Worksheet Ch 4 Igneous Rocks JReddick

Geology 101 – Physical Geology Name: ____________________________ Date: ____________ Dr. Sampere 1 What is a Volcano? A volcano is a vent or opening from which melt that originates inside the Earth emerges onto the planet’s surface or rises into the air in episodes called volcanic eruptions. 2 What is the difference between an Extrusive and Intrusive Igneous Rock? Intrusive igneous rock hardens below the surface, while extrusive igneous rock solidifies above the surface. 3 Would it be true to say that that magma can be found just about anywhere at depth within the Earth? No, magma forms only in special places where conditions favor melting of preexisting solid rock. 4 How does “decompression melting” work? When the pressure pushing on hot rock drops, decompression occurs. The pressure dropped as the rock rose from one position to a higher point. When rock rises from a lower point to a higher one, the pressure is much reduced, but the rock only cools somewhat, causing it to begin to melt. 5 What are the main volatiles that cause flux melting? The main volatiles that cause flux melting are water and carbon dioxide 6 What percent silica does a Felsic melt contain? Felsic melt contains 66%-76% silica 7 What two minerals are in high abundance in mafic melts? The two minerals high in abundance in mafic melts are Magnesium oxide and iron oxide 8 Partially melting a Mafic source rock might become a ______ melt? Partially melting a mafic source rock might become a mafic magma. 9 Which has a higher viscosity, mafic or felsic melts? Felsic has a higher viscosity than mafic. 10 Name two factors can affect the cooling rate of molten rock? The two factors that affect the cooling rate of molten rock are the size and the shape of the magma or lava body and the depth. 11 Fractional crystallization can produce a more_____ lava. Fractional crystallization can produce a more felsic lava 12 What is the difference between a sill and a Dike? A dike cuts across layers while a sill injects along layers paralleling them. 13 Name a few Batholiths along Western North America. The Mojave Desert and The Sierra Nevada Batholith 14 When were these Batholiths formed? The Mojave Desert was from 17.8 million years ago and The Sierra Nevada Batholith 85-105 million years ago. 15 What is a Pluton? How is it different from a Batholith? Plutons form when volcanoes of magma cool slowly at depth and solidifies. Batholiths are an intrusion of many plutons in an area that makes up a composite body that may be hundreds of kilometers long. 16 What two characteristics can describe igneous Rocks? Color and texture 17 Fine grained crystalline rocks are also aphanitic