ROCKS OF EARTH'S CRUST
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abyssal –абиссальный, глубинный
adjacent –смежный, примыкающий
ash – зола
belt – пояс; лента; ремень
body – тело, вещество; solid (liquid, gaseous) bodies твердые (жидкие, газообразные) вещества; породная масса; массив; месторождение; пласты
common – обычный; общий
cool – охлаждать(ся); остывать; прохладный; ant heat – нагревать(ся)
dimension – измерение; plural размеры; величина; syn measurement, size
dust – пыль
dyke – дайка
extrusion – вытеснение; выталкивание; ant intrusion вторжение; геол. интрузия (внедрение в породу изверженной массы)
fine – тонкий, мелкий; мелкозернистый; высококачественный; тонкий; прекрасный, ясный (о погоде); изящный; fine-graded (fine-grained) мелкозернистый, тонкозернистый
flow – течь; литься; л течение; поток; flow of lava поток лавы
fragmentary –обломочный, пластический
glass – стекло; glassy –гладкий, зеркальный; стеклянный
gold – золото
igneous – магматический
inclined – наклонный
mica – слюда
permit – позволять, разрешать; syn allow, let; make possible
probably – вероятно; syn perhaps, maybe
shallow –мелкий; поверхностный; ant deep глубокий
sill – силь, пластовая интрузия
stock – шток, небольшой батолит
vein – жила, прожилок, пропласток
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IGNEOUS ROCKS
Igneous rocks have crystallized from solidified magma. Igneous rocks can be classified in a number of ways and one of them is based on mode of occurrence. They occur either as intrusive (below the surface) bodies or as extrusive masses solidified at the Earth’s surface. The terms “intrusive” and “extrusive” refer to the place where rocks solidified.
The grain size of igneous rocks depends on their occurrence. The intrusive rocks generally cool more slowly than the extrusive rocks and crystallize to a larger grain size. The coarser-grained intrusive rocks with grain size of more than 0.5 mm called plutonic or abyssal are referred to as intrusive igneous rocks because they are intruded into older pre-existing rocks. Extrusive or volcanic rocks have even finer grains, less than 0.05 mm and are glassy.
Exposed igneous rocks are most numerous in mountain zones for two reasons. First, the mountain belts have been zones of major deformation. Second, uplifts in mountain belts have permitted plutonic masses to be formed.
The largest bodies of igneous rocks are called batholiths. Batholiths cooled very slowly. This slow cooling permitted large mineral grains to form. It is not surprising that batholiths are composed mainly of granitic rocks with large crystals called plutons. As is known, granites and diorites belong to the group of intrusive or plutonic rocks formed by solidification of igneous mass under the Earth’s crust. Granites sometimes form smaller masses called stocks, when the occurrence has an irregular shape but smaller dimensions than the batholiths.
Laccoliths and sills, which are very similar, are intruded between sedimentary rocks. Sills are thin and they may be horizontal, inclined or vertical. Laccoliths are thicker bodies and in some cases they form mountains.
Dykes are also intrusive bodies. They range in thickness from a few inches to several thousand feet. Dykes are generally much longer than they are wide. Most dykes occupy cracks and have straight parallel walls. These bodies cool much more rapidly and are commonly fine-grained. For example, granite may occur in dykes that cut older rocks.
Pegmatites (quartz, orthoclase and mica) also belong to the group of plutonic or intrusive rocks. They occur in numerous veins which usually cut through other plutonites, most often granite, or adjacent rocks.
Extrusive igneous rocks have been formed from lava flows which come from fissures to the surface and form fields of volcanic rocks such as rhyolite, andesite, basalt, as well as volcanic ashes and dust, tuff, etc. As a rule, these rocks of volcanic origin cool rapidly and are fine-grained. It is interesting to note that basalt is the most abundant of all lava types. It is the principal rock type of the ocean floor.
Igneous rocks are rich in minerals that are important economically or have great scientific value. Igneous rocks and their veins are rich in iron, gold, zinc, nickel and other ferrous metals.
УПРАЖНЕНИЯ
Укажите, какие утверждения являются верными, а какие – нет. Если утверждение верное, отметьте TRUE (T). Если утверждение неверное, отметьте FALSE (F).
1. Igneous rocks have crystallized from solidified magma.
2. The intrusive rocks generally cool less slowly than the extrusive rocks.
3. The largest bodies of igneous rocks are called dykes.
4. Batholiths cooled very slowly.
5. As is known, granites and diorites belong to the group of extrusive rocks.
6. Most dykes occupy cracks and have straight parallel walls.
7. Pegmatites occur in numerous veins which usually cut through other plutonites.
8. Igneous rocks are poor in minerals.