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decompression – зниження тиску in volume – в об’ємі
trigger – грати роль спускового reduce – знижувати, зменшувати
механізму
volatile - летючий, той, що швидко rift apart - розколювати,
випаровується розщеплювати; розколюватися,
розщеплюватися
сonversely - навпаки

Task 2. Look at Figure 4.1. It is a schematic diagram illustrating a typical
geothermal gradient (increase in temperature with depth) for the crust and upper
mantle. Also illustrated is an idealized curve that depicts the melting point
temperatures for the mantle rock peridotite. Notice that when the geothermal
gradient is compared to the melting point curve for peridotite, the temperature at
which peridotite melts is everywhere higher than the geothermal gradient. Thus,
under normal conditions the mantle is solid. Special circumstances are required to
generate magma. Study the schematic diagram. It will help you understand
increase in temperature better when talking about origin of magma.

Task 3. Read the following text, translate it into Ukrainian.

Origin of Magma
Most magma originates in the uppermost mantle. The greatest quantities are
produced at divergent plate boundaries in association with seafloor spreading. Lesser
amounts form at subduction zones, where oceanic lithosphere descends into the mantle.
In addition, magma can originate far from plate boundaries.
Earth’s crust and mantle are composed primarily of solid, not molten, rock.
Although the outer core is fluid, this ironrich material is very dense and remains deep
within Earth. So, where does magma come from?
INCREASE IN TEMPERATURE. Most magma originates when essentially
solid rock, located in the crust and upper mantle, melts. The most obvious way to
generate magma from solid rock is to raise the temperature above the rock’s melting
point. Although the rate of temperature change varies considerably from place to place,
it averages about 25 °C per kilometre in the upper crust. This increase in temperature
with depth, known as the geothermal gradient, is somewhat higher beneath the oceans
than beneath the continents. As shown in Figure 4.1, when a typical geothermal gradient
is compared to the melting point curve for the mantle rock peridotite, the temperature at
which peridotite melts is everywhere higher than the geothermal gradient. Thus, under
normal conditions, the mantle is solid. Tectonic processes exist that can increase the
geothermal gradient sufficiently to trigger melting. In addition, other mechanisms exist
that trigger melting by reducing the temperature at which peridotite begins to melt.
DECREASE IN PRESSURE: DECOMPRESSION MELTING. Pressure
also increases with depth. Melting, which is accompanied by an increase in volume,
occurs at higher temperatures at depth because of greater confining pressure.
Consequently, an increase in confining pressure causes an increase in the rock’s melting
temperature. Conversely, reducing confining pressure lowers a rock’s melting
temperature. When confining pressure drops sufficiently, decompression melting is
triggered. Decompression melting occurs where hot, solid mantle rock ascends in zones
of convective upwelling, thereby moving into regions of lower pressure. This process is
responsible for generating magma along divergent plate boundaries (oceanic ridges)
where plates are rifting apart.
ADDITION OF VOLATILES. Another important factor affecting the melting
temperature of rock is its water content. Water and other volatiles act as salt does to

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