I am doing a graduate thesis on soils formed from ultramaficmafic rocks in the ga piedmont at the university of georgia, and i cannot seem to find an answer to this deceptively simple question. 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. Mafic and ultramafic rocks, and platinum mineralisation potential, in. Multiple generations of maficultramafic rocks from the. Ultramafic rocks are dominated by pyroxene or olivine, and may contain a small amount of calciumrich plagioclase. Metamorphism of mafic rocks l clinopyroxene breaks down to a number of mafic minerals, depending on grade. Mostly k spar no quartz syenite pegmatitic mostly feldspar. For best results viewing and printing pdf documents, it is recommended that you download the documents to your. Mafic and intermediate plutonic rocks learning goals. They provide an opportunity to explore the interaction between crust and mantle and to refine the tectonic setting of uht metamorphism and hightemperature magmatism in the dsgc belt. Rocks that contain a significant amount of silica silicarich tend to be light in color and not as dense.
Plagioclase makes up the continuous reaction series. Maficultramafic igneous rocks and associated carbonatites of the. What acreage or percentage of the continental us is covered by ultramafic mafic rocks. Compositional trend of amphiboles in the mafic rocks from the. In order for a rock to be classified as felsic, it generally needs to contain more than 75% felsic minerals. Mineralogic contents felsic rock, with predominance of quartz, alkali feldspar andor feldspathoids. A mixture of minerals implies the presence of more than one mineral grain, but not necessarily more than one type of mineral. At kohikalawur, along the southeast foot of kohe saymahmude ghazi east of the logar river, seven chromite lenses as much as 4. Mountain, about 9 miles to the northeast in the mcclure. Rocks that do not contain a lot of silica silicapoor tend to be dark in color and dense. Difference between mafic and felsic compare the difference. The sapat maficultramafic complex, kohistan arc, north pakistan article pdf available in geological society london special publications 741. Basement here refers to the crystalline layer of variable composition below the oldest dated sequence of sedimentary, volcanic, or metamorphic rocks. Some intrusions are rootless and are invasive into sedimentary sequences.
Of the oxides, silica sio 2 is usually the most abundant. Examine one thin section from each of the following groups and provide a sketch, rock description and rock name. Felsic is a term that is used to refer to igneous rocks rich in mineral feldspar. 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. Felsic and mafic rocks, division of igneous rocks on the basis of their silica content. The three minerals at the bottom do not form by reaction with the firstformed crystals. A dyke is an intrusive body that is discordant with the country rock. Igneous rocks and processes revised on 102011 page 5 of 10 finegrained or aphanitic. Represents fertile mantle that has not undergone a melt extraction event. Tracing the styles of maficfelsic magma interaction. Mafic rocks are rich in minerals such as pyroxenes and amphiboles. I guess that in x6 they have made a start, but it isnt fixed quite yet. Mineral deposits related to mafic igneous rocks include podiform chromite, ultramafichosted talcmagnesite, and serpentinehosted asbestos. Silica content in mafic rocks is around 50% by weight.
Files are available under licenses specified on their description page. Igneous rocks aphanitic andor vesicular pegmatitic or phaneritic glassy pyroclastic mostly feldspar minerals mostly mafic minerals mostly k spar mostly plagioclase 4585% mafic 85100% mafic quartz no quartz felsic. They are usually light in colour and have specific gravities less than 3. Any calculation obviously depends on the directory path too, so deciding to archive andor adding a date or something else to make it unique could be enough to push new files. Mafic is an adjective describing a silicate mineral or igneous rock which is rich in magnesium and iron. Ophiolites and other maficultramafic complexes in alaska by w. Mafic rocks, including the volcanic rocks and dolerites from this study, crop out in the cenxi and wuzhou areas at the ne end of the dsgc belt fig. These minerals are high in magnesium and ferric oxides, and their presence gives mafic rock its characteristic dark colour. Felsic rocks are light in color and are composed of feldspars and silicates.
What acreage or percentage of the continental us is covered by ultramaficmafic rocks. Pdf the main mafic dyke swarms of the sao francisco craton range in age from late archean to the early neoproterozoic, and record extensional and. Common mafic rocks include basalt, diabase and gabbro. Pdf intrusive rocks in the longwood range represent a component of the permian brook street terrane. Please note that some geologists with questionable motives switch the order of the magnesium and iron and come up with the term femag. 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. Includes the monument dike swarm of northwestern grant county or061, the chief.
The most common felsic rock is granite, but others include quartz, muscovite, orthoclase, and the. Pdf the sapat maficultramafic complex, kohistan arc, north. Isotopic evidence suggests that the primary source of the. Ultramafic rocks comprised of forty to one hundred percent percent olivine. In terms of chemistry, mafic rocks are on the other side of the rock spectrum from the socalled felsic rocks. 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. Mafic rock, in geology, igneous rock that is dominated by the silicates pyroxene, amphibole, olivine, and mica.
All structured data from the file and property namespaces is available under the creative commons cc0 license. Relating to or containing a group of darkcolored silicate minerals, composed chiefly of magnesium and iron, that occur in igneous rocks, including. In terms of chemistry, felsic rocks are on the other side of the rock spectrum from the mafic rocks. Mafic volcanic rocks are melanocratic to mesocratic igneous rock which crystallized from a basaltic magma within the oceanic and continental. Mafic and ultramafic xenoliths from volcanic rocks of the. Choose the best possible answer to the following questions about key concept 3 compositions of igneous rocks and their meaning. Pdf the sapat maficultramafic complex, kohistan arc. 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. 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. How to classify igneous rocks into ultramafic, 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. The derivation of the term is ma for magnesium and fic for iron from ferric. F coarsegrained intrusives are the least permeable and likely to resist metamorphic changes. Mafic simple english wikipedia, the free encyclopedia.
