Common rock forming mafic minerals include olivine, pyroxene, amphibole, biotite and other micas, augite and the calciumrich plagioclase. Felsic, intermediate and mafic igneous rocks differ in their mineral composition. Maps of geological sections in the field showing metamafic rocks as deformed dykes preserved in alrich. Mafic rocks have between 45 and 55% of silica, whereas felsic rocks have over 65% of silica, the highest of all types. Once the groups have separated their rocks, ask the class what characteristics they selected to help them classify the rocks. Multiple generations of maficultramafic rocks from the. The book summarizes the occurrence, geochemistry, mineralogy, petrology and phaseequilibria studies in air and under high pressures related to the most intriguing group of potassiumrich mafic and ultramafic rocks, often including host of exotic mineral assemblages including feldspathoids. Common mafic rocks include basalt, diabase and gabbro. Multiple mafic magmatic and highgrade metamorphic events.
Examine one thin section from each of the following groups and provide a sketch, rock description and rock name. Alternatively, you can download the file locally and open with any standalone pdf reader. Mafic lava, before cooling, has a lower viscosity than felsic lava due to its lower silica content. First determine composition, which is based on mineral content or color, if you cant see minerals. Pdf intrusive rocks in the longwood range represent a component of the permian brook. True the processes of crystal settling and assimilation have been shown to produce large quantities of felsic magma from mafic magmas. Mafic rocks often also contain calciumrich varieties of.
If oceanic crust is melted, then a rock rich in darksilicate minerals. A magma consists mostly of liquid rock matter, but may contain crystals of various minerals, and may contain a gas phase that may be dissolved in the liquid or may be present as a separate gas phase. Parent material of igneous rocks forms from partial melting of rocks magma at surface is called lava general characteristics of magma general characteristics of magma. Pdf geochemistry and geochronology of the accreted mafic. Ultramafic rocks also referred to as ultrabasic rocks, although the terms are not wholly equivalent are igneous and metaigneous rocks with a very low silica content less than 45%, generally 18% mgo, high feo, low potassium, and are composed of usually greater than 90% mafic minerals dark colored, high magnesium and iron content. Intermediate rocks are composed of the minerals amphibole and feldspar and contain a combination of light and dark minerals. Range of spinel compositions in terrestrial mafic and. Ultramafic rocks comprised of forty to one hundred percent percent olivine. The term is a portmanteau, made up from magnesium and ferric mafic minerals are usually dark in color and have a specific gravity greater than 3. Igneous hypabyssal mafic hypabyssal hypabyssalbasalticandesite stock or pipe comments gabbro dikes, sills, and at least one plug intrude steens basalt in northern pueblo mountains and are substantial in size, but too small to appear on state geologic map or252. Both types of mafic rocks were apparently generated during the same magmatic event that produced the ryokesanyo granites. Igneous rocks are formed by the solidification and cooling of magma in volcanic areas.
Among those bodies emplaced in an orogenic environment one can distinguish synvolcanic bodies, both intrusive and extrusive, emplaced before the peak of orogenesis. Late neoproterozoic layered mafic intrusion of arcaffinity in. In other words, if the rock it intrudes into is in horizontal layers, a dyke would cut the layers. Includes the monument dike swarm of northwestern grant county or061, the chief joseph dike swarm. The mafic rocks become younger eastwards, matching the alongarc age trend of the associated cretaceous granites nakajima et al. Represents fertile mantle that has not undergone a melt extraction event.
What acreage or percentage of the continental us is covered by ultramafic mafic rocks. All structured data from the file and property namespaces is available under. Mafic and intermediate plutonic rocks learning goals. Due to the color of the minerals forming them, the rocks are either light or dark. The only rocks in each district that are actually sulfide undersaturated are mafic lavas with rocks were sulfide saturated as magmas, but oxidized lavas or nonquenched samples apparently lost most or all of their magmatic endowment of sulfides before solidification. General characteristics of magma igneous rocks form as molten rock cools and solidifies general characteristics of magma parent material of igneous rocks forms from partial melting of rocks magma at surface is called lava rocks formed from lava extrusive, or volcanic rocks rocks formed from magma at depth intrusive, or plutonic rocks the. Mgo for the neoproterozoic, paleozoic, and middle triassic mafic rocks from the.
Mafic rocks also happen to be the most abundant rock type that makes up the earths crust. Introduction to igneous rocks an igneous rock is any crystalline or glassy rock that forms from cooling of a magma. Role of magmatic sulfides and mafic alkaline magmas in the. Due to the color of the minerals forming them, the rocks. The belts of mafic ultramafic rocks and major shear zones bounding the two contrasting. Igneous rocks are formed by the cooling and crystallization of magma. Young mafic back arc volcanic rocks as indicators of.
