Mafic simple english wikipedia, the free encyclopedia. These are both made up words used to indicate the chemical composition of silicate minerals, magmas, and igneous rocks mafic is used for silicate minerals, magmas, and rocks which are relatively high in the heavier elements. Mafic inclusions, aggregates, and dikes in granitoid rocks. Mafic 4552% silica igneous rocks are dark colored because they are largely composed of caplagioclase and pyroxene. 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. Basalt is finegrained, whereas gabbro is coarsegrained. Common rockforming mafic minerals include olivine, pyroxene, amphibole, biotite and other micas, augite and the calciumrich plagioclase feldspars. Note that rocks with glassy or pyroclastic textures may be described by the above compositions, but that for these specimens the final rock name must still. A mixture of minerals implies the presence of more than one mineral grain, but not necessarily more than one type of mineral. Which rock most probably formed directly from lava a b. Amonomineralic igneous rock bpolymineralic igneous rock cmonomineralic sedimentary rock dpolymineralic sedimentary rock 2. Mafic is used for silicate minerals, magmas, and rocks which are relatively high in the heavier elements.
Geochemical data from ordovician and silurian mafic rocks in the wilmington complex in delaware, the james run formation in cecil county, maryland, and the wissahickon formation in delaware and pennsylvania were collected in conjunction with preparation of a new geologic map of the delawarepennsylvania piedmont. Igneous rocks that crystallize slowly beneath the earth s surface. Intrusive rocks in the longwood range represent a component of the permian brook street terrane. How to classify igneous rocks into ultramafic, mafic. C1 rocks and magmas a rock is defined as a consolidated mixture of minerals. A good deal of liberty has also been taken in the interpretation of the data so that the whole web page is coherent. Mafic minerals are usually dark in color and have a specific gravity greater than 3. Continental crust is less than 1% of earths mass, so there isnt a lot of felsic material in the earth.
Metamorphism of mafic rocks l clinopyroxene breaks down to a number of mafic minerals, depending on grade. Includes the monument dike swarm of northwestern grant county or061, the chief joseph dike swarm. 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. Three major groups of mafic igneous rocks were identi. The classification scheme for plutonic rocks, including mafic and ultramafic rocks, is included in this weeks lab handout also posted on the web 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. Mafic dikes and sills intrude sediments of the late jurassic early cretaceous. Common mafic rocks include basalt and its coarsegrained intrusive equivalent, gabbro. Orthomagmatic sulphide mineralization was known prior to 1994 in older 1400 ma anorthositic and mafic rocks, notably of the harp lake and michikamau intrusions. Learn vocabulary, terms, and more with flashcards, games, and other study tools.
Basalt is the most common extrusive volcanic igneous rock. In turn, the mafic oceanic crust created felsic continental crust from partial melting of hydrated basalt. Generation of eoarchean continental crust from altered. Besides showing a strong depletion in highly incompatible elements, both mafic and intermediate rocks of the dniesterbug series have deep negative spikes for sr, p, and ti. The minerals found in these types of deposits and the deposit. Mafic rocks have between 45 and 55% of silica, whereas felsic rocks have over 65% of silica, the highest of all types. A rock with majorly dark minerals form mafic rocks but with more fractionation during. 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.
Geochemical data of mafic rocks in delaware piedmont, pa and. Some intrusions are rootless and are invasive into sedimentary sequences. Mafic and ultramafic rocks, and platinum mineralisation. Felsic rocks are mostly feldspar especially kfeldspar, at least 10% quartz, and less than 15% mafic minerals biotite, hornblende. The maficultramafic rocks of the late archaean highgrade metamorphic terrain of bhavani shear zone in the south india were delineated using the tir bands of aster remote sensing data.
Mafic igneous rock found in the proterozoic north shore volcanics 2. Classifying igneous rocks mafic 4552% silica igneous rocks are dark colored because they are largely composed of caplagioclase and pyroxene. 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. Igneous rock identification university of washington. Common mafic rocks include basalt, diabase and gabbro. Some units show evidence for intrusion into wet, unconsolidated sediments, indicating that intrusion was approximately contemporaneous with sedimentation. Lightcolored minerals, including quartz, potassium feldspar orthoclase, and narich plagioclase, are felsic and the igneous rocks made mainly of these lightcolored minerals are called felsic rocks. Pdf intrusive rocks in the longwood range represent a component of the permian brook street terrane. Plank3 abstract geochemical data from ordovician and silurian mafic rocks in the wilmington complex in delaware, the james run. Metamorphism of mafic rocks first evident in the greenschist facies, which correlates with the chlorite and biotite zones of the associated pelitic rocks ftypical minerals include chlorite, albite, actinolite, epidote, quartz, and possibly calcite, biotite, or stilpnomelane fchlorite, actinolite, and epidote impart the green. The querigut maficfelsic rock association comprises two main was under way by 310 ma. Isotopic evidence suggests that the primary source of the. What acreage or percentage of the continental us is covered by ultramaficmafic rocks.
