THE AGES OF BOMA MIGMATITES AND OF THE WEST CONGOLIAN OROGENY. PRELIMINARY DATA ON THE AGES OF THE MAYUMBIAN AND AN EARLIER FORMATION (in French)
The oldest, (2760 plus or minus 500) million years or older, is interpreted as representing an episode of an orogenic cycle, older than the Mayumbian orogeny. The next event, also only approximately dated between 1480 and 1800 million years is the Mayumbian orogeny. The last major event, of which a late tectonic phase is circa 615 million years old, is the West-Congolian orogeny which is followed by posttectonic pegmatites and veins spanning the interval between 520 (pegmatites) to circa 445 (last veins) million years. Numerous biotites have, by both the Rb--Sr and the K--Ar method, yielded apparent ages similar to those of the last post-tectonic veins, though their true age be certainly older. This is also the case for-a K--Ar age on microcline. These results indicate that these apparent ages on biotite and microcline are probably caused by a post-tectonic hydrothermal event and/or by the uplift which took place at the same time, after the West Congolian folding. It therefore follows that low Rb-- Sr apparent ages on biotites are not necessarily caused by superimposed tectonics or by an important metamorphism. (auth)
- Research Organization:
- Originating Research Org. not identified
- NSA Number:
- NSA-18-005476
- OSTI ID:
- 4131435
- Journal Information:
- Ann. Soc. Geol. Belg., Bull., Vol. Vol: 86; Other Information: EUR 450.f. Orig. Receipt Date: 31-DEC-64
- Country of Publication:
- Country unknown/Code not available
- Language:
- French
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