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Paleomagnetic Investigations was concentrated at Stonington (UK station), Horse- shoe, and Porquoi Pas Islands; Adelaide Station in (UK); Cone Island off Adelaide Island; Argentine Islands Station (UK); Palmer Station (U.S.) on LEROY SCHARON ; Almirante Brown (); De- Department of Earth Sciences ception, Livingston, Half Moon, Bellingauzen Station Washington University (St. Louis) (U.S.S.R.), and Signy Island. Analysis of the data accumulated from the core A paleomagnetic program begun in 1966-1967 as drilled in Marie Byrd Land is confirming the concept part of the three-year concentrated geological inves- that Antarctica consists of three separate geological tigation of Marie Byrd Land has been augmented by units: (1) —probably moved from additional work in East Antarctica (1967-1969) and the Indian Ocean; (2) —a con- the Antarctic Peninsula (1970). The program still tinuation of the Andes Mountains orogeny; and maintains the original objective of determining large- (3) . Charles Scharnberger of the scale tectonic movements in Antarctica as related to Washington University rock magnetic laboratory will the Gondwanaland breakup and movement of the present data at the SCAR/JUGS Symposium on present continental masses. Antarctic and Solid Earth Geophysics in From November 1967 to February 1969, as part Oslo indicating that a block consisting of West Ant- of the exchange-scientist program with the 13th Sov- arctica and Nev; Zealand separated from Gondwana- iet Antarctic Expedition, oriented rock specimens land during a pre-Cretaceous episode of sea-floor were drilled for paleomagnetic work on Fildes Penin- spreading (Fig. 1). Later, by the initiation of spread- sula of King George Island during the construction ing on the Albatross Cordillera, this block was broken, of the Soviet Unions Bellingauzen Station, and at its causing West Antarctica and New Zealand to drift stations Moiodezhnaya and Mirnyy in East Antarc- to their present positions. tica. In 1970, under the auspices of the exchange sci- entist program with Great Britain, similar drilling of oriented cores was made in many localities in the Antarctic Peninsula. Charnockite masses, making up the Haswell group of islands off the coast of Mirnyy, have yielded satis- Paleomagnetism and . Geochemistry factory paleomagnetic data, but final results depend on Rb/Sr dating. Analysis of Precambrian meta- of igneous Rocks From lies Amsterdam, morphics and selected small areas of fine-grained Kerguelen, and Crozet granite(?) at Molodezhnaya is now in progress. Core drilling of igneous intrusives and extrusives N. D. WATKINS Department of Geology Florida State University

The 1969 paleomagnetic survey of lies Crozet, Kerguelen, and Ile Amsterdam (Fig. 1) was ex- tended during January and February of 1970 by Mr. A. Hajash, at the generous invitation of Ad- ministrator Pierre Rolland of the Territoire des Terres Australes et Antarctiques Françaises, who

90E rovided transport aboard the vessel Gallieni from VIe de la Reunion, helicopter transport on the islands, and all other logistic support. Laboratory examination of the samples taken has provided the following results: 1. All lavas so far collected on Ile de lEst (Cro- zet) and lie Amsterdam are of normal polarity, with the mean virtual geomagnetic pole close to the pres- ent geographic pole. This result is consistent with re-

Figure 1. A Lower Cretaceous reconstruction which places the pole for West Antarctica in a position con- Now at Graduate School of , Narragan- sistent with those for other continents. sett Marine Laboratory, University of Rhode Island.

