Dolomitic Marbles Research Articles

Use of Total Organic Carbon (TOC) as tracer of diffuse infiltration in a dolomitic karstic system: The Nerja Cave (Andalusia, southern Spain)

Recent studies in several karstic systems in France have highlighted that Total Organic Carbon (TOC) was a relevant parameter in order to characterise the behaviour of aquifers, to differentiate the water types that participate in karstic flow (fast infiltration, unsaturated zone, saturated zone) and to evaluate their vulnerability. This study on TOC dynamics at the experimental site of the Nerja Cave has been performed to test the potential of this tracer in a particular climatic (Mediterranean climate), lithologic (dolomitic marbles) and hydrodynamic (diffuse flow behaviour) context. TOC evolution, compared to those of classical tracers used in hydrogeology, permits the understanding of the hydrodynamical behaviour of the unsaturated zone of this dolomitic aquifer, whose response to precipitation is slower than that commonly obtained in karstic aquifers of calcareous nature.

Model study of initial adsorption of SO2 on calcite and dolomite

The rate of calcareous stone degradation is to a significant extent controlled by their surface chemistry with SO2. Initial surface sulphite is converted to a harmful gypsum upon, e.g. NO2 catalysed oxidation. However, it has been observed by scanning electron microscopy that the lateral distributions of gypsum crystals differ between calcitic and dolomitic marbles. The first-principles density functional theory is employed to understand the origin of these fundamentally different morphologies. Here, the stability differences of surface sulphite at calcite CaCO3 (s) and dolomite CaxMg1−xCO3 (s) are determined. A qualitative difference in surface sulphite stability, favouring the former, is reported. This is taken to imply that calcitic micro-crystals embedded in a dolomitic matrix act as sinks in the surface sulphation process, controlled by SO2 diffusion. The subsequent formation of gypsum under such conditions will not require SO42− (aq) ion transport. This explains the homogeneous distribution of gypsum observed on the calcitic micro-crystals in dolomite. In contrast, sulphation on purely calcitic marbles never reaches such high SO2 coverage. Rather, upon oxidation, SO42− (aq) transport to nucleation centres, such as grain boundaries, is required for the growth of gypsum crystals.

Hydrogeology of the Venetia Diamond Mine, South Africa

Venetia Mine is located in the northern part of the Limpopo Province. The mean annual rainfall for the area is 344mm and the mean annual evaporation is in the order of 2650mm/annum. Geologically, Venetia Mine is situated in the Central Zone of the Limpopo Belt where a large variety of rock types are developed. These include quartzites, dolomitic marbles, magnetite rich quartzites, amphibolites, gneisses and schist’s. During the hydrogeological investigation a number of boreholes were drilled and were subjected to numerous conventional and unconventional aquifer tests. The country rock of the mine is hydraulically tight but has a large storage capacity for groundwater. Faults and fractures within the country rock enhance the hydraulic conductivity in places and serve as drainage lines into the open pit. The kimberlite may be divided into two significant horizontal hydrogeological units, the so-called “overshot zone” created by drilling and blasting and the undisturbed kimberlite. The “overshot zone” has a high density of artificial fractures and is between 2m and 5m thick. Test pumping of the in-situ kimberlite of the Venetia Diamond Mine has revealed unusually high hydraulic values. Post closure, evaporation might exceed the inflow of groundwater into the pit. It will, therefore, either be dry except for runoff from precipitation or develop into a brine lake where accumulation of salts will take place in the pit. The drawdown of the groundwater table will continue indefinitely because evaporation exceeds recharge. A pit lake model is planned to simulate post closure conditions.

