Dike Rocks Research Articles

Age and Petrogenesis of Paleoproterozoic Diorites from Dikes of the Baikal Uplift of the Siberian Craton

Abstract ––We carried out a detailed geological, geochronological, geochemical, and isotope study of diorites from a dike located in the central part of the Baikal uplift of the Siberian craton. The geochemical and isotope data obtained for diorites of the studied intrusion were compared with coeval mafic and intermediate igneous rocks of the southern part of the Siberian craton. The U–Pb (ID-TIMS) baddeleyite age of 1862 ± 7 Ma has been estimated for diorite from a dike located in the area of the Onguren Village. The obtained data are the first reliable age determination for the Paleoproterozoic mafic and intermediate igneous rocks of the Baikal uplift, which are part of the South Siberian postcollisional magmatic belt. The dike is of NE strike. The dike rocks correspond in chemical composition to diorites and are highly differentiated varieties (mg# = 36.5–37.4). There are no significant variations in the composition of diorites in the marginal and central parts of the dike. The rocks are characterized by low contents of TiO2, P2O5, and Nb, high contents of Th, Zr, Ba, and LREE, and low negative values of εNd(T) (–5.9 to –6.2). We assume that the diorites formed from the enriched subcontinental lithospheric mantle. The obtained geochemical and isotope data show similar negative values of εNd(T) from –4.3 to –11.6 for most of Paleoproterozoic mafic and intermediate igneous rocks of the South Siberian postcollisional magmatic belt within the Aldan Shield, the Baikal uplift, and the Irkut block of the Sharyzhalgai uplift. These rocks correspond in geochemical features to rocks resulted from the melting of subduction-modified lithospheric mantle sources in the postcollisional extension setting at the final Paleoproterozoic stage of formation of the Siberian craton.

Титанониобаты и ториевые минералы в карбонатизированных флюидоэксплозивных дайках Среднего Тимана

Rare-metal and thorium mineralization (uranium pyrochlore, niobaeschynite-(Ce), aeschynite-(Ce), thorite, and thorianite) was studied in the dike complex of fluid-explosive rocks of the Middle Timan. The source of thorium and rare-metal-rare-earth elements was carbonate-alkaline solutions of carbonatites, paragenetically associated with the formation of dike rocks.

Unraveling 800 Ma of pegmatite formation in the western Grenville Front tectonic Zone near Sudbury, Canada

The origin of pegmatites has been at the core of petrological research for decades, but despite much effort their origin remains controversial – protracted fractionation of a causative felsic magma versus anatexis of an appropriate protolith. To address this controversy, we present the results of U-Pb analyses (zircon (n = 774), monazite (n = 230), xenotime (n = 295)) for 32 well characterized pegmatites from an extensive swarm of felsic dike rocks outcropping, along a 12 km transect ca. 12 km south of Sudbury (Ontario, Canada) in the westernmost part of the Grenville Front Tectonic Zone (GFTZ). Collectively these rocks exhibit a remarkably large morphological, textural and mineralogical variation related to the crystallization of three distinct pegmatite-forming events that span 800 Ma. The derived concordant U-Pb ages of the dated phases coincide with the late Paleoproterozoic (ca. 1740 Ma) Yavapai orogeny, the Mesoproterozoic (ca. 1450–1430 Ma) Chieflakian event, and the early Neoproterozoic (ca. 1000–970 Ma) Grenville orogeny. Field observations and related geochemical data suggest the two older events are genetically related to regional magmatism (i.e., fractionation of a progenitor), whereas the Neoproterozoic pegmatites were generated via partial melting of an appropriate protolith at depth. The data therefore support a duality of models for pegmatite genesis. We emphasize the important role of imaging (CL and BSE) as an integral part of our protocol, as this revealed widespread coupled dissolution-precipitation (CDP) replacement textures and metamictization in both zircon and xenotime, the latter due to high U contents (i.e., >1000 pm). Interestingly, the Neoproterozoic pegmatites show similar U(±Th), Nb(±Ta) and REE enrichments like their contemporaneous Sveconorwegian counterparts. Many zircons record U-Pb system resetting at ca. 220–200 Ma which is possibly related to the far-field effects of the onset of the Central Atlantic Magmatic Province (CAMP) related to the opening of the Atlantic Ocean. Finally, this study shows that anatexis is a viable process of rare-element pegmatite formation, even in areas rich in potential parental granites, which suggests that anatectic rare-element pegmatites might be globally under-recognized.

