Kamafugitic diatremes: their textures and field relationships with examples from the Goiás alkaline province, Brazil |
| |
| Authors: | Tereza Cristina Junqueira-Brod Jos Carlos Gaspar Jos Affonso Brod Camilla Vasconcelos Kafino |
| |
| Institution: | aInstituto de Geociências, Universidade de Brasília, Campus Asa Norte, 70.910-900 Brasília, DF, Brazil;bCNPq—Brazilian Council for Research and Development, Brazil;cPIBIC/UnB/CNPq, Brazil |
| |
| Abstract: | Kamafugitic rocks intruded the Precambrian basement and Phanerozoic sediments at the northeast border of the Paraná basin as part of the Late Cretaceous Goiás alkaline province (GAP). Plutonic complexes dominate the north of the province, whereas lavas and pyroclastic rocks prevail in the south. The central GAP is characterized by kamafugitic diatremes, which may crop out continuously for up to 850 m and consist of a central breccia body, surrounded and overlain by lava flows and crosscut by dykes. The breccias contain some special spheroidal juvenile fragments—namely, accretionary and armored lapilli, frozen droplets, spinning droplets, and wrapped fragments—whose textural and mineralogical aspects are described in detail. Irregularly shaped tuff pockets that occur within the breccias contain textures and structures similar to those of subaerial surge deposits and formed in confined, high gas to solid+liquid ratio domains in the conduit. Diatreme emplacement affected the country rock through thermal metamorphism, development of columnar jointing, and formation of peperite-like mixtures. There is no evidence of phreatomagmatic activity in the diatremes, and CO2, rather than H2O, seems to have been the major volatile component of the kamafugitic magmas. This finding implies that features such as accretionary lapilli and peperites are not exclusively associated with H2O-dominated processes. |
| |
| Keywords: | Breccia Kamafugite Lapilli Peperite Surge |
| 本文献已被 ScienceDirect 等数据库收录！ |
|
