摘要:

Fifty three new heat flow measurements together with 16 published data indicate that the heat flow (average of best values equals 1.74 μcal/cm2s) through basins of the southern California borderland is intermediate between heat flows through the Sierra Nevada and the Basin and Range provinces. In general, geothermal gradients in the borderland decrease with depth in the sediments, corresponding to an increase in thermal conductivity of 2–3% per meter. Owing to rapid sedimentation, surface heat fluxes may be locally masked from their steady state values by as much as 30%. Topographic corrections are usually less than 5%. Seasonal bottom water temperature variations are insignificant, but long‐term climatic change in the last 37,000 yr may have reduced the gradient by 2–3%. Anomalous values were found in close proximity to turbidity current channels. The heat flow distribution shows two significant geographic trends. First, heat flows increase systematically southeastward in response to a late Cenozoic southeastward‐migrating triple junction. Second, heat flows increase slightly toward the continent, suggesting that the offshore basins were formed progressively landward. In specific basins the measured values are uniform (standard deviation ≦ 0.1 HFU, where 1 HFU = 1 μcal cm−2s−1), but in other basins, only the corrected values are uniform. In the Santa Cruz Basin the corrected values are dominated by a north‐s

ISSN:0148-0227    

DOI:10.1029/JB080i026p03733

年代:1975

数据来源: WILEY

摘要:

Charpy impact specimens prepared from a piece of the octahedrite Henbury have been tested at 195° and 300°K in a pendulum hammer machine. The energies absorbed during fracture were 5.0 ft lb (6.9×104dyn cm) and 20.0 ft lb (2.8×105dyn cm), respectively. Thus the specimen tested at the lower temperature was almost totally brittle, while that tested at the higher temperature exhibited significant ductility. These results provide preliminary verification of a recent prediction (Johnson and Remo, 1974) that material from octahedrites should exhibit a ductile‐brittle transition, with the transition to brittleness occurring, under impact conditions, at about

ISSN:0148-0227    

DOI:10.1029/JB080i026p03744

年代:1975

数据来源: WILEY

摘要:

An anisotropic yield surface is used to characterize behavior of rocks and soils in the nonlinear regime. Expressions for the stress rate tensor and the rate of change of plastic volume in terms of the strain rate tensor are obtained by means of the associated flow rule. The model leads to a theoretical expression for the amount of dilatancy in terms of common material properties. This theoretical approach is valid for unloading as well as loading behavior and provides a more realistic description of unloading behavior than the isotropic hardening models currently in use.

ISSN:0148-0227    

DOI:10.1029/JB080i026p03749

年代:1975

数据来源: WILEY

摘要:

Studies of magnetic properties of several samples of Singhbhum dolerites from Bihar, India, showed some interesting features. The saturation intensity versus temperature curves indicated a considerable leftover intensity (about 30–60%) beyond a temperature of 675°C. Values of saturation intensity were much higher than those of magnetite. These observations indicated the probable existence of a small fraction of iron in the samples. The iron could have been produced by alteration of titanomagnetite as a result of regional or contact metamorphism of the newer dolerit

ISSN:0148-0227    

DOI:10.1029/JB080i026p03755

年代:1975

数据来源: WILEY

摘要:

Cosmic ray muon‐induced26Al was measured in terrestrial silicate rock by low‐level γγ coincidence spectrometry with improved statistics. A positive result was obtained for the first time. The measured activity of 0.0068 ± 0.0028 dpm26Al/kg SiO2is well reproduced by a theoretical estimate of the production rate at a depth of 5 meters water equivalent underground. The result is discussed with respect to the erosion rate of the geological sample during the last millions of

ISSN:0148-0227    

DOI:10.1029/JB080i026p03757

年代:1975

数据来源: WILEY

摘要:

Chrysoberyl, which is isostructural with olivine, has a low mean atomic weightof 18.2 and a small molar volume of 34.3 cm2/mol. The single‐crystal elastic constants in units of Mbar are (based upon a density of 3.72 g/cm3and crystallographic axesb>c>a)C11= 5.277,C22= 4.387,C33= 4.658,C44= 1.444,C55= 1.458,C66= 1.518,C12= 1.25,C23= 1.28, andC13= 1.11. Calculated aggregate constants are bulk modulusK= 2.40 Mbar, shear modulusG= 1.60 Mbar, compressional velocityVp= 11.0 km/s, and shear velocityVs= 6.56 km/s. The elastic constant values of chrysoberyl do not fit into current velocity‐density systematics of olivine structure compounds, even with an ionic size correction. The measured bulk modulus of Al2BeO4, however, is predicted to within 4% by taking the molar volume average of the bulk moduli of BeO and Al2O3. This method of averaging is successful because beryllium is in tetrahedral coordination and aluminum is in octahedral coordination in both Al2BeO4and the oxides and because the average Be‐O and Al‐O bond lengths in Al2BeO4are close to those in the

