Minerals In Volcanic Rocks Research Articles

Snow survey within the copper ore deposits in the mining regions of the Urals

The paper presents the results of studies of dust residues of snow cover within various climatic zones and copper deposits of the Ural region. Snow cover research is one of the methods for environmental assessment of territories. This concerns the study of dust residues from snow cover samples, as shown by the example of the territories of the Northern and Southern Urals at different stages of work on copper deposits. The initial stage of study and development is considered using the example of porphyry copper deposits in the Chelyabinsk region, where snow samples reveal organic matter in dust residues, typical birch seeds, a small amount of minerals at a low dust load (P ˂ 100 kg/day per km2). For the deposits of the Ivdel region (Northern Urals), the dust residues largely contain organic dust, fragments of ore minerals (pyrite, chalcopyrite) and minerals of volcanic rocks and metasomatic rocks. The maximum value of the dust load is set for the Novo-Shemurskoye deposit currently being developed. A study of dust residues in the zone of influence of the Karabash copper smelter (before its reconstruction) has shown that in some parts of the sanitary protection zone the level of snow cover pollution is very high with dust load values up to 12,633 kg/day per km2, which is determined primarily by the widespread use of crushed copper smelting slag. In general, the study of dust residues of snow cover provides information about both the ecological state of the territories and the mineral composition of the residues, which must be used for practical purposes.

Concurrent magma mixing and crystallization processes revealed by clinopyroxene macrocrysts from Lamont guyot lavas in NW Pacific

Minerals in volcanic rocks have been commonly used to reconstruct the physicochemical conditions of crystallization and magma chamber processes (magma mixing and recharge) prior to eruption which are fundamental to deduce the petrogenesis of volcanic rocks. Here we present mineral chemistry including in situ major-trace element and Sr isotopic data for clinopyroxene (Cpx) and plagioclase macrocrysts from lavas collected from Lamont guyot in the Wake seamount group, NW Pacific. The Cpx macrocrysts display normal and reverse zoning or complex zoning (e.g., combination of reverse, normal, sector and/or patchy zoning). The normally-zoned Cpx macrocrysts are euhedral and in Fe Mg equilibrium with the host rock compositions. In contrast, the cores of reversely- and complexly-zoned Cpx macrocrysts are in textural (e.g., resorption texture) and chemical (very low Mg#) disequilibrium with their host rock compositions. These reversed cores, however, form coherent compositional trends with and display parallel trace element patterns to the normally zoned Cpx crystals, suggesting that these resorbed cores are most likely antecrysts which crystallized from progenitor melts. The continuously changing major-trace element contents with Cpx Mg# values can be explained by crystallization of these Cpx crystals from melts that progressively fractionate Cpx, plagioclase and Fe Ti oxides. Together with those of the complexly-zoned plagioclase, the complex zoning patterns and large ranges of La/Yb and Sm/Yb ratios at a restricted Cpx Mg# range record magmatic processes of fractional crystallization and mixing in the magma plumbing system. The Cpx crystals from a single lava sample have various 87 Sr/ 86 Sr ratios (0.7025–0.7042) extending from HIMU (high μ = 238 U/ 204 Pb) to FOZO (focal zone) mantle components suggesting that the large 87 Sr/ 86 Sr variation in Cpx could be explained by mixing between HIMU and FOZO components. Our data suggest that frequent recharging of melts derived from different mantle sources and concurrent mixing and crystallization are important processes that shape the currently observed compositional variation of Lamont guyot lavas. • Textural and compositional zoning of Cpx from Lamont seamount lavas, NW Pacific • Cpx shows large trace element and 87 Sr/ 86 Sr variations at a restricted Mg# range. • Reverse and complex zoning textures of Cpx record magma recharge and mixing. • Mixing of multiple batches of HIMU- and FOZO-derived melts. • Concurrent mixing and crystallization played a key role in forming the Cpx crystals.

