Meet a Passive MarginHave you ever wondered what is buried beneath a seashore? This schematic cross

Meet a Passive MarginHave you ever wondered what is buried beneath a seashore? This schematic cross section diagram of a passive margin shows exactly that for many common shorelines, the type found away from active plate boundaries.Passive margins form when continents rift apart and the remnants are illustrated in this cross section. The portion labeled part 1 is the stable part of the continent deep inland; unfaulted and away from the rift. The parts labeled 7 are normal faults; these form when the continent is pulled apart and the land begins sinking down to fill the gap.All these segments are floating on part labeled 4, the mantle that is still solid but is hot enough for minerals to flow. Label 2 shows oceanic crust, formed when the continents on both sides of the rift have pulled apart so much that the mantle in-between melts and fills the space. Label 5 is, of course, the ocean.Label 6 is a common feature that shows up in seismic reflections. At the boundary where sediments begin to drape on the chunks of continent below, there will be layers that dip towards the continent as their surface has rotated while moving on the faults. Finally, label 3 shows the sediments that erode from the continent and are deposited near the ocean’s edge.Geologic settings like this one, formed near the ocean edge, are some of the most heavily populated in the world. Cities are commonly built on those sediments when they’re on shore and the offshore portion commonly holds oil and natural gas reservoirs. The legacy of that rifting can be found in the behavior of those cities; wide-scale subsidence or sinking of cities can happen as the sediments and faults deep below continue moving and settling downwards.-JBBImage credit:https://wikimediafoundation.org/wiki/File:Passive_margin.svgRead more:http://jersey.uoregon.edu/~mstrick/AskGeoMan/geoQuerry26.html -- source link
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