Occurrence Of Rocks Research Articles

Methods of determination of spatial distribution of minor-amplitude faults and fissures in thin-layered coal-bearing geological medium

A problem of determining location of faults and fissured in geological medium which appear in the process of formation of the main types of geological structures: shears, nappes, faults, grabens, axes of folding and compression zones is considered. Areal seismic records of MCDP 3D obtained in the mine field of “Krasnolimanskaya” mine (Donetsk district) were used as initial data. It is located on the monocline of the southwestern part of Kalmius-Torets basin in the hanging wing of the Central nappe with amplitude up to 310m. Monocline occurrence of rocks is complicated by numerous disjunctive faults of the faulting type with amplitudes up to 95m. The main marker for identification for presence of a fault on the seismic records of MCDP 3D under conditions of horizontally-layered medium is interruption and (or) displacement of the axis of reflected waves phase synchronism. In some cases a diffracted wave appears in the place of horizon rupture. Provided that in the case of complicated geology it seems impossible to identify minor-amplitude displacements and discordant occurrence of reflecting margins related to faults. For spatial identification of the fault structures position the results of solving the inverse seismic problem are proposed – logarithmic decrements of fading (LDF) with their method of calculation that was put forward by the author previously. Temporal cross-sections of LDF have the same permissive ability as seismic data of MCDP 3D. Such a detail allows separating out minor-amplitude derangements related to faults and fissures. Special feature of temporal data of LDF is in the point that the identifiers of discordant occurrence of reflecting margins are their absorbing properties. The examples of vertical and horizontal LDF sections of a seismic cube 3D where a lot of deep and surface faults can be traced are given in the paper. Taking into account the complexity of mapping the planes of faults in three-dimensional space a method of automatic determination of the point of drastic change of absorbing properties of the medium (on each of horizontal cuts of the cube) with application of wavelet analysis has been proposed. A matrix of attributes is created of such points by which the planes of faults are plotted.

Implications for the origins of Eoarchean ultramafic rocks of the North Atlantic Craton: a study of the Tussaap Ultramafic complex, Itsaq Gneiss complex, southern West Greenland

Ultramafic rocks found within the ~ 3.81 Ga Itsaq Gneiss Complex (IGC) have some mantle-like geochemical characteristics that have led to them being used to directly constrain the nature of the Eoarchean mantle. The discrimination of mantle peridotites that are the residues of partial melting, from cumulate peridotites generated by crystal accumulation from mantle-derived magmas can be difficult in ancient, altered ultramafic rocks whose field relations have been obscured by multiple tectonic episodes. Hence it is important to scrutinize significant individual occurrences of Eoarchean ultramafic rocks in some detail prior to using them to constrain the nature of Earth’s early mantle. Here we present mineral chemistry, whole rock major-, trace-, and platinum-group-element abundances, and Re–Os isotope compositions of a previously unstudied large ultramafic enclave in the IGC—the Tussaap Ultramafic Complex (TUC)—with the aim of documenting its origin. High FeO contents of up to 15.5 wt% and correlations between MgO and Os provide strong evidence that the TUC evolved through fractional crystallization rather than partial melt extraction. In addition, co-variations of major elements in the TUC lithologies can be modeled via fractional crystallization of picritic basalts using MELTS. Later alteration and metasomatism of these ultramafic rocks has largely overprinted primary mineral chemistry and resulted in a redistribution of light rare earth elements, rendering these tools ineffective for ascertaining the origin of the TUC or quantifying some of the petrogenetic processes that formed the body. In addition, it is clear that many geochemical features used to identify residual mantle peridotites can also be produced by cumulate or alteration processes, such as some variations in olivine and chromite chemistry, whole rock Al/Si vs Mg/Si systematics, and trace and platinum group element patterns. Finally, combined discrimination diagrams for high field strength elements and moderately high 187Os/188Os ratios suggest the parental melt of the TUC partially assimilated basaltic crust prior to precipitating the TUC cumulates. As such, these rocks represent a variably obscured record of Eoarchean crystal fractionation from mantle-derived melts. Despite not being prima facie mantle rocks, it is possible that such early formed ultramafic cumulates in nascent continents found their way into the later-stabilized roots of Archean cratons, helping to explain the high compositional variability of cratonic peridotites.

