Platinoids in the Kaalamo Differentiated Massif in the Northern Ladoga Region,Karelia, Russia

The Kaalamo massif is located in the Northern Ladoga region, Karelia, on the extension of the Kotalahti Belt of Ni-bearing ultramafic intrusions in Finland. The massif, 1.89 Ga in age, is differentiated from pyroxenite to diorite. Nickel–copper sulfide mineralization with platinoids is related to the pyroxenite phase. The ore consists of two mineral types: (i) pentlandite–chalcopyrite–pyrrhotite and (ii) chalcopyrite, both enriched in PGE. Pd and Pt bismuthotellurides, as well as Pd and Pt tellurobismuthides, are represented by the following mineral species: kotulskite, sobolevskite, merenskyite, michenerite, moncheite, keithconnite, telluropalladinite; Pt and Pd sulfides comprise vysotskite, cooperite, braggite, palladium pentlandite, and some other rare phases. High-palladium minerals are contained in pentlandite–chalcopyrite–pyrrhotite ore. Native gold intergrown with kotulskite commonly contains microinclusions (1–3 μm) of Pd stannides: paolovite and atokite. Ore with 20–60% copper sulfides (0.2–6.0% Cu) contains 5.1–6.6 gpt PGE and up to 0.13–2.3 gpt Au. Pd minerals, arsenides and sulfoarsenides of Pt, Rh, Ir, Os, and Ru are identified as well. These are sperrylite, ruthenium platarsite, hollingworthite, and irarsite; silvery gold and paolovite have also been noted. All these minerals have been revealed in the massif for the first time. The paper also presents data on the compositions of 25 PGE minerals (PGM) from Kaalamo ores.     

Immiscibility between Fe- and Si-Rich Silicate Melts in Mesoproterozoic Ferrobasalt of the Ladoga Graben,Karelia, Russia

Doklady Earth Sciences - Evidence for liquid immiscibility between Fe-rich and Si-rich silicate melts in ferrobasalt of the Ladoga Graben in the Baltic Shield belonging to the Mesoproterozoic...     

Geochemical Constraints for the Genesis of Post-collisional Magmatism and the Geodynamic Evolution of the Northern Taiwan Region

Taiwan is an active mountain belt created by the oblique collisionof the northern Luzon arc with Asia. Late Pliocene extensionalcollapse of the northern Taiwan mountain belt (NTMB) was accompaniedby magmatism that formed the Northern Taiwan Volcanic Zone (NTVZ;2·8–0·2 Ma). The geochemical characteristicsof the NTVZ magmas can thus provide constraints both for themantle source composition and the geodynamic processes operatingin the late orogenic stage of the region. The NTVZ volcanicrocks consist dominantly of calc-alkaline andesites and basalts,along with subordinate but heterogeneous lavas including low-K,shoshonitic and ultrapotassic magmas. From the NE to the SWin the NTVZ, the magmas show systematic compositional variationsfrom low-K to calc-alkaline and then shoshonitic. This spatialgeochemical variation, characterized by southwesterly increasein potassium and incompatible trace elements, appears to besubparallel to the southwestern part of the modern Ryukyu subductionsystem. Sr–Nd isotope ratios of the NTVZ volcanic rocks(⁸⁷Sr/⁸⁶Sr     

Geodynamic setting of gold deposits in Eastern and Central Trans-Baikal (Chita Region, Russia)

It is proposed that there are three types of gold deposits in Eastern and Central Transbaikalia (Trans-Baikal province), namely: (i) high-sulphide intrusion-related deposits with some signs of porphyry deposits, (ii) low-sulphide intrusion-related deposits, and (iii) low-sulphide epithermal Au–Ag deposits. Most of the gold deposits belong to the first two types, and their ages are Middle–Late Jurassic. Deposits of the third type are not numerous, and their age is Early Cretaceous.The majority of the gold mineralization is spatially related to the two branches of the Mongolia–Okhotsk suture, along which Siberia collided, at the Early/Middle Jurassic boundary, with the Mongolia–North China continent and the Onon island-arc terrane located between the two continents. Collision-related thrusting, folding and magmatism lasted until the latest Jurassic, when they gave way to post-collisional rifting that continued until the end of Early Cretaceous.According to their age, relation to magmatism and tectonic framework, the intrusion-related deposits (high- and low-sulphide) were formed in a regional collisional setting. Extensional environments at that time existed only in local areas in the roofs of great magmatic chambers. Low-sulphide epithermal deposits were formed during Early Cretaceous post-collisional rifting.     

