Three-dimensional gravity analysis of the Pacific-Antarctic east Pacific rise at 36.5°S, 49.8°S and 54.2°S

• Main Author: Enriquez, Kelly D.
• Other Authors: Chen, Y. John, Beals, Ken, Trehu, Anne, Guenther, Ronald, Geosciences, Oregon State University. Graduate School
• Format: Master Thesis
• Language: English; unknown
• Published: Oregon State University
• Subjects: Gravity anomalies > Antarctic Ocean; Marine geophysics > South Pacific Ocean; Marine geophysics > Antarctic Ocean; Submarine topography > Antarctic Ocean; Gravity anomalies > South Pacific Ocean; Submarine topography > South Pacific Ocean; Antarc*; Antarctic; Antarctic Ocean
• Online Access: https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/8336h465v

Three-dimensional gravity analysis is the process of removing the predictable components from the free-air gravity anomalies and has proven to be useful for interpreting the subsurface structures and active processes at mid-ocean ridges. The three-dimensional effects of the seafloor and Moho topography, assuming a constant crustal thickness and constant crust and upper mantle densities, are subtracted from the free-air anomalies, yielding the mantle Bouguer anomalies. Mantle Bouguer anomalies at mid-ocean ridges are believed to be largely due to the three-dimensional thermal structure, which can be predicted using a simple passive flow model. When the gravity contribution from the predicted thermal structure is removed from the mantle Bouguer anomalies, the residual mantle Bouguer anomalies are created, which represent lateral variations in the crustal thickness and/or density variations from the assumed model. Three-dimensional gravity analysis has been carried out over three areas along the Pacific-Antarctic East Pacific Rise (EPR): (1) the eastern intersection of the Menard transform with the EPR, (2) the overlapping spreading center (OSC) at 36.5°S and, (3) the western intersection of the Raitt transform with the EPR. This geophysical analysis provides an essential tool for understanding the subsurface crustal/upper mantle structure of the fast spreading EPR, and more specifically at transform and nontransform offsets along the EPR. Several interesting features were observed at the eastern intersection between the Menard transform and the EPR. The continuous nature of the residual mantle Bouguer anomalies along the ridge axis suggests that the 60 km of ridge axis surveyed here has a fairly uniform crustal/upper mantle structure. Significant features are not observed in the residual mantle Bouguer anomalies at the ridge-transform intersection or along the eastern 75 km of the Menard transform. At the ridge-transform intersection, fresh lavas from the observed overshot ridge have filled in the transform valley ...