Tectonic Clash Slides
7TH GRADE EARTH SCIENCE
UNIT: PLATE TECTONICS
Tectonic Clash:
Earth's Moving Plates
Investigate how colossal lithospheric plates crash, split, and scrape past each other to shape continents and oceans.
Divergent
Spreading Apart
Convergent
Colliding Together
Transform
Sliding Past
Foundational Concepts
The Engine Beneath Our Feet
The Lithosphere
Earth's rigid outer shell is cracked into tectonic plates that drift on molten rock.
The Asthenosphere
A hot, ductile mantle zone that flows slowly, carrying the rigid plates above.
Convection Currents
Deep heat rises, cools near the crust, and sinks. This endless thermal cycle drives all plate motion!
Rate of Movement
2 to 10 cm / year
(About as fast as your fingernails grow!)
✓
Oceanic Crust: Thin, dense basalt that readily sinks into the mantle.
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Continental Crust: Thicker, buoyant granite that resists sinking.
Key Takeaway: Boundaries are where intense geologic action occurs!
Plate Motion Mechanics Slide 2 of 8
Classification Framework
Three Ways Plates Meet
Divergent
Moving Apart ⬅️ ➡️
Plates pull apart. Magma wells up to generate fresh oceanic crust.
Crust Action:
Constructive (Creates crust)
Convergent
Crashing In ➡️ ⬅️
Plates push together. One subducts or both crumple upward into mountain chains.
Crust Action:
Destructive (Recycles crust)
Transform
Sliding Past ⬆️ ⬇️
Plates slide horizontally. Extreme friction catches rock until sudden rupture occurs.
Crust Action:
Conservative (No crust lost)
Overview of Boundary Dynamics Slide 3 of 8
BOUNDARY TYPE 1 Tensional Stress (Pulling Apart)
Divergent Boundaries: Spreading Centers
Geologic Anatomy of Seafloor Spreading
OCEAN BASIN Plate A ⬅️ ➡️ Plate B MANTLE MAGMA RISES RIDGE
New Crust Created
•
Underwater Ridges
•
Shallow Quakes
Key Landforms
- › Mid-Ocean Ridges: Continuous mountain chains along ocean floors.
- › Rift Valleys: Deep splits when continents tear apart on land.
Real-World Examples
1. Mid-Atlantic Ridge
Widens the Atlantic Ocean by ~2.5 cm every year.
2. East African Rift Zone
Actively tearing Africa into two distinct landmasses.
Divergent Boundary Mechanics Slide 4 of 8
BOUNDARY TYPE 2 Compressional Stress (Pushing Together)
Convergent Boundaries: Collisions & Subduction
SCENARIO A Destructive Margin
Subduction Zones
Dense oceanic crust dives beneath buoyant continental crust and melts in the hot mantle.
Deep Trenches & Volcanic Arcs
Forms ocean trenches and chains of explosive volcanoes on the over-riding plate.
Examples:
Cascade Mountains • Andes Mountains • Mariana Trench
SCENARIO B Continental Smash
Continental Collisions
Two buoyant continental plates collide. Neither can sink, so rock crumples skyward!
Non-Volcanic Fold Mountains
Tremendous folding and powerful earthquakes occur, without volcanic eruptions.
Example:
Himalayan Mountains (India colliding into Asia, still rising!)
Convergent Boundary Mechanics Slide 5 of 8
BOUNDARY TYPE 3 Shearing Stress (Sliding Horizontally)
Transform Boundaries: Faults & Friction
Stick-Slip Mechanics
Plates lock together with massive friction. Stress builds over decades until the rock breaks with explosive energy:
⚡ Sudden Slip = Severe Earthquake!
Volcanoes?
NO 🚫
No magma pathway
Crust Fate?
CONSERVED ⚖️
None made or lost
CASE STUDY California, USA
The San Andreas Fault
The Pacific Plate grinds northwest past the North American Plate at ~5 cm per year.
Offsets stream beds, fences, and highways
Causes frequent shallow earthquakes
LA will eventually slide alongside San Francisco!
Transform Boundary Mechanics Slide 6 of 8
Synthesis & Quick Reference
Comparing the Three Boundaries
| Feature | Divergent ⬅️ ➡️ | Convergent ➡️ ⬅️ | Transform ⬆️ ⬇️ |
|---|
| Motion | Pulling apart | Colliding together | Grinding side-by-side |
| Stress Type | Tension | Compression | Shear |
| Crust Fate | Created (Constructive) | Destroyed/Recycled | Conserved (No change) |
| Key Landforms | Mid-ocean ridges, rift valleys | Trenches, volcanoes, fold mountains | Fault lines, offset features |
| Earthquakes? | Yes (shallow & mild) | Yes (deep & severe) | Yes (shallow & frequent) |
Summary Comparison Chart Slide 7 of 8
Active Review
Boundary Detective: Name That Boundary!
01
Case File Alpha
"Scientists locate an undersea mountain range where magma wells up and new basalt cools."
Boundary Type: [ ? ? ? ]
02
Case File Beta
"A continental plate crumples against another continental plate, thrusting giant peaks upward."
Boundary Type: [ ? ? ? ]
03
Case File Gamma
"Fences in a valley are cleanly severed and offset 4 meters horizontally after a shallow tremor."
Boundary Type: [ ? ? ? ]
Discussion Prompt: Which type of plate boundary poses the most danger to human cities, and why?
Slide 8 of 8
Tectonic Clash Worksheet
7th Grade Earth Science Plate Boundaries Unit
Tectonic Clash Worksheet
Name:
Date: Period:
1
The Engine of Plate Motion (Vocabulary Match)
Write the letter of the correct definition next to each tectonic term:
1. Lithosphere
2. Asthenosphere
3. Convection Current
4. Oceanic Crust
A. Circular mantle flow driving plate motion.
B. Dense, thin basalt layer that sinks easily.
C. Semi-fluid, ductile layer beneath plates.
D. Rigid outer shell of crust and upper mantle.
2
Divergent Boundaries (Pulling Apart)
Stress: Tension
Question 2A: What geologic process occurs along the center of a mid-ocean ridge as plates pull apart? Explain why divergent boundaries are considered "constructive."
Underwater Example: Mid-Atlantic Ridge (widens the ocean by ~2.5 cm/yr)
Continental Example: East African Rift Valley (crust is actively splitting)
3
Convergent Boundaries (Crashing Together)
Stress: Compression
Depending on what crust types meet, convergent boundaries produce completely different landforms:
Subduction Zone (Oceanic vs. Continental)
Dense oceanic plate dives beneath continental plate into the mantle.
List two landforms created:
Continental Collision (Cont. vs. Cont.)
Two buoyant continental plates collide; neither can sink into the mantle.
What landform is built? Give an example:
Plate Boundaries Study Sheet Page 1 of 2
Tectonic Clash: Investigation Guide Student Name: ___________________________
4
Transform Boundaries (Sliding Past)
Stress: Shear
Plates grind horizontally past one another along strike-slip faults like California's San Andreas Fault.
Question 4A: Why do transform boundaries cause severe earthquakes but almost never produce volcanic mountains?
5
Plate Boundary Master Matrix
Complete the chart comparing all three boundary types:
| Boundary | Relative Motion | Crust: Made, Lost, or Conserved? | One Real Example |
|---|
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