Diversity of igneous rocks from the Isachsen Dome, Ellef Ringnes Island, Canadian High Arctic

The sedimentary deposits of the central Sverdrup Basin on Ellef Ringnes Island were affected by both salt diapirism and igneous activity of the Cretaceous High Arctic Large Igneous Province (HALIP). Occurrences of mafic igneous rocks on the centre of salt domes are usually assigned to the Cretaceous magmatism. Petrographic, geochemical, Sr–Nd isotope, and geochronological (Ar–Ar dating) studies on six rock fragments collected on the top of Isachsen Dome reveal a larger variability in the composition and the age compared to HALIP-related rocks from elsewhere on Ellef Ringnes Island. A blocky fragment of tholeiitic hornblende dolerite with an Ar–Ar age of 121 Ma is interpreted to originate from an in-situ intrusion and was uplifted by evaporite diapirism. The other samples are small, sub-rounded pebbles, which represent three different parent rock types. A kaersutite-bearing alkali basalt was possibly formed during the Triassic or Permian. A leucocratic, albitised rock fragment has experienced contact metasomatism at 102 Ma, and three very similar tholeiitic basalt fragments probably derived from the margin of a dyke were auto-hydrothermally affected at 69 Ma. The inferred source area of these exotic pebbles is the segment of the Arctic continental margin in the northeast that was repeatedly affected by igneous events between the Carboniferous and latest Cretaceous and that was uplifted and eroded during the Eocene. The rock fragments were probably deposited as Palaeogene sediments above the rising Isachsen diapir shortly before or as the head of the salt dome has pierced the Earth’s surface. Glacial transport up the top of Isachsen Dome during the Late Wisconsinan glaciation is not very likely due to the contrast between the north to northwest directed ice-flow direction reported in the literature and the assumed northeastern source area of the pebbles; however, it cannot be completely excluded.

Lightweight concrete with expanded aggregate from siliceous rocks

The purpose of this study is to develop technology for the production of a new building composite made of silicon-containing rocks. An aggregate is foamed granules obtained on the basis of diatomite with the addition of caustic soda, dolomite, water and liquid glass. The material composition, materials processing, physical and mechanical properties have been observed. The problem of alkali-silicate interaction typical for traditional Portland cement and glass phase is solved through the use of magnesia binder. Samples on Portland cement and magnesia binder were obtained, the aggregate content was varied. Some aggregate fractions were used to obtain high packing density in the composite. Concrete was estimated according to density, compressive strength and tensile strength, water absorption and thermal conductivity. Analysis of the material structure was made. The results of the study of the microstructure of synthesized concrete indicate the presence of a cement matrix in which granules of various sizes are tightly packed. The results of X-ray phase analysis of synthesized concrete indicates that the cement matrix consists of forsterite crystals. Approximate savings in the use of concrete with the developed aggregate is about 10-20%. Such savings are possible due to the fact the surface occurrence of siliceous rocks allows them to be mined in an open way with minimal costs compared to other rocks, with a lower calcination temperature during material creation.

The ~500 Ma Asaji ultramafic–mafic intrusion in Kyushu, southwest Japan: Implications for boninitic magmatism in a late Cambrian nascent arc

