Common in chondrite, achondrite, and stonyiron meteorites. Peridotites can also form as cumulates in layered intrusions, peridotites from these layered igneous complexes vary widely, reflecting the relative proportions of pyroxenes, chromite, plagioclase, and amphibole. The chlorite seems to have been first crystallized. Peridotite is derived from the earths mantle, either as solid blocks and fragments, or as crystals accumulated from magmas that formed in the mantle. Geochemistry of serpentinized peridotites from the mariana. Minerals free fulltext petrology of peridotites and nd. Geological magazine by henry woodward 1905 e dunites with partially serpentinized olivine and chromic iron. Both dunites and harzburgites in this area preserve lattice preferred orientations in olivine, with a strong a axis lineation plunging gently to the nnw miller and mogk, 1987. The origin of large mantle dunites is considered critical for models of melt migration in the mantle.
The andaman ophiolite, india, is located at the southeastern end of the tethyan ophiolites. The peridotites and dunites show chemical overlap for chromian spinels fig. The compositions of peridotites from these layered igneous complexes vary widely, reflecting the relative proportions of pyroxenes, chromite, plagioclase, and amphibole. The northern extension of the semail ophiolite in the uae is dominated by tectonic mantle peridotites and gabbros. Dunites are 90% olivine varieties of peridotites, which are ultramafic intrusive igneous rocks. Although chrysotile asbestos may commonly be encountered in all serpentinized ultramafic rock types, optimum development of economically exploitable fiber generally occurs in dunites, peridotites, or harzburgites. The errotobbio et peridotite in the ligurian alps of n italy represents the mantle section of the voltri massif, the largest ophiolite exposure in the european alps. The peridotites comprise harzburgites and dunites with podiform chromitite deposits. Global variations in abyssal peridotite compositions sciencedirect. Problem is that dunite is already one of peridotites.
The day book dunite of western north carolina appears to represent a metamorphosed sliver of mantle rocks, but it has not been serpentinized. Petrological and geochemical investigations of the lijiatun dunites from the sulu ultrahighpressure uhp terrane indicate a complex petrogenetic history involving melt. Pbs socal and kcet are collaborating with kpcc and laist to bring you a daily reporter roundup discussing the latest regional news about covid19. Ultramafic rocks are mainly peridotites, dunites, pyroxenites and gabbros closely associated with metabasic rocks and bif. Phyllosilicateseens 2110 mineralogytulane university prof. In contrast peridotites from the conical seamount define a trend of increasing. They are composed of gabbronorites, olivine norites, gabbroanorthosites with pyroxenites, peridotites, dunites, shristemites, plagioclase pyroxenites, plagioclase peridotites and troctolites. I bought this book for a friend of mine that grew up in san luis obispo, ca.
It is concluded that the twin sisters dunite mass moved and deformed while still hot enough to. It is a common component of oceanic lithosphere, and is derived from the upper mantle. A very limited amount of gabbroic lithologies 1 kg in total were recovered at the scc and ccc, limited to small intrusions within mantle peridotites. A peridotite is an ultramafic rock containing more than 40% olivine mg 2 sio 4. Major and trace element compositions of minerals in the lherzolites suggest their residual origin after lowdegree of partial melting with less flux. He sent me an article that was written in the local newspaper about these people called the dunites that lived in the pismo beach dunes in the 1930s i think. It is noted for its low silica content, and contains very little or no feldspar orthoclase, plagioclase. Diversity among peridotites in the western gneiss region.
Diamonds were found together with chromospinel, moissanite, graphite, zircon, corundum, garnets. The rocks which have been so frequently referred to as the typical. Dunite is an igneous plutonic rock of ultramafic composition with coarsegrained granular or. The cumulative dunites were formed via crystal cumulation from mantle magmas and. Multiple episodes of melting, depletion, and enrichment of. Ultramafic rocks are those containing 18 % mgo and dunites, peridotites and metamorphic rocks talc carbonate and serpentinite. Peridotite is a generic name used for coarsegrained, darkcolored, ultramafic igneous rocks. The large compositional variations in spinels from extremely depleted, megacrystalline harzburgite dunites in the udachnayaeast kimberlite pipe, yakutia, apparently reflect multistage metasomatism. Motivated by observations of reactive dunite channels in ophiolites, models for reactive flow in deformable permeable media have been developed that show that fluid flow along a solubility gradient will lead to flow localization and the development of a coalescing network of highporosity melt channels surrounded by extremely low porosity regions aharonov et al. Magnetic properties of a suite of variably serpentinized peridotites from the dongbo ophiolite, sw. From most reduced to most oxidized, spinel compositions divide into.
