GLG101 Exam 2 Study Guide - C hapter 5 Igneous Envi...

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Chapter 5: Igneous Environments Sketch and describe an igneous system and show where the main igneous textures form. (5.1B) o A – Pegmatite forms when water dissolved in the magma helps to grow large crystals. o B – Coarse-grained igneous rocks form at a depth. o C – Crystals have time to grow in the magma chamber and form a porphyrtitic texture. o D – Fine-grained igneous rocks form where the magma has only had enough time to grow small crystals. o E - Volcanic glass forms when magma erupts on the surface and cools quickly. Volcanic breccias can form in many ways including explosive eruptions of ash and rocks fragments. o F – Pyroclastic flows flow rapidly downhill. o G – Vesicles form when gases dissolved in the magma accumulate as bubbles o H – Volcanic ash erupts and settles back down to Earth. Sketch an oceanic divergent boundary (mid-ocean ridge), and describe why melting occurs along this type of boundary and why the resulting magmas are basaltic (mafic). (5.6A) In addition, describe the types of igneous rocks that form along oceanic divergent margins. (5.6B) o A – Mid-Ocean Ridge A – Mantle rocks are mostly solid and crystalline structure, not molten. The mantle’s high temperature and pressure allow these rocks to flow as a weak solid. B – Decompression melting occurs when the solid asthenosphere rise to fill the area between the separating plates. C – Buoyant magma rise away from unmelted residue in mantle and accumulates in the magma chambers.
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