Rheological properties of concentrated allophane, halloysite, and kaolinite suspensions

This study investigated the rheological properties of concentrated suspensions of allophane, halloysite, and kaolinite, which are representative of a series of weathering products of volcanic glass and feldspar minerals in volcanic rocks and deposits, to elucidate the mechanism of landslide generation involving these materials. All suspensions generally showed shear thinning during flow curve measurements, as represented by a steady decrease of viscosity with increasing shear strain rate from 0.1 to 1000 s−1. A difference among them was that the kaolinite suspension showed unstable flow behavior at high solid concentration, and the halloysite suspension had a similar behavior at low solid concentration. The shear stress at the beginning of flow—which represents the yield stress of the suspension—showed a power law correlation with the solid volumetric fraction, and that for kaolinite agreed well with previous static yield stress measurements. The stress of the halloysite suspension deviated from the power law curve at solid fraction < ~0.15. Dynamic viscoelasticity tests indicated that all suspensions showed a power law correlation between the modulus value and solid fraction. The crossover strain (when a solidlike-to-liquidlike transition occurs) of the kaolinite suspension was almost constant within the investigated solid fraction range, whereas that of the halloysite suspension decreased noticeably at solid fraction < ~0.15. Overall, the allophane suspension had the weakest strength and lowest resistance to oscillatory strain at a given solid fraction condition. The rheological properties of halloysite observed here may be related to the occurrence of flow-like, long-distance landslides in volcanic areas containing weathered tephra.

Diffusion chronometry of volcanic rocks: looking backward and forward

Diffusion of elements that result in compositional zoning in minerals in volcanic rocks may be used to determine the timescales of various volcanic processes (e.g., residence times in different reservoirs, ascent rates of magmas). Here, we introduce the tool and discuss the reasons for its gain in popularity in recent times, followed by a summary of various applications and some main inferences from those applications. Some specialized topics that include the role of diffusion anisotropy, isotopic fractionation by diffusion, image analysis as a tool for expediting applications, and the sources of uncertainties in the method are discussed. We point to the connection between timescales obtained from diffusion chronometry to those obtained from geochronology as well as various monitoring tools. A listing of directions in which we feel most progress is necessary/will be forthcoming is provided in the end.

3He/4He Signature of Magmatic Fluids from Telica (Nicaragua) and Baru (Panama) Volcanoes, Central American Volcanic Arc

Constraining the magmatic 3He/4He signature of fluids degassed from a magmatic system is crucial for making inferences on its mantle source. This is especially important in arc volcanism, where variations in the composition of the wedge potentially induced by slab sediment fluids must be distinguished from the effects of magma differentiation, degassing, and crustal contamination. The study of fluid inclusions (FIs) trapped in minerals of volcanic rocks is becoming an increasingly used methodology in geochemical studies that integrates the classical study of volcanic and geothermal fluids. Here, we report on the first noble gas (He, Ne, Ar) concentrations and isotopic ratios of FI in olivine (Ol) and pyroxene (Px) crystals separated from eruptive products of the Telica and Baru volcanoes, belonging to the Nicaraguan and Panamanian arc-segments of Central America Volcanic arc (CAVA). FIs from Telica yield air corrected 3He/4He (Rc/Ra) of 7.2–7.4 Ra in Ol and 6.1–7.3 in Px, while those from Baru give 7.1–8.0 Ra in Ol and 4.2–5.8 Ra in Px. After a data quality check and a comparison with previous 3He/4He measurements carried out on the same volcanoes and along CAVA, we constrained a magmatic Rc/Ra signature of 7.5 Ra for Telica and of 8.0 Ra for Baru, both within the MORB range (8 ± 1 Ra). These 3He/4He differences also reflect variations in the respective arc-segments, which cannot be explained by radiogenic 4He addition due to variable crust thickness, as the mantle beneath Nicaragua and Panama is at about 35 and 30 km, respectively. We instead highlight that the lowest 3He/4He signature observed in the Nicaraguan arc segment reflects a contamination of the underlying wedge by slab sediment fluids. Rc/Ra values up to 9.0 Ra are found at Pacaya volcano in Guatemala, where the crust is 45 km thick, while a 3He/4He signature of about 8.0 Ra was measured at Turrialba volcano in Costa Rica, which is similar to that of Baru, and reflects possible influence of slab melting, triggered by a change in subduction conditions and the contemporary subduction of the Galapagos hot-spot track below southern Costa Rica and western Panama.

