Paleomagnetic results from the Kirkpatrick Basalt Group, Victoria Land
References Ball, H. W., Borns, H. W., Hall, B. A., Brooks, H. K., Carpenter, F. M., and Delevoryas, T. 1979. In B. Laskar and C. S. Raja Rao (Eds.), Fourth International Gondwana Symposium (Vol. 1). Delhi: Hindustan Publishing Corporation. Gair, H. S. 1967. The geology from the upper Rennick Glacier to the coast, northern Victoria Land. New Zealand Journal of Geology and Geophysics, 10, 309-344.
Gair, H. S., Sturm, A., Carryer, S. J., and Grindley, G. W. 1969. The geology of northern Victoria Land (Folio 12, Plate 12). In V. C. Bushnell
Paleomagnetic results from the Kirkpatrick Basalt Group, Victoria Land WILLIAM C. MCINTOSH New Mexico Bureau of Mines and Mineral Resources Socorro, New Mexico 87801
PHILIP R. KYLE Department of Geoscience New Mexico Institute of Mining and Technology Socorro, New Mexico 87801
and C. Craddock (Eds.), Geologic maps of Antarctica 1:100,000, Antarctic maps folio series. New York: American Geographical Society. Kyle, P. R., and Cole,
J.
W. 1974. Structural control of volcanism in the
McMurdo volcanic group. Bulletin Volcanologique, 38, 16-25.
Nathan, S., and Schulte, F. J. 1968. Geology and petrology of the Campbell-Aviator Divide, northern Victoria Land, Antarctica. New Zealand Journal of Geology and Geophysics, 11, 960-975. Tasch, P. 1970. Antarctic and other Gondwana conchostracans and insects: New data; Significance for continental drift. In S. H. Haughton (Ed.), Second Gondwana Symposium. Pretoria, South Africa: Council of Scientific and Industrial Research.
samples from 15 sites in 15 flows) (figure 1). Paleomagnetic results show that the samples possess strong normal remanence, with stability equal to or greater than that of Ferrar Supergroup dolerites and gabbros. The natural remanent magnetization (NRM) includes a small viscous component that is readily removed by alternating field demagnetization in fields of 20 to 50 millitesla. The mean VGP of the David Glacier samples lies at 55°S 138°W, which is nearly coincident with the average of VGP's previously reported from the Ferrar Supergroup. The mean VGP of the Mesa Range samples, however, lies significantly farther south at 64°S 150°W (figure 2) (page 22). It is unlikely that the anomalously high latitude of the mean of the Mesa Range samples is an effect of unremoved viscous or chemical components, tectonic tilting or rotation, or incomplete averaging of paleosecular variation. In addition, an VGP
ERIC M. CHERRY and HALLAN C. NOLTIMIER 162E
Department of Geology and Mineralogy Ohio State University Columbus, Ohio 43210
-i s
Several previous paleomagnetic studies have been made of Jurassic-age antarctic igneous rocks, including (as summarized and referenced in the table): (1) Ferrar Dolerite sills from four localities along the Transantarctic Mountains; (2) Forrestal Gabbros from the Dufek Stratiform Intrusion; (3) Kirkpatrick Basalt lava flows from the Queen Alexandra Range in the central Transantarctic Mountains; and (4) tholeiites from Queen Maude Land. The results have shown generally high stabilities and predominantly normal polarities. The average virtual geomagnetic pole (vcP) is near 55°S 140°W, in good agreement with Jurassic VGP's of Africa, South America, India, and Australia in their Gondwanaland configurations (Schmidt 1976). The purpose of the present study was to investigate further the paleomagnetism of the Kirkpatrick Basalts. Oriented samples were collected from Kirkpatrick Basalts in the David Glacier Area, southern Victoria Land (55 samples from 25 sites in 24 flows), and at the Mesa Range, northern Victoria Land (60 20
I I 158E 15YE -7548'S BRIMSTONEPEAK 7 to I I I to6
Li
etop5
SECTION PEAK 1.2
c_3"\
Gorgon Itol4
li
-75303
GRIFFIN NUNATAK 10km 1
10 km
DAVID GLACIER AREA MESA RANGE AREA Figure 1. Map showing location of sample sites in the David Glacier area, southern Victoria Land, and at the Mesa Range, northern Victoria Land.
