40Ar‐39Ar studies of whole rock nakhlites: Evidence for the timing of formation and aqueous alteration on Mars     

Timothy D. Swindle  Eric K. Olson 《Meteoritics & planetary science》2004,39(5):755-766

Abstract— 20–25 mg whole rock samples of the nakhlites Lafayette and Nakhla have been analyzed via the ⁴⁰Ar‐³⁹Ar technique, in part to verify their formation ages, but primarily, in an attempt to determine the timing of aqueous alteration in these martian meteorites. As in previous studies, plateaus in apparent age are observed at about 1300 Ma (1322 ± 10 for Lafayette, 1332 ± 10 and 1323 ± 11 for Nakhla), presumably corresponding to crystallization ages. The plateaus are not entirely flat, perhaps reflecting the effects of recoil during creation of ³⁹Ar in the nuclear irradiation. The first 5–20% of the K‐derived Ar released from all three samples give apparent ages <1300 Ma. Coupled with the fact that chronometric isotopic studies of nakhlites typically show some disturbance, we believe the low temperature pattern represents more recent (than 1300 Ma) formation of martian aqueous alteration products such as iddingsite. No low temperature plateaus are observed. This is consistent with petrographic evidence for multiple formation events, although the lack of low temperature plateaus is far from conclusive. On the other hand, if there was a single time of alteration, we believe that it will be difficult, if not impossible, to determine it using the K‐Ar system.  相似文献   

Combining borehole temperature and meteorologic data to constrain past climate change     

David S. Chapman  Timothy J. Chisholm  Robert N. Harris 《Global and Planetary Change》1992,6(2-4)

Geothermal observations from a suite of boreholes in western Utah, USA, combined with meteorologic data at nearby weather stations are used to test the hypothesis that temperatures in the earths subsurface contain an accurate record of recent climate change. The change in air temperature over the last hundred years successfully predicts detailed subsurface temperature profiles to better than ±0.05°C, indicating that ground temperatures tract air temperatures over long periods and that climate change signals are conducted into, and recorded in, the solid earth by the process of heat conduction. We combine borehole temperature data with meteorologic data from the nearest weather station to determine the time averaged difference between surface ground temperature and surface air temperature for borehole-weather station pairs and to infer the long term mean air temperature prior to the observational record. For our western Utah sites the preobservational mean temperature is close to the average surface air temperature for this century suggesting that up to 0.5°C of warming deduced from the last 100 years of weather station data may be attributed to recovery from a cool period at the turn of the century.  相似文献   

Inertial Waves and the Earth's Outer Core     

K. D. Aldridge 《Geophysical Journal International》1975,42(2):337-345.

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Teleseismic and Earth Noise Monitoring with the Block-Moore Quartz Accelerometer     

Timothy Whorf 《Geophysical Journal International》1972,31(1-3):205-238

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Developing the Gaia Theory. A Response to the Criticisms of Kirchner and Volk     

Timothy M. Lenton  David M. Wilkinson 《Climatic change》2003,58(1-2):1-12

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Spectrophotometry of Saturn and its rings from 60 to 180 microns     

Gary Melnick  Ray W. Russell  Timothy R. Gosnell  Martin Harwit 《Icarus》1983,53(2):310-318

We observed Saturn at far-infrared and submillimeter wavelengths during the Earth's March 1980 passage through the plane of Saturn's rings. Comparison with earlier spectroscopic observations by D. B. Ward [Icarus32, 437–442 (1977)], obtained at a time when the tilt angle of the rings was 21.8°, permits separation of the disk and ring contributions to the flux observed in this wavelength range. We present two main results: (1) The observed emission of the disk between 60 and 180 μm corresponds to a brightness temperature of 104 ± 2°K; (2) the brightness temperature of the rings drops approximately 20°K between 60 and 80 μm. Our data, in conjunction with the data obtained by other observers between 1 μm and 1 mm, permit us to derive an improved estimate for the total Saturnian surface brightness of (4.84 ± 0.32) × 10^?4W cm^?2 corresponding to an effective temperature of 96.1 ± 1.6°K. The ratio of radiated to incident power, P_R/P_I, is (1.46 ± 0.08)/(1 - A), where A is the Bond albedo. For A = 0.337 ± 0.029, P_R/P_I = 2.20 ± 0.15 and Saturn's intrinsic luminosity is L_S = (2.9 ± 0.5) × 10^?10L_⊙.  相似文献   

Association announcements     

E. H. T. Whitten  E. H. Timothy Whitten 《Mathematical Geology》1981,13(3):243-260

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Third William Christian Krumbein Medallist: Frederik Pieter Agterberg     

E. H. Timothy Whitten 《Mathematical Geology》1978,10(6):699-700

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The P-SV inverse problem for a layered elastic medium: what data are required?     

Timothy J. Clarke 《Geophysical Journal International》1984,79(2):565-572

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Spline-surface interpolation, spatial filtering, and trend surfaces for geological mapped variables     

E. H. Timothy Whitten  Maria E. V. Koelling 《Mathematical Geology》1973,5(2):111-126

Spline surfaces are interpolated for top of the Dundee Limestone of the central Michigan Basin, USA. The requirement of gridded data render spline functions inappropriate tools for representing many types of geological mapped data. Comparisons are drawn with maps for the same Michigan data based on trend surfaces and spatial filtering.  相似文献