The Pacific-Antarctic Ridge (PAR, Antarctic Pacific Ridge, South Pacific Rise, South Pacific Ridge) is a divergent tectonic plate boundary located on the seafloor of the South Pacific Ocean, separating the Pacific Plate from the Antarctic Plate. It is regarded as the southern section of the East Pacific Rise in some usages, generally south of the Challenger Fracture Zone and stretching to the Macquarie Triple Junction south of New Zealand.

The divergence rate between the two plates along the ridge is believed to vary from about 5.4 centimetres per year (2.1 in/year) near 65°S to 7.4 centimetres per year (2.9 in/year) near the Udintsev Fracture Zone at 55°S.

The ridge is related to the Late Cretaceous breakup of Gondwana. To the southeast the historic Bellingshausen Plate separated the Pacific and Antarctic plates between about 84 to 61 million years ago. Until about 33 million years ago, the Proto-Antipodes Fracture Zone well to the south separated two independent spreading centers, now merged, being the Antarctic–Pacific Ridge and that of the Antarctic–Campbell Plateau.

The Louisville Ridge

Stretching for 4,300 km north-west from the Eltanin Fault System which intersects the Pacific-Antarctic Ridge to the Osbourn Seamount at Tonga and Kermadec Junction is a long line of seamounts called the Louisville Ridge – the longest such chain in the Pacific – thought to have formed from the Pacific Plate sliding over a long-lived center of upwelling magma called the Louisville hotspot.

See also

• Hollister Ridge
• Oceanic ridge
• List of tectonic plate interactions