（U-TH)/HE DATING-A NEW METHOD OF LOW-TEMPERATURE THERMOCHRONOMETRY
Received date: 2001-06-23
Revised date: 2001-09-25
Online published: 2002-02-01
Recent technical and interpretational advances in (U-Th)/He dating have produced an interest in the low-temperature thermochronometric capabilities of He dating. A wide range of applied studies has confirmed the scientifically reasonable of the method in constraining the tectonics and topographic development from many place of the world. Compared with fission track, K-Ar, Ar-Ar dating methods, the age of (U-Th)/He dating is scientifically reasonable. The basic principle of (U-Th)/He dating is that 238U, 235U and 232Th decay to 4He and although these isotopes are seldom in concentrations above a few hundred ppm. A He age is determined by comparing the accumulated 4He in a mineral with the concentration of the parent elements. Actually the age are measured by the slope of isochrons which is 4He versus ［U+(F×Th)］weighted by the reciprocal of the squared analytical error. After understanding the relative diffusion of He by temperature and size of mineral, the correcting constraint has been carried out. The 3He is much less than 4He and 3He is originally from cosmic there is very few 3He in the surface of the earth.. During the measure the 3He is neglect. Laboratory He diffusion experiments suggest that (U-Th)/He system's closure temperature is lower than other isotopic system ( apatite only yields a closure temperature of 75℃). Suppose the earth surface temperature of 10 ℃ and geothermal gradient of 25 ℃/km, it is equivalent to depths of 1 to 3 km beneath the earth's surface. Thus the system can be applied to investigate some geologic processed in the almost uppermost part of the crust, for example, volcanism, large-scale fault slip and landscape development even petroleum exploration. The concentrations of U, Th, He in sample of several mg are measured by mass spectrometer. Compared with fission track technique the (U-Th)/He method have some advantages of efficiency in science and saving samples and labor. There are still some technical difficulties with (U-Th)/He dating such as it is impossible to identify and take out the U and Th rich mineral inclusions usually zircon in an apatite. These mineral inclusions contribute He but do not contribute U and Th during measuring process. Erroneously high He ages thus result. Although the technique is under improving, it is still a potential and efficient technique on low-temperature thermochronometry and thermal developing progress.
Key words： (U-Th)/He; Dating; Low teperature thermochronometry.
WU Qian-hong , LIU Hou-chang . （U-TH)/HE DATING-A NEW METHOD OF LOW-TEMPERATURE THERMOCHRONOMETRY[J]. Advances in Earth Science, 2002 , 17(1) : 126 -131 . DOI: 10.11867/j.issn.1001-8166.2002.01.0126
［1］ Hurley P M. The helium age method and distrivution and migration of helium in rocks ［A］.In: Faul H ed. Nuclear Geology ［C］. New York: John Wiley & Sons Inc，1954. 301-329.
［2］ Damon P E， Green W D. Investigations of the helium age dating method by stable isotope-dilution technique［A］. In: International Atomic Energy Agency， Radioactive Dating ［C］. Vienna：International Atomic Energy Agency, 1963. 55-71.
［3］ Zeitler P K, Herczeg A L, McDougall I, et al.(U-Th)/He dating of apatite: a potential thermochronometer, ［J］. Geochimica et Cosmochimica Acta,1987, 51:2 865-2 868.
［4］ Wernicke R S, Lippolt H J. Botryoidal hematite from the Schwarzwald (Germany): heterogeneous uranium distributions and their bearing on the helium dating method［J］. Earth and Planetary Letters, 1993, 114: 287-300.
［5］ Ziegler J F. Helium Stopping Powers and Ranges in All Elemental Matter ［M］. New York: Pergamon Press, 1977.
［6］ Farley K A, Wolf R A, Silver L T. The effects of long alpha-stopping distances on (U-Th)/He age ［J］. Geochimica et Cosmochimica Acta, 1996, 60(21):4 223-4 229.
［7］ Wolf R A, Farley K A. Silver L T. Helium diffusion and low-temperature thermochronometry of apatite ［J］. Geochimica et Cosmochimica Acta, 1996, 60(21): 4 231-4 240.
［8］ Reiners P W, Farley K A.Helium diffusion and (U-Th)/He thermochronometry of titanite ［J］. Geochimica et Cosmochimica Acta, 1999，63(22):3 845-3 859.
［9］ Reiners P W, Farley K A. Helium diffusion and (U-Th)/He thermochronometry of zircon［A］. In: Noble W P, O'Sullivan P B, Brown R W, eds. 9th Internatioal Conference on Fission Track Dating and Thermochronology［C］. Lorne: Geological society of Australia , Victoria Australia, 2000, 58:283-284.
［10］ Warnock A C,Zeitler P K, Wolf R A, et al.An evaluation of low-temperature apatite U-Th/He thermochronometry ［J］. Geochimical et Cosmochimica Acta, 1997,61(24):5 371-5 377.
［11］ Stockli D E, Farley K A,Dumitru T A, Intercalibration and Intergration of apatite(U-Th)/He and fission-track thermochronometers on an exhumed extensional falut block,White Mountains, eastern California, USA［A］. In: Noble W P, O'Sullivan P B, Brown R W, ed. 9th Internatioal Conference on Fission Track Dating and Thermochronology［C］. Lorne: Geological society of Australia , Victoria Australia, 2000, 58:305-307.
［12］ Kohn B P, Farley K A, Pillans B. (U-Th)/He and fission track dating of the Pleistocene Rangitawa Tephra,north island, New Zealand:a comparative study［A］. In: Geological society of Australia ed. 9th Internatioal Conference on Fission Track Dating and Thermochronology［C］. Geological society of Australia, Victoria Australia, 2000.207-208.
［13］ Reiners P W, Brady R, Farley K A, et al. Helium and argon thermochronometry of the Gold Butte block, south Virgin Mountains, Nevada［J］. Earth and Planetary Science Letters, 2000, 178: 315-326.
［14］ Lippolt H J, Wernicke R S, Bahr R. Pargenetic specularite and adularia (Elba Italy): concordant (U-Th)-He and K-Ar ages［J］.Earth and Planetary Science Letters, 1995,132: 43-51.
［15］ House M A, Wernicke B P, Farley K A. Dating topography of the Sierra Nevada, California, using apatite (U-Th)/He ages［J］. Nature, 1998, 396(5): 66-69.
［16］ House M A, Wernicke B P, Farley K A, et al. Cenozoic thermal evolution of the central Sierra Nevada, California, from (U-Th)/He thermochronometry［J］. Earth and Planetary Science Letters, 1997,151:167-179.
［17］ House M A, Farley K A, Kohn B P. An empirical test of helium diffusion in apatite:borehole data from the Otway basin, Austraia［J］. Earth and Planetary Science Letters, 1999,170: 463-474.
/
| 〈 |
|
〉 |
甘公网安备62010202000687
