Temperature, \'C 300 500 100 Homblende Pyroxene horntels homeis 10 (10) 20 30 Ec

Question

Temperature, 'C 300 500 100 Homblende Pyroxene horntels homeis 10 (10) 20 30 Eclogte Figure 1.56 Metamorphic facles as functions of temperature and pressure (depth). Dashed curve is average continental geothermal gradient. because temperature is the single important variable. The facies recognized are named for specific minerals: sanidinite, the high-temperature facies, is characterized by the presence of the mineral sanidine, a variety of K-feldspar, grading outward from the heat source through the hornfels facies to the zeolite or low-temperature facies. The high pressure and low-to- moderate temperature facies is known as "blueschist" Rocks formed in this facies lend to be schistose in texture and contain Simplified Table Relating Rock Type, Metamorphic Grade, and Index Minerals Table 1.12 Metamorphic Index Mineral Rock Type Grade Slate minerals that give the rocks a bluish color, thus the name. Low to intermediate Chlorite Intermediate to high Garnet High The facies relationships associated with regionalPiylite Schist Gneiss Granulite Very high metamorphism are more complex due to the fact that not only are there two variables, both temperature and pressure, but the size of the area affected is such that there is a wide variety of rock types involved. Not all facies may be present in a given region. Figure 1.56 is a schematic diagram of temperature and pressure relationships of the commoaly recognized metamorphic facies. the gradual change from shale to slate to phyllite to schist Metamorphic grade is the measure of the intensity of to gneiss (pronounced "nice") to granulite (see table 1.12). In metamorphism to which a given rock has been subjected. this simplified presentation, slate represents low-grade meta- Low-grade metamorphism occurs in the marginal area: high- morphism: phyllite, low to intermediate;, schist, intermediate grade metamorphism occurs where the effects of temperature to high; and gneiss and granulite, high-to very-high-grade and pressure have been most intense; and intermediate-grade metamorphism. As metamorphic grade increases, there are metamorphism lies in between. Table 1.12 is a simplified corresponding mineralogic and textural changes that occur schematic showing the relationship between metamorphic within the rocks. grade, rock type, and the index minerals associated with each. Index minerals are those minerals that are stable over a specific range of temperature and pressure conditions and Texture and Composition hat are useful in determining metamorphic grade (ig. 157. of Metamorphic Rocks rade. The sequence of increasing metamorphic 5 PARTI The metamorphism of shale, sedimentary ock, provides a simple way of illustrating metamorphic e, a common sedimentary Metamorphic textures consist of two main types, oliated and nonfoliated. The mineral constituents of foliated metamorphic grade shows rocks are oriented in a parallel or subparallel arrangement. rocks are

Explanation / Answer

Exercise 5

Based on the law of superposition, which states that the layer on top is younger than the layer on the bottom and the principle of cross-cutting relations which state that the rock that cross-cuts is younger than the rock it cuts across we can find out the columnar section to be

10.Alluvium

9.Unconformity

8.Basalt

7.Arkose

6.Conglomerate

5.Unconformity

4.Granite

3.Sandstone

2.Shale

1.Limestone

2) Had the metamorphic rocks been included we would have seen contact metamorphism around the batholith of the granite as well as the basaltic dikes. This would have formed aureoles of metamorphic rocks around the intrusion of varying grades. As we move away from the intrusion the temperature drops and hence we will find lower grades of metamorphic rocks away from the intrusion-host rock boundary. The high-grade metamorphic zones closer to the intrusions would develop high-temperature mineral assemblage and as we move away lower temperature minerals will be formed.

Exercise 6

Ans1) Based on the cross-cutting principle and the intrusion of the foliated metamorphic rock in the granite we can say that the country rock is the foliated metamorphic rock.

Ans 2) We can see that the trend of the country rock is defined by the alternate layers of light and dark gray bands in the foliated metamorphic rock. The granite intrusion can be seen clearly cross-cutting this trend all along the cross-section and hence the granite has a discordant relationship with the host rock.

Ans 3) The granite occurs a large batholith from which we can see many dikes coming out.

Ans 4) Since the basalt dikes cuts right across the granite, therefore from the principle of cross-cutting we can say that the basalt dikes are younger than the granite.

Ans 5) Based on the principle of cross-cutting relations which state that the rock that cross-cuts are younger than the rock it cuts across we can find out that

3. Basalt dike

2. Granite

1.Foliated metamorphic rock

Related Questions

Navigate

• Browse (All)
• Browse T
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.