evolved magmatic systems are predominantly associated with alkali environments. Therefore, it was decided to identify the content of REE in alkali igneous rocks of the Winna Góra basalt quarry located in Lower Silesia, Poland. In this study, a commercially available basalt aggregate from Winna Góra deposit located in the south-western part of Poland near Jawornik was examined for REE content. Mineral content and chemical composition were examined with a light microscope, XRD and XRF, whereas trace element content was measured with the ICP-MS technique. A new method of sample preparation for the purpose of REE identification in basalt aggregate based on pressure microwave mineralisation was developed. Mineral composition and TAS diagram classify aggregate as tephrite. The mineral composition of samples reflects typical mafic and ultramafic rocks. Quantitative mineralogical analysis by the Rietveld method showed that the main minerals are anorthite (46.7%) and augite (37.4%) with a minor content of forsterite (7.5%), nepheline (7.4%) and apatite below 1%. The total content of REE does not exceed 132 ppm. Chondrite normalised curves show the highest concentration of La and Pr. In the case of HREE, the majority of elements (Eu, Tb, Dy, Ho, Er, Yb) concentrations were below 1 ppm, a Tm and Lu were not detected. The low enrichment in HREE was also reflected in La/Gd ratios. Obtained results are comparable to the REE contents in the western part of the Cenozoic European Volcanic Province. [ABSTRACT FROM AUTHOR]

Currently, the metals of Rare Earth Elements (REEs) have become very critical to various modern technologies ranging from cell phones and televisions to LED light bulbs and wind turbines. This work was carried out as the Pakistani contribution to the National-scale Geochemical Survey of South and Central Asia (NGSSCA) project. The objective of this study was to document and study the amounts and distribution of REEs in stream sediment of Pakistan, where such national-scale geochemical mapping was launched for the first time. A total of 4277 regular and 168 duplicate samples were collected, encompassing approximately 360,000 km2 of Pakistani outcrop regions. The findings from the geochemical analysis of stream sediment in Pakistan revealed a spectrum in the total Rare Earth Elements (ΣREE) concentration, spanning from 10.22 mg/kg to 1403.1 mg/kg, averaging at 132.5 mg/kg. LREEs are relatively enriched compared to HREEs with an average of LREEs/HREEs of 3.08. The distribution patterns of REEs in stream sediment are demonstrated. It's has been concluded that high concentrations of REEs are mainly distributed in the Himalayan fold and thrust belt, the Karakoram terrane and the Kohistan island arc in the northern part of Pakistan. The bedrock mineralogy and lithology significantly affect the distribution patterns of REEs in stream sediments. The national geochemical mapping of Pakistan provides a useful method for locating alkaline igneous rocks and identifying potential REE mineralization. • The first National-scale Geochemical Mapping in Pakistan was launched. • The bedrock mineralogy and lithology affect the distribution of REEs in stream sediments. • Some new target areas/belts for the REE mineralization are predicted. [ABSTRACT FROM AUTHOR]

[Display omitted] • Triassic syenitic complexes in Songxian were emplaced at 235–210 Ma. • Two types of syenites, alkali-feldspar syenite and aegirine-augite syenite, might originate from two different magma episodes. • The parental magma was formed by mixing of mantle-derived melts and crustal materials. • The subduction of oceanic crust led to back-arc extension and crust-mantle interaction. Alkaline igneous rocks usually provide significant information on the mantle-derived components, magmatic processes and crust–mantle interaction due to their deep source. The Songxian syenite, located in the Xiong'er terrane of the Qinling Orogen, is one of the most typical alkaline intrusions in the Early Mesozoic. Geochemical, geochronological and in situ Sr–Nd–Hf isotopic analyses were conducted on the alkali-feldspar syenite and aegirine-augite syenite samples collected from the Songxian syenite, in order to reveal the magma sources, petrogenesis and possible geodynamic implications. All the rock samples are enriched in alkali (Na 2 O + K 2 O = 11.74 to 15.14 wt%), light rare earth elements and large ion lithophile elements, and depleted in high field strength elements. Zircon LA–ICP–MS U–Pb dating of medium- and fine-grained alkali-feldspar syenites yield emplacement ages of 235.5 ± 0.9 Ma and 232.7 ± 3.3 Ma, respectively. In addition, the aegirine-augite syenite generally developed as dyke or vein cutting through the two types of alkali-feldspar syenite in the field, indicating multiple pulses of magmatism. In-situ Sr-Nd isotopic analyses on magmatic apatite yielded (87Sr/86Sr) i ratios from 0.707959 to 0.710414 and ε Nd (t) from −19.3 to −13.9 for alkali-feldspar syenite, while the analyses for aegirine-augite syenite yielded (87Sr/86Sr) i ratios from 0.717948 to 0.721470 and ε Nd (t) from −25.5 to −24.5. The difference suggests that the Songxian syenite may be generated from multi-stage magmatic episodes. The first magmatic incident mainly originated from the partial melting of the enriched lithospheric mantle, mixed with the lower crust-derived melts. The second mixing magma might involve more proportion of Archean to Paleoproterozoic crust-derived materials. During the Early Mesozoic, the Mian-Lue oceanic slab subducted northward to the asthenosphere mantle and induced asthenosphere upwelling. Under the tectonic setting, the mixture of enriched mantle- and crust-derived melts occurred to form the Songxian syenite. [ABSTRACT FROM AUTHOR]