Geodynamic Model of the Neoproterozoic Evolution of the Yenisei Paleosubduction Zone (Western Margin of the Siberian Craton), Russia

Geotectonics - The article proposes a model of collisional and accretionary events of the Neoproterozoic at the western margin of the Siberian Craton based on the results of geological,...     

Blastomylonite Complexes of the Western Yenisei Ridge (Eastern Siberia,Russia): Geological Position,Metamorphic Evolution and Geodynamic Models

Geotectonics - Metapelites and metabasites within the Yenisei regional shear zone of the Yenisei Ridge underwent strong deformations with substrate recrystallization and blastomylonite formation...     

Granitoids of the Kongo Magmatic Zone of the Omolon Massif (Northeastern Russia): Rock Composition,Age, and Geodynamic Setting

Geotectonics - In our study we analyzed the composition of granitoid rocks within the Kongo magmatic zone of the Omolon median mass. The studied calc-alkaline granitoids cut through the Early...     

U-Pb geochronology of zircons from metasediments of the Ladoga Group (North Ladoga Region,Baltic Shield)

During our study we obtained the first age datings of detrital zircons from metasandstones of the Ladoga Group (North Ladoga Region, Russia) with the U-Pb isotopic method using the SHRIMP-II ion microprobe. The data obtained made it possible to clarify the lower age limit of sedimentation and to obtain additional age data for evaluating the chemical composition and an age of source areas. This work presents the results of isotopic-geochemical (Sm-Nd) and geochemical studies of metasediments. High LREE concentrations, a high La/Sc ratio and a low Cr/h ratio, and the presence of a distinct Eu-minimum (Eu/Eu* = 0.54–0.72) indicate a significant role of acidic terrigenous material in source areas. In addition, the data of the isotope analysis of detrital zircons show that sediments of the Ladoga Group accumulated from the destruction of Proterozoic rocks (1.9–2.0 Ga; a proportion in sediments is 60–70%) and, to a lesser extent, Archean rocks (2.54–2.74 and 2.9–3.01 Ga; the proportion in sediments is 30–40%). One of the Archean source areas could be granite-gneisses of the Pitkyaranta-Koirinoya dome structure with the U-Pb zircon age of 2659 ± 15 Ma. We have established the lower age limit of sedimentation as 1.9 Ga within the measurement error. The Sm-Nd model ages obtained (2.5–2.6 Ga for sediments of the Ladoga Group and over 3.4 Ga for granite-gneisses of the dome structure) suggest a significant contribution of ancient crustal source area into source rocks. Our age data agree well with those for svecofennides of Finland.     

俯冲带楔体中逆冲构造的形成及演化：构造物理模拟实验研究

通过交换不同的边界条件来进行构造物理模拟，重塑及研究岩石圈中各种构造现象发生及发展的过程与机制，并与自然界中存在的构造现象进行对比，是构造物理模拟所具有的独特优越性。实验以俯冲带楔体中及其底部逆冲断层形成过程中的几何学、运动学的研究为主题，以底部摩擦强度（俯冲片与传送带间的摩擦）及插入厚度的变化为边界条件进行的。实验证实了俯冲带中楔体底部及其下部俯冲片中存在的构造底侵作用；底部不同的摩擦强度与不同的插入厚度对楔体前缘、内部及底部逆冲构造的形成演化及其组合形式有如下影响：（１）楔体前缘逆冲断层系之间的间距随底部摩擦强度增强而加大；（２）当底部摩擦强度大时，楔体前缘逆冲叠瓦扇构造表现出一种前导主叠瓦扇（Ｌｅａｄｉｎｇｎｉｍｂｒｉｃａｔｅｆａｎ），反之则显示尾（Ｔｒａｉｌｉｎｇ）叠瓦扇组合特点；（３）插入厚度对楔体内部的反向逆冲构造的形成及演化具明显的影响。     

On Geodynamic Evolution of Simao Region (Southwestern Yunnan, China) during Late Paleozoic and Triassic

