88 Rocks. The Rock Cycle. rocks 1. The Rock Cycle at a Destructive Plate Boundary. The Rock Cycle: generation of Igneous Rocks

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Plate Boundary When the term destructive is used, it is in the sense

Rocks Magma is generated by partial melting of crust.

When magma enters a cooler environment, crystallization can begin.

1 88 Rocks David L. Dillon, M.Sc. The Rock Cycle 9/28/05 1 9/28/05 2 The Rock Cycle at a Destructive Plate Boundary When the term destructive is used, it is in the sense that crust is consumed in the The Rock Cycle: generation of Igneous Rocks Magma is generated by partial melting of crust. Magma migrates into areas of lower pressure. When magma enters a cooler environment, crystallization can begin. Plutonic igneous rocks are formed within the crust and volcanic igneous rocks are formed at, or on surface. process. 9/28/05 3 9/28/05 4 rocks 1

Texture and Context Plutonic rocks cool within the crust. This allows time for crystals to grow to visible size.

The rate of cooling is so fast that visible crystals are uncommon.

9/28/05 5 Phaneritic vs Aphanitic These rocks are roughly the same size and of essentially the same mineral composition.

The aphanitic one, on the left, cooled at surface, while the phaneritic one at the right cooled within the crust.

Pyroclastic literally of fiery fragments applies to pieces that have been ejected from a volcano.

2 Texture and Context Plutonic rocks cool within the crust. This allows time for crystals to grow to visible size. The term phaneritic applies to even the smallest grains. Volcanic rocks cool at, or on surface. The rate of cooling is so fast that visible crystals are uncommon. The term aphanitic applies to the smallest grains that can only be seen with the aid of a magnifier of some sort. 9/28/05 5 Phaneritic vs Aphanitic These rocks are roughly the same size and of essentially the same mineral composition. The major difference is the environment of crystallization. The aphanitic one, on the left, cooled at surface, while the phaneritic one at the right cooled within the crust. Andesite Diorite 9/28/05 6 Texture and Context II In volcanic rocks, there are other textures to be found. Pyroclastic literally of fiery fragments applies to pieces that have been ejected from a volcano. Vesicular refers to rocks that contain gas cavities. Glassy is used to describe rocks that cooled so quickly that the remaining liquid did not crystallize. 9/28/05 7 Pyroclastic Both of the eruptions shown here ejected hot material out of their craters. The volcanic bomb at the right is an example of a pyroclast from a basaltic eruption. 9/28/05 8 rocks 2

Vesicular Both of these rocks exhibit vesicles.

can float on water. Glassy Glassy texture is recognizable by the lustre of the surface.

$The surface is a series of cleavage planes and fractures of microscopic crystals.$ 9/28/05 9 9/28/05 10 Porphyritic Magma can move during crystallization.

9/28/05 9 9/28/05 10 Porphyritic Magma can move during crystallization.

The images here are of aphanitic porphyritic rocks.

The otherwise invisible grains can be seen at this scale.

3 Vesicular Both of these rocks exhibit vesicles. The one at the right is vesicular basalt and the one below is pumice so vesicular that it can float on water. Glassy Glassy texture is recognizable by the lustre of the surface. In aphanitic rocks, crystallization has occurred. The surface is a series of cleavage planes and fractures of microscopic crystals. Glass does not exhibit this, but does show continuous shiny surfaces. 9/28/05 9 9/28/05 10 Porphyritic Magma can move during crystallization. When it moves into a zone of faster cooling, two sizes of crystals result. The images here are of aphanitic porphyritic rocks. The lower image is of a thin section under a microscope. The otherwise invisible grains can be seen at this scale. The Rock Cycle: generation of Sedimentary Rocks Weathering and erosion allow for the transportation of fragments and solutes under gravity. Animal and plant remains may end up in sediments because this occurs at surface. Eventually, sediment becomes lithified via compaction, dehydration and cementation. 9/28/ /28/05 12 rocks 3

Sediments have sources, transportation media and depositional environments, prior to becoming rock.

Transport is by wind, water, ice or a combination of these.

Sedimentary Systems 9/28/05 13 Sedimentary Systems II Where glaciers exist, unsorted glacial till is deposited by

In shallow tropical waters, dissolved matter helps form reefs.