Interpretation of the origin of analcimes with mineralogical, microtextural, and geochemical investigations: a case study from Aktepe region (NE of Kalecik, Ankara, Central Anatolia, Turkey)

The presence of analcime minerals in volcanic rocks is a topic requiring attention during classification of rocks. In fact, when transformation from leucite to analcime is present, the original chemistry of the rock will change and this situation will cause falsification in identification of the original character of the rock. As a result, it is important to determine the origin of the analcime in rocks containing analcime. This study focuses on the investigation of the origin of analcimes occurring in alkaline volcanic rocks (tephrite, phonotephrite) of the Aktepe region, located in the northeastern part of Ankara (Central Anatolia, Turkey). These volcanic rocks consist of abundant clinopyroxene, analcime, Fe-Ti oxides, minor olivine pseudomorphs, and scarce microcrystals of feldspar. The analcime phenocrysts are typically euhedral to anhedral (nearly rounded) in shape with up to 1 cm diameter and there are no other hydrous minerals in the samples. Leucite-like crystals are rarely preserved in the cores of larger analcime crystals and twin lamellas observed in them could demonstrate this preservation. Even partially transformed leucites are rare but not impossible to find in nature because of the rapid kinetics of the transformation of leucite to analcime. Examination of microprobe and EDS spectra, corona-type texture observed around the analcime–leucite interface suggest that some leucite crystals did not transform entirely to analcime crystals and a progressive transformation of leucite into analcime occurred locally in the region. Analcime and preserved leucite-like crystal existence could also be seen from the obtained X-ray diffractograms. The fresh fracture surfaces of separated large analcime crystals have microporous texture indicating a characteristic feature of analcimes that formed by an ion-exchange process from leucite. Geochemically, calculations of gains and losses of Na and K contents from the original bulk-rock chemical composition reveal that Na content increase is counterbalanced by a decrease in K content. This could also be strongly explained by an analcimization process and/or progressive transformation of leucite into analcime. It is concluded that analcimes formed secondarily from leucite by an ion-exchange process after cooling of magma via graded infiltration of Na-bearing fluids into the Aktepe ultrapotassic alkaline volcanic rocks.

Copper and Li diffusion in plagioclase, pyroxenes, olivine and apatite, and consequences for the composition of melt inclusions

Silicate melt inclusions are an important tool to reconstruct original concentrations of volatiles and metals in silicate melts, as these constituents are partly lost during magma solidification. However, melt inclusions analyzed in co-precipitated minerals in volcanic rocks commonly show strongly divergent Cu contents, raising doubts about the validity of their composition. To understand the origin of this divergence a multiple approach was followed. First, the phenomenon was documented by recording petrographic details of five volcanic samples and analyzing 189 melt inclusions by laser-ablation ICP-MS. Second, diffusion experiments on gem-quality plagioclase, clinopyroxene, orthopyroxene, apatite and olivine were performed in a gas mixing furnace to constrain diffusion coefficients of Cu and to a lesser extent of Li. Third, re-equilibration experiments were performed on melt inclusions within plagioclase crystals to induce changes in their Cu and Li contents.The LA-ICP-MS analyses reveal that plagioclase-hosted and orthopyroxene-hosted melt inclusions in volcanic rocks commonly contain an order of magnitude more Cu than melt inclusions in co-precipitated clinopyroxene and olivine. Plagioclase-hosted melt inclusions in intrusive rocks, on the other hand, do not show this divergence. The diffusion experiments conducted on minerals find that Cu and Li diffusion in plagioclase is extremely fast (log D = −13.0 to −11.5 m2 s−1 at 1000 °C) and in both cases occurs via two separate diffusion mechanisms. Copper diffusion coefficients in apatite, clinopyroxene, orthopyroxene and olivine are 2–3 orders of magnitude lower but are still high compared to most other elements. Both the re-equilibration experiments on melt inclusions and quantitative modeling based on the measured diffusion coefficients demonstrate that at 1000 °C plagioclase-hosted melt inclusions can re-equilibrate their Cu and Li content with that of the surrounding magma within a few hours to a few weeks, whereas apatite-, clinopyroxene-, orthopyroxene- and olivine-hosted melt inclusions require tens of years to hundreds of years to do so. Abnormally high Cu contents of plagioclase- and orthopyroxene-hosted melt inclusions appear to result from postentrapmental Cu gain. In the case of orthopyroxene-hosted melt inclusions Cu seems to have been gained as a consequence of postentrapmental sidewall crystallization, which triggered the formation of sulfide globules that acted as a Cu sink. This process likely occurred at depth in magma chambers. Plagioclase-hosted melt inclusions, on the other hand, seem to have gained Cu in exchange for hydrogen that diffused out of the melt inclusions during or after volcanic eruption. Our results suggest that Cu (and also Li) concentrations measured in melt inclusions have to be generally treated with caution, and that particular prudence has to be used in the case of plagioclase and orthopyroxene hosts.