ＩＮＴＲＯＤＵＣＴＩＯＮＴｈｅＳｉｍａｏｒｅｇｉｏｎ (ＳＷＹｕｎｎａｎ ,Ｃｈｉｎａ) ,ｓｉｔｕａｔｅｄｂｅ ｔｗｅｅｎｔｈｅＡｉｌａｏｓｈａｎｂｅｌｔｉｎｔｈｅｅａｓｔａｎｄｔｈｅＬａｎｃａｎｇｊｉａｎｇｚｏｎｅｉｎｔｈｅｗｅｓｔ (Ｆｉｇ .1) ,ｉｓａｋｅｙａｒｅａｔｏｃｈｒｏｎｏｌｏｇｉｃａｌｌｙｃｏｎｓｔｒａｉｎｌａｔｅＰａｌｅｏｚｏｉｃｃｏｍｐｒｅｓｓｉｏｎａｌｄｅｆｏｒｍａｔｉｏｎｓａｎｄｔｈｕｓｏｆｐｒｉｍｅｉｎ ｔｅｒｅｓｔｗｈｅｎｄｉｓｃｕｓｓｉｎｇｔｈｅｐｌａｔｅ ｔｅｃｔｏｎｉｃｈｉ…     

Segmented, curved faults: the example of the Balduini Thrust Zone, Northern Apennines, Italy

Meso- and micro-structural studies of the well-exposed Balduini Thrust (Northern Apennines, Italy) indicate that the structure formed during a single folding event, contemporaneous with diagenesis, and is a zone comprising curved, en-échelon fault segments. The geometry of each segment is arcuate with pure compression at one end and right-lateral displacement along the other. The thrust developed during the Tortonian within a single mud-rich formation, the Upper Eocene–Upper Oligocene Scaglia Cinerea, but rheological variations within the unit led to differences in deformation style; zones of scaly fabric are discontinuous and calcite veins vary in abundance. The mesoscopic morphology of the veins and the distribution of calcium carbonate along the formation indicate variations in the distribution of fluids at the time of deformation, which affected both diagenesis and the structural response of the material. Systematic variations of mechanical properties within the thickness of the Scaglia Cinerea Formation account for the curvature of the propagating thrust. Together with the heterogeneity of the stress field, the confinement of the arcing thrust to this single, weak unit lead to repeated initiation of new fractures and hence segmentation of the propagating thrust. Geometric analysis of the calcite veins and their microscopic characters suggests that hydrofracturing was involved, with the Scaglia Cinerea Formation experiencing high fluid pressure followed by rapid water expulsion. The Balduini Thrust is therefore an example of a fluid-driven, refracted compound shear zone. The analysis presented here provides insights into the three-dimensional arrangement of fault zones and fluid-migration patterns during regional faulting.     

The Ore Mineralogy of the Kedrovskoe Gold Deposit (the Muya Region,the Republic of Buryatia,Russia)

The ore mineralogy of the largest quartz vein, Osinovaya, at the Kedrovskoe gold deposit has been studied. Three stages of mineral formation, namely, marcasite–pyrrhotite–pyrite, gold–polysulfide, and hypergenic stages are identified. Native gold is attributed to the gold–polysulfide stage and is represented by two generations. The earlier high fineness generation (600–870, 780–820 prevails) cements the fragments of pyrite grains or forms inclusions in pyrite, and the later low fineness generation (520–580, 540–580 prevails) is associated with sphalerite–chalcopyrite–galena veinlets in pyrite. The disappearance of arsenious pyrite, the increase in iron content of sphalerite, and the change in pyrite to pyrrhotite with depth is recorded.     

Allanite-(Ce): a Typical Mineral of Metakimberlite from the Lake Kimozero Area,Karelia

Paleoproterozoic kimberlite from the Kimozero area in Karelia is the oldest rock of this type in Russia. It is strongly tectonized, metamorphosed, and it finally transformed into metakimberlite of the prehnite-pumpellyite facies with widespread lanthanide minerals: allanite-(Ce), bastnaesite-(Ce), bastnaesite-(La), parisite-(Ce), and monazite-(Ce). The contacts between their crystals and other metamorphic minerals, e.g., titanite, antigorite, and tremolite, are characterized by induction surfaces of concerted growth. Among lanthanide minerals, allanite-(Ce) is the most abundant. It occurs close to clinochlore pseudomorphs after phlogopite or as intergrowths with titanite in aggregates of tremolite–actinolite, calcite, and dolomite. Allanite crystals from the Kimozero area are not zonal, but vary in lanthanide contents and the Fe³⁺/Fe²⁺ ratio in grains no more than tens of microns from one another. Kimozero allanite mostly belongs to the allanite–ferriallanite series (up to 30% of ferriallanite endmember); the lesser amount corresponds to the allanite–Cr-bearing allanite series. At the late stage of metamorphism, allanite was partly replaced with parisite, bastnaesite, or monazite.     

