Carbonate metamorphism

Table 4.6. Mineralogical matrix (molar fractions) of a metamorphic carbonate.

A sample of metamorphic carbonate contains calcite CaC03, dolomite Cao.5Mgo.5CO3, and diopside CaMgSi206. A chemical analysis on the calcinated (C02-free) rock indicates the following molar proportions 0.525 (0.03) CaO, 0.225 (0.01) MgO, and 0.25 (0.02) Si02 with standard deviations given in parentheses. Find the molar proportions of each mineral in the rock and their standard deviation. 

Metasedimentary rocks formed in these two eons extending from 590 to 4,000 Ma B.P., but differ both in lithological abundances and geochemistry, for instance their Sr/ Sr ratios in carbonates are <0.703 for the Archean and <0.704 for the post-Archean. As might be expected almost all such rocks have undergone extensive metamorphism. Carbonates have been used to evaluate the history of the isotopic composition of seawater. As postdepositional alteration is... 

To solve this problem, we need to make computer calculations on the long-term global carbon cycle including the effect of terrestrial biota, ocean circulation pattern, and metamorphic activities which are not included in Kashiwagi et al. (2000) s computation. 

Carbon dioxide gas can be useful in a variety of chemical experiments, too. The procedure for making carbon dioxide gas is essentially the same as it is for making hydrogen and hydrogen sulfide gases, except marble chips are used. Marble is a metamorphic rock that is created when limestone is placed under great pressure at high temperatures. Both limestone and marble are made up of calcium carbonate ... 

Limestone varieties differ greatly from one another in their texture and the impurities they contain, and consequently they also differ in color. The color of limestone may vary from white (when it contains practically no impurities) to off-white and even to intensely colored. Minor inclusions within the limestone structure are often of silica, usually in a concentration below 5%, as well as feldspar and clay in still lesser amounts. Many types of limestone also include embedded fossils. Much limestone deposits in the outer crust of the earth are altered during geologic metamorphic processes that involve mainly pressure and heat but also liquids and gases. Marble, for example, a metamorphic rock derived from calcium carbonate, is white when composed only of this substance colored metal ions and other impurities impart to marble a wide range of colors such as red, yellow, and green and also give... 

Zinc is the 24th most abundant element in the earth s crust. The Zn concentration in the lithosphere is 50-70 mg/kg (Vinogradoc, 1959 Adriano, 2001). Basic igneous rocks contain higher Zn (70-130 mg/kg) than metamorphic and sedimentary rocks (80 mg/kg). Carbonate and limestones contain low Zn (16-20 mg/kg) (Aubert and Pinta, 1977). The total Zn concentration in the soils of the world ranges from 10 to 300 mg/kg (Swaine, 1955), with average concentrations from 50 to 100 mg/kg (Aubert and Pinta, 1977). Arid and semi-arid soils vary from trace levels (subdesert soils) to 900 mg/kg (saline alkali soils) (Aubert and Pinta, 1977). The average Zn concentration in the arid and semi-arid soils of the U.S. (62.9 mg/kg) is... 

The average selenium content of the earth s crust is about 0.8 mg/kg (Aubert and Pinta, 1977). Carbonated rocks contain higher Se (0.8 mg/kg) than metamorphic and sedimentary rocks (0.6 mg/kg) and igneous rocks (0.5 mg/kg) (Aubert and Pinta, 1977). Most of the world s soils contain 0.03-2 mg/kg Se (Ure and Berrow, 1982) with a mean of 0.4 mg/kg. In the U.S., the total Se concentration ranges from trace amounts to 82 mg/kg (Adriano, 2001). 

The basement is made up of crystalline schists of the meso-metamorphic Somes Series. Sedimentation started during Permian with detritic deposits interbedded with rhyolites. The overlying Triassic deposits are unconformable and include detritic formations (Lower Triassic) and massive layers of carbonate rocks (Middle Triassic). The absence of the Upper Triassic is due to the uplift of the region during the Kimmeric tectonic phase. 

The REE data suggest that these carbonate rocks cannot be carbonatites of mantle origin. However, it is noteworthy that the range of compositional variations of typical carbonatite family rocks overlaps with those of sedimentary, metamorphic, and endogenic carbonate rocks (Samoilov 1991). Samoilov (1991) explained that one reason for the significant compositional variations of the carbonatites were due to different types of the associated alkaline rocks under different geologic-tectonic settings. 

The geology of Cyprus is dominated by four distinct terranes - the Troodos Ophiolite Complex composed of mafic and ultramafic rocks, the Circum-Troodos Sedimentary Sequence containing calcarenites, siltstones and carbonates, the Mamonia Complex composed of igneous, sedimentary and metamorphic rocks and the Kyrenia Terrain containing a series of allochthonous massive and recrystallised limestones dolomites and marbles. These terranes generate highly varied landscapes (Fig 1). 

I, 4 in hydrocarbons to 2 in pyridine (3 - 11,0) and again decreases to 1,5 in alcohols. Calculated on this basis value 3 of coal increases droningly with increasing the content of carbon from 70 % till 87 % and in a case of more metamorphized coal is sharply decreased again. Data concerning to the extraction of Greta coal are evidence of maximal yield of extract (more than 20 %) under it treatment with ethylendiamine and dimethylformamide (3 -... 

Klein C (1974) Greenalite, stilpnomelane, minnesotaite, crocidolite, and carbonates in a very low-grade metamorphic Precambrian iron-formation. Can Min 12 475-498 Klein C (1978) Regional metamorphism of Proterozoic iron-formation, Labrador Trough, Canada. Am Min 63 898-912... 

Concerning estimation of the activity of CO2 in the fluid phase, besides carbonate equilibria (discussed in some detail in section 8.10), equilibria in the CaO-Si02-C02 system are also important. In the medium-low metamorphism of limestones, the equilibrium... 

Mel nik Y. P. (1972). Thermodynamic parameters of compressed gases and metamorphic reactions involving water and carbon dioxide. Geochem. Int., 9 419-426. 

Marbles occur in many regional and contact metamorphic terrains in the world and isotopic studies of marbles have been carried out and report by many authors. Carbon isotope studies of marbles can be useful, in many cases, to reveal the origin of carbonates because differences in carbon isotope ratios of marbles can reflect different origins. 

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