| Popis: |
Short-wavelength gravity lineations aligned parallel to the direction of absolute motion of the Pacific plate, and a newly discovered series of linear, elongate volcanic ridges in the south-central pacific Ocean are just two of the many geophysical and geochemical anomalies that have been observed in this area. These Puka Puka volcanic ridges can be traced for 2600 km along the trough of a major gravity lineation and stretch from close to the East Pacific Rise, in the east, to the Tuamotu Islands in the west. The ridges were the focus of a recent cruise to this area that collected high quality gravity and multi-beam swath bathymetry data, in addition to dredge samples that are suitable for radiometric age dating. A complete 2-D lithospheric flexure analysis of these new data reveals that each of the volcanic ridges is associated with an unusually low effective elastic plate thickness. Previous workers showed this region to be characterised by lower than expected elastic thickness values, which were interpreted in terms of both regional and more localised thermal anomalies in the oceanic lithosphere. The new flexure results obtained for the volcanic ridges in this study confirm these low values. Lithospheric stretching and small-scale convection models that have been put forward to explain the origin of the lineations and volcanic ridges have been re-examined in light of these new results but neither is found to satisfactorily explain all of the observations. |
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