Marble Outcrops Research Articles

Caracterización petrográfica y geoquímica del batolito Cerro Aspero-Alpa Corral (32°34'-32°42' LS y 64°43'-64°52' LO), provincia de Córdoba, Argentina

The Cerro Aspero-Alpa Corral (CA-AC) batholith is a 440 km 2 granite body present in the Southern edge of the Eastern Pampean Ranges, Cordoba province, central Argentina. The intrusive body of probably paleozoic age shows both post-tectonic and epizonal character. Country rocks include Upper Precambrian-Lower Paleozoic metasedimentary rocks mainly represented by mica-schists, gneisses and migmatites, locally interrupted by minor amphibolite and marble outcrops. This paper deals with representative petrographic and geochemical data that characterize a 150 km 2 central stripe between 32°34'-32°42'S and 64°43'-64°52'W. Three granitic facies have been distinguished based on their distinctive modal mineralogy and texture, and upon well known chemical parameters. A K-feldspar megacryst porphydic-type is the areally prevalent facies, but dykes of micro- leucogranites and biotite-phenocryst bearing granite are also well represented. They are all monzogranites of subalkaline and peraluminous chemistry. Their mineralogy shows variable proportions of QAP constituents and micas, with minor phases represented by Fe-Ti oxides, apatite (Ap), titanite (Tt), allanite (Aln). Microgranular enclaves, abundantly distributed in the porphydic facies, provide valuable information for a better understanding of parental magma evolution. The high-Ca content of the melt makes this body quite distinctive compared to its larger northern neighbour, the Achala batholith. Pegmatite and aplite bodies, as well as fluorite bearing breccias and quartz veins, barren or mineralized, are also present within the CA-AC batholith.

Analysis of mid-infrared spectral characteristics of rock outcrops and an evaluation of the kahle model in predicting outcrop thermal inertias

This paper summarizes the results of an analysis of emissive spectra acquired at wavelengths of 8.2–13.6μm from multiple targets on granite, amphibolite, and calcareous marble outcrops in the Clare River synform near Tweed, Ontario. Prominent spectral features are noted for all three rock types. The effects of surface contaminants such as lichens are examined. Results indicate that many of the diagnostic spectral features in granite, although damped, remain apparent in surfaces with as much as 71% lichen cover. Cloud cover is also shown to have a significant damping effect on the emissive spectrum. Spectral measurements were carried out in support of an experiment to investigate the accuracy with which the Kahle (1977) numerical model can be used to predict the thermal inertia of rock outcrops in situ. Diurnal surface temperature differences were computed from emission spectra of selected targets on each rock outcrop. The surface temperatures, as well as meteorological data, were inputs to the model. Predicted values from the model were then compared against measured thermal inertias from rock cores removed from each spectral target. Results indicate a mean overestimate in the model's thermal inertia of 25%. A major contributing factor may be inherent errors in the model itself. The model is shown to be quite sensitive to errors in the estimate of the surface albedo, as well as the diurnal range in surface temperature.

SIGNIFICANCE OF CORRENSITE IN SOILS OF SOUTHEASTERN ONTARIO

Samples were collected from Ap/Ah and Bm horizons of 10 soils from southeastern Ontario. The soil reaction ranged from medium acid to mildly alkaline. Mineralogical analysis of the various particle-size fractions showed the presence of corrensite, talc and graphite in the assemblage. These three minerals were also present in large amounts in marble outcrops, where they were formed by hydrothermal alteration and metamorphism. The significance of inherited interstratified minerals in the soils was considered from the analytical aspect: the first-order basal reflection should be confirmed because higher orders could be confounded with other mineral reflections; and from the pedogenetic aspect: failing to recognize an inherited interstratified mineral would be misleading in the interpretation of soil evolution. Key words: Grenville province, interstratified mineral, corrensite, talc, graphite, inherited minerals

Effects of glaciations upon karst aquifers in Canada

In Canada there are ∼5.7 · 10 5 km 2 of limestone and marble outcrop, ∼6 · 10 5 km 2 of dolomite and ∼8 · 10 4 km 2 of sulfate rocks. In addition, halite subscrops beneath 5 · 10 5 km 2 of the central Prairie region and interacts with modern groundwater circulation to a varying extent. More than 90% of the total outcrop-subcrop has been repeatedly glaciated. The most recent glaciation (Late Wisconsin) terminated 13,000–5000 yrs. B.P. in different areas. Carbonate terrains still partly buried by glacier ice may be inspected in the Rocky Mountains. Nine distinct effects of glacial action upon the propagation and efficiency of karst aquifers are recognized. Destructive effects include erasure, dissection, infilling and injection. Bedrock solution may be inhibited during non-glacial periods by a cover of glacial drift rich in carbonate clasts. Glacial burial may also preserve an aquifer and enhance its storage characteristics. Aquifer expansion may be stimulated by raising the hydrostatic head or steepening hydraulic gradients, or by crustal flexure during deglacial isostatic rebound. The differing effects make general prediction of the state of an aquifer in glaciated terrains difficult.

