Upper cross section:
Latest: Erosion at H
Faulting at F and Y
Deposition of W
Eruption of L
Deposition of E
Erosion at R
Intrusion of D - or any time hereafter!
Deposition of M
Deposition of C
Deposition of O
Erosion at Q
Faulting along Z (note that the fault is straight, not folded)
Folding
Deposition of X
Deposition of T
Deposition of J
Deposition of A
Earliest: Deposition of K
Points to note:
This is a region that first underwent compression (note the folding and thrust-faulting at Z) and later underwent extension (note the normal faults at F and Y).
Middle cross section:
Latest: Intrusion and extrusion of B
Erosion at T
Intrusion of R
Intrusion of U
Deposition of Z
Deposition of M
Erosion at L
Faulting at J
Deposition of P
Deposition of H
Deposition of Q
Erosion at S
Intrusion of A
Intrusion of D
Earliest: Intrusion of N
Points worth noting:
We can determine the age relation of A to B, even though they don't cross-cut each other.
Some thick mass of rock older than N had to exist, and N was intruded into it, and then all that overlying rock was eroded.
Bottom cross section:
Latest: Deposition of T
Erosion at I
Faulting at J Faulting at M follows after U; its relation to J is uncertain.
Deposition of U
Depositon of A
Erosion at P
Faullting at D
Intrusion of S
Faulting at Q and R
Deposition of G
Deposition of B
Deposition of Z
Deposition of X
Deposition of C
Earliest: Deposition of H
Note that this cross section records two phases or tectonic history. The first, in which normal faults Q, R, and D formed, was a period of extension. The second, in which reverse faults J and M formed, was a period of compression.
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