Composition and structural state of coexisting feldspars, Salton Sea geothermal field

McDowell, S. Douglas

doi:10.1180/minmag.1986.050.355.11

Cited by 23 publications

(17 citation statements)

References 11 publications

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“…permeability distribution, composition of host carbonate), fluid composition (e.g. degree of supersaturation, pH ;Flehmig 1977;Senderov et al 1975Senderov et al , 1992, and possibly also temperature (Bachinski & Mfiller 1971;McDowell 1986). On the basis of available data it is not possible to unambiguously identify the key factor(s) that determined feldspar growth and composition in these carbonate rocks.…”

Section: Discussionmentioning

confidence: 97%

Authigenic potassium feldspar: a tracer for the timing of palaeofluid flow in carbonate rocks, Northern Calcareous Alps, Austria

Spötl

Kunk

Ramseyer

et al. 1998

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Feldspar is a common authigenic constituent in Permian carbonate rocks which occur as tectonically isolated blocks within the evaporitic Haselgebirge m61ange in the Northern Calcareous Alps (NCA). Coexisting with pyrite, anhydrite, (saddle) dolomite, magnesite, fluorite and calcite, K-feldspar and minor albite record an event of regionally extensive interaction of hot brines with carbonate rocks. Detailed petrographic, crystallographic and geochemical studies reveal a variability in crystal size and shape, A1-Si ordering, elemental and stable isotopic compositions of the K-feldspar, which is only partially consistent with the traditional view of authigenic feldspar as a well-ordered, compositionally pure mineral. 4~step-heating measurements of authigenic potassium feldspar from several localities yield two age populations, an older one of 145-154 Ma, and a younger one of c. 90-97 Ma. Most age spectra reflect cooling through the argon retention temperature interval, which was rapid in some localities (as indicated by plateau ages) and slower in others. Rb-Sr isotope data are more difficult to interpret, because in many K-feldspar samples they are controlled largely by Sr-bearing inclusions. The Jurassic 4~dates are interpreted as minimum ages of feldspar growth and hence imply that fluid-rock interaction is likely to be simultaneous with or to slightly predate m61ange formation. Deformation associated with the closure and subduction of the Meliata-Hallstatt ocean south of the NCA during the Upper Jurassic is regarded as the principal geodynamic driving force for both enhanced fluid circulation and m61ange formation. Some localities were reheated beyond the argon retention temperature for microcline during mid-Cretaceous nappe stacking of the NCA, thus obliterating the older signal.The almost ubiquitous presence of basinal fluids, and their complex interaction with sedimentary rocks, is amply documented by a wealth of both direct (e.g. deep crustal drilling) and indirect (e.g. mineralization) observations. Placing precise constraints on the absolute timing of individual reactions between palaeoftuids and the host rock, however, remains a major challenge, particularly in carbonate lithologies. Many studies of diagenesis have relied on isotopic dating of authigenic K-mica, which is a standard method in the study of sandstones, but its use is severely limited in carbonate rocks, because interpretation and integration of these results with paragenetic information is often ambiguous, and because detrital contamination poses a major problem.

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Section: Discussionmentioning

confidence: 97%

Authigenic potassium feldspar: a tracer for the timing of palaeofluid flow in carbonate rocks, Northern Calcareous Alps, Austria

Spötl

Kunk

Ramseyer

et al. 1998

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“…The dissolution of evaporites probably contributed to the concentrated brine of the geothermal fi eld (see below; McKibben et al 1988b). Drill holes to depths of 3.2 km have identifi ed (in the central portion of the geothermal fi eld) an upper sequence of unconsolidated lacustrine claysilt-gravel-evaporite (0.4 km thick), and a lower sequence of consolidated deltaic-lacustrine sandstone-siltstone-shale-evaporite, at depths >1 km the sediments are recrystallized to dense hornfels that are highly fractured (McDowell andElders 1980, 1983;. Sandstone is predominately quartz-feldspar-lithic wackes, with calcite cement and clay matrix.…”

Section: Salton Trough California and Baja Californiamentioning

confidence: 99%

“…1, and State 2-14 drill holes are the basis of a number of studies of hydrothermal metamorphic phase relations, mineralogy and ore genesis in the SSGS (e.g. Skinner et al 1967;Keith et al 1968;Muffl er and White 1969;McDowell andElders 1980, 1983;Bird and Helgeson 1981;Bird and Norton 1981;McKibben and Elders 1985;McDowell and Paces 1985;McDowell 1986;Caruso et al 1988;Cho et al 1988;McKibben et al 1987;Shearer et al 1988;Bird et al 1988a;Charles et al 1988;Enami et al 1992Enami et al , 1993. The delineation of four major metamorphic mineral zones (dolomite-ankerite zone at <190°C, chlorite-calcite zone between 190° and 325°C, biotite zone between 325° and 360°C, and garnet zone at >360°C) was fi rst made by McDowell and Elders (1980) through study of drill cuttings from Well Elmore 1.…”

Section: Salton Trough California and Baja Californiamentioning

confidence: 99%

Epidote in Geothermal Systems

Bird

Spieler

2004

Reviews in Mineralogy and Geochemistry

104

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“…All feldspars are end-member K feldspar in composition, suggesting they are authigenic. Detrital feldspars are heterogeneous (e.g., McDowell, 1986). Anhedral crystals of titanomagnetite were observed in many samples.…”

Section: T E M Images and S T E M Chemical Datamentioning

confidence: 99%

Smectite-Illite Transition in Barbados Accretionary Wedge Sediments: Tem and Aem Evidence for Dissolution/Crystallization at Low Temperature

Buatier

1992

Clays and clay miner.

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Abstract--Sediments from depths to 670 m in the Barbados accretionary complex and transecting the d6collement zone have been studied by transmission and analytical electron microscopy (TEM/AEM). The sediments consist of claystone and mudstone intercalated with layers of volcanic ash. Smectite comprises the bulk of the noncalcareous sediments and forms a continuous matrix enveloping sparse, irregular, large grains of illite, chlorite, kaolinite and mixed-layer illite/chlorite of detrital origin at all depths. The detrital origin ofillite is implied by illite-smectite textural relations, well-ordered 2Mpolytyp-ism, and a muscovite-like composition. K is the dominant interlayer cation in smectite at all depths, in contrast to the Na and Ca that are normally present in similar rocks.Deeper samples associated with the d6collement zone contain small (up to 100 ~ thick) illite packets included within still-dominant subparallel layers of contiguous smectite. AEM analyses of these packets imply illite-like compositions. Selected area electron diffraction (SAED) patterns show that this illite is the 1Md polytype. Packets display step-like terminations like those seen in illite of hydrothermal origin. The data collectively demonstrate that smectite transforms progressively to illite via a dissolution-recrystallization process within a depleting matrix ofsmectite, and not by a mechanism of layer replacement. This illite seems to form at depths as shallow as 500 m and temperatures of 20"--300C, which is in marked contrast to the much higher temperature conditions normally assumed for this transformation. This implies that the high water/rock ratios associated with the d6collement zone are significant in promoting reaction.

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Composition and structural state of coexisting feldspars, Salton Sea geothermal field

Cited by 23 publications

References 11 publications

Authigenic potassium feldspar: a tracer for the timing of palaeofluid flow in carbonate rocks, Northern Calcareous Alps, Austria

Authigenic potassium feldspar: a tracer for the timing of palaeofluid flow in carbonate rocks, Northern Calcareous Alps, Austria

Epidote in Geothermal Systems

Smectite-Illite Transition in Barbados Accretionary Wedge Sediments: Tem and Aem Evidence for Dissolution/Crystallization at Low Temperature

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