Mineralogy of K-Rich Rocks from the Jharia Basin in Jharkhand: Indications for Cretaceous Lamproite Magmatism in Eastern India

AbstractPotassic dikes of early Cretaceous age (ca. 115 Ma) are emplaced in the Gondwana sedimentary basins of the Damodar valley in eastern India. Two potassic dikes in the Jharia basin (Ena and Moonidih) are characterized by the presence of olivine macrocrysts and phenocrysts, together with microphenocrysts of olivine, phlogopite–biotite, ilmenite, and apatite. These are set in a groundmass of phlogopite, apatite, ilmenite, spinel, and K-feldspar. Microphenocrystal and groundmass Al-Na-poor diopside and Al-poor Ti-rich amphibole are present in the Ena dike, whereas rutile, pyrite, galena, Zr-Ti-rich garnet, and quartz are minor phases occurring in the Moonidih dike. Two populations of relatively fresh olivine (I and II) are found in the Ena dike, in contrast to the Moonidih dike, where olivine macrocrysts and microphenocrysts are completely replaced by secondary magnesite, serpentine, and talc. The occurrence of fresh olivine in the Ena dike is reported for the first time in the Jharia basin. High forsterite (Fo) and Ni together with low Ca and Mn contents of the olivine-I macrocrysts suggest a mantle-derived xenocrystic origin. In contrast, the olivine-II population has high Ca and Mn, but relatively low Fo and Ni, suggesting a magmatic origin. Rimward decreasing Al and increasing Fe contents in zoned phlogopite crystals, plus the presence of groundmass spinel with compositions along the titanomagnetite trend (T2), indicate the lamproitic affinity of the K-rich dike rocks. Using a mineralogical-genetic classification scheme, the Ena and Moonidih dikes are classified as olivine-phlogopite-diopside-apatite-amphibole-feldspar lamproite and olivine-phlogopite-apatite-feldspar lamproite, respectively. We use the compositional variations of phlogopite, amphibole, apatite, and spinel to understand better the magmatic evolution and crystallization history of these potassic dikes. The Cretaceous lamproite magmatic event in eastern India was sourced from ancient metasomatized lithospheric mantle, with low-degree partial melting either triggered in the periphery of the impinging Kerguelen mantle plume head or induced by distant subduction.

PYROXENES OF ALKALINE-ULTRABASIC ROCKS FROM NORTH-WESTERN PART OF THE UKRAINIAN SHIELD

In alkaline-ultrabasic rocks from North-Western part of the Ukrainian Shield pyroxenes are predominantly presented by diopsides with various contents of Cr2O3 (up to 2.4%, chrome diopside), Na2O and Al2O3 (to 7.6%). But correlation between contents of Al2O3 and Na2O generally is absent except two samples. Natrium goes into composition of acmite, cosmochlore or jadeite minals. In pyroxenes with high Al2O3 aluminum goes into tetrahedral positions. Pyroxenes (include aegirines) with increase TiO2 content (to 1.5%) rarely occur. Aegirine and intermediate between latter and diopside aegirine-diopsides have limited development. They could crystallize in at least eroded dike rocks that consist of melteigite porphyres with high agpaicity ((Na+K)/Al ≈1). Majority of studied pyroxenes crystallized from magnesian (to 22% MgO) primitive alkaline-ultrabasic melts in hypabyssal intrusions. It is supposed that limited amount of intermediate aegirine-diopsides or a gap in series diopside-aegirine is caused by the crystallization of alkaline and subalkaline amphiboles.

In situ elemental and Sr-Nd isotopic compositions of hydrothermal apatite from the Shazhou U deposit in the Xiangshan complex: Implications for the origins of ore-forming fluids of volcanic related U deposits in South China

