Unit D Chapter 2 Lesson 3 Pgs D56-D61

Formation of Metamorphic Rocks  Metamorphism is the process by which any kind of rock is changed into metamorphic rock.  Metamorphic rock forms deep in earth’s crust and needs tremendous heat and pressure in order to form. (Heat is the most important cause of metamorphism) The boundaries of oceanic and continental tectonic plates is where most metamorphic rock forms. They are heated from magma and undergo intense pressure from the collision.

Formation of Metamorphic Rocks  Metamorphic rocks are made from rocks that already exist, called parent rocks.  The type of new rock that forms is also determined by what type of metamorphism happens. When granite (above) undergoes metamorphism it can turn into gneiss (below) Granite would be the “parent” rock.

The Two Degrees of Metamorphism  Rocks undergo two types of metamorphism. Hi grade and Low Grade  If a metamorphic rock went through low- grade metamorphism, then the rocks change only slightly because heat and pressure was less intense. Shale (above) is a sedimentary rock. When it undergoes Low-Grade Metamorphism, it changes into slate. (below) The change is not drastic.

The Two Degrees of Metamorphism  If a metamorphic rock went through high-grade metamorphism, the rocks change completely because of extreme heat and pressure.  Limestone is the parent rock for Marble. The two rocks are completely different and changed drastically. From this limestone to… This marble….big difference.

Two Ways Metamorphism Can Happen  Metamorphism usually occurs under two conditions:  Regional Metamorphism this occurs around plate boundaries, most metamorphic rocks are formed this way. The pressure from plates colliding affects large areas of rock. Bet you can’t guess the names of the ways metamorphism can happen.

Two Ways Metamorphism Can Happen.  Contact Metamorphism This occurs when magma rises through the crust and touches(comes in contact with) existing rock and bakes them until their entire structure changes.  Sometimes rocks can go through metamorphism if ground water is super- heated from magma under it, and the water heats the surrounding rock. This “black smoker” is a volcanic vent in the ocean. The heater water can cause crystals to break down and reform.

Two Types of Metamorphic Rock  Metamorphic Rock is broken down into two main groups.  Foliated Have layers or bands that you can see  Non-Foliated Do not appear to be layered. Slate is “foliated.” The layers are easy to see. Quartzite is a non-foliated rock with no layers.