Geochemistry of tectonically expelled fluids from the northern Coast ranges, Rumsey Hills, California, USA

Journal Article · Fri Apr 01 04:00:00 EST 1994 · Geochimica et Cosmochimica Acta; (United States)

DOI:https://doi.org/10.1016/0016-7037(94)90530-4· OSTI ID:7273162

Davisson, M L ^[1]; Presser, T S ^[2]; Criss, R E ^[3]

---

1. Lawrence Livermore Lab., CA (United States)
2. Geological Survey, Menlo Park, CA (United States)
3. Univ. of California, Davis, CA (United States)

Tectonic compression has created abnormally high pressure on deep basinal fluids causing their expulsion from areally exposed Upper Cretaceous rock along the eastern margin of the California Coast ranges. The fluids emerge as near-neutral, perennial sodium chloride springs at high elevations of a west-vergent fault propagation fold axis. Spring waters range from [approximately]1000 to 27,000 mg/L TDS. The least saline water ([delta][sup 18]O = -7.5%) closely represents local meteoric water that mixes with saline fluid ([delta][sup 18]O = +5.3%) and forms a slope of [approximately]3.5 on a [delta]D vs. [delta][sup 18]O plot. A Na (125 to 8000 mg/L TDS) Cl (150 to 17,000 mg/L) plot shows a linear dilution trend that extends close to, but below, the values for modern seawater. Calcium (75-3000 mg/L) is considerably enriched relative to seawater and forms a nonlinear trend with chloride. In detail, the [open quotes]Na deficit,[close quotes] defined by the difference between the measured Na content and the Na concentration on a hypothetical seawater dilution line, is approximately balanced by the Ca excess, similarly defined by the seawater dilution line. This relationship strongly suggests that the fluid is diluted seawater that is being modified by active albitization of plagioclase at different depths. Simultaneous B and [sup 18]O enrichment of the fluids, accompanied by deuterium depletion, further suggest that the seawater modification is influenced by clay diagenesis. Bicarbonate and SiO[sub 2] concentrations show an inverse correlation with Cl, with most waters being saturated or slightly oversaturated with calcite and quartz at the discharge temperatures.

• OSTI ID: 7273162
• Journal Information: Geochimica et Cosmochimica Acta; (United States), Journal Name: Geochimica et Cosmochimica Acta; (United States) Vol. 58:7; ISSN GCACAK; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
ANORTHOSITES
CHEMISTRY
CLAYS
DIAGENESIS
FLUIDS
GABBROS
GEOCHEMISTRY
HYDROGEN COMPOUNDS
IGNEOUS ROCKS
MODIFICATIONS
ORIGIN
OXYGEN COMPOUNDS
PLUTONIC ROCKS
ROCKS
SEAWATER
TECTONICS
WATER