Torlesse geology of Kakahu, South Canterbury

The Torlesse rocks of Kakahu, South Canterbury, New Zealand, consist of metasiltstone, metagreywacke, conglomerate, chert, metavolcanics, and marble. These rocks belong to textural zones 1 & 2A and the prehnite-pumpellyite metamorphic facies. Laminated, often graded, bedding occurs, but the rocks are generally devoid of sedimentary structures. Conglomerate is uncommon and was found at only three localities. Thirteen occurrences of chert up to 160 m thick are recorded, and radiolaria are provisionally identified in some chert thin sections. Two adjacent lithologies of intercalated metavolcanics and marble outcrop in the lower Kakahu gorge. The westernmost lithology is a 140–m–thick sequence of sixteen bedded units of metatuff, grey marble, and metasiltstone. The second lithology which lies directly to the east of the former is 90 m of intercalated poorly schistose hematitic metavolcanics and white marble. The Kakahu marble is a 30–m–thick grey marble which has yielded a fauna of upper Carboniferous conodonts. Conodonts of similar age have also been obtained from the grey marble which is interbedded with metatuff and metasiltstone in the lower Kakahu gorge. Three phases of folding are recognised. Tight mesoscopic F1 folds are preserved only in the bedded cherts and interbedded metavolcanic and marble rocks. Macrosconic F2 folding was accompanied by the formation of the regional schistosity (S2). S2 was macroscopically folded during F3 deformation. Resistant marker lithologies are traceable along strike for up to 500 m, their abrupt terminations appear to have been produced by tectonic shearing. There is abundant evidence of transposition and shearing in the metasiltstone and metagreywackes, and the whole comprises a tectonic mélange.

Solution of marble in the karst of the Pikikiruna range, Northwest Nelson, New Zealand

The paper reports the first research on karst solution processes and rates in New Zealand. The study area is an IHD representative basin in the northwest corner of the South Island in a mountain range consisting principally of Ordovician marble. The climate is sunny and warm (17°C) in summer and wet and cool (7°C) in winter. Average precipitation is 2,158 mm of which 525 mm evapotranspires, yielding a discharge of 51–75 l/s/km2 in the river basin studied. Almost half of the catchment of 45.1 km2 consists of karst which occurs mainly as a doline covered plateau at 600–900 m within which most drainage is subterranean. Water tracing is with fluorescein defined drainage patterns. Marble solution was established by estimating inputs, throughputs and outputs of water and dissolved calcium and magnesium in both autogenic and allogenic karst drainage systems. Particular attention was paid to estimating errors. Water samples for chemical analysis were taken irregularly for approximately one year, and a rating curve relating chemical load to discharge was established. The best estimate of solution loss from the basin yields a mean rate of 100 ±M24 m3/km2/a. Of this 80 per cent is derived from solution of marble by autogenic waters, mostly in the top 10–30 m of the marble outcrop. The remaining 20 per cent is accomplished by allogenic stream solution. Approximately 9.9 per cent of the dissolved calcium and magnesium load leaving the basin originates from non-karst rocks and 4.6 per cent is initially introduced by rainfall. River flows that are exceeded only 5 per cent of the time transport approximately 44 per cent of the annual dissolved load, while mean to low flows that occur for 75 per cent of the time transport 35 per cent of the annual solute load. This confirms the importance of low frequency-high magnitude events, but indicates also that in corrosion systems high frequency events of moderate to low magnitude can also accomplish significant work.

Petrographic and trace-element distribution studies on the dolomite-calcite in the regional metamorphic marble of the Griesscharte, Tyrol, Austria/Italy

Petrographic investigations on the light yellow marble outcrops in the Griesscharte, Tyrol, Austria/Italy revealed them to be dolomite. The white to blue-grey veins in these marbles were those of calcite. Inside these calcites and along the calcite-dolomite phase boundaries minute and microscopically unidentifiable crystallites (⩽ 10 μ) were observed. These crystallites were recognised by X-ray diffractometry as dolomite and their form and distribution were established by scanning electron microscopy. Trace-element distributions on the calcite-dolomite neighbours were studied by neutron-activation method to elucidate the formation mechanism of these calcites in the marble. Genetic relationships of the dolomite crystallites, the calcite host and the surrounding dolomite marble have been discussed in the light of the petrographic and chemical studies. These findings substantiate a deposition of a new formed vein of calcite from the solution circulating in the fissures of the dolomite marble during prograde metamorphism rather than a simple deposition of mobilized sedimentary calcite. The dolomite crystallites in the calcite seem to have been formed post-tectonically, partly by the nucleation in the calcite cleavage planes during Mg-metasomatism and partly from the exsolutions during retrograde metamorphism.