Isotopic Studies of the Origin of the Cameroon Line Magmas

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This project is an isotopic investigation of the age and origin of processes operating in the Cameroon Line, a 1600 km. long chain of 70 to 30 million year old plutons, and 30 to 0 million year old volcanoes which is virtually unique among intraplate basalt provinces in traversing both oceanic and continental lithosphere. Recent work has shown that 1) the basalts have identical chemistry in oceanic and continental sectors, 2) phonolites are common in the oceanic but rare in the continental sector, 3) rhyolites are common in the continental sector but absent from the oceanic sector, 4) amphibole is abundant in the oceanic sector but scarce in the continental sector, 5) the basaltic lavas display a progression to more radiogenic Pb with time in both oceanic and continental sectors, 6) there is a remarkable lead isotopic anomaly at the continent/ocean boundary in that the volcanics immediately to either side have a uniform, highly radiogenic signature ragardless of lad concentration. A comprehensive Rb-Sr and 40AR-39Ar dating study of the plutons and volcanic centers will be conducted to provide critical information to test kinematic models for the origin of the Cameroon Line and provide a framework for petrological investigations. Detailed Nd, Sr, Pb, O, H and He isotopic studies of long lived volcanic centers, the plutonic centers and mantle nodules will be conducted. This should shed light on how mantle sources change with time and provide tests to some current models for the generation of intraplate magmas.