Lithostratigraphy of the Mesoproterozoic Windpoort Granite (Spektakel Suite), western Namaqualand, South Africa

2019 ◽  
Vol 122 (2) ◽  
pp. 249-256
Author(s):  
C.H. de Beer ◽  
P.H. Macey
Keyword(s):  
South Africa ◽  
Alkali Feldspar ◽  
Metamorphic Rocks ◽  
Leucocratic Granite

AbstractThe Windpoort Granite is a porphyritic, leucocratic granite belonging to the Spektakel Suite, a group of late- to post-tectonic granites intruded into the orthogneisses and supracrustal metamorphic rocks in western Namaqualand. Like other granites of this type, it is devoid of penetrative tectonic foliation, at most displaying a magmatic foliation parallel to the boundaries of the intrusion. Its main characteristic setting it apart from other Spektakel Suite granites in western Namaqualand is its tightly packed arrangement of small stubby alkali feldspar phenocrysts. Its U-Pb LA-ICPMS age of 1087 ± 11 Ma agrees with the age of other Spektakel Suite granites showing similar field relationships. It classifies geochemically as a highly potassic monzogranite with more evolved compositions than all other plutons of the Spektakel Suite.

Geochronological and Petrogenetic Studies of High-Grade Metamorphic Rocks and Intrusives in Namaqualand, South Africa

1975 ◽  
Vol 16 (1) ◽  
pp. 154-188 ◽  
Author(s):  
T. N. CLIFFORD ◽  
J. GRONOW ◽  
D. C. REX ◽  
A. J. BURGER
Keyword(s):  
South Africa ◽  
Metamorphic Rocks ◽  
High Grade

scholarly journals Petrography, modal composition and tectonic provenance of some selected sandstones from the Molteno, Elliot and Clarens Formations, Karoo Supergroup, in the Eastern Cape Province, South Africa

2018 ◽  
Vol 10 (1) ◽  
pp. 821-833 ◽  
Author(s):  
Priscilla Chima ◽  
Christopher Baiyegunhi ◽  
Kuiwu Liu ◽  
Oswald Gwavava
Keyword(s):  
South Africa ◽  
Depositional Environments ◽  
Source Rocks ◽  
Late Triassic ◽  
Metamorphic Rocks ◽  
Eastern Cape Province ◽  
Eastern Cape ◽  
Rock Fragments ◽  
Clastic Sediments ◽  
Cape Fold Belt

Abstract The Late Triassic - Early Jurassic non marine clastic sediments of the Molteno, Elliot and Clarens Formations were studied to deduce their mineralogy and tectonic provenance. The study is based on road-cut exposures of the formations in the Eastern Cape Province of South Africa. Petrographic studies based on quantitative analysis of the detrital minerals shows that the clastic sediments (mostly sandstones) are predominantly made up of quartz, feldspars, and metamorphic and igneous rock fragments. Among the main detrital framework grains, quartz constitutes about 62-91%, feldspar 6-24% and 3-19% of lithic fragments. The sandstones can be classified as both sublitharenite and subarkose. Although, most of the sandstones (> 70 %) plotted in the sub-litharenite field. Petrographic and XRD analyses revealed that the sandstones originated from granitic and metamorphic rock sources. The QFL (Quartz-feldspar-lithic fragments) ternary diagrams indicate that the sandstones were derived from recycled or quartzose source rocks reflecting a craton interior or transitional continental setting which probably came from the Cape Fold Belt. This possibly revealed that most of the sandstones might have been derived as a result of weathering and erosion of igneous and metamorphic rocks in the Cape Supergroup. The study has revealed the depositional environments, and provide a basis for the description and interpretation of the sedimentology of the Molteno, Elliot and Clarens Formations.

scholarly journals Mineralogical characteristics and the gem quality of corundum in Khe tre area, Eakar, Daklak

2015 ◽  
Vol 18 (4) ◽  
pp. 55-66
Author(s):  
Ngoc Kim Bui ◽  
Hoang Kim Nguyen
Keyword(s):  
Heat Treatment ◽  
Alkali Feldspar ◽  
Mineralogical Composition ◽  
Treatment Method ◽  
Metamorphic Rocks ◽  
Mineral Inclusions ◽  
Mineralogical Characteristics ◽  
Heat Treatment Method ◽  
Dark Blue