It contains lots of darksilicate minerals like pyroxene and amphibole, with smaller quantities of biotite mica and olivine. At kohikalawur, along the southeast foot of kohe saymahmude ghazi east of the logar river, seven chromite lenses as much as 4. Maficultramafic rocks as mantlederived magmas produced in diverse tectonic settings can offer. Contain variable but greater than 10% of both ortho and clinopyroxene, and accessory phases.
This page was last edited on 25 december 2019, at 03. This is the rock type that is found in oceanic crust. Felsic rocks are light colored because they contain light. Give each student a tray of igneous rocks see list of suggested rocks in materials or use the recommended virtual rock collection. As a whole, rocks of this type are referred to as mafic, because. These rocks are usually darker in color and higher in density than felsic rocks. Petrographic analysis of igneous and metamorphic rocks. Once the groups have separated their rocks, ask the class what characteristics they selected to. The term roughly corresponds to the older basic rock class. Igneous rocks and processes revised on 102011 page 5 of 10 finegrained or aphanitic. They are usually light in colour and have specific gravities less than 3. In terms of chemistry, felsic rocks are on the other side of the rock spectrum from the mafic rocks. It makes sense to use different names because rocks of different grain sizes form in different ways and in different geological settings. Metamorphic petrology 1 metamorphic processes, contact, regional, t.
The word felsic is a term used in geology to refer to silicate minerals, magma, and igneous rocks which are enriched in the lighter elements such as silicon, oxygen, aluminium, sodium, and potassium. Reserves were estimated in 1950 to be 840 t assaying 42. Thus, understanding what mafic rocks are and how they form is very important to understanding the earths. Therefore, rocks are divided into ultramafic, mafic, intermediate, and felsic. Implications for pge fractionation and mineralization. Pdf geochemical characteristics of mafic and ultramafic. Pdf origin of the fanjingshan maficultramafic rocks. The major types of sedimentary rocks distribution of sediments on the earths surface.
A mixture of minerals implies the presence of more than one mineral grain, but not necessarily more than one type of mineral. Geochemical evidence for the production of granitoids. Geochemical characteristics of mafic rocks from the xinlin. The coursegrained version of an ultramafic rock is peridotite, and the finegrained version is komatiite. A mafic rock is gabbro if it is coursegrained, and basalt if finegrained. Platinum and palladium in maficultramafic igneous rocks. Publications on spinels particularly chromites have routinely used compositional fields based on the spinel prism to compare populations of analyses. Geochemical characteristics of mafic and ultramafic rocks from the naga hills.
Mafic simple english wikipedia, the free encyclopedia. The temperature of cooling determines which types of minerals are found in the rock and helps scientists classify the rock as felsic, intermediate or mafic. Now we will examine some mafic and intermediate plutonic rocks under the microscope. Geochemistry and geochronology of the accreted mafic rocks from the hengchun peninsula, southern taiwan. Origin of the fanjingshan maficultramafic rocks, western jiangnan orogen, south china. Pdf documents opened from your browser may not display or print as intended.
Rocks that begin their cooling at low temperatures are rich in minerals containing silicon, potassium and aluminum. All minerals are rock, but not all rock is mineral solid naturally occurring inorganic chemical composition crystal internal structure igneous require another rock coal any rock type can become any other rock type or it can become itself again. Ultramafic and related mafic rocks can conveniently be classified in terms of the tectonic environment in which they were emplaced. A rock can be composed of one or many different minerals, but there are only 3 primary classes of rocks. In terms of chemistry, mafic rocks are on the other side of the rock spectrum from the socalled felsic rocks. Felsic and mafic rocks, division of igneous rocks on the basis of their silica content. Basalt is finegrained, whereas gabbro is coarsegrained. Most mafic minerals are dark in color, and common rock forming mafic minerals include olivine, pyroxene, amphibole, and biotite. Download the latest version of adobe reader, free of charge. They occur in a high proportion of terrestrial mafic and ultramafic rocks, and a very large volume of microprobe data is available on their compositions. Dikes, plugs, and sills of basalt, diabase, gabbro, and lesser andesite that fed many of the miocene basalt and andesite flows in units tc and tba. They are rich in iron fe and magnesium mg and low in aluminum al. Rocks formed from lava are extrusive, or volcanic rocks. Some intrusions are rootless and are invasive into sedimentary sequences.
Ultramafic and related mafic rocks can conveniently be classified in terms of the. Identify igneous rockforming minerals based on their optical properties demonstrate the operation of the petrographic microscope in plane and crossed polarized light. Igneous rocks form as molten rock cools and solidifies general characteristics of magma. Some pictures from the trip peninsular ranges batholith, san diego county, april 2930. The spatial distribution of some major and trace element and isotopic characteristics of backarc plio. An igneous rock or a part of an igneous rock with a finegrained or aphanitic texture has crystals, but they are too small to recognized with the unaided eye. Continental crust is less than 1% of earths mass, so there isnt a lot of felsic material in the earth. Implications for petrogenesis, geoscience frontiers 2017, doi.