It is thought that the continental crust that ultimately became Japan (i.e., proto-Japan) formed during the early Cambrian near the margin of the South China block following its separation from the Australian block. However, the onset of timing of subduction and details of the magmatic evolution of the region are poorly understood, due mainly to the sporadic occurrence of Cambrian rocks. A high-temperature metamorphic complex is distributed throughout eastern Kyushu island, Japan. At the northeastern end of the complex, a narrow zone of ultramafic–mafic rocks includes a late Cambrian ophiolitic assemblage, namely the Asaji ultramafic–mafic intrusion. The ultramafic cumulates in the intrusion consist of harzburgite (spinel–olivine–orthopyroxene), lherzolite–olivine websterite (olivine–orthopyroxene–clinopyroxene ± spinel), and websterite (orthopyroxene–clinopyroxene ± olivine), which formed in that order during differentiation of a parental magma. The chemical compositions of clinopyroxene and spinel from the cumulates show strongly depleted features (e.g., spinel Cr# [= atomic Cr/(Cr + Al)] ≤ 0.91 and TiO2 < 0.3 wt%, and clinopyroxene YbN < 2) and comparable to those of spinel in boninites. In addition, the calculated trace element composition of melts in equilibrium with clinopyroxene from the ultramafic rocks closely resembles the composition of the North Tongan boninite. These petrological and geochemical features suggest that the Asaji ultramafic–mafic intrusion consists of cumulates from a boninitic magma. The presence of boninitic magmatism suggests that the Asaji ultramafic–mafic intrusion was the result of subduction initiation and the infiltration of water into hot asthenosphere during the formation of nascent arc crust.

Study of hydrocarbon generation and 1D-2D modeling of hydrocarbon migration at the Karanj and Parsi oilfields, Southern Dezful Embayment, SW Iran

Abstract This study is a 2D basin modeling to determine the petroleum system (i.e. Cretaceous-Neogene play) of the Karanj and Parsi oilfields in the Southern Dezful Embayment, SW Iran. This system is characterized by occurrence of source rocks of Middle Cretaceous, Late Cretaceous and Paleocene to Eocene (Kazhdumi, Pabdeh and Gurpi Formation), reservoirs of Upper Cretaceous and Late Oligocene–Early Miocene (Ilam-Sarvak and Asmari formations), and seals of Paleocene and Miocene (Pabdeh and Gachsaran Formation). Considering temperature, transformation ratio and vitrinite reflectance, the maturity of source rocks (Kazhdumi, Pabdeh and Gurpi Formation) was investigated. A maturity history analysis showed that the maturity of Kazhdumi, Pabdeh and Gurpi Formation started during 70–60 and 4 Ma, respectively. Generation and expulsion of hydrocarbons started ~16 Ma in the Kazhdumi Formation and ~3 Ma in the Pabdeh Formation that continued up to the present. The analysis of the transformation ratio indicates transformation of significant amounts of Kazhdumi source rocks for generating hydrocarbons. Migration of hydrocarbons from the Kazhdumi Formation is mainly vertically upward. From Pabdeh Formation migration is both vertically upward (to the Asmari reservoir) and downwards (to the Ilam-Sarvak reservoir). However, some local traps have formed due to the hydrocarbon accumulation above the faults. Our results reveal that petroleum generation, migration and entrapment occurred at proper timing which facilitated the migration of hydrocarbons and their accumulation in the reservoirs.

Factors controls on weathering in the Ba River drainage basin, South Central Vietnam: Clay mineralogical investigations

Clay minerals of Miocene sedimentary rock and river sediment samples were collected from the Ba River basin in Southern Central Vietnam to evaluate controlling factor on weathering in Miocene and the present time. The analysis results display that Miocene andesitic sedimentary rocks contain high smectite (average 72%) with moderate kaolinite (24%), while Miocene felsic sedimentary rocks consist of high kaolinite (65%) with moderate smectite (25%). River sediments are represented by moderate smectite (43%) and kaolinite (37%). Based on the formation and typical distribution of clay minerals in the Ba River basin can be caused by the occurrence of felsic intrusive rocks and eruptive rocks along with the weak tectonics and tropical East Asia monsoon climate during the Miocene and in the present time. This indicates that lithological composition of parent rocks and East Asian monsoon conditions are significant roles in controlling weathering process, while tectonics play only a subordinate role in the Ba River basin.