Geology, mineralogy, geochemistry, and zonation of the Bajiazi dolostone-hosted Zn–Pb–Ag skarn deposit, Liaoning Province, China

The Bajiazi Zn–Pb–Ag skarn deposit is located in northwest Liaoning Province, China. The orebodies occur in a contact zone between Yanshanian (170–177.4 Ma) quartz monzodiorite and Middle Proterozoic dolomitic marble of the Gaoyuzhuang Formation as well as along the NW- and NS-trending fault systems in carbonate wall rocks. Metasomatic mineralization zoning in the deposit is very pronounced. From the intrusive contact zone to dolomitic marble along the NW-trending fault system, three ore-bearing skarn zones may be distinguished: magnesian skarn zone (Fe–Mo)→manganoan–magnesian skarn zone (Cu–S–Fe–Pb–Zn–Ag)→manganoan skarn zone (Zn–Pb–Ag). Magnesian skarn is composed of diopside, forsterite, tremolite, spinel, phlogopite, chondrodite, and serpentine, accompanied by magnetite, pyrite, and molybdenite. Manganoan–magnesian skarn consists mainly of manganoan diopside, manganoan tremolite, mangano-anthophyllite, and manganocummingtonite with minor spessartine and pyroxmangite, The associated ore minerals are pyrite, pyrrhotite, and chalcopyrite, with subordinate magnetite, sphalerite, galena, and Ag-bearing minerals. Manganoan skarn is composed chiefly of spessartine, pyroxmangite, magnesian rhodonite, manganocummingtonite, and manganopyrosmalite, with the associated ore minerals sphalerite, galena, alabandite, and Ag-bearing minerals. Studies of fluid inclusions and S, Pb, O, and H isotopic compositions suggest that ore-bearing fluids flowed from the deep contact zone of the intrusion in the southeast to the shallow depth in the northwest with decreasing temperatures, oxidation state, and increasing pH. When the ore-bearing fluids migrated, their frontal part constantly reacted with the dolomitic carbonate wall rocks to form different types of skarn and mineralization. Sulfur and lead (zinc) were mainly derived from the deep lower crust, while the Middle Proterozoic wall rocks may have provided most Al, Si, Mg, Ca, and Mn for the formation of skarns. The zonal model reflecting the variations in metallization assemblage, skarn mineralogy, composition, δ 34S isotope values, and fluid inclusion characteristics can be used as a guide to exploration for Zn–Pb–Ag skarn deposits.

Chromian tourmaline and associated Cr-bearing minerals from the Nevado-Fildbride Complex (Betic Cordilleras, SE Spain)

AbstractChromian tourmaline, in association with other Cr-bearing minerals (amphibole, mica, epidote, chlorite, titanite, rutile and chromian spinel), occurs in fine calc-schist levels within metacarbonate rocks from the Nevado-Filabride Complex, SE Spain. Electron microprobe analyses of tourmaline and coexisting minerals document both chemical differences dependent on the host-rock type and an irregular distribution of Cr at grain scale. Tourmaline is Na-rich dravite, with average Mg/(Mg+Fe) ratios of 0.83 and 0.63 a.p.f.u. and Cr contents of 0.32 and 0.18 a.p.f.u., in dolomitic and ankeritic marbles, respectively. Tourmaline contains small but significant concentrations of Zn (av. 0.01 a.p.f.u.) and in ankeritic marble it also contains Ni (av. 0.04 a.p.f.u.). Zn-rich chromian spinel appears as small relict inclusions in silicates, with average Cr, Fe, Al and Zn contents of 1.201, 1.241, 0.411 and 0.107 a.p.f.u., respectively. Amphibole, epidote, mica and chlorite show average Cr contents of 0.088, 0.138, 0.115 and 0.267 a.p.f.u., respectively, in dolomitic marbles, and 0.103, 0.078, 0.065 and 0.185 a.p.f.u., respectively, in ankeritic marbles. Cr-silicates formed through metamorphic reactions involving detrital Cr-rich spinel, in addition to clay minerals and carbonates. The B necessary to form tourmaline was probably derived from the leaching of underlying evaporitic rocks.

