Hjort Trench
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The Hjort Trench is a linear
topographic Topography is the study of the forms and features of land surfaces. The topography of an area may refer to the land forms and features themselves, or a description or depiction in maps. Topography is a field of geoscience and planetary scien ...
depression south of
Macquarie Island Macquarie Island is an island in the southwestern Pacific Ocean, about halfway between New Zealand and Antarctica. Regionally part of Oceania and politically a part of Tasmania, Australia, since 1900, it became a Tasmanian State Reserve in 197 ...
in the southwest
Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the contin ...
. Geologically, the depression is considered to be the seafloor expression of an ocean-ocean subduction zone, where the
Australian plate The Australian Plate is a major tectonic plate in the eastern and, largely, southern hemispheres. Originally a part of the ancient continent of Gondwana, Australia remained connected to India and Antarctica until approximately when India broke ...
is thrusting beneath the Pacific Plate. As the southernmost portion of the Macquarie Ridge Complex, the Hjort Trench lies in an area of diagonal convergence produced by the transform fault evolution of the
Emerald Fracture Zone The Emerald Fracture Zone () is an undersea fracture zone running the distance from the southwest corner of the Campbell Plateau to the northern tip of Iselin Bank. The name was proposed by Dr. Steven C. Cande of the Scripps Institution of Oceano ...
. Frequent seismic events, most less than deep, characterize the
transpression In geology, transpression is a type of strike-slip deformation that deviates from simple shear because of a simultaneous component of shortening perpendicular to the fault plane. This movement ends up resulting in oblique shear. It is generally v ...
along this
plate boundary Plate tectonics (from the la, label=Late Latin, tectonicus, from the grc, τεκτονικός, lit=pertaining to building) is the generally accepted scientific theory that considers the Earth's lithosphere to comprise a number of large ...
.Lodolo, E. and F. Coren (1994). "The Westernmost Pacific Antarctic plate boundary in the vicinity of the Macquarie triple junction." (In C.A. Ricci, ed. Terra Antarctica, vol.1). pp. 158–161 The trench is named in honour of the Norwegian oceanographer
Johan Hjort Johan Hjort (18 February 1869, in Christiania – 7 October 1948, in Oslo) was a Norwegian fisheries scientist, marine zoologist, and oceanographer. He was among the most prominent and influential marine zoologists of his time. The early yea ...
.


Geomorphology

The deepest point of Hjort Trench is approximately below sea level. To the east, the Hjort ridge follows the general curve of the trench, separating the trench from the Hjort Plateau. The trench and ridge are the southern part of the Macquarie Fault Zone which is formed from oceanic crust.


Incipient subduction

The Hjort Trench lies in an area of transpression where the plate boundary transitions from a transform boundary to a convergent one. This is known as earthquake focal mechanisms are both thrust and dextral strike-slip types as found in such areas. As such, this region provides an example of how a transform boundary with a vertical or near-vertical transform fault becomes an area of under-thrusting. Subduction, that is described as atypical, as lighter oceanic crust generated from the
Southeast Indian Ridge The Southeast Indian Ridge (SEIR) is a mid-ocean ridge in the southern Indian Ocean. A divergent tectonic plate boundary stretching almost between the Rodrigues Triple Junction () in the Indian Ocean and the Macquarie Triple Junction () in the ...
is subducted under heavier oceanic crust from the extinct spreading center of the Australia-Pacific plate, appears to have commenced.


See also

* Macquarie Fault Zone *
Macquarie Triple Junction The Macquarie Triple Junction is a geologically active tectonic boundary located at at which the Indo-Australian Plate, Pacific Plate, and Antarctic Plate collide and interact. The term Triple Junction is given to particular tectonic boundaries ...
*
Oceanic trench Oceanic trenches are prominent long, narrow topographic depressions of the ocean floor. They are typically wide and below the level of the surrounding oceanic floor, but can be thousands of kilometers in length. There are about of oceanic tren ...


References

{{Coord, 58, 30, S, 157, 45, E, type:landmark, display=title Plate tectonics Macquarie Island Oceanic trenches of the Pacific Ocean Subduction zones