Maria Cristina Motta de Toledo

DEZ MOTIVOS PARA A INCLUSÃO DE TEMAS DE GEOLOGIA NA EDUCAÇÃO BÁSICA

Education is privileged to form a responsible and consequent citizenship due to the introduction of a broad environmental concern, amongst other concepts. There are at least ten reasons for the insertion of a geologic culture in this framework. The insertion will widely benefit the Brazilian education, as follows: (1) the Science curricula of basic education is fragmentary and too much superficial. (2) the humanist formation, inherent to the practice of Earth Sciences, should induce solidary and humanist attitudes in the new generations, develop critical thinking and the capacity of observation. Geology allows one to think about the rational use of the technological applications and advances of Science; it supplies (3) a broad vision of the Earth Systems, needed to understand the complex dynamics of the planet. The theoretical body of Geology brings a (4) time perspective of the changes that have affected the planet and living organisms. The particular situation of Geology, the unique science which has experienced a scientific revolution in the XX th Century, offers the students an (5) education on the causes of geologic risks and their consequences for the human kind, and allows many examples on (6) participation of Geology in modern discoveries of Science. It introduces the most current discussion of (7) the question of the available resources versus sustainability of life. It also constitutes a (8) preparation and orientation for further studies or critical reflections on the human activities on Earth. More can be learned on the methodological aspects of Science, since Geology favors (9) an education on varied scientific procedures. The Information Society, whose dominant role is felt in all sectors of human activity, constitutes another reason: (10) Geosciences helps to create a planetary perspective. The development of a geologic culture extends beyond the mere domain of the recent advances of Science & Technology; therefore, it allows to bring the real world into the classroom and, overall, it allows to move the classroom towards the real world. Geology concepts help a search for a more practical and efficient education, since it is supported by an existential reality that will allow people to retain such knowledge through life.

Carbonatites from Eastern Paraguay and genetic relationships with potassic magmatism: C, O, Sr and Nd isotopes

SummaryGeochemical characteristics were systematically determined for Early Cretaceous samples of carbonatitic rocks from Eastern Paraguay (Rio Apa, Amambay and Central Provinces). The data show that all the occurrences have an enriched isotopic signature and that the carbonatites have negligible or absent crustal signature. A petrogenetic model (parent liquids, fractional crystallization, hydrothermal interactions and weathering) is proposed as a function of incompatible trace element, stable (O-C) and radiogenic (Sr-Nd) isotope variations with the aim to test the significance of carbonatitic complexes as a marker of the metasomatized subcontinental lithospheric mantle. The results indicate that the carbonatites and primary carbonates from eastern Paraguay, and those from the north eastern Paraná Basin (SE Brazil), were affected by metasomatic events distinct in time and composition.ZusammenfassungDie geochemischen Charakteristika von frühkretazischen Karbonatitproben aus Ostparaguay (Rio Alpa, Amambay und Zentrale Provinzen) wurden untersucht. Die Daten belegen, daß alle Vorkommen eine isotopische Anreicherungssignatur zeigen und daß ihnen eine entsprechende Krustensignatur fehlt. Ein Petrologisches Modell (Ausgangsschmelze, fraktionierte Kristallisation, hydrothermale Interaktion und Verwitterung) wird auf Grund der Verteilung der inkompatiblen Spurenelemente, der stabilen (C-O) und radiogenen (Sr-Nd) Isotope vorgeschlagen. Es versucht die Bedeutung der Karbonatitkomplexe als „Markerhorizonte” des metasomatischen subkontinentalen Mantels zu überprüfen. Die Ergebnisse zeigen, daß die Karbonatite und die primären Karbonate in Ostparaguay, und jene aus dem Paraná Becken SüdostBrasiliens durch zeitlich und zusammensetzungsmäßig unterschiedliche metasomatische Prozesse erfaßt wurden.

Weathering and the formation of hillslope deposits in the tropical highlands of Itatiaia — southeastern Brazil