• In situ Sr-Nd isotopes of apatite are effective in tracing origins of ore forming fluids in the Shazhou U deposit. • The reducing U-poor fluid was derived from mantle-derived magma which formed the mafic dikes in wall rocks. • The oxidizing U-rich fluid originated from percolation of meteoric water in the adjacent red-bed basins. • The Late Cretaceous mafic magmatism and red-bed basins are two key factors controlling U mineralization in South China. The origin of ore-forming fluids of volcanic related U deposits remains controversial. This study reports in situ elemental and Sr-Nd isotopic compositions of apatite associated with U mineralization from the Shazhou volcanic related U deposit in South China, which provides a new perspective to constrain the origin and evolution of its ore-forming fluids. Hydrothermal apatites from the hematized rocks and U-mineralized rocks show distinct textures and chemical features, indicating two types of fluids involved in the U mineralization process. The hematitization fluid was oxidizing and enriched in U and Cl. A reducing fluid with lower Cl/F and U was introduced and mixed with the oxidizing hematitization fluid to cause U precipitation. Apatite from the hematized rocks has a lower 87 Sr/ 86 Sr (0.709246–0.714383) than that of apatite in U ore veins (0.710383–0.719318). The εNd(t) of apatite in the hematized rocks is from −7.6 to −9.4, whereas apatite in U ore veins has higher εNd(t) ranging from −1.2 to −8.4, close to that of mafic dikes intruded into the volcanic rocks. In situ Sr-Nd isotopes of apatite indicate the oxidizing fluid originated from the red-bed basins, whilst the origin of the reducing fluid was related to the mantle-derived mafic dikes. The reducing fluid has experienced assimilation by the metamorphic basement rocks to gain higher radiogenic strontium. This study demonstrates that in situ elemental and Sr-Nd isotopic compositions of apatite are effective in identifying different ore-forming hydrothermal fluids and constraining their origins and chemical evolution.

Ultrapotassic Aluminosilicate Melts: Specifics of Formation by the Example of Synnyrites from the Synnyr Massif

Abstract —To reveal the formation conditions of synnyrites in the Synnyr alkaline pluton, we studied melt inclusions in the minerals of shonkinites and pseudoleucite syenites, in apatite segregations in pyroxenites, shonkinites, and synnyrites, and in the minerals of later monchiquite–camptonite dikes. Based on the obtained and earlier published data, a conclusion has been drawn that all plutonic rocks of the massif formed from the same parental alkali-basaltic magma during long-term crystallization differentiation and fractionation in a closed system excluding a release of volatile components. Similar minerals in the rocks crystallized at similar temperatures in the same sequence: clinopyroxene (1280–1150 °C) → leucite (1250–1200 °C) → K-feldspar (1200–1180 °C) → apatite (above 1180–1050 °C) → nepheline and kalsilite. The composition of the parental magma during crystallization evolved toward an increase in Si, Al, and K contents and a decrease in Fe, Mg, and Ca contents, i.e., toward melaphonolite and phonolite melts. The differentiation and fractionation processes led to the separation of minerals according to their specific gravity: Heavy minerals (clinopyroxene, ore minerals, and apatite) descended to the bottom of the magma chamber, forming the lower melanocratic series, and light minerals (leucite, K-feldspar, and foids), together with the residual melt, accumulated in the upper horizons of the chamber, forming the upper leucocratic series of rocks. During crystallization, the amount of fluids increased. At 920–830 °C, the fluids contained 3033–4051 mg/kg CO2, 397–644 mg/kg H2O, and 42.7–83.7 mg/kg CO. At the early high-temperature stage, when the amount of fluids was insignificant, the trend of magma transformation coincided with the trend of basaltoid crystallization. This fact is evidenced by the homogenization temperatures and chemical composition of inclusions in the minerals of monchiquite–camptonites and alkali basaltoids, similar to those in the plutonic rocks of the massif. Clinopyroxene crystallized in dike rocks at 4.58 kbar at a depth of 10–12 km. At the stage of crystallization of feldspars, when the amount of fluids in melts significantly increased during the formation of plutonic rocks and drastically decreased during the formation of basaltoids, the formation trends of these rocks became different. The trend of basaltoid crystallization was directed toward trachyte melts with an increase in Si contents and a decrease in Fe, Mg, Al, and alkali contents. During the formation of plutonic rocks of the massif, the high water pressure prevented the formation of plagioclase, and the melts became more enriched in Al and K and acquired a high-alumina ultrapotassic composition, forming kalsilite–nepheline–K-feldspar synnyrites at the final stages of transformation. A conclusion has been drawn that synnyrites crystallized from the residual products of differentiation and fractionation of alkali-basaltic magma in the temperature range slightly above 1050–1180 °C in a closed system excluding a release of volatiles. The occasional occurrence of synnyrites is due to the limited natural occurrence of closed magma chambers, macroanalogs of inclusions of mineral-forming media in minerals.