To the problem of origin of the Bug series rocks

The age of the Bug series rocks is an object for discussion. Isotopic methods do not give a distinct answer, because in the same outcrop, the same sample and even in the same crystal of zircon several dates of formation are to be found with evident significance. Involvement of additional criteria is required to determine the time of the Bug series formation. While examining the phase composition and the initial source of the material we need taking into account temperature and pressure distribution in the depth of formation of rocks, which are on the surface nowadays. Mineral and chemical composition of rocks and tectonic structure of including patterns have been considered. It has been shown that the composition of the Bug series is an indicator of time of formation. Carbonatites and calcyphyres, carbonate-magnetite rocks are not produced earlier than ~2.0 Ga ago. A considerable part of the stratum is presented by high-clayish and graphite shale, quartzite, and ultrabasite that occur jointly only in this period of time. Arrangement of the structures is subdued to tectonic control by zones of deep faults. Smaller fault zones are determinative in the pattern of structures themselves and in manifestations of metasomatic processes. By the moment of their formation the level outcropped on the modern surface occurred at a depth more than 20 km that makes sedimentary nature of composing rocks doubtful. It has been shown that the most part of rocks attached to the Bug series are crystallization products of magmatic melts as well as carbonate, silicate (water-silicate with chlorine), hydrocarbon fluids in faults (permeable zones) of crystalline basement in diapason of PT -conditions, corresponding to high amphibolites-granulites metamorphic facies. The pattern of these structures in projection is similar to the section of volcano-tectonic apparatuses at a depth not less than 20 km. In the structures small by their area, the rocks formed at different depths (from 300 to 200 km) from melts and fluids in different chemical media are presented. High temperature multiple metasomatism has been superposed. A conclusion has been made that the pattern of the structures of Khashchevato-Zavalye block and the Golovaniv suture zone does not reflect the succession of primary sedimentary rocks occurrence but a result of multiple crystallization and metasomatic re-crystallization of melts and fluids.

Investigations on radioelements occurrences in rocks in Kakuri Area of Kaduna North West, Nigeria

Detailed investigations on Radioelements occurrences in rocks in Kakuri Area Kaduna North West Nigeria were carried out in this work using Geochemical ground follow-up methods. The methods employed include Atomic Absorption Spectrometric (AAS) and Assay of rock samples from the area. Fresh rock samples were collected with hammer and identified as follows: Granite gneiss, Granite, Migmatites and Gneiss. Analysis was made on the powdered rock samples and histograms were plotted to determine the activity of Radioelement concentrations: Potassium, Thorium and Uranium in each of the samples analyzed. Results of the investigations showed high concentration of potassium (40K) and other Radioelements, thorium and uranium in the area. Generally, the results delineate the three Radioelements in terms of their anomaly pattern within the study area.Keywords: Geochemical Survey; Aeroradiometric Anomaly; Fresh Rocks; Radioelements and Kakuri Area

Andesite, Construction material, Kulon Progo , Yogyakarta, Indonesia.

The construction projects that are currently being carried out in Kulon ProgoRegency, Yogyakarta Special Province, Indonesia, started on 2018, are large-scale projects. The projects include the construction of airports, seaports, industrial estates, southern crossing lanes and the construction of Menoreh lanes. The large-scale projects require a very large supply of andesite rocks for material construction. In Kulon Progo Regency itself, there is a huge potential of andesite rock relate to two geological formations (Kebo Butak and Andesite Intrusion) exist in the region, which is found mostly in Kokap District and partly in Temon District. One parameter that determines the quality of andesite rock is their compressive strength. Due to weathering, not all of the andesite in both formation can be classified as good quality rocks. According to Indonesian Standard, theminimum compressive strength of natural stone for stakes and curbstone is 500 kg/cm2 , for lightweight building foundation is 800 kg/cm2 , for medium building foundations is 1000 kg/cm 2and for heavy building foundations is 1500 kg/cm 2 . Based on this background, this paper have objectives to know the quality of andesite rock exist in the research area and to determine the zonation of good quality andesite rock for building androad materials in the research area. Field observation were conducted to map the occurrence of andesite rock. Totally 68 rock samples were collected during field observation and tested by point load test method to know its compressive strength value. The distribution of good quality rock in the research area were determine based on spatial analysis procedure in geographical information system. Results show that andesite rocks found in research area have a compressive strength ranging from 167.12 kg/cm 2 to 2783.37 kg/cm 2 . From 53 samples taken from igneous rock intrusion, it showed that 7.55 % had low quality, 13.21 % had medium quality, 30.19 % had good quality and 49.06 % had very good quality. From the 16 samples taken from the Kebobutak Formation, it showed that 12.50 % had low quality, 18.75 % had good quality and 67.75 % had very good quality. The final map of rock quality zonation reveals 28.92 % of research area classify as low quality, 2.52 %medium quality, 37.68 % good quality and 30.88 % very good quality. It can be concluded that almost 70 % of andesite in the Kokap and Temon District can be used for the running large scale projects.

