Granitic Inclusions Research Articles

MARBLE MÉLANGE: COMPOSITION VARIATIONS AND FORMATION MECHANISMS

The Olkhon terrane in the Western Baikal area accommodates four types of carbonate-silicate mixtures: injection (protrusion), metamorphic-boudinated, mingling, and tectonite marble mélange. The outcrops of injection mélange consist of a carbonate matrix with inclusions of native silicic rocks found in the immediate vicinities, commonly cover large areas and lack any distinct linearity in the map view. Mélange of the metamorphic boudinage type comprises diopsidite and tremilote-diopsidite fragments in a dolomitic or calcite-dolomitic matrix. Its origin is apparently due to tectonism and related metamorphism of quartz sandstones in Neoproterozoic strata on the passive margin of the Siberian craton. Mingling mélange appears as calcite marble or carbonate-silicate (calciphyre) veins with metadolerite and granite inclusions of different sizes. The veins formed by intrusion of carbonate and silicate melt batches and subsequent fragmentation of silicate rocks that crystallized earlier. Marble tectonites localized in narrow zones record the late phase of ductile marble injection.

Late Roman coarse wares from the Roman villa of Torre Llauder (Barcelona, Spain): Archaeometric characterisation

Torre Llauder is a Roman villa located next to the city of Iluro (Mataró, Barcelona), which transformed into a small village during Late Antiquity. To investigate the provenance and technology of Late Roman coarse wares, and particularly cooking wares, used in this site between the 6th and the 7th centuries AD, 47 samples were selected including cooking pots and casseroles, and samples of common wares, and storage vessels. Archaeometric study of these ceramics was performed through X-ray fluorescence (WD-XRF) for the chemical characterisation, X-ray diffraction (XRPD) for the identification of the main crystalline phases, and optical microscopy by thin section analysis for the petrographic characterisation. The results show that the cooking wares share strong similarities both in chemical composition, and petrographic features. A large petrographic fabric group characterised by granitic inclusions can be further divided into four fabrics on textural grounds. The comparison of the pottery composition with the geology of the area supports the hypothesis of a regional origin for most of the fabrics defined. The clays used for most cooking and common wares were probably derived from a common granitic area in the Maresme region, and likely from a granodioritic batholith. Some samples may have been produced in neighboring areas.

Mining-Induced Deformation in the Malmberget Mine

The Norra Alliansen orebody of the Malmberget sublevel caving mine consists of iron ore interspersed with biotite schist and granitic inclusions. The schist is squeezed between the ore and the host rock and in direct contact with the ore along the majority of the length of the footwall. The schist exhibits high deformation when exposed to stress. SMART cable bolt roof deformation measurements are re-analyzed to draw conclusions regarding the patterns of deformation in the mine. Each bolt’s head is placed at the origin of a spherical coordinate system and the radius and inclination angle between the bolt and every production blast occurring during the bolt’s recorded lifetime are calculated. The deformation experienced by each instrument is investigated by comparing the long-term recorded movements with the developed geometric variables. Patterns of deformation magnitude and rate are found with respect to production-blast distance and inclination angle, instrument location, rock quality designation, and likely mining-induced stresses. Results show that deformation magnitude tends to be higher when driven by production blasting occurring on the production level above the instrumentation when accounting for the effects of distance, but average deformation magnitude for very-near production blasts tends to be higher than that for production blasts occurring directly above the instrument. Correlations also exist between the measured RQD, estimated rockmass parameters, and the measured deformation. Empirical evidence allows the identification of six scenarios which account for 91% of the recorded high-deformation-rate events. These scenarios help determine which production activities are most likely to cause high deformation rates.

Palaeomagnetic Study of Dated Pre-Cambrian Rocks of the Front Range, Colorado-Wyoming

Summary The mean direction of remanent magnetization, after partial a. c. demagnetization, of Pre-Cambrian rocks from the Front Range of Colorado and Wyoming gives a palaeomagnetic pole position at 8°N, 29°E. Rock types sampled include andesite dykes, diorite inclusions in granite, and a highly oxidized red granite, all with a radiogenic age of 1.41 G. Y. This preliminary study suggests there are at least two and probably as many as four field reversals recorded in these rocks, and that remanent directions from andesite dykes may be useful in determining tectonic rotation of the Front Range.