Geochemistry and Petrogenesis of Lower Jurassic Mafic Rock Suites in the External Rif Belt, and Chemical Geodynamics of the Central Atlantic Magmatic Province (CAMP) in Northwest Morocco

We present new field evidence, geochemical and isotopic data, and age constraints on Lower Jurassic mafic rock suites within a >200-km-long curvilinear belt in the Rif orogenic belt in northern Morocco and show that these rock assemblages formed as part of the Central Atlantic Magmatic Province (CAMP). The CAMP represents a large igneous province that straddles the edges of the modern peri-Atlantic continents. It developed ~200 Ma, following the initiation of the breakup of Pangea. Main magmatic rocks in the Rif External Zone include basaltic lavas, massive dolerite, and isotropic and cumulate gabbros, all intruded by dolerite and trondhjemite dikes and sills. Available U-Pb zircon ages from dolerite, gabbro, and trondhjemite dike rocks are , , and , respectively. Based on their geochemical affinities and isotopic compositions, the analyzed rocks define basalt-dolerite and gabbro-cumulate gabbro-trondhjemite groups. The basalt-dolerite group samples are subalkaline in nature and have low TiO2 contents, whereas the gabbro-cumulate gabbro-trondhjemite group samples are alkaline and display high TiO2 values. Most samples are tholeiitic in character and show large-ion lithophile and light rare earth element enrichment and high field strength element depletion compared with normal mid-ocean ridge basalt (MORB). Samples of both groups display low 143Nd/144Nd201 Ma (0.51182–0.51262) and high 87Sr/86Sri ratios with ɛNd values ranging from −1.51 to +4.85. The basalt-dolerite group rocks have enriched MORB compositions, compatible with the low-Ti CAMP suites, whereas the gabbro-cumulate gabbro-trondhjemite group rocks have oceanic island basalt compositions reminiscent of high-Ti CAMP suites in other continents. Magmas of the gabbro-cumulate gabbro-trondhjemite group underwent differentiation through tholeiitic fractionation. Magmas of the rocks of both groups included melt components, originated from partial melting of a previously subduction-modified subcontinental lithospheric mantle. Our results indicate that the Early Jurassic CAMP magmatism in northern Morocco marked a major episode of continental magmatism before the opening of the Maghrebian Tethys between Africa and Iberia in the latest Jurassic.

Activity-educational aspects of geological excursions

The purpose of this article is to discuss the educational tour as a form of educational process in the activity-the educational aspect of the geological excursion in the study of rock outcrops career «Borok» of Novosibirsk as a geological object of interest for educational tours and training-practical work. To write the article, we used methods of comparative analysis, generalization, field geological observations, sampling, cross-section sketches, descriptions of outcrops, including working with a mountain compass and methods of conducting a training geological-geographical and geoecological route, drawing up a map of the territory, laboratory studies of rocks. The absolute advantage of the Borok quarry is its location, as well as optimal conditions for a thorough inspection and description of rock outcrops. Branched dikes and veins are visible in the walls of the quarry, as well as the overlap of igneous Paleozoic rocks with sedimentary later deposits. Dumps of various Intrusive igneous, dike rocks and pegmatites, hydrothermal veins with ore minerals are of educational interest during excursions. The Borok quarry cooperates with schools, colleges, and Universities in Novosibirsk and is a platform for educational excursions to the production site and a place for training practices, as well as a venue for educational Olympiads in Geology and Geoecology. On the example of one of the production facilities of the city of Novosibirsk - the stone quarry «Borok», the possibilities of organizing and conducting geological excursions in order to study the geological structure of the territory, consolidate theoretical geological and geoecological knowledge, acquire skills in educational and practical work and analyze the results obtained are demonstrated.

Carbonatite-Like Rock in a Dike of the Aikhal Kimberlite Pipe: Comparison with Carbonatites of the Nomokhtookh Site (Anabar Area)

Abstract ––A dike of rock similar in composition to carbonatites has been found in the Aikhal diamondiferous pipe of the Alakit–Markha field of the Yakutian kimberlite province (YaKP). The fine-grained rock of essentially carbonate composition (dolomite and calcite) rich in thin-platy phlogopite contains minerals typical of carbonatites: monazite, baddeleyite, and pyrochlore. In the high contents and distribution of incompatible elements the rock differs significantly from kimberlites and is transitional from kimberlites to carbonatites. The content of incompatible elements in this rock is 3–5 times lower than that in carbonatite breccias of the pipes in the Staraya Rechka kimberlite field of the YaKP (Nomokhtookh site). The compositions of accessory trace element minerals from the Aikhal dike rock and the Nomokhtookh carbonatite breccias are compared. An assumption is made that the high contents of incompatible elements in the carbonatite-like rock, which caused the crystallization of accessory minerals, are due to the differentiation of kimberlite melt/fluid. The high Sr isotope ratios indicate that the rock altered during hydrothermal and metasomatic processes. The obtained data on the composition of the carbonatite-like rock cannot serve as an argument for the genetic relationship between the Aikhal kimberlites and typical carbonatites. The genetic relationship between kimberlites and carbonatites in the northern fields of the YaKP remains an open issue.