164 ANTARCTIC JOURNAL

90 30 45 60 75 Gravity Tides at

vP4•7/1i HAGER, P R( SLICHTER, C. L. 20 PEUNION —QQGIQL4RACUUU ?3NI 20 L. B. 4 _ MA R. HOLBROOK and B. V. JACKSON

30 Institute of Geophysics and Planetary Physics University of California, Los Angeles

St.PAUL3 40 / 40 During the period January 1970 to the present, ( two gravity-tide meters have been in almost contin- cl CZETIS t000 uous operation at South Pole, under the supervision P9 L,KERGUELEN of Mr. Erik Syrstad. His monthly reports indicate 50— / 50 that the systems have been operating normally and Mc DONALD HEARD ATLANTIC - INDIAN RIDGE that satisfactory tape recordings are being obtained. Meter #4, which accompanied Syrstad to Pole p Station, provides a duplicate system for Meter #6, 60 & \ oo which continues its recordings from the 1969 season. 30 45 60 75 90 Mercator projection The drift rate of Meter #4 has proved to be unusually Bathy,etIy in Fathoms low—only 1 1/2 microgals per day over periods of several months. ^MID .11AN RIDGE CRESTAL ZONE An unexpected and interesting observation in the 1969 records at Pole is seen in Fig. 1. This figure Figure 1. Map of southern Indian Ocean, showing lo- cations of Crozet, Kerguelen, and lie Amsterdam, and shows the observed long-period tide in comparison major tectonic elements. with the smooth tidal curve representing the theo- retical tide on a symmetrical rigid earth. Riding on this observed long-period tide is a small ripple with striction of the outcrops to the Brunhes geomagnetic a period of 24 hours and amplitude about 1 microgal epoch (t = 0 to 0.69 my.). (1 microgal= 10_c cm/sec). This ripple is seen 2. Potassium-argon age determinations confirm more clearly in the lower trace, from which the long- that a reversed to normal polarity lava sequence on period fortnightly and monthly tides have been re- Ile Possession (Crozet) is the Brunhes/Matuyama moved. No tides of diurnal or semi-diurnal period polarity boundary at t = 0.69 m.y. should exist at Pole on a truly symmetrical earth. 3. A lava sequence from Ile Foch (on the north- A diurnal gravity tide having an approximate central side of Kerguelen) contains a polarity change jugal at Pole, if produced by an asym- and is Lower Oligocene or Eocene, according to pre- amplitude of 1 metrical distribution of the water tide in the southern liminary potassium-argon age determinations. All oceans, implies that this asymmetry is of the order lavas collected from sequences close to the perma- of 1 foot—a significant tidal amplitude. This esti- nent base of Port-aux-Français on Kerguelen are of mate is obtained as follows: Let the excess tidal normal polarity. amplitude be of equilibrium type, thus varying as 4. Geochemical analyses of lava sequences from where is the co-latitude. Let the fraction Ile de lEst (Crozet) reveal oceanites, ankaramites, sin 9 cos 0 0 of the total 360° sector subject to the daily anomalous olivine basalts, and feldsparphyric basalts. All ob- If the Pacific Ocean sector is the pertinent served geochemical trends may be reproduced by tide be a. a might be as large as The direct water subtraction of varying amounts of chromite, olivine, one, /. attraction at Pole due to such a tide within the and low-titanium clinopyroxene from an alkali basalt parent, as the result of fractionation of these co-latitude band 01, 02 is three phases under low-pressure conditions, or as the result of different degrees of partial melting of 02 g =: 2Y2KAJ sin20 cosO (1—cos9) —/2dO mantle material (Gunn et al., in press). D 01 Further field collections are planned, and labora- 02 tory studies of petrology, geochemistry, and paieo- = —KA [1/3 cos 3/20+ 1/5 cos 5/201 (1) magnetism are continuing.

Reference Here Kc/2irpGa=1.O74aX 10 and A is the anom- alous tidal amplitude in cm. An appropriate co-latitude Gunn, B. M., R. Coy-Yll, N. D. Watkins, C. E. Abranson, band for the southern (water) hemisphere is 01 = 20, and J. Nougier. In press. Geochemistry of an oceanite- ankaramite-basalt suite from East Island, Crozet Archi- pelago. Contributions to Mineralogy and Petrology. Bartol Research Foundation, Swarthmore, Pennsylvania.

September—October 1970 165