ANTARCTIC JOURNAL
Paleomagnetic results from Ferrar Supergroup igneous rocks8 Remanence
Virtual geomagnetic pole
PolarN 1 N2 AF ity DEC - INC K a95 'W 'S DP DM
Study
Kirkpatrick Basalts 15 20 60 Mesa Range (1)b David Glacier (2) 12 30-50 29 Brimstone Peak 13 30-50 26 Gorgon Peak 25 30-50 55 Mean Queen Alexandra Range (3) 12 SEP Storm Peak SEP 14 Mount Falls SEP 26 Mean Ferrar Dolerite 46 22.5 83 Wright and Victoria Valleys (4) 5 NAM 57 Ferrar Glacier (5) 7 SEP Queen Alexandra Range (6) 9 15 13 Beardmore Glacier (7) Forrestal Gabbro Dufek Intrusion (8)
- 30
Queen Maude Land Tholeiites Theron Mountains (9)
8
8 NRM
N
266
—80
174
N N N
263 274
—74 —73
156 122 141
N N N
253 225 241
—64 —71 —68
N N N N
250 255 225 244
—68 —76 —72 —75
63 52 18
150
64
3
3
4 4 7
142 130 138
56 56 55
6 6 11
7 6 12
7 4
129 137 133
44 54 49
9 7
11 8
3 3 5 11
140 142 140 139
45 58 54 59
4 5 8 18
5 5 10 20
137
60
11
11
136
54
16
16
N&R N&R
64 —68 34
12
in aAbbreviations: N, = number of samples; N 2 = number of sites; AF = alternating field demagnetization level, in milliteslas; DEC = mean declination, 05 denote percent corfidence; 'W and degrees; INC = mean inclination, in degrees; K = Fisher precision parameter; ci95 = semi-angle of the cone of 95 the position of the estimated paleomagnetic pole; DI' and DM = 95 percent probability errors in this estimate, along and at right angles to the paleomeridian, respectively; N = normal; SEP = stable endpoint; NRM = natural remanent magnetization; R = reversed.
b Numbers in parentheses indicate sources: (1) this report; (2) this report, Cherry (1981), Cherry and Noltimier (1982); (3) Ostrander (1971); (4) Bull, Irving,
and Willis (1962), Bull and Irving (1960); (5) Turnbull (1959); (6) Ostrander (1971); (7) Briden and Oliver (1963); (8) Beck, Burmester, and Sheriff (1979), Burmester and Sheriff (1980); (9) Blundell and Stevenson (1959).
c Dashes = not reported.
incremental argon-40/argon-39 (Ar 4('/Ar39 ) age obtained from a flow at the base of the Mesa Range is 174.2 ± 1.0 million years (P. R. Kyle and J . F. Sutter unpublished data, New Mexico Institute of Mining and Technology, 1982). This age is indistinguishable from reliable radiometric ages determined for other Ferrar Supergroup rocks (Kyle, Elliot, and Sutter 1981). The significance of the high-latitude VGP from the Mesa Range samples remains uncertain. It is notable, however, that similar anomalous VGP's have been reported from Tasmanian dolerites (Schmidt and McDougall 1977) that are closely related to the Ferrar Supergroup rocks in age and geochemistry. This work was supported by National Science Foundation grants DPI' 77-21590 and DPP 80-20002.
Blundell, D. J . , and Stevenson, P. J . 1959. Paleomagnetism of some dolerite intrusions from the Theron Mountains and Whichaway Nunataks, Antarctica. Nature, 184, 1860. Briden, J . C., and Oliver, R. L. 1963. Paleomagnetic results from the Beardmore Glacier region, Antarctica. New Zealand Journal of Geology and Geophysics, 6, 388-394. Bull, C., and Irving, E. 1960. The paleomagnetism of some hypabyssal intrusive rocks from south Victoria Land, Antarctica. Geophysical Journal of the Royal Astronomical Society, 3, 211-214. Bull, C., Irving, E., and Willis, I. 1962. Further paleomagnetic results from south Victoria Land, Antarctica. Geophysical Journal of the Royal Astronomical Society, 6, 320-336. Burmester, R. F., and Sheriff, S. D. 1980. Paleomagnetism of the Dufek Intrusion, Pensacola Mountains, Antarctica. Antarctic Journal of the U.S., 15(5), 43-45.
References
Cherry, E. M., 1981. A paleomagnetic investigation of Jurassic Kirkpatrick Basalt flows from south Victoria Land, Antarctica. Unpublished senior thesis, Ohio State University.
Beck, M. E., Jr., Burmester, R. F., and Sheriff, S. D. 1979. Field reversal and paleomagnetic pole for Jurassic Antarctica, EOS, Transactions of
Cherry, E. M., and Noltimier, H. C. 1982. Paleomagnetic results: Kirkpatrick Basalts at Brimstone Peak and Gorgon Peak, Antarctica. EOS, Transactions of the American Geophysical Union, 63, 616.
the American Geophysical Union, 60, 818, 1982 REVIEW
21
Kyle, P. R., Elliot, D. H., and Sutter, J. E 1981. Jurassic Ferrar Supergroup tholeiites from the Transantarctic Mountains, Antarctica, and their relationship to the initial fragmentation of Gondwana. In M. M. Cresswell and P. Vella (Eds.), Gondwana Five. Rotterdam: A. A. Balkema. Ostrander, J. H. 1971. Paleomagnetic investigations of the Queen Victoria Range, Antarctica. Antarctic Journal of the U.S., 6 (5), 183-185. Schmidt, P. W. 1976. The non-uniqueness of the Australian Mesozoic paleomagnetic pole position. Geophysical Journal of the Royal Astronomical Society, 47, 285-300.
