Igneous Rocks Quiz

Igneous Rocks: A Detailed Overview

• Igneous rocks are formed through the cooling and solidification of magma or lava.

• Magma can be derived from partial melts of existing rocks in either the mantle or crust of a planet.

• Igneous rocks occur in a wide range of geological settings, including shields, platforms, orogens, basins, large igneous provinces, extended crust, and oceanic crust.

• Igneous and metamorphic rocks make up 90-95% of the top 16 kilometres of the Earth's crust by volume.

• Igneous rocks can be either intrusive or extrusive.

• Intrusive rocks are formed from magma that cools and solidifies within the crust of a planet, while extrusive rocks are formed by the cooling of molten magma on the Earth's surface.

• The central cores of major mountain ranges consist of intrusive igneous rocks.

• The molten rock, which typically contains suspended crystals and dissolved gases, is called magma. When magma reaches the surface, it is called lava.

• The volume of extrusive rock erupted annually by volcanoes varies with plate tectonic setting.

• Igneous rocks are classified according to mode of occurrence, texture, mineralogy, chemical composition, and the geometry of the igneous body.

• Texture refers to the size, shape, and arrangement of the mineral grains or crystals of which the rock is composed.

• The chemistry of igneous rocks is expressed differently for major and minor elements and for trace elements.Classification and Origin of Igneous Rocks

• There are three main magma series: tholeiitic, calc-alkaline, and alkaline.

• These magma series occur in various plate tectonic settings, such as mid-ocean ridges, back-arc basins, oceanic islands, island arcs, and continental large igneous provinces.

• The distribution of these magma series is related to depth and the age of the subduction zone.

• The classification of igneous rocks was based on the geological age and occurrence of the rocks until the 20th century.

• In 1902, a "quantitative" classification based on chemical analysis was proposed by Charles Whitman Cross, Joseph P. Iddings, Louis V. Pirsson, and Henry Stephens Washington.

• The concept of normative mineralogy, introduced by Cross and his coinvestigators, has endured and inspired a flurry of new classification schemes.

• By 1989, a single system of classification had been agreed upon, which was further revised in 2005.

• The Earth's crust averages about 35 kilometers thick under the continents and only 7-10 kilometers beneath the oceans.

• Rocks may melt due to a decrease in pressure, change in composition, increase in temperature, or a combination of these processes.

• Water lowers the solidus temperature of rocks at a given pressure, while carbon dioxide has a relatively less important role in magma formation.

• Increase in temperature is the most typical mechanism for the formation of magma within continental crust.

• Most magmas are mixes of melt, crystals, and sometimes gas bubbles, and they can separate as magmas evolve.