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Isotope dating of Antarctic rocksP. N. Webb a & Guyon Warren aa New Zealand Geological Survey, Department of Scientificand Industrial ResearchPublished online: 09 Feb 2012.

To cite this article: P. N. Webb & Guyon Warren (1965) Isotope dating of Antarcticrocks, New Zealand Journal of Geology and Geophysics, 8:2, 221-230, DOI:10.1080/00288306.1965.10428108

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Dow

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1965] 221

ISOTOPE DATING OF ANTARCTIC ROCKS

A SUMMARY-2

P. N. WEBB and GUYON WARREN

New Zealand Geological Survey, Department of Scientific and Industrial Research

(First submitted for publication, 6 May 1963; as finally revised, 29 July 1964)

ABSTRACT

Details of 141 isotope dates obtained from Antarctic rocks and reported in recent literature are listed. Accompanying each date are details of the rock type analysed, the laboratory method used, the locality at which the sample was collected, the country in which the sample was processed, and a reference to the original publica­tion. Revised ages are listed for 90 determinations summarised in an earlier paper.

Details of 141 potassium-argon, strontium-rubidium, and lead-uranium isotope dates obtained from Antarctic rocks are listed in Table 1, and their geographic distribution shown in Fig. 1. Where geographic coordinates are not given in the original publication, the approximate figures have been taken from other scientific literature or gazetteers.

A comprehensive survey of isotope dating is presented in a monograph published by the New York Academy of Sciences in 1961 and entitled "Geochronology of Rock Systems". This publication embraces three main aspects of geochronology: the methodology of the U /Pb, Sr/Rb, and A/K geochronometers, the geological time scale, and the history of the basement rocks of the continents. Only one paper in this monograph (Starik et al., 1961) deals specifically with isotope dating of Antarctic rocks. The in­formation in this Soviet paper was presented earlier in the Reports of the 21st Session of the International Geological Conference (Starik, Krylov, et al., 1960).

Of the 231 dates summarised in this and an earlier paper (Webb, 1962), 137 originate from Soviet laboratories. The great majority of Soviet results were obtained by A/K analysis of whole rocks. In discussing their results, and the methods employed, Starik et at. (1961, p. 577) comment:

"Age determinations by the K-Ar method on whole rocks rather than on individual minerals may raise doubts that are entirely justified .... It has now been established that the most reliable determinations of absolute age by the K-Ar method are obtained from micas. . . . A number of determinations we have made of the age of Antarctic rocks by the K-Ar method, directly on the rocks themselves and on micas taken from them, indicate the agreement of the results is satisfactory, with the qualification that feldspar rocks give a more recent age, as a rule, than other rocks of the same age, or micaceous rocks. Particularly large discrepancies are observed between micas and feldspars from pegmatites."

N.Z. J. Geol. Geophvs. 8 : 221-30

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228 NZ. JOURNAL OF GEOLOGY AND GEOPHYSICS [MAY

TABLE 2-Revision of Figures in Earlier Summary (Webb, 1962).

This list repeats, in exact original order, the ages tabulated in the earlier summary of published isotope dates (Webb, 1962), and gives, where necessary, revised figures for each date using the same decay constants for K'o and Rb" as those adopted in this paper. Determinations using Pb isotopes have not been altered. Ages from A/K or Sr/Rb ratios for which the decay constant used in the original calculation is not known are repeated as originally published, followed by an asterisk (*).

A serial number is given to each determination.

The revised figures are incorporated with those of Table 1 1n the locality map (Fig. 1).

---~--------

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1 176 176 r375 61 760 777 2 199 199 34 470 j458 62 700 713 3 183 183 1468 63 730 747 4 184 184 L485 64 730 747 5 195 195 35 535 516 65 700 708 6 195 195 36 555 535 66 705 723 7 176 176 37 490 476 67 950 950* 8 189 189 38 1070 1147 68 1120 Sl120 • 9 193 193 39 1270 1312 11120*'

10 400 386 40 20 ~20' 69 1075 f1050* 11 420 405 41 468 468* 11100* 12 450 434 42 509 509* 70 780 741 13 460 443 43 450 458 71 1020 1045 14 390 376 44 430 443 72 660 675 15 400 386 45 440 453 73 720 731 16 460 443 46 455 463 74 1020 1044 17 475 458 47 525 540 75 450 461 18 478 454 48 430 443 76 450 458 19 465 442 49 925 949 77 450 458 20 458 435 50 1070 1099 78 485 458 21 457 434 51 515 523 79 445 453 22 476 452 52 %0 560* 80 170 175 23 481 457 53 915 910* 81 450 461 24 493 468 54 915 920* 82 500 512 25 455 432 55 9451 83 460 463 26 483 459 56 945~ 920* 84 425 434 27 506 481 57 945j -970* 85 445 458 28 471 447 r1190 86 315 318 29 474 450 58 1300 j 1215 87' 305 313 30 525 494 11262 8-g 410 420 31 530 498 L1350 89 400 410 32 510 479 59 950 973 90 520 501 33 500 470 60 940 968

NOTES 'Published figure "about 20 m.y.".

'Sr/Rb.

'A/K. 'Coordinates given as 70 0 32' S, 163 0 15' E by Starik et al. be in the Mirnyy Region (93 0 E) by Starik et al. (1961).

(1959); but stated to

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~ ~

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1965] WEBB AND WARREN - DATING OF ANTARCTIC ROCKS 229

Picciotto and Coppez (1963) review, in French, 15 papers dealing with age determinations on Antarctic rocks. They recalculate all previous Antarctic A 40 /K4D and Sr87/Rb87 dates, using revised decay constants. This has the effect of reducing slightly most of the earlier-published ages.

