Abstract
The deep structure of the Ontong-Java Plateau (OJP) in the westcentral Pacific is investigated through a 2-year deployment of four PASSCAL seismic stations used in a passive tomographic experiment. Single-path inversions of 230 Rayleigh waveforms from 140 earthquakes mainly located in the Solomon Trench confirm the presence of an extremely thick crust, with an average depth to the Mohorovicic discontinuity of 33 km. The thickest crusts (38 km) are found in the southcentral part of the plateau, around 2°S, 157°E. Lesser values remaining much thicker than average oceanic crust (15-26 km) are found on either side of the main structure, suggesting that the OJP spills over into the Lyra Basin to the west. Such thick crustal structures are consistent with formation of the plateau at the Pacific-Phoenix ridge at 121 Ma, while its easternmost part may have formed later (90 Ma) on more mature lithosphere. Single-path inversions also reveal a strongly developed low-velocity zone at asthenospheric depths in the mantle. A three-dimensional tomographic inversion resolves a low-velocity root of the OJP extending as deep as 300 km, with shear velocity deficiencies of ~5%, suggesting the presence of a keel, dragged along with the plateau as the latter moves as part of the drift of the Pacific plate over the mantle.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 29-51 |
| Number of pages | 23 |
| Journal | Physics of the Earth and Planetary Interiors |
| Volume | 118 |
| Issue number | 1-2 |
| DOIs | |
| State | Published - Feb 2000 |
Funding
The operation of the PASSCAL program greatly relied upon the help volunteered by many individuals, at the PASSCAL center and on the sites. In addition to thanking the wonderful people of the islands for their gracious hospitality, we are particularly indebted to Frs. Jim Croghan and Patrick Sullivan and Mr. Mike Toolan (Chuuk), Frs. Greg Muckenhaupt and Francis Hezel (Pohnpei), Mr. Lugo Skilling (Kosrae), Frs. Bernhard Lahn and Bernhard Braun and Mr. Lionel Aingimea (Nauru), for their logistical support, and for regular data retrieval and maintenance. Robert Busby and Paul Friberg (ex-PASSCAL, Palisades, NY) provided invaluable technical support. Guust Nolet suggested the use of the PWI method, and extended hospitality to WPR at Princeton, where Sergei Lebedev also provided help and support. Discussions with Ray Russo and Craig Bina are acknowledged. We thank Carol Stein for providing and discussing a file of regional heat flow data. Many figures were drafted using GMT software ( Wessel and Smith, 1991 ). The PASSCAL project in Micronesia was supported by the National Science Foundation, under grant EAR-93-16396.
Keywords
- Ontong-Java Plateau
- Rayleigh waveform
- Solomon Trench
ASJC Scopus subject areas
- Astronomy and Astrophysics
- Geophysics
- Physics and Astronomy (miscellaneous)
- Space and Planetary Science