The empirical age‐depth relation and depth anomalies in the Pacific Ocean Basin

Abstract

This paper presents a new age‐depth relation and a comprehensive depth anomaly map for the Pacific Ocean. Age, depth, and sediment thickness were averaged for each 1°×1° area. Bathymetry was corrected for isostatic effects due to sediment and water load and for the variation of sound velocity in water. Seafloor existing at extreme distance from hot spot tracks is found to be anomalously deep. Hot spots were treated as thermal anomalies, and data within 800 km of them were eliminated from further analysis. An age‐depth equation was determined by fitting a least squares line to the remaining data. The resulting depth versus age distribution confirms the linear dependence of depth on √age up to 80 Ma. All older seafloor is within 800 km of hot spots or hot spot tracks and is shallower than predicted. This “flattening” of the age‐depth distribution requires that a separate function be fit to data older than 80 Ma. As a result, data representing the deepest seafloor (older than 80 Ma) were selected for curve fitting, and the age‐depth distribution was approximated by an exponential function. It is impossible to distinguish between the infinite half space and cooling plate models of the lithopshere using the age‐depth data from the Pacific Ocean. A depth anomaly map prepared by comparing observed depth with the depth predicted by the new age‐depth formula shows several newly recognized features, including swells over the Louisville Ridge in the South Pacific and in the Gulf of Alaska Seamounts.