Tectonic erosion and crustal relamination during the India-Asian continental collision: Insights from Eocene magmatism in the southeastern Gangdese belt

Understanding the processes of tectonic erosion and crustal relamination during continental collision has important implications for the growth and differentiation of the continental crust. The discrepancy in isotopic compositions between the pre- and syn-collision magmatic rocks from the Gangdese belt in south Tibet provides an opportunity for studying these processes during the India-Asian collision. The Nyingchi granites and Confluence hornblende gabbros from the eastern Gangdese belt have zircon U-Pb ages of ca. 50 Ma. The Nyingchi granites have high Sr/Y and (Dy/Yb)N ratios, indicating that the magma was generated under eclogite-facies conditions. Their Sr-Nd-Pb-Hf isotopic compositions require significant incorporation of ancient supracrustal materials from the Gangdese belt and the Indian continent. The Confluence hornblende gabbros display arc-like trace element patterns but have enriched Sr-Nd-Pb-Hf isotopic compositions compared with those from the Jurassic-Cretaceous arc magmatic rocks, indicating significant input of ancient components into their mantle sources. The occurrence of the Cenozoic felsic metamorphic rocks in the lower crust of the Gangdese belt allows us to propose that the Nyingchi high Sr/Y granites were derived from partial melting of relaminated crustal materials which were removed from the Gangdese belt by tectonic erosion and the subducted Indian continent. The Confluence gabbros were sourced from lithospheric mantle which was metasomatized by inputs from relaminated crustal materials derived from the Gangdese belt and the subducted Indian continent. The estimated tectonic erosion rate is 150–188 km3/km/my, indicating significant crustal loss occurred during continental collision. Our study demonstrates that tectonic erosion and crustal relamination play an important role in the refinement of the composition of continental crust during continental collision.

Morphological indications of hypogene speleogenesis in caves of the Urals (Russia)

Approximately all types of surface and underground karst elements are represented in the Urals. Rock formations are elongated in the longitudinal direction, which allows for a comparative analysis of the processes in karst landscapes in different latitudinal geographic areas. During the long geological history of the Urals, karst development occurred in conditions of extensive occurrence of soluble rocks in the territory and in the geological section in cratons, folded zones and depressions. The most intense karstification occurs in Paleozoic sediments. Sulfate rocks (gypsum and anhydrite) located on the eastern margins of the East European Craton and adjacent parts of the Ural Foredeep are the most karstified. These deposits are also intercalated with thin layers of limestone and dolomite of the Irenskaya Suite, and to a lesser extent—limestones and dolomites of the Filippovsky Unit of the Kungurian Stage and limestones of the Artinskian Stage of Lower Permian. Salt-bearing and sulfate deposits are mainly found in the Ural Foredeep. Karst development in the Devonian, Carboniferous, and Permian carbonate strata with a total thickness of more than 2000 m is typical for the folded zone of the West Ural and Central Ural uplifts. The western slope of the South Urals is the most intensely karstified. Hypogenic karst cavities occur from the Polar to the Southern Urals on the western and eastern slopes. The article presents the most interesting examples of hypogenic speleogenesis in the Ural.

