Jurassic magmatic bodies of mountainous Crimea in the Bodrak River catchment (Southwestern Crimea)

The synthetic (geological and petrochemical) study of Jurassic magmatic bodies in the catchment of the Bodrak River (mountainous Crimea) is conducted. Their structural position and a Middle Jurassic age were determined. The magmatic bodies of mountainous Crimea were compared to those of the Lozovskaya zone. The study considers the geodynamic settings of the Middle Jurassic magmatism in mountainous Crimea.     

New paleomagnetic data of the Middle Jurassic igneous complex in the Bodrak River valley, Mountainous Crimea

In this paper, the results of paleomagnetic studies for the Middle Jurassic subvolcanic bodies and volcanogenic-sedimentary rocks that are exposed in the Bodrak River valley within the limits of the second range of the Crimean Mountains are presented. Detailed magnetic cleanings showed the applicability of most of the sampled objects for paleomagnetic studies. The natural remanent magnetization of the examined sample is usually the sum of two components; the most stable of them possesses a bipolar distribution, indicating its primary character. The similarity between the paleomagnetic directions of subvolcanic bodies and nearly coeval volcanogenic-sedimentary rocks, which occur at angles of about 60°, suggests the disturbed occurrence of the igneous bodies. These results can be used for further detailed paleomagnetic studies of the Middle Jurassic igneous complexes in Mountainous Crimea for paleomagnetic reconstruction and the solution of local geological and structural geological problems.     

Lithology, spore-pollen spectra, and conditions of formation of deposits of the Chenka Formation of the Southwest Crimea

In this work the study results of two detailed sections of the Chenka Formation of the Southwest Crimea are given. Based on the chemical composition of deposits, possible sedimentation settings, and their position in the general structure of the Jurassic-Cretaceous complexes of the Southwest Crimea, as well as the first palynological age datings we obtained, it is proposed that the age of the Chenka Formation deposits is Bathian-Callovian and that they accumulated within the distal part of a large river valley estuary.     

Complex deposits in the Lo Gam structure,northeastern Vietnam: mineralogy,geochemistry, and formation conditions

The Pb–Zn deposits in the Lo Gam structure, northeastern Vietnam, account for>80% of all the Pb and Zn resources of Vietnam. All the deposits make up four isolated ore districts (Thai Nguyen, Cho Don, Cho Dien, Na Son), which can be combined in one metallogenic zone extending for >100 km from southeast to northwest. The Pb–Zn deposits in all the ore districts show some similarity to stratiform (Mississippi-type) deposits: confinement to Devonian carbonate sediments; localization at the intersection of faults of different orientations; vein and stockwork (pocket-vein-disseminated) morphology of the mineralized zones; evidence for hydrothermal-metasomatic formation (carbonate-rock marbleization, quartz–carbonate veins, etc.); and low and moderate mineralization temperatures (<250 °C). On the other hand, some differences from stratiform deposits are observed: widespread occurrence of Permo-Triassic igneous rocks in the above ore districts; absent tabular orebodies, which are typical of stratiform deposits; large set of trace elements (In, Bi, Sb, Au, Ag, Cu, Cd) not typical of stratiform deposits; and an endogenic primary source, as evidenced by the isotope composition of sulfur (δS³⁴= 2.68‰), which is close to meteoritic, and the set of trace elements, which are mainly of deep genesis. All this indicates that the above Pb–Zn deposits within the carbonate units are low-and moderate-temperature hydrothermal-metasomatic products associated with active magmatism which took place in this region in the Permo-Triassic.The differences in the mineral composition of the deposits, as well as in the trace-element set and contents at different deposits, clearly indicate an intricate ore formation process and the relation of the deposits with magmatism of different compositions. The simple mineral composition and the limited set of trace elements (Cd, Ag, Sb, As) at the Lang Hich deposit are closer to the characteristics of stratiform deposits. Also, manifestations of magmatism are almost absent here. On the contrary, unusually high (ppm) In (75.8), Sn (307.5), Cu (1080), Ag (157.7), Bi (99), and As (13,650) contents were observed at the deposits of the Cho Don and Cho Dien districts, with widespread granitoid magmatism in the Phia Bioc complex. Rare-earth mineralization (orthite) and high Mo, Re, and Rb contents at the deposits of the Na Son district are probably due to the widespread occurrence of stratified alkaline volcanics and their subvolcanic analogs, which belong to the Pla Ma complex (ξγPZ₂ pm).     

First find of serpentinite in the cliffs of the Heracleian Peninsula of Southwestern Crimea

This paper reports on the geological position and composition of serpentinite and serpentinitized peridotite, which we were the first to find in the cliffs of the southern part of the Heracleian Peninsula of Southwestern Crimea. In combination with pillow lava, gabbro, fragments of parallel dikes, and jasper, these rocks form an ophiolite association, which formerly belonged to the ancient crust of a back-arc basin that had reached the spreading stage of development.     

The structure and formation conditions of the upper Jurassic succession in the area of Mount Pakhkal-Kaya (Crimea)

It has been found that the section in Mount Pakhkal-Kaya consists of three structural units separated by almost bedding-plane faults presumably arranged in a normal stratigraphic succession: conglomerate succession (I, ?J₃ox (Oxfordian)), carbonate succession (II, ?J₃km(Kimmeridgian)-tt(Tithonian)), and a conglomerate-breccia unit) (III, J3km-tt). Each of these successions corresponds to a certain stage of basin evolution, viz., formation of a Gilbert-type delta and the accumulation of a carbonate platform rimmed with a shoal and destruction of the platform margin during its periodic exposures.     