Abstract Deposits of cobbles and boulders found hanging on midslopes of the Itatiaia Plateau reflect tectonic reactivation and a large range of climate-controlled processes, probably including frost weathering. These processes, more efficient in detaching debris from freefaces, were replaced, at the end of the Pleistocene, by colluviation. On the lower slopes of the plateau, less coarse CI and CII colluvia evince the reworking of upslope materials freed in former phases of weathering or erosion. Interpretation of hillslope processes was based upon the sedimentological, mineralogical and micromorphological characteristics of colluvia. CI may have originated in mass movements reaching deep into the regolith. CII colluvia were probably deposited by shallow processes, which reworked initially highly evolved materials, including on the way downslope poorly weathered rock fragments. Changes in weathering characteristics and hillslope processes suggest variations in environmental conditions of the Itatiaia Plateau since the Late Pleistocene. Coarser deposits would be associated to the wet and cold conditions of the Last Glacial Maximum. In the end of the Pleistocene, warmer and still humid conditions would have favored weathering and mass movement processes triggering the first generation of colluvia (CI). Discontinuous stone-lines found on mid-slopes would represent a short return to colder and eventually drier conditions. In the last 8,000 years, prevailing humid climates, with temperature excursions larger than those observed at present, encompassing phases of more intense gelifraction, would explain the deposition of CII sequences. However, such variations were not sufficient to interrupt the geochemical weathering trend toward kaolinitic and gibbsitic materials that persisted after the Last Glacial Maximum. Environmental fluctuations of small amplitude and a decrease in the intensity of slope denudation during the Holocene seem to follow the general trend previously recognized in the neighboring highlands of Campos do Jordao.

Thermal treatment of aluminous phosphates of the crandallite group and its effect on phosphorus solubility

Optimization in the use of phosphate rocks is important and the residues of fertilizer production in the form of crandallite may be suitable for agronomic use after calcination. With the objective of evaluating the effect of thermal treatment of the aluminous phosphates of the crandallite group as related to solubility, crystalline structure and morphology, samples from the mine residues of three Brazilian phosphate deposits (Tapira-MG, Catalao-GO, and Juquia-SP) were collected, air-dried, and screened to 100 mesh. Sub samples were thermally treated at 300, 500, 700, and 900°C for 2 hours. Treated and untreated materials were analyzed by X-ray diffraction, scanning electronic microscopy, energy dispersive X-ray spectrometry, and for the total and soluble P contents. The treatment of samples: (i) raised P solubility in neutral ammonium citrate solution, (ii) caused the disorganization of the crystalline structure of crandallite at 500°C and above, and (iii) altered their morphology (cracking and rounding). The increase in P solubility of samples after calcination indicates that the agronomic utilization of these marginal P sources may be of interest since plant growth may be favored due to higher P availability. New studies to evaluate these materials in order to determine their agronomic effectiveness must be carried out to establish adequate conditions that favor their use by plants.

Towards the thermodynamic treatment of humic substances in soils

This paper presents a model for understanding the thermodynamic stability of humic substances in soil-plant-water environments. During the past few decades, a great amount of research has been devoted to the structural and physico-chemical properties of humic substances, and very many results have accumulated. As a contribution to interpretations of the evolution of organic matter in soils, this paper presents an approach based on an imaginary atomic-group differentiation (CH2O-CO-CH2-C) derived from the elemental species composition (CHON) and on the stoichiometry of the reactions, without which it would seem impossible to outline any thermodynamic reasoning, and to delineate any mass balance or account for transfers in soil - plant - water systems.

Agronomic Evaluation of Calcined Crandallite from Three Brazilian Phosphate Deposits

Abstract Samples from the weathering mantle containing crandallite of three Brazilian phosphate deposits, Tapira, Catalão, and Juquiá, were characterized, calcined, and agronomically evaluated. The calcination process increased total phosphorus (P) and neutral ammonium citrate soluble (NAC) P contents of all samples. The NAC solubility of original Tapira, Catalão, and Juquiá was about 5% of total P, whereas for calcined samples it was 54, 16, and 53%, respectively. In a greenhouse study, rates of P were applied at 0, 10, 20, 40, 80, and 120 mg P kg−1 from the calcined materials and MCP (monocalcium phosphate) to an Ultisol cropped with upland and flooded rice for 65 days. The results showed that the calcined P samples increased dry‐matter yield and P uptake with increasing rates of P applied for both crops. Tapira and Juquiá were more effective for flooded than for upland rice. The calculated values of relative agronomic effectiveness of Tapira, Catalão, and Juquiá with respect to MCP were 57, 48, and 53% in dry‐matter yield for upland rice and 64, 50, and 69% for flooded rice, respectively.

