Modal Composition Research Articles

Olivine-norite rock detected by the lunar rover Yutu-2 likely crystallized from the SPA-impact melt pool.

Chang’E-4 landed in the South Pole-Aitken (SPA) basin, providing a unique chance to probe the composition of the lunar interior. Its landing site is located on ejecta strips in Von Kármán crater that possibly originate from the neighboring Finsen crater. A surface rock and the lunar regolith at 10 sites along the rover Yutu-2 track were measured by the onboard Visible and Near-Infrared Imaging Spectrometer in the first three lunar days of mission operations. In situ spectra of the regolith have peak band positions at 1 and 2 μm, similar to the spectral data of Finsen ejecta from the Moon Mineralogy Mapper, which confirms that the regolith's composition of the landing area is mostly similar to that of Finsen ejecta. The rock spectrum shows similar band peak positions, but stronger absorptions, suggesting relatively fresh exposure. The rock may consist of 38.1 ± 5.4% low-Ca pyroxene, 13.9 ± 5.1% olivine and 48.0 ± 3.1% plagioclase, referred to as olivine-norite. The plagioclase-abundant and olivine-poor modal composition of the rock is inconsistent with the origin of the mantle, but representative of the lunar lower crust. Alternatively, the rock crystallized from the impact-derived melt pool formed by the SPA-impact event via mixing the lunar crust and mantle materials. This scenario is consistent with fast-cooling thermal conditions of a shallow melt pool, indicated by the fine to medium-sized texture (<3 mm) of the rock and the SPA-impact melting model [Icarus 2012; 220: 730–43].

Electron microprobe petrochronology of monazite-bearing garnet micaschists in the Oetztal-Stubai Complex (Alpeiner Valley, Stubai)

Monazite dating in metapelites is an emerging method to investigate polymetamorphic areas. A protocol for Th–U–Pb dating of monazite by electron microprobe was adopted for a JEOL JXA-8530F. It was applied to the Variscan and Early-Alpine metamorphic Austroalpine Oetztal-Stubai Complex (OSC). In the Alpeiner Valley in the Stubai region, the Schrankogel complex is the eastern succession of the Central Metabasite Zone. In this part, metabasites are alternating with metapelites. In 4 samples from micaschist lenses, dominantly Carboniferous monazite isochrone ages at 335 ± 4 Ma, 320 ± 4 Ma; 319 ± 4 Ma and 319 ± 4 Ma were obtained. The micaschist samples with diverse modal compositions and variable bulk rock Ca contents of calculated assay, display distinct monazite microstructures, as quantified by automated SEM-MLA (mineral liberation analysis) routines. Clusters of small monazite could indicate new crystallization and yielded isochrones at 313 and 304 Ma. In contrast, corona structures of apatite and allanite around large monazites with isochrones between 350 and 315 Ma suggest a decomposition during decreasing temperature. Garnets in metapelitic assemblages display growth zonations with low pyrope contents in the cores and pyrope-rich rims. A prograde metamorphism with high pressure amphibolite-facies peak conditions at ~ 12 kbar and ~ 680 °C, and a post Pmax path with decompression to 4 kbar and 640–600 °C was estimated from the micaschists and from zoned Ca-amphiboles in retrogressed amphibolitized eclogites. The P–T path entered the monazite stability field during the decompression. This signals a Carboniferous age of the metamorphism. A minor population in one sample is composed of sporadic Permian single monazite ages. A Cretaceous monazite population is lacking. In the wide parts of the Austroalpine basement with Carboniferous-to-Cretaceous mica mixing ages, monazite age populations allow to discriminate a distinct Permian metamorphic event.

Petrography and geochemistry of the Lower Silurian sandstones from the Angzanggou Formation in the North Qilian Belt, China: implications for provenance, weathering and tectonic setting

