Temporal chemical variations within lowermost jurassic tholeiitic magmas of the Central Atlantic Magmatic Province

Abstract

The Central Atlantic Magmatic Province (CAMP), of greater extent than any other large igneous province (LIP) yet identified surrounds the Central Atlantic in eastern North America, northeastern South America, western Africa, and southwestern Europe. It covers over 7 x 10 9 km 2 and was active for no more than 4 Ma. Virtually all CAMP rocks are mafic tholeiites, and include both intrusives and extrusives. The most extensive intrusives, diabase (dolerite) dikes, occur in three main swarms on Pangaea: NW-, NE-, and NS trending. These mafic tholeiites can be classified based on their Ti contents into low-Ti (LTi), intermediate-Ti (ITi), and high-Ti (HTi). The NE swarm contains primarily the ITi magma type, whereas the NW swarm is heterogeneous and contains all three types. The N-S swarm contains highly evolved (high-Fe) quartz tholeiites in North America and ITi rocks in South America. These dike swarms can be correlated across the Atlantic basin on the basis of composition and attitude. The two principal magma types within the CAMP, LTi and ITi, were derived from mantle sources that were compositionally similar and contained both continental lithospheric and asthenospheric components. Compared with other large igneous provinces the CAMP basalts show depleted geochemical characteristics. Compositional differences between them are primarily due to differences in depth and degree of melting; LTi represents the deepest and greatest degrees of melting. The temporal progression of the chemical characteristics indicate deeper melting with time, which is consistent with a shallow (such as crustal thinning) and passive origin for the break-up of the Pangaean continent.