Chapter 2 includes a summary of some of the aspects of Physical Geology that are important to Environmental Geology. The topics covered include:
|It is important to understand the types of mineral bonding, including ionic and covalent bonds, the internal structures (lattices) of minerals, mineral compositions and mineral groups, and especially the compositions and structures of silicate minerals.
|The relationships between the three types of rocks: igneous, sedimentary and metamorphic, can be understood through the rock cycle. Igneous rocks are formed from magma, either at depth in the crust or at surface during a volcanic eruption. Igneous rocks can be felsic if they are dominated by light-coloured minerals like feldspar and quartz, mafic if they are dominated by dark minerals like pyroxene or olivine, or intermediate if they are somewhere in between. Sedimentary rocks are called “clastic” if they are composed of weathered fragments of other rocks or “chemical” if they are made up of minerals that have precipitated from ions that were in solution. Metamorphic rocks form from either igneous or sedimentary rocks that have been heated enough so that one or more of their minerals becomes unstable and is converted into a different form.
|2.3 Earth’s Interior
|The Earth’s interior is made up of the crust—the upper 5 to 40 km of rigid rock, which is mostly granite on the continents and mostly gabbro and basalt under the oceans. The mantle is made up of ultramafic rock and can be divided into an upper rigid layer (lithospheric mantle), a semi-molten layer (asthenosphere) and all of the rest, which is plastic but solid. The core, which is dominated by iron, has a liquid outer part and a solid inner part. Convection in the liquid part of the core generates the Earth’s magnetic field.
|2.4 Plate Tectonics
|The Earth’s lithosphere is divided into many large and small tectonic plates and the plates are moving in different directions. At plate boundaries places are either converging, diverging, or sliding past one-another. These boundaries are the most common sites of earthquakes and volcanoes.
|2.5 Geosphere Earth Systems
|Although most Earth system processes involve geosphere components in some way, there are some important such processes that take place entirely within the geosphere, invisible to us. One of these is the interchange between water and the hot rock adjacent to a divergent boundary (a spreading ridge), and another is within subduction zones where water that is released from subducting ocean crust interacts with other rock, and promotes melting of hot mantle rock.
Answers for the review questions can be found in Appendix 1
- Name the mineral group for the following minerals: calcite (CaCO3), hematite (Fe2O3), galena (PbS), olivine (FeSiO4)
- What is the configuration of the silica tetrahedra in micas, in olivine and in quartz?
- What processes must take place to transform rocks into sediment?
- What are the processes that lead to the formation of a metamorphic rock?
- What must happen within a magma chamber for fractional crystallization to take place?
- Explain what accounts for the difference in crystal size in fine-grained versus coarse-grained igneous rocks.
- What are the minimum and maximum diameters of sand grains?
- What is the difference in the formation of a clastic sedimentary rock versus a chemical one?
- What conditions lead to the formation of a foliated metamorphic rock?
- What are the typical thickness of the continental crust and the oceanic crust? What is the difference in their overall composition?
- Why is the asthenosphere weaker than the rest of the mantle?
- What are the general directions (N, SW, etc.) and approximate rates of motion (cm/y) of the Pacific Plate and the Africa Plate?
- What is the cause of the melting that leads to volcanism at a subduction boundary? What about at a divergent boundary?
- How does water get incorporated into oceanic crustal rock near to a divergent boundary?