Chapter 7: Conservation of Mass and Momentum
One of the earliest block diagrams (see above) in the literature of structural
geology (Argand, 1911) illustrates a part of the Penninic Alps of Switzerland
and begs the question: how can we understand the processes that produce
such ornate structures? In the title of a 1999 paper the authors of this
textbook asked the related question: can we understand tectonic processes
and their structural products without appeal to a complete mechanics?
Our answer was, and is ‘no’. To address variations in velocity
in 3D space and time we formulate in this chapter the governing equations
of continuity and motion from the fundamental laws of mass and momentum
conservation. Here we provide the links between concepts of calculus and
physics taught in undergraduate courses and the concepts of continuum
mechanics required to practice modern structural geology.