Seismic recognition of igneous rocks of the Deepwater Taranaki Basin, New Zealand, and their distribution

ABSTRACTNumerous igneous bodies within the Deepwater Taranaki Basin are recognised mainly from seismic data and range from Early Cretaceous to Pliocene in age. They were all emplaced within an intra-plate setting but are scattered apparently at random in time and space. This paper describes the occurrences of igneous rocks within the basin as interpreted from seismic data, and discusses their possible origin. There are no indications of hotspot tracks within the Zealandia micro-continent so an alternative origin is sought. Previous authors see the main cause of volcanism as decompression melting due to localised lithospheric detachment and the movement of the Zealandia plate across the mantle as incidental. It is suggested that the movement of the Zealandia lithosphere, in the order of 4000 km to the north-northwest since the Cretaceous, may have caused drag across the asthenosphere, which in turn created transient small-scale convection cells that assisted the process of decompression melting as a modification to the accepted theory.

Palaeoarchaean deep mantle heterogeneity recorded by enriched plume remnants

The thermal and chemical state of the early Archaean deep mantle is poorly resolved due to the rare occurrences of early Archaean magnesium-rich volcanic rocks. In particular, it is not clear whether compositional heterogeneity existed in the early Archaean deep mantle and, if it did, how deep mantle heterogeneity formed. Here we present a geochronological and geochemical study on a Palaeoarchaean ultramafic–mafic suite (3.45-Gyr-old) with mantle plume signatures in Longwan, Eastern Hebei, the North China Craton. This suite consists of metamorphosed cumulates and basalts. The meta-basalts are iron rich and show the geochemical characteristics of present-day oceanic island basalt and unusually high mantle potential temperatures (1,675 °C), which suggests a deep mantle source enriched in iron and incompatible elements. The Longwan ultramafic–mafic suite is best interpreted as the remnants of a 3.45-Gyr-old enriched mantle plume. The first emergence of mantle-plume-related rocks on the Earth 3.5–3.45 billion years ago indicates that a global mantle plume event occurred with the onset of large-scale deep mantle convection in the Palaeoarchaean. Various deep mantle sources of these Palaeoarchaean mantle-plume-related rocks imply that significant compositional heterogeneity was present in the Palaeoarchaean deep mantle, most probably introduced by recycled crustal material. Deep mantle heterogeneity and large-scale deep mantle convection has been operating since the Palaeoarchaean, according to enriched plume signatures found in a 3.45-billion-year-old ultramafic–mafic suite from the North China Craton.

Reflection of sequence of geodynamic processes in geological structure of the Bug area

The age of formations composing granulite blocks of the Ukrainian Shield is a pro-blem for disputes. In order to ascertain the primary genesis and conditions of transduction of the Bug area rocks it is proposed to find out how was deep process realized according to composition of magmatic and chemogenic-sedimentary rocks. Description of formations was used and sequence of geological events, given in the paper [Venidictov, 1986] for the Upper Bug area. During the period that began not later than 2.5 Ga and lasted up to 2.0 Ga three tectono-magmatic cycles happened that can be compared with a regime “folded area”. Application of over-all schemes allows to ascertain composition and temperatures of melts and fluids sup-plied to the crust (thermodynamic regime), and to appraise the character of interactions (metasomatic substitution, crystallization, melting-dissolution etc.) between deep material (of the known composition and temperature) and crust material at the ascertained depth (with known lithostatic pressure and temperature). Regime “folded area” is cha-racterized by magmatic rocks generated at depths 220, 150, 100, 50 km. Underlaying of the crust by mantle (ultrabasic) melts and replenishment of melting layers with their upper edge at depths 50 and 20 km, occurs repeatedly, that assumes complication of ba-sic regime. It has been determined that in the Bug area temperatures and pressures of metamorphic transformations exceeded those ones needed for production of the layer of partial melting in the crust. To present-day erosion section the level of asthenosphe-re position, where granites attached to the berdychiv complex was drawn. Sequence of occurrence was replaced by the order of incorporation and substitution. Primary sedimentary rocks were not preserved and there is no relation between occurrence of rocks and their age.

