4. Plate Interiors Metamorphism
Contact metamorphism - burial metamorphism
In relatively thick depositional basins, the deeply buried sedimentary and volcanic material can be subjected to temperatures of 200-300ºC, sufficient high to cause recrystallization. The classic terrane is a thick stack (> 10 km) of volcanoclastic rocks, like in southernmost New Zealand (Mesozoic). Although of regional extent, burial metamorphism has little or no associated penetrative ductile deformation so that relict depositional fabrics are usually preserved in rocks now composed of low-T minerals such as zeolites. Heated, advecting aqueous fluids in the deep basins are most likely to be involved. Thick piles of sedimentary and volcanic rocks, accumulated along passive continental margins, such as along the eastern and Gulf of Mexico coasts, that experience burial metamorphism, may subsequently undergo deformation as changes in plate motion occur. In this polymetamorphism, the earlier simple burial effects may be completely obscured.
Noch einzuarbeitender Bildkommentar:
Figure: Schematic cross section through a distensive intraplate setting. At the upper crust level, this is the setting of burial metamorphism of the zeolite-facies series at low T and P. At the deeper crust, amphibolite to granulite facies with migmatites develops. Burial metamorphism occurs in areas that have not experienced significant deformation or orogen. Source: MBG