Measurements of strong‐field magnetization over the temperature range −196° to 700°C have been made on forty‐eight drill core samples of tholeiitic basalt from Alae and Makaopuhi lava lakes, Kilauea volcano, Hawaii. These samples were originally obtained at temperatures ranging from 50° to 1020°C. Nearly all samples contain abundant hemoilmenite with Curie temperatures in the range −100° to −160°C. Samples quenched from high temperatures (800° to 1000°C) have second Curie temperatures ranging from 150° to 290°C, due to unoxidized titanomagnetite, and samples obtained at lower temperatures (50° to between 400° and 700°C) have second Curie temperatures ranging from 500° to 580°C. This transition from medium to high Curie temperatures occurs between 850° and 300°C, varying from one drill hole to another, and is accompanied by a marked increase in the strong‐field magnetization at room temperature. Oxidation of original titanomagnetite to Ti‐poor titanomagnetite containing ilmenite lamellas is the cause of the increase in Curie temperature. Comparison of the compositions of the oxide minerals with the oxygen fugacity data of Sato and Wright and the equilibrium reaction data of Buddington and Lindsley shows that oxygen fugacity was controlled largely by the buffering action of the oxide minerals; hence titanomagnetite was oxidized, whereas the more abundant hemoilmenite was little changed as the lava cooled. This oxidation occurred at temperatures well below equilibrium, the difference being generally of the order of 100°C but as much as 400°C. We conclude that in some basaltic lavas the magnetic minerals may form through subsolidus reactions at temperatures well below their final Curie temperatures. In such lavas the natural remanent magnetization is a mixture of thermoremanent magnetization and high‐temperature chemical remanent magnetization.

Sixty-two samples from well-established comagmatic granitoid sequences and certain unassigned formations and plutons of the central part of the Sierra Nevada batholith between latitudes 37° and 38° N. have been dated by the isotopic U-Pb method on zircon. The U-Pb ages indicate the following age distribution of the granitoids: (1) The axial part of the batholith is occupied by Cretaceous granitoid sequences that are progressively younger eastward over a 37-m.y. interval extending from about 125 m.y. to about 88 m.y. ago. (2) A single, but extensive, Triassic sequence with an optimum average age of about 210 m.y. is present in the east side of the batholith. (3) Plutons and granitoid sequences of Jurassic age, most of them with U-Pb ages between 186 and 155 m.y., occur in both margins and locally in the interior of the batholith. The distribution of Jurassic ages suggests that prior to the emplacement of the Cretaceous granitoids, Jurassic granitoids were widely distributed across the central Sierra Nevada but were not emplaced in a west-to-east succession as were the Cretaceous granitoids. Few of our ages fall between 155 and 125 m.y. However, a U-Pb age of 144 m.y. has been reported on the Sage Hen Flat pluton in the White Mountains, and U-Pb ages between 134 and 128 m.y. have been reported on remnants of older granitoids farther south in the Sierra Nevada, which are associated with roof pendants and septa. Also, numerous K-Ar ages on hornblende in the range of 152 to 131 m.y. have been reported on samples collected farther north along the west side of the batholith. The distribution of U-Pb ages is consistent with the interpretation that in the central Sierra Nevada, a belt of Cretaceous granitoids trending about N. 20° W. crosses a belt of Jurassic granitoids trending about N. 40° W. However, the U-Pb ages provide little support for the existence of five cyclic intrusive epochs for California and western Nevada. Comparison of the U-Pb ages on zircon with the K-Ar ages on biotite and hornblende shows generally good agreement for the younger granitoids but decreasing agreement for increasingly older granitoids. Most of the K-Ar ages on biotite and many on hornblende from older granitoids appear to have been reduced as a result of reheating by younger plutons. The dispersion of K-Ar ages reflects the complex structural and thermal history of the batholith.

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Thermal conductivity measurements at 35°C under 30 bars uniaxial pressure were made on 61 samples of olivine‐bearing basalt with solidity γ (1 − ф, where ф is porosity) ranging from 2 to 98%.Two series of tests were made, one with air and the other with water in the pores. Conductivity varies with γ, the abundance of olivine phenocrysts, and the nature of the pore fluid. From the lowest to the highest γ, the observed conductivities range from 0.2 to 4.3×10−3 cal/cm s °C for samples with air in the pores and from 2.0 to 5.8×10−3 cal/cm s °C for samples with water in the pores. Differences in vesicle size in samples of the same total porosity do not affect the thermal conductivity. The measured conductivities were compared with values calculated on the basis of 11 theoretical models and combinations using conductivities of air and water and a reasonably well determined conductivity of fully solid basalt. For air‐saturated samples the values calculated by several models compare well with observed values for samples with solidity of <0.9. Samples with high solidity have measured conductivities appreciably less than the conductivity determined for fully solid rock; in olivine‐poor samples the difference is 40%. For water‐saturated samples the measured values also are less than the value for solid rock, 15% less for olivine‐poor samples. We postulate that the difference between observed and calculated conductivities for both air‐ and water‐saturated samples is due to the insulating effect of micropores and thin microfractures that were formed during initial cooling of the volcanic samples; these micropores and microfractures were not completely filled with water during our measurements of water‐saturated samples. In still‐cooling newly formed lava the microfractures will not yet have opened, and the conductivity of the lava may be higher than what would be predicted from our measurements. When empirical correction factors are used to account for the insulating effect of the microfractures and micropores, the conductivity of basalt can be predicted by two models. When the mean of the parallel and series models is used, the conductivity of both air‐ and water‐saturated samples can be predicted within 0.3×10−3 cal/cm s °C from the mineral and pore fluid compositions, conductivities, and proportions. With a quadratic model the values for the square root of conductivity form linear plots against solidity, requiring only the porosity and abundance of olivine phenocrysts of Hawaiian basalts to estimate conductivity within 0.2×10−3 cal/cm s °C.