The present list (Table 1), as originally compiled by Webb, has been revised by Warren to the same standard constants-i.e., all ages from A/K determinations are based on calculations using AeK1D = 5·85 X 10-11 yr-1 (Aldrich and Wetherill, 1958), and ages from Sr/Rb determina­tions use A,8Rb87 = 1·47 X 10-11 yr-1 (Glendenin, 1961). In most cases the revised figure has been taken directly from Picciotto and Coppez (1963). Ages listed for Pb isotope determinations are those originally published.

Table 2, also prepared by Warren, presents revised figures for the ages given in the earlier summary (Webb, 1962), all dates having been given serial numbers (1-90). All determinations from both Tables of this paper are shown diagrammatically on a map of Antarctica (Fig. 1).

Picciotto and Coppez (1963) note that in the Russian literature the same sample may appear in two publications with slightly different ages. They attribute this to the use of different decay constants or different values of argon content.

In this paper the column showing geological period (see Table 1 of Webb, 1962) has been intentionally omitted, owing to the uncertainty of the relation between numerical ages and period divisions and to the uncertainty in the age figures themselves. Kulp (1961) gives a widely accepted scheme showing the absolute ages of geological periods.

REFERENCES

(1)

ALDRICH, L. T.; WETHERILL, G. W. 1958: Geochronology by Radioactive Decay. Ann. Rev. Nuclear Sci. 8: 257-98.

(2)

ANGINO, E. E.; TURNER, M. D.; ZELLER, E. ]. 1962: Reconnaissance Geology of Lower Taylor Valley, Victoria Land, Antarctica. Bull. Geol. Soc. Amer. 73: 1553-62.

(3) BELLAIR, P.; DELBOS, L. 1962: Age absolu de la derniere granitisation en Terre

Adelie. C.R. Acad. Sci. 254 (8): 1465-6.

(4) EVERNDEN, ]. P.; RICHARDS, ]. R. 1962: Potassium·Argon Ages in Eastern Australia.

]. Geol. Soc. Aust. 9 (1): 1-49.

(5)

FORD, A. B.; HUBBARD, H. A.; STERN, T. W. 1963: Lead-Alpha Ages of Zircon in Quartz Monzonite Porphyry, Thiel Mountains, Antarctica-A Preliminary Report. U.S. Geol. Surv. Prof. Pap. 450-E, Article 208: E 105-8.

(6) GLENDENIN, L. E. 1961: Present Status of the Decay Constants. Ann. New York

Acad. Sci. 91 (2): 166-80.

GeDlogy-6

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(7) HALPERN, M. 1962: Potassium-Argon Dating of Plutonic Bodies in Palmer Peninsula

and Southern Chile. Science 138 (3546): 1261. (See also correction note in Science 139 (3560): 1191, 22 March 1963.)

(8) KRYLOV, A. YA.; SlLlN, Yu. I; ATRAsHENoK, L. YA; LOVTSYUS, A. V. 1961: Absolute

Age of Rocks from Mirnyy District in Antarctica. (In Russian.) Geokhimiya 11: 1034-5.

(9) KuLP,]. L. 1961: Geologic Time Scale. Science 133 (3459): 1105-14.

(10) McDoUGALL, I. 1963: Potassium-Argon Age Measurements on Dolerites from Ant­

arctica and South Africa. J. Geophys. Res. 68 (5): 1535-45.

(11) PASTEELS, P.; DEUTSCH, S. 1963: Age Measurements of Antarctic Rocks (Queen Maud

Land). Nature (Lond.) 199 (4897): 996-7.

(12) PEARN, W. c.; ANGINO, E. E.; STEWART, D. 1963: New Isotope Measurements from

the McMurdo Sound Area, Antarctica. Nature (Lond.) 199 (4894): 685.

(13) PICCIOTTO, E.; COPPEZ, A. 1963: Bibliographie des Mesures d'Ages Absolus en

Antarctique. Ann. Soc. Geol. Be/g. 85 (8): 264-308.

(14) STARIK, I. YE,; KRYLOV, A. YA.;. RAVICH, M. G.; SILlN, Yu. I. 1960: The Age of

East Antarctic Rocks. (In Russian.) DoH 21 Int. Geol. Congr. Prob. 3: 149-57.

(15) STARIK, I. YE.; KRYLOV, A. YA.; RAVICH, M. G.; SILlN, Yu. I. 1961: The Absolute

Ages of East Antarctic Rocks. Ann. New York Acad. Sci. 91: 576-82.

(16) STARIK, I. YE.; RAVICH, M. G.; KRYLOV, A. YA.; SILIN, Yu. 1. 1959: On the Absolute

Age of Rocks of the East Antarctic Platform. (In Russian.) Dokl. Akad. Nauk SSSR 126 (1): 144-6.

(17) STARIK, I. YE.; RAVICH, M. G.; KRYLOV, A. YA.; SILlN, Yu. 1.; ATRASHENOK, L. YA.;

LoVTSYUS, A. V. 1960: New D8ta on the Absolute Age of Rocks in Eastern Antarctica. (In Russian.) DoH. Akad. Nauk SSSR 134 (6): 1421-3.

(18) VORONOV, P. S.; KRYLOV, A YA. 1961: Age of Ancient Rocks of Antarctica. (In

Russian.) Inf. Bull Sov. Antant. Exped. 28: 11-15.

(19) WEBB, P. N. 1962: Isotope Dating of Antarctic Rocks: A Summary-l. N.Z. J. Geol.

Geophys. .5 (5): 790·-6.

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