Eclogites and Blueschist in Relation to Subduction Zones and Plate Tectonics

Plate tectonic theory is important in explaining the reason the world today is made of many land fragments and is not a single piece. It expounds on how the outer shell of the earth is made of plates that move over the mantle. Stern, further elaborates plate tectonics as the movement of the thermal earth boundary horizontally over asthenosphere and is fastened by the lithosphere sinking in several subduction zones. This movement is responsible for the formation of some new discovered kind of rocks like Eclogitesand Blueschists.

Eclogite is a rare type of metamorphic rock that is a geological significance. The process ensuing in the formation of eclogites requires a situation with temperature and pressure difference. Blueschists also are formed in a metamorphic process related to the continental and subduction collision and reflect high-pressure burials at low temperatures.Due to the space-time distribution of the belts of blueschist and eclogite within the plate tectonic field has led to a better grasp of progeny at plate boundaries that are converging and continent evolution.

There are three main divisions of eclogites which are grouped, A, B, and C. Group A eclogites are former basaltic intrusions contained in metamorphic rocks and mostly contain cyanide, Zoisite, and quartz. Group B eclogites are usually xenoliths or inclusions in great depths. On the other hand, group C eclogites are composed of the former subducting oceanic lithosphere and mostly bear Epidote, retail, and amphiboles.

Characteristics of Eclogites and Blueschists

Since the discovery of eclogiteby Hauy, the rock has contributed significantly to the development of various concepts in the field of metamorphisms like the mineral facies concept, metamorphic rocks in igneous rocks existence and volume law.

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Eclogites are made up of mainly pyrope-rich garnet and pyroxene impact. These rocks are responsible for its characteristic color. The rocks are mostly present in the upper mantle in regions of subducted oceanic plates. It is characterized by pressures exceeding 1.2 GPA, which is existent in 45 km and below. The temperatures associated with it are between 400 °C and 500 °C. The range is below the average crustal temperature increasing observed to increase at 25 °C per kilometer. The fact means that the formation of eclogites takes place at low temperatures that are prevalent in the subduction zones where the oceanic lithosphere that is cool with basaltic components diffuses into the mantle. It is common in more in-depth parts of subducting parts and aid in keeping the plate tectonic conveyor belt operating as it drags down the subducting slab.

Eclogites can exist as xenoliths with an alkaline characteristic that is unusual. Eclogites are mostly accompanied by garnet peridotite. The eclogites and the peridots are found to be diamond bearing. This characteristic affirms that the rocks are from deep in the mantle where the temperature is more than 400 °C.

Blueschist rocks are a type of schist rocks also commonly referred to as the glaucophane schist. The schist is a metamorphic rock that is strongly foliated. It is basalt rock that has undergone metamorphosis at high pressure and low temperature, and it is composed of the glaucophanic amphibole. These rocks appear in the lithospheric plate subduction since they require colder upper mantle gathers that exist in the subduction zones. Due to this the space-time distribution of the belts of blueschist and eclogite within the plate tectonic field has led to a better grasp of progeny at plate boundaries.They can be subdivided further into four categories which include the crosstie-pumpellyite granofels, glaucophane schist, Epidote glaucophane and jadeite bearing glaucophane phengite schist Kabir & Takasu. It forms on subduction zones at the boundaries of convergent plate boundaries.

Therefore, blueschist rocks have a basaltic composed structure. It may also consist riebeckite mostly in the metamorphic schists of regional types. Riebeckite is a silicate mineral which when mixed with magnesioriebeckite, a solid solution is formed. Distribution of the blueschist rock belt.

Comparison Between Archaeologists and Bblueschists

Eclogites and blueschists have several similarities and differences clear from a comparison of their various characteristics. The similarities range from the point of location in the mantle, the type of rock, conditions of formation and mode of existence. On the other hand, they differ mainly in their composition and physical appearance. Both eclogite and blueschist rocks are both metamorphic types of rocks.

Eclogite rocks form from the metamorphism of mafic rocks at high ultrahigh pressure and low thermal gradients.On the other hand blueschist rocks form from the metamorphism of basalt or rocks that are of a related chemical composition to basalt at high pressure and relativistic temperatures. From the formation process. Another similarity in the formation process also is that the formation process is that they both the two kinds of rocks undergo metamorphism at high temperatures and low temperatures. According to Nelson, for high-pressure metamorphism to take place, the temperatures have to be high,and temperatures are above 320oC.

Both the Eclogite and blueschist rocks, mostly exist in the subduction zones a fact attributed to their formation conditions. Another main similarity in the two rocks is that they both exist in different forms. The fact is affirmed by the three groups A, B, and C classifications of the eclogite rocks. On the other hand, the blueschist rocks are divided into four main categories which are the crosstie pumpellyite granofels, glaucophane schist, Epidote glaucophane and jadeite bearing glaucophane phengite schist.

On the other hand, the rocks differ in two main areas which are their composition, physical appearance. Regarding composition, eclogites are made up of mainly pyrope-rich garnet and pyroxene impact. Blueschist on the other hand rocks has basaltic composition chemical structure or consist of riebeckite mostly in the metamorphic schists of regional type. The different composition structures result in different physical appearance. Eclogites have a characteristic red and green color due to the prop-rich garnet and pyroxene impact constituents in its structure. Blueschist, on the other hand, is blue as the name suggests. The characteristic color is attributed to glaucophane, zodiac amphibolite or crosstie present in its structure.

The Western Gneiss Region is approximately 50000 km2 large and lies along the Southwest Norway coast. To grasp the dynamics behind continental collision and subduction, there is a need to know aspects like thermal evolution, tectonic controls, fluid flux and reaction rates of metamorphism. WGR is exposed well, therefore accessible, a fact that ensures it is possible to collect all the required information to understand the continental collision and subduction dynamics. This accessibility is also aids in the research on eclogites that are prevalent in the area and on the factors affecting their formation.

In WGR, the region in Southern Scandinavian Caledonides has an exposed structural level that is low. Within the Scandinavian Caledonideseclogites are widely distributed. It is situated in a sizeable tectonic window being neighbored by the Caledonia allochthon outcrop made of thick layers of thrust sheets. To the east of the allochthon is Baltic Foreland mostly made up of metavolcanics, metasediments, and Proterozoic gneisses. A Paleozoic sedimentary cover and Baltic base gneiss layers make up the allochthon. There has been a complex evolution of the basement gneisses contact and the autochthonous cover that depicts proof of eastward or southeast directed thrusting that is succeeded by reverse motion west or northwest.

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Eclogites and Blueschist in Relation to Subduction Zones and Plate Tectonics. (2022, Apr 25). Retrieved from

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