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Use the space to describe each. Seafloor Spreading
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Seafloor spreading is the process by which new oceanic crust is created at mid-ocean ridges and slowly moves away from the ridge crest, causing ocean basins to widen. It is a key mechanism of plate tectonics.
Key points
- Mechanism: Mantle upwelling and partial melting at divergent plate boundaries produce magma that rises, cools, and solidifies into basaltic oceanic crust at a mid-ocean ridge. As new crust forms, older crust is pushed laterally away from the ridge.
- Driving forces: Mantle convection, ridge-push from elevated ridge topography, and slab-pull at subduction zones all contribute to plate motion and spreading.
- Observable features at spreading centers: mid-ocean ridges (often with central rift valleys), pillow lavas, high heat flow, hydrothermal vents, and frequent shallow earthquakes.
- Evidence supporting seafloor spreading:
- Symmetrical magnetic stripes on either side of ridges recording reversals of Earth’s magnetic field (Vine–Matthews–Morley hypothesis).
- Age pattern of oceanic crust: youngest at the ridge, progressively older away from it; the oldest oceanic crust is about ~200 million years old.
- Heat flow is higher at ridges and decreases away from them.
- Drilling samples confirm rock types and ages predicted by spreading.
- Rates and effects: Spreading rates vary from a few millimeters to over 10 cm per year (e.g., Mid-Atlantic Ridge ~2–5 cm/yr; East Pacific Rise faster). Seafloor spreading creates new ocean floor and, balanced by subduction, drives continental drift, mountain building, volcanism, and the recycling of crust into the mantle.
Historical note: The concept was central to confirming plate tectonic theory in the 1960s (work by Harry Hess, and Vine and Matthews).
Key points
- Mechanism: Mantle upwelling and partial melting at divergent plate boundaries produce magma that rises, cools, and solidifies into basaltic oceanic crust at a mid-ocean ridge. As new crust forms, older crust is pushed laterally away from the ridge.
- Driving forces: Mantle convection, ridge-push from elevated ridge topography, and slab-pull at subduction zones all contribute to plate motion and spreading.
- Observable features at spreading centers: mid-ocean ridges (often with central rift valleys), pillow lavas, high heat flow, hydrothermal vents, and frequent shallow earthquakes.
- Evidence supporting seafloor spreading:
- Symmetrical magnetic stripes on either side of ridges recording reversals of Earth’s magnetic field (Vine–Matthews–Morley hypothesis).
- Age pattern of oceanic crust: youngest at the ridge, progressively older away from it; the oldest oceanic crust is about ~200 million years old.
- Heat flow is higher at ridges and decreases away from them.
- Drilling samples confirm rock types and ages predicted by spreading.
- Rates and effects: Spreading rates vary from a few millimeters to over 10 cm per year (e.g., Mid-Atlantic Ridge ~2–5 cm/yr; East Pacific Rise faster). Seafloor spreading creates new ocean floor and, balanced by subduction, drives continental drift, mountain building, volcanism, and the recycling of crust into the mantle.
Historical note: The concept was central to confirming plate tectonic theory in the 1960s (work by Harry Hess, and Vine and Matthews).
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