Osbourn Trough

Its basement is known to be oceanic basaltic crust with compositional affinity with a Pacific mid-ocean ridge basalt ( MORB ) mantle source. The ocean depth ranges between to over the trough which has been characterised as having at least three segments, each of which has an axial valley up to wide bounded by ridges up to high. about midway between the two large oceanic plateau. The Manihiki Plateau is now to the north and to its south is the Hikurangi Plateau, away, near New Zealand. To the east the trough finishes at the Wishbone–East Manihiki scarp. The Osbourn Trough was active during the period of the Cretaceous Normal Superchron ( C34 normal magnetic polarity period, Chron 34n ) which lasted for almost 40 million years. Further the Osbourn Trough is a more prominent feature in gravity anomaly studies than in bathymetric data. This uniformity over such a large area of ocean floor lead to its first description as a possible spreading center in 1997 and means spreading stopped by end of the Chron 34n. The Glomar Challenger had surveyed part of the area by 1987 but the global magnetism data was not available to allow an understanding that a large undersea feature existed. == Tectonics ==

The precise timing of the Osbourn Trough formation has been a matter of some debate as it is important to dating geological events in the South Pacific region, in particular subduction cessation. The first rifting must have occurred prior to 115 million years ago. Spreading between the Manihiki and Hikurangi Plateau ceased when Hikurangi LIP collided with the Chatham Rise east of New Zealand and this event, which must have been no more distant in time than 101 million years ago, has been dated at 86 million years ago, but is now with Pacific Plate reference frame modelling believed to be up to 7 million years more recent. == See also ==