| Reference Type | Journal (article/letter/editorial) |
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| Title | Composition and structural state of coexisting feldspars, Salton Sea geothermal field |
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| Journal | Mineralogical Magazine | ISSN | 0026-461X |
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| Authors | McDowell, S. Douglas | Author |
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| Year | 1986 (March) | Volume | 50 |
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| Issue | 355 |
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| Publisher | Mineralogical Society |
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| Download URL | https://rruff.info/doclib/MinMag/Volume_50/50-355-75.pdf+ |
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| DOI | doi:10.1180/minmag.1986.050.355.11Search in ResearchGate |
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| Generate Citation Formats |
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| Mindat Ref. ID | 3817 | Long-form Identifier | mindat:1:5:3817:5 |
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| GUID | 0 |
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| Full Reference | McDowell, S. Douglas (1986) Composition and structural state of coexisting feldspars, Salton Sea geothermal field. Mineralogical Magazine, 50 (355) 75-84 doi:10.1180/minmag.1986.050.355.11 |
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| Plain Text | McDowell, S. Douglas (1986) Composition and structural state of coexisting feldspars, Salton Sea geothermal field. Mineralogical Magazine, 50 (355) 75-84 doi:10.1180/minmag.1986.050.355.11 |
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| In | (1986, March) Mineralogical Magazine Vol. 50 (355) Mineralogical Society |
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| Abstract/Notes | AbstractActive metamorphism of fine grained sandstone in the c.16000 year old Salton Sea geothermal system has produced a suite of chemically equilibrated coexisting authigenic alkali feldspars and re-equilibrated detrital feldspars in the 250–360°C temperature range. At c.335°C the average compositions, 2 Vs, and (t1o+t1m) and Z ordering parameters of coexisting authigenic feldspars are [Or0.52Ab97.40An2.08, 2Vx = 91.3±4.8, (t1o + t1m) = 0.89±0.05, Z = 0.79±0.09], and [Or94.42 Ab5.10An0.48, 2Vx = 70, (t1o + t1m) = 0.90, Z = 0.81]. At c.360°C authigenic albite becomes more An-rich and less ordered [Or1.21Ab92.83An5.97, 2Vx = 87.5±3.4, (t1o + t1m) = 0.85±0.03, Z = 0.70±0.07] and K-feldspar is no longer stable. Detrital plagioclase (An up to 40%) is preserved metastably to temperatures up to c.190°C in strongly carbonate-cemented sandstone which forms part of a geothermally produced permeability cap. It undergoes rapid alkali exchange at temperatures near 200°C, and by 250°C no plagioclase with An-content over 12% is observed. At > 250°C authigenic and most detrital alkali feldspar compositions are in excellent agreement with the Bachinski and Muller (1971) microcline-low-albite solvus. |
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