40Ar-39Ar from the Sabongari and Nana igneous complexes within the central part of Cameroon line (central Africa)

The Sabongari and Nana volcano-plutonic complexes are two of about sixty complexes that outcrop along the Cameroon Line. In both complexes, granites and rhyolites are the prevalent rock types among plutonic and volcanic rocks, respectively. The Nana complex has never been dated, while data ranging from 77 to 49 Ma have been reported for the Sabongari intrusive rocks. These ages appeared inconsistent with field relationships, the oldest ones 77 and 74 Ma being obtained on microgranites that form a WSW-ENE alignment of small plugs within the main granite. We performed Ar-40-Ar-39 laser step-heating analyses on a plutonic and a volcanic rock for each complex. The age obtained on Sabongari granite, 57.70 +/- 0.44 Ma, is about 1 Ma older than the age obtained on a related trachyte, and consistent with field relationships. Rocks from the Nana complex are younger than those from Sabongari, ranging from 52 to 49 Ma. This is the second paper with Ar-40-Ar-39 data on the Cameroon Line anorogenic complexes after that on the Hossere Nigo complex, sited at about 240 km to the NE of the study area. Both results challenge earlier K-Ar and Rb-Sr model ages along the Cameroon Line. More Ar-40-Ar-39 data on a large number of complexes are necessary to better understand their spatial relationships over time.