The accumulated petrological and geochemical data for dunites suggest that a common process for the formation of dunite is the interaction of olivine. Corundum and the peridotites of western north carolina. Peridotites usually contain olivine as their primary mineral, frequently with other mafic minerals such as pyroxenes and amphiboles. Cao values in the host peridotites are extremely low, probably because of subsolidus effects. Other minerals that coexist with olivine are lowca orthopyroxene opx, highca clinopyroxene cpx, and chromian. The book contains 57 pages of keys lor calculntion 164.
Dunite channels within a harzburgite layer from the horoman. Ocean drilling program leg 125 recovered serpentinized harzburgites and dunites from a total of five sites on the crests and flanks of two serpentinite seamounts, conical seamount in the mariana. The et mantle peridotite was i exhumed from lithospheric mantle depths during lithosphere extension, ii exposed at the seafloor of the jurassic ligurian tethys and iii subducted during closure of the basin, reaching. The oceanic crust is 99% basalt, which is an igneous rock of mafic composition. Garnetbearing peridotites in the western gneiss complex wgc have been classed into two groups based upon bulk composition the mgcr type generally accepted to be derived from subcontinental mantle and the feti type metamorphosed ultramafic parts of layered intrusions into continental crust. A general term for a coarsegrained plutonic rock composed chiefly of olivine with or without other mafic minerals such as pyroxenes, amphiboles, or micas, and containing little or no feldspar.
Independent pt estimates here are consistent with regional diamond stability. The laterite deposits are the product of chemical and physical weathering of dunites and peridotites of komatiitic affinity. Serpentinite is a metamorphic rock, the result of alteration of olivinerich peridotites dunites in the presence of water. The fe isotope variations of the minerals together with petrological features and major elemental compositions, suggest a residual origin for the harzburgites and an accumulation process associated with the dunite. With an extended treatise on crystallography and by edward salisbury dana. Pdf the mantle and crustal evolution of two garnet.
Zlatogorsk, aiyrtau, north kazakhstan region, kazakhstan. Concerning corundum in the basic magne sian rocks, very similar, and in some respects supplementary, hypotheses were deduced by the one from a study of the mines in the peridotites and by the other from the petrology of the corundumbearing amphibolites and anorthosites. The box in the upper right corner indicates the scale of the lithologic section preserved in oman. The preoceanic evolution of the errotobbio peridotite. Minerals free fulltext abyssal peridotite as a component. In the rocks shown below, the greenish material is forsterite olivine magnesiumrich mg,fe 2 sio 4. Among orogenic peridotites, dunites suffer the weakest crustal metasomatism at the slabmantle interface and are the best lithology to trace the origins of orogenic peridotites and their initial geodynamic processes. Veins, dikes, and pods of the uae mantle peridotites. Peridotite dunite peridotite is a very dense, coarsegrained, olivinerich, ultra mafic intrusive rock. Dunite may also form by the accumulation of olivine crystals on the floor of large basaltic or picritic magma chambers. A short chapter on komatiites cornes down on the side. The black, granular part of the rock shown above is chromitite, which forms a band running through greenishcolored serpentinite. The dunites by norman hammond goodreads share book.
Peridotite is an igneous type of rock that is composed primarily of olivine. It is a common constituent of magnesiumrich, silicapoor igneous rocks. Ophiolites, diamonds, and ultrahighpressure minerals. Spinel peridotites from a variety of island arcs have been utilised to calculate the redox state of the mantle wedge above subduction zones. Below you will find example usage of this term as found in modern andor classical literature. The origin and mode of emplacement of alpinetype peridotites and their. Jul 14, 2017 we investigated the upper mantle peridotites of the skenderbeu massif, situated at this transition within the ophiolite, to document the geochemical fingerprint of the inferred tectonic switch. Mantle peridotites harzburgites to dunites are abundant in the ccc, whereas only gabbroic rocks were collected at the ncc.
The dunites was a bohemian community in southern san luis obispo county populated by artists, hermits, mystics, and nature lovers. If the address matches an existing account you will receive an email with instructions to reset your password. Skarns are rocks that originate from contact metamorphism of limestones or dolostones, and show evidence of having exchanged constituents with the intruding magma. Dunite channels within a harzburgite layer from the. Bennett, in earths oldest rocks second edition, 2019.
