Ar-Ar dating of authigenic K-feldspar

Quantitative modelling of radiogenic argon-loss through subgrain boundary networks

D. F. Mark, S. P. Kelley, M. R. Lee, J. Parnell, S. C. Sherlock, D. J. Brown

Research output: Contribution to journalArticle

25 Citations (Scopus)

Abstract

We have analysed two distinct generations of authigenic K-feldspar in Fucoid Bed sandstones from An-t-Sron and Skiag Bridge, NW Highlands, Scotland, which have experienced post-growth heating to levels in excess of the predicted Ar-closure temperature. Authigenic K-feldspars show microtextural similarities to patch perthites; that is subgrains separated by dislocation-rich boundary networks that potentially act as fast diffusion pathways for radiogenic argon.

The two generations of authigenic K-feldspar in the Fucoid Bed sandstones can be distinguished by different microtextural zones, bulk mineral compositions, fluid-inclusion populations, and inferred temperatures and chemistries of parent fluids. Ar-Ar age data obtained using high-resolution ultraviolet laser ablation, show that the first cementing generation is Ordovician and the second cementing generation is Silurian.

Modelling of Ar diffusion using subgrain size as the effective diffusion dimension and a simplified tectono-thermal thrust model assuming transient heating of the Fucoid Beds is inconsistent with observed data. Removal of heat from the thrust zone through rapid flushing of heated fluids rather than transient heating can be invoked to explain the observed Ar-Ar ages for both generations of cement. Alternatively, Ar-diffusion modelling using overgrowth thickness as the effective diffusion dimension instead of subgrain size also yields models that are consistent with both the Fucoid Bed palaeothermal maxima and determined Ar-Ar age ages for the two generations of K-feldspar cement. Based on this alternate explanation, we propose a theoretical microtextural model that highlights fundamental differences between the microtextures of deuterically formed patch perthites and authigenic K-feldspars, explaining the apparent robustness of authigenic K-feldspar with respect to Ar-retention. (C) 2008 Elsevier Ltd. All rights reserved.

Original languageEnglish
Pages (from-to)2695-2710
Number of pages16
JournalGeochimica et Cosmochimica Acta
Volume72
Issue number11
Early online date8 Apr 2008
DOIs
Publication statusPublished - 1 Jun 2008

Keywords

  • alkali feldspars
  • fluid-flow
  • diffusion profiles
  • brine migration
  • excess argon
  • overgrowths
  • resolution
  • events
  • ion
  • microtextures

Cite this

Ar-Ar dating of authigenic K-feldspar : Quantitative modelling of radiogenic argon-loss through subgrain boundary networks. / Mark, D. F.; Kelley, S. P.; Lee, M. R.; Parnell, J.; Sherlock, S. C.; Brown, D. J.

In: Geochimica et Cosmochimica Acta, Vol. 72, No. 11, 01.06.2008, p. 2695-2710.

Research output: Contribution to journalArticle

Mark, D. F. ; Kelley, S. P. ; Lee, M. R. ; Parnell, J. ; Sherlock, S. C. ; Brown, D. J. / Ar-Ar dating of authigenic K-feldspar : Quantitative modelling of radiogenic argon-loss through subgrain boundary networks. In: Geochimica et Cosmochimica Acta. 2008 ; Vol. 72, No. 11. pp. 2695-2710.
@article{4e6325b9ed554469b6707edb74bc3189,
title = "Ar-Ar dating of authigenic K-feldspar: Quantitative modelling of radiogenic argon-loss through subgrain boundary networks",
abstract = "We have analysed two distinct generations of authigenic K-feldspar in Fucoid Bed sandstones from An-t-Sron and Skiag Bridge, NW Highlands, Scotland, which have experienced post-growth heating to levels in excess of the predicted Ar-closure temperature. Authigenic K-feldspars show microtextural similarities to patch perthites; that is subgrains separated by dislocation-rich boundary networks that potentially act as fast diffusion pathways for radiogenic argon.The two generations of authigenic K-feldspar in the Fucoid Bed sandstones can be distinguished by different microtextural zones, bulk mineral compositions, fluid-inclusion populations, and inferred temperatures and chemistries of parent fluids. Ar-Ar age data obtained using high-resolution ultraviolet laser ablation, show that the first cementing generation is Ordovician and the second cementing generation is Silurian.Modelling of Ar diffusion using subgrain size as the effective diffusion dimension and a simplified tectono-thermal thrust model assuming transient heating of the Fucoid Beds is inconsistent with observed data. Removal of heat from the thrust zone through rapid flushing of heated fluids rather than transient heating can be invoked to explain the observed Ar-Ar ages for both generations of cement. Alternatively, Ar-diffusion modelling using overgrowth thickness as the effective diffusion dimension instead of subgrain size also yields models that are consistent with both the Fucoid Bed palaeothermal maxima and determined Ar-Ar age ages for the two generations of K-feldspar cement. Based on this alternate explanation, we propose a theoretical microtextural model that highlights fundamental differences between the microtextures of deuterically formed patch perthites and authigenic K-feldspars, explaining the apparent robustness of authigenic K-feldspar with respect to Ar-retention. (C) 2008 Elsevier Ltd. All rights reserved.",
keywords = "alkali feldspars, fluid-flow, diffusion profiles, brine migration, excess argon, overgrowths, resolution, events, ion, microtextures",
author = "Mark, {D. F.} and Kelley, {S. P.} and Lee, {M. R.} and J. Parnell and Sherlock, {S. C.} and Brown, {D. J.}",
year = "2008",
month = "6",
day = "1",
doi = "10.1016/j.gca.2008.03.018",
language = "English",
volume = "72",
pages = "2695--2710",
journal = "Geochimica et Cosmochimica Acta",
issn = "0016-7037",
publisher = "PERGAMON-ELSEVIER SCIENCE LTD",
number = "11",

