Stover, L. E. and A. D. Partridge. 1973. Tertiary and Late Cretaceous recycled palynomorphs in surficial sediments of the Ross Sea, Antarc- spores and pollen from the Gippsland Basin, southeastern Australia. tica. Marine Geology, 59:187-214. Proceedings of the Royal Society, Victoria, 85(2):237-286. Webb, P. N. and D. M. Harwood. 1987. Late Neogene terrestrial flora of Truswell, E. M. 1983. Recycled Cretaceous and Tertiary pollen and spores Antarctica: Its significance in interpreting Late Cenozoic glacial his- in antarctic marine sediments: a catalogue. Palaeontographica, Abt. B, tory. Antarctic Journal of the U.S., 22(2): 7-11. 186:121-174. Webb, P. N. and D. M. Harwood. 1992. Pliocene fossil Nothofagus (South- Truswell, E. M. 1986. Palynology. InP.J. Barrett (Ed.), Antarctic Cenozoic ern Beech) from Antarctica: Phytogeography, dispersal strategies and history from the MSSTS-1 drillhole, McMurdo Sound. New Zealand survival in high southern latitude glacial-deglacialpaleoenvironments. DSIR Miscellaneous Bulletin, 237:131-134. Proceedings from NATO Science Advanced Institute Series. In J. Alden Truswell, E. M. 1990. Cretaceous and Tertiary vegetation of Antarctica: (Ed.), Forest Development in Cold Climates, Plenum Press. A palynological perspective. In T. N. Taylor and E. L. Taylor (Eds.), Wise, S. W., Jr., J. Breza, D. M. Harwood, and W. Wei. 1991. Paleogene Antarctic paleobiology—Its role in the reconstruction of Gondwana. glacial history of Antarctica. In D. W. Muller, J . A. Mackenzie, and New York: Springer-Verlag, 71-88. H. Weissert (Eds.), Controversies in Modern Geology. London: Aca- Truswell, E. M. and D. J. Drewry. 1984. Distribution and provenance of demic Press, 133-171.