4 Sediments have sources, transportation media and depositional environments, prior to becoming rock. Sources are previously existing rocks as well as plant and animal remains. Transport is by wind, water, ice or a combination of these. Deposition occurs where the medium no longer can carry the load. Sedimentary Systems 9/28/05 13 Sedimentary Systems II Where glaciers exist, unsorted glacial till is deposited by the ice. Rivers transport boulders, cobbles, sand, silt and mud. These are deposited and reworked. In shallow tropical waters, dissolved matter helps form reefs. Desert winds transport fine material and deposit sand dunes while evaporation of groundwater forms chemical sediments. 9/28/05 14 Weathering These are granites that have undergone weathering: 1 shows how weathering rounds planar surfaces and; 2 exhibits exfoliation. 1 Chemical and physical weathering affects the outer rind of the rock the most. This liberates fragments and solutes that can then be transported. 2 9/28/05 15 Weathering II These minerals, found in both igneous and metamorphic rocks, react with carbonic and other atmospheric acids. 9/28/05 16 rocks 4

This is the end of a glacier, where till is

9/28/05 17 This is what it deposits, glacial

9/28/05 18 This is a braided river several

5 This is the end of a glacier, where till is deposited and a river system begins. 9/28/05 17 This is what it deposits, glacial till. Unsorted fragments, or clasts. 9/28/05 18 This is a braided river several kilometres downstream This is what it deposits. Cobbles, sand and gravel, 9/28/05 from glacial ice. 19 9/28/05 which become conglomerate. 20 rocks 5

The longer a fragment is in a river system, the more it is subject to abuse in the form of hydration reactions, abrasion, and impaction.

E R The result is coarser and unsorted material near the source and finer well-sorted sediment at the mouth E 9/28/05 of the system.

A swamp environment is indicated by: a) the fine clastic component implying quiet water; B) the blackness of the rock implying low oxygen in the

Limestone and the Reef Environment Limestone is the abundant biogenic rock formed in warm shallow water.

6 The longer a fragment is in a river system, the more it is subject to abuse in the form of hydration reactions, abrasion, and impaction. Clast Sorting and sediment maturity Fragments get sorted with respect to mineralogy, size and roundness by these phenomena, as well as R U turbulence. E R The result is coarser and unsorted material near the source and finer well-sorted sediment at the mouth E 9/28/05 of the system. 21 9/28/05 22 M A T U I M M A T Swamps This is a black shale containing a fern frond. A swamp environment is indicated by: a) the fine clastic component implying quiet water; B) the blackness of the rock implying low oxygen in the depositional environment and c) the presence of land plant remains. When plant remains dominate the sediment, the resulting rock is coal. Limestone and the Reef Environment Limestone is the abundant biogenic rock formed in warm shallow water. Depending on structure, one can tell something of the environment in which it was deposited: 1 contains the 1 remains of reef building animals; 2 is made of oyster shell fragments indicating the turbulence found near a beach and; 3 is micritic limestone probably from a lagoon. 9/28/ /28/05 24 rocks 6

Distance from Shore Turbulence is strongest near shore and where river currents enter standing bodies of water.

Pebbles are deposited at or near shore, sands reach beyond this zone.

The Rock Cycle: Generation of Metamorphic Rocks Pre-existing igneous and sedimentary rocks are susceptible to

This occurs in the solid state up to the point when partial melting occurs and beyond within whatever solid

9/28/05 25 9/28/05 26 Types of Metamorphism Contact metamorphism occurs due to the heat of an intruding body of

7 Distance from Shore Turbulence is strongest near shore and where river currents enter standing bodies of water. As a result, the finest fragments are transported the farthest. Pebbles are deposited at or near shore, sands reach beyond this zone. Silts go farther seaward and mud goes farthest from shore. The Rock Cycle: Generation of Metamorphic Rocks Pre-existing igneous and sedimentary rocks are susceptible to change as a result of increasing temperature and pressure. This occurs in the solid state up to the point when partial melting occurs and beyond within whatever solid remains. 9/28/ /28/05 26 Types of Metamorphism Contact metamorphism occurs due to the heat of an intruding body of magma. Regional metamorphism is due to crustal thickening associated with plate collisions. Contact Metamorphic Rocks Contact metamorphic rocks are best identified in field context. That is, in association with a heat source. They can also be recognised by the fact that heating tends to result in the randomization of linear elements and the mineral content is different from that of igneous rocks. 9/28/ /28/05 28 rocks 7

Regional Metamorphic Rocks Regional metamorphic rocks are recognised by the alignment of

As metamorphic grade increases, crystal grains increase in size and they become more aligned.

changes occur. These are summarized for a shale precursor in the figure below.

8 Regional Metamorphic Rocks Regional metamorphic rocks are recognised by the alignment of linear and planar minerals in them. This is because the crystals grow during compression (I.E. Within a stress field.). Foliation The alignment of planar mineral grains is referred to as foliation. As metamorphic grade increases, crystal grains increase in size and they become more aligned. 9/28/ /28/05 30 Mineralogical Change With increasing metamorphic grade, mineralogical changes occur. These are summarized for a shale precursor in the figure below. Clays are converted to albite, quartz and chlorite, which in turn react to form other minerals at higher grades. Changes in Lustre The growth of crystal grains results in changes in the appearance of the rock. 1 The progression from dull to a satiny sheen to sparkling to banded is exemplified by 1 slate, 2 phyllite, 3 schist, and 4 gneiss. 2 9/28/ /28/ rocks 8

Granoblastic Granoblastic is a texture of metamorphic rocks that contain mineral grains that are equi-dimensional.

