Metamorphic Rocks

Standards  Classify matter in a variety of ways  Describe the composition and structure of Earth’s materials, including: the major rock types (i.e., sedimentary, igneous, metamorphic) and their formation

Properties of Metamorphic Rocks Metamorphic means change in form. Metamorphic rocks are formed when existing rocks undergo changes. Sedimentary & igneous rocks can change into metamorphic rocks, and metamorphic rocks can change into different metamorphic rocks.

Properties of Metamorphic Rocks During the process of metamorphism, rocks and minerals change in response to changes in temperature, pressure or other environmental changes. The mineralogy, texture and/or chemical composition of the rocks may alter during metamorphism. Most metamorphic reactions (changes) occur while the rocks are in a solid state (if the rock becomes liquid, it is an igneous rock).

Texture Changes The average size of crystals in the rock usually increases. The shape and arrangement of crystals in the rock change Ex: limestone changes to marble: still made of the mineral calcite, but it is now dense and its texture is coarse with irregularly shaped, interlocking grains.

Mineral Changes In general, if the original (parent) rock contains one mineral, metamorphism produces a rock of the same mineral. Ex: limestone changes to marble, both are made of calcite If multiple minerals are present in the parent rock, the new metamorphic rock may have different minerals. Ex: shale contains clay minerals, quartz & feldspar. During metamorphism, these minerals change to chlorite.

Formation of Metamorphic Rocks Metamorphic rocks are formed by high temperature and/or pressure

Formation of Metamorphic Rocks 1.Temperature induced changes Elevated temperatures cause metamorphism: Lower temperatures cause slow changes and produce less of a change. Higher temperatures cause faster changes and produce a greater change

Formation of Metamorphic Rocks 2.Pressure induced changes Chemical reactions are sensitive to pressure (measured in kilobars). Greater amounts of pressure will produce greater changes.

Formation of Metamorphic Rocks 2.Pressure induced changes Deformation – change in the shape of rocks or minerals in response to mechanical forces Tectonic activity causes pressure that creates foliation in metamorphic rocks. Foliation is a set of flat or wavy planes in a metamorphic rock

Formation of Metamorphic Rocks Types of foliation: Slaty cleavage – rock splits into thin sheets Schistosity – wavy, parallel arrangements of minerals Gneissic – alternating layers, or bands, of light and dark minerals

Types of Metamorphism 1.Regional metamorphism 2.Contact metamorphism 3.Metasomatism

Regional Metamorphism Caused by burial or strong tectonic forces that impose high temperatures and pressures on the rocks over a large area. Pressure plays a greater role than heat Most metamorphic rocks are of this type. These rocks are foliated.

Regional Metamorphism Types of regional metamorphic rocks: Rock NamesParent Rock Slate………………..shale Phyllite……………..shale Schist………………shale Gneiss……………..shale, granite or conglomerate

SlatePhyllite Schist Gneiss

Contact Metamorphism Caused by heat and pressure produced by a nearby igneous intrusion. Does not cover large areas like in regional metamorphism. Heat plays a greater role than pressure. These rocks are called granoblastic and are non-foliated.

Contact Metamorphism Types of contact metamorphic rocks: Rock NamesParent Rock Metaconglomerate……...conglomerate Quartzite…………………sandstone Marble……………………limestone

Metaconglomerate Quartzite Marble Sugary Texture

Metasomatism Super-heated water enters pore spaces or fractures in rocks and creates metamorphic changes. Many deposits of valuable metal ores, such as copper, zinc and lead, are formed in this way.