Discriminate competing rock histories using relationships

1. Define the geological question

A mineral inventory can be consistent with several geological histories. Quartz and feldspar may occur in an igneous source and in sediment derived from it. To order processes, examine relationships: inclusions, cross-cutting contacts, baked zones, depositional structures and later deformation. Each observation needs a location and an explicit interpretation.

2. Build the mechanism and evidence ledger

Rounded granite clasts enclosed in a sediment imply that their granite source existed before deposition. Conversely, an igneous body cutting and baking that sediment indicates later intrusion at that contact. These statements compare events; neither gives an absolute age. The virtual packet restricts attention to a single granite generation and one sediment body so the competing claims can be tested clearly.

Candidate A crystallizes granite, exposes and erodes it, then deposits sediment. Candidate B deposits sediment, then intrudes magma that crystallizes as granite. Minerals alone fit both. Granite clasts favor A; a cutting baked contact favors B under the stated body identities. Candidate consistency is not a measured probability.

If a real region contains both relationships, do not erase one to preserve a preferred story. There may be older source granite and a younger intrusion, reworked clasts or mistaken body correlation. A stronger history distinguishes units and predicts another observable relationship. The rock cycle is a network of possible transformations, not a mandatory one-way conveyor.

3. Reconstruct a worked example

With minerals only, both histories remain possible. Adding granite clasts makes only the granite-first history consistent. Replacing that evidence with a cutting baked contact supports the intrusion-later history instead.

4. Predict and investigate

Predict first: Which spatial relationship would distinguish an older granite source from a younger intrusion?

Swap each evidence packet while holding the chosen history fixed, then compare both histories for each packet. Draw the event sequence and state an additional observation that would distinguish two granite generations from one.

5. Test a changed case

Apply the mechanism to a changed case

A region contains granite clasts in sediment and a granite body cutting that sediment. What revision avoids forcing a single contradictory generation?

Retain the calculation, evidence and assumptions before opening public feedback.

Compare a worked response

Test an older source granite followed by erosion/deposition and a younger intrusion, with mapping or age evidence to distinguish the bodies. The observations alone do not establish that explanation uniquely, but it is a coherent alternative to discarding a contact.

6. Retain evidence and its limits

Keep the first prediction, complete ledger, changed case and rejected alternative in the lesson notebook. Supplied observations and bounded CPU models are not actual specimen handling, fieldwork or independently assessed competence. Record source purpose and uncertainty rather than treating public feedback as independent reasoning.

Mechanism and classification reference, checked 30 October 2026. Original teaching prose, numerical packets and questions; no source illustration or exercise is copied.

Cross-cutting, inclusions and baked-contact interpretation supplies the relative-event mechanism used here; this introductory case does not replace the later stratigraphic reconstruction module.