| Reference Type | Journal (article/letter/editorial) |
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| Title | Exsolution and alteration microtextures in alkali feldspar phenocrysts from the Shap granite |
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| Journal | Mineralogical Magazine | ISSN | 0026-461X |
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| Authors | Lee, Martin R. | Author |
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| Waldron, Kim A. | Author |
| Parsons, Ian | Author |
| Year | 1995 (March) | Volume | 59 |
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| Issue | 394 |
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| Publisher | Mineralogical Society |
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| Download URL | https://rruff.info/doclib/MinMag/Volume_59/59-394-63.pdf+ |
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| DOI | doi:10.1180/minmag.1995.59.394.06Search in ResearchGate |
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| Generate Citation Formats |
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| Mindat Ref. ID | 2612 | Long-form Identifier | mindat:1:5:2612:7 |
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| GUID | 0 |
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| Full Reference | Lee, Martin R., Waldron, Kim A., Parsons, Ian (1995) Exsolution and alteration microtextures in alkali feldspar phenocrysts from the Shap granite. Mineralogical Magazine, 59 (394) 63-78 doi:10.1180/minmag.1995.59.394.06 |
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| Plain Text | Lee, Martin R., Waldron, Kim A., Parsons, Ian (1995) Exsolution and alteration microtextures in alkali feldspar phenocrysts from the Shap granite. Mineralogical Magazine, 59 (394) 63-78 doi:10.1180/minmag.1995.59.394.06 |
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| In | (1995, March) Mineralogical Magazine Vol. 59 (394) Mineralogical Society |
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| Abstract/Notes | AbstractAlkali feldspar phenocrysts (bulk composition Or75.0Ab24.6An0.4) in the subsolvus Shap granite comprise a fine-scale mixture of subregular pristine crypto- and micro-perthites with altered, micropore-rich feldspar with irregular microstructures. The regular perthites are strain-controlled intergrowths of Albite and/or Periclinetwinned albite exsolution lamellae within tweed orthoclase. The microperthites formed at ⩽ 590°C by heterogeneous nucleation of thin albite films which coarsened to > 1 µm length. Cryptoperthites developed at < 400°C by homogeneous nucleation of sub-µm long platelets between films. Platelets are coherent, but the coarser microperthite lamellae are semi-coherent, with pairs of misfit dislocations sub-regularly spaced along the albite-orthoclase interface. As much as 30% of any one feldspar crystal is turbid, a result of the formation of numerous µm to sub-µm sized micropores during deuteric alteration. In some areas, deuteric fluids gained access to the interior of feldspar crystals by exploiting semi-coherent film lamellae. Albite was selectively dissolved and micropore-rich irregular microcline was reprecipitated in its place. In other parts of the feldspars deuteric recrystallization completely cross-cuts the pristine microtextures and patch perthites have formed. These are coarse, incoherent to semi-coherent intergrowths of irregular microcline (replacing tweed orthoclase) and Albite-twinned albite. The deuteric reactions occurred at < 400°C; the main driving force for dissolution and reprecipitation was decrease in the elastic strain energy at the coherent interfaces of crypto-and micro-perthite lamellae, and the recrystallization of tweed orthoclase to irregular microcline. |
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