ISSN:0148-0227    

DOI:10.1029/JB080i026p03761

年代:1975

数据来源: WILEY

摘要:

A sample assembly has been designed for ultrasonic velocity measurements in rocks and crystals at elevated temperature and pressure. The new assembly can be used without coupling bonds for determiningVpandVs. The assembly permits control of pore pressure with varying confining pressure and temperature for pores connected to the surface of the rock. Either pulse transmission time or pulse interferometric measurements can be made. Transducer delays are determined as a function of pressure and temperature by using theZdirection of single‐crystal quartz as an acoustic standard. We have measured the pressure and temperature derivatives of a compressional wave interference frequency in theZdirection of quartz to 250°C and 4 kbar using the phase comparison technique. At 25°C andP= 1 bar we find thatF0= 20.664 ± 0.0044 MHz, (∂F/∂T)P= −1.579 ± 0.0214 kHz/°C, and (∂F/∂P)T= 0.09729 ± 0.00125 MHz/kbar. ThePandSvelocity data as a function of pressure and temperature to 7 kbar and 300°C are plotted for a Franciscan lawsonite metagraywacke core, illustrating the accuracy of pressure‐temperature‐velocity

ISSN:0148-0227    

DOI:10.1029/JB080i026p03765

年代:1975

数据来源: WILEY

摘要:

Systematic rare earth and minor element concentration variations occur in postglacial tholeiites which were extruded along the axial zone of the Reykjanes ridge. The northward increase in total Fe and Ti is partly responsible for an increase in the peak magnetic intensity of the lava flows between 60°N and 62°45′N. Three pillow lava types can be distinguished magnetically: high‐remanence lavas which coagulated into small pillows, intermediate‐remanence lavas, and low‐remanence lavas which are made up of large pillows. From approximately 62°45′ latitude northward the peak magnetic intensity of the different pillow lava types decreases, despite a continued increase of the magnetic mineral content (as suggested by a further increase in total Fe and Ti). This can be explained by oxidation of the titanomagnetite, due to an increase in the degree of degassing and H2O dissociation of the tholeiites emplaced at a depth less than 400 m. Magnetic anomaly amplitudes over the axial zone of the ridge increase between 60°N and 62°45′N and decrease from the latter latitude northward. The amplitude pattern therefore closely resembles that obtained for the peak intensity variations of the tholeiites. This suggests that the ‘telechemical’ hypothesis may

ISSN:0148-0227    

DOI:10.1029/JB080i026p03769

年代:1975

数据来源: WILEY

摘要:

The effect of pressure on the melting temperature of iron has been measured by passing current through a very fine wire of pure iron held under pressure in a diamond anvil pressure cell. The temperature was measured by optical pyrometry, and the pressure was calculated from the lattice parameters of iron at room temperature after being heat‐treated. On the basis of recent work by Strong et al. on measuring the δ‐γ‐liquid triple point and the initial slope between γ and liquid iron, we have calculated the melting temperature for γ iron to about 200 kbar. A third‐order polynomial equation fitted to our data yields the following equation:Tm= 1718 + 3.85(P− 52) − 1.95×10−2(P− 52)2+ 6.24×10−5(P − 52)3, whereTmis the melting temperature in degrees Celsius andPis the pressure in kilobars. When the linear relationship ofTm‐ΔV/V0proposed by Kraut and Kennedy (1966) was used, the extrapolation of the present data to the inner core‐outer core boundary, 3.3 Mbar, yields temperatures between 3460° and 3870°C if the inner core consis

ISSN:0148-0227    

DOI:10.1029/JB080i026p03777

年代:1975

数据来源: WILEY

摘要:

The effects of variations in fluid pressure in large, thin, horizontal aquifers and reservoirs are analyzed by assuming a condition of no horizontal strain. The results indicate that the difference in induced effective horizontal and vertical stresses, coupled with the initial stresses, determines the stability to induced faulting. Conditions characterized by thrust faulting are found to be the least stable, and those characterized by normal faulting to be the most stable. The stability to induced faulting is shown to decrease with increasing values of the intermediate effective principal stress in regions characterized by normal and wrench faulting. However, this effect is not present in regions characterized by thrust faulting.

ISSN:0148-0227    

DOI:10.1029/JB080i026p03783

年代:1975

数据来源: WILEY