Metamorphic charnockite in contact aureoles around intrusive enderbite from Natal, South Africa

In the Port Edward area of southern Kwa-Zulu Natal, South Africa, charnockitic aureoles up to 10 m in width in the normally garnetiferous Nicholson's Point Granite, are developed adjacent to intrusive contacts with the Port Edward Enderbite and anhydrous pegmatitic veins. Mineralogical differences between the country rock and charnockitic aureole suggest that the dehydration reaction Bt + Qtz → Opx + Kfs + H2O and the reaction of Grt + Qtz → Opx + Pl were responsible for the charnockitization. The compositions of fluid inclusions show systematic variation with: (1) the Port Edward Enderbite being dominated by CO2 and N2 fluid inclusions; (2) the non-charnockitized granite by saline aqueous inclusions with 18–23 EqWt% NaCl; (3) the charnockitic aureoles by low-salinity and pure water inclusions (<7 EqWt% NaCl); (4) the pegmatites by aqueous inclusions of various salinity with minor CO2. As a result of the thermal event the homogenization temperatures of the inclusions in charnockite show a much larger range (up to 390 °C) compared to the fluid inclusions in granite (mostly <250 °C). Contrary to fluid-controlled charnockitization (brines, CO2) which may have taken place along shear zones away from the intrusive body, the present “proximal” charnockitized granite formed directly at the contact with enderbite. The inclusions indicate contact metamorphism induced by the intrusion of “dry” enderbitic magma into “wet” granite resulting in local dehydration. This was confirmed by cathodoluminescence microscopy showing textures indicative for the local reduction of structural water in the charnockite quartz. Two-pyroxene thermometry on the Port Edward Enderbite suggests intrusion at temperatures of ∼1000–1050 °C into country rock with temperature of <700 °C. The temperature of aureole formation must have been between ∼700 °C (breakdown of pyrite to form pyrrhotite) and ∼1000 °C. Charnockitization was probably controlled largely by heat related to anhydrous intrusions causing dehydration reactions and resulting in the release and subsequent trapping of dehydration fluids. The salinity of the metamorphic fluid in the contact zones is supposed to have been higher at an early stage of contact metamorphism, but it has lost its salt content by K-metasomatic reactions and/or the preferential migration of the saline fluids out of the contact zones towards the enderbite. The low water activity inhibited the localized melting of the granite. Mineral thermobarometry suggests that after charnockite aureole genesis, an isobaric cooling path was followed during which reequilibration of most of the aqueous inclusions occurred.