AbstractThe North Qilian Orogenic Belt is on the northeastern margin of the Tibetan Plateau. It is connected with the Alxa Block in the north and the Tethyan orogenic assemblage in the south. The Lower Silurian Angzanggou Formation, deposited in the northern area of the North Qilian Orogenic Belt, is the most important for revealing the architecture and orogenic processes of the North Qilian Belt. Provenance analysis of the Angzanggou Formation can reveal not only the tectonic evolution of the central orogenic belt of China but also Palaeozoic Asia plate reconstructions. Petrographic analysis indicated that the compositional and textural maturity of the sandstones was low. The detrital composition of the Angzanggou Formation samples consists of quartz (8–14 %), feldspar (6–29 %) and lithic fragments (56–86 %). The sandstones could be classified as litharenites or feldspathic litharenites. The detrital modal composition suggests that these sandstones were probably deposited in a fore-arc basin. The element ratios and some discrimination diagrams based on geochemistry indicate that felsic and intermediate rocks were the main source rocks. The SiO2/Al2O3 ratio, the index of chemical variability and the Th/Sc versus Zr/Sc discrimination diagram suggest that the compositional maturity and degree of recycling were moderate to low. The index of alteration (CIA) and the A–CN–K diagram indicate the intensity of weathering was moderate. The discrimination diagrams based on major and trace elements and petrographic discrimination diagrams imply that the Angzanggou Formation rocks were derived from a continental island arc, and a sedimentary cover probably overlaid the volcanic arc. Therefore, we infer that during Early Silurian time the North Qilian Belt sediments accumulated in a fore-arc basin.

Química mineral e condições de cristalização (P-T-ƒO2) do Plúton Maravilha, Domínio PEAL (Província Borborema)

O Plúton Maravilha, localizado no Domínio Pernambuco-Alagoas, tem dimensão de aproximadamente 200 km2, alongado em direção WSW-ENE. Apresenta composição modal tonalítica, textura fanerítica inequigranular, por vezes porfirítica, com quantidades variáveis de plagioclásio, biotita, anfibólio e quartzo, por vezes microclínio, presença de epídoto magmático, tendo como principais fases acessórias titanita, apatita, zircão e allanita. Neste trabalho foram analisadas as principais fases minerais presentes no plúton, visando a compreender sua evolução petrogenética e condições de cristalização. Em porções mais deformadas, o plúton apresenta-se fortemente foliado, marcado pela presença de biotitas primárias, em vasta maioria, cloritizadas nas bordas, podendo ser produto de hidrotermalismo ou de estágios iniciais de reações metamórficas, sendo classificadas entre a solução sólida eastonita-siderofilita. Os anfibólios são predominantemente magmáticos, classificados em grande maioria como pargasita e ferro-pargasita. Cálculos geobarométricos mostram valores de 6 a 7,18 kbar, enquanto a geotermometria foi estimada entre 706 e 785ºC, utilizando o conteúdo de AlIV em plagioclásios e anfibólios em equilíbrio. A presença da assembleia magnetita+titanita+quartzo em equilíbrio, os valores de Fe# na biotita e anfibólios, assim como cristais de magnetita euédricos a subédricos associados à titanita euédrica losangular como fases precoces, indicam que o magma progenitor era relativamente oxidado.

Multi-scale development of a stratiform chromite ore body at the base of the dunitic mantle-crust transition zone (Maqsad diapir, Oman ophiolite): The role of repeated melt and fluid influxes

A stratiform chromite ore body crops out in the lower part of the dunitic mantle-crust transition zone (DTZ) that developed at the top of a mantle diapir in the Maqsad area in the Oman ophiolite. It is made of layers ranging in thickness from a few mm to a maximum of 3 m, and in modal composition from massive to antinodular and disseminated ore. The ore body is about 50 m thick and its lateral extent does not exceed several hundred meters. The layering dips gently to the southeast, parallel to that of the overlying gabbroic cumulates. The chromite composition is typical of a MORB kindred - moderate XCr (100 × Cr/(Cr + Al) atomic ratio), ranging from 48 to 60, and relatively high TiO2 content, ranging from about 0.3 to 0.5 wt% -, a characteristic shared by most lithologies issued from the igneous activity of the Maqsad diapir. The silicate matrix is essentially made of slightly serpentinized olivine with minor clinopyroxene and rare pargasitic amphibole, orthopyroxene and garnet. This strongly contrasts with the nature of the mineral inclusions mostly made of the assemblage amphibole-orthopyroxene-mica, enclosed in the chromite grains and represented in abundance all along the ore body whatever the ore grade. The inclusions demonstrate the involvement of a silica- and water-rich melt and/or fluid, in addition to MORB, in the early stages of chromite crystallization. The chemical composition of chromite, silicate matrix, together with the one of silicate inclusions display well-defined evolutions vertically along the stratiform chromitite. At the scale of the ore body, the compositional trends are independent of the ore concentration but the major kinks in these trends are well-correlated with levels of magmatic breccias. This shows that abrupt chemical changes can be attributed to sudden melt ± fluids injection events followed mainly by melt-fluid-rock interaction and in a lesser extent by quieter evolution by fractional crystallization. At the thin section scale, second order chemical variations, essentially in the Mg# (100 × Mg/(Mg + Fe2+) atomic ratio) of chromite and Fo of olivine, are clearly attributable to re-equilibration between these two solid phases, possibly in the presence of an interstitial melt/fluid.

