Plate Tectonics
Instructional Objectives
Instructional Materials
Open Source textbook, Physical Geology, 2nd Edition — https://opentextbc.ca/physicalgeology2ed/
READ Chapter 1, pages 17 – 20.
Supplemental Text –> Chapter(s) on “Plate Tectonics — the Unifying Theory” in a “Earth Revealed” text
Read the instructor notes on Plate Tectonics
Continental Drift Links to an external site. — {Old Theory}
Continents Move Freely over the Earths Surface due to “Isostacy”
Mountain Ranges Formed when Continents “Bumped” Into Each Other or “Plowed” through a Stationary Oceanic Crust
Continents will “Fit Together” like a Jig-Saw Puzzle
Pangaea — the Super-Continent when all the Continents were one
Laurasia — landmass of North America, Greenland & Eurasia {when Pangaea started to break-up}
Gondwana {also Gondwanaland} — Africa, South America, Australia, Antarctica and India {when Pangaea started to breakup}
Sea-Floor Spreading Links to an external site. — {Old Theory}
Only sea floor forms at the mid-oceanic ridges and moves apart like a Conveyor Belt.
Sea Floor Crust was Re-Introduced Into the Mantle by Plunging beneath a Continent or Island Arc Belt
Differs from “Continental Drift” in which Continents “Plowed” through a Stationary Oceanic Crust
Combines in part the theories of continental drift and sea-floor spreading
Theory of the earth’s surface divided into large “plates of crustal material” that move slowly & change in size
Plate is defined as a Large, Mobile Slab of Rock that is Part of the Earth’s Surface.
A Plate may be made of only Sea Floor Crust or a COMBINATION of Sea Floor & Continental Crust.
Intense Geologic Activity takes place at the Plate Boundaries
a. 8 Major Plates and Numerous smaller ones
b. Plates move due to Convection Currents in the Mantle and Subduction of the Crust
c. Hot areas of convection {Mantle Plumes} form below the plates
HOT SPOTS {Mantle Plumes Links to an external site.} — Occur Beneath BOTH Oceanic & Continental Crusts
Animation Links to an external site.
a. Small Plumes Links to an external site. — Create(d) Oceanic Islands {Hawaiian Islands} and heat continents locally {Yellowstone National Park, Wyoming}
b. Large Plumes Links to an external site. — Move large crustal masses {Divergence of the African Rift Valley – Gulf of Aden – Red Sea}
c. Large Plumes can become a Divergent Plate Boundary
Animation Links to an external site.
Plate Tectonics
Animation Links to an external site.
Three Types of Plate Boundaries Links to an external site.
A. Diverging Plate Boundary Links to an external site. — Plates moving APART
i.e..– {Iceland & the Mid Oceanic Ridge, African Rift Valley, etc.}
1. Mid-Oceanic Ridge Links to an external site. {includes ICELAND} Animation Links to an external site.
2. CONTINENTAL Rift Valley Links to an external site. {i.e..– Africa, Red Sea, Dead Sea Valley}
a. Continental Crest is Stretched & Thinned then a Grabben Valley forms. If it continues an OCEAN will form {i.e..– Atlantic Ocean}
b. Hot molten Mantle Material may be ejected {i.e..– Iceland}
c. Transform Faults Links to an external site. form along Fracture Zones
1. Transform Faults & Fractures —
a. Occur at mid-oceanic ridges
b. Not a true transform plate boundary
c. Specialized type of fault associated with plate tectonics
B. Transform Plate Boundary Links to an external site. — Plates moving {Horizontally} by Each Other
1. San Andreas Fault in California {Strike-Slip Fault}
C. Converging Plate Boundary Links to an external site. — Plates moving TOGETHER
1. SUBDUCTION Links to an external site. —
a. Oceanic crust dives UNDER oceanic crust {i.e. Japanese Islands & Aleutian Island Arcs}
b. Oceanic crust dives UNDER continental crust {i.e. Andes Mountains}
2. COLLISION — Continental crust CRASHES INTO continental crust {Himalayas}
Virtual Field Trip – ISRAEL, Dead Sea Rift Valley (Plate Tectonics)
The northern Dead Sea Rift Valley “terminus” is north of the Sea of Galilee in the Mount Hermon area of Lebanon, Syria and Israel. From this point it runs south, through the Jordan Valley (from the Sea of Galilee to the southern-most area of the Dead Sea) where it joins the Aqaba Rift valley.
