Authigenic layer silicate minerals in borehole Elmore 1, Salton Sea Geothermal Field, California, USA

McDowell, S. Douglas; Elders, W. A.

doi:10.1007/bf00371699

Cited by 245 publications

(148 citation statements)

References 30 publications

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“…The first vector corresponds to the muscovite=py-rophyllite substitution, while the second is the Tschermak substitution between muscovite and celadonite. Both substitutions lead toward the muscovite corn= position with increasing temperatures, and closely par= allel trends of hydrothermal systems seen elsewhere (McDowell and Elders, 1980;Bishop and Bird, 1987;Cathelineau and Izquirdo, 1988;Cathelineau, 1988).…”

Section: Illitessupporting

confidence: 66%

“…An implicit assumption is that there is no tetrahedral ordering, the illite is purely dioctahedral, the two octahedral units in chlorite are equivalent, and there is no ordering on octahedral sites. End member activities were calculated from chemical composition ofchlorite-illite pairs reported by Jahren and Aagaard (this issue) and McDowell and Elders (1980). The results are both given in Table 1 and depicted in Figure 3, The calculated activities exhibit a temperature dependence, but the two data sets define separate trends' 9 The activity of the chlorite components do show opposing temperature dependence, caused mainly by the decreasing octahedral Mg occupancy with increasing temperature.…”

Section: End Member Activities and Reaction Quotientmentioning

confidence: 96%

“…Activities of end members of chlorite and illite calculated by assuming ideal mixing on homological sites. Source of chemical data: Jahren and Aagaard (this issue) and McDowell and Elders (1980).…”

Section: End Member Activities and Reaction Quotientmentioning

confidence: 99%

“…We have followed the estimation procedures of Helgeson et al (1978), where the enthalpy of the Tschermak substitution reaction in various mineral groups is assumed TEMPERATURE (*C) Figure 4. Coupled Tschermak substitution in chlorite-illite pairs from arenites (Jahren and Aagaard, this issue) and bydr 9 feldspathic sandstones from the Salton Sea area (McDowell and Elders, 1980). The symbols correspond to calculated reaction quotients of reaction (7) while the heavy line denotes the equilibrium constant for the same reaction along an average North Sea gradient.…”

Section: Equilibrium Calculationsmentioning

confidence: 99%

“…A number of recent studies have attempted to establish the compositional variations found in these minerals as a function of pressure and temperature (McDowell and Elders, 1980;Curtis et al, 1985;Cathelineau and Neiva, 1985;Bishop and Bird, 1987;Cathelineau and Izquirdo, 1988;Cathelineau, 1988;Velde and Medhioub, 1988;Jahren and Aagaard, 1989;Jahren, 1991;Hillier and Velde, 1991). This large accumulation of compositional data offers a new base from which to examine chlorite-illite equilibrium relations in this temperature-pressure range.…”

Section: Introductionmentioning

confidence: 99%

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Diagenetic Illite-Chlorite Assemblages in Arenites. II. Thermodynamic Relations

Aagaard

Jahren

1992

Clays and clay miner.

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Abstract--The internal equilibrium status among chlorite-itlite pairs has been evaluated through coupled substitution reactions. Compositional data of chlorites and illites from arenites at present burial temperatures between 90 ~ and 180~ have been used to calculate end member activities and reaction quotients of the combined Tschermak reaction:Muscovite + Clinochlore = MgAl-celadonite + Amesite.The reaction quotient data in the 90 ~ to 180~ temperature range have then been compared with the equilibrium curve for the same reaction, and found to be in reasonable agreement. This indicates that chlorites and illites in these arenites grow at near equilibrium conditions.The data set has also been compared with chlorite-illite pairs from hydrothermally altered arenites of the Salton Sea area. For chlorite-iUite containing assemblages, these data agree well with the diagenetic ones. The introduction of biotite at higher temperatures alters with the iron-magnesium distribution and breaks down the substitution relationship between chlorite and illite.The model predicts an increasing stability of muscovite and clinochlore components with increasing temperature, while celadonite and amesite would be stabilized with increasing pressure. This is consistent with high pressure occurrences of phengite. However, at the low pressure region of diagenesis and hydrothermal alteration, the temperature effect is dominant.

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Section: Illitessupporting

confidence: 66%

Section: End Member Activities and Reaction Quotientmentioning

confidence: 96%

Section: End Member Activities and Reaction Quotientmentioning

confidence: 99%

Section: Equilibrium Calculationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Diagenetic Illite-Chlorite Assemblages in Arenites. II. Thermodynamic Relations

Aagaard

Jahren

1992

Clays and clay miner.

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Seismic imaging of the metamorphism of young sediment into new crystalline crust in the actively rifting Imperial Valley, California

Han

Hole

Stock

et al. 2016

Geochem Geophys Geosyst

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Plate-boundary rifting between transform faults is opening the Imperial Valley of southern California and the rift is rapidly filling with sediment from the Colorado River. Three 65-90 km long seismic refraction profiles across and along the valley, acquired as part of the 2011 Salton Seismic Imaging Project, were analyzed to constrain upper crustal structure and the transition from sediment to underlying crystalline rock. Both first arrival travel-time tomography and frequency-domain full-waveform inversion were applied to provide P-wave velocity models down to 7 km depth. The valley margins are fault-bounded, beyond which thinner sediment has been deposited on preexisting crystalline rocks. Within the central basin, seismic velocity increases continuously from 1.8 km/s sediment at the surface to >6 km/s crystalline rock with no sharp discontinuity. Borehole data show young sediment is progressively metamorphosed into crystalline rock. The seismic velocity gradient with depth decreases approximately at the 4 km/s contour, which coincides with changes in the porosity and density gradient in borehole core samples. This change occurs at 3 km depth in most of the valley, but at only 1.5 km depth in the Salton Sea geothermal field. We interpret progressive metamorphism caused by high heat flow to be creating new crystalline crust throughout the valley at a rate comparable to the 2 km/Myr sedimentation rate. The newly formed crystalline crust extends to at least 7-8 km depth, and it is shallower and faster where heat flow is higher. Most of the active seismicity occurs within this new crust.

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