1 The Renaissance of ( U - Th ) / He Chronometry
نویسندگان
چکیده
Radioactive decay of naturally occurring nuclides provides the basis for the nearly all quantitative temporal constraints on geophysical phenomena, from climate dynamics on scales of 10-10 yr, to planetary differentiation over 10-10 yr. In general there are few geologic problems that are not accessible by radioisotopic chronometers, partly because of the wide range of radioactive parent nuclides (and decay rates), contrasting chemical behaviors of parent and daughter atoms during common geologic processes, and ever-advancing geoanalytical techniques. Despite broad success however, radioisotopic techniques are still difficult to apply to many important geologic phenomena requiring temporal constraints, such as the timing and rates of shallow crustal processes that are critical aspects of geomorphology and neotectonics. Motivated partly by the need for such low-temperature chronometers, the last 10-15 years has seen renewed interest in the chronometric potential of uranium and thorium decay to helium. Unusual characteristics of the (U-Th)/He system, which originally led to its premature diagnosis as unreliable, actually make it uniquely suited for a wide range of many previously inaccessible geologic problems. (U-Th)/He chronometry is based on the α-decay of (production of He nuclei from) uranium and thorium (a generally insignificant amount of He is also produced by Sm→Nd decay). The fundamental age equation for the system is:
منابع مشابه
1 ARHDL Report 1 28 December 2006 Measurement of parent nuclides for ( U - Th ) / He chronometry by solution sector ICP - MS
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