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Active Tectonics: Studies in Geophysics
TABLE 13.1 Classification of Methods Applicable to Dating Active Tectonisma
Relative Dating Methods
3. Other Radiologic
4. Simple Process
5. Complex Processes
1. Historical records
5. Uranium series
7. Fission track
8. Uranium trend
9. Thermoluminescence and electron-spin resonance
10. Cosmogenic isotopes other than carbon-14 (10Be,36Cl, 26Al, and others)
11. Amino-acid racemization
12. Obsidian hydration
13. Tephra hydration
15. Soil development
16. Rock and mineral weathering
17. Progressive landform modification
18. Deposition rate
19. Geomorphic position and incision rate
20. Deformation rate
24. Fossils and artifacts
25. Stable isotopes
26. Tektites and microtektites
aAll methods listed are briefly described in Table 13.2. Methods given in italics are discussed in the text.
eruption or a paleomagnetic reversal, precise age control can be obtained.
A dating technique, whether it be primarily a numerical, relative-dating, or correlation method, may be converted to the other two categories of methods (Table 13.1). For example, the relative-dating methods of amino-acid racemization or soil development can also serve either as local correlation techniques or, if calibrated by numerical dating, as numerical techniques.
Table 13.2 briefly summarizes 26 different dating methods noting their general applicability to studies of active tectonism, the age range of each method and the optimum accuracy within parts of this age range, and the basis of the method and the key problems in its use. The six columns (Table 13.1) are discussed in the next six sections. Beyond those given in Table 13.2, the criteria for selecting individual methods for discussion include at least two of the following: (1) the method is particularly applicable to dating active tectonics, (2) the method provides a good illustration of the six general categories (columns of Table 13.1), and (3) the method has complexities or problems that merit discussion.
After this manuscript was completed, two books on Quaternary dating methods became available (Mahaney, 1984; Rutter, 1985). The reader interested in more extensive description and references to the literature may wish to consult these books.
Annual methods (Table 13.1, column 1), generally accurate to the nearest year, provide the most precise dating of active tectonism. But excepting varve chronology, annual methods span too short a time interval to assess active tectonism, particularly in the western hemisphere. Only limited use has been made of dendrochronology and varve chronology.
In the western hemisphere, historical records of faulting are restricted to about 200 yr (Bonilla, 1967). Based on the long historical records of seismicity from China (3000 yr) and Japan and the Middle East (2000 yr), Allen (1975, p. 1041) concluded that historical seismicity there shows “surprisingly large long-term temporal and spatial variations. The very short historical record in North America should, therefore, be used with extreme caution in estimating possible future seismic activity. The geologic history of late Quaternary faulting is the most promising source of statistics on frequency and location of large shocks.”
Because radiometric methods (Table 13.1, column 2) yield accurate numerical ages, samples for such dating are searched for in geologic studies of active tectonism. In many cases datable materials cannot be found. Additionally, radiometric methods may be subject to major errors and should be evaluated in their geologic context by other methods that, although not as precise, will normally be a valid indicator of the general age.
Carbon-14 dating is generally the most precise and applicable numerical method for dating prehistoric faulting. Indeed, the chronology of the late Quaternary and particularly the Holocene (past 10 ka) is based on this method (for review, see Grootes, 1983). The analytical uncertainty is generally less than a few percent.
Two applications of carbon-14 dating to active tec-