Divergent Boundaries Flashcards
What characterizes divergent boundaries?
Divergent boundaries are where tectonic plates move apart, leading to the formation of new oceanic lithosphere, mid-ocean ridges, and rift zones.
How do passive and active continental margins differ?
Passive margins have a broad, gently sloping shelf, low seismicity, and little volcanism; active margins are tectonically active with subduction zones, trenches, and significant earthquakes.
What are the main features of a passive continental margin?
They include a continental shelf, a steep continental slope, and a gradual continental rise formed by sediment deposition
What distinguishes active continental margins?
Active margins feature deep-ocean trenches, accretionary wedges, and negative gravity anomalies due to subduction processes.
What are some key characteristics of the ocean floor?
It is relatively young, composed mainly of basalt, and features include seamounts, guyots, coral atolls, and aseismic ridges.
What is seafloor spreading?
Seafloor spreading occurs at mid-ocean ridges where plates diverge, magma rises to form new oceanic crust, and the lithosphere moves away like a conveyor belt.
What features are associated with mid-ocean ridges?
They are characterized by high heat flow, a central rift valley (in slower-spreading ridges), seismicity, transform faults, and hydrothermal activity (“black smokers”).
What are the four distinct layers of oceanic crust?
The layers include: (1) unconsolidated sediments, (2) pillow lavas, (3) sheeted dike complexes, and (4) underlying gabbroic rocks (ophiolite complexes).
What role does hydrothermal circulation play at mid-ocean ridges?
Seawater percolates through fractured crust, gets heated, dissolves metals, and precipitates them as mineral-rich “black smoker” deposits on the seafloor.
How are submarine canyons formed?
They are carved by turbidity currents—dense mixtures of water and sediment—that flow down steep slopes, often after subaerial erosion during low sea levels.
What is continental rifting?
Continental rifting occurs when a continent splits apart, eventually forming a new ocean basin as rift valleys evolve into spreading centers.
What mechanisms can initiate continental rifting?
Rifting may be driven by mantle plumes/hotspots that cause doming and stretching, or by tectonic forces like slab pull and slab suction.
Why does oceanic lithosphere subduct?
Older, colder oceanic lithosphere becomes denser as it cools, making it heavier than the underlying mantle and causing it to subduct at convergent boundaries.
What evidence supports the demise of oceanic plates?
Magnetic stripe data and plate reconstructions show that entire ocean basins, like the Farallon Plate, have been subducted over time, leaving smaller remnant plates.
How does the supercontinent cycle relate to divergent boundaries?
The breakup and dispersal of supercontinents create new divergent boundaries; future plate motions may lead to collisions, closures of ocean basins, and further reassembly of continents.