These include the volcanic haib subgroup and vioolsdrif granite suite along the orange. Some of the mafic magma cools in massive magma chambers to form massive gabbros. Igneous rocks, sedimentary rocks and metamorphic rocks. Ultramafic rocks comprised of forty to one hundred percent percent olivine. 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. Tracing the styles of maficfelsic magma interaction. Data from these rocks can be used to interpret ancient volcanic activity. A strong negative anomaly of nbta is characteristic for intermediate rocks of the series, whereas mafic rocks reveal either weak or no such anomalies. Fast gives you small crystals and slow cooling gives you large crystals. Due to the color of the minerals forming them, the rocks are either light or dark. These are both made up words used to indicate the chemical composition of silicate minerals, magmas, and igneous rocks. Ternary classification of felsic to mafic igneous rocks. Bateman abstract analytic data are reported herein for a comprehensively studied suite of samples of mafic inclusions, aggregates or.
Igneous rocks choose the best possible answer to the following questions about key concept 3 compositions of igneous rocks and their meaning. A rock can be composed of only one type of mineral. Space does not permit detailed discussion of pros and cons. Igneous rock textures the crystal size of the rock is related to the speed of the rock cooling. Geochemical data of mafic rocks in delaware piedmont, pa.
Contain variable but greater than 10% of both ortho and clinopyroxene, and accessory phases. Breaking off large blocks of rock remnants of which are called xenoliths melting of surrounding country rock. 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. Mafic and ultramafic rocks are classified on the basis of the modal abundances of olivine, orthopyroxene, clinopyroxene, and plagioclase. These minerals are high in magnesium and ferric oxides, and their presence gives mafic rock its characteristic dark colour. The top diagram is for extrusive rocks and the lower is for intrusive rocks. Thus, igneous rocks which contain mainly of darkcolored minerals will probably be mafic in composition. Rock cycle the series of processes in which rock forms, changes from one type to another, is destroyed, and forms again by geological processes much of the rock in the earths continental crust has. Generation of igneous rocks at divergent plate margins. The minerals found in these types of deposits and the deposit types themselves are described and discussed individually, mineral resource tracts and. In contextgeologylangen terms the difference between ultramafic and mafic is that ultramafic is geology describing igneous rocks that contain magnesium and iron and only a very small amount of silica, such as are found in the earths mantle while mafic is geology describing rocks, such as silicate minerals, magmas, and volcanic and intrusive. Lecture notes petrology earth, atmospheric, and planetary. Represents fertile mantle that has not undergone a melt extraction event.
Rhyolite is an example of a base your answers to questions 3 and 4 on the two tables below and on your knowledge of earth science. Mafic rock is commonly contrasted with felsic rock, in which lightcoloured minerals predominate. Chemical analyses of the most abundant components in rocks usually are presented as oxides of the elements. Igneous rocks and plate tectonics over geologic time these processes first created oceanic crust from ultramafic mantle rocks. Which rock most probably formed directly from lava cooling quickly at earths surface. Petrogenesis of mafic to felsic plutonic rock associations oxford. Through various parts of the spreading process, permeability can be generated in both the intrusive gabbros and extrusive basalts. The lower part of oceanic crust is comprised of gabbro. Textures of plutonic rocks university of washington. Felsic and mafic rocks, division of igneous rocks on the basis of their silica content.
Igneous rocks aphanitic andor vesicular pegmatitic or phaneritic glassy pyroclastic mostly feldspar minerals mostly mafic minerals mostly k spar mostly plagioclase. 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. Mafic and ultramafic rocks, and platinum mineralisation potential, in. We are adding some published abstracts to each data series and this is helped by authors sending us.
Mafic rocks that constitute the igneous oceanic crust are created at midocean ridge seafloor spreading centers as a byproduct of partial melt from upwelling mantle. What acreage or percentage of the continental us is covered by ultramafic mafic rocks. The petrogenesis and tectonic implications of blue ridge. Intermediate rocks are roughly even mixtures of felsic minerals mainly plagioclase and mafic minerals mainly hornblende, pyroxene, andor biotite. Mafic rock is commonly contrasted with felsic rock, in which. Rocks and the rock cycle the rock cycle any of the three major types of rock can be changed into another of the three types.
277 408 314 72 214 1034 1593 1131 140 1176 946 1585 646 888 1322 1509 665 192 810 1593 517 1358 176 1413 902 383 1529 931 1298 713 658 312 430 1119 601 394 1608 1240 1132 332 1451 395 261 311 1088 1150 1156 297 1416