The baroclinic response to wind in a multiarm multibasin reservoir

AbstractField data, a three‐dimensional hydrodynamic numerical model, and modal decomposition were used to examine the baroclinic response to wind in two interconnected multiarm lakes, Knewstubb and Natalkuz Lakes (British Columbia, Canada). Similar to lakes of simpler geometry, the first‐vertical first‐horizontal mode (V1H1) of Knewstubb and Natalkuz Lakes was found to be the most energetic mode. This V1H1 dominance is attributed to similarity between the relatively uniform distributions of along‐thalweg wind and surface‐layer flow for the V1H1 mode. Two bathymetric features, the geometric constriction between Knewstubb and Natalkuz Lakes, and changes in thalweg orientation relative to the wind field act to create subbasins in which wind forcing causes local metalimnetic tilts. These subbasin scale tilts deepen the metalimnion at the downwind ends of the subbasins, raise the metalimnion at the upwind ends, and are superimposed on the lake‐wide V1H1 tilt. The metalimnetic tilts in the subbasins are attributed to higher horizontal modes that are equivalent to V1H1 modes of the subbasins. Because the thickness of the metalimnion is significant, the subbasin metalimnetic tilts occur with variations in the metalimnetic thickness along the subbasins; the metalimnion is compressed at the downwind end and expanded at the other end of each subbasin. This variability in thickness leads to metalimnetic intrusions following the relaxation of wind forcing. The findings of this study contribute to characterizing the baroclinic response to wind in lakes of complex bathymetry. In particular, this study helps in understanding the effect of bathymetric features on modal composition of the baroclinic response.

Magnesium isotopic composition of metasomatized upper sub-arc mantle and its implications to Mg cycling in subduction zones

Dehydration of subducting oceanic crust and underlying serpentinized mantle is potentially the most important source of fluids for element cycling between surface-processed materials and the interior of the Earth. Magnesium (Mg) isotopes -have been proposed as a promising tracer of dehydration of serpentinites because of their high Mg contents and distinctive Mg isotopic signatures relative to the mantle, which is difficult to identify using other isotopes. To constrain the primary controls on Mg isotope cycling in subduction zones, here we analyze a suite of well-characterized sub-arc mantle xenoliths from the Avacha volcano in southern Kamchatka arc, Russia. They are comparable in modal and/or chemical composition to serpentinized fore-arc harzburgites and sub-arc harzburgite xenoliths from the western Pacific. Despite evidence for ubiquitous slab-related fluid metasomatism, the 23 spinel harzburgite xenoliths and four pyroxenite metasomatic veins display mantle-like δ26Mg values from −0.30 to −0.21‰. Mineral separates have similar δ26Mg values, with an average of −0.26 ± 0.04‰ (2SD, n = 17) for olivine, −0.23 ± 0.04‰ (2SD, n = 17) for orthopyroxene, and −0.24 ± 0.10‰ (2SD, n = 5) for late-stage interstitial clinopyroxene. The lack of a clear slab-derived δ26Mg signature in the Avacha sub-arc peridotites is probably due to their high MgO contents and low fluid/rock mass ratios during flux melting and metasomatism. We also compare published δ26Mg data for four volcanic arcs distributed worldwide. This inter-arc comparison reveals that the thermal structure of a subduction zone appears to exert a strong control on the efficiency of Mg isotope cycling from the downgoing slab to the mantle wedge and subsequently to the arc magmas; those arcs that permit large-scale dehydration of Mg-rich serpentinized slab mantle, coupled with available channelized fluid pathways, are more likely to produce isotopically diverse arc magmas.

