Ocean Crust and Ophiolites

by

Joe Cann, Mike Nuttall, Alistair Scott, Andy Barnicoat and Eddie McAllister
University of Leeds

The module comprises five main sections accessible from this main menu

This courseware module is intended for second year students and presents basic concepts of processes associated with the creation of new ocean crust at mid-ocean ridges, and in back arc basins. The fundamental processes are magmatic, tectonic and hydrothermal and are illustrated by examples from the ocean floor and from ophiolite complexes. The module assumes a basic first year knowledge of plate tectonics, geological structures and igneous rocks.

The aims of the module are:

To introduce students to modern concepts of ocean crust genesis;
To show how igneous, tectonic and hydrothermal processes can interact and feedback to each other in active regions;
To give students experience of field relations on the ocean floor and in ophiolite complexes;
To allow students to experiment with simple models of igneous, tectonic and hydrothermal processes at spreading centres.

Information from the graph is needed to answer the question posed

Description of the module

The module occupies about 19Mb and consists of five sections accessed via a main menu.

1. Introduction

This section gives an introduction to the aims and prerequisites of the module and explains how to work and navigate through it.

2. Constructing the Ocean Crust

This section deals first with splitting and spreading of the lithosphere, generation of melt in the mantle and the structure of the ocean crust as deduced from seismic evidence and from ophiolites. The rock units of ophiolites as they appear in the field are illustrated using pictures of ophiolites in Cyprus and Oman, with annotation to each picture that can be switched on and off. Finally a comparison is made between ophiolites studied on land and the structure of oceanic lithosphere.

Part of the description on the creation of the lower crust

3. Magmatic Processes in Crustal Construction

This section starts at the ocean floor with a discussion of volcanology illustrated by deep-tow side-scan sonar images. It moves to the upper crust by considering the geometry of the construction of a lava-dyke pile at a spreading centre. Seismic evidence for the existence and size of a magma chamber follows, and questions about controls and how the lower crust forms from it. Finally, the upper mantle is considered, notably the processes by which melt is removed from it and how podiform chromite ore may form.

The formation of chromite orre is considered in the section on the upper mantle

4. Spreading rate and Segmentation

This section looks at the range of spreading rates, then at the effect of spreading rate on volcanism and tectonism, its effect on the magma chamber and finally at segmentation of spreading centres. Extensive use is made of colour images of sea-floor bathymetry.

A question and answer about propogating rifts from the Spreading Rate and Segmentaion section

5. Hydrothermal Processes

This section covers two related topics; black smokers and hydrothermal systems of ophiolites. For black smokers the characteristics of vent fields, chimneys and plumes are described, then black smoker chemistry and the source of heat for vent fields. For hydrothermal systems of ophiolites their relationship to black smoker fields is discussed then aspects of massive sulphide deposits, stockworks and alteration pipes, and finally hydrothermal reaction zones.

Running the software

Navigation around the module is by means of buttons along the base of the screen. Users are encouraged to complete all the interactions on one page before proceeding to the next, but are not forced to do so. A glossary provides definitions of terminology used in the module.

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