Damage Constitutive Model of Loaded Orthotropic Rock under Freeze-thaw Cycles

In this paper the orthotropic damage constitutive model of loaded rock in cold environment is established according to the orthotropic characteristics of the one in freeze-thaw cycles, based on the strength of rock microelements subject to Weibull random distribution, and the macroscopic statistical damage model of rock. This model could reflect the environment of natural rock occurrence more truthfully, and revealed the law of rock damage evolution under freeze-thaw environment. The research results would have important theoretical and practical significance for the evaluation of safety and stability of engineering construction in cold area.

Tokoro Belt (NE Hokkaido): an exhumed, Jurassic – Early Cretaceous seamount in the Late Cretaceous accretionary prism of northern Japan

AbstractThe Tokoro Belt exposed in NE Hokkaido (Japan) represents part of a Late Cretaceous accretionary complex, which includes variously metamorphosed volcanic rocks that are interbedded with chert, lenticular limestone and some fore-arc sedimentary rocks. The Tokoro Belt is notably different from other Late Cretaceous accretionary complexes around the Pacific Rim because of widespread occurrence of basalts and volcaniclastic rocks in it. The Nikoro Group, characterized by widespread occurrence of volcanic rocks, is divided into western, eastern and southern sections based on the internal structure, geochemical affinities and metamorphic grades of their volcanic lithologies. OIB (ocean island basalt)-type volcanic rocks with low-grade metamorphic overprint predominate in the western and southern sections, whereas MORB (mid-ocean ridge basalt)- and OIA (ocean island alkaline basalt)-type rocks in the eastern section with partly high-pressure metamorphism make up the northern part of the eastern section. Trace element patterns display transitional trends from MORB to OIA geochemical affinities. OIB-type rocks display trace element characteristics similar to those of shield volcano lavas on Hawaii, rather than small and mainly alkaline, Polynesian hotspot lavas; furthermore, they show significant HREE (heavy rare earth element) enrichment probably caused by plume–ridge interaction. Widespread OIBs in the Tokoro Belt represents tectonic slices of a large (&gt;80 km wide) Hawaiian-style, seamount shield volcano on the Izanagi oceanic plate that was accreted into the continental margin of Far East Asia in the Late Cretaceous.

Genetic basis of unexplained erythrocytosis in Indian patients.

To evaluate the spectrum of genetic defects in Indian patients with unexplained erythrocytosis. Fifteen families (18 patients) with unexplained erythrocytosis were enrolled after excluding polycythemia vera and secondary erythrocytosis. Focused Sanger sequencing from genomic DNA was performed for EPOR (exon 8), VHL (exons 2-3), EGLN1 (exons 2-5), EPAS1 (exon 12), and all exons of HBB, HBA1, and HBA2 genes. Eleven of the 18 patients (including two pairs of brothers) had Chuvash polycythemia, that is, homozygosity for VHL:c.598C>T (p.Arg200Trp). Three patients (two of whom were brothers) had HBB mutations associated with increased oxygen-affinity hemoglobin-one had a heterozygous Hb McKees Rocks HBB:c.438T>A (p.Tyr146*), and two brothers showed heterozygous Hb Rainier HBB:c.437A>G (p.Tyr146Cys). No pathogenic variants were found in the remaining four cases. A gene-by-gene Sanger sequencing approach could determine a genetic basis for erythrocytosis in 11 of the 15 (73%) Indian families, with homozygous VHL:c.598C>T (p.Arg200Trp) being the commonest pathogenic variant. This first study from the Indian subcontinent provides a rationale for analyzing this variant in patients with suspected congenital erythrocytosis from this region. Rare first occurrences of Hb McKees Rocks and Hb Rainier in Indians are also being reported.

