EarthRef.org Reference Database (ERR) -- Richardson et al. 1980

Vein smectites with large RB/Sr enrichments from extensively altered basaltic oceanic crust in Deep Sea Drilling Project hole 417A in the western Atlantic define a highly constrained Rb/Sr isochron age of 108¿3 m.y. This age is idential to a less constrained age of 108¿17 m. y. for vein smectites with lower Rb/Sr enrichments from adjacent hole 418A and to the 108 m.y. age of crust formation derived by paleontological and magnetic anomaly correlation. Reasonable agreement exists between the 87Sr/86Sr ratio of vein calcites from both sides and the seawater 87Sr/80Sr ratio at the time. Pervasive low-temperature alteration in the contrasting environments of 417 and 418 appears to be coeval and essentially coincident with basement formation. Alteration may be used to advantage in determining ages of old oceanic crust. Vein smectites with large RB/Sr enrichments from extensively altered basaltic oceanic crust in Deep Sea Drilling Project hole 417A in the western Atlantic define a highly constrained Rb/Sr isochron age of 108¿3 m.y. This age is idential to a less constrained age of 108¿17 m. y. for vein smectites with lower Rb/Sr enrichments from adjacent hole 418A and to the 108 m.y. age of crust formation derived by paleontological and magnetic anomaly correlation. Reasonable agreement exists between the 87Sr/86Sr ratio of vein calcites from both sides and the seawater 87Sr/80Sr ratio at the time. Pervasive low-temperature alteration in the contrasting environments of 417 and 418 appears to be coeval and essentially coincident with basement formation. Alteration may be used to advantage in determining ages of old oceanic crust.