Relief evolution of the Quadrilatero Ferrifero (Minas Gerais, Brazil) by means of (Be-10) cosmogenic nuclei

This paper investigates the evolution of the relief within the so-called Iron Quadrangle (Quadrilatero Ferrifero) in Minas Gerais, Brazil, by means of quantification of erosion processes, which affected the principal rock types of the region. The method used is based on measurement of in-situ produced cosmogenic Be-10 concentration in fluvial sediments. The results indicate that the regional landscape evolution is controlled by lithotypes: the most resistant areas correspond to substrates developed on itabirites and quartzites (long-term erosion rates between 0.29 to 2.35 m/My), whereas the most fragile ones developed on schistphyllitcs (long-term erosion rates between 7.95 to 11.82 m/My) and granite-gneisses (long-term erosion rate at 12.92 m/My)

Radioactivity Dosage of Ornamental Granitic Rocks Based on Chemical, Mineralogical and Lithological Data

One hundred samples of granitic rock were collected from granite traders in Belo Horizonte. Autoradiography, optical microscopy, diffractometry, and chemical analysis (X-ray spectrometry, X-ray fluorescence, neutron activation, gravimetry and electron probe microanalysis) were used to determine the mineral assemblages and lithotypes. Autoradiographic results for several samples showed the presence of monazite, allanite and zircon. Chemical analysis revealed concentrations of uranium of {le} 30ppm, and thorium {le} 130ppm. Higher concentrations generally correlated with high concentrations of light rare earths in silica-rich rocks of granitic composition. Calculations were made of radioactive doses for floor tiles in a standard room for samples with total concentration of uranium and thorium greater than 60ppm. On the basis of calculations of {sup 232}Th, {sup 40}K and {sup 226}Ra from Th, K and U analysis, the doses calculated were between 0.11 and 0.34 mSv/year, which are much lower than the acceptable international exposure standard of 1.0 mSv/year

Magmatic garnet in the Cordilleran-type Galiléia granitoids of the Araçuaí belt (Brazil) : Evidence for crystallization in the lower crust

Magmatic garnet, together with epidote, is a rare mineral association in cordilleran-I-type granitoids and of special petrogenetic significance. The metaluminous to slightly peraluminous (ASI\ua0=\ua00.97\u20131.07) Galil\ue9ia batholith (Brazil) is a large (ca. 30,000\ua0km2), Neoproterozoic (ca. 632\u2013570\ua0Ma) weakly foliated calc-alkaline granitoid body, characterized by the widespread occurrence of garnet (grossular 25\u201343\ua0mol%) and epidote (pistacite 9.3\u201322.7\ua0mol%). Field, petrographic and mineral chemical evidence indicates that garnet, epidote, biotite as well as white mica crystals (low-Si phengite), are magmatic. There is no difference in bulk rock major and trace element composition between the Galil\ue9ia granitoids and other garnet-free cordilleran-type granitoids worldwide. This evidence strongly suggests that the origin of the uncommon garnet\ua0+\ua0epidote parageneses is related to the conditions of magma crystallization, such as pressure, temperature and water content. Comparison between the mineral assemblages and mineral compositions from this study and those recorded in crystallization experiments on metaluminous calc-alkaline magmas, as well as within garnet-bearing metaluminous volcanic rocks and granitoids, indicates that the supersolidus coexistence of grossular-rich garnet, epidote and white mica is consistent with magma crystallization at pressures greater than 0.8\ua0GPa (above 25\ua0km depth) and at temperatures below 700\ua0\ub0C, i.e. near the water saturated solidus. Furthermore, resorption textures around garnet (plagioclase\ua0\ub1\ua0quartz coronas) and epidote suggest that these minerals have been partially consumed prior to complete crystallization. These findings demonstrate that at 630\ua0Ma the crust underneath the Ara\ue7ua\ued Orogen was already at least 25\u201330\ua0km thick and relatively cool. However, this contrasts with the marked high heat flow registered from the neighbour Carlos Chagas Batholith located 50\ua0km to the east. In fact such granitoids record granulite-facies metamorphism at the same pressure and time (ca. 570\ua0Ma) of Galil\ue9ia granitoids crystallization. Thus, a more suitable geodynamic scenario is required in order to explain these two contrasting thermal regimes within the same orogen. Eventually, field, petrographic and mineral chemical analogies with similar garnet-bearing granitoids located in the fore-arc settings of the British Columbia subduction zone, possibly imply that the Galil\ue9ia granitoids represent \u201crare\u201d garnet- and epidote-bearing metaluminous Cordilleran-I-type granites which can only form in a fore-arc setting

Denudation rates of the Quadrilatero Ferrifero (Minas Gerais, Brazil): preliminary results from measurements of solute fluxes in rivers and in situ-produced cosmogenic Be-10

