AGES OF PEGMATITE AND VEIN MINERALS OF SOUTHERN KIVU (EASTERN CONGO). PRELIMINARY INDICATION ON AGES OF SUCCESSIVE PEGMATITE PHASES

Journal Article · Mon Jan 01 04:00:00 EST 1962 · Bulletin de la Societe Belge de Geologie, de Paleontologie et d'Hydrologie (Belgium)

OSTI ID:4724261

Monteyne-Poulaert, G; Delwiche, R; Safiannikoff, A; Cahen, L

The ages of pegmatite and vein minerals connected with the Kibara-Urundi- Karagwe Ankolean belt are reported. Ages of 12 minerals from Southern Kivu (Eastern Congo) have been obtained by the strontium,-- rubidium and lead-uranium methods. The ages fall into four age groups: (1) muscovite and microcline from a pegmatite of the Lugusha river are circa 1115 m.y. old; (2) muscovites and microclines from various pegmatites near Kamituga and the Lugusha river have ages of circa 905 m.y.; (3) two uranium minerals from one of these pegmatites, at Kobokobo, are circa 845 m.y. old; and (4) the last event is dated at circa 550 m.y. and corresponds to post-tectonic intrusions of uranium-bearing veins and thin microcline, quartz, amphibole veins, Group 1 is also represented in Northern Katanga; group 2 is found in Northern Katanga, Kivu and Rwanda; group 3 is at present restricted to Kivu; and group 4 is represenfed both in Kivu and Rwanda. The three first age groups are post-tectonic events of the KibaraUrundi-Karagwe Ankolean cycle; the orogeny is therefore older than 1115 m.y. The last is in the post-Katangan time range. The pegmatites of Southern Kivu, the intrusions of which are post-tectonic events of the Wbara-Urundi belt, are known to occur in successive phases. Three of these are, at present, dated. The ages found are in the correct order of succession: (1) the first phase corresponds to the emplacement of graphic pegmatttes (quartz and microcline with little muscovite) and belongs to age group 1 (1115 m.y.); (2) the next dated phase (or phases) is characterized by well developed muscovite and microcline crystals and corresponds to age group 2 (circa 905 m.y.); (3) the last dated phase is the uranium-bearing one of 845 m.y. (group 3). All phases are known to occur in the complex Kobokobo pegmatite. These preliminary data are discussed. It is concluded that in the Kibara-Urundi-Karagwe Ankolean belt the development of successive pegmatite phases forming the aftermath of one single orogenic cycle is drawn out over a very long period, of the order of 250 m.y. An A-K apparent age of 540 m.y. has been found on a microcline which is 1115 m.y. old. A similar age discrepancy occurs for another sample consisting of a single mica layer, one extremity of which is muscovite and the other extremity, biotite. The Sr--Rb age of the muscovite is 925 m.y., whereas the biotite is 550 m.y. The two young'' apparent ages are in excellent agreement and are also in agreement with the age of the youngest thermal event in the area. This is taken to show that this event was responsible for leakage of argon from the microcline and loss of strontium 87 from the biotite 550 m.y. ago from minerals respectively 1115 and 925 m.y. old. The strontium 87 lost by the biotite does not appear to have migrated to the muscovite. (auth)

• Research Organization: Originating Research Org. not identified
• NSA Number: NSA-17-008394
• OSTI ID: 4724261
• Journal Information: Bulletin de la Societe Belge de Geologie, de Paleontologie et d'Hydrologie (Belgium), Journal Name: Bulletin de la Societe Belge de Geologie, de Paleontologie et d'Hydrologie (Belgium) Vol. Vol: 71: No. 2; ISSN BSBPA
• Country of Publication: Country unknown/Code not available
• Language: French

Related Subjects

AGE ESTIMATION
ALUMINUM SILICATES
AMPHIBOLES
ARGON
BIOTITE
CALCIUM SILICATES
CONGO KINSHASA
DIFFUSION
DISTRIBUTION
FELDSPARS
GEOCHEMISTRY
GEOLOGY
GEOLOGY, MINERALOGY, AND METEOROLOGY
IRON SILICATES
LEAD
LEAKS
MAGNESIUM SILICATES
MICA
MICROCLINE
MINERALS
MUSCOVITE
PEGMATITES
POTASSIUM SILICATES
QUANTITY RATIO
QUARTZ
ROCKS
RUBIDIUM
STRONTIUM
STRONTIUM 87
URANIUM
URANIUM MINERALS