The Mariana plate is a micro

tectonic plate Plate tectonics (, ) is the scientific theory that the Earth's lithosphere comprises a number of large tectonic plates, which have been slowly moving since 3–4 billion years ago. The model builds on the concept of , an idea developed durin ...

located west of the

Mariana Trench The Mariana Trench is an oceanic trench located in the western Pacific Ocean, about east of the Mariana Islands; it is the deep sea, deepest oceanic trench on Earth. It is crescent-shaped and measures about in length and in width. The maxi ...

which forms the basement of the

Mariana Islands The Mariana Islands ( ; ), also simply the Marianas, are a crescent-shaped archipelago comprising the summits of fifteen longitudinally oriented, mostly dormant volcanic mountains in the northwestern Pacific Ocean, between the 12th and 21st pa ...

which form part of the Izu–Bonin–Mariana Arc. It is separated from the

Philippine Sea plate The Philippine Sea plate or the Philippine plate is a tectonic plate comprising oceanic lithosphere that lies beneath the Philippine Sea, to the east of the Philippines. Most segments of the Philippines, including northern Luzon, are part of ...

to the west by a

divergent boundary In plate tectonics, a divergent boundary or divergent plate boundary (also known as a constructive boundary or an extensional boundary) is a linear feature that exists between two List of tectonic plates, tectonic plates that are moving away fr ...

with numerous

transform fault A transform fault or transform boundary, is a fault (geology), fault along a plate boundary where the motion (physics), motion is predominantly Horizontal plane, horizontal. It ends abruptly where it connects to another plate boundary, either an ...

offsets. The boundary between the Mariana and the Pacific plate to the east is a

subduction Subduction is a geological process in which the oceanic lithosphere and some continental lithosphere is recycled into the Earth's mantle at the convergent boundaries between tectonic plates. Where one tectonic plate converges with a second p ...

zone with the Pacific plate subducting beneath the Mariana. This eastern subduction is divided into the Mariana Trench, which forms the southeastern boundary, and the Izu–Ogasawara Trench the northeastern boundary. The subduction plate motion is responsible for the shape of the Mariana plate and back arc.

Geological history

Subduction at the Mariana plate has been going on for over 50 million years. Some theories of the origin of this microplate is that when the Pacific plate began to subduct beneath the Philippine plate the

volcanism Volcanism, vulcanism, volcanicity, or volcanic activity is the phenomenon where solids, liquids, gases, and their mixtures erupt to the surface of a solid-surface astronomical body such as a planet or a moon. It is caused by the presence of a he ...

and spreading ridge started to make an arc. This geological activity caused the section of the Philippine plate to break off and become the Mariana microplate. The Mariana Islands consist of volcanoes that are active and dormant and are made up of

volcanic A volcano is commonly defined as a vent or fissure in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often fo ...

and

sedimentary Sedimentary rocks are types of rock formed by the cementation of sediments—i.e. particles made of minerals (geological detritus) or organic matter (biological detritus)—that have been accumulated or deposited at Earth's surface. Sedime ...

rocks from the

Pleistocene The Pleistocene ( ; referred to colloquially as the ''ice age, Ice Age'') is the geological epoch (geology), epoch that lasted from to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fin ...

Defining features

As the Pacific plate subducts beneath the Mariana plate, it creates a trench. This is the

, and it is the deepest

trench A trench is a type of digging, excavation or depression in the ground that is generally deeper than it is wide (as opposed to a swale (landform), swale or a bar ditch), and narrow compared with its length (as opposed to a simple hole or trapping ...

in the world. Another result of this subduction is the

. These are formed from dehydration of the subducting, old

oceanic crust Oceanic crust is the uppermost layer of the oceanic portion of the tectonic plates. It is composed of the upper oceanic crust, with pillow lavas and a dike complex, and the lower oceanic crust, composed of troctolite, gabbro and ultramaf ...

creates melt, and the melt rises to the surface through a volcano. This

has been occurring for almost 50 million years. The rock type in the area is volcaniclastic sediments on top of

igneous Igneous rock ( ), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rocks are formed through the cooling and solidification of magma or lava. The magma can be derived from partial ...

rocks. The source of these rocks are from crustal spreading. Just off the eastern coast of Mariana there are big seamounts made of serpentinized periodic. They are formed from mud volcanism. The composition for the

seamount A seamount is a large submarine landform that rises from the ocean floor without reaching the water surface (sea level), and thus is not an island, islet, or cliff-rock. Seamounts are typically formed from extinct volcanoes that rise abruptly a ...

s differs in the Izu–Ogasawara Trench and Mariana systems which indicate regional changes in geology.

Tectonic behavior

Eastern convergent boundary

The tectonic plate is approximately 100 km thick and converging to the east at a rate of 50–80 mm/yr with the Pacific plate subducting at 60–100 mm/yr This eastern subduction is divided into the Mariana Trench, which forms the southeastern boundary, and the Izu–Ogasawara Trench the northeastern boundary. The Izu–Ogasawara Trench and Mariana subduction zones are traveling at different rates. While the northern section of the Izu–Ogasawara Trench plate is subducting at 44 mm/yr, the southern section subducts at 14 mm/yr. The subducting Pacific plate dips at about 10 degrees and directed 83 degrees west of north. The northern subduction zone is expanding by rifting while the southern contains a

strike slip fault In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic ...

. Seismologists have been studying how the subducting slabs underneath the Mariana island arc are entering the lower mantle and being redirected horizontally, deflecting off the upper to lower mantle transition zone.

Western divergent boundary

The Mariana plate is also separating at a rate of 30 mm/yr from the Philippine Plate to the west. The Mariana Trough is located on the western side of the island arc along with the back arc basin. Around 3 Ma the basin began spreading at 4.7 cm/yr. Due to the back arc spreading in the Mariana Trough the islands are moving east while the Philippine Sea plate is staying almost stationary.

Future of plate

Since there is volcanism happening on the Mariana back arc ridge and basin, this system could continue to grow but combining the rate of separation from the Philippine plate along with the subduction destroying the Mariana plate it is possible this microplate could eventually dissipate. The rate of subduction is greater than the rate of uplift. The collision of aseismic ridges and the axis of the trench explain how the plate curvature is evolving.

References

{{East Asia plates Tectonic plates Geology of the Pacific Ocean