On the continents and under the depths of the oceans, the structure of the earth's crust is different. In the lowland areas, the crust is about 40 kilometers thick, under mountain ranges it is even larger - up to 80 kilometers. Under the deep sea, the thickness of the crust is less, from 5 to 15 kilometers. On average, under the continents the crust lies at a depth of 35 km, and under the oceans - 7 km. Each species has a different structure, which raises the question of what types of the Earth's crust form the Pacific plate?
Differences in the structure of the continental and oceanic crust
In addition to differences in thickness, differences in the structure of the crust of the oceanic and terrestrial types are observed. The mainland consists of three layers: sedimentary (topmost), granite (middle layer) and basalt (lower). The oceanic crust consists of sedimentary and basaltic layers.
The boundary between the continental and oceanic crust is not always traced, it is often blurred. For example, the margins of the basin of the seas, where the structure of the earth's crust is close to the oceanic type, can adjoin the edge of the continental platform. In such places there is practically no granite layer, but the upper sedimentary layer is highly developed.
The border of oceans and seas is represented by island arcs. The crust in these areas is similar in structure and thickness to the mainland type. And these are not all types.
Types of oceanic crust
And what types of crust form the Pacific plate and what types generally exist? There are several categories of structures of oceanic types of crust.
- Oceanic continental. This type is found on the shallows and represents a direct continuation of the continental structures within the shelf. The thickness of the crust in this place is up to 35 kilometers. The structure of the shelf is the same as that of the mainland type: there are basalt (lower), granite (middle) and sedimentary (upper, forming the planet's surface) layers. But even with all three layers, the earth’s shelf crust has a powerful sedimentary layer.
- Geosynclinal marine type. It is found in the hollows of the seas. This species underlies the Bering, Black, Okhotsk, Mediterranean, Caribbean seas, etc. For this type of crust, the granite layer is gradually wedged out.
- Suboceanic. Located within the continental slope. In its lower part, a decrease in the granite layer is observed.
- Type of oceanic ridges and uplifts. It is characterized by a complex relief involving faults. This type includes mid-ocean ridges, mountainous countries located in the Pacific Ocean.
Different types can form one plate. But the Pacific lithosphere plate is formed only by the crust of the oceanic type.
Pacific plate
The largest lithospheric plate is the Pacific. Since the development of the earth's crust, it is in constant motion and gradually its size decreases.
In the south, the plate borders on the Antarctic plate. The border between them runs along the Pacific-Antarctic Range. In the north, the plate forms the Aleutian Trench, and in the west - the Mariana Trench.
The plate moves north, forming the San Andreas Fault.
Features of the Pacific Plate
Knowing what types of the Earth’s crust the Pacific plate is formed, we can formulate its difference from the Earth’s crust.
The first and main difference is the absence of a granite layer. In this type of plate there are only two layers, and in the mainland there are three. Different age plates. Oceanic is considered young, and terrestrial - older.
Knowing what types of the earth's crust the Pacific plate is formed and what is its thickness, you can understand why it is bent under the mainland. The latter is thicker and more powerful, has a hard layer. But the oceanic type is considered soft, thin. Thickness is clearly visible in the places where ridges form - the closer the oceanic ridge, the younger the crust.
Scientists suggest that the growth goes from the ridges to the continents, and then there is a lowering of the layers under the weight of the continental type of crust. During this process, island arcs, gutters, protrusions, and deflections arise. Thus, two zones are distinguished: spreading and subduction. The first zone is the oceanic crust formation site, and the subduction zone is the place where the crust begins to sink under the mainland.
A vivid example of the transition of the crust from one type to another on the Pacific plate is the Mariana Trench. This is a transitional region with a distinct island arc, a large depth of the trench and intense seismic activity.