Evaluation of the volatilization and infiltration effects on the stable isotopic and mineralogical variations in the carbonate rocks adjacent to the Cretaceous Muamsa Granite, South Korea

The Muamsa Granite in the Hwanggangri Mineralized Zone, South Korea, intruded the Cambro-Ordovician Samtaesan Formation, which dominantly consists of calcitic marble and dolomitic marble with minor intercalations of pelitic rock and amphibolite. Intrusion of the granite caused an isotopic depletion of 13C and 18O in the carbonate rocks. Calcitic carbonates show systematic depletion from unrecrystallized limestone through calcitic marble to skarn. It was initiated with volatilization accompanying calcsilicate-forming reactions, and then, with increased permeability, H 2O-rich siliceous fluids of igneous origin actively infiltrated the system promoting fluid-rock interaction. For the skarn fluid infiltration yielded fluid–rock ratios as high as 4.2 in open system, and caused increased 18O depletion rates compared to the volatilization stage. More than 70% of the isotopic depletion in the calcitic marble is attributed to the infiltration process. With such strong infiltration, mineral assemblages such as phlogopite in the absence of K-feldspar, phlogopite+diopside, and wollastonite are commonly observed in the marble. The dolomitic marble was comparatively less depleted in heavy isotopes compared to the calcitic marble and formed under a wide range of X CO2 and low fluid–rock ratios (<1.0). Active decarbonation in dolomitic marble was restricted by silica-poor dolomite protolith, which caused limited fluid infiltration and resulted in high X CO2 mineral assemblages represented by dolomite+calcite+diopside+forsterite and more 13C-depleted nature compared to dolomite+calcite+tremolite+forsterite assemblage.

A methodology for quantitative determination of minor components in minerals based on FT-Raman spectroscopy: The case of calcite in dolomitic marble

A methodology based on FT-Raman spectroscopy and standard addition was developed for the analysis of minerals and was applied successfully for the quantitative determination of calcite in Ekeberg marble. The areas of the overlapping ν 1 vibration modes of the dolomitic (1098 cm −1) and calcitic (1086 cm −1) carbonate groups were used, after deconvolution, for constructing a calibration curve. Application of the calibration curve on Raman spectra obtained from an Ekeberg sample yielded the calcite content which was found to be 5.7% (w/w).

A rare earth element-rich carbonatite dyke at Bayan Obo, Inner Mongolia, North China

¶A carbonatite dyke, extremely enriched in rare earth elements (REE), is reported from Bayan Obo, Inner Mongolia, North China. The REE content in the dyke varies from 1 wt% to up to 20 wt%. The light REEs are enriched and highly fractionated relative to the heavy REEs, and there is no Eu anomaly. Although carbon isotope δ13C (PDB) values of the carbonatites (−7.3 to −4.7‰) are within the range of normal mantle (−5±2‰), oxygen isotope δ18O (SMOW) (11.9 to 17.7‰) ratios apparently are higher than those of the mantle (5.7±1.0‰), indicating varying degrees of exchange with hydrothermal fluids during or after magmatic crystallization. The carbonatite is the result of partial melting followed by fractional crystallization. Primary carbonatite melt was formed by less than 1% partial melting of enriched mantle, leaving a garnet-bearing residue. The melt then rose to a crustal magma chamber and underwent fractional crystallization, producing further REE enrichment. The REE and trace element distribution patterns of the carbonatites are similar to those of fine-grained dolomite marble, the ore-host rock of the Bayan Obo REE–Nb–Fe giant mineral deposit. This fact may indicate a petrogenetic link between the dykes described here and the Bayan Obo mineral deposit.

Formation and evolution processes of the Salanfe W–Au–As-skarns (Aiguilles Rouges Massif, western Swiss Alps)