Mineral chemistry of the Xiasai Ag–Pb–Zn deposit in the central Yidun Terrane, SW China: Insight into Ni–Ag–Bi mineralization and formation conditions

Sulfides and sulfosalts are major ore minerals for most of Ag–Pb–Zn deposits and can be used to study enrichment and distribution of ore-forming elements and formation conditions. The Xiasai Ag–Pb–Zn deposit (Zn 0.141 Mt @ 4.30%, Pb 0.132 Mt @ 4.03%, Ag 1028 t @ 337.8 g/t, Cu 10058 t @ 0.56%, and Sn 20000 t @ 0.75%) is a hydrothermal vein-type deposit in the central Yindun Terrane, SW China. It consists of proximal quartz-cassiterite veins and distal Ag–Pb–Zn sulfide veins to a Cretaceous monzogranite. Three successive mineralization sub-stages are recognized for Ag–Pb–Zn veins, i.e., arsenopyrite + coarse-grained pyrite (Py1) + pyrrhotite, sphalerite + chalcopyrite + fine-grained pyrite (Py2), and silver-minerals + native bismuth + galena.Nickel-minerals, such as breithauptite and ullmannite were identified as inclusions hosted within pyrrhotite using Energy Dispersive X-ray Spectroscopy (EDS) and Electron probe microscopy (EPM) analysis and mapping. Trace amounts of invisible silver have been detected in chalcopyrite and galena, whereas a significant amount of silver is incorporated in pyrargyrite, freibergite, miargyrite, and electrum as intimate intergrowths with galena or inclusions within galena. A high content of invisible bismuth is detected within galena (0.21–16.95 wt%), as well as numerous grains of native bismuth occur as inclusions in galena. Based on the Bi concentrations determined and the modal composition a large-sized bismuth deposit would be estimated with about 23,800 t of Bi resource. The presence of nickel-minerals and native bismuth, together with Zn/Cd ratios (58–151) of sphalerite, indicate that the ore-forming materials are derived from the Xiasai monzogranite.Based on mineral assemblages and chemical features for sulfides and sulfosalts, the formation of Ag–Pb–Zn ores was triggered by a decrease in temperature, fs2, fO2, and sulfidation. The early episode of arsenopyrite, Py1, pyrrhotite, and nickel-minerals formed at temperature of 320–470°C, lower fs2 and decreasing sulfidation conditions from low alkaline fluids. In contrast, the late episode of silver-minerals, native bismuth, and galena deposited at 160–270 °C with a lower fs2 state and neutral or acidic pH. However, a slight increase of fs2, fO2, and sulfidation (intermediate sulfidation) occurred during precipitation of Zn–Cu.

Reconstruction of Paleo depth and Paleo temperature from C- O stable isotope records of Mishrif Formation, southern Iraq

Stable isotopes 18O/16O and 13C/12C in the carbonate rocks of the Mishrif Formation are examined here to define the depositional characters in the basin includes paleo temperatures and paleo depth.&#x0D; The Mishrif formation (Cenomanian – Early Turonian) has extensive distribution in Iraq and Middle East. Mishrif Formation composed of organic detrital limestone. Four boreholes in four oilfields, Noor – well (11), Amarah – well (14), Buzurgan – well (24), Halfaya – well (8), in south east of Iraq have been studied.&#x0D; The studied samples have negative δ18O isotope values studied well, with Average (-4.11‰), (-4.47‰), (-4.48‰), (-4.18‰) in the studied wells respectively. Carbon Isotope composition positive values in the study samples, with average (2.32‰), (1.84‰), (2.20‰), (2.24‰) are studied well respectively. The Stable isotope (18O/16O and 13C/12C) of Mishrif Formation provide the first records of paleotemperature for the (Cenomanian – Early turanian ) which indicate moderate during deposition.&#x0D; The plot of depositional environment refers to warm water carbonate sediment and the bulk samples cluster tightly to small positive reflect modal isotope composition of dominant skeletal marine carbonate. The paleo-salinity (Z values) provide the marine deposits in studied samples. As the paleo-temperature was high temperature by (T values). The paleo depth he all studied samples in the four oilfields are fall in the same level which is in the upper part of Thermocline this indicate the moderate depth

Skarn formation and tin enrichment during regional metamorphism: The Hämmerlein polymetallic skarn deposit