Collisional granitoids of the Dzhida zone of the Central Asian Fold belt,Southwestern Transbaikalia: Age and conditions of the formation

This paper considers the geological structure, composition, and age of the Darkhintui, Barun-Gol, and Khuldat granitoid plutons of the Dzhida zone of Caledonides of the Central Asian Fold belts. These plutons were formed in the Late Cambrian-Early Ordovician in the range between 490 ± 2 and 477 ± 6 Ma, after tectonic juxtaposition of the oceanic and island-arc complexes of the Dzhida Zone and volcanogenic-carbonate-terrigenous rocks of the Khamardaban zone, i.e., at the collisional stage of the region evolution. Geological, geochronological, geochemical, and Nd isotope data indicate that the collisional granitoids of the Dzhida zone were derived by melting of continental crust thickened through accretion. The sources for parental melts of the granitoids were presumably Vendian-Early Cambrian juvenile igneous rocks of ophiolite and island-arc complexes, as well as the crustal material of the Lower Paleozoic flyschoid sediments of the back-arc basin of the Dzhida zone and metaterrigenous rocks of the Khamardaban zone.     

Lower-middle Eocene formations of the Crimea: Facial peculiarities and forming conditions

This work considers the structure and conditions of the formation of deposits of the Simferopolskoe regional stage of the Crimea. The deposits of this stage include planktonic foraminifera zones Morozovella aragonensis and Acarinina bullbrooki and nanoplaktonic zones Marthasterites tribrachiatus (the upper part), Discoaster lodoensis, Discoaster sublodoensis (lower part). The deposits of this interval throughout most of the Crimea represent a nummulitic bank, which formed in shallow warm-water basin and was isolated carbonate platform. The distribution of rocks of this regional stage, the facial change, and a number of interruptions are shown in the chronostratigraphic profile. The facial transitions within the carbonate platform point to variations in the basin’s depth, as well as periodical changes in the relative sea level, which were not only of a eustatic nature, but were determined by the periodic rise of the Simferopol Uplift.     

Danian deposits of the Crimea: Facies peculiarities and conditions of sediment accumulation

The Danian deposits of the Crimea are described. Emphasis is placed on the characteristics of the rock of a well-exposed section in the Crimean piedmont. The depositional environment and paleogeography of different sections of the Crimea are reconstructed. The sequences and the system tracts that are distinguished in the Danian deposits fix the alternation of transgressive-regressive episodes. It is revealed that the stratigraphic completeness of Danian sections and variations in their thickness are determined not only by the sea-level fluctuations, but also by the tectonic events that manifested themselves in the growth of the Simferopol’skoe rise and the formation of trough-like structures in eastern Crimea.     

Composition and conditions of formation of the parental melts of Jurassic dolerites of southwestern Crimea: Evidence from melt inclusions in olivine phenocrysts

This study focuses on Jurassic shallow intrusions and subvolcanic bodies from around Trudolyubovka village in the southwestern Crimea. All the rocks are similar in mineral composition and have similar geochemical features and occur in close spatial and geological association. This allows us to assign the intrusions to a single magmatic series and interpret them as differentiation products of a single parental melt. The investigation of melt inclusions in olivine from the most magnesian sample showed that the composition of igneous melts ranged from basalt to basaltic andesite of a moderately potassic subalkaline affinity. Compared with N-MORB, they are enriched in LILE, but have similar HFSE and REE contents. The early magmatic melts crystallized at temperatures ranging from 1240 to 1125°C, pressures of 6–8 kbar, and an oxygen fugacity of ΔQFM = +0.6; and later melts crystallized at 1090–940°C, ~1.5 kbar, and oxygen fugacity increasing from ΔQFM + 0.9 to ΔQFM + 2.3. The minimum pressure of groundmass crystallization was estimated as 40–60 bar. The primitive melts were formed in a mature island arc or an active continental margin setting by ~13% melting of a DMM-like source. The melting occurred at spinel-facies depths under the influence of a slab-derived fluid at a temperature 25°C below the dry peridotite solidus.     

Stanniferrous granites of Vietnam: Rb-Sr and Ar-Ar isotope age,composition, sources,and geodynamic formation conditions

Doklady Earth Sciences - Stanniferrous granite-leucogranite massifs in Vietnam to which the bedrock and placer commercial deposits of cassiterite are associated (Timtuc etc.) are of late Cretaceous...     

Serpentinization and alteration in an olivine cumulate from the Stillwater Complex,Southwestern Montana

Some of the olivine cumulates of the Ultramafic zone of the Stillwater Complex, Montana, are progressively altered to serpentine minerals and thompsonite. Lizardite and chrysotile developed in the cumulus olivine and postcumulus pyroxenes; thompsonite developed in postcumulus plagioclase. The detailed mineralogy, petrology, and chemistry indicate that olivine and plagioclase react to form the alteration products, except for H₂O, without changes in the bulk composition of the rocks.     

华南花岗质潜火山杂岩与富铀矿的成矿关系及找矿前景

本文探讨了华南地区火山岩型或花岗岩型富铀矿，与岩浆旋回晚期的构造－岩浆活动的关系，火山岩型富铀矿离不开大规模火山活动的晚期次火山活动，而花岗岩型富铀矿，则与主侵入晚期的中细粒，不等粒小岩体密切相关，经过长期研究，根据岩浆作用性质，将这套独具特色并与富铀矿的形成息息相关的岩定，定为花岗质潜火山杂岩。     

The types of breccia of the ophiolite assemblage of Southwestern Crimea and their significance for the paleogeodynamics of the region

This paper describes the types of breccia of the eastern part of Cape Fiolent, including verd antique (ophicalcite) for the first time, whose formation is associated with ophiolite. It has been shown that the formation of the ophiolite assemblage of the area occurred in the intersection zone of the rift valley and transform fault.