Interaction between mafic dike rocks and salt deposits in the Rhine Graben, southwest Germany

ABSTRACT Dikes of primitive olivine melilitites and monchiquites intruded into an Oligocene (Rupelian) potash salt deposit near Buggingen (SW Germany). Ocelli and amygdules reveal distinct mineral assemblages depending on whether the dike rocks are in direct contact with the potash layer or with bituminous shales (Fish Shale). Samples in contact with the potash salt layer show roundish textures that contain smectite ± talc ± chlorite, calcite, and in cases anhydrite and halite, while those close to the bituminous shale mainly comprise smectite, calcite, zeolite group minerals, and analcime. No textural or mineralogical evidence for high-temperature (magmatic) interaction between the dike rocks and the evaporites was observed. This is presumably related to (1) a very low magmatic water activity in the magma, which prevented exsolution of aqueous fluids and appreciable dissolution of the salt, and (2) fast cooling of the magmas, inhibiting melting of the salt deposits and potential liquid mingling and/or assimilation processes. Halite formation in the dike rocks is, rather, related to later, post-magmatic hydrothermal fluids that previously interacted with the salt-rich host rocks. Alteration of the initially glassy groundmass to smectites and zeolites caused an enrichment of Na in the residual fluid, but halite saturation was not attained, as indicated by the absence of groundmass halite. Only fluid–rock interaction in millimeter-sized vugs caused halite precipitation via desiccation by swelling of previously formed clay minerals. Locally, the boron silicate datolite formed in pseudomorphs after olivine. Its precipitation was controlled by the Si and B supply provided by the breakdown of serpentine and smectite.

Щелочно-ультраосновные породы Новобобровского рудного поля (Средний Тиман): минералогия, петрография

Minerals of disintegrated alkaline-ultrabasic dike rocks exposed by wells within the rare-metal–rare earth Novobo-brovsky ore field (Middle Timan) were studied. Microprobe studies were conducted in CCU "Geoscience" (Syktyvkar) and the Institute of Experimental Geology, RAS (Chernogolovka). Primary mineral parage-neses are difficult to diag-nose due to strong secondary alteration of rocks. The primary minerals are phlogopite (XMg = 0.64–0.89) and minerals of the chromespinelides group (the central parts are represented by chrompicotite, and the marginal zones – by ferrich-romite); the secondary minerals are represented by the chlorites group (talcochlorite, clinochlorite, pennine). The rock is saturated with numerous xenoliths of quartzite sandstones, and has also undergone fenitization processes, which is why the development of rare metal–rare earth mineralization is observed in the rock: columbite, rutile ↔ Nb-rutile ↔ ilme-norutil, monazite, Th-monazite, more rare phosphates (complex phosphates and hydroaluminophosphates of lead similar in composition to dragmanite, differing by the presence of Mn, Ba, K). The studied primary mineral parageneses are typical for the picrite-lamprophyre Chetlas dike complex developed here; the superimposed rare-metal–rare-earth mineralization is specific for dike rocks developed within the ore fields of the Kosyu ore cluster.

Magma Genesis and Arc Evolution at the Indochina Terrane Subduction: Petrological and Geochemical Constraints From the Volcanic Rocks in Wang Nam Khiao Area, Nakhon Ratchasima, Thailand

