Key to Interpreting a Structural Block Diagram
     There are two links here, the first to the homework block diagram problem (from the Lecture Notebook), and the second the key (solution) to the problem.
   The Block Diagram
   The Key to the Block Diagram - a .pdf file requiring an Adobe Acrobat reader, available on most computers.


A Talk Through the Interpretation
    Solving these problems often gives people fits. People new to it just don't get it sometimes and it is frustrating and irritating.
   What is most important is that you must be logical in your approach. An intuitive, holistic, grasp of the deep essence of what it means to be a rock just does not work. This is nitty-gritty understanding built piece by piece into an interpretation.

   To begin, always, go to the bottom of the diagram and number the rock unit there #1. Oldest things are always on the bottom (via superposition.) After all, everyone has to start at the bottom and work their way up. For example, E is on the bottom of the block, and is therefore the oldest. Note G is not on the bottom because it cross cuts E.
   From there go to the next rock up, and the next, etc. numbering each rock in order of occurrence by superposition. The next three units are H, I, and J (block), followed by B and A (block).

   Look for all deformational events, folding, faulting, and label them for type (anticline, syncline, etc.) and stress (compression, tension, shear.) H, I, and J are folded into an anticline and syncline (block). But note F and G, and B and A, and the thrust fault, are not folded (block).

   Look for all cross cutting relationships, faults, dikes, etc. Number them in order of occurrence (remember the thing cut the most is the oldest.) For example, E is cut by C (block), C is cut by G (block), G is cut by D (block), D is cut by F (block), F is cut by B (block).
   There are other cross cutting relationships: D is cut by the lower fault, but not F (block). And H, I and J are cut by C (block).
   There is also a fault in the back corner that cuts D (block); the little "u" and "d" indicate "up" and "down."
   All these must be put in order (see key); number them to keep track.

   Now, you must also be able to interpret each kind of rock. Look at each rock type and label it for igneous, sedimentary, metamorphic, and any more specific interpretations you can make. This is a key to the nonconformity. Observe that E is a schist, a deep forming metamorphic rock, and H is a sandstone, a surface forming rock (block). To get the sandstone on top of the schist there had to be a lot of erosion - a noncomformity.
   Also, H, I, and J have been folded, but not B and A (block). There is an angular unconformity between them.

   This analysis has now given you a good look at the individual rock and structural relationships, and with everything labeled for sequence you can begin to look at how all the pieces fit together. So, start at the bottom again and fit all you superposition relationships, unconformities, deformation events, and cross cutting relationships together into one sequence.
   OBSERVE: Every individual rock unit, and each episode of faulting, and each igneous intrusion is, of course, an event and is numbered separately. But the following are also events and these must also be included in the numbered sequence (see key): Periods of Deformation (horizontality violated), Unconformities (period of uplift and erosion), episodes of metamorphism (burial and baking), and any other events which are distinct from the events above and below in the sequence.