Tin-bearing greisens of Mount Bischoff, northwestern Tasmania, Australia

The large Mount Bischoff tin deposit occurs within an inlier of Precambrian sedimentary rocks which are surrounded by lower Paleozoic and Tertiary sedimentary and volcanic rocks. Tin is contained within a network of altered Devonian porphyry dikes (endogreisens), replaced dolomite (exogreisen), mineralized hydrobreccias, thin veins, and alluvials.Greisen-style alteration of porphyry dikes is zoned inward and downward from nearly fresh beta -form quartz + K-feldspar dike material through muscovite + fluorite + or - tourmaline greisen and topaz + quartz greisen to quartz greisen. Tin grades of up to 2 wt percent occur within endogreisen, with higher grades occurring near the topaz + quartz-quartz greisen contact.Replacement of dolomite by greisen assemblages and greisen-style alteration of porphyry dikes were cogenetic. The mineral assemblages and the spatial distribution of greisen minerals, such as mica, topaz, and tourmaline, in endo- and exogreisens are similar. Topaz, quartz, fluorides, cassiterite, and tourmaline occur in endo- and exogreisen, although the proportion of fluoride minerals (sellaite and fluorite) is high where dolomite is replaced. Within exogreisens the highest grades of Sn occur at the contact between topaz-bearing endo- and exogreisens, grades obtained from drill core range up to 22 wt percent (1.3-m intersection).The greisens were overprinted by assemblages containing phyllosilicates (chlorite, talc, phlogopite, serpentine, phengite), carbonates (magnesite, siderite, dolomite), abundant sulfides (pyrrhotite + or - pyrite, sphalerite), late fluorite, and later argillic alteration. Only limited quantities of dolomite were replaced by these later postgreisen assemblages.Fluid inclusion temperatures range from 90 degrees to near 500 degrees C, with the greisen being produced between approximately 340 degrees to 420 degrees C or higher and the later overprints at progressively lower temperatures. Salinities at the greisen stage of mineralization were high, with measurements commonly between 30 to 40 percent total dissolved salts. Ca-Na-K-Fe-Mn chlorides, possible fluorides, CO 2 , and hydrocarbons(?) were deduced as components of the fluid phase. Lesser amounts of dissolved Si, Al, and B and rare Ti, Ca, La, P, Sn, Cu, and S were inferred from daughter mineral identifications.The deposit was formed from acidic and relatively reduced hydrothermal solutions in subvolcanic conditions, at a depth of approximately 1 km, above a leucogranite pluton (granite inclusions exist in the dikes). High-level brecciation was cogenetic with porphyry dike intrusion and both occurred in several separate intrusion-mineralization cycles.

Sr, Nd, O and H isotopic ratios in Ascension Island lavas and plutonic inclusions; cogenetic origin

Eighteen basic rocks from Ascension Island (South Atlantic) give a mean 87Sr/ 86Sr ratio of 0.70311 ± 17 for both volcanics and plutonic inclusions. The late-stage differentiated rocks (rhyolites and granitic inclusions) have much higher 87Sr/ 86Sr ratios, up to 0.712. All these rocks display the same range of Nd isotopic compositions (ε Ndvalues from6.9to11.1with a mean on12samples of8.4 ± 0.6) implying a cogenetic relation between the two sequences. The D/H systematics lead to the same conclusion. In the Nd Sr diagram, the data plot close to the mantle array and show a positive correlation. This suggests a mixing between a depleted MORB-type mantle, i.e. the upper mantle, and a hot-spot with less depleted geochemical characteristics, i.e. the OIB mantle source. The total range of δ 18O values lies between 4.8‰ for plagioclase cumulates and 6.7‰ for the most evolved rocks (peralkaline granites and comendites). The basic rocks have values around 5.3‰, typical of mantle-derived material. These oxygen data indicate that the high 87Sr/ 86Sr ratios in the most evolved rocks (both volcanic and plutonic terms) result from the combination of two different processes: incorporation of slight amounts (< 1%) of high-temperature altered oceanic crust by the magma in the late stages of the differentiation process and then in-situ Rb decay since the time of formation of these rocks. Both processes were very effective because of the high Rb and low Sr contents of these evolved rocks. Oxygen isotope systematics in the Ascension Island granites and rhyolites indicate that a fractional crystallization process alone does not produce δ 18O values higher than 6.7‰, i.e. that the ultimate δ 18O enrichment, relative to the initial basic magma, is not greater than 1.5‰.

Geological and fluid inclusion studies of the Dongpo tungsten skarn ore deposit, China