This paper investigates the denudation rates in the Quadrilatero Ferrifero, Minas Gerais State (Brazil). The aim is to compare chemical weathering rates from measurements of solute fluxes in rivers and long-term mean erosion rates deduced from in situ-produced cosmogenic Be-10 concentrations measured in fluvial sediments. Both water samples and sediments were collected in fifteen stations (checkpoints) located in four hydrographic basins with low anthropogenic perturbations. Depending of the type of substratum, three degrees of chemical denudation rates from water samples are observed: (i) high rates in marbles; (ii) medium rates in schists, phyllites, granites, gneisses and migmatites; (iii) low rates in quartzites and itabirites. Preliminary results of long-term erosion rates deduced from in situ-produced Be-10 are comparable with those of chemical rates. (c) 2005 Elsevier B.V. All rights reserved

New U-Pb ages and lithochemical attributes of the Ediacaran Rio Doce magmatic arc, Araçuaí confined orogen, southeastern Brazil

The Ara\ue7ua\ued orogen of southeastern Brazil, together with its counterpart located in Africa, the West Congo belt, formed through closure of a gulf connected to the Adamastor Ocean by the end of the Ediacaran and beginning of the Cambrian. Convergence of the margins of the gulf led to the development of the Rio Doce magmatic arc between 630Ma and 580Ma on a continental basement mostly composed of Rhyacian orthogneisses. The Rio Doce arc mainly consists of tonalite-granodiorite batholiths, generally crowded with mafic to dioritic enclaves, and minor gabbronorite-enderbite-charnockite plutons, suggesting mixing processes involving crustal and mantle sources. We investigate the basement, magma sources and emplacement ages of the Rio Doce arc. Our data suggest the arc comprises three main granitic rock groups: i) Opx-bearing rocks mostly of enderbite to charnockite composition; ii) enclave-rich tonalite-granodiorite (ETG); and iii) enclave-poor granite-granodiorite with minor tonalite (GT). The Opx-bearing rocks are magnesian, calc-alkalic to alkali-calcic and metaluminous. Together, the ETG and GT rock groups range in composition from tonalite to granite, are metaluminous to slightly peraluminous, show a predominantly medium- to high-K, expanded calc-alkaline signature, and other geochemical and isotopic attributes typical of a pre-collisional volcanic arc formed on a continental margin setting. Mineralogical, chemical, and geochronological data suggest the involvement of HT-melting of granulitic (H2O-depleted) sources of Rhyacian age for the generation of Opx-bearing granitic rocks, additionally to magma mixing and fractional crystallization processes. In conclusion, the studied rock groups of the Rio Doce arc were likely formed by interactions of mantle and crustal processes, in an active continental margin setting. These processes involved ascent of mantle magmas that induced partial melting on the continental basement represented by the Rhyacian gneisses

Relationship of Ki‐67 labeling index to DNA‐ploidy, S‐phase fraction, and outcome in prostate cancer treated with radiotherapy

BACKGROUND Our purpose was to evaluate the relationship of Ki‐67 labeling index (Ki67‐LI) to deoxyribonucleic acid (DNA) ploidy, S phase fraction (SPF), other clinical prognostic factors, and clinical outcome for patients with prostate cancer treated by external beam radiotherapy. METHODS Tissue was retrieved from 42 patients who underwent transurethral resection of the prostate before treatment with external beam radiotherapy between 1987–1993. DNA histogram profiles were classified as diploid (diploid + near‐diploid) and nondiploid (tetraploid + aneuploid). Immunohistochemical staining of Ki‐67 by the MIB‐1 monoclonal antibody was used to calculate Ki67‐LI. Median patient follow‐up was 62 months. Treatment failure was defined as two consecutive rises in serum prostate‐specific antigen (PSA) or clinical evidence of disease recurrence. RESULTS The mean and median Ki67‐LIs were 3.1 and 2.4, respectively (range, 0–12.4). Mean Ki67‐LI values were significantly associated with higher stage, Gleason score, and pretreatment PSA. Nondiploid tumors had significantly higher Ki67‐LIs, as did patients who failed radiotherapy over the follow‐up period. SPF was not significantly correlated with Ki67‐LI. As a categorical variable, the most significant relationships were seen when Ki67‐LI was subdivided into thirds around the median (Ki67‐LI ≤1.5%, Ki67‐LI >1.5–3.5%, and Ki67‐LI >3.5%). This trichotomous variable correlated significantly with pretreatment PSA (P = 0.0008), tumor stage (P = 0.016), Gleason score (P = 0.024), and treatment failure (P = 0.0015), but not with DNA‐ploidy (P = 0.15). In actuarial univariate analyses, Ki67‐LI appeared to be a more significant predictor of patient outcome (P = 0.003) than DNA‐ploidy (P = 0.035). CONCLUSIONS The Ki67‐LI correlated with known prognostic factors such as pretreatment PSA, tumor stage, and Gleason score, and was also weakly related to DNA‐ploidy. In comparison to DNA‐ploidy, Ki67 LI seems to be a better correlate of treatment outcome. Prostate 41:166–172, 1999. © 1999 Wiley‐Liss, Inc