The island you live on, Hispaniola, sits right on the boundary between the Caribbean plate and the North American plate. That is why the Septentrional fault and the Puerto Rico trench are part of the Dominican geological landscape. Why is the planet's geological activity concentrated at the edges of a few giant blocks, and what moves them?
From continental drift to plate tectonics
If you mark on a world map the epicenters of earthquakes and the active volcanoes of the last decade, you won't see random dots: you will see continuous lines surrounding huge, almost quiet zones. Those lines are the boundaries of the plates.
A plate may contain only oceanic crust (like the Pacific plate, almost entirely oceanic), only continental crust, or both at once (like the South American, North American, African, or Eurasian plates, the latter including Europe). The Caribbean plate is a small plate, mostly oceanic, on which a large part of the Antilles rests.
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Explain what a lithospheric plate is and name three plates: one containing Europe, an American one, and one that is almost entirely oceanic.
Explain what a lithospheric plate is and name three plates: one containing Europe, an American one, and one that is almost entirely oceanic.
State whether the following statement is true or false and justify your answer: "Continents move because the lithospheric plates on which they rest move."
State whether the following statement is true or false and justify your answer: "Continents move because the lithospheric plates on which they rest move."
High-precision GPS measurements show that the Caribbean plate moves about 2 cm each year relative to the North American plate, sliding sideways toward the east, at roughly the speed at which fingernails grow. What internal mechanism pushes masses of rock covering millions of square kilometers?
The ultimate engine is the Earth's internal heat: the hot mantle rises, cools near the surface, and sinks again, like water boiling in a pot.
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State and briefly describe two forces that contribute to the movement of lithospheric plates.
State and briefly describe two forces that contribute to the movement of lithospheric plates.
A mid-ocean ridge separates two plates at a rate of $2.5\ \text{cm/year}$ on each flank. Calculate how many kilometers the ocean will have widened after $10$ million…
A mid-ocean ridge separates two plates at a rate of $2.5\ \text{cm/year}$ on each flank. Calculate how many kilometers the ocean will have widened after $10$ million years. Remember that total widening takes both flanks into account.
In Iceland the ground opens into cracks through which lava pours out; in the Andes huge volcanoes rise next to deep ocean trenches; in California two blocks rub sideways past each other with no volcanoes. And in Hispaniola, the Septentrional fault is a boundary where the Caribbean plate and the North American plate slide sideways past each other. Why does contact between plates produce such different landscapes and hazards?
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The diagram shows the three types of margins that can exist between two lithospheric plates. State which type of plate margin (divergent, convergent or transform)…
The diagram shows the three types of margins that can exist between two lithospheric plates. State which type of plate margin (divergent, convergent or transform) corresponds to each number and explain what happens to the plates in each case.
In subduction zones, one plate slides beneath another. Describe two geological phenomena associated with these zones and give a real example of a subduction zone.
In subduction zones, one plate slides beneath another. Describe two geological phenomena associated with these zones and give a real example of a subduction zone.
The San Andreas Fault in California is a transform margin. Explain the relative movement of the plates at this type of margin, what hazard it creates, and why volcanoes…
The San Andreas Fault in California is a transform margin. Explain the relative movement of the plates at this type of margin, what hazard it creates, and why volcanoes do not form there.
At the highest elevations of Mount Everest (above $8\ 000\ \text{m}$ in altitude), there are limestone strata containing abundant Mesozoic marine fossils. At the same…
At the highest elevations of Mount Everest (above $8\ 000\ \text{m}$ in altitude), there are limestone strata containing abundant Mesozoic marine fossils. At the same time, despite the violence of earthquakes in the Himalayas, no active surface volcanism is recorded, unlike what happens in the Andes mountain range.
a) Justify in terms of density and buoyancy why the subduction of continental lithosphere does not occur in the collision between the Indian and Eurasian plates, explaining what crustal deformation phenomenon replaces subduction.
b) Explain the sequence of tectonic events that allows ancient marine sediments from the Tethys Ocean to be found today at the highest peak on the planet.
c) Argue why there are dozens of active volcanoes in the Andes and none in the Himalayas, relating the presence or absence of arc magmatism to the thermal and melting fate of the colliding plate.
An oceanographic vessel records the magnetic anomalies of the seafloor along a transect perpendicular to an ocean ridge. The data reveal that the last global magnetic…
An oceanographic vessel records the magnetic anomalies of the seafloor along a transect perpendicular to an ocean ridge. The data reveal that the last global magnetic reversal (which occurred $780\ 000$ years ago) is found in basaltic stripes located $15.6\ \text{km}$ to the east and $15.6\ \text{km}$ to the west of the central rift.
a) Justify how the symmetry of the magnetic stripes originates from the cooling of magma and explain why this pattern constituted definitive proof of seafloor spreading.
b) Calculate the total spreading rate of this seafloor (in $\text{cm/year}$).
c) If at a different ridge the same anomaly from $780\ 000$ years ago is located $62.4\ \text{km}$ from the rift, interpret what differences exist between both margins regarding the rate of crust generation and tectonic dynamism.
Back to the beginning: the geological activity of Hispaniola is concentrated at plate boundaries because the Caribbean plate and the North American plate slide sideways past each other (transform), and there is also subduction off Puerto Rico.
Summary
Let's practice! 3 medium exercises in this section