The Dongpo tungsten ore deposit, the largest scheelite skarn deposit in China, is located at the contact of a 172-m. y. biotite granite with a Devonian marble. The mineralization associated with the granite includes W, Bi-Mo, Cu-Sn and Pb-Zn ores. Several W mineralization stages are shown by the occurrence of ore in massive skarn deposits and in later cross-cutting veins. The high garnet/pyroxene ratio, the hedenbergite and diopside-rich pyroxene and the andradite-rich garnet show the deposit belongs to the oxidized skarn type. Detailed fluid inclusion studies of granite, greisen, skarn and vein samples reveal three types of fluid inclusion: (1) liquid-rich, (2) gas-rich and (3) inclusions with several daughter minerals. Type (3) is by far the most common in both skarn and vein samples. The dominant daughter mineral in fluid inclusions is rhembic, highly birefringent, and does not dissolve on heating even at 530°C. We assume that this mineral is calcite. The liquid phase in most of the fluid inclusions has low to moderate salinities: 0–15 wt. %; in a few has higher salinities (30–40 wt. % NaCl equivalent). The homogenization temperatures of inclusions in the skarn stage range from 350°C to 530°C, later tungsten mineralization-stage inclusions homogenize between 200°C and 300°C, as do inclusions in veins. Fluid inclusions in granite and greisen resemble those of the late tungsten mineralization stage, with low salinity and homogenization temperatures of 200°–360°C. The tungsten-forming fluids are probably a mixture that came from biotite granite and the surrounding country rocks.

北海道中央部，二また・トムラウシ火砕流たい積物中の花こう岩質包有物のＫ‐Ａｒ年代

北海道中央部，二また・トムラウシ火砕流たい積物中の花こう岩質包有物のＫ‐Ａｒ年代

Petrological significance of granitic inclusions from Pliocene-early Pleistocene pyroclastic flow deposits in central Hokkaido, Japan.

Mineral and chemical compositions of granitic inclusions in the Pliocene-early Pleistocene rhyolitic pyroclastic flow deposits of central Hokkaido are very similar to those of the host rhyolitic pyroclastic flow deposits, but different from those of the basement Tertiary granites. The Sr isotope ratios of both of the pyroclastic flow deposits and the granitic inclusions range from 0.7032 to 0.7040, which are notably lower than those of the Tertiary granites (0.7050-0.7054) and the metamorphic rocks (0.7044-0.7071) of the Hidaka Belt. Such evidence indicates that the granitic inclusions are not derived from the basement rocks, but are co-magmatic with the rhyolitic pyroclastic flows. The water vapor pressure and temperature of the magma which produced both the rhyolitic pyroclastic flows and the granitic inclusions are estimated to be 1 kb and 600°-750°C. Hence, it may be interpreted that the rhyolitic pyroclastic flows are eruptive equivalents of a shallow granitic pluton. The low Sr ratios suggest that the source material of the volcano-plutonic association may not be ascribed to the older upper crust, but to a certain kind of lower crust or upper mantle material.

Some Syenitic Inclusions in Granite from Tanekawa, Setana-gun, Hokkaido

Some Syenitic Inclusions in Granite from Tanekawa, Setana-gun, Hokkaido

Rb–Sr Study of Shock-metamorphosed Inclusions from the Onaping Formation, Sudbury, Ontario

Sixteen inclusions from the Onaping Formation, a possible meteorite impact breccia at Sudbury, Ontario, were analyzed for Rb, Sr, and Sr isotopic composition. Inclusions ranged from weakly shocked granitic rocks to heterogeneous glassy inclusions (impact melt?). Strongly shocked and glassy inclusions yield separate isochrons of 1430 ± 65 m.y. and 1480 ± 55 m.y., respectively (λ 87Rb = 1.39 × 10−11 y−1). Twenty-eight samples, including data for Onaping Formation samples from the literature, have an isochron age of 1515 ± 65 m.y. Isochron initial 87Sr/86Sr ratios range from 0.714 to 0.717, The Onaping samples thus appear anomalously younger than the 1700 m.y. ages reported for the geologically younger Nickel Irruptive and Whitewater sediments. If the highly shocked granitic inclusions and glasses in the Onaping Formation are relatively susceptible to radiogenic Sr loss during subsequent thermal events, the data are compatible with an impact origin for the Sudbury structure. The whole-rock ages, combined with reported mineral ages, suggest a metamorphic event in the Sudbury area 1400–1500 m.y. ago.