Corundum in Khe Tre area essentially distributes in pegmatite bodies that intruded the granite of Ea Dui complex ((P-Ted) and metamorphic rocks of Ea Rock formation (PR2er). Corundum mainly developed within pegmatite bodies and in contact metasomatic endozone between pegmatite and granite or gneiss. Mineralogical composition of pegmatite is as follows; Major minerals: alkali feldspar (orthoclas, microlin) 60 -70 %, quartz ~ 15 %; Minor minerals: plagioclase, biotite, muscovite Accessory minerals: garnet, zircon, sphene, apatite,...The corundum here was found in intergrowth with feldspar and characterized by dark to dark blue (very rare) hue, opaque diaphaneity, subhedral to anheral crystals and few mineral inclusions. The size of corundum crystals varies from about 2 cm to 5 cm. Rough corundum crystals are rarely of gem value. Most of them can be used only as abrasibve material. For improvement of corundum to be used as gemstones, heat treatment method was proposed.

Rb-Sr and Sm-Nd Mineral Isochron Ages of the Metamorphic Rocks in the Namaqualand Metamorphic Complex, South Africa

2002 ◽  
Vol 5 (4) ◽  
pp. 771-779 ◽  
Author(s):  
M. Yuhara ◽  
T. Miyazaki ◽  
J. Ishioka ◽  
S. Suzuki ◽  
H. Kagami ◽  
...  
Keyword(s):  
South Africa ◽  
Metamorphic Rocks ◽  
Metamorphic Complex ◽  
Mineral Isochron

Time and Latitude in South Africa

1972 ◽  
Vol 1 ◽  
pp. 27-38
Author(s):  
J. Hers
Keyword(s):  
South Africa ◽  
Cape Town ◽  
Astronomical Observations ◽  
Royal Observatory ◽  
The Republic ◽  
Astronomical Determination ◽  
Limited Accuracy ◽  
Better Than

In South Africa the modern outlook towards time may be said to have started in 1948. Both the two major observatories, The Royal Observatory in Cape Town and the Union Observatory (now known as the Republic Observatory) in Johannesburg had, of course, been involved in the astronomical determination of time almost from their inception, and the Johannesburg Observatory has been responsible for the official time of South Africa since 1908. However the pendulum clocks then in use could not be relied on to provide an accuracy better than about 1/10 second, which was of the same order as that of the astronomical observations. It is doubtful if much use was made of even this limited accuracy outside the two observatories, and although there may – occasionally have been a demand for more accurate time, it was certainly not voiced.

TEM/AEM characterization of fine-grained clay minerals in very-low-grade rocks: Evaluation of contamination by empa involving celadonite family minerals

1996 ◽  
Vol 54 ◽  
pp. 694-695
Author(s):  
Gejing Li ◽  
D. R. Peacor ◽  
D. S. Coombs ◽  
Y. Kawachi
Keyword(s):  
Electron Microscopy ◽  
Volcanic Rocks ◽  
Analytical Electron Microscopy ◽  
Metamorphic Rocks ◽  
New Mineral ◽  
Chemical Compositions ◽  
Low Grade ◽  
Fine Grained ◽  
Depth Analysis ◽  
Mineral Aggregates

Recent advances in transmission electron microscopy (TEM) and analytical electron microscopy (AEM) have led to many new insights into the structural and chemical characteristics of very finegrained, optically homogeneous mineral aggregates in sedimentary and very low-grade metamorphic rocks. Chemical compositions obtained by electron microprobe analysis (EMPA) on such materials have been shown by TEM/AEM to result from beam overlap on contaminant phases on a scale below resolution of EMPA, which in turn can lead to errors in interpretation and determination of formation conditions. Here we present an in-depth analysis of the relation between AEM and EMPA data, which leads also to the definition of new mineral phases, and demonstrate the resolution power of AEM relative to EMPA in investigations of very fine-grained mineral aggregates in sedimentary and very low-grade metamorphic rocks.Celadonite, having end-member composition KMgFe3+Si4O10(OH)2, and with minor substitution of Fe2+ for Mg and Al for Fe3+ on octahedral sites, is a fine-grained mica widespread in volcanic rocks and volcaniclastic sediments which have undergone low-temperature alteration in the oceanic crust and in burial metamorphic sequences.

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