Oceanic trench the level of the surrounding oceanic floor. The greatest ocean depth measured is in the Challenger Deep of the Mariana Trench, at a depth of below sea level. Oceanic lithosphere moves into trenches at a global rate of about 3 km/yr. There are approximately of convergent plate margins, mostly around the Pacific Ocean—the reason for the reference “Pacific-type” margin—but they are also in the eastern Indian Ocean, with relatively short convergent margin segments in the Atlantic Ocean and in the Mediterranean Sea. Globally, there are over 50 major ocean trenches covering an area of 1.9 million km or about 0.5%
Philippine Trench a M 8.2. The trench reaches one of the greatest depths in the ocean, third only to the Mariana trench and the Tonga trench. Its deepest point is known as Galathea Depth and reaches 10,540 meters (34,580 ft) or (5,760 fathoms). Sedimentation of the Philippine trench contains slightly metamorphosed, calc-alkalic, basic, ultrabasic rock and sand grains. The southern area of the trench contains homogenous, blue, clay silt and was poor in lime. Sand grains that were also found contained fresh basaltic andesite. The sediments found in the trenches are hypothesized to have been deposited by turbidity currents. A turbidity current