The whole rock srnd isotopes in the granitoids are quite similar to those of late cretaceous mafic rocks in the gangdese batholith. Basalt is the most common extrusive volcanic igneous rock. Origin of igneous rocks download ebook pdf, epub, tuebl, mobi. Files are available under licenses specified on their description page. Apr 20, 2010 looking at the words separately, mafic refers to the chemical composition of the rock. I am doing a graduate thesis on soils formed from ultramafic mafic rocks in the ga piedmont at the university of georgia, and i cannot seem to find an answer to this deceptively simple question. How are felsic, intermediate and mafic igneous rocks. Chemical analyses of the most abundant components in rocks usually are presented as oxides of the elements.
Part or all of this report is presented in portable document format pdf. Mafic is an adjective describing a silicate mineral or igneous rock which is rich in magnesium and iron. Geochemical characteristics of mafic and ultramafic rocks from the. Chemically speaking, theyre rich in magnesium and iron. The lower part of oceanic crust is comprised of gabbro. In addition, both synmagmatic zircons and relict zircons with late cretaceous upb ages exhibit almost the same hfo isotope compositions to those of the slightly earlier mafic rocks. Mafic rocks are darker and are composed of magnesium and iron. To identify name igneous rocks, you determine two things about the rock. A dyke is an intrusive body that is discordant with the country rock.
Igneous rocks and plate tectonics over geologic time these processes first created oceanic crust from ultramafic mantle rocks. Compositional trend of amphiboles in the mafic rocks from the hongseong area. Felsic simple english wikipedia, the free encyclopedia. If you do not see its contents the file may be temporarily unavailable at the journal website or you do not have a pdf plugin installed and enabled in your browser. Rocks with compositions between mafic and felsic are termed intermediate, while those with an overwhelming predominance of ferromagnesian minerals are. C1 rocks and magmas a rock is defined as a consolidated mixture of minerals.
Platinum and palladium in maficultramafic igneous rocks, northwestern alaska. Mafic rocks are rich in minerals such as pyroxenes and amphiboles. The mafic rocks of the xinlin ophiolite including the gabbro, diabase and metabasalt show flat ree pattern laybn 0. Mafic and ultramafic xenoliths from volcanic rocks of the western united states. Most mafic minerals are dark in color, and common rockforming mafic minerals include olivine, pyroxene, amphibole, and biotite. The precambrian rocks have received attention in the current exploration activity for base and precious metals. Metamorphism of mafic rocks l clinopyroxene breaks down to a number of mafic minerals, depending on grade. Geochemistry of an alaskantype maficultramafic complex in. In turn, the mafic oceanic crust created felsic continental crust from partial melting of hydrated basalt. In order for a rock to be classified as felsic, it generally needs to contain more than 75% felsic minerals. Pdf mafic and ultramafic rocks, and platinum mineralisation. Classifying igneous rocks mafic 4552% silica igneous rocks are dark colored because they are largely composed of caplagioclase and pyroxene. The following 3 files are in this category, out of 3 total.
Mg andesitic 51% to 58% sio 2 lavas in the southern puna 24s to 27s of the central andean volcanic zone cvz reflect varying continental lithospheric thickness and the thermal state of the underlying mantle wedge and subducting plate. Geo 3004 rocks, fossils, and global tectonics quiz 7 university of texas, san antonio geo 3004 spring 2012 geo 3004 rocks, fossils, and global tectonics quiz 7. A rock can be composed of only one type of mineral. All structured data from the file and property namespaces is available under the creative commons cc0 license. Maficultramafic intrusions of alaskantype form along major structures as uplifted fragments from great.
Of the oxides, silica sio 2 is usually the most abundant. Mafic is an adjective describing a silicate mineral or igneous rock that is rich in magnesium and iron, and is thus a portmanteau of magnesium and ferric. Compared to felsic igneous rocks, mafic igneous 6 which. Ask students to look at the rocks and determine some way to classify their rocks. Then determine the texture of the rock and based on the two, identify t he rock name. Difference between tholeiitic rocks and alkali basalts. Mafic rocks show basalticsubalkaline to alkaline nature. More information about viewing, downloading, and printing report files can be found here. Introduction to basic geologic principles earth, environmental and. Felsic rocks are light in color and are composed of feldspars and silicates. Multiple mafic magmatic and highgrade metamorphic events revealed by zircons from meta mafic rocks in the daqingshanwulashan complex of the khondalite belt, north china craton. The most common felsic rock is granite, but others include quartz, muscovite, orthoclase, and the sodiumrich plagioclase. Name the 2 factors that affect the composition of igneous rocks.
1569 1016 1523 1005 1605 77 279 846 1208 57 1383 808 1530 1493 947 226 1135 956 879 1454 1046 562 29 1459 540 1135 607 95 1310 417 475 868 1525 289 1327 1057 406 1528 1055 428 465 522 1370 316 209 1411