Isotopic Studies of the Origin of the Cameroon Line Magmas

该项目是对长达1600公里的喀麦隆线上作业过程的年代和起源进行的同位素调查。7000万至3000万年前的深成岩和3000至000万年前的火山组成的长链，这在板内玄武岩省份中几乎是独一无二的，既横跨大洋又横跨大陆岩石圈。最近的研究表明：1)玄武岩在大洋段和大陆段具有相同的化学特征；2)声石在大洋段常见，但在大陆段很少见；3)流纹岩在大陆段很常见，但在大洋段不存在；4)角闪石在大洋段很丰富，但在大陆段很少。5)玄武岩熔岩在大洋和大陆部分都表现出随时间推移而更具放射性成因的铅。6)大陆/海洋边界存在显著的铅同位素异常，因为紧邻两侧的火山岩具有统一的高放射性特征，而不具有LAD浓度。将对深成岩和火山中心进行全面的Rb-Sr和40Ar-39Ar测年研究，以提供关键信息，以测试喀麦隆线起源的运动学模型，并为岩石学研究提供框架。将对长寿火山中心、深成中心和地幔结核进行详细的Nd、Sr、Pb、O、H和He同位素研究。这应该有助于阐明地幔来源如何随时间变化，并为目前一些板内岩浆产生的模型提供测试。

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.