Hopkins 1914 was the first to describe mafic rocks in eastcentral georgia as a belt of hornblende gneiss and gabbrodiorite which extends from monroe county northeastward to elbert county. Identify igneous rockforming minerals based on their optical properties demonstrate the operation of the petrographic microscope in plane and crossed polarized light. Chemical analyses of the most abundant components in rocks usually are presented as oxides of the elements. A rock can be composed of only one type of mineral. Mafic is a term used by geologists to describe igneous rocks and minerals. Endnote needs a tool to run to shorten all the pdf and pdf folder names for existing libraries.
Petrogeochemistry, genesis and economic aspects of mafic. C1 rocks and magmas a rock is defined as a consolidated mixture of minerals. Mafic minerals are generally dark in colour usually green, brown or black. Perley introducfion mafic and ultramafic rocks which have been metamor phosed to various degrees, are relatively common throughout the appalachian blue ridge and piedmont provinces figure 1. Therefore, rocks are divided into ultramafic, mafic, intermediate, and felsic. The mesoproterozioc 1600 to ma is repre sented by the namaqua metamorphic complex in the south, which comprises granitic gneisses, metasediments and felsic to mafic instrusions, and by the volcano sedimentary sinclair supergroup of central namibia, with its associated granites e. Rocks formed from lava are extrusive, or volcanic rocks. 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. Most mafic minerals are dark in color, and common rockforming mafic minerals include olivine, pyroxene, amphibole, and biotite.
Highly heterogeneous late mesozoic lithospheric mantle beneath the north china craton. How are felsic, intermediate and mafic igneous rocks. Chemically speaking, theyre rich in magnesium and iron. Igneous rocks form as molten rock cools and solidifies general characteristics of magma. The most common examples of rocks classified as mafic are gabbro, dolerite, and basalt. The minerals found in these types of deposits and the deposit types themselves are described and discussed individually, mineral resource tracts and areas of interest are. Compositional trend of garnet and feldspar in the mafic rocks from the hongseong area of the gyeonggi massif, south korea. F if water unavailable, mafic igneous rocks will remain largely unaffected, even as associated sediments are completely re equilibrated. Range of spinel compositions in terrestrial mafic and.
Geology 111 b4 rocks and magmas vancouver island university. F hydration of original mafic minerals generally required. Pdf mafic and ultramafic rocks, and platinum mineralisation. Felsic simple english wikipedia, the free encyclopedia. Felsic, intermediate and mafic igneous rocks differ in their mineral composition. Medlin and hurst 1967 examined the greene county area and mapped amphibo lite with quartz megacrysts metagabbro. Part or all of this report is presented in portable document format pdf. 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.
Igneous rocks form from cooling and crystallization of molten rock magma. Now we will examine some mafic and intermediate plutonic rocks under the microscope. The complex is similar in composition to part of the mafic and ultramafic rock complex at iron. Mafic rocks have between 45 and 55% of silica, whereas felsic rocks have over 65% of silica, the highest of all types. This lesson will examine the definition of this term and how to relates to earth processes. The term roughly corresponds to the older basic rock class. Highly heterogeneous late mesozoic lithospheric mantle. Contain variable but greater than 10% of both ortho and clinopyroxene, and accessory phases. Igneous rocks form the framework for the earths crust. 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. Since new minerals are created during metamorphism, the end product metamorphic. Common rockforming mafic minerals include olivine, pyroxene, amphibole, biotite and other micas, augite and the calcium. Geological survey editorial standards or with the north american stratigraphic code. Volumetrically small ultramafic layers occur plagioclase wehrlite, and thin veins of felsic rocks ranging from quartz diorite to trondhjemite.
Igneous rocks and processes revised on 102011 page 3 of 10 reaction series contains all of the common ironforming ferromagnesian minerals. This page was last edited on 25 december 2019, at 03. Mafic rocks are darker and are composed of magnesium and iron. Reserves were estimated in 1950 to be 840 t assaying 42. Mafic lava, before cooling, has a lower viscosity than felsic lava due to its lower silica content. In other words, if the rock it intrudes into is in horizontal layers, a dyke would cut the layers. Intermediate rocks are composed of the minerals amphibole and feldspar and contain a combination of light and dark minerals. Mafic and ultramafic xenoliths from volcanic rocks of the western united states. Most of these rocks are gray though mafic rocks are also found in brown, green, and even black colors. Publications on spinels particularly chromites have routinely used compositional fields based on the spinel prism to compare populations of analyses. In practice, this means that the average dimension of the crystals is less than 1 millimeter. Mafic rocks that constitute the igneous oceanic crust are created at midocean ridge seafloor spreading centers as a byproduct of partial melt from upwelling. Mafic magmas are usually produced at spreading centers, and represent material which is newly differentiated from the upper mantle. Greenishgray to dusky green, fine to mediumgrained, massive to amygdaloidal metabasalt with darkgray to white, mediumgrained mafic lithic and crystal tuff, and minor purple phyllite and metasedimentary rocks.
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