Test yourself

Task: Tell whether the sentences are true or false. Correct the false ones.

1. Earth’s crust and mantle are composed primarily of molten rock.

2. The decrease in temperature with depth is known as the geothermal gradient.

3. Pressure increases with depth.

4. Water content is another important factor affecting the melting temperature of rock.

5. During the crystallization process, the composition of the remaining liquid portion of the magma does not change.

6. According to Bowen’s reaction series, if the solid components of a magma remain in contact with the remaining melt, they will chemically react and change mineralogy.

7. The formation of one or more secondary magmas from a single parent magma is called magmatic differentiation.

8. The process of magma’s migration through the crust when it may incorporate some of the surrounding host rock is called assimilation.

9. The composition of magma can be altered through magma mixing.

10. The unmelted crystals are those of minerals with lower melting temperatures.

Unit 5 magma Part 2

Task 1. Read and memorize the following words:

invariably - незмінно, постійно	concordant - який узгоджується, відповідає; гармонічний
emplacement – місце розташування	dike – дайка
preexisting – існуючий; той, що існував раніше	sill - силь; пластова інтрузія
bedding surface –поверхня, яка утворена осадовими породами	solitary - окремий
columnar jointing – колоноподібне з’єднання	aerial - легкий
cut across – охоплювати, включати	conduit - трубопровід, водовід (підземний) ; акведук
discordant - суперечний, невідповідний, дискордантний; який не узгоджується	shallow - мілкий, мілководний; неглибокий
eroded - розмитий; вивітрений; еродований	fissure – розлом, тріщина
intrusion - інтрузія магми; проникнення (солі, виверженого матеріалу)	fracture –розлом, тріщина
massive - щільний, ненашарований; однорідний	sedimentary bed – осадовий пласт
range - ставити, розташовувати по порядку;	swarm- маса
reflect – відображати	tensional forces – сили напруги
stretch - розтягувати, витягувати, подовжувати	radiate - розходитися променями; виходити з однієї точки (лінії); поширювати
tabular - пластовий, плитчастий, плитоподібний; пластинчастий, шаруватий

Task 2. Read the following text, translate it into Ukrainian.

Intrusive Igneous Activity

When magma rises through the crust, it forcefully displaces preexisting crustal rocks referred to as host or country rock. Invariably, some of the magma will not reach the surface but will instead crystallize or “freeze” at depth where it becomes an intrusive igneous rock.

Nature of Intrusive Bodies. The structures that result from the emplacement of magma into preexisting rocks are called intrusions or plutons. Intrusions are known to occur in a great variety of sizes and shapes. Some plutons have a tabular (tabletop) shape, whereas others are best described as massive. Also, some of these bodies cut across existing structures, such as sedimentary strata; whereas others form when magma is injected between sedimentary layers. Because of these differences, intrusive igneous bodies are generally classified according to their shape as either tabular or massive and by their orientation with respect to the host rock. Igneous bodies are said to be discordant if they cut across existing structures and concordant if they form parallel to features such as sedimentary strata.

Tabular Intrusive Bodies: Dikes and Sills. Tabular intrusive bodies are produced when magma is forcibly injected into a fracture or zone of weakness, such as a bedding surface. Dikes are discordant bodies that cut across bedding surfaces or other structures in the host rock. By contrast, sills are nearly horizontal, concordant bodies that form when magma exploits weaknesses between sedimentary beds. In general, dikes serve as tabular conduits that transport magma, whereas sills store magma. Dikes and sills are typically shallow features, occurring where the host rocks are sufficiently brittle to fracture. Although they can range in thickness from less than a millimeter to over a kilometer, most are in the 1- to 20-meter range. Dikes and sills can occur as solitary bodies, but dikes in particular tend to form in roughly parallel groups called dike swarms. These multiple structures reflect the tendency for fractures to form in sets when tensional forces stretch brittle country rock. Dikes can also occur radiating from an eroded volcanic neck, like spokes on a wheel. In these situations the active ascent of magma generated fissures in the volcanic cone out of which lava flowed. In many respects, sills closely resemble buried lava flows. Both are tabular and can have a wide aerial extent, and both may exhibit columnar jointing.

Task 3. Answer the following questions, using the vocabulary from Task 1.

1. What is host or country rock?

2. What is the name of the structures that result from the emplacement of magma into pre-existing rocks?

3. Do intrusions occur in a great variety of sizes and shapes?

4. What shape do some plutons have?

5. What differences influence the classification of intrusive igneous bodies?

6. What igneous bodies are said to be discordant? concordant?

7. When are tabular intrusive bodies produced?

8. What is a dike?

9. What is a sill?

10. What is a difference between a dike and a sill?

11. What is a dike swarm?

12. What tendency do dike swarms reflect?

Task 4. Look at Figure 5.1A, B and C. Figure A shows Salt River Canyon, Arizona. The dark, essentially horizontal band is a sill of basaltic composition that intruded horizontal layers of sedimentary rock. Figure B shows the vertical structure that looks like a stone wall - a dike, which is more resistant to weathering than the surrounding rock. This dike is located west of Granby, Colorado, near Arapaho National Forest. Figure C depicts columnar jointing in basalt, Giants Causeway National Park, Northern Ireland. These five-to seven-sided columns are produced by contraction and fracturing that result as a lava flow or sill gradually cools. Using the information from the text, compare the sill, the dike and the columnar jointing.

Task 5. Find English equivalents for the following (see the text). Try to build up your own sentences with them.

Підніматись вверх скрізь земну гору; основна або місцева гірська порода; досягнути поверхні землі; кристалізуватись на глибині; велике різноманіття розмірів та форм; пластова або плитоподібна форма; включати в себе існуючі структури; вводитись між шарами осадових порід; примусово вводитись у розлом або тріщину; використовувати слабкі місця між осадовими шарами; служити у якості пластових або плитоподібних трубопроводів; транспортувати магму; зберігати магму; відображати тенденцію формування групових розломів; спиці колеса; бути дуже схожим на підземні потоки лави.

Task 6. Give a short summary of the text from Task 2.