R.H. Mariner

Chemical Geothermometers and Their Application to Formation Waters from Sedimentary Basins

Chemical geothermometers, based on the concentration of silica and proportions of sodium, potassium, lithium, calcium, and magnesium in water from hot springs and geothermal wells, have been used successfully to estimate the subsurface temperatures of the reservoir rocks. Modified versions of these geothermometers and a new chemical geothermometer, based on the concentrations of magnesium and lithium, are developed to estimate the subsurface temperatures (30°C to 200°C) in sedimentary basins where water salinities and hydraulic pressures are generally much higher than those in geothermal systems. The new Mg-Li geothermometer, which can be used to estimate subsurface temperatures as high as 350°C for waters from sedimentary basins and geothermal systems, is given by:

Excess nitrogen in selected thermal and mineral springs of the Cascade Range in northern California, Oregon, and Washington: sedimentary or volcanic in origin?

t = \frac{{2200}} {{\log \left( {\frac{{\sqrt {Mg} }}{{Li}}} \right) + 5.47}} - 273,

Magmatic intrusion west of Three Sisters, central Oregon, USA: The perspective from spring geochemistry

where t is temperature (°C) and Mg and Li concentrations are in mg/L.

Geothermometry and water-rock interaction in selected thermal systems in the cascade range and modoc plateau, western United States

In north-central Oregon a large area of near-zero near-surface conductive heat flow occurs in young volcanic rocks of the Cascade Range. Recent advective heat flux measurements and a heat-budget analysis suggest that ground-water circulation sweeps sufficient heat out of areas where rocks younger than 6 Ma (million years ago) are exposed to account for the anomalously high advective and conductive heat discharge measured in older rocks at lower elevations. Earlier workers have proposed that an extensive midcrustal magmatic heat source is responsible for this anomalously high heat flow. Instead, high heat flow in the older rocks may be a relatively shallow phenomenon caused by regional ground-water flow. Any deeper anomaly may be relatively narrow, spatially variable, and essentially confined to the Quaternary (less than 2 Ma) arc. Magmatic intrusion at a rate of 9 to 33 cubic kilometers per kilometer of arc length per million years can account for the total heat flow anomaly. Deep drilling in the areas of high heat flow in the older rocks could indicate which model is more appropriate for the near-surface heat flow data.

Isotope geochemistry of minerals and fluids from Newberry volcano, Oregon

Abstract Anomalous N2/Ar values occur in many thermal springs and mineral springs, some volcanic fumaroles, and at least one acid-sulfate spring of the Cascade Range. Our data show that N2/Ar values are as high as 300 in gas from some of the hot springs, as high as 1650 in gas from some of the mineral springs, and as high as 2400 in gas from the acid-sulfate spring on Mt. Shasta. In contrast, gas discharging from hot springs that contain nitrogen and argon solely of atmospheric origin typically exhibits N2/Ar values of 40–80, depending on the spring temperature. If the excess nitrogen in the thermal and mineral springs is of sedimentary origin then the geothermal potential of the area must be small, but if the nitrogen is of volcanic origin then the geothermal potential must be very large. End-member excess nitrogen (δ15N) is +5.3‰ for the thermal waters of the Oregon Cascades but is only about +1‰ for fumaroles on Mt. Hood and the acid-sulfate spring on Mt. Shasta. Dissolved nitrogen concentrations are highest for thermal springs associated with aquifers between 120 and 140°C. Chloride is the major anion in most of the nitrogen-rich springs of the Cascade Range, and N2/Ar values generally increase as chloride concentrations increase. Chloride and excess nitrogen in the thermal waters of the Oregon Cascades probably originate in an early Tertiary marine formation that has been buried by the late Tertiary and Quaternary lava flows of the High Cascades. The widespread distribution of excess nitrogen that has been generated in low to moderate-temperature sedimentary environments is further proof of the restricted geothermal potential of the Cascade Range.

Thermal waters along the Konocti Bay fault zone, Lake County, California: a re-evaluation

Abstract Temperatures of aquifers feeding thermal springs and wells in Long Valley, California, estimated using silica and Na-K-Ca geothermometers and warm spring mixing models, range from 160/dg to about 220°C. This information was used to construct a diagram showing enthalpy-chloride relations for the various thermal waters in the Long Valley region. The enthalpy-chloride information suggests that a 282 ± 10° C aquifer with water containing about 375 mg chloride per kilogram of water is present somewhere deep in the system. That deep water would be related to ∼ 220°C Casa Diablo water by mixing with cold water, and to Hot Creek water by first boiling with steam loss and then mixing with cold water. Oxygen and deuterium isotopic data are consistent with that interpretation. An aquifer at 282°C with 375 mg/kg chloride implies a convective heat flow in Long Valley of 6.6 × 10 7 cal/s.

A landslide in Tertiary marine shale with superheated fumaroles, Coast Ranges, California

A geochemical investigation of springs near Three Sisters volcanoes was conducted in response to the detection of crustal uplift west of the peaks. Dilute, low-temperature springs near the center of uplift show 3 He/ 4 He ratios

Mantle fluids in the San Andreas fault system, California

7RA (RA is the ratio in air), and transport in total ;16 MW of heat and ;180 g/s of magmatic carbon (as CO2). These anomalous conditions clearly reflect the influence of magma, but they seemingly predate the onset of the present uplift and derive from a previous event. Episodes of intrusion may thus be more common in this area than the age of eruptive vents would imply.