Active hydrothermal metamorphism in the Cerro Prieto geothermal system, Baja California, Mexico: a telescoped low P/T facies series. [Abstract only]

Journal Article · Tue Mar 01 00:00:00 EST 1983 · Geol. Soc. Am., Abstr. Programs; (United States)

OSTI ID:6369160

Schiffman, P ^[1]; Elders, W A; Williams, A E; McDowell, S D; Bird, D K

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1. Univ. of California, Riverside

In the Cerro Prieto geothermal system, carbonate-cemented, quartzo-feldspathic sediments of the Colorado River delta are being actively recrystallized into calc-silicate metamorphic rocks through intense fluid/rock interaction with alkali chloride brine (1.5 x 10/sup 4/ ppM TDS) at temperatures between 200/sup 0/ and 370/sup 0/C, fluid pressures <0.25 Kb, lithostatic pressures <1.0 Kb, and oxygen fugacities close to the QFM buffer. Petrologic investigations of cuttings and core from more than 50 wells in this field reveal a prograde series of calc-silicate mineral zones with index metamorphic minerals: wairakite (wr), epidote (ep), prehnite (pr), and calcic clinopyrosene (cpx). The compositions of these and other key phases: wr (Ca/Ca + Na + K + 0.97), ep (Fe/Fe + Al/sup vi/ = 0.11 to 0.31), pr (Fe/Fe + Al/sup vi/ = 0.01 to 0.28), cps (close to Wo/sub 50/ and Mg/Mg + Fe + Mn = 0.23 to 0.90), actinolite (0.20 Al/sup iv//15 cations and Mg/Mg + Fe + Mn = 0.67 to 0.82), biotite (Mg/Mg + Fe + Mn = 0.58 to 0.87) and microcline (Or/sub 96 to 100/) reflect recrystallization under low fluid pressures, relatively low f/sub O/sub 2//, and varying brine compositions. Divariant mineral assemblages in this system comprise a very low P/T facies series encompassing the clay-carbonate, zeolite, greenschist, and amphibolite facies and reflect equilibrium occurring in response to both increasing temperature and decreasing CO/sub 2/ pressure. Similar facies series, characterized by telescoped devolatization mineral reactions, are becoming increasingly recognized in other active geothermal systems above 300/sup 0/C. However, close analogues in the fossil geologic record are as yet unidentified.

• OSTI ID: 6369160
• Journal Information: Geol. Soc. Am., Abstr. Programs; (United States), Vol. 15:5
• Country of Publication: United States
• Language: English

Related Subjects

15 GEOTHERMAL ENERGY
CERRO PRIETO GEOTHERMAL FIELD
HYDROTHERMAL ALTERATION
BRINES
EPIDOTES
METAMORPHISM
MEXICO
WAIRAKITE
ZEOLITES
ALKALINE EARTH METAL COMPOUNDS
ALUMINIUM COMPOUNDS
ALUMINIUM SILICATES
CALCIUM COMPOUNDS
CALCIUM SILICATES
DEVELOPING COUNTRIES
GEOTHERMAL FIELDS
INORGANIC ION EXCHANGERS
ION EXCHANGE MATERIALS
IRON COMPOUNDS
IRON SILICATES
LATIN AMERICA
MATERIALS
MINERALS
NORTH AMERICA
OXYGEN COMPOUNDS
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
150202* - Geology &amp; Hydrology of Geothermal Systems- Non-USA- (-1989)