| Full text | |
| Author(s): |
Velazquez, Victor Fernandez
[1]
;
Giannini, Paulo Cesar Fonseca
[2]
;
Riccomini, Claudio
[2]
;
Sallun, Alethea Ernandes Martins
[3]
;
Hachiro, Jorge
[2]
;
Gomes, Celso de Barros
[2]
Total Authors: 6
|
| Affiliation: | [1] Univ Sao Paulo, Escola Artes Ciencias & Humanidades, BR-03828080 Sao Paulo - Brazil
[2] Univ Sao Paulo, Inst Geociencias, BR-05508080 Sao Paulo - Brazil
[3] Inst Geol, Secretaria Meio Ambiente, BR-04301903 Sao Paulo - Brazil
Total Affiliations: 3
|
| Document type: | Journal article |
| Source: | EPISODES; v. 31, n. 3, p. 302-308, SEP 2008. |
| Web of Science Citations: | 6 |
| Abstract | |
The Patino Formation sandstones, which crop out in Aregua neighborhood in Eastern Paraguay and show columnar joints near the contact zone with a nephelinite dyke, have as their main characteristics the high proportion of syntaxial quartz overgrowth and a porosity originated from different processes, initially by dissolution and later by partial filling and fracturing. Features like the presence of floating grains in the syntaxial cement, the transitional interpenetrative contact between the silica-rich cement and grains as well as the intense fracture porosity are strong indications that the cement has been formed by dissolution and reprecipitation of quartz from the framework under the effect of thermal expansion followed by rapid contraction. The increase of the silica-rich cement towards the dyke in association with the orthogonal disposition of the columns relative to dyke walls are indicative that the igneous body may represent the main heat source for the interstitial aqueous solutions previously existing in the sediments. At macroscopic scale, the increasing of internal tensions in the sandstones is responsible for the nucleation of polygons, leading to the individualization of prisms, which are interconnected by a system of joints, formed firstly on isotherm surfaces of low temperature and later on successive adjacent planes towards the dyke heat source. (AU) | |
| FAPESP's process: | 97/01210-4 - Petrology and geochemistry of alkaline rocks |
| Grantee: | Celso de Barros Gomes |
| Support Opportunities: | Research Projects - Thematic Grants |
| FAPESP's process: | 01/10714-3 - The alkaline magmatism evolution in the South American Platform: petrogenetic and geodynamical implications |
| Grantee: | Celso de Barros Gomes |
| Support Opportunities: | Research Projects - Thematic Grants |