}

TY - JOUR

T1 - Ar-Ar dating of authigenic K-feldspar

T2 - Quantitative modelling of radiogenic argon-loss through subgrain boundary networks

AU - Mark, D. F.

AU - Kelley, S. P.

AU - Lee, M. R.

AU - Parnell, J.

AU - Sherlock, S. C.

AU - Brown, D. J.

PY - 2008/6/1

Y1 - 2008/6/1

N2 - We have analysed two distinct generations of authigenic K-feldspar in Fucoid Bed sandstones from An-t-Sron and Skiag Bridge, NW Highlands, Scotland, which have experienced post-growth heating to levels in excess of the predicted Ar-closure temperature. Authigenic K-feldspars show microtextural similarities to patch perthites; that is subgrains separated by dislocation-rich boundary networks that potentially act as fast diffusion pathways for radiogenic argon.The two generations of authigenic K-feldspar in the Fucoid Bed sandstones can be distinguished by different microtextural zones, bulk mineral compositions, fluid-inclusion populations, and inferred temperatures and chemistries of parent fluids. Ar-Ar age data obtained using high-resolution ultraviolet laser ablation, show that the first cementing generation is Ordovician and the second cementing generation is Silurian.Modelling of Ar diffusion using subgrain size as the effective diffusion dimension and a simplified tectono-thermal thrust model assuming transient heating of the Fucoid Beds is inconsistent with observed data. Removal of heat from the thrust zone through rapid flushing of heated fluids rather than transient heating can be invoked to explain the observed Ar-Ar ages for both generations of cement. Alternatively, Ar-diffusion modelling using overgrowth thickness as the effective diffusion dimension instead of subgrain size also yields models that are consistent with both the Fucoid Bed palaeothermal maxima and determined Ar-Ar age ages for the two generations of K-feldspar cement. Based on this alternate explanation, we propose a theoretical microtextural model that highlights fundamental differences between the microtextures of deuterically formed patch perthites and authigenic K-feldspars, explaining the apparent robustness of authigenic K-feldspar with respect to Ar-retention. (C) 2008 Elsevier Ltd. All rights reserved.

AB - We have analysed two distinct generations of authigenic K-feldspar in Fucoid Bed sandstones from An-t-Sron and Skiag Bridge, NW Highlands, Scotland, which have experienced post-growth heating to levels in excess of the predicted Ar-closure temperature. Authigenic K-feldspars show microtextural similarities to patch perthites; that is subgrains separated by dislocation-rich boundary networks that potentially act as fast diffusion pathways for radiogenic argon.The two generations of authigenic K-feldspar in the Fucoid Bed sandstones can be distinguished by different microtextural zones, bulk mineral compositions, fluid-inclusion populations, and inferred temperatures and chemistries of parent fluids. Ar-Ar age data obtained using high-resolution ultraviolet laser ablation, show that the first cementing generation is Ordovician and the second cementing generation is Silurian.Modelling of Ar diffusion using subgrain size as the effective diffusion dimension and a simplified tectono-thermal thrust model assuming transient heating of the Fucoid Beds is inconsistent with observed data. Removal of heat from the thrust zone through rapid flushing of heated fluids rather than transient heating can be invoked to explain the observed Ar-Ar ages for both generations of cement. Alternatively, Ar-diffusion modelling using overgrowth thickness as the effective diffusion dimension instead of subgrain size also yields models that are consistent with both the Fucoid Bed palaeothermal maxima and determined Ar-Ar age ages for the two generations of K-feldspar cement. Based on this alternate explanation, we propose a theoretical microtextural model that highlights fundamental differences between the microtextures of deuterically formed patch perthites and authigenic K-feldspars, explaining the apparent robustness of authigenic K-feldspar with respect to Ar-retention. (C) 2008 Elsevier Ltd. All rights reserved.

KW - alkali feldspars

KW - fluid-flow

KW - diffusion profiles

KW - brine migration

KW - excess argon

KW - overgrowths

KW - resolution

KW - events

KW - ion

KW - microtextures

U2 - 10.1016/j.gca.2008.03.018

DO - 10.1016/j.gca.2008.03.018

M3 - Article

VL - 72

SP - 2695

EP - 2710

JO - Geochimica et Cosmochimica Acta

JF - Geochimica et Cosmochimica Acta

SN - 0016-7037

IS - 11

ER -