The Hämmerlein Sn-rich polymetallic skarn deposit (Erzgebirge, Germany), which is hosted by Variscan schists and gneisses, includes garnet, amphibole, pyroxene, and magnetite skarns that formed during regional metamorphism at ∼340 Ma. The skarn deposit was overprinted during the intrusion of the ca. 320 Ma Eibenstock granite. Tin was introduced into the system during regional metamorphism at 340 Ma (Sn mostly hosted in silicate minerals) and after the intrusion of the Eibenstock granite at c. 320 Ma (Sn hosted in cassiterite). The emplacement of late stage melts of the Eibenstock granite also resulted in the formation of cassiterite-quartz veins in the schists hosting the Hämmerlein skarns and at some distance in the formation of several cassiterite greisen.Major, trace, and rare earth element data of the skarn units and their hosts rocks demonstrate that skarns formed from impure carbonates with variable proportions of silicate minerals. Depending on the original modal compositions of the skarns and their host rocks, the mineralizing fluid selectively added and removed elements, which resulted for the skarns and the schist ore in a general enrichment in Sn, In, Cu, and W and a noticeable depletion in Al and Sr. The Sr, Nd, and Pb isotopic composition of the skarns, schists, and gneisses resembles those of the metamorphic rocks of the Erzgebirge rather than those of the granites, possibly indicating that the geochemical signature of granite-derived fluids had been severely altered during fluid-rock interaction before these fluids reached the skarns, schists, and gneisses. Similarly, the Li and B isotopic composition of the skarn samples reflects the likely range of possible source rocks for metamorphic fluids, rather than the composition of the granite-derived fluid. In contrast, the Li and B signature of greisen samples shows a variable mixture of material derived from the granite and the metasedimentary rocks, respectively.Our data show that a first Sn enrichment took place when the Paleozoic sedimentary rocks were affected by regional metamorphism at ca. 340 Ma. Fluids derived from these siliciclastic sedimentary protoliths mobilized and transported Sn and Fe. These fluids reacted with the impure carbonates, resulting in decarbonation and the formation of calc-silicate minerals and biotite in the various skarn types. The changing fluid composition as well as the incorporation of Fe in skarn silicates and formation of Fe-oxides resulted in the incorporation of Sn into silicate minerals. During or after the emplacement of the Eibenstock granite, the original skarn was to a variable extent retrogressed and Sn was released from Sn-bearing calc-silicates and biotite. During this event additional Sn was added to the skarn and the hosting schists. Released Sn and newly added Sn precipitated as cassiterite.

Electrical conductivity of OH-bearing omphacite and garnet in eclogite: the quantitative dependence on water content

Eclogite is potentially an important constituent in local regions in the deep crust and upper mantle. The electrical conductivity of omphacite and garnet in eclogite has been measured at 1 GPa and 350–800 °C with pre-annealed OH-bearing samples. The conductivities were determined using a piston–cylinder apparatus and a Solartron-1260 Impedance/Gain Phase Analyser in the frequency range of 106–1 Hz. The sample water contents show almost no change before and after the experimental runs. The conductivity of both omphacite and garnet increases with temperature, and the activation enthalpy is ~ 82 kJ/mol for omphacite and 90 kJ/mol for garnet, which is nearly independent of water content in each mineral. The conduction is probably dominated by protons, and for both minerals, the conductivity increases linearly with water content, with a water content exponent of ~ 1. These data are used to model the bulk conductivity of an eclogite with different water contents and modal compositions. In combination with reported data, the conductivity of the eclogite is similar to that of typical granulites above 600 °C, but is much larger than that of olivine, assuming small to moderate water contents. This would mean that the contribution of eclogites, if present, to the electrical structure of the deep continental crust cannot be easily separated from that of granulites, and that the regional enrichments of eclogites in the upper mantle may cause high electrical anomalies. The results also provide information for the electrical property of orogen-related thickened deep crust where eclogites may be locally abundant, e.g., in the Dabieshan region and the Tibet plateau. At mantle depths, eclogitized portions of subducted slabs are usually of very low conductivities as suggested by geophysical observations, implying small water contents in the constitutive omphacite and garnet and the limited ability of these minerals in recycling water into the deep mantle.

Hydrochloric Acidic Processing of Titanite Ore to Produce a Synthetic Analogue of Korobitsynite

The modal composition of (apatite)-nepheline-titanite ore and its geological setting within apatite deposits of the Khibiny Massif allow selective mining of titanite ore and its hydrochloric acidic processing. The reaction of titanite with concentrated hydrochloric acid produces hydrated titanosilicate precipitate (TSP) which, in turn, can be a precursor in titanosilicate synthesis. It is particularly noteworthy that a synthetic analogue of korobitsynite, Na5(Ti3Nb)[Si4O12]2O2(OH)2·7H2O, was synthesized by means of TSP alteration by alkaline hydrothermal solution at 200 °C within three days. The titanosilicate obtained this way has comparatively weak cation-exchange properties regarding Cs+ and Sr2+ cations and considerable photocatalytic activity occurring under visible light, which allows the use of a synthetic korobitsynite analogue (SKR) for production of self-cleaning, sterilizing, and anti-fouling building materials.

