Cameroon Line magmatism: conventional K/Ar and single-crystal laser 40Ar/39Ar ages of rocks and minerals from the Hossere Nigo anorogenic complex, Cameroon
✍ Scribed by J.B. Kamdem; M. Kraml; J. Keller; F. Henjes-Kunst
- Publisher
- Elsevier Science
- Year
- 2002
- Tongue
- English
- Weight
- 198 KB
- Volume
- 35
- Category
- Article
- ISSN
- 1464-343X
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✦ Synopsis
Hossere Nigo is one of several anorogenic plutonic complexes in the north-eastern part of the Cameroon Line (CL), West Africa. It is a dominantly gabbroic ring structure with a core of monzonitic to syenitic intrusive bodies. Previous geochronological work in the CL indicates a time span from 67 to 31 Ma for plutonism and from 42 Ma to Recent for volcanism. No age data for Hossere Nigo were available so far. Therefore, six whole rock samples were dated by the conventional K/Ar method. The model ages obtained range from 82 to 69 Ma but are, however, in conflict with the relative succession of emplacement. We therefore performed 40 Ar= 39 Ar laser fusion analyses on single crystals of phlogopite separated from one of the conventionally dated rocks. Their 40 Ar= 39 Ar isochron age of 65:0 AE 0:8 Ma (1r) is about 7 Ma younger than the related whole rock K/Ar date. Elevated whole rock ages are ascribed to hydrothermal overprinting and associated uptake of excess argon. By contrast, the reported Ar/Ar age provides a precise and accurate fix point for an early stage of CL intrusive magmatism.