Age and Geodynamic Conditions of Formation for the Neoproterozoic Gold-Bearing Granitoids in the Eastern Sayan

Geotectonics - The paper discusses the results of petrogeochemical and geochronological studies of the Tainsky granitoid stock containing the Tainsky gold deposit in the East Sayan. The Tainsky...     

Fluid-Controlling Significance of the Nosappu Fracture Zone and Conditions for the Formation of Methane Fluxes and Gas Hydrates (Sea of Okhotsk Region)

It has been observed that the intensity of underwater gas flares unexpectedly increased after the deep-focus (625.9 km) earthquake that occurred in the Sea of Okhotsk on August 14, 2012. In this regard, we have analyzed the data resulting from interpretation of the focal mechanism for the strike-slip earthquakes which occurred in the Benioff seismic zone of the subducting Pacific Plate within the Sea of Okhotsk region over the period from 1977 to 2010. The NNW sinistral and NE dextral faults are found to form a conjugate system due to the WNW stress field. We have established that the dextral faults are mostly common at a depth of about 200 km along the Kuril Islands extension, while the sinistral ones are concentrated in the Nosappu Fracture Zone and traced to the NNW down to a depth of 680 km. The area of the gas flare discharge and gas hydrate accumulations have the same (NNW) direction. Thus, we have revealed that the Nosappu Fracture Zone appears to be a structure which controls fluid fluxes, providing permeability of the subducting slab of the Pacific Plate for ascending fluids from the lower mantle.     

黑龙江杂岩带的形成演化及地质意义

黑龙江杂岩带呈南北向带状展布于佳木斯地块西缘,出露于嘉荫—牡丹江缝合带以东.研究证明其主体形成时代为晚海西期到印支期,地球化学特征显示其极可能形成于佳木斯与松嫩地块(松花江—嫩江地块)间板块俯冲碰撞或陆间洋盆消失闭合的环境.综合佳木斯地块同位素研究成果,结合该区古生物的研究和地质特点,推演出依兰地区黑龙江杂岩的形成演化...     

Application of the Engineering-Geological Conditions in Land-Use Plans in the Petrvald Region(Czech Republic)

The objective of this paper is to demonstrate necessity to inform relevant parties about engineering-geological conditions for various practical purposes,especially including appropriate land-use planning.However,the relationship between relevant geological information and the geological environment is vital for foundation engineering purposes,especially where demanding structures are involved.This information is most conveniently structured when accumulated information concerning engineering-geological zones is utilized.This necessarily includes knowledge of rock workability and also of the pre-Quaternary bedrock,and these characteristics were then related to the current built-up area and future development according to the land-use plans in a case study are from the Petrvald Region(Czech Republic).The geological environment of area has been severely influenced by anthropogenic effects of deep black coal mining.Results of this research showed that future development should be founded on spoil banks,dumps,and settling basins. According to the land-use plan,this zone occupies 44.9%of the area of interest,and its materials predominantly emanate from mining in the Ostrava-Karvina Coal District.For future foundation structures planned there,it is imperative to consult detailed engineering-geological study.However, attention to and reliance on this necessity is not reflected in the existing land-use plan.     

藏北羌塘盆地菊花山地区晚三叠世古岩溶不整合面的发现及其意义

菊花山地区出露的肖茶卡组—那底岗日组,其接触关系清楚,是北羌塘盆地代表性的剖面。在对该剖面中两者之间的砾岩进行详细的野外观测和分层取样分析的基础上,确定了肖茶卡组顶部与那底岗日组底部之间的砾岩为上、下两套不同成因、不同性质的砾岩组合。下套角砾岩以钙质、铁泥质胶结为特征,是肖茶卡组沉积期后海平面下降,出现广泛暴露、风化溶蚀形成的岩溶角砾岩;上套砾岩以凝灰质胶结为特征,是岩溶角砾未固结之前,发生构造活动产生的火山碎屑、熔岩流携带、搬运松散岩溶角砾再次沉积形成的那底岗日组底砾岩。从而确定了肖茶卡组与那底岗日组为岩溶不整合接触关系。该岩溶不整合面是羌塘盆地构造演化分析的重要证据,也是油气勘探的重要标志层。     

Mineral chemistry,petrogenesis and evolution of the Ghorveh-Seranjic skarn,Northern Sanandaj Sirjan Zone,Iran

Mineralogy and Petrology - The Ghorveh-Seranjic (GS) skarn is located in the northern part of the Sanandaj-Sirjan zone, NW Iran, which is part of Alpine-Himalaya orogenic belt. The GS metamorphic...