Petrogenesis of the ca. 820–810 Ma felsic volcanic rocks in the Bikou Group: Implications for the tectonic setting of the western margin of the Yangtze Block

The petrogenesis of Neoproterozoic igneous rocks at the northwestern margin of the Yangtze Block and their tectonic setting are controversial. Here we present whole–rock major and trace elements and Nd–Hf isotopic data for felsic volcanic rocks from the Bikou Group. These ca. 820–810 Ma volcanic rocks consist of dacite and rhyolite with SiO2 ranging from 64.4 to 77.0 wt%. Most rocks show decreasing P2O5 with increasing SiO2 and Th and have I–type granite affinities (metaluminous volcanic rocks). However, four rhyolites from the lower part of the Bikou Group show A–type granite affinities (alkaline rhyolites), characterized by high 10,000*Ga/Al and FeOt/(FeOt + MgO) ratios and high (Zr + Nb + Ce + Y) contents. The felsic volcanic rocks commonly have relatively high Zr saturation temperature (up to 960 °C) and most of the felsic volcanic rocks have εNd(t) and εHf(t) values lower than the contemporaneous basalts in the Bikou Group, but higher than the basement rocks in the study area. Among them, four alkaline rhyolites have εNd(t) and εHf(t) values higher than the metaluminous volcanic rocks in the lower Bikou Group. We propose that the metaluminous volcanic rocks were likely produced by partial melting of newly underplated basaltic crust, with involvement of different proportions of basement rocks, whereas a two–stage model is proposed for the formation of the alkaline rhyolites, i.e. partial melting of newly underplated basaltic crust forming early granitoids, followed by low pressure partial melting of these granitoids to generate the alkaline rhyolitic magma. Combined with previous studies, the bimodal occurrence of volcanic rocks within the Bikou Group, and the A–type granite affinity of some rhyolites, as well as the presence of ocean island (OIB)–type basalts in the upper part of Bikou Group, suggest an extensional setting. This is consistent with opening of the Kangdian rift basin to the southwest at this time. We thus propose that the ca. 820–810 Ma Bikou bimodal volcanic rocks formed in response to the breakup of the Rodinia supercontinent.

Petrogenetic controls on the origin of tourmalinite veins from Mandrolisai igneous massif (central Sardinia, Italy): Insights from tourmaline crystal chemistry

An inclusive study of tourmaline, a well-known petrogenetic indicator, allowed the reconstruction of late-stage evolution of B-bearing Variscan granodioritic magmas in Sardinia batholith (Italy). Tourmaline samples from Mandrolisai igneous massif were chemically and structurally investigated by electron microprobe analysis, single-crystal X-ray diffraction, Mössbauer, infrared and optical absorption spectroscopy.Tourmaline aggregates occur both as large crystals displaying graphic textures with quartz, in aplite layers and pegmatite dykes within tonalitic granodiorite, and as fine-grained assemblages, in tourmalinite veins crystallized along fractures within metamorphic country rocks. Tourmaline was identified as schorl in pegmatites and as dravite in veins, both with relevant foitite and magnesio-foitite components. Petrological and mineralogical constraints based on mineral oxythermobarometry and tourmaline crystal chemistry converged towards crystallization temperatures in the range 650–400 °C at about 2.2 kbar, under NNO conditions that remained almost unvaried during the whole magma crystallization path. In the reconstructed scenario, Mandrolisai tourmaline recorded the late stages of consolidation of a single granodioritic magma batch, whose crystallization path locally led to residual concentration of B in the melt. Due to melt/hydrous fluid immiscibility processes, B enrichment promoted the crystallization of the large tourmaline + quartz assemblages in pegmatites. Late B-bearing fluids triggered metasomatic reactions and favored the precipitation of fine-grained tourmaline in tourmalinite veins under a brittle solid-state regime, which overprinted a fracture network of the country rocks previously formed under magmatic flow conditions.Mandrolisai granodiorites are metaluminous (ASI = 0.93–0.95), that is far from the compositional characters of typical B-bearing magmas, mostly felsic and markedly peraluminous (ASI > 1.2). The uncommon occurrence of tourmaline-bearing rocks in Mandrolisai may be an evidence of the limited control exerted by Al2O3 saturation on the origin of tourmaline. Conversely, a more important role of B contents, likely coming from crustal sources, may be invoked for tourmaline saturation in the magma.