Metamorphism of Precambrian Granitic Xenoliths in a Mica Peridotite at Rose Dome, Woodson County, Kansas: Part 2, Petrologic and Mineralogic Studies

Field, drill-core, petrographic, and mineralogic studies show that the Precambrian granitic rocks exposed on Rose Dome, Woodson County, Kansas, were emplaced as inclusions of basement rock in a mica peridotite magma that intruded the Pennsylvanian section of Rose Dome during Late Cretaceous time. High temperatures of the alkaline ultramafic magma (probably greater than 800° C) led to metamorphism of the granitic inclusions and the formation of high sanidine and high albite from original microcline and albite. Contact metamorphic effects on country rock include the development of buchite-like sanidine-magnesian biotite hornfels from Weston Shale (Pennsylvanian) that was intruded by the mica peridotite. The high temperatures of the peridotite magma also led to partial melting of the granitic rocks; a quartzofeldspathic matrix shows volcanic textures and binds mineral and rock fragments together to produce the varied range of textures and structures of the granitic xenoliths. Partial melting of the granitic rocks accounts for those features that led earlier workers to conclude that the “granite” on Rose Dome had intruded the Pennsylvanian section. Those features included xenoliths of hornfels enclosed by granitic material and apparently intrusive relationships between the granitic rocks and metamorphosed shale. The lack of concordance in the Rb-Sr ages of the granitic rocks (Part 1) may stem partly from melting of the “granite” and exchange of ions with the mica peridotite magma, from the “sampling” of different levels of granitic crust by the upwelling peridotite magma, or from weathering.

Oriented inclusions in granite; further evidence for floored magma chambers

Oriented inclusions in granite; further evidence for floored magma chambers

Alkali Feldspars from Gneisses and Granites of the Västervik Area, SE. Sweden

Abstract Metamorphosed Precambrian sedimentary rocks and associated late-kinematic granites of the Vastervik area in southeastern Sweden contain abundant potassium feldspar. The alkali feldspar from the metasediments shows zero to low obliquity and contains from 8 to 10 % albite in solid solution. In the granitic rocks, and in the accompanying pegmatites and aplites, the potassium feldspar is microcline, containing 1 to 3 % albite The potassium feldspar of contact rocks and inclusions in granite is also microcline The formation of monoclinic potassium feldspar in the metasediments is the result of regional metamorphism in the upper part of the amphibolite facies. The widespread association with sillimanite suggests a temperature of formation above that of the triple point of andalusite—sillimanite—kyanite. In the granites, a monoclinic ancestry of the potassium feldspar is indicated, but transformation to the triclinic form has taken place, and unmixing has resulted in a nearly pure potassium feldspar. So...

Progressive Replacement of Limestone Inclusions in Granite at Ballynacarrick, Co. Donegal

AbstractLimestone inclusions in granite show a skarn armour made up of definite mineral zones. From the limestone side these are in order: grossular zone (with or without idocrase), clinozoisite zone, plagio-clase-pyroxene zone, and finally a hornblendic or dioritic zone that passes into the biotite-granite or granodiorite of the district. These different zones were not static but moved into the limestone, each zone replacing the one preceding it and being replaced by the zone following it. A mechanism by which limestone inclusions disappear in granite is clearly exemplified.

Igneous rocks of the Highwood Mountains, Montana: Part V. Contact Metamorphism

Very near the contacts of the stocks the sediments have been replaced by sanidine and diopside, through magmatic reaction. An irregular zone of indurated sediments, produced largely by hydrothermal agents, extends outward from the stocks for as much as half a mile. Locally, more intense hydrothermal metamorphism has formed orthoclase and fibrous amphibole with some diopside and locally garnet, phlogopite, spinel, and cordierite. Along the dikes metamorphism extends out from the contacts for a distance of a few inches up to 5 feet. Thermal metamorphism produced recrystallization of the fine interstitial material of the sandstone. Aegirite, calcite, hematite, and pyrite were deposited by hydrothermal solutions. Magmatic reaction produced diopside. Reaction between sandstone and the magma of the headed dike caused a progressive replacement of plagioclase and quartz by potash feldspar. Granitic inclusions in the biotite phonolite dikes have a marginal shell in which plagioclase has been replaced by orthoclase. Surrounding each inclusion is a zone of mixed rock which contains quartz grains much embayed and surrounded by 0.1 mm. prisms of pyroxene.