General characteristics of the geochemical evolution of silicic melts during the development of massive sulfide magmatic ore systems: Evidence from the investigation of melt inclusions

The investigation of melt inclusions in the minerals of volcanic rocks from the massive sulfide deposits of Siberia and the Urals revealed some specific features in the development of their magmatic ore systems. It was shown that the petrochemical and rare earth element compositions of melt inclusions reflect the geodynamic conditions of their formation: island arc conditions for the massive sulfide deposits of Rudny Altai, eastern Tuva, and the Salair Range and a back arc basin environment for the Yaman-Kasy deposit. The silicic melts of inclusions from the volcanic rocks of massive sulfide deposits show some specific features with respect to the contents of volatile components. In all of the ore deposits studied, fluorine content was always low (0.03–0.08 wt %), whereas chlorine content (0.13–0.28 wt %) was higher than the average value for silicic melts (0.17 wt %). There is a strong differentiation of water content in melt inclusions, both between deposits and between various volcanics from a single deposit. Ore-bearing melts show the highest water contents of 3.34–4.07 wt %. High Cu contents in the silicic melts of the Yubileinoe and Kyzyl-Tashtyg deposits (up to 7118 and 3228 ppm, respectively) may indicate the affinity of some ore components to particular silicic magmas. This is supported by the elevated contents of Cu in the porphyry Cu deposits of Romania (Valea Morii), Mongolia (Bayan Ula), and Bolivia. On the other hand, the silicic melts of inclusions from the molybdenum-uranium deposit of the Strel’tsovka ore field show high contents of another group of ore components (U and F).

Precise dating of biotite in distal volcanic ash: Isolating subtle alteration using 40Ar/39Ar laser incremental heating and electron microprobe techniques

Precise dating of K-rich minerals in volcanic rocks via the 40 Ar/ 39 Ar geochronometer has become crucial to resolving many geological problems. In some cases, ash beds containing biotite phenocrysts but lacking sanidine are the only datable horizons at key stratigraphic intervals, necessitating comparison of sanidine and biotite ages within the same chronostratigraphic framework. To assess the integrity of biotite and evaluate the accuracy of ages obtained from this often problematic mineral, incremental heating 40 Ar/ 39 Ar experiments were performed on large, millimeter-sized, euhedral biotite crystals from four key Eocene tuffs in the Green River and Wind River Basins and are compared with sanidine 40 Ar/ 39 Ar ages. Unaltered biotite crystals with homogenous K-compositions from two tuff beds yielded concordant plateau ages that are indistinguishable from cogenetic sanidine ages. In contrast, biotite crystals from two other tuffs yielded discordant spectra, with relatively young initial steps followed by older, down-stepping apparent ages. Plateau ages from the discordant experiments are older than the sanidine ages by 1 to 14%. Integrated (total fusion) ages from these experiments exhibit scatter toward both younger and older ages that correlate with the degree of spectral discordance. Electron microprobe transects reveal that biotite crystals yielding discordant age spectra contain 1-10 μm thick K-depleted (&lt;8% K 2 O) alteration zones along internal cleavage planes that are absent in biotite crystals yielding concordant age spectra. We propose that these altered zones promote open-system behavior. Phenomena such as loss of K or 40 Ar*, 39 Ar K recoil into internal K-depleted phases, and 39 Ar K recoil entirely out of internally corroded biotite crystals are all potential mechanisms that can be related to this alteration. Due to the presence of these multiple potential pathways that promote the gain or loss of isotopes, such altered biotite crystals are unsuitable for high-resolution 40 Ar/ 39 Ar dating, comparisons with sanidine ages, or calibration of the geomagnetic polarity timescale.