At Salanfe (Aiguilles Rouges Massif, Swiss Alps) several stratabound W–Au–As-skarn bodies were formed at the contact between pre-Ordovician marble lenses and paragneiss in close proximity to an anatectic leucogranite of Late Palaeozoic age. Anatexis and leucogranite formation occurred at peak metamorphic conditions of P=0.45 GPa and T~650–700 °C. This metamorphic event, dated at 317 Ma in the adjacent Mont Blanc Massif, was related to dextral transpression following continental collision. Structural evidence indicates that the initial stages of skarn formation also occurred under the above P–T conditions. The main stratiform skarn body (Robert) consists of a massive facies close to the marble and of a banded facies on the paragneiss side. The massive facies resulted from the replacement of former dolomite marble, whereas the banded facies resulted mostly from the replacement of thin carbonate layers intercalated in the paragneiss. In the massive facies, the prograde stage skarn is composed by hedenbergite with increasing Fe concentrations through skarn evolutionary stages, whereas in the banded facies it consists of diopside–plagioclase–quartz. The imprint of the retrograde stage is minor and unevenly distributed, with replacement of the pyroxene by magnetite/haematite–calcite–quartz close to the marble and by chlorite–epidote close to the paragneiss. The economic ore minerals are scheelite, arsenopyrite, loellingite and gold and are mainly associated with the prograde skarn stage. Most of the scheelite mineralization occurs during the early prograde stage, probably at temperatures higher than 600 °C, and is associated with pyroxene (hedenbergite 55). Arsenopyrite and loellingite precipitated after scheelite at temperatures between 600 and 350 °C and are associated with hedenbergite>80. Gold occurs both in the final prograde stage and in the retrograde stage. Minor second generation scheelite is associated with epidote and chlorite of the retrograde stage. Lead isotopes indicate that skarn ore minerals were precipitated by a low Th/U fluid like that in equilibrium with the anatectic leucogranite. Oxygen isotopes support the contention that the prograde skarn was formed by a fluid in equilibrium with the leucogranite, mixed with increasing amounts of CO2 approaching the skarn–marble contact. Oxygen and hydrogen isotopes suggest the intervention of a non-magmatic fluid (meteoric, connate?) during the retrograde stage. The Salanfe skarns were formed at deep crustal levels by fluids in equilibrium with an anatectic leucogranite, possibly channelled along permeable paragneiss during regional-scale transpression, and could be the deep expression of a widespread W–Au hydrothermal ore event that occurred along the European Variscides at 310–305 Ma.

Human impact on karst: the example of Lusaka (Zambia)

Lusaka, the capital of Zambia with over 2,000,000 inhabitants, is built on an extensive plateau composed mainly of schists and dolomitic marbles, constituting a very important aquifer that provides the city with almost half of its drinking water needs. Recent demographic growth, leading to uncontrolled urban expansion, and mismanagement of the water resource and of urban waste has lead, in the past 20 years, to an overexploitation of the aquifer and to a generalised water quality depletion, putting in serious danger the future social and economical development of the capital. This third world city has, for these reasons, become a terrifying example of human impact on a vulnerable karst environment, and if no measures will be taken in the very near future, quality of life in the city will be at serious risk.

Carbon recycled into deep Earth: Evidence from dolomite dissociation in subduction-zone rocks: Comment and Reply

[Zhu and Ogasawara (2002)][1] interpret the textures and mineralogy of dolomitic marbles from the Kokchetav massif in terms of pressure-induced dissociation of dolomite (dol) to aragonite (ara) + magnesite (mag). On the basis of this assumption they postulate a minimum metamorphic pressure of 7.85

Geology, geochemistry and Ar–Ar geochronology of the Nangimali ruby deposit, Nanga Parbat Himalaya (Azad Kashmir, Pakistan)

The Nangimali ruby deposit in the southern part of the Nanga Parbat Himalaya, has been investigated through field work, geochemistry, stable and radiogenic isotopes. It outcrops in the Shontar valley in a large north-vergent syncline consisting of high-grade metamorphic gneisses capped by a metasedimentary series dominated by marbles and amphibolites. The ore-body is stratiform. Ruby is found within 0.1–2 cm thick shear-veinlets and gash veins cutting dolomitic marbles and carbonate-bearing bands. The marbles of the Nangimali Formation display restricted ranges in δ 18O (from 23.6 to 27.6‰ relative to SMOW) and in δ 13C (from −1.9 to 2.6‰ relative to PDB). Fluid infiltration along the shear-zone in the marble has no effect on the isotopic signatures of the carbonates. Fluids are metamorphic and CO 2 is derived from the decarbonation of marbles. Mass-balance and geochemical analyses suggest that the mobilisation by the fluids of aluminium and chromium in the marbles is sufficient to enable the formation of ruby in the shear-zone. Rubies have been indirectly dated using a stepwise 40Ar– 39Ar laser heating technique on syngenetic phlogopites. The Miocene age records a Neogene cooling in the South of the Nanga Parbat massif and a minimum formation age for ruby of 16 Ma.

