Is there a publication or citation based indicator of the pace of change in a field?
Although far from perfect,
Citation half life is one citation-based indicator often used to quantify how quickly a field or journal is moving. It basically looks at how long a paper takes to get half of all its citations. So for example, a fast moving field might have a citation half-life of 4 years, whereas a slower moving field might have a citation half-life of over 10 years. 

In the Journal Citation Reports you can see these values for each journal.

Of course, there is the question of what exactly this means. For example, I believe fields like statistics and mathematics have much longer citation half lives, perhaps because seminal articles remain important.  

Understanding citation half-life is also important when you want to compare impact factors for journals across fields, or compare citation counts and h-indexes across scholars.