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Discussion and Debate
Discussion and Debate
Physical & Life Sciences
Man made earthquakes.
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<blockquote data-quote="Ophiolite" data-source="post: 75590229" data-attributes="member: 234799"><p>As I said, it's not a problem for the point you are making, but from the broader geological perspective it is misleading. The distribution of crustal thicknesses is bimodal because of the distinct differences between continental and oceanic crust. </p><p></p><p>Oceanic crust is comparatively thin and very simply organised (superficial sediments/basaltic pillow lavas and sheeted dykes overlying layered basic and ultrabasic rocks). It forms at mid-ocean ridges and is consumed at subduction zones (or occasionally thrust onto continental margins where they form ophiolite complexes). No oceanic crust has been found older than 200 million years.</p><p></p><p>In contrast continental crust is thick and very complex (Stable cratons of intensely folded and deformed metamorphic rock, sometimes overlain by thick near horizontal sedimentary deposits and unstable orogenic zones with extensive mixtures of sedimentary, igneous and metamorphic rocks.) Continental crust forms from igneous activity based upon partial melting of upper mantle and of descending slabs of oceanic crust. Some continental crust dates back to almost 4 billion years (and individual crystals to almost 4.4 bya)</p></blockquote><p></p>
[QUOTE="Ophiolite, post: 75590229, member: 234799"] As I said, it's not a problem for the point you are making, but from the broader geological perspective it is misleading. The distribution of crustal thicknesses is bimodal because of the distinct differences between continental and oceanic crust. Oceanic crust is comparatively thin and very simply organised (superficial sediments/basaltic pillow lavas and sheeted dykes overlying layered basic and ultrabasic rocks). It forms at mid-ocean ridges and is consumed at subduction zones (or occasionally thrust onto continental margins where they form ophiolite complexes). No oceanic crust has been found older than 200 million years. In contrast continental crust is thick and very complex (Stable cratons of intensely folded and deformed metamorphic rock, sometimes overlain by thick near horizontal sedimentary deposits and unstable orogenic zones with extensive mixtures of sedimentary, igneous and metamorphic rocks.) Continental crust forms from igneous activity based upon partial melting of upper mantle and of descending slabs of oceanic crust. Some continental crust dates back to almost 4 billion years (and individual crystals to almost 4.4 bya) [/QUOTE]
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Man made earthquakes.
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