Use of hydrodynamic and hydrochemistry to characterise carbonate aquifers. Case study of the Blanca-Mijas unit (Málaga, southern Spain)

To validate the geological and piezomet- ric subdivision of two carbonate massifs in southern Spain, and to carry out a characterisation of aquifer behaviour, 23 representative springs and wells were monitored at the end of the dry season. Tempera- ture, pH and electrical conductivity and major ions were measured. Calcite (SIc) and dolomite (SId) saturation indexes, PCO2 and cation exchange index (CEI) were calculated with the SOLUTEQ code. Water flow and electrical conductivity were also monitored at the eight main springs. Sierra Blanca and Sierra Mijas constitute an important carbonate hydrogeological unit in southern Spain, supplying water to 250,000 people on the Costa del Sol. Hy- drochemically, two basic types of aquifer behaviour can be distinguished: conduit and diffuse flow sys- tems. The former are found in the calcareous mar- bles of the western Sierra Blanca. They present a calcium-bicarbonate hydrochemical facies with low mineralization, and with quick outflow and water chemistry variations in response to rainfall; hydro- chemical time series present frequency distributions with several modes. The diffuse flow systems are characteristic of the dolomitic marbles of eastern Sierra Blanca and Sierra Mijas. These waters are more highly mineralised and present a calcium- magnesium bicarbonate facies. They are character- ised by slight discharge fluctuations, with nearly unimodal frequency distributions. Aquifer beha- viour affects groundwater exploitation in terms of the success of boreholes and the specific yield of the pumping wells, which are less in the conduit flow systems in western Sierra Blanca.

Phlogopite and Coesite Exsolution from Super-Silicic Clinopyroxene

We document the exsolution of phlogopite and coesite/quartz from pre-existing super-silicic clinopyroxene in dolomite marble from the Kokchetav massif, northern Kazakhstan. The exsolution texture was formed by clinopyroxene decomposition through the reaction (3enstatite + 2KalSi2O6)cpx = phlogopite + 4coesite. Phlogopite exsolution must have occurred at pressures less than 8.0 GPa (at 1000°C), where the garnet + super-silicic clinopyroxene + phlogopite assemblage was stable, based on experimentally defined phase relations. Observations described in this report suggest that the precursor clinopyroxene was stable at pressures higher than 8 GPa (>1000°C), implying that the dolomite marble was subducted to mantle depths greater than 240 km. Such pro-found subduction could be an important mechanism to transport abundant H2O and potassium into the deep Earth.

Carbonate-hosted talc deposits in the contact aureole of an igneous intrusion (Hwanggangri mineralized zone, South Korea): geochemistry, phase relationships, and stable isotope studies

Many talc deposits occur in the Hwanggangri Mineralized Zone (HMZ) in dolomitic marbles of the Cambro-Ordovician Samtaesan Formation within 1 km of the contact with the Cretaceous Muamsa Granite. Talc commonly forms fine-grained, fibrous aggregates, or pseudomorphs after tremolite; abundant tremolite is included as impurities in the talc ore. Talc generally was derived from tremolite in calc-silicate rock within the dolomitic marble. Calc-silicate rock, consisting mainly of tremolite and diopside, was generated from silicic metasomatism during the prograde stage, which promoted decarbonation reactions until dolomite was exhausted locally. Hydrothermal alteration of calc-silicate rock to talc is marked by the addition of Mg and Si, and the leaching of Ca; Cr, Co, and Ni were relatively immobile during the retrograde stage. Contact metamorphism related to the granite intrusion generated the successive appearance of tremolite, diopside, and forsterite, or wollastonite-bearing assemblages in the marble, depending on the bulk rock composition. The X CO 2 content of the metamorphic fluids rose initially above X CO 2 =0.6, and decreased steadily toward a water-rich composition with increasing temperature above 600 °C in the calcitic marble, while buffered reaction of the dolomitic marble occurred at higher X CO 2 conditions above 600 °C. Talc mineralization developed under metastable conditions with infiltration of large amounts of igneous fluids along a fault-shattered zone during the retrograde stage and is characterized by the loss of Ca 2+ with the addition of Mg 2+. Oxygen and carbon isotopic variations of carbonate and calc-silicate minerals are in agreement with theoretical relationships determined for decarbonation products of contact metamorphism. Talc formation temperatures obtained from oxygen isotope fractionation, T– X CO 2 relationships, and activity diagrams range from 380 to 400 °C.