Occurrence and problems of high fluoride waters in Turkey: an overview

Endemic dental fluorosis was first observed in Turkey in Isparta Province, located in the SW of Anatolia, with mottled enamel related to the high levels of fluoride (1.5-4.0 ppm) in drinking waters, about 55 years ago. The origin of fluoride was attributed to the contents of minerals in volcanic rocks, consisting of pyroxene, hornblende, biotite, fluorapatite and glassy groundmass minerals. It was also reported about 35 years ago that severe dental and skeletal fluorosis has been observed in human beings and livestock in Dogubeyazit and Caldiran areas, located around Tendurek Volcano in eastern Turkey, where natural waters contained fluoride levels between 2.5 and 12.5 ppm. It was hypothesised that fluoride, which might be transported by fumaroles or escaped from devitrified lavas, could be held on the surface of some minerals and then exchanged with OH(-) in ground waters with high pH at the foothills of the young Tendurek Volcano. Endemic dental and skeletal fluorosis was also observed in the inhabitants in Kizilcaoren Village of Beylikova Town in Eskişehir Province situated in the midwest of Turkey, where the fluoride content of the drinking waters ranged from 3.9 to 4.8 ppm. The origin of high fluoride in the natural waters was related to the fluorspar deposits, occurring in the catchment area near the village. During the survey in the Güllü Village of Esme-Usak, located in south-midwest of Turkey, it was observed that most of the inhabitants born and raised in the village and aged between 10 and 30 years, showed mild to moderate levels of mottled enamel. The fluoride contents of the deep well waters used for drinking in the village, varied from 0.7 to 2.0 ppm. Amorphous microscopic fluorite existing in the Pliocene lake limestones was considered as a possible origin of fluoride in the waters.

Evaluation of volcanic reservoirs with the “QAPM mineral model” using a genetic algorithm

Gas-bearing volcanic reservoirs have been found in the deep Songliao Basin, China. Choosing proper interpretation parameters for log evaluation is difficult due to complicated mineral compositions and variable mineral contents. Based on the QAPF classification scheme given by IUGS, we propose a method to determine the mineral contents of volcanic rocks using log data and a genetic algorithm. According to the QAPF scheme, minerals in volcanic rocks are divided into five groups: Q(quartz), A (Alkaline feldspar), P (plagioclase), M (mafic) and F (feldspathoid). We propose a model called QAPM including porosity for the volumetric analysis of reservoirs. The log response equations for density, apparent neutron porosity, transit time, gamma ray and volume photoelectrical cross section index were first established with the mineral parameters obtained from the Schlumberger handbook of log mineral parameters. Then the volumes of the four minerals in the matrix were calculated using the genetic algorithm (GA). The calculated porosity, based on the interpretation parameters, can be compared with core porosity, and the rock names given in the paper based on QAPF classification according to the four mineral contents are compatible with those from the chemical analysis of the core samples.

Imaging global chemical and thermal heterogeneity in the subcontinental lithospheric mantle with garnets and xenoliths: Geophysical implications

Suites of mantle-derived xenoliths in volcanic rocks provide estimates of the geothermal gradient and composition of the subcontinental lithospheric mantle (SCLM) at the time of the volcanic eruption. The development of single-grain thermometry and barometry, applied to xenocryst minerals in volcanic rocks, has greatly expanded the number of localities for which such data can be obtained and made it feasible to map the geology of the SCLM on a broader scale, both vertically and laterally. From garnet xenocrysts, it is possible to derive profiles showing mean values of olivine composition, bulk-rock composition, density and seismic velocities, as well as geotherm parameters and constraints on the thickness of the SCLM. Geochemical profiles, coupled with Re–Os dating of peridotites and their enclosed sulfide minerals, show that Archean or Proterozoic SCLM is preserved at shallow levels beneath many areas of younger tectonothermal age; this implies rapid vertical variations in Vs and Vp with depth, which may affect seismic interpretations. Data from several hundred localities worldwide define a secular evolution in the composition of the SCLM, related to the tectonothermal age of the overlying crust. Archean SCLM is typically strongly depleted in basaltic components, highly magnesian and thick (160–250 km), and has low geotherms; Phanerozoic SCLM is typically fertile (rich in basaltic components), Fe-rich, thin (50–100 km) and has a range of high geotherms; Proterozoic SCLM (much of which may be reworked Archean mantle) tends to be intermediate in all respects. The correlated variations in SCLM fertility, lithospheric thickness and geotherm reinforce the effects of each on seismic velocity, and produce more rapid lateral variations in seismic response than would result from thermal effects alone. These correlations are the key to using seismic tomography images to map the lateral extent of different types of SCLM.

