Earth Systems 3209

1. Earth Systems 3209 Reference: Chapters 2, 3, 6, 7; Appendix A & B Unit: 3Earth’s Materials

2. Unit 3: Topic 5.4 Metamorphic Environment - Contact Focus on . . . • describing the environments (location) associated with contact metamorphism. • illustrating how contact metamorphism can be used to help identify an intrusion from a buried lava flow.

3. Metamorphism • Metamorphism literally means to “change form.” These changes take thousands to millions of years to complete. During this period of change minerals within the rocks flow in solid state and can change on the atomic scale. • Metamorphism most often occurs during one of two geologic events: • mountain building(regional metamorphism) • intrusion of molten rock(contact metamorphism) Text Reference: Pages 198-201

4. Contact Metamorphism • This type of metamorphismoccurs when rock is in contact with magma/lava (Heat). • The changes are caused primarily by the high temperatures of the molten rock, which in effect “bake” the surrounding rock. • Examples include Marble and Hornfels. Contact Metamorphism is indicated by the “xxxx” in the diagram.

5. Contact Metamorphism • WHERE DOES CONTACT METAMORPHISM OCCUR? 1) beneath lava flows 2) adjacent to magma intrusions 3) bordering dykes and sills Dyke = Vertical Sill = Horizontal

6. Contact Metamorphism B is a magma intrusion and R is a buried lava flow. • Contact metamorphism can distinguish between a buried lava flow and an igneous intrusion …. • Buried Lava Flow Contact Metamorphism is located below the Lava Flow (Only). • Magma Intrusion Contact Metamorphism is located above and Below the Magma Intrusion.

7. Contact Metamorphism – “Chilled Margins” • When lava “pours” over rock or magma “intrudes” rockit starts to cool and crystallize. • The contact metamorphism occurs where the hot lava or magma “touches” the old, previously existing rock.

8. Contact Metamorphism – “Chilled Margins” • Look at the magma intruding through a rock unit! This magma starts to cool slowly so crystals grow to be large. • HOWEVER, the magma cools faster on the outsides since the cold, previously existing rock unit causes it to cool faster. • THEREFORE, you get larger crystals toward the center and smaller crystals on the outside edges.This gives a chilled effect!

9. Once molten rock Example 1: Which is the main factor causing contact metamorphism? (A) chemical fluids (B) heat (C) original rock (D) pressure What feature is represented by “xxxx” in the diagram below? (A) contact metamorphism(B)faulting(C) regional metamorphism(D)unconformity

10. Example 2: What will the rocks surrounding the magma chamber in zone Y be exposed to? contact metamorphism lithification regional metamorphism (D) sedimentation

11. Your Turn . . . Take the time and complete the following questions . . .(Solutions to follow) Question: How can contact metamorphism distinguish an igneous intrusion from a buried lava flow?

12. Solutions . . . Question: How can contact metamorphism distinguish an igneous intrusion from a buried lava flow? Answer: Contact metamorphism would reveal if an igneous rock unit was an intrusion or a lava flow by looking at where the contact metamorphism is located. An intrusion would have contact metamorphism above and below the igneous rock unit, whereas, a lava flow would only show metamorphism below the igneous rock unit.

13. Summary . . . Overview of Points covered: • Contact Metamorphism: • Forms in areas of high heat. • Associated with; • Lava flows • Intrusions • Dykes and sills • Used to identify intrusion from a buried lava flow