Brittle fault arrays in the Royal Skelton Névé, and in the Cenozoic from about 30 million years ago to the present within the McMurdo Volcanic province. Sys- Society Range, southern tematic mapping of the distribution, geometry, and displacement Victoria Land patterns of brittle fault arrays within the Royal Society Range is being carried out in the present study in order to investigate the structural development of this major transverse step in the Transantarctic Mountains. TERRY WILSON J. During the 1991-1992 season, field studies were carried out in the foothills of the Royal Society Range between Ferrar Glacier Byrd Polar Research Center and Radian Glacier, and in exposures around the margins of the and Blue Glacier (figure 1). The initial field party, including Peter Department of Geological Sciences Braddock, Robert Janosy, Timothy Stepp, and Terry Wilson, was Ohio State University deployed to the ridge north of Garwood Valley on 4 November Columbus, Ohio 43210 1991. Field work was carried out on foot from helicopter-de- ployed base camps at Garwood, Marshall Ridge, Shangri-la, Lake Keyhole, Rücker Ridge, and Bettle Peak. Helicopter-supported The Transantarctic Mountains form the uplifted margin of the day trips were made to the ridge north of Marshall Valley, west antarctic rift system (Fitzgerald et al. 1986; Stern and ten Holiday Peak, Herbertson Glacier, Cathedral Rocks, the Walcott Brink 1989; Behrendt and Cooper 1991), which developed during Glacier area, Hobbs Peak, and Salmon Hill. In mid-December, the the breakup of the Gondwana supercontinent in the Mesozoic party, with mountaineer Mike Roberts, transversed the northern and Cenozoic. Compared to other rift-flank uplifts, the and eastern portions of Blue Glacier by skidoo to investigate Transantarctic Mountains have more dramatic vertical relief and localities throughout that region. Field work was completed on a greater length, comparable to mountain belts formed at conver- 21 December. gent plate boundaries. The structural architecture of the Multiple brittle fault sets are present at all of the field sites Transantarctic Mountains differs from other rift margins in visited; representative data from several localities are presented having a uniform tilt direction and a range-parallel segmenta- in figure 1. The combined data from the five localities show tion into blocks separated by transverse physiographic troughs, considerable scatter in fault plane orientation, but the statistical rather than the typical along-axis segmentation into blocks with contour plot of poles to the fault planes defines five distinct fault alternating tilt direction bounded by morphologically high trans- sets within the region (figure 1B). The parallelism between the verse structures. My previous structural studies in southern dominant fault sets at each locality and prominent local physi- Victoria Land have shown that Cenozoic fault arrays define a ographic features is of particular interest. At Cathedral Rocks regional extension direction that is oriented obliquely to the and Herbertson Glacier, the fault sets parallel the Ferrar Glacier trend of the Transantarctic Mountains, possibly resulting in trend (figure 1), where a major transverse fault has been inferred reactivation and opening of the transverse structures as pull- (Gunn and Warren 1962; Findlay et al. 1984; Fitzgerald 1987). At apart basins and explaining their unusual morphology (Wilson Marshall Ridge and the locality along the western Blue Glacier, 1990, 1992). fault sets parallel the ridge trends. Faults developed on the ridge The most prominent transverse break in the Transantarctic east of Lake Penny (figure 2) have a west-northwest trend parallel Mountains occurs along the southern end of the Royal Society to the major linear trough occupied by Radian Glacier (figure lÀ). Range, where the mountain chain steps westward toward the These relations demonstrate a fundamental structural control on Byrd Glacier. During Mesozoic-Cenozoic rifting, this transverse the morphology of the Royal Society Range, particularly the zone was the site of voluminous magmatism in the Jurassic, now transverse structures that segment the Transantarctic Mountains represented by extensive outcrops of Ferrar dolerite around the along their length.

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VN 3 7 4 :.: c •

CO

=:^ 0 - M

N 0 km

B Ni

V . I, N=232

Figure 1. Geologic sketch map (A) of study area modified from Findlay et al. (1984). Black denotes metasedimentary rocks. Stipple pattern denotes igneous rocks of the Granite Harbour Intrusive Complex. Horizontal line pattern denotes Beacon and Ferrar Supergroup rocks. Heavy dot-dash lines mark trends of transverse physiographic troughs occupied by Ferrar Glacier and Radian Glacier. Heavy dashed line indicates trend of the structural front of the Transantarctic Mountains. Lower hemisphere stereographic projections show representative structural data for brittle faults at selected localities in the study area. Great circle curves denote fault planes. Dots are striae on fault planes. Arrows show motion of hanging wall above fault plane. CR denotes Cathedral Rocks. HR denotes ridge along Herbertson Glacier. MR denotes Marshall Ridge. PR denotes ridge east of Lake Penny. WB denotes ridge on the western edge of Blue Glacier. (B) Compilation of fault plane data from the five localities shown in A, showing five discrete fault sets within the region. Note that all but the N10W set consists of two pairs of fault planes with conjugate geometry. Shading indicates concentrations of poles to (i.e., lines perpendicular to) fault planes. Small black dots are Individual fault plane poles. Average fault plane orientations are shown by black symbols on the Iefthand plot and by corresponding great circle curves on the righthand plot. Circles mark the N30E set. Triangles mark the N60E set. Squares mark the N80E set. Diamonds mark the N40W set. The star marks the N1 OW set.