Schmidt, P. W., and McDougall, I. 1977. Paleomagnetic and potassiumargon dating studies of the Tasmanian dolerites. Journal of the Geological Society of Australia, 25, 321-328. Turnbull, C. 1959. Some paleomagnetic measurements in Antarctica. Arctic, 12, 151-157.
Figure 2. The mean virtual geomagnetic poles (vGP's) of Ferrar Supergroup rocks from eight localities form an elongate pattern extending from 45°S to 640S. The mean VGP of David Glacier samples agrees with average VGP of previous studies, but the mean VGP of Mesa Range samples is significantly different. Circles represent results of previous studies; the solid triangle is their average. Squares show the results of this study, and hollow triangles are the study localities. Ellipses of 95 percent confidence are shown for the David Glacier and Mesa Range mean VGP'S and for the average of previous studies. VGP'S and locations are numbered as In the table.
Petrographic and chemical study of orbicular rocks in western Taylor Valley, southern Victoria Land* PETER S. DAHL and DONALD F. PALMER Department of Geology Kent State University Kent, Ohio 44242
During the 1980-81 and 1981-82 austral field seasons we mapped and sampled orbicular rocks at several locations in Taylor Valley and at Granite Harbor. We are principally interested in elucidating the mechanism(s) by which orbicular rocks form and in obtaining new information regarding processes of assimilation and chemical transfer in silicate magmas. Taylor Valley is uniquely suited for such a study because orbicules in various stages of development are preserved in outcrop. In an
*Con tribu ti on 247, Department of Geology, Kent State University 22
earlier article (Dahl and Palmer 1981), we presented a detailed map showing the geometry of orbicule zones in western Taylor Valley as well as their spatial relationships with Larsen granodiorite and the nearby Skelton Group metasediments. In this article we describe the petrographical, mineral-chemical, and bulk-chemical profiles of a single representative orbicule from the western Taylor Valley area. We then use these profiles to outline the chemical transfer process involved in formation of this orbicule. A polished thin section of this orb (specimen TG81-106D) is shown in figure 1. The core of this orbicule (figure 1, left) contains the minerals biotite (dark-colored), diopside (intermediate-colored), and plagioclase (light-colored) in equigranular texture. This assemblage is identical to that in some of the gneisses found in place in the nearby Skelton metasediments. Hence, orbicule cores are thought to represent unassimilated metamorphic xenoliths. The shell structure in orbicular specimen TG81-106D consists of an inner feldspathic region and an outer shell region, the latter dominated by coarse radial hornblende (dark-colored) and plagioclase crystals (figure 1). The inner feldspathic zone contains clusters of intergrown diopside and biotite which occur as "islands" in a "sea" of coarse plagioclase. This part of the shell is thought to represent partially melted xenolith in which the present diopside-biotite clusters persist as unmelted remnants. Quartz and microcline are notably absent in both the orbicule core and shell. ANTARCTIC JOURNAL
Gair, H. S., Sturm, A., Carryer, S. J., and Grindley, G. W. 1969. The geology of northern Victoria Land (Folio 12, Plate 12). In V. C. Bushnell
Paleomagnetic results from the Kirkpatrick Basalt Group, Victoria Land WILLIAM C. MCINTOSH New Mexico Bureau of Mines and Mineral Resources Socorro, New Mexico 87801
PHILIP R. KYLE Department of Geoscience New Mexico Institute of Mining and Technology Socorro, New Mexico 87801
and C. Craddock (Eds.), Geologic maps of Antarctica 1:100,000, Antarctic maps folio series. New York: American Geographical Society. Kyle, P. R., and Cole,
J.
W. 1974. Structural control of volcanism in the
McMurdo volcanic group. Bulletin Volcanologique, 38, 16-25.
Nathan, S., and Schulte, F. J. 1968. Geology and petrology of the Campbell-Aviator Divide, northern Victoria Land, Antarctica. New Zealand Journal of Geology and Geophysics, 11, 960-975. Tasch, P. 1970. Antarctic and other Gondwana conchostracans and insects: New data; Significance for continental drift. In S. H. Haughton (Ed.), Second Gondwana Symposium. Pretoria, South Africa: Council of Scientific and Industrial Research.
samples from 15 sites in 15 flows) (figure 1). Paleomagnetic results show that the samples possess strong normal remanence, with stability equal to or greater than that of Ferrar Supergroup dolerites and gabbros. The natural remanent magnetization (NRM) includes a small viscous component that is readily removed by alternating field demagnetization in fields of 20 to 50 millitesla. The mean VGP of the David Glacier samples lies at 55°S 138°W, which is nearly coincident with the average of VGP's previously reported from the Ferrar Supergroup. The mean VGP of the Mesa Range samples, however, lies significantly farther south at 64°S 150°W (figure 2) (page 22). It is unlikely