5.2 Precambrian and Lower Palaeozoic Basement

The Precambrian and Lower Palaeozoic Basement of the British Isles is a series of nine discrete, exotic terranes whose boundaries are fault systems that have undergone large but usually unknown amounts of lateral and vertical movement over time (Figure 11 and Author(s): The Open University

5.1 Introduction

Figure 9
Figure 9 Lithotectonic units of the British Isles

In previous sections, it was revealed that in the British Isles, the Phanerozoic er
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4.5 How wide were the oceans?

Once evidence has been found to prove the existence of an ancient ocean, is it possible to calculate its maximum width? Palaeomagnetic studies can give geologists an idea of the palaeolatitude (N–S) of the ocean but not its palaeolongtitude (E–W), so depending on its orientation, an indication of how wide it was may not be possible. However, an approximate indication of how wide the former oceans were can be obtained by examining the fossil faunal assemblages that are present (e.g.
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4.3.2 Stage 2: Embryonic ocean basin formation (southern Red Sea stage)

If extension and rifting progresses sufficiently, this will lead to the development of an embryonic ocean along the site of the earlier rift zone (see Figure 6b). Prior to true oceanic lithosphere being produced, basaltic magma will be repeatedly intruded into the continental lithosphere along fractures and shear
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4.3.1 Stage 1: Continental rifting (northern Red Sea stage)

There are two mechanisms for breaking up a continental plate, the simplest of which is to pull it apart under lithospheric extension, forcing the mantle to rise up to occupy the ‘space’ that otherwise would be left by the thinned overlying plate (Figure 6a). Continued extension of this already thinned plate wi
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4.3 Continental extension

Understanding how and why continental plates break apart is extremely important, as this step precedes the formation and development of all new ocean basins. A generalised model for the extension, rifting and separation of continental plates has been developed by examining currently active rifting environments, such as the East African and Red Sea rifts, and comparing these with mature basins, such as the Atlantic Ocean. The East African and Red Sea rifts are regarded as representing continen
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4.2 Revealing past plate tectonic events

In Section 3 we referred to the Caledonian and Variscan Orogenic Belts. These are interpreted as representing past destructive plate margins or more strictly speaking, representing the final phases of ocean closure that resulted in continental collision. Section 4 explores the extent to which it is possible to detect different
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4.1 Introduction

In the theory of plate tectonics there are three main types of plate boundary, namely: constructive, destructive and conservative plate boundaries.

Figure 5
Figure
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3 A global view of Earth history

Figure 3, below, shows how the Earth's continents have drifted across the globe over the past 550 million years. This is a reconstruction of continental configurations of the Earth's landmasses during the Phanerozoic Eon. Note how northern and southern parts of the British Isles (red) were dispersed over two continents/tectonic plates until the end of the Devonian (a–d), and that all the landmasses formed one supercontinent during the Permo-Triassic (f).


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Learning outcomes

By the end of this unit you should be able to:

  • summarise and identify descriptions of the principal features of the main lithotectonic units of the British Isles, namely the Precambrian Basement, the Caledonian Orogenic Belt, the Variscan Orogenic Belt, the Older Cover and the Younger Cover;

  • identify any of the main terranes making up the British Isles on the basis of a description of its age, main rock types, dominant structures, and plate tectonic setting.


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3.14 Questions on the Moon

Now try to answer the following questions, to remind you of some of the things you have learned and test your understanding of them.

Question 1

3.9 Moon41: Apollo 15 station 2

The panorama was collected by James B. Irwin at Station 2. David Scott is to the left of the rover. He is examining a boulder. The large hill to the left of the rover is the summit of Mt. Hadley Delta. (QuickTime, 400KB, note: this may take some time to download depending on your connection speed)

3.8 Moon40: Apollo 14 station H

The panorama was collected by Edgar Dean at station H. Alan Shepard is to the left of the lander aiming the TV camera at the MESA. (QuickTime, 500KB, note: this may take some time to download depending on your connection speed)

3.7 Moon39: Apollo 14 station C

The panorama was collected by Alan Shepard at station C-Prime. (QuickTime, 500KB, note: this may take some time to download depending on your connection speed)

3.5 Moon37: Apollo 12 station 3

The panorama was collected by Charles "Pete" Conrad. (QuickTime, 500KB, note: this may take some time to download depending on your connection speed)

3.4 Moon36: Apollo 12 station 2

Pete Conrad took this pan early in EVA-1 from a position due west of the Lunar Module. Al Bean can be seen in several frames taking documentation photos of the Solar Wind Collector (SWC) that he has just deployed. (QuickTime, 500KB, note: this may take some time to download depending on your connection speed)

2.6 The surface

David A. Rothery Teach Yourself Planets, Chapter 6, pp. 66–75, Hodder Education, 2000, 2003.

Copyright © David Rothery

Look at the Moon even with the unaided eye, and you will see that it has dark patches on a paler background (Figure 2). This simple observation picks out the two distinct types of crust on the Moon. The paler areas are the lunar highlands, and the darker areas are the lunar ‘seas’ or maria (singular: mare). Both the highla
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6.4.1 Writing a chemical equation to describe a chemical process

Natural gas, which is largely methane, is burned to provide heat for cooking and domestic heating and as an industrial power source. This process of burning involves the reaction of methane with oxygen in air to produce carbon dioxide and water.

A chemical equation can be constructed for the reaction of methane with oxygen to give carbon dioxide and water as the products.

  1. The first step is to write the formulas of the reactants on the left and t
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6.1 Introduction

The previous sections in this unit include many terms which may have been unfamiliar to you: for example, atom, element, compound, molecule and bond. Chemistry has a language all of its own and grasping the terminology can be as much of a problem as understanding the chemistry itself. In Section 6, you will consider the language of chemistry before returning to the examination of bonding.


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3 What are compounds?

Activity 1: Elements and compounds

0 hours 10 minutes

Click on the video clip to watch Elements and Compounds, which focuses on water and its constituent elements.

Click below to v
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