Evolução supérgena do carbonatito de Juquiá (SP)

Weathering of rocks of the alkaline carbonatitic complex of Juquia (State of Sao Paulo, Brasil) resulted in a phosphatic residual ore with average 16% P2O5 The primary rock cantains iron and manganese -rich dolomite and apatite (fluorhydroxiapatite). Magnetite, baryte and ph1ogopite appear as accessories. Up to 50% ofthe carbonatite may be occupied by apatite, which is the main reason for the preservation of primary structures in the weathering mantle and for the high content in P2O5 . The weathering facies are consequent to dissolution of carbonates followed by recycling of primary apatite, with formation of secondary apatite. The mineralogical and chemical compositions of the material, and their morphological relations indicate the following dinamic behavior for the maio chemical elements: - strong depletion of CO3(2-), Mg2+, H4SiO4, SO4(2-) and K+; - recycling on the profile of PO4(3-), Ca2+, Ba2+ and, subordinately, CO3(2-); - retention of Fe3+, Ti4+, Al3+ and Mn4+.

Os fosfatos aluminosos da série da crandallita: uma revisão

Crandallite series minerals have general formula A AI3 (PO4) (PO(3)0H) (OH)6, where A are big cations like Na+, K+, Ca2+, Pb2+, Ba2+, Sr2+, ETR3+, and others with coordination 12, and several cationic and anionic substitutions may occur. They are often formed by weathering processes on different P-rich original materiaIs. Detritical deposits may also contain crandallite mineraIs, because of their high stability. They have been mentioned as the main source of phosphorus in soils. The recent increase in their recognition in marine sediments may modify former ideas about P quantities in this stage of its geochemical cycle. Crandallite phosphates, when associated with phosphatic ore,are generally considered harmful to mining and processing. lu Brazil, unlike other countries, they are not considered as raw material for phosphatic fertilizers. Their open structure, high stability, and relative abundance may represent enough arguments to find applications in different sectors. This paper presents a bibliographic review of mineralogical, geochemical and genetic aspects of the mineraIs of this series.

Morfogênese quaternária e intemperismo: colúvios do Planalto do Itatiaia

On the lower slopes of the ltatiaia Plateau (2,300 -2,500m) are found two generations of colluvia, which indicate phases of intensification of slope erosion. A generallateritic trend characterizes the regolith and colluvia. Micromorphological analysis of the colluvia shows a mixture of materials at different stages of weathering, especially in C II, which presents stronger contrasts than is usual at any given levei of weathering profiles. C I colluvia, which are clayey, rich in fragments of underlying rocks show little pedogenic development and less weathering contrasts, might have originated in mass movements reaching deep into the regolith. In C II, rock and weathering relicts are less common and skeleton grains smaller, indicating provenance from materiais originally more evolved. The mixture of materiais at extreme degrees of weathering suggests reworking by surficial colluviation processes with the inclusion of poorly weathered rock fragments by downslope transportation. The presence of different processes acting on the slopes allows inference on past environments on the plateau. There would have been a transition from wet, more stable climates, perhaps warmer (favorable to the weathering of the regolith), to a phase of intensification or concentration of rainfall, which would explain the mudflows which deposited C I. In the last 8,000 years, conditions still humid but with stronger oscillations of temperature, as well as phases of more intense gelifraction, would explain the deposition of the weathered materiais of the C II sequences. Such variations, however, were not sufficient to divert the lateritic trend ofthe weathering, that would have persisted after the last glacial maximum.

Eficiência agronômica de compostos organominerais obtidos pelo processo humifert

The traditional production process of phosphate fertilizers can generate high amounts of residues with appreciable amounts of P that represent a subutilization of the phosphate rock. With the objective of utilizing these residues the Humifert process was created and consists in the nitric acid treatment of a mixture of phosphatic (low or high contents of P) and organic materials in a chamber, with the goal of increasing P solubility and the agronomic effectiveness (AE). The present work has the objectives of generating information relative to the organophosphate compounds from the process. Several tests were applied as related to the operating conditions of the equipment. Two agronomic experiments were conducted. The first experiment tested the Patos de Minas phosphate rock (PR) and organic matter, submitted or not to the Humifert process, with maize as the testing crop. The second experiment used the P sources Arad PR and Tapira residue, and organic matter, also submitted or not to the Humifert process. As to test also the residual effect of the diverse P sources the testing crops were now corn followed by three successive harvests of brachyaria grass. In both experiments the dry-matter yield (DMY) of the crops were evaluated by mean statistics. In the first experiment the MCP lead to higher DMY and the mixture PMT was superior to the control. In the second experiment, although also the MCP was superior in the first crop (maize) in the overall of all harvests the Arad PR was equal to the MCP. Although some advantages in terms of increase in DMY due to the Humifert process, the solubility and agronomic results indicate that more research is necessary as to adequate the reaction to obtain better quality P sources.