Quantitative comparison of microfabric and magnetic fabric in black shales from the Appalachian plateau (western Pennsylvania, U.S.A.)

Anisotropy of magnetic susceptibility (AMS) has been shown to be a good proxy for crystallographic preferred orientation (texture). However, it is not clear in detail how different factors, e.g. modal composition and preferred orientation, define the total AMS in a rock. Black shale samples from a drill core on the Appalachian Plateau in western Pennsylvania were analyzed with respect to their microfabric as determined by texture and microstructure, and AMS. Low- and high-field AMS, which was measured at room temperature, reveals that the AMS of the samples is dominated by the para- and diamagnetic phases. Synchrotron diffraction was applied to determine the texture of all relevant mineral phases incorporated in the samples. Muscovite and chlorite pole figures show single maxima perpendicular to the foliation, reflecting dominant flattening strain. From these textures and the modal compositions, AMS models were calculated using the intrinsic magnetic anisotropy of the single crystals. The modeled and measured AMS are comparable in terms of their principal directions and shapes of the anisotropy ellipsoid for the dominantly paramagnetic samples, with the maximum susceptibility axes oriented subhorizontal to the NE-SW. Both, textures and AMS, indicate that the samples have undergone largely bedding compaction with a weak tectonic overprint linked to the Alleghenian orogeny. Our results suggest that the microfabric and the magnetic fabrics on the plateau, 200 km away from the Allegheny Front, detect the tectonic shortening. The AMS modeling demonstrates how the contribution of the intrinsic AMS of each mineral controls the AMS of the whole rock.

Djerfisherite in monticellite rocks of the Krestovskaya Intrusion (Polar Siberia)

Djerfisherite in the monticellite rocks of the Krestovskaya Intrusion is found in primary melt inclusions, mono- and polysulfide globules, and in the djerfisherite–hydrogarnet segregations. Melt inclusions are represented by three types. Type I is observed in the cores of perovskite phenocrysts and monticellite grains and corresponds to one of the early crystallization stages of the parental larnite-normative alkali ultrabasic magma enriched in water and other volatiles. Daughter phases of the inclusions are clinopyroxene, serpentine, phlogopite, apatite, nepheline, hydrogarnet, magnetite, djerfisherite, pectolite, and calcite. In some type I inclusions, melt at 1230–1250°C was immiscibly split into two fractions: alkali silicate fraction and highly fluidized water-bearing low-silica fraction enriched in alkali, sulfur, and CO2. The types II and III inclusions in perovskite, monticellite, Ti-garnet, and melilite were formed through the spatial separation of immiscible phases. This follows from the similarity of the modal composition of types II and III melt inclusions to the normative composition of immiscible fractions of type I inclusions. Type II inclusions contain mainly water-bearing silicate daughter phases (hydrogarnet, serpentine, phlogopite, and pectolite), as well as djerfisherite, calcite, and magnetite, Type III inclusions contain clinopyroxene, nepheline, apatite, magnetite, djerfisherite, calcite, and pectolite. The djerfisherite–hydrogarnet segregations are confined to the Ti-magnetite and perovskite phenocrysts and fractures radiating from them in monticellite. The mineral composition of the djerfisherite–hydrogarnet segregations together with their surrounding is similar to the composition of type II inclusions containing similar water-bearing silicates, djerfisherite, calcite, and magnetite.&#x0D; Such similarity gives grounds to relate the formation of the djerfisherite–hydrogarnet segregations, as type II inclusions, with the spatial separation and crystallization of highly fluidized low-silica melt enriched in water, alkalis, sulfur, and CO2. According to the homogenization experiment, the crystallization of highly fluidized melt at 990–1090°C was accompanied by silicate–sulfide immiscibility and the formation of globular, emulsion-like, and myrmekite structures in the djerfisherite–hydrogarnet segregations, as well as mono- and polysulfide globules with djerfisherite in the hydrogarnet–calcite–serpentine substrate. The formation of ferrobrucite–carbonate–hydrogarnet globules in the djerfisherite–hydrogarnet segregations was also related to melt liquation, which again confirms the magmatic origin of the latter. Sometimes, djerfisherite in the djerfisherite–hydrogarnet segregations becomes coarser and forms rims, bands, and veinlets, which is likely explained by the high mobility and low viscosity of sulfide melt. Scarce grains of heazlewoodite, godlevskite, and pentlandite hosted in the djerfisherite–hydrogarnet segregations frequently have the same shape as djerfisherite, which indirectly suggests their simultaneous crystallization from the same melt. The chemical composition of the djerfisherite from mono- and polysulfide globules, djerfisherite–hydrogarnet segregations, and type I inclusions, as most Yakutian kimberlites, is characterized by the high (12.1–16.7 wt %) Ni and low (0.1–0.9 wt %) Cu contents. The composition of the djerfisherite from types II and III inclusions differs in the lowered (3.3–1.6 wt %) Ni and elevated (40.9–53.2 wt %) Fe contents; type III inclusions have high Cu content: from 7.6 to 10.6 wt %.

