The Juan Fernandez Plate is a small

tectonic plate 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 te ...

(

microplate A microplate, also known as a microtiter plate (''Microtiter'' is a registered trademark in the United States, therefore it should not be used generically without attribution), microwell plate or multiwell, is a flat plate with multiple "wells" ...

) in the

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 ...

. With a surface area of approximately 10⁵ km², the microplate is located between 32° and 35°S and 109° and 112°W. The plate is located at a

triple junction A triple junction is the point where the boundaries of three tectonic plates meet. At the triple junction each of the three boundaries will be one of three types – a ridge (R), trench (T) or transform fault (F) – and triple junctions can ...

between the

Antarctic Plate The Antarctic Plate is a tectonic plate containing the continent of Antarctica, the Kerguelen Plateau, and some remote islands in the Southern Ocean and other surrounding oceans. After breakup from Gondwana (the southern part of the superconti ...

, the Nazca Plate, and the Pacific Plate. Approximately 2,000 km to the west of

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the sout ...

, it is, on average, 3,000 meters deep with its shallowest point coming to approximately 1,600 meters, and its deepest point reaching 4,400 meters.Anderson-Fontana, S., J. F. Engeln, P. Lundgren, R. L. Larson, and S. Stein
Tectonics and evolution of the Juan Fernandez microplate at the Pacific-Nazca-Antarctic triple junction
J. Geophys. Res., 91, 2005–2018, 1986.

Discovery

The Juan Fernandez Microplate was first discovered in 1972 via

seismicity Seismicity is a measure encompassing earthquake occurrences, mechanisms, and magnitude at a given geographical location. As such, it summarizes a region's seismic activity. The term was coined by Beno Gutenberg and Charles Francis Richter in 19 ...

charts, which showed semi-circular patterns at the Pacific-Nazca-Antarctica triple junction. This implied that shear zone was present that were inconsistent with existing plate theories in the area. The microplate, as it is known today, was first mapped and named in 1983, during a Sea Beam survey that specifically mapped the East Pacific Rise (EPR) between the Easter and Juan Fernandez microplates. The first sonar mapping of the JF Microplate was performed in 1983. Shortly after, the RV Endeavor performed another geological survey defining the boundaries of the plate and clearly identifying the key features of the triple junction of which the Juan Fernandez Microplate is the center. Since then, the growth of the plate has been theorized to be influenced by spreading ridges between the Pacific and JF Plates, accretion onto the plate by the Nazca and JF shear zones, and

compression Compression may refer to: Physical science *Compression (physics), size reduction due to forces *Compression member, a structural element such as a column *Compressibility, susceptibility to compression * Gas compression *Compression ratio, of a ...

of both the northernmost and southeastern points of the JF Microplate.Yelles-Chaouche, A., J. Francheteau, and P. Patriat
"Evolution of the Juan Fernandez microplate during the last three million years"
Earth Planet. Sci. Lett., 86, 269–286, 1987.Larson, R. L., R. C. Searle, M. C. Kleinrock, H. Schouten, R. T. Bird, D. F. Naar, R. I. Rusby, E. E. Hooft, and H. Lasthiotaki
Roller-bearing tectonic evolution of the Juan Fernandez microplate
Nature, 356, 571–576, 1992.

Morphology and geological history

This microplate is estimated to have formed approximately 3–4 Ma ago. Once one single spreading center, the

East Pacific Rise The East Pacific Rise is a mid-ocean rise (termed an oceanic rise and not a mid-ocean ridge due to its higher rate of spreading that results in less elevation increase and more regular terrain), a divergent tectonic plate boundary located alon ...

at this location split in two and resulted in two separate spreading ridges between the Nazca Plate and the Pacific Plate. The two spreading ridges, along with the Chile Rise, bounded the JF microplate. These two spreading centers then accreted material onto the JF microplate until it grew into the recognizable shape it is today. As it grew, the northern boundary of the microplate most likely experienced compression due to extreme clockwise rotational force provided by the eastern shear of the Nazca Plate and the western shear of the Pacific Plate. As the Nazca plate has a close coupling to the northern boundary of the plate, rotation of the JF Microplate was at its peak during its beginning stages of formation nearing rotational speeds of 32° per Ma. However, approximately 2.5 Ma ago, the south-eastern tip of the microplate collided against a

fracture zone A fracture zone is a linear feature on the ocean floor—often hundreds, even thousands of kilometers long—resulting from the action of offset mid-ocean ridge axis segments. They are a consequence of plate tectonics. Lithospheric plates on eit ...

within the Antarctic Plate thus causing compression of the microplate against the Antarctic Plate and therefore stagnating its rotational motion down to approximately 9° per Ma at approximately 1 Ma ago. The original couplings causing shear then changed from the Pacific-JF and Nazca-JF boundaries to the Atlantic-JF boundary and Nazca-JF boundaries. The past 1 Ma has not seen any significant change in plate rotation and growth rate since.

Rotation

Since the earliest surveys of the area, theories about the movement of the JF Microplate have evolved to include compression of the plate through rotational movement and also shear zones between two major plates and the JF Microplate driving this clockwise rotational movement. The Pacific Plate is estimated to have a spreading rate anywhere between 13 and 16 cm/yr in relation to the Juan Fernandez MicroPlate. This spreading ridge supplies

magma Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma is found beneath the surface of the Earth, and evidence of magmatism has also been discovered on other terrestrial planets and some natural sa ...

to the west of the plate, acting as a lubricant. In the development stages of the microplate, the Pacific Plate also shared a coupled shear section to the south of the microplate and, together with the Nazca Plate, drove fast rotation of the microplate.Kleinrock, M. C., and R. T. Bird
"Southeastern boundary of the Juan Fernandez microplate: Braking microplate rotation and deforming the Antarctic plate"
J. Geophys. Res., 99, 9237–9261, 1994. Approximately 2.5 Ma ago the JF Microplate began decoupling from the Pacific Plate and coupling with the Antarctic Plate. The latter severely braked the rotational movement of the microplate. Now, the Nazca and Antarctica Plates, are the plates that share the current shear zones with transform faulting between them and the JF Plate. The Nazca Plate shears to the east while the Antarctica Plate shears relatively to the west, and this continues to drive the rotation of the microplate clockwise as well as consequential compression however at a much slower rate. Compression has been observed on the Juan Fernandez Microplate at the Pacific-Nazca-JF triple junction and the Nazca-Antarctic-JF triple junction, due to the slightly irregular shape of the plate which does not rotate perfectly about its center.

Possible future fates

Some researchers claim that as the triple Junction that the JF Microplate shares with the Pacific Plate and the Antarctic Plate shifts southwest, the plate will continue to have unimpeded clockwise rotational movement for the foreseeable future. Other researchers propose that due to the extent of compression between the JF Microplate and the Antarctic Plate, the microplate will accrete onto the Antarctic plate within the next million years and simply extend the triple junction between the Pacific, Antarctic, and Nazca plate to the current location of the Pacific-Nazca-Juan Fernandez triple junction.Bird, R. T., D. F. Naar, R. L. Larson, R. C. Searle, and C. R. Scotese (1998)
"Plate tectonic reconstructions of the Juan Fernandez microplate: Transformation from internal shear to rigid rotation"
J. Geophys. Res., 103(B4), 7049–7067, doi:10.1029/97JB02133.

References

{{DEFAULTSORT:Juan Fernandez Plate Geology of the Pacific Ocean Tectonic plates