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8.1.1: 8.1.1 Regional Metamorphism

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    Figure 8.3: Regional metamorphism is more intense at depth

    The most significant causes of metamorphism are mountain building processes (tectonism) that bury, while heating and squeezing, rocks. This kind of metamorphism, called regional metamorphism, creates large metamorphic terranes, regions characterized by distinctive metamorphic rocks and intensity of metamorphism that may vary laterally. Regional metamorphism occurs because both pressure and temperature increase with depth in Earth (Figure 8.3). The deeper the rocks, the greater the metamorphism. The photos below show two outcrops of regional metamorphic rocks. The schist outcrop on the left (Figure 8.4) is in Vermont’s Green Mountains; it formed about 450 million years ago during metamorphism associated with the Taconic Orogeny. The gneiss seen in outcrop on the right (Figure 8.5) is much older; it is from Precambrian terrane 750 km northwest of the Green Mountains, near Sudbury, Ontario.

    Figure 8.4: Outcrop of schist, Green Mountains, Vermont
    Figure 8.5: Outcrop of gneiss near Sudbury, Ontario

    Mountain building brings rocks from deep in Earth to the surface. So, many examples of regional metamorphism are found in mountain belts, for example the outcrop in Green Mountains in Figure 8.4, above. Other examples are found in Precambrian shields, relatively flat-lying areas that may be thousands of kilometers across, that are the exposed roots of ancient mountains. The gneiss seen in Figure 8.5 is from the Canadian Shield in central Ontario.

    This page titled 8.1.1: 8.1.1 Regional Metamorphism is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Dexter Perkins via source content that was edited to the style and standards of the LibreTexts platform; a detailed edit history is available upon request.