Traveling Wave Analysis of Non-Thermal Far-Field Blooming in High-Power Broad-Area Lasers

With rising current, the lateral far-field angle of high-power broad-area lasers widens (far-field blooming), which can be partly attributed to non-thermal effects due to carrier-induced refractive index and gain changes that become the dominant mechanism under pulsed operation. To analyze the non-thermal contribution to far-field blooming, we use a traveling wave-based model that properly describes the injection of the current into and the diffusion of the carriers within the active region. Although no pre-assumptions regarding the modal composition of the field is made and filamentation is automatically accounted for, the highly dynamic time-dependent optical field distribution can be very well represented by only a few modes of the corresponding stationary waveguide equation obtained by a temporal average of the carrier density and field intensity. The reduction of current spreading and spatial holeburning by selecting proper design parameters can substantially improve the beam quality of the laser.

Immature beach/dune sands along a passive continental margin: Composition, grain size and hydraulic properties of coastal sands, Parque del Plata and Las Vegas, Uruguay

AbstractThe modal composition of sandstones has long been used as a tool for palaeotectonic and palaeoenvironmental analyses. Herein it is demonstrated that caution must be used when beach sand composition is utilized to assess tectonic provenances at both the local and continental scales. The occurrence of quartz arenites and compositionally mature sands along the coast of Brazil corresponds well to their passive margin location. However, modern sands from some beach locations in coastal Uruguay are less compositionally mature compared to the quartz arenites found in coastal Brazil. Along the beaches of Las Vegas and Parque del Plata, the composition of the beach and dune sands is impacted by the transport of continental outwash sediments derived from the Palaeozoic and Precambrian rocks in the interior to the beach by a low‐gradient stream, Arroyo Solis Chico, and the erosion of Pleistocene‐age formations that crop out on the beach and along an erosional scrap. The mean beach composition ratio of monocrystalline quartz to feldspar to rock fragments plus composite quartz grains is 67.5/8.0/24.5 compared to the ratio along the coast of Brazil at 86/4/10. The beach and coastal dunes environment studied is representative of about 35% of coastal Uruguay. At the smaller scale, changes in the textural properties of the beach and dune sands (grain‐size distribution and roundness) are caused by the addition of the sediment derived from erosion and stream transport. Porosity values show little influence and range between 0.35 and 0.36, but hydraulic conductivity is influenced to a greater degree, ranging from 18.5 to 31 m/day. Within one kilometre down‐drift of the river, the mean grain diameter and the mean hydraulic conductivity increase to the same values found in the up‐gradient area before influence of the sediment flux, due to the offshore transport of the finer sediment fraction during down‐gradient movement along the beach. The Arroyo Solis Chico area demonstrates that abrupt changes in composition and hydraulic properties can occur over short distances in sands deposited in passive margin environments. The potential for this local variability in sand composition and hydraulic properties should be considered in the analyses of ancient marine sandstones deposited in beach and coastal dunes environments.

Parâmetros Normativos das Rochas Ornamentais Pegmatíticas do Seridó Oriental Paraibano - Pedra Lavrada/PB

The rocks studied in the present work are known commercially as White Fuji, Capuccino Fuji and Golden Fuji. They come from the same mining front located in the municipality of Pedra Lavrada/PB. They have a similar mineral composition, consisting mainly of quartz, plagioclase, muscovite, microcline and garnet with modal composition between 5% and 34% and accessory minerals, with a modal composition of less than 5%, especially sericite, biotite and opaque. Petrographically correspond to pegmatites with isotropic structure, mineral granulation ranging from medium to very coarse, high degree of mineral microcracking, incipient to moderate mineral alteration and predominant concave-convex mineral contacts. The values obtained for the physical-mechanical properties indicate that the pegmatites investigated can be used as ornamental and coating rock, however, reservations regarding the use of the White Fuji pegmatite are required, as a function of their performance in the porosity, water absorption, uniaxial compressive strength and flexural strength exhibit values lower than the limits established by current standards. The results obtained in the radon exhalation of the studied rocks are considered high: White pegmatite (215,0 Bq/m 3 ), Capuccino (176,3 Bq/m 3 ) and Golden (156,0 Bq/m 3 ). The results for radon gas exhalation efficiency demonstrate that the amount of 222 Rn effectively emanated in the rocks is small relative to the total amount of 222 Rn generated. The simulation for indoor environments shows that the dosimetric values obtained for White pegmatite were 0,88 pCi/L; 0,73 pCi/L for Cappuccino pegmatite and 0,64 pCi/L for Golden pegmatite revealing values below the dosimetric limit suggested by the United States Environmental Protection Agency.