Marble (1) is composed of calcite or dolomite, whereas quartzite (2) is made of quartz.

Death by asphyxiation for example has occurred on a number of occasions to large numbers of people and livestock as a result of

Volcanic eruptions have incinerated whole cities.

Because CO 2 is more dense than air it flowed down valleys with enough speed to flatten vegetation.

9 Granoblastic Granoblastic is a texture of metamorphic rocks that contain mineral grains that are equi-dimensional. This is the case with marble and quartzite. They can be distinguished form each other on the basis of mineralogy. Marble (1) is composed of calcite or dolomite, whereas quartzite (2) is made of quartz. Risks and the Rock Cycle During the generation of new rocks, a number of processes can affect health and well being. Death by asphyxiation for example has occurred on a number of occasions to large numbers of people and livestock as a result of volcanic activity. The subduction of plate material brings about earthquakes and the associated risks of tsunamis and landslides. Volcanic eruptions have incinerated whole cities /28/ /28/05 33 Lake Nyos, Cameroon On August 21,1986, a cloud of CO 2 gas was released from the lake. Because CO 2 is more dense than air it flowed down valleys with enough speed to flatten vegetation. 1,700 deaths were caused by suffocation. 845 people were hospitalized. Pyroclastic Flows This is Montserrat. The volcano in the island of Martinique. This pyroclastic flow came down a river valley and formed a new beach and delta. Such flows typically reach speeds several times faster than the fastest sprinters. 9/28/ /28/05 36 rocks 9

Mount Vesuvius and Pompeii Between Naples and

both Herculaneum and Pompeii were buried in

People and their animals were asphyxiated by the

Monsoon rains enhanced by typhoons Aere and

9/28/05 38 Earthquakes On Friday, December 26,

3 magnitude earthquake levelled the city of Bam

10 Mount Vesuvius and Pompeii Between Naples and ancient Pompeii lies Mount Vesuvius. In 79 A.D. both Herculaneum and Pompeii were buried in pyroclastic flow debris. People and their animals were asphyxiated by the fumes as well as being buried in scalding fragments. Naples Pompeii 9/28/05 37 Flooding These images are of the Philippines. The left image was taken July 31, 2004 and the other August 30. Notice how the area to the north of the bay is blue instead of green in August. This is the hydrosphere in motion. Monsoon rains enhanced by typhoons Aere and Chaba devastated this area. 9/28/05 38 Earthquakes On Friday, December 26, 2003 a 6.3 magnitude earthquake levelled the city of Bam in south-eastern Iran. Over 25,000 people were killed. Earthquake triggered Landslides June 22, 2004 a deeper earthquake of magnitude 6.3 killed 500 people in the Qazvin Province of Iran. Some of the damage was due to rock slides as evidenced by the remains of this car and the rock strewn highway on the right. Prior to December 2003 after January /28/ /28/05 40 rocks 10

The Frank Slide 1903 An estimated 182,000,000,000,000 kg (one hundred million tons) of

76 people were buried in their sleep in a 100 second interval.

WSC, B&G, and Collip. Map #2 is between Collip and the greenhouses.

Rocks assignment 9/28/05 41 9/28/05 42 Rocks assignment II You are expected to classify the

11 The Frank Slide 1903 An estimated 182,000,000,000,000 kg (one hundred million tons) of limestone slid into the valley and onto the town of Frank, Alberta. 76 people were buried in their sleep in a 100 second interval. You are expected to find these map areas: Map area #1 is the specimen boulder collection near WSC, B&G, and Collip. Map #2 is between Collip and the greenhouses. Map #3 is between NCB and Staging Building. Rocks assignment 9/28/ /28/05 42 Rocks assignment II You are expected to classify the numbered rocks on map #1 by choosing: Igneous; Sedimentary; or Metamorphic. Rocks assignment II You are expected to be able to identify rocks in the area of maps #2 and #3. Be sure to use the charts provided. 9/28/ /28/05 44 rocks 11

Figure 1. Random orientation of crystal grains in an igneous rock, granite.

Figure 1. Random orientation of crystal grains in an igneous rock, granite. ES088 The Earth s Crust: Rocks Earth system forensics might well start with a disciplined look at materials and how they are formed. When you are given a piece of rock, it is important to remember that