Typical Characteristics
NVPM are the result of rifting when a continent breaks up to form an ocean, producing transitional crust without volcanism. Extension causes a number of events to occur. First is lithospheric thinning, which allows asthenospherc upwelling; heating further erodes the lithosphere, furthering the thinning process. The extensional forces also cause listric faults and continentward dipping reflectors that help identify NVPM and distinguish them from VPM, characterized by seaward-dipping seismic reflectors. The main difference between NVPM and VPM is that in the latter case, the mantle is hot enough to melt and produce voluminous basalts, whereas in the former case the mantle doesn't melt and there is little or no volcanism. Instead, extension simply pulls the crust away, exposing or "unroofing" the mantle, exposing serpentinized peridotite. The mantle doesn't melt because it is cold or upwells slowly, so there are no igneous rocks like there are in VPM. The basalts and granites are replaced with serpentinized peridotite, accompanied by unique serpentothemal and hydrothermal activity. Increasing density of the lithosphere as it cools and sediment accumulation causes subsidence.
Read more about this topic: Non-volcanic Passive Margins
Famous quotes containing the word typical:
“The books may say that nine-month-olds crawl, say their first words, and are afraid of strangers. Your exuberantly concrete and special nine-month-old hasn’t read them. She may be walking already, not saying a word and smiling gleefully at every stranger she sees. . . . You can support her best by helping her learn what she’s trying to learn, not what the books say a typical child ought to be learning.”
—Amy Laura Dombro (20th century)