Talc is an mgrich mineral, and thus soapstones from ultrabasic igneous protoliths, like peridotites, dunites, and pyroxenites, usually by hydrothermal alteration. Page 332 he calls attention to the occurrence of corundum chiefly in chlorite veins and says. Spatial distribution of melt conduits in the mantle. The serpentinite itself contains scattered black chromite crystals. Other minerals that coexist with olivine are lowca orthopyroxene opx, highca clinopyroxene cpx, and chromian spinel always present in very low modal abundance. Mineralogy and geochemistry of peridotites and chromitites in the.
Minerals free fulltext petrology of peridotites and. Abyssal and suprasubduction peridotites in the lajishan. The host alkali basalt is of asthenosphere origin, and. According to the iugs classification le bas and streckeisen, 1991, they are defined as a coarsegrained ultramafic rock type, containing more than 40 % olivine. The peridotites are mostly harzburgite with little lherzolites and contain various intermittent veins, dikes, and pods. Petrology of peridotites and related gabbroic rocks around the. Petrogenesis of dunite xenoliths from koolau volcano, oahu. The mantle and crustal evolution of two garnet peridotite suites from the western gneiss region, norwegian caledonides. Peridotite has a coarse grain and may contain small amounts of other elements, such as spinel, chromite and plagioclase and amphibole. These terms are used to describe the aggregate of mineralsglass within a rock. Sahamas preface and in three short contributions by rittmanns coworkers, the term rittmann norm. Often fine to medium grained more ferich dunites, mineral zoning indicates metasomatism. Rittmann does suggest, however, some probable assemblages for these rocks.
If you got here via a search engine, check out the blog archive at right theres a lot to see. Typical peridotite sample dunite, left and large olivine crystal right. Evaluation of ultramafic deposits in the eastern united states and. Here, we present petrological data on a forearc peridotite suite obtained as xenoliths in an alkali basalt dike 7. Significance of large, refractory dunite bodies in the upper mantle of. The origin of dunite and chromitite association is still a debated topic. Paleoproterozoic ophiolite remnants in the northern margin. The northern group is dominated by harzburgites and less common dunites, with garnetbearing varieties widely distributed throughout. If you want to enlarge an image beyond what the interface allows, use save image as, or drag it the enlarged image to your desktop and enlarge it further with graphics. Characteristic of charnockites and the granulite metamorphic facies, in regionally metamorphosed rocks and metagabbros. Definition of dunites with photos and pictures, translations, sample usage, and additional links for more information.
Peridotite, a coarsegrained, darkcoloured, heavy, intrusive igneous rock that contains at least 10 percent olivine, other iron and magnesiarich minerals generally. Geochemistry of serpentinized peridotites from the mariana forearc conical seamount, odp leg 125. The dunites are formed by focussing of melts into discrete. This blog provides a selection of images mostly photomicrographs of peridotites. Implications for the elemental recycling at subduction zones. The peridot pendant kindle edition by homes, emma j download it once and read it on your kindle device, pc, phones or tablets. Dunite is an igneous plutonic rock of ultramafic composition with coarse grained granular or. Harzburgites and serpentinized dunites are characterized by ushaped rare earth element patterns and low pdgroup platinumgroup elements resembling the geochemical features of suprasubduction peridotites. Lherzolites show typical features of relatively fertile abyssal peridotites, with ironrich olivine, alspinel, and aluminous pyroxene. Peridotite is a dense, coarsegrained igneous rock consisting mostly of the minerals olivine and. Carbonatitic metasomatism in orogenic dunites from. Jan 10, 2018 ophiolites, diamonds, and ultrahighpressure minerals.
Chapter e in mineral deposit models for resource assessment. The following textural terms are commonly used for plutonic rocks. The dongbo peridotites in this study consist of five dunite samples and 28 harzburgite samples. As discussed above, both of these rocks show wholerock and mineral compositions similar to those of typical ophiolitic peridotites which are considered as the fragments of suboceanic lithosphere dilek and furnes, 2011. Cumulate peridotites often have cumulate textures and exhibit preferred crystal orientation. The peridot pendant kindle edition by homes, emma j. Most of these deposits have been examined during various recon naissance surveys on associated minerals such as corun. The preserved dunites may have been thinned, for example, via simple shear, during transposition resulting from corner flow. Formation of podiform dunites in the lycian peridotite nappes agla koycegiz, sw turkey article pdf available in ofioliti 341. I wrote peridotites, pyroxenites but it was expanded to peridotites, dunites and pyroxenites.