1992 REVIEW 7 fracture arrays associated with fault planes are predominantly normal with right- and left-slip components. Where preserved locally, superposed sets of striae on fault surfaces indicate that dominantly strike-slip transport occurred after dominantly nor- mal, dip-slip motion. These data are being analyzed graphically to reconstruct shortening and extension directions from the faut population data. The relative chronology of the fault sets has been determined from crosscutting relations observed in the field. The N30 conjugate fault set is clearly the oldest, because it is parallel to, and locally intruded by, the regionally developed Vanda dik swarm (Janosy and Wilson, this issue). The N60E and N40W fault sets are younger than the N30E set, and sparse data sugget that the northwest set is the younger of the two. The N1 OW anc1 N80E fault sets are the youngest in the region. These sets ar approximately parallel and perpendicular to the regional tren4l of the mountains in southern Victoria Land, suggesting the have been active during the morphologic uplift of the mountain in the Cenozoic. Field studies during the 1992-1993 field seaso will focus on determining the geometry of faulting associate with the Jurassic Ferrar dolerites and with Cenozoic McMurd volcanic rocks in order to better constrain the absolute ages of the fault sets. This research was supported by National Science Foundation grant DPP 90-18055.

References

Anderson, E. M. 1951. The Dynamics of Faulting and Dyke Formation with Application to Britain. Edinburgh: Oliver and Boyd, Ltd., 206 pp. Behrendt, J. C. and A. Cooper. 1991. Evidence of rapid Cenozoic uplift of the shoulder escarpment of the Cenozoic West Antarctic rift system and a speculation on possible climate forcing. Geology, 19:315-319. Figure 2. Exposure is located on the ridge east of Lake Penney. The Findlay, R. B., D. N. B. Skinner, and D. Craw. 1984. Lithostratigraph peaks of Mt. Dromedary are visible in the background. and structure of the Koettlitz Group, McMurdo Sound, Antarctica New Zealand Journal of Geology and Geophysics, 27:513-536. Fitzgerald, P. G. 1987. Uplift history of the Transantarctic Mountains in the Ross Sea sector and a model for their formation. Doctoral Dissertation Several lines of evidence indicate that the discrete fault sets University of Melbourne, Victoria, Australia, 327 pp. were formed and subsequently moved at markedly different Fitzgerald, P. G., M. Sandiform, P. J. Barrett, and A.J.W. Gleadow. 1986 Asymmetric extension associated with uplift and subsidence in th times in the development of the Transantarctic Mountains. Four Transantarctic Mountains and Ross embayment. Earth and Planetary of the five fault sets consist of pairs of fault planes with the Science Letters, 81:67-78. conjugate geometry and moderate to steep, opposing dips typ- Gunn, B. M. and G. Warren. 1962. Geology of Victoria Land between th ical of normal fault sets (Anderson 1951). Instead of the dip slip Mawson and Mullock Glaciers, Antarctica. New Zealand Geological motion this interpretation would require, however, striae pre- Survey Bulletin, 71:157. served on the fault surfaces document moderate- to low-angle, Janosy, R. and T. J. Wilson. 1992. Structural investigations of Earl oblique slip directions on all the sets (figure 1A). This difference Paleozoic mafic dike swarms in the Royal Society Range, Southern between fault geometry and predicted slip direction, the diverse Victoria Land. Antarctic Journal of the U.S., this issue. motion directions on parallel faults within a set, and the occur- Stern, T. A. and U. S. ten Brink. 1989. Flexural uplift of the Transantarctic rence of multiple sets of striae on individual fault surfaces all Mountains. Journal of Geophysical Research, 94:10315-10330. Wilson, T. 1990. Mesozoic and Cenozoic structural patterns in the indicate that preexisting fracture surfaces were reactivated re- J. Transantarctic Mountains, southern Victoria Land. Antarctic Journal of peatedly during episodic rifting of the region. the U.S., 25:31-35. Displacement directions derived from the offset of Wilson, T. J. 1992. Mesozoic and Cenozoic kinematic evolution of the metasedimentary layering and extensive aplite and lampro- TransantarcficMountains. In Yoshida (Ed.) Recent Progress in Antarc- phyre dike swarms and from the orientation patterns of minor tic Earth Science. Tokyo: Terra Scientific Publishing Company, in press.

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