The Home of Rock¡ªLithosphere

The Home of Rock¡ªLithosphere
As the name suggests, the lithosphere is composed of rock, including the earth#8217;s crust and the top of the upper mantle. If we want to understand the concept of the lithosphere, we must understand what are the crust and the upper mantle? Further more, we would learn about the distribution of rocks in the earth#8217;s crust.
We all know that the Earth is an ellipsoid with a radius of more than 6,370 km, which from the surface to the core can be divided into three parts: the earth#8217;s crust, mantle and core. The Earth's crust is the surface layer. As the Earth's surface was covered by land and sea, therefore, there are oceanic crust and continental crust. Generally, the continental crust thickness is ranging from 33 to 35km, and the thickest region is about 50-70 km. China's Qinghai-Tibet Plateau with the world's thickest crust, its average thickness reaches to 70 kilometers.

Continental crust was usually divided into three levels, which was composed of three different elements from the rock. The top layer is sedimentary rock, followed by granite layer and basalt layer. The ocean crust thickness is very slight, from 6 to 8 km average; the top of the oceanic crust is thin marine sediments, followed by basalt, which was formed by the effect of sea water and portrayed as "pillow" one after another. Geologists called such basalt "pillow lava", which is a geological phenomenon wouldn#8217;t be seen in the mainland basalt. Deep-sea drilling and seismic study found that below the oceanic crust basalt also developed a wall-like gabbro and diabase, and the ultramafic rock alteration formed serpentinite.

Seeing from the oceanic crust and continental crust structure, there is certain regularity in the distribution of rocks in earth#8217;s crust. The most obvious difference between continental crust and oceanic crust is that there is no granite layer in the oceanic crust, while there is a large area of

granite in continental crust.

After generally learned about the structure of crust, it is common sense for people to ask: What any other kind of rocks was the mantle composed of? Is there any difference between the rock in the crust and them? In the structure of the Earth, the mantle is 2,800 km, which divided into two parts the upper mantle and lower mantle. The upper mantle was mainly formed by peridotite rocks, and the lower mantle is formed by the high density iron magnesium oxide component.

According to the results of research on geophysical measurements, the upper mantle is mainly composed of the mafic and ultramafic rocks on the top. But olive rocks have a higher proportion than the Salic and Simatic rocks in the crust. As the top of crust and upper mantle are composed of rocks, the geologists made them collectively known as the lithosphere. The thickness of the lithosphere is inhomogeneity. It was usually thought that in the mid-oceanic ridge the lithosphere thickness is close to zero. Compared with the radius of the earth, at the lower part of the mainland about 100-150 km the lithosphere thickness is very thin, almost negligible.

As early as 1926, seismologist had discovered that there is a low speed belt under the rigid asthenosphere. The low-speed belt is equivalent to rheosphere, and its depth is around 100-250 kilometers. In fact, the rheosphere is not soft. From calculations and simulated experiments, we knew that only about 0.5% of the local area was melted in the rheosphere. However, because the lithosphere is more rigid, rheosphere has a bit of plastic and mobility.
In 1910, Germany meteorologists A. Wigner proposed continental drift theory. The plate tectonics theory came out till the 1960s. The essence of this theory is the lithosphere plate kinematics, which continuous seismic activities belt split the lithosphere into several different sizes of plates drifting on the rheosphere. In fact, not only in the continental plates are drifting, but the oceanic plates are also drifting. Scientists have found the continental drift evidence by many ways like the ancient climate, paleontology, paleomagnetism and abyssal sea drilling.

It has a very close relationship among lithosphere plate movement and the formation and evolution of rock. For example, metamorphic and igneous rock band regularly were distributed in the plate edge, and rock assemblage will also be changed after different types of plates, the worldwide modern active volcano is also mainly located in the plate boundary. The famous Pacific Rim "volcanic chain" is volcanic activities belt, concentrated by two thirds of the world active volcanoes. At the same time, the volcanic activities belt is frequently to be the seismic activity areas.