Layered peridotites and massive dunites and harzburgites. The relationships between velocity and mineralogy are reported for rocks containing olivine, pyroxene, and serpentine. Use features like bookmarks, note taking and highlighting while reading the peridot pendant. Ultramafic rocks are scattered as lenses and pods throughout the orthogneisses and supracrustal rocks figs. Ultramafic rocks peridotites, dunites, pyroxenites occur at the base of the stillwater and bushveld complexes, and are overlain by a variety of norites, troctolites, gabbros, and anorthosites. Its peridotites consist of spinel harzburgites, dunites and chromitites. The nature of chrysotile asbestos occurrences in southern. New discoveries and concepts on upper mantle petrogenesis.
Multistage evolution of forearc mantle peridotites of. The most dramatic examples of this are the dunite channels that form during reactive melt flow in the shallow upper mantle kelemen et al. Peridotites are the main lithology of the earths upper mantle. Ophiolites commonly host podiform chromite deposits that are associated with dunites within peridotites coleman, 1971. Peridotites and corundum university of chicago press. Changes in the redox regime are reflected in the compositions of different parts of mineral grains. One of these days i might get the chance to read it. Great overview of the mix of eccentric characters who made up this dunelandscape community of individuals.
Petrogenesis of dunitetroctolite from the uraniwa hills will be shown in a separate paper. Magnetic properties of serpentinized peridotites from the dongbo. Shear wave velocities for similar aggregates are 4. Iron isotopic constraints on the origin of peridotite and. We examine petrology and mineralogy of two lherzolites and a completely serpentinized dunite associated with lherzolite from the middle andaman island. Dunites are shown in green, the crust in blue, and melt is presumed to be present throughout the red and yellow region. The archean layered complexes were derived from magma of ultramafic composition in contrast to magmas of tholeiitic parentage that. The mantle peridotites of the lizard complex, southwest england, preserve direct and indirect evidence for several deformation episodes. Pdf formation of podiform dunites in the lycian peridotite.
These rocks generally contain high amounts of fe and trace metals such as cr and ni alexander et al. These data are interpreted as the interaction and channelling of subduction zone melts through a reduced oceanic mantle. Peridotite article about peridotite by the free dictionary. Photomicrographs of peridotites, dunites, chromitite and.
The tectonic evolution of peridotites in the lizard ophiolite complex, southwest england. Textures of plutonic rocks university of washington. Peridotite, a coarsegrained, darkcoloured, heavy, intrusive igneous rock that contains at least 10 percent olivine, other iron and magnesiarich minerals generally pyroxenes, and not more than 10 percent feldspar. Download scientific diagram photomicrographs of peridotites, dunites, chromitite and orthopyroxenite from cost range ophiolites. Refer to the lab handout on volcanic rocks because many of the same terms apply to plutonic rocks, e. Serpentinized peridotites were already sampled at a. The day book dunite of western north carolina appears to. The dominant rock types in the chicheng peridotites are harzburgites and dunites. Its a similar situation if i write vegetables and fruits and it is changed to vegetables, apples and fruits. A new descriptive stratiform chromite deposit model was prepared which will provide a framework for understanding the characteristics of stratiform chromite deposits worldwide.
Over 700 types of igneous rocks have been described, most of them having formed beneath the surface of earths crust. Lateritic nickel mineralization of the yilgarn craton. Most tabular dunites have a nw strike, with steep dips as mentioned above. May 20, 2016 peridotites are the main lithology of the earths upper mantle. Granites and similar rocks, known as metagranitoids, form much of the continental crust. As in the southern group, the peridotites are porphyroclastic, but. Usgs scientific investigations report 20105070e schulte, ruth f.
Compositional heterogeneity and melt transport in mantle. These deposits are coexistent with the blue ridge mountains, and outcrop in a belt about 300 miles long. These cumulate dunites typically occur in thick layers in layered intrusions, associated with cumulate layers of wehrlite, olivine pyroxenite, harzburgite, and even chromitite a. Odp leg 125 recovered serpentinized harzburgites and dunites from three sites on the crests and flanks of the active conical seamount.
685 1140 190 160 1479 1223 521 878 734 863 1199 1334 1398 625 76 58 1178 235 1330 1321 612 121 954 1240 1305 618 1186 274 1226 82 646 1116 1180 845 1225 721 1423 1105