The Dead Sea Rift Valley is the northernmost extension of the Great Rift Valley of Asia and Africa. Even near its termination, or as the boundary between Israel and Jordan, the steep sides of the Rift Valley are clearly seen. The tectonic nature of this “Rift – Plate Margin” feature are evidenced in numerous faults, earthquakes, as well as igneous activity. (NOTE the dike cutting through limestone strata in the photograph)
dike cutting through limestone strata
This area of Israel and Jordan was once a marine system in which layers of carbonates (limestones) and clastics (shales) were deposited in thick continous layers during the Cretaceous. Rifting and Transtensional forces have vertically “ripped” these sedimentary layers apart forming steep valley walls. One can stand on either side of the Jordan River Valley, on either the Jordan or Israel borders, and see a mirror image of this dissected strata.At the terminus of the rift in the Lebanon, Syria, Israel area, the lithilogy is dominated by volcanic extrusives
In this Virtual Field Trip we will look at the edges of the steep rift valley in the areas of Masada and Qumran areas of the Dead Sea, as well as the Sea of Galilee. In many of the pictures you will notice that the preferred building stone is a white, Cretaceous, fossiliferous limestone, common throughout Israel.
Discussion: Plate Tectonics
1: In the Discussion/Bulletin Board section post your thoughts, in an Original Post, concerning this unit, after you have, at a minimum, watched any appropriate video sections.
2: In the Discussion/Bulletin Board section respond to at least two of your classmates posts.
3: If a Virtual Field Trip is available one of your discussions should concern the Virtual Field Trip.
RESPOND TO THESE TWO STUDENT POSTS
1.Alex Balke
Nov 19 1:40pm
Reply from Alex Balke
I think it’s amazing how differently the continents used to look. At one point, they were all a massive supercontinent called Pangea, but gradually split apart from one another to form the land we know today. There have been many theories as to why and how this occurred, with one of the first to be widely accepted being the theory of continental drift. It states that continents moved across the Earth’s surface due to “isostacy”. It essentially means that the Earth’s crust floats on its mantle, which is much denser. Because of this, parts of the surface can rise or fall depending on thickness and density. Additionally, it states that mountain ranges formed when continents rammed into each other, and the stationary oceanic crust was pushed downward while the continental crust was pushed upward. Another theory was the idea of sea floor spreading. It states that the sea floor only forms at mid-oceanic ridges, and then slowly moves apart like a conveyor belt. It becomes a part of the mantle by plunging beneath a continent.
The theory most of the world accepts today, however, is the theory of plate tectonics. It takes some aspects of continental drift and sea floor spreading, but elaborates on them and add newly discovered information. The Earth, it states, is divided into several continental plates (7 major ones recognized, with other minor ones also present), which move extremely slowly and can change in size. All plates are made of sea floor crust, though some contain continental crust. Plate boundaries can create intense geologic activity, such as earthquakes and volcanoes. Mantle plumes, which form below plates with both oceanic and continental crust, are considered hotspots for these activities. Plates have three different boundary types: Diverging, where the plates move apart, Transform, where they move horizontally by each other, and Converging, where they move together. The fact that each of them are responsible for creating different geological occurrences is fascinating.
2.Michelle Gonzalez Rojas
Nov 19 10:36am
| Last edited Nov 19 10:40am
Reply from Michelle Gonzalez Rojas
The Dead Sea Rift Valley presents a fascinating example of plate tectonics at work, illustrating the dynamic processes that shape our planet. This region, located at the northernmost extension of the Great Rift Valley, highlights the interaction between tectonic plates and the resulting geological features.
The steep sides of the Rift Valley, visible between Israel and Jordan, demonstrate the effects of rifting and transtensional forces, which have pulled apart sedimentary layers to form striking valley walls. The area’s history as a marine system during the Cretaceous is evident in its fossiliferous limestone deposits, still used as building materials today. It’s incredible to consider how these natural processes not only formed the landscape but also provided resources for human use.
One aspect I found particularly interesting is the contrast in lithology between the regions near the Dead Sea and the Sea of Galilee. While the Dead Sea area is dominated by sedimentary rocks like limestones and shales, the Sea of Galilee features volcanic extrusives such as basalt. This variation reflects the geological complexity of the Rift Valley, where tectonic activity has shaped the landscape differently over time.
The Dead Sea Rift Valley also provides a glimpse into the broader Great Rift Valley system, extending from Southwest Asia to East Africa. This interconnected system highlights how plate boundaries influence both local and global geology. The seismic activity and volcanism in this region remind us of the Earth’s continuous evolution, driven by plate motions.
Beyond its geological marvels, the Dead Sea Rift Valley is also home to profound historical and cultural treasures, particularly in the Qumran area. I especially enjoyed reading about this during the virtual field trip. As a Christian woman, I found the information deeply relevant and captivating. The incredible historical significance of the Qumran area stood out to me.
It is fascinating to learn how the Dead Sea Scrolls were accidentally discovered by shepherds and how they provide insights into the religious practices and texts of ancient times. The mention of the “Temple Scroll,” anointing oil, and incense linked to the Temple in Jerusalem adds a beautiful connection to biblical history. I also appreciate how the Shrine of the Book was created to preserve these treasures—it reflects the importance of safeguarding such meaningful artifacts for generations to come.