World Library  
Flag as Inappropriate
Email this Article

Diabase

Article Id: WHEBN0001050784
Reproduction Date:

Title: Diabase  
Author: World Heritage Encyclopedia
Language: English
Subject: Palisades Sill, Jotnian, Dike (geology), Geology of Tasmania, Ouimet Canyon
Collection: Aphanitic Rocks, Mafic Rocks, Ophitic Rocks, Subvolcanic Rocks
Publisher: World Heritage Encyclopedia
Publication
Date:
 

Diabase

Diabase

Diabase or dolerite or microgabbro[1] is a mafic, holocrystalline, subvolcanic rock equivalent to volcanic basalt or plutonic gabbro. Diabase dikes and sills are typically shallow intrusive bodies and often exhibit fine grained to aphanitic chilled margins which may contain tachylite (dark mafic glass). Diabase is the preferred name in North America, dolerite is the preferred name in most of the rest of the world, where sometimes the name diabase is applied to altered dolerites, though many petrologists prefer the name microgabbro to avoid this confusion.

Contents

  • Petrography 1
  • Locations 2
  • Use 3
  • See also 4
  • References 5
  • External links 6

Petrography

Diabase normally has a fine, but visible texture of euhedral lath-shaped plagioclase crystals (62%) set in a finer matrix of clinopyroxene, typically augite (20–29%), with minor olivine (3% up to 12% in olivine diabase), magnetite (2%), and ilmenite (2%).[2] Accessory and alteration minerals include hornblende, biotite, apatite, pyrrhotite, chalcopyrite, serpentine, chlorite, and calcite. The texture is termed diabasic and is typical of diabases. This diabasic texture is also termed interstitial.[3] The feldspar is high in anorthite (as opposed to albite), the calcium endmember of the plagioclase anorthite-albite solid solution series, most commonly labradorite.

Locations

A diabase dike crosscutting horizontal limestone beds in Arizona
Diabase boulders at Devil's Den on the Gettysburg Battlefield, Pennsylvania, USA.

Diabase is usually found in smaller relatively shallow intrusive bodies such as dikes and sills. Diabase dikes occur in regions of crustal extension and often occur in dike swarms of hundreds of individual dikes or sills radiating from a single volcanic center.

The Palisades Sill which makes up the New Jersey Palisades on the Hudson River, near New York City, is an example of a diabase sill. The dike complexes of the British Tertiary Volcanic Province which includes Skye, Rum, Mull, and Arran of western Scotland, the Slieve Gullion region of Ireland, and extends across northern England contains many examples of dolerite dike swarms, towards the Midlands other examples include Rowley Rag. Parts of the Deccan Traps of India, formed at the end of the Cretaceous also includes dolerite.[4] It is also abundant in large parts of Curaçao, an island off the coast of Venezuela.

In Western Australia a 200 km long dolerite dike, the Norseman–Wiluna Belt[5] is associated with the non-alluvial gold mining area between Norseman and Kalgoolie, which includes the largest gold mine in Australia,[6] the Super Pit gold mine. West of the Norseman–Wiluna Belt is the Yalgoo–Singleton Belt, where complex dolerite dike swarms obscure the volcaniclastic sediments.[7]

The vast areas of mafic volcanism/plutonism associated with the Jurassic breakup of Gondwanaland in the Southern Hemisphere include many large diabase/dolerite sills and dike swarms. These include the Karoo dolerites of South Africa, the Ferrar Dolerites of Antarctica, and the largest of these, indeed the most extensive of all dolerite formations worldwide, are found in Tasmania. Here, the volume of magma which intruded into a thin veneer of Permian and Triassic rocks from multiple feeder sites, over a period of perhaps a million years, may have exceeded 40,000 cubic kilometres.[8] In Tasmania dolerite dominates much of the landscape, particularly alpine areas.

Ring dikes are large, near vertical dikes showing above ground as circular outcrops up to 30 km in diameter, with a depth from hundreds of metres to several kilometres. Thicker dikes are made up of plutonic rocks, rather than hypabyssal and are centred on deep intrusions.

Use

Diabase is used as crushed stone and as ornamental stone. In Tasmania, being one of the most common rocks found, it has been used as a building stone, for landscaping and to erect dry-stone farm walls.

See also

References

  1. ^ "BGS Rock Classification Scheme - Dolerite (Synonymous with Microgabbro)". British Geological Survey. Retrieved 24 August 2015. 
  2. ^ Klein, Cornelus and Cornelius S. Hurlbut, Jr.(1986) Manual of Mineralogy, Wiley, 20th ed., p. 483 ISBN 0-471-80580-7
  3. ^ Morehouse, W. W. (1959) The Study of Rocks in Thin Section, Harper & Row, p. 160
  4. ^ Continental Flood Basalts (and Layered Intrusions)
  5. ^ 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. ISBN 0-909869-55-3
  6. ^ 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): 109–127.  
  7. ^ 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): 571–577.  
  8. ^ Leaman, David 2002, "The Rock that Makes Tasmania", Leaman Geophysics, ISBN 0-9581199-0-2 p. 117

External links

  • Collection of dikes in the Fish River Canyon, Namibia
This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and USA.gov, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for USA.gov and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
 
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
 
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.
 


Copyright © World Library Foundation. All rights reserved. eBooks from Project Gutenberg are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.