Volcanic rocks and associated dikes have been exposed in Wang Nam Khiao area, Nakhon Ratchasima Province, northeastern Thailand where complex tectonic setting was reported. These volcanic rocks are classified as rhyolite, dacite, and andesite while dikes are also characterized by andesitic composition. These dikes clearly cut into the volcanic rocks and Late Permian hornblende granite in the adjacent area. Rhyolite and dacite are composed of abundant plagioclase and quartz whereas andesite and andesitic dike contain mainly plagioclase and hornblende with minor quartz. The volcanic rocks typically show plagioclase and hornblende phenocrysts embedded in fine-grained quartz and glass groundmass whereas dike rocks contain less glass matrix with more albitic laths. P-T conditions of crystallization are estimated, on the basis of Al-in-hornblende geobarometry and hornblende geothermometry, at about 4.5 – 5.5 kbar, 861 – 927 oC and 4.8 – 5.5 kbar, 873 – 890 oC for the magma intrusions that fed volcanic rocks and andesitic dikes, respectively. Whole-rock geochemistry indicates that these rock suites are related to calc-alkaline hydrous magma. The enriched LILE (e.g. Rb, Sr) and depleted HFSE (e.g. Nb, Ce, Ti), with similar REE patterns indicate arc magmatism. The results of this study are comparable to the continental arc magmatism along the Loei Fold Belt as a consequence of the Late Permian Palaeo-Tethys subducted beneath Indochina Terrane.

The influence of the soil constitutive models on the seismic analysis of pile-supported wharf structures with batter piles in cut-slope rock dike

Abstract In coastal regions, earthquakes caused severe damage to marine structures. Many researchers have conducted numerical investigations in order to understand the dynamic behavior of these structures. The most frequently used model in numerical calculations of soil is the linear-elastic perfectly plastic model with a Mohr-Coulomb failure criterion (MC model). It is recommended to use this model to represent a first-order approximation of soil behavior. Therefore, it is necessary to accommodate soil constitutive models for the specific geotechnical problems. In this paper, three soil constitutive models with different accuracy were applied by using the two-dimensional finite element software PLAXIS to study the behavior of pile-supported wharf embedded in rock dike, under the 1989 Loma Prieta earthquake. These models are: a linear-elastic perfectly plastic model (MC model), an elastoplastic model with isotropic hardening (HS model), and the Hardening Soil model with an extension to the small-strain stiffness (HSS model). A typical pile-supported wharf structure with batter piles from the western United States ports was selected to perform the study. The wharf included cut-slope (sliver) rock dike configuration, which is constituted by a thin layer of rockfill overlaid by a slope of loose sand. The foundation soil and the backfill soil behind the wharf were all dense sand. The soil parameters used in the study were calibrated in numerical soil element tests (Oedometer and Triaxial tests). The wharf displacement and pore pressure results obtained using models with different accuracy were compared to the numerical results of Heidary-Torkamani et al.[28] It was found that the Hardening Soil model with small-strain stiffness (HSS model) gives clearly better results than the MC and HS models. Afterwards, the pile displacements in sloping rockfill were analyzed. The displacement time histories of the rock dike at the top and at the toe were also exposed. It can be noted that during the earthquake there was a significant lateral ground displacement at the upper part of the embankment due to the liquefaction of loose sand. This movement caused displacement at the dike top greater than its displacement at the toe. Consequently, the behavior of the wharf was affected and the pile displacements were important, specially the piles closest to the dike top.

Age, Composition, and Geodynamic Setting of Granitoids and Dike Rocks from Cape Svyatoy Nos, Eastern Arctic

Abstract—Granitoids and dikes of Svyatoy Nos pluton of Cape Svyatoy Nos in the northwestern part of Verkhoyansk-Kolyma folded area, cutting terrigenous and volcanogenic-sedimentary rocks of Upper Jurassic–Lower Cretaceous, are considered. Obtained U‒Pb SIMS geochronological data on zircons from granitoids and dike rocks indicate, that their crystallization ages correspond to Aptian‒Albian (119–111 Ma). Petrography and geochemical affinitites of rocks allow to refer granitoids and felsic dikes to I-type granites. Similarity in chemical composition with coeval granitoids of Great Lyakhovsky Island, the most northern member of Chokhchuro‒Chokurdakhsky submeridional belt of granitoids and Aptian‒Albian granitoids of sublatitudinal belt of Anyui‒Chukotka fold belt is shown. Earlier it was established by many authors, that intrusion of Aptian-Albian granitoids and dikes (117–105 Ma) on the Arctic margin of Chukotka and in the northwestern part of Verkhoyansk‒Kolyma folded area occurred during extension. Aptian‒Albian age, post-shortening character of intrusion and similarity of Svyatoy Nos granitoids in chemical composition with mentioned above Aptian-Albian granitoids allow to refer them to a single stage of postcollisional extension.

