|
| << vorige | volgende >> |
Tijdschrift beschrijving
Alle jaargangen van het bijbehorende tijdschrift
Alle afleveringen van het bijbehorende jaargang
Alle artikelen van de bijbehorende aflevering
Details van artikel 3 van 8 gevonden artikelen
| Titel: |
Gamma-spectrometric Surveys in Differentiated Granites. II: the Joaquim Murtinho Granite in the Cunhaporanga Granitic Complex, Paraná, SE Brazil |
| Auteur: |
Francisco José Fonseca Ferreira Allan Fruchting Gilson Burigo Guimarães Luizemara Soares Alves Victor Miguel Oliveira Martin Horstpeter Herberto Gustavo José Ulbrich |
| Verschenen in: |
Geologia USP. série científica |
| Paginering: | Jaargang 9 (2009) nr. 1 pagina's 55-72 |
| Jaar: |
2009 |
| Inhoud: |
Detailed mapping at the NW corner of the large Neoproterozoic Cunhaporanga Granitic Complex (CGC), Paraná state, SE Brazil, redefined the Joaquim Murtinho Granite (JMG), a late intrusion in CGC with an exposed area of about 10 km2, made up mainly by evolved“alaskites” (alkali-feldspar leucogranites). This unit is in tectonic contact with the Neoproterozoic- Eocambrian volcano-sedimentaryCastro Group, to the W, and is intrusive into other less evolved granitic units of the CGC to the E. Petrographically, JMG shows mainlymesoperthite and quartz, with subordinate amounts of altered micas and some accessory phases, mainly zircon. The equi to inequigranulargranites are usually deformed with cataclastic textures, are often brecciated, and may have miarolitic structures. Formation of latealbite, sericite, carbonate and hematite was caused by deuteric and hydrothermal alteration. A gamma-ray spectrometric survey at 231stations which measured total counts (TC), Ueq K%, eU ppm and eTh ppm was used to construct several direct and derived maps. Comparedto neighboring units the JMG has signifi cant anomalies, especially in the TC, %K, eTh and eU maps, although the differences areless obvious in some derived maps. These evolved granites are enriched in these three elements. Geochemical behavior of K, Th and Uis used to analyse the results observed in maps. Enhanced weathering under a subtropical climate with moderate to high average temperaturesand heavy rainfall affects mainly feldspars and biotite, and may also destabilize most U and Th-bearing accessory phases. Th is most likely retained in restite minerals in soils, being relatively immobile, while part of U may migrate as uranyl ion in oxidizing media. K is especially affected by feldspar alteration to K-free clays (mainly kaolinite), and may be completely leached. Gamma-ray spectrometricmethods are valid tools to study facies in granitic rocks, especially in those that are enriched in K, Th and U. |
| Uitgever: |
Instituto de Geociências da USP (provided by DOAJ) |
| Bronbestand: |
Elektronische Wetenschappelijke Tijdschriften |
Details van artikel 3 van 8 gevonden artikelen
| << vorige | volgende >> |