Societies and Academies

PARIS. Academy of Sciences, August 20.—M. Maurice Lévy in the chair.—New observations on the high valley of Dordogne, by M. A. Michel-Lévy. Owing to the cuttings recently made for the railway between Queuille and Mont-Dore, some new facts on the geology of this valley have been discovered. On the left flank of the valley the deposit of labradorite can be traced up to the Capucin. More to the south an outcrop of trachyte, rich in black mica and amphibole, can be followed up to near the ravines of Riveaugrand. The right flank of the Mont-Dore valley shows clearly the prolongation of the lower andesite of the Grand Cascade. A trachytic dyke has also been recently discovered by M. Paul Gautier in the first ravine west of Compissade, which is rich in granitic inclusions.—On the existence of Ceratitis capitata, var. hispanica, in the neighbourhood of Paris, by M. Alfred Giard. During the present spring a large proportion of the apricots at Courbevoie, near Paris, fell off the trees in a green state, and the remainder, although apparently exceptionally fine when ripe, where found to be honeycombed with larvæ. This larvae were found, on development, to give rise to Ceratitis capitata, a species that has already been found to be very destructive to many kinds of fruit in the Azores, at Madeira, the Cape of Good Hope, Algeria and Malta. This is its first appearance near Paris, possibly owing to an ' exceptionally favourable spring. Means for combating this scourge are suggested, as it is of the first importance that it should not become acclimatised in Paris.—Observations on shooting stars made from August 11 to August 14 at the Observatory of Paris, by Mile. D. Klumpke, About thirty meteors were observed during four nights, of which some came from Perseus and others from the polar region. The former were white, short and very rapid, the latter luminous and coloured.—Observations of the sun made at the Observatory of Lyons with the Brunner equatorial during the first quarter of 1900, by M. J. Guillaume. The results are given in three tables showing the number of spots, their distribution in latitude, and the distribution of faculæ in latitude.—On the composition of the air in a vertical section, and on the composition of the upper layers of the terrestrial atmosphere, by M. G. Hinrichs. By applying a formula of Laplace, the composition of the air is deduced at different levels. From these calculations, carbon dioxide would disappear at 30,000 metres, argon at 60,000 metres. At 100,000 metres the air would consist of oxygen 0.3, nitrogen 4.6 and hydrogen 95.1 per cent.—On the dielectric cohesion of gases, by M. Bouty. When a gas contained in an insulating vessel is placed in a constant electric field, there is a certain critical pressure above which the gas acts as a dielectric, and below which the discharge passes. The relation between this critical pressure (P) and the field (y volts per centimetre) has been studied for three gases—hydrogen, air and carbon dioxide. For low pressures the relation found is y = a + c2/P2 For higher pressures the curve is practically coincident with the asymptote, y = a + b(p + π).—On the extraction of oxygen from the air by solution at a low temperature, by M. Georges Claude. Various solvents for air have been tried at low temperatures in the hope of discovering a liquid in which the difference of solubility of the two gases would be very marked. The experiments, however, were unsuccessful, as it was found that at low temperatures the solubility of the nitrogen increased, so that starting with a mixture containing 65 per cent, of oxygen, after solution and boiling out, the amount of oxygen was practically unchanged, amounting in no case to more than 70 per cent.—On the pyrogallol-sulphpnic acids, by M. Marcel Delage.—On the dextrins of saccharification, by M. P. Petit. The results obtained by the action of diastase upon starch were very divergent, depending upon the age of the diastase and the conditions under which it had been preserved. On the use of sodium peroxide for making wholesome wells containing carbonic acid, by M. E. Derennes. The use of milk of lime for the absorption of dangerous amounts of carbonic acid contained at the bottom of a well has the disadvantage that the residual gas may consist almost entirely of nitrogen. The substitution of sodium peroxide for lime would ensure as much oxygen being given off as carbon dioxide absorbed.