ГЕОЛОГІЧНА БУДОВА ТА ПЕТРОГРАФІЯ ОСТРОВІВ ВЕДЕЛЬ (АРХІПЕЛАГ ВІЛЬГЕЛЬМА, ЗАХІДНА АНТАРКТИКА)

The Vedel Islands are a small island group that is part of the Wilhelm archipelago in the West Antarctica. They are located near the Graham Coast of the Antarctic Peninsula at a distance of 12 km from Akademik Vernadsky Ukrainian Antarctic Station. Until recently, the Vedel Islands were a "white spot" on all existing geological maps. In 2019, during the seasonal work of the 24th Ukrainian Antarctic expedition, the authors first carried out field geological researches on the Vedel Islands. The main goal of the geological survey was reconnaissance and large-scale geological mapping. The general ideas about the geological structure of the study area were developed by further processing of the collected materials. The preliminary data about the mode of occurrence, the geological ages, the petrographic peculiarities and the ore potential of the local rocks were also obtained. It was first established that multiple-aged intrusive-magmatic formations take part in the geological structure of the Vedel Islands. The intermediate compositions of the plutonic rocks namely the diorites and quartz diorites are the most common among them. The gabbroids and the tonalites are less common. The least common ones are hypabyssal and subvolcanic dike rocks namely microdiorites and diabases. The plutonic rocks were formed in at least three intrusive phases with a homodromous order of their intrusions. The most ancient among them are gabbroids. The Early Cretaceous age for their formation is assumed by analogy with the petrographically similar rocks of the Tuxen-Rasmussen layered gabbroid intrusion (TRGI). The tonilites are the youngest plutonic rocks on the Vedel Islands. It is assumed that their formation at a deep level took place in the Late Cretaceous, although their tectonic exhumation and the final erosion outcropping occurred in the Paleogene and ended in the Neogene. In the process of the exhumation, the plutonic rocks were intruded by hypabyssal dikes of microdiorites. The youngest subvolcanic diabase dykes intruded the tonalites supposedly after their complete erosion outcropping i. e. in Neogene or even Quaternary. Like TRGI and other layered gabbroid intrusions of the Wilhelm archipelago, the Vedel island gabbroids contain iron-titanium oxide-ore and copper-silicate mineralization, which requires further study. The additional researches are also needed to clarify the age, origin, petrography and mineralogy of the numerous veins of aplite-pegmatoid granite which intrude gabbroids and diorites on the Vedel Islands.

ОНГОНИТОВЫЕ ДАЙКИ ВОСТОЧНОГО КАЗАХСТАНА И СПЕЦИФИКА ИХ РУДОНОСНОСТИ

Goal of the research is to study regularities, age, material composition and ore content of ongonite-like dike belts of East Kazakhstan. Methods are field works carried out within Kalba-Narym shear zone where dike belts are developed. Geological and structural position of dikes and their age ratio to granitoids of Kalba-Narym pluton and ore formations have been determined. The samples were selected from varieties of ongonite dikes. Microprobe analyses have been carried out on a scanning election microscope JSM 6390 with an energy-dispersive add-on device, besides, mass-spectrometer researches have been conducted on ICP-MS. The purpose of these is to identify mineralogical and geochemical specialization of dike rocks. Findings. The following has been found due to the conducted researches and comparison analysis with other regions: Two groups of heterochronous dike belts were formed during Hercynian Period in geological structures of East Kazakhstan comprised in general system of Central Asian belt. The dike belts belong to gabbro- diorite – granodiorite – plagiogranite series, and the groups are of pre-batholite (C2-3–C3) and post-batholite (P2) types. Late postbatholite dikes of quartz porphyrites and quartz albitophyres of Mirolyubovsky complex (P2) refer to ongonites. Probably, they are derivatives of deep residual magma chambers. In the course of the work, ongonites geochemical differentiation into rare metals(Ti, Nb, Li, Sn, W and other) and rare alkalies has been established. The researches have shown that ongonite-like dikes are of post-mineral nature that is proved by their position in relation to ore bodies and by other factors. Besides, no rare metal ore of practical significance has been found within these dikes. Scientific novelty and practical application. It can be assumed that greater development of gabbro- diorite – granodiorite – plagiogranite dikes within the known and supposed ore fields, as well as specialization of rocks that dikes are composed of, enable to consider them as prospecting indicators of concealed rare metal objects. To study dike formations of this kind is very important for reconstruction of geodynamic environments, for development of correlation patterns of granitoid magmatism and for studying ore formation processes. By all means, all this can be used in geologic mapping practice, especially on the closed territories.

