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Rate of Al-Si ordering in sanidines from an ignimbrite cooling unit

Rate of Al-Si ordering in sanidines from an ignimbrite cooling unit
Rate of Al-Si ordering in sanidines from an ignimbrite cooling unit
X-ray difiraction studies of monoclinic alkali feldspars [016 (AbfAn)27] from a 300-meter-thick ignimbrite indicate that those feldspars in the central portion of the unit are significantly more ordered than those near the margins. The variations in degree of order are indicative of structural states that cover most of the more disordered half of the range between high sanidine and orthoclase. Further Al-Si ordering is believed to have become ineffective at temperatures below approximately 500 c, based upon the lack of significant K-Na unmixing The length of time required for feldspars to order to their observed state can be estimated by calculation of the time required for the ignimbrite to cool from 800 c, the approximate emplacement temperature, to 500 c; this period was found to be a few hundred to 650 years, depending upon the cooling effects of rain water from above and ground water from below.
0003-004X
1208-1221
Scott, R.L.
e52f1c33-a425-4017-8106-d36b08d38b9a
Bachinski, S.W.
8ff43924-3881-4672-b908-8d70c5233316
Nesbitt, R.W.
6a124ad1-4e6d-4407-b92f-592f7fd682e4
Scott, M.R.
465fbbad-9229-4813-801c-0ab721536a6b
Scott, R.L.
e52f1c33-a425-4017-8106-d36b08d38b9a
Bachinski, S.W.
8ff43924-3881-4672-b908-8d70c5233316
Nesbitt, R.W.
6a124ad1-4e6d-4407-b92f-592f7fd682e4
Scott, M.R.
465fbbad-9229-4813-801c-0ab721536a6b

Scott, R.L., Bachinski, S.W., Nesbitt, R.W. and Scott, M.R. (1971) Rate of Al-Si ordering in sanidines from an ignimbrite cooling unit. American Mineralogist, 56, 1208-1221.

Record type: Article

Abstract

X-ray difiraction studies of monoclinic alkali feldspars [016 (AbfAn)27] from a 300-meter-thick ignimbrite indicate that those feldspars in the central portion of the unit are significantly more ordered than those near the margins. The variations in degree of order are indicative of structural states that cover most of the more disordered half of the range between high sanidine and orthoclase. Further Al-Si ordering is believed to have become ineffective at temperatures below approximately 500 c, based upon the lack of significant K-Na unmixing The length of time required for feldspars to order to their observed state can be estimated by calculation of the time required for the ignimbrite to cool from 800 c, the approximate emplacement temperature, to 500 c; this period was found to be a few hundred to 650 years, depending upon the cooling effects of rain water from above and ground water from below.

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Published date: 1971
Organisations: Geochemistry

Identifiers

Local EPrints ID: 361872
URI: https://eprints.soton.ac.uk/id/eprint/361872
ISSN: 0003-004X
PURE UUID: fc4a6301-c0eb-41e1-8b10-fcd149596c9e

Catalogue record

Date deposited: 04 Feb 2014 17:07
Last modified: 18 Jul 2017 02:57

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