ＣＳＤ理論とその火山岩への適用の問題点

The size of minerals in volcanic rocks is typically shown to be exponentially distributed. Rnadolph and Larson first proposed the CSD theory to explain the crystal size distribution. Marsh applied the CSD theory to explain the size distributions in volcanic rocks. Some problems on master equation that Marsh used, however, found, and related with the initial and boundary conditions. I show the CSD theory to use Rnadolph and Larson's method, and point out difference of Marsh's method. According to the CSD theory, an exponential size distribution may be obtained at steady state condition in open system, if growth rate and nucleation rate are kept constant. Such conditions may occur in magma chambers. Other models that explain size distribution of minerals in rocks are also reviewed. For instance, growth probability model that was proposed by Maaloe also explains the exponential size distribution in a close system.

Regional variation of phenocrystic opaque minerals in volcanic rocks of NE. Japan arc(Abstracts of Papers Presented at the Spring Meeting of the Society, 1982)

Regional variation of phenocrystic opaque minerals in volcanic rocks of NE. Japan arc(Abstracts of Papers Presented at the Spring Meeting of the Society, 1982)

Paleointensity determination by a modified thellier method

It has been frequently observed that the ferromagnetic minerals in volcanic rocks may undergo some physical/chemical changes when they are heated in a laboratory. For paleointensity determinations, it is therefore desirable to use the Thellier method, in which internal consistency of the data assures that such undesirable changes did not take place in a particular sample. The most serious drawback of this method is that it requires a considerable number of heatings and coolings and measurements of the remanent magnetization. Following a suggestion of Kono, a modified version of Thellier's technique was developed and applied to a historical lava flow of Hawaii and Oligocene rhyolites and welded tuffs of San Juan volcanic field, Colorado, U.S.A. Samples were heated only once to each temperature and cooled under a magnetic field applied perpendicular to the NRM directions. Results were compared to those obtained by the conventional Thelliers' technique. It was found that the modified method gives results as satisfactory as the original method. With the selection of appropriate samples, the modified method will cut down the time required for the experiment to almost half of what is required in the original method, without losing the merits of Thelliers' technique.

High Temperature Experiments Related to Fe-Ti-oxide Minerals in Volcanic Rocks

High Temperature Experiments Related to Fe-Ti-oxide Minerals in Volcanic Rocks

Oxygen isotope fractionation in igneous rocks

The 18O/ 16O ratios of coexisting silicate minerals in igneous and metamorphic rocks are approximately proportional to the following chemical index:Si+ 0.58Al equivalents/total cation equivalents Measured phenocryst-groundmass isotopic fractionations in volcanic rocks are negligible ( ±0.2per mil) when corrected for differences in their chemical indices. Apparently, solid and liquid silicates of equivalent chemistry do not fractionate the isotopes of oxygen with respect to one another. Isotopic zoning within phenocrysts and whole-rock isotopic variations accompanying magmatic differentiation are thus expected to be minimal and chiefly due to variations in chemical index. Isotopic fractionations among minerals in plutonic rocks are considerably larger than those found among similar minerals in volcanic rocks. Furthermore, continental plutonic rocks are commonly enriched in 18O relative to oceanic volcanic rocks of equivalent chemistry.

Pyralspite Garnets in Volcanic Rocks

A pyralspite garnet from a cavity in rhyolite at the Thomas Range, Utah, U., S., A., was analysed as shown in Table 1., It is high in Mn content, being mainly composed of the spessartine and almandine molecules., Pyralspites occurring as porphyritic minerals in volcanic rocks are poorer in Mn than those from cavities and lithophysae in volcanic rocks (Fig., 1)., Pyralspites from granites are generally poorer in Mn than those from pegmatites (Fig., 2)., According to a crystallo-chemical consideration, pyralspite poor in Mn is stable under a narrower range of physico-chemical conditions than those richer in Mn., The physico-chemical conditions under which porphyritic minerals and granites were formed, were more favourable for the generation of pyralspite than those under which cavities, lithophysae, and pegmatites were formed., Therefore, pyralspite poor in Mn could be generated as porphyritic minerals and in granites, but not in cavities, lithophysae, and pegmatites.,