Diabase
Diabase(/ˈdaɪ.əˌbeɪs/), also calleddolerite(/ˈdɒl.əˌraɪt/) ormicrogabbro,[1] is amafic,holocrystalline,subvolcanic rockequivalent tovolcanicbasaltorplutonicgabbro.Diabasedikesandsillsare typically shallow intrusive bodies and often exhibit fine-grained toaphaniticchilled marginswhich may containtachylite(dark mafic glass).
Diabaseis the preferred name in North America, whiledoleriteis the preferred name in the rest of the English-speaking world, where sometimes the namediabaserefers to altered dolerites and basalts. Some geologists prefer to avoid confusion by using the namemicrogabbro.
The namediabasecomes from the Frenchdiabase,and ultimately from the Greekδιάβασις(meaning "act of crossing over, transition" )[2]whereas the namedoleritecomes from the Frenchdolérite,from the Greekdoleros( “deceitful, deceptive” ), because it was easily confused withdiorite.
Petrography
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Diabase normally has a fine but visibletextureofeuhedrallath-shapedplagioclasecrystals(62%) set in a finer matrix ofclinopyroxene,typicallyaugite(20–29%), with minorolivine(3% up to 12% in olivine diabase),magnetite(2%), andilmenite(2%).[3]Accessory and alterationmineralsincludehornblende,biotite,apatite,pyrrhotite,chalcopyrite,serpentine,chlorite,andcalcite.The texture is termeddiabasicand is typical of diabases. This diabasic texture is also termedinterstitial.[4]Thefeldsparis high inanorthite(as opposed toalbite), thecalciumendmemberof the plagioclase anorthite-albite solid solution series, most commonlylabradorite.
Locations
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Diabase is usually found in smaller, relatively shallow intrusive bodies such asdikesandsills.Diabase dikes occur in regions ofcrustal extensionand often occur indike swarmsof hundreds of individual dikes or sills radiating from a singlevolcaniccenter.
ThePalisades Sillwhich makes up theNew Jersey Palisadeson theHudson River,nearNew York City,New York, United States, is an example of a diabase sill. The dike complexes of theBritish Tertiary Volcanic Provinceincludes Skye, Rum, Mull, and Arran of westernScotland,theSlieve Gullionregion ofIreland,and dolerite dike swarms extending across northernEnglandtowards the Midlands, for exampleRowley Rag.Parts of theDeccan Trapsof India, formed at the end of theCretaceous,also include dolerite.[5]It is also abundant in large parts ofCuraçao,an island off the coast ofVenezuela.Another example of diabase dikes has been recognized in theMongoarea within theGuéra MassifofChadin Central Africa.[6]
In theDeath Valleyregion of California,Precambriandiabase intrusions metamorphosed pre-existingdolomiteinto economically importanttalcdeposits.[7]
In the Thuringian-Franconian-Vogtland Slate Mountains of centralGermanythe diabase is entirely ofDevonianage.[8]They form typical domed landscapes, especially in theVogtland.Onegeotouristattraction is theSteinerne RosenearSaalburg,a natural monument, whose present shape is due to the typical weathering of lava pillows.
