Texas A&M University (TAMU) GEOL101 Principles Of Geology Exam 1 Practice Exam

The correct answer is that metamorphic rocks are formed mainly through regional metamorphism. Regional metamorphism occurs over large areas and is typically associated with tectonic forces like mountain building, where rocks are subjected to significant pressure and temperature changes. This process alters the mineral composition and structure of pre-existing rocks, transforming them into metamorphic rocks. Metamorphic rocks exhibit features such as foliation, which is the alignment of mineral grains under directed pressure, and are often formed from sedimentary or igneous parent rocks. For instance, shale can transform into schist or gneiss through regional metamorphism. The large-scale nature of regional metamorphism contrasts with contact metamorphism, which occurs in localized areas typically around igneous intrusions. Other types of rocks, such as igneous, sedimentary, and volcanic rocks, form through different geological processes: igneous rocks crystallize from molten magma, sedimentary rocks form from the accumulation and compaction of sediments, and volcanic rocks are related to volcanic activity at or near the earth's surface. Thus, the distinctive formation processes for these rock types clarify why the correct selection is metamorphic rocks.