At one of the places in India, you will find a region made up of sheets of lava which had oozed out from huge cracks on the Earth’s surface millions of years ago. This unique phenomenon is found at -Required to answer. Single choice.
(1 Point)
a. Deccan Trap
b. Nilgiris
c. Coral Islands
d. Lakshadweep Island
Answers
Answer:
4 Igneous Processes and Volcanoes
KEY CONCEPTS
By the end of this chapter, students should be able to:
Explain the origin of magma it relates to plate tectonics
Describe how the Bowen’s Reaction Series relates mineral crystallization and melting temperatures
Explain how cooling of magma leads to rock compositions and textures, and how these are used to classify igneous rocks
Analyze the features of common igneous landforms and how they relate to their origin
Explain partial melting and fractionation, and how they change magma compositions
Describe how silica content affects magma viscosity and eruptive style of volcanoes
Describe volcano types, eruptive styles, composition, and their plate tectonic settings
Describe volcanic hazards
Igneous rock is formed when liquid rock freezes into a solid rock. This molten material is called magma when it is in the ground and lava when it is on the surface. Only the Earth’s outer core is liquid; the Earth’s mantle and crust is naturally solid. However, there are a few minor pockets of magma that form near the surface where geologic processes cause melting. It is this magma that becomes the source for volcanoes and igneous rocks. This chapter will describe the classification of igneous rocks, the unique processes that form magmas, types of volcanoes and volcanic processes, volcanic hazards, and igneous landforms.
Pahoehoe lava flow in Hawaii
Lava flow in Hawaii
Lava cools quickly on the surface of the earth and forms tiny microscopic crystals. These are known as fine-grained extrusive, or volcanic, igneous rocks. Extrusive rocks are often vesicular, filled with holes from escaping gas bubbles. Volcanism is the process in which lava is erupted. Depending on the properties of the lava that is erupted, the volcanism can be drastically different, from smooth and gentle to dangerous and explosive. This leads to different types of volcanoes and different volcanic hazards.
An intrusive igneous mass now exposed at the surface by erosion
Half Dome, a mass of intrusive igneous rock in Yosemite National Park, now exposed by erosion.
In contrast, magma that cools slowly below the earth’s surface forms larger crystals which can be seen with the naked eye. These are known as coarse-grained intrusive, or plutonic, igneous rocks. This relationship between cooling rates and grain sizes of the solidified minerals in igneous rocks is important for interpreting the rock’s geologic history.
Granite is a classic coarse-grained (phaneritic) intrusive igneous rock. The different colors are unique minerals. The black colors are likely two or three different minerals.
If magma cools slowly, deep within the crust, the resulting rock is called intrusive or plutonic. The slow cooling process allows crystals to grow large, giving intrusive igneous rock a coarse-grained or phaneritic texture. The individual crystals in phaneritic texture are readily visible to the unaided eye.
Porphyritic teture with large crystals in a finer grained groundmass
Porphyritic texture
Some igneous rocks have a mix of coarse-grained minerals surrounded by a matrix of fine-grained material in a texture called porphyritic. The large crystals are called phenocrysts and the fine-grained matrix is called the groundmass or matrix. Porphyritic texture indicates the magma body underwent a multi-stage cooling history, cooling slowly while deep under the surface and later rising to a shallower depth or the surface where it cooled more quickly.
Pegmatic texture with large grains of minerals, mostly of felsic composition
Pegmatitic texture
Residual molten material expelled from igneous intrusions may form veins or masses containing very large crystals of minerals like feldspar, quartz, beryl, tourmaline, and mica. This texture, which indicates a very slow crystallization, is called pegmatitic. A rock that chiefly consists of pegmatitic texture is known as a pegmatite. To give an example of how large these crystals can get, transparent cleavage sheets of pegmatitic muscovite mica were used as windows during the Middle Ages.
A lava rock full of bubbles called scoria
Scoria, a vesicular extrusive igneous rock
All magmas contain gases dissolved in solution called volatiles. As the magma rises to the surface, the drop in pressure causes the dissolved volatiles to come bubbling out of solution, like the fizz in an opened bottle of soda. The gas bubbles become trapped in the solidifying lava to create a vesicular texture, with the holes specifically called vesicles. The type of volcanic rock with common vesicles is called scoria.
Explanation:
C.