Lab 2

Question 1

The Wilson Cycle

Answer 1

1. Opening - embryonic, young, mature
2. Closing - declining, terminal, relic/scare/sutur

Helps us understand the context in which tectonic boundaries form during the fragmentation and collision of continents

Question 2

Opening stages - Embryonic

The Wilson Cycle

Answer 2

• The fragmentation of a continent is thought to begin when the lithosphere is uplifted into a dome by buoyant material from an underlying mantle plume or mantle plumes
• The buoyancy of the mantle plume causes the dome to fracture in a radial pattern, with three arms spaced at approximately 120° (like the Mercedes Benz logo)

Question 3

Opening stages - Embryonic: what is the 3-point fracture called?

The Wilson Cycle

Answer 3

• A triple junction—a very young divergent boundary where the extensional tectonic regime leads to the formation of normal faults and rift valleys on a continent.
• These continental rift valleys become centers of volcanic activity and, due to their low topography, often develop lakes.
• A modern example of this stage in the Wilson tectonic cycle can be observed in the East African Rift System

Question 4

Opening stages - Young

The Wilson Cycle

Answer 4

• In the ‘young’ stages of rifting, the extension of the crust advances to the point where oceanic crust begins to form along the rift zone.
• At this stage, the base of the rift subsides so much that the ocean floods the area, creating a narrow sea with straight margins.
• This can be seen in the Red Sea and the Gulf of Aden which, together with the East African Rift System, form a triple junction
• It is common for one arm of a triple junction to stop rifting and not form ocean crust. This is called a failed rift.

Question 5

Opening stages - Mature

The Wilson Cycle

Answer 5

• Mature ocean basins are characterized by a widening ocean with little to no subduction along its margins. The Atlantic Ocean is currently in this stage.
• Thus, the area where oceanic lithosphere meets continental lithosphere is a passive margin.
• Technically, passive margins are not considered true tectonic boundaries, as they do not represent an active plate margin but rather the area where oceanic and continental lithosphere meet within the same plate

Question 6

Closing Stages - Declining

The Wilson Cycle

Answer 6

• The weight of sediments accumulating at the edge of the continent, combined with the increasing density of the oceanic crust as it ages and cools, **causes the oceanic lithosphere to break away from the continental lithosphere, initiating subduction **
• At this point, the ocean basin begins to shrink. A modern example is the Pacific Ocean, which is mostly surrounded by subduction zones (Pacific Ring of Fire)

Question 7

Closing Stages - Terminal

The Wilson Cycle

Answer 7

• At the terminal stage, the ocean has contracted to a narrow sea where very little oceanic lithosphere remains between continents.
• Typically, the spreading ridge (divergent boundary) has already been subducted.
• A modern example is the Mediterranean Sea, a remnant of the ancient Tethys Ocean, which has been closing as the African Plate moves northward towards the Eurasian Plate

Question 8

Closing Stages - Relic / Scar / Suture

The Wilson Cycle

Answer 8

• By this stage, no oceanic lithosphere remains between the two continents apart from portions “snipped off” during the collision.
• The continents have collided, forming large mountains representing the point of collision or “suture” where the two continents have been “stuck” together.
• EX: HIMALAYAS

Question 9

The Wilson Cycle