Showing items 1 - 4 of 4

Your selections:

A study of the piezoelectric behaviour of quartz and quartzites

Metamorfe studies van granoliete en verwante hoë-graadse gesteentes in die Suidelike Grenssone van die Limpopo-Metamorfekompleks in Suid-Afrika

The Limpopo Complex of Southern Africa: outstanding issues with emphasis on ultrahigh-temperature-high-pressure metamorphism and granitoid magmatism

  • Authors: Belyanin, Georgy Aleksandrovich
  • Date: 2012-06-07
  • Subjects: Metamorphism , Granitoid magmatism , Magmatism , Limpopo Complex (South Africa) , Metamorphic rocks
  • Type: Thesis
  • Identifier: uj:8713 , http://hdl.handle.net/10210/5065
  • Description: Ph.D. , Preserved Archean crust dominantly recording lower temperature conditions (greenschist to amphibolites facies), the earliest widespread record of ultrahigh- temperature metamorphism occur in the Neoarchean. Considering that, collisional tectonic setting has been postulated as a possible tectonic scenario for the generation of ultrahigh-temperature metamorphism, sites where Archean cratons underwent collision can be potential sites for preservation of ultrahigh-temperature metamorphic granulites. The Limpopo Complex is a high-grade metamorphic terrain considered to have formed by collision in Neoarchean time between the Archean Kaapvaal and Zimbabwe cratons.Detailed petrographic and mineral chemical characterization of representative high Mg-Al granulites from the Southern Marginal Zone, Central Zone and the Northern Marginal Zone – forming the three subzones of the Limpopo Complex – was carried out. Evidence for the preservation of mineral assemblages considered diagnostic of ultrahigh- temperature metamorphic conditions, such as orthopyroxene+sillimanite±quartz, high-Al/(MgTs) orthopyroxene, sapphirine+quartz, spinel+quartz, corundum+quartz and antiperthite, are shown from these high Mg-Al granulites. Most of these mineral assemblages are reported for the first time from the Limpopo Complex. In addition, two unique textures are also reported – one, the discovery of corundum lamellar intergrowth with orthopyroxene from a high Mg-Al granulite from the Southern Marginal Zone, and second, the rare occurrence of sapphirine+quartz post dating orthopyroxene+sillimanite±quartz from two Mg-Al granulites from the Central Zone. Pressure-temperature calculations including representative P-T phase diagrams computed for the bulk compositions of the granulites studied clearly indicate ultrahigh- temperature conditions for all the three subzones. In contrast to two previous studies, one each for the Southern Marginal Zone (~950°C) and the Central Zone (~930°C), this study presents higher temperature estimates of ~1050 to ~1100°C for the three subzones. Together with examples of ultrahigh-temperature metamorphic conditions reported by the two previous studies, this study shows that the ultrahigh-temperature event reported here has affected the length and breadth of the three subzones of the Limpopo Complex. Further, the high-pressure conditions inferred from the early composition of orthopyroxene from the unique orthopyroxene-corundum intergrowth and the P-T phase diagrams computed for representative granulites from the three zones suggest a common high pressure event in all the three sub zones of the Limpopo Complex.
  • Full Text:

The nature and origin of the polymetallic Salt River massive sulfide deposit, Northern Cape Province, South Africa

  • Authors: Osburn, Keith Craig
  • Date: 2012-06-07
  • Subjects: Namaqua Metamorphic Province , Sedimentation and deposition , Geology (Kakamas, South Africa) , Salt River sulfide deposit , Petrology , Metamorphic rocks , Geology, Stratigraphic
  • Type: Thesis
  • Identifier: uj:8667 , http://hdl.handle.net/10210/5022
  • Description: M.Sc. , The Salt River deposit is a poly-metallic base metal deposit with a Zn-Cu-Pb metal content that occurs southwest of the town of Kakamas within the Northern Cape Province, South Africa. The Salt River deposit occurs within the Geelvloer Formation of the Bushmanland Subprovince of the Proterozoic Namaqua Metamorphic Province (NMP). This study constitutes the first detailed study of the host rock succession to the Salt River deposit, by investigating the lithostratigraphy, petrography geochemistry and geochronology. During the course of the study, various styles of wall-rock alteration were identified and investigated to determine their effect on the host rock succession. A further aim of this study was to classify the Salt River deposit and compare it to neighboring deposits occurring in the NMP. Geochronological studies were undertaken to define the age of mineralization. Detailed logging of exploration diamond drill core combined with petrographic investigation was used to define thirteen distinct lithotypes. The stratigraphy is dominated by felsic grey gneisses and mafic amphibolites, minor calc-silicate rocks, granitic augen gneisses, pegmatites and two lithologies that represent the metamorphosed equivalents of hydrothermally-altered host rock. Lithostratigraphic investigations yielded a rather uniform succession containing four distinct marker beds defined by their common occurrence and ease of correlation across various boreholes.
  • Full Text:
  • 1
  • Disclaimer
  • Privacy
  • Copyright
  • Contact