Ponta Grossa and Castro zones in Paraná talc district, Brazil, ore properties and mineral industry

Talc deposits of Paraná district occur as layers, lenses, veins and irregular bodies. The country rocks are dolomite marbles of the late proterozoic Itaiacoca Group. The talc ores are generally in situ, formed by metamorphic and hydrothermal processes, but there are some deposits that present concentrations of alloctone materials. These materials are partially remobilized by carstic dissolution and/or by colluvionar transport. Talc ores differ due their chemical composition, morphology, associated minerals, whiteness and some other properties. The talc minerals in the district of Paraná can be unctuous and not unctuous, platy and powdery, sparry and micro-crystalline and some form massive and disseminated ore deposits. The Southern zone or Ponta Grossa zone exhibits a talc ore more lamellar, platy, unctuous, softness and more varied associated minerals than the ore situated in Northern zone or Castro zone in which the talc is more powder in natural way. There is one deposit in the São José mine that belongs to the Ponta Grossa zone, that is an exception comparing with the other deposits in terms of its presented characteristics. The parameters that govern the specific nature of each commercial talc grade as well as its use in industrial applications including the polypropylene manufacturing are discussed in this paper.

New occurrences of willemite-franklinite assemblages in Bergslagen, central Sweden

Two new occurrences of willemite coexisting with franklinite are described from the Bergslagen region. At the Garpenberg Norra Pb-Zn mine (Hedemora, Dalarna) willemite and franklinite occur in silicate skarn rocks in association with clino-amphibole, phlogopite, quartz, galena, sphalerite, fluorite and barite. At the Hasselhojden metacarbonate quarry (Hallefors, Orebro) the two minerals appear with mainly sphalerite in talc-bearing dolomite marble. Based on electron-microprobe (EMP) analyses, willemite from Garpenberg Norra contains 0.4–2.1 MnO, 0.2–1.5 MgO and 0.1–1.2 Fe2O3, whereas at Hasselhojden the mineral has 0.4 Fe2O3 as the main impurity (all in wt.%). Mossbauer spectroscopy and EMP data show that Fe is dominantly triva-lent and to some extent substitutes for Si in these willemite samples. Franklinite from Hasselhojden contains up to 7.6 wt.% V2O5, incorporated according to the substitution 2 (Zn, Fe)2+ + V5+ = 3 Fe3+.

Origin of a Dolomite-Related Jade Deposit at Chuncheon, Korea

The Chuncheon nephrite deposit in Korea is among the largest nephrite jade deposits worldwide. The deposit is hosted in Precambrian dolomitic marble and amphibole schist that were intruded by the posttectonic (Late Triassic) Chuncheon granite. Carbonates in the dolomitic marble and nephrite deposit have oxygen and carbon isotope compositions in the range of –0.1 to +18.2 per mil and –4.3 to +0.9 per mil, and –0.4 to +3.5 per mil and –9.9 to –4.7 per mil, respectively. These data are in agreement with decarbonation processes driven by fluid infiltration forming the nephrite deposit from dolomitic marble in the temperature range of 330° to 430°C. Stable isotope compositions of silicates from the nephrite deposit are homogeneous and extremely depleted in 18 O and D; tremolite has δ 18 O = –9.9 to –7.9 per mil and δ D = –118 to –105 per mil; diopside has δ 18 O = –13.6 to –11.5 per mil; three samples of grossular have δ 18 O = –4.4, +10.4, and +11.5 per mil; clinochlore has δ 18 O = –9.5 to –9.0 per mil, and δ D = –103 to –94 per mil; and two talc veins have δ 18 O = –7.7 and –7.3 per mil, and δ D = –86 and –90 per mil. Quartz and amphibole in nearby amphibole schists also have variable oxygen isotope compositions of –4.7 to +0.5 per mil and –8.4 to –0.6 per mil, respectively, and are not in isotopic equilibrium. It is suggested that the formation of this nephrite deposit postdated the metamorphism of the country rocks. The distinctly negative δ 18 O values also indicate that the infiltrated fluid was mainly of meteoric origin and its circulation was most likely related to the intrusion of the nearby posttectonic Chuncheon granite. Model calculations demonstrate that the fluid/rock ratios were high, that both oxygen and hydrogen isotope compositions of nephrite were mainly buffered by the fluid phase, and that X CO 2 of the fluid phase was very low during the nephrite formation. These conditions contrast with the formation of nephrite deposits that are spatially associated with serpentinites (e.g., Fengtien nephrite deposit, Taiwan). Such deposits are formed by fluid infiltration during regional metamorphism and their oxygen isotope compositions are mainly buffered by the host serpentinite.