Conditions of accumulation and fractionation of zirconium and hafnium in alkaline-carbonatite systems

The patterns of the distribution and fractionation of strategic metals (Zr, Hf) in the Kugda intrusion (Polar Siberia) have been studied. The contents of these elements significantly exceed their concentrations in other rocks (Zr 246 ppm, Hf 7.4 ppm). A significant increase in Zr and Hf from early rocks (olivinite and melilite rocks) to later differentiation products, syenites with up to 570 ppm of Zr and 16 ppm of Hf, has been revealed. During the evolution of the Kuga magmatic system, notable fractionation of Zr and Hf occurred. The Zr/Hf ratios in the dike rock, similar in composition to the primary Kugda Massif magma, and the early intrusions are fairly close to that of chondrite (Zr/Hf = 37 [1]), while in the latest phases this ratio increases by almost 5-fold. Our study showed that the distribution coefficient of Hf (Kd = 0.58) in alkaline pyroxenes is noticeably higher than that of Zr (Kd = 0.40). Consequently, fractionation of this mineral leads to an increase in the Zr/Hf ratio in the residual liquids. Another mineral concentrating up to 400 ppm of Zr and up to 1520 ppm of Hf is perovskite, which has a very wide crystallization field in the rocks of the Kugda Massif, especially in the earliest olivinite. The data obtained showed that the Zr/Hf ratio in the perovskite of olivinite varies between 2327, that is, noticeably below both the chondritic and the primary magma values. Early crystallization of perovskite is the main reason for increasing the Zr/Hf ratio in melilitolites (up to 54). Thus, the main process of forming the Kugda Massif was continuous crystallization differentiation, accompanied by a noticeable fractionation of rock-forming and accessory minerals (pyroxene and perovskite).

Preparation of Stone Castings from Olivine Dolerite

The subject of this study is olivine dolerite, a holocrystalline variety of basic volcanic and dike rocks of the normally alkaline rock subclass of the basalt family. Based on innovative methods combining physicochemical computer simulation and experimental studies, we have developed processes for preparing melts and modifying the composition of this magmatic rock for the fabrication of glass-ceramic materials. Such melts offer mineralogical and chemical homogeneity and high flowability, and their crystallization behavior meets requirements for stone casting. The mineralogical composition of such melts can be modified by melting in different atmospheres (oxidizing, reducing, and inert).

Geochemical features of dike rocks of the Argentine islands and the near area of the antarctic peninsula (Western Antarctica)

The block of the Antarctic Peninsula is part of a magmatic arc formed along the southwestern part of the paleo-Pacific margin of the Gondwana supercontinent. Currently, subduction processes continue only in its northwestern part — in the region of the South Shetland islands, and to the southwest of it — there is a passive segment of the continental margin, within which the Argentine islands are located. Here, subduction was completed in the late Miocene-Early Pliocene. In the geological structure of the Argentine islands archipelago, the rocks of the Upper Jurassic volcanic group (AP Volcanic Group) and intrusive batholiths of the batholiths (AP batholiths) are distinguished. In them, there are numerous dikes of basic, medium and acidic compositions. The activation of dyke magmatism on the passive margin of the Antarctic Peninsula was probably connected with subduction processes in its northwestern part.The age sequence of dike formation in the rocks of the Antarctic Peninsula (AP) volcanic Group and intrusions of the gabbroids and granitoids of the Andean complex in the Argentine Islands and the near area of the Antarctic Peninsula is determined. The early dikes of the dacites in the volcanogenic stratum of the AP volcanic Group and the gabbrodiabases in the gabbroids of the Andean complex have a submeridional and northwestern strike. After the introduction of the granitoids of the Andean complex, dikes predominantly of the sublatitudinal and northeasterly strike are formed. The early dikes in the gabbroids of the Andean complex are Fe-Ti cumulates, and in granodiorite intrusions they are represented by aplites, probably formed from the residual magma of these intrusions. Later dikes were formed, probably due to the melting of the metasomatized mantle source at moderate depths under the influence of plumes. To their primitive (initial) melts, the composition of high-magnesian dike rocks is probably close. Products of deep mantle (plume) sources in the sample of selected samples were not detected. The dike rocks of this region according to their geochemical characteristics correspond to the mature island-arc formations of the calc-alkaline series.