The Bafq-Saghand metallogenic belt is located in the central part of the Kerman–Kashmar tectonic zone and contains 39 individual occurrences of iron oxide-apatite ± REE mineralizations. These mineral concentrations, e.g., Chadormalu, Choghart, Sechahun, and Esfordi, comprise a total of ~ 1500 million tons of iron ore with an average grade of ~ 55% Fe. In terms of origin, time, and geodynamic setting, several modes of formation have been suggested for these ore deposits, including magmatic, hydrothermal, and banded iron formation scenarios. In the present study, the tectonic setting and metallogeny of iron oxide-apatites of the Bafq-Saghand belt are investigated utilizing trace element geochemistry, age dating, and oxygen isotope analyses. The geochemical characteristics of apatite and magnetite and the δ18O values of magnetite (from − 0.1 to + 2.2 ‰) indicate a dominantly magmatic-hydrothermal (δ18O > + 0.9 ‰) formation process, although primary magmatic mineralizations were locally leached and hydrothermally redeposited (e.g., samples with δ18O < + 0.9 ‰). The Cambrian volcano-sedimentary host rocks to the mineralization is intruded by calc-alkaline tonalite, trondhjemite, granodioritic, dioritic, and granitic rocks that formed in association with subduction of the Proto-Tethys Ocean under the Gondwana supercontinent in the Neoproterozoic to Early Cambrian (525–547 Ma). Additionally, a later geodynamic episode produced intrusions of alkaline syenite and monzosyenite bodies during a continental rifting event. We provide new geochronological constraints for these younger alkaline igneous rocks that document a temporal range from 421 to 447 Ma for their intrusion. In combination with the previously reported overlapping ages of the older calc-alkaline magma bodies (525–547 Ma) with the volcano-sedimentary host rock (528 Ma) and the iron oxide mineralization (510–539 Ma), we can now exclude continental rifting as a geodynamic processes that is linked to ore formation in the region. Our results corroborate that the Bafq iron ore mineralization formed during subduction of the Proto-Tethys Ocean under the Gondwana supercontinent in a near surface continental margin setting. [ABSTRACT FROM AUTHOR]

Despite an apparent north/south topographic dichotomy that formed È4.0 Ga, the young Martian meteorites (Ç2.4 Ga) and first-order remote sensing observations revealed a surface of Mars that is uniformly basaltic. This simplistic vision has been challenged by the discovery of a brecciated meteorite and additional spacecraft data that all point to the presence of alkaline igneous rocks, thereby demonstrating an unexpected igneous diversity on Mars. In the present paper, we review a variety of effusive alkaline rocks (basalts to trachytes) recognized so far in the southern hemisphere of Mars as observed from a unique 4.47 Ga Martian meteorite, as well as ground, and orbital data. The complementary of effusive alkaline rocks and plutonic orthopyroxene-rich rocks in early Mars is discussed. We propose that mantle-derived magmas at high extent of melting at rather low pressure either erupted forming orthopyroxene-rich lavas, or crystallized at shallow crustal depths, fractionating orthopyroxene which sank to the bottom of the chamber and residual alkaline magmas which erupted at the surface of Mars. Widespread low pressure fractionation processes could also be related to heavy bombardment on the early Martian crust generating melt sheets that ultimately differentiated. The Noachian crust is more diverse than being merely basaltic. [ABSTRACT FROM AUTHOR]

Machine learning models enable interpretation of orbital spectral measurements of Venus using laboratory calibration data collected at Venus surface temperatures. Partial least squares models show that total iron content can be accurately predicted using data from the six bands (two in the 1.02 μm window). Prediction errors on total wt% FeO are ±0.50 for common subalkaline volcanic rocks. Accuracy is ±0.42 for wt% FeO in alkaline rocks, and ±2.47 for all 18 igneous samples studied to date. These robust capabilities will allow discrimination of basalt versus rhyolite/granite and elucidate the rock type of the enigmatic tessera terrain on Venus. Plain Language Summary: Because the surface of Venus is robed by a thick CO2‐rich atmosphere and dense clouds, it has long been thought that orbital spectroscopic measurements of its surface were unfeasible. However, a small range of the CO2 spectrum near 1 μm lacks absorption features, providing windows that enable surface analyses. This paper uses a machine learning method known as partial least squares regression to quantify how igneous rock types such as basalt and rhyolite can be distinguished using 440°C laboratory data for those six bands. This advance will make it possible to unequivocally distinguish between basalt and granite/rhyolite rock types on the surface of Venus and resolve questions of its geological history. Key Points: Accuracies of wt% FeOtotal are ±0.50 for subalkaline rocks, ±0.42 for alkali rocks, and ±2.47 for 440°C lab spectra of bothSix‐band remote sensed spectra can easily distinguish basalt (x¯ = 9.80 wt% FeO) from granitic/rhyolitic (x¯ = 2.19 wt% FeO) rocksPartial least squares models show that total iron content can be accurately predicted from high‐temperature lab spectra [ABSTRACT FROM AUTHOR]