Thermal tresses and microcracking in calcite and dolomite marbles via finite element modelling

Abstract Microstructure-based finite element simulations were used to study the thermomechanical behaviour of calcite and dolomite marbles. For a given mineral microstructure, thermal stresses and elastic strain energy varied with the single-crystal elastic constants and coefficients of thermal expansion. Moreover, they were a strong function of crystallographic texture. Given the same morphological microstructure and crystallographic texture, calcite had larger thermal stresses and elastic strain energy than dolomite. Hence, calcite has an earlier onset of microcracking upon either heating or cooling, and has a greater extent of microcracking at a given temperature differential. However, the variation in thermal stresses and microcracking propensity for either mineral with different randomly assigned textures was greater than the variations between the two minerals. The measured bulk thermal expansion anisotropy suggested that the random representations had some degree of texture. Simulations using the actual texture of the real microstructure, as determined by electron-backscattered diffraction, showed the largest degree of bulk thermal expansion anisotropy, the smallest strain energy, and hence the smallest amount of thermal microcracking. Microstructure-based finite element simulations are considered an excellent tool for elucidating myriad influences of microstructure and physical properties on the thermal degradation of marbles and other rocks.

Tectonic significance of mafic volcanic rocks in a Mesozoic sequence of the Menderes Massif, West Turkey

The Mesozoic platform sequence of the Menderes Massif consists of thick succession of detrital and carbonate rocks. In this sequence there are mafic metavolcanic rocks at two different levels. The first level of mafic metavolcanic intercalations is in the Late Triassic detrital-rich series located in the Caltasi Formation, which is the lowermost unit of the Mesozoic platform. The second level of the mafic metavolcanic rocks is located in the Late Cretaceous–(?)Paleocene Selcuk Formation laying on top of the platform sequence. The Caltasi Formation, which is composed of mica-schists, thinly-bedded cherts, calc-schist and mafic volcanic intercalations unconformably overlie the Bayindir Formation, which consists of mica-schists, phyllites, and white quartzites of Palaeozoic or probably older age. The mafic volcanic rocks in the Caltasi Formation are alkaline basalts with within plate characteristics and are formed during an intraplate extension. The Caltasi Formation is conformably overlain by the Kayaalti Formation represented by calc-schists, dolomitic marbles, and rudist- and emery-bearing massive marbles in ascending order. The Selcuk Formation overlies the Kayaalti Formation and consists of a mica-schist matrix with allochthonous blocks of mafic volcanic rocks, metaperidotites, metagabbros and massive marbles. The mafic volcanic rocks in the Selcuk Formation are tholeiitic basalts and are petrologically similar to mid-oceanic basalts. The geological and geochemical characteristics of the mafic metavolcanic rocks in the Caltasi Formation indicate that during the Late Triassic, the Menderes platform was segmented, probably by the opening of a branch of the Neotethyan Ocean. Between the Late Triassic and the Late Cretaceous, the Menderes carbonate platform was built up. During the Latest Cretaceous–Early Paleocene, a slab of oceanic crust obducted on this platform and provided slices of mafic metavolcanic rocks into the Selcuk Formation.