Which two types of rocks does earth crust mainly consist of?
Answers
Answer:
Earth's crust is rich in igneous rocks such as granite and basalt. Metamorphic rocks have undergone drastic changes due to heat and pressure. Slate and marble are familiar metamorphic rocks. Sedimentary rocks are formed by the accumulation of material at Earth's surface
Explanation:
Earth's crust is a thin shell on the outside of Earth, accounting for less than 1% of Earth's volume. It is the top component of lithosphere: a division of Earth's layers that includes the crust and the upper part of the mantle.[1] The lithosphere is broken into tectonic plates that move, allowing heat to escape from the interior of the Earth into space.
The crust lies on top of the mantle, a configuration that is stable because the upper mantle is made of peridotite and so is significantly more dense than the crust. The boundary between the crust and mantle is conventionally placed at the Mohorovičić discontinuity, a boundary defined by a contrast in seismic velocity.
Geologic provinces of the world (USGS)
Shield
Platform
Orogen
Basin
Large igneous province
Extended crust
Oceanic crust:
0–20 Ma
20–65 Ma
>65 Ma
The crust of Earth is of two distinct types:
Oceanic: 5 km (3 mi) to 10 km (6 mi) thick[2] and composed primarily of denser, more mafic rocks, such as basalt, diabase, and gabbro.
Continental: 30 km (20 mi) to 50 km (30 mi) thick and mostly composed of less dense, more felsic rocks, such as granite.
Because both continental and oceanic crust are less dense than the mantle below, both types of crust "float" on the mantle. This is isostasy, and it's also one of the reasons continental crust is higher than oceanic: continental is less dense and so "floats" higher. As a result, water pools in above the oceanic crust, forming the oceans.
The temperature of the crust increases with depth,[3] reaching values typically in the range from about 200 °C (392 °F) to 400 °C (752 °F) at the boundary with the underlying mantle. The temperature increases by as much as 30 °C (54 °F) for every kilometer locally in the upper part of the crust, but the geothermal gradient is smaller in deeper crust
Abundance (atom fraction) of the chemical elements in Earth's upper continental crust as a function of atomic number. The rarest elements in the crust (shown in yellow) are not the heaviest, but are rather the siderophile (iron-loving) elements in the Goldschmidt classification of elements. These have been depleted by being relocated deeper into Earth's core. Their abundance in meteoroid materials is higher. Additionally, tellurium and selenium have been depleted from the crust due to formation of volatile hydrides.
The continental crust has an average composition similar to that of andesite.[5] The most abundant minerals in Earth's continental crust are feldspars, which make up about 41% of the crust by weight, followed by quartz at 12%, and pyroxenes at 11%.[6] Continental crust is enriched in incompatible elements compared to the basaltic ocean crust and much enriched compared to the underlying mantle. Although the continental crust comprises only about 0.6 weight percent of the silicate on Earth, it contains 20% to 70% of the incompatible elements.
Most Abundant Elements of Earth's Crust Approximate % by weight
O 46.6
Si 27.7
Al 8.1
Fe 5.0
Ca 3.6
Na 2.8
K 2.6
Mg 1.5
Oxide Percent
SiO2 60.6
Al2O3 15.9
CaO 6.4
MgO 4.7
Na2O 3.1
Fe as FeO 6.7
K2O 1.8
TiO2 0.7
P2O5 0.1