Gondwanaland and Australia
[edit]Ageological eventknown as theOenpelliDolerite intrusive event occurred about 1,720 million years ago in westernArnhem Land,in theNorthern Territory,[9]forming curved ridges of Oenpelli Dolerite stretching over 30,000 square kilometres (12,000 sq mi).[10]Further west, on the northern coast of Arnhem Land, a "subsurface radial dyke swarm" known asGaliwinkuDolerite, taking its name from theAboriginalname for Elcho Island, occurs on theGove Peninsulaand continues under theArafura Seaand onWessel Islands,including Elcho andMilingimbi Islands.[11]
In theYilgarn CratonofWestern Australia,aProterozoic200-kilometre (120 mi) long dolerite dike, theNorseman-Wiluna greenstone belt[12]is associated with the non-alluvialgoldmining area betweenNorsemanandKalgoorlie,which includes the largest gold mine in Australia,[13]theSuper Pit gold mine.West of the Norseman–Wiluna Belt is theYalgoo-Singleton greenstone belt,where complex dolerite dike swarms obscure the volcaniclastic sediments.[14]Large dolerite sills such as the Golden Mile Dolerite can exhibit coarse-grained texture, and show a large diversity in petrography and geochemistry across the width of the sill.[15]
The vast areas of mafic volcanism/plutonismassociated with theJurassicbreakup of theGondwanasupercontinent in theSouthern Hemisphereinclude many large diabase/dolerite sills and dike swarms. These include theKaroodolerites ofSouth Africa,theFerrar DoleritesofAntarctica,and the largest of these, the most extensive of all dolerite formations worldwide, are found inTasmania.Here, the volume ofmagmawhich intruded into a thin veneer ofPermianandTriassicrocks from multiple feeder sites, over a period of perhaps a million years, may have exceeded 40,000 cubic kilometres.[16]In Tasmania, dolerite dominates much of the landscape, particularly alpine areas, with many examples ofcolumnar jointing.
Early Jurassicactivity resulted in the formation ofdolerite intrusion in ProspectinSydney,[17]andquarryingofbasaltforroadstoneand other building materials has been an important activity there for over 180 years.[18][19]
Use
[edit]Diabase is crushed and used as aconstruction aggregatefor road beds, buildings, railroad beds (rail ballast), and within dams and levees.[20][21]
Diabase can be cut for use asheadstonesand memorials; the base of theMarine Corps War Memorialis made of black diabase "granite" (a commercial term, not actual granite). Diabase can also be cut for use as ornamental stone for countertops, facing stone on buildings, and paving.[21]A form of dolerite, known asbluestone,is one of the materials used in the construction ofStonehenge.[22]
Diabase also serves as local building stone. In Tasmania, where it is one of the most common rocks found,[23]it is used for building, for landscaping and to erectdry-stonefarm walls. In northernCounty Down,Northern Ireland, "dolerite" is used in buildings such asMount Stewarttogether with Scrabo Sandstone as both are quarried at Scrabo Hill.
Balls of diabase were used by the ancient Egyptians as pounding tools for working softer (but still hard) stones.[24]
See also
[edit]References
[edit]- ^ "BGS Rock Classification Scheme - Dolerite (Synonymous with Microgabbro)".British Geological Survey.Retrieved24 August2015.
- ^"diabase".Oxford English Dictionary(Online ed.).Oxford University Press.(Subscription orparticipating institution membershiprequired.)
- ^Klein, Cornelus and Cornelius S. Hurlbut Jr.(1986)Manual of Mineralogy,Wiley, 20th ed., p. 483ISBN0-471-80580-7
- ^Morehouse, W. W. (1959)The Study of Rocks in Thin Section,Harper & Row, p. 160
- ^Continental Flood Basalts (and Layered Intrusions)
- ^Nkouandou, Oumarou Faarouk; Bardintzeff, Jacques-Marie; Mahamat, Oumar; Fagny Mefire, Aminatou; Ganwa, Alembert Alexandre (2017-05-22)."The dolerite dyke swarm of Mongo, Guéra Massif (Chad, Central Africa): Geological setting, petrography and geochemistry".Open Geosciences.9(1): 138–150.Bibcode:2017OGeo....9...12N.doi:10.1515/geo-2017-0012.ISSN2391-5447.
- ^Miller, MB, and Wright, LA. 2007, "Geology of Death Valley National Park (Third Edition)", Kendall Hunt Publishing, p 19.
- ^Henningsen, Dierk; Katzung, Gerhard (2006).Einführung in die Geologie Deutschlands(in German) (7th ed.). Munich: Spektrum Akademischer Verlag. p. 69.ISBN3-8274-1586-1.
