GK
ECOLOGY BIODIVERSITY CONSERVATION ENVIRONMENTAL ISSUES
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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Uniform throughout.
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Higher in continental lithosphere.
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Lower at mid oceanic ridges.
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Higher in subduction zones.
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Detailed explanation-1: -The highest gradients, 40–80 K km−1, are measured at oceanic spreading centers (mid-ocean ridges) or at island arcs where magma is close to the surface. The lowest gradients occur at subduction zones where cold lithosphere descends into the mantle. The gradient in old stable continental crust is 20–30 K km−1.
Detailed explanation-2: -Continental crust has a median gradient of around 34 ∘ C / k m while oceanic crust is almost double that at 66 ∘ C / k m (or 62 ∘ C / k m if we exclude hydrothermal effects by limitings data to less than 200).
Detailed explanation-3: -The geothermal gradient is defined as the increase in temperature with depth in the Earth. In normal continental crust a typical geothermal gradient within the first 3 to 5 kilometers (2 or 3 miles) of Earth’s surface is about 25°C/km.
Detailed explanation-4: -The average geothermal gradient in the shallow crust is 2.5 – 3oC/100 m, but there is considerable variation depending on the proximity to subduction zones (where the geotherm is depressed by the down-going slab of cold oceanic crust), magmatic arcs and rifts that tend to be hotter, and cold intraplate settings.