Introduction
Dividing the P-T space of metamorphism to several subdivisions independent of the composition of the metamorphosed rock would immensely facilitate communication among petrologists regarding the grade of metamorphism. In 1915, Eskola introduced the concept of metamorphic facies to accomplish such a classification. Eskola emphasized the mineral assemblages (in mafic rocks) rather than index minerals.
A facies may be defined as: “A group of mineral assemblages, each developing in the rock a specific chemical composition, and is characteristic of the P and T under which the rocks were metamorphosed”. Therefore, if the bulk composition of the rock and the P and T at which it crystallized, is known, consequently prediction of the mineral assemblage can occur.
"What are the key mineral assemblages and reactions in rocks of the eclogite facies,
The eight metamorphic facies originally defined by Eskota were greenchist, pyroxene hornfels, amphibolite, granulite, sanidinite , glaucophene schist ( blueschist) and eclogite facies( Figuire 1).
In the eclogite facies, metabasaltic rocks contain the characteristic assemblage of omphacitic pyroxene + almandine-pyrope-grossular garnet, creating dense, beautiful green and red rocks (Table 1) .Plagioclase is not present in the eclogite facies rocks due to his stability. The accessory minerals are kyanite, quartz, rutile, orthopyroxene and coesite. Eclogites are high-pressure rocks that formed in a wide range of temperatures (temperatures over 600 0 C in Figure 1).
Figure 1: Pressure-temperature diagram showing the fields of the various metamorphic facies.
The blueschist facies to eclogite facies transition involves glaucophane and paragonite reacting to form the garnet-omphacite assemblage:
Gln + Pg = Prp + Jd+ Qtz + H2O
at pressures greater than 1.2 GPa. But glaucophene alone may remain stable into the eclogite facies.
Which minerals/reactions provide evidence for their distinctive conditions of formation?
Eclogites are very dense rocks with a density ever greater than some ultramafic mantle rocks and due to the high desnsity of eclogites, their origin can be readily related to very high pressure conditions during formation. Eclogites occur in very differrnt geodynamic settings. Low-temperature eclogites ( glaucophane + paragonite = garnet + omphacite ) may result from subduction of oceanic lithosphere and form from blueschists (high-pressure low-temperature eclogites), such an example is the Alps. Intermiduate eclogites may result from stacking of the continental crust from amphibolites (medium-temperatures eclogites). At high-temperature, hydrates are absent from eclogite and kyanite is often a characteristic additional mineral besides Grt + Omp. High- temperature eclogites form in settings of collision or extension where the geotherm is abnormally “hot” due to magmatic heat transfer from the mantle.
The shelf-edge includes carbonate-to-clastic facies transition and tectonic uplift and erosion of the carbonates followed by deposition of the clastics. The Saint Peter Sandstone is a well-sorted, almost pure quartz arenite deposited during a major mid-Ordovician low stand. Clastics spread across an exposed carbonate platform by transportation. This is shown by the well-rounded, frosted texture of the quartz grains.
When standing on top of the butte, the rock that makes up a majority of the area is quartzite. Quartzite is a metamorphic rock that forms when existing rock is exposed to extreme amounts of heat and pressure (4). The quartzite that is found on Kamiak Butte was formed sometime around 1.47 to 1.4 billion years ago during the Paleozoic period of the Precambrian era. Many of the metamorphic rocks have been fractured and decayed due to physical and chemical weathering, but because quartzite consists of one of the strongest minerals quartz...
Herndon J. M, 2005, Current Science, Scientific Basis of Knowledge of Earth’s Composition, 88, 1034-1036)
Shown in the picture above is volcanic extrusive igneous rock known as andesite. They were imported here to Laguna Beach to help minimize erosion (Merton Hill, p. 10-11). Extrusive Igneous rocks are formed on Earths surface due to lava quickly cooling or mixing with different materials such as ash or cinders from an eruption. There are two different types of extrusive igneous rocks; Plutonic and Volcanic. Andesite is known for being gray in color and being made up of very coarse grainy textures, which make it much harder to break down than sedimentary rocks. Unlike loose gravel and other sediments igneous rocks are known for being able to slow down seismic waves from earthquakes which cause less damage to surface structures.
Plummer, C.C., McGeary, D., and Carlson, D.H., 2003, Physical geology (10th Ed.): McGraw-Hill, Boston, 580 p.
Froede, Carl R. “Stone Mountain Georgia: A Creation Geologist's Perspective.” CRS Quartely 31, no. 4 (March 1995): 6.
Quartzite is a non-foliated metamorphic rock. This rock is intrusive and forms when exposed to extreme amounts of heat and pressure. Over a billion years ago, there was an ocean where Kamiak Butte is. This ocean floor was made of sand, as time went on oceans receded and the exposed sand underwent processes that turned it into sandstone – or as we learned in class the process of lithification. Years later, this sandstone would morph into the quartzite that is present now.2
"Sedimentary Rocks." Backyard Nature with Jim Conrad. N.p., 18 May 2015. Web. 25 Oct. 2015.
Bibliography Wikipedia. The World of the. Gould, Stephen. Jay. Charles Lyell, Principles of Geology.
Aluminum is the most abundant metallic constituent in the crust of the earth; only the nonmetals oxygen and silicon are more abundant. Aluminum is never found as a free metal; commonly as aluminum silicate or as a silicate of aluminum mixed with other metals such as sodium, potassium, iron, calcium, and magnesium. These silicates are not useful ores, for it is chemically difficult, and therefore an expensive process, to extract aluminum from them. bauxite an impure h...
Krajick, Kevin. "Tracking Myth to Geological Reality." American Association for the Advancement of Science. 310.5749 (2005): 762. Print. .
Basalt forms due to the partial melting of the layer of the mantle called the asthenosphere. The asthenosphere is the plastic zone of the mantle beneath the rigid lithosphere. Mantle plumes coming from the mesosphere can cause the asthenosphere to melt with heat or even if pressure decreases, which is called decompression melting (Richard 2011). The magma that forms from this melting is mafic magma that solidifies once it reaches the earth’s surface and cools quickly. The above process mainly occurs mainly during intraplate igneous activity which is the main explanation for volcanic activity that occurs a long distance away from a plate boundary. If the tectonic plate above the mantle plume is moving it can create a string of volcanic activity such as in Hawaii. See Fig 2.
The Rock Cycle The Rock Cycle is a group of changes. Igneous rock can change into sedimentary rock or metamorphic rock. Sedimentary rock can change into metamorphic rock or into igneous rock. Metamorphic rock can change into igneous or sedimentary rock. Igneous rock forms when magma cools and makes crystals.
mineral equilibria of metamorphic carbonate ejecta (2). Fluid inclusions ([CO.sub.2] and [H.sub.2]O-[CO.sub.2]) in clinopyroxenes from cumulate and nodules indicate a trapping pressure of 1.0 to 2.5 kbar at about 1200 [degrees]C, suggesting that these minerals crystallized at depths of 4 to 10 km (3). The differentiated magma fraction was about 30% of the total magma in the reservoir, and a volume of about 2 to 3 [km.sup.3] was