Petrology of Spinel-Gedrite-Cordierite Symplectites Replacing Andalusite in Migmatites from the Sarabi Area, Hamedan, Sanandaj–Sirjan Zone, Iran

Metapelitic migmatites in the Hamedan area of Sanandaj–Sirjan Zone, Iran, contain spinel + gedrite + cordierite (± biotite, ± staurolite, ± ilmenite) symplectite, replacing andalusite in metatexite and diatexite. P-T conditions of metamorphism for cordierite-hornfels, andalusite-cordierite-hornfels and migmatites were estimated as 600°C, 2.2 kbar; 645°C, 2.9 kbar and 760°C, 3.7 kbar respectively, using calculated pseudosections for an average composition in the NCKFMASH system. Calculated pseudosection is in accordance with field and petrographic observation, except that symplectite minerals does not appear in the model, suggesting that formation of symplectite was affected by effective bulk compositions (EBC), rather than whole-rock composition. So EBC model was calculated using modal abundance and average composition of symplectite minerals. In pseudosection calculated for EBC, spinel + gedrite + cordierite is stable over wide range of P and T. Peak metamorphic condition for symplectites are estimated as 750°C at 4.1 kbar. Staurolite-bearing symplectites appeared during retrograde isobaric path at 600°C and 4.1 kbar. Based on calculated pseudosections and estimated P and T, an isobaric retrograde anticlockwise P-T path is proposed for the Sarabi migmatites. Metamorphism and migmatization in the area is linked to the major plutonism phases of the Sanandaj–Sirjan Zone in Middle-Jurassic under high T-low P conditions, during the evolution of Neo-Tethys.

Prediction Approach for Petrothermal Properties in Al Hashimiyya Basalts-Jordan

Thermal conductivity and mineral composition of flood basalt in Al Hashimiyya city were correlated. Representative thin sections were optically analyzed for their mineral constituents and micro fractures. Findings of this study will contribute to a comprehensive understanding of the correlation between selected petrological characteristics of basalts and their heat conduction properties. It found that a 10% increase of opaque and ferromagnesian minerals volume in the studied basalts leads to a thermal conductivity increasing by 0.4 W•m−1•K−1. This may considerably contribute to provide an alternative to direct measurements of the thermal conductivity in Jordan basalts if a sufficient mineralogical data set is achievable. Thus, the prediction of thermal conductivity through modal mineral composition may become a significant feature for efficient geothermal system exploration in basaltic rocks. The results can be brought together into a petrophysical and hydrogeothermal model for better reservoir characterization. Such models will improve the assessment of the basalt’s suitability as a geothermal reservoir for cooling and heating utilizations.

A Method for the Evaluation of Generator Damping During Low-Frequency Oscillations

A new generator phasor measurement unit can provide a generator internal response during transient periods, thereby enabling online evaluation of generator damping in detail. In this paper, a method for the online detailed evaluation of the generator damping contribution during oscillation periods based on the damping loss factor (DLF) and multi-scale chirplet sparse signal decomposition (MCSSD) is proposed. First, the DLF in a simple elastic oscillation system, which can be used to quantitatively evaluate the damping characteristics of components, is introduced. After analyzing the feasibility of using the DLF during low-frequency oscillation, the generator damping loss factor (GDLF) is established to quantitatively evaluate the generator damping contribution, including the effects of the excitation system, governor system, and generator winding. Next, the modal composition of the generator dissipation energy is studied to extend the application of the GDLF to a multi-machine power system. Finally, a method for the online evaluation of generator damping during low-frequency oscillation based on the GDLF and MCSSD is presented. The proposed method is examined in detail using a single-machine infinite-bus system and then further demonstrated by applying it to a practical power system with multiple electromechanical oscillations.