- ^Ranford, Cath; Melville, Paul; Bentley, Craig (August 2008)."Wellington Range Project Northern Territory EL 5893 Relinquishment Report"(PDF).Report No.: WR08-02. Cameco Australia Pty Lt.Retrieved5 Oct2020.
- ^"Definition card for: Oenpelli Dolerite".Australian Stratigraphic Units Database.Australian Government. Geoscience Australia.Retrieved5 October2020.
Text was copied from this source, which is available under aAttribution 3.0 Australia (CC BY 3.0 AU)licence.
- ^"Definition card for: Galiwinku Dolerite".Australian Stratigraphic Units Database.Australian Government. Geoscience Australia.Retrieved5 October2020.Text was copied from this source, which is available under aAttribution 3.0 Australia (CC BY 3.0 AU)licence.
- ^Hill R.E.T,Barnes S.J.,Gole M.J., and Dowling S.E., 1990. Physical volcanology of komatiites; A field guide to the komatiites of the Norseman-Wiluna Greenstone Belt, Eastern Goldfields Province, Yilgarn Block, Western Australia., Geological Society of Australia.ISBN0-909869-55-3
- ^O'Connor-Parsons, Tansy; Stanley, Clifford R. (2007). "Downhole lithogeochemical patterns relating to chemostratigraphy and igneous fractionation processes in the Golden Mile dolerite, Western Australia".Geochemistry: Exploration, Environment, Analysis.7(2): 109–27.doi:10.1144/1467-7873/07-132.S2CID140677224.
- ^Wanga Q.; Campbella I. H. (1998). "Geochronology of supracrustal rocks from the Golden Grove area, Murchison Province, Yilgarn Craton, Western Australia".Australian Journal of Earth Sciences.45(4): 571–77.Bibcode:1998AuJES..45..571W.doi:10.1080/08120099808728413.
- ^Travis, G.A.; Woodall, R.; Bartram, G.D. (1971), "The Geology of the Kalgoorlie Goldfield", in Glover, J.E. (ed.),Symposium on Archaean Rocks,Geological Society of Australia (Special Publication 3), pp. 175–190
- ^Leaman, David2002, "The Rock that Makes Tasmania", Leaman Geophysics,ISBN0-9581199-0-2p. 117.
- ^Jones, I., and Verdel, C. (2015). Basalt distribution and volume estimates of Cenozoic volcanism in the Bowen Basin region of eastern Australia: Implications for a waning mantle plume. Australian Journal of Earth Sciences, 62(2), 255–263.
- ^Robert Wallace Johnson (24 November 1989).Intraplate Volcanism: In Eastern Australia and New Zealand.Cambridge University Press. pp. 4–.ISBN978-0-521-38083-6.
- ^Wilshire, H.G. (1967) The Prospect Alkaline Diabase-Picrite Intrusion New South Wales, Australia. Journal of Petrology 8(1) pp.97-163.
- ^Allen, George (Spring 2004)."Clayton Quarry".Mount Diablo Interpretive Association. Archived fromthe originalon 2017-11-16.Retrieved2017-03-30.
- ^ab"Diabase Rock".comparerocks. Archived fromthe originalon 2017-03-31.Retrieved2017-03-30.
- ^John, Brian S.; Jackson Jr., Lionel E. (31 December 2008)."Stonehenge's Mysterious Stones".Earth magazine.American Geosciences Institute.Retrieved8 November2019.
- ^"Tasmanian Viticultural Soils and Geology"(PDF).Tasmania Department of Primary Industries, Water and Environment / University of Tasmania / Tasmanian Institute of Agricultural Research.Retrieved8 November2019.
- ^Kelany, Adel; Harrell, James A.; Brown, V. Max (2010)."Dolerite pounders: Petrology, sources, and use".Lithic Technology.35(2): 127–148.doi:10.1080/01977261.2010.11721087.JSTOR23273763.S2CID127942498.
Dolerite pounders are hand-held stone tools that were widely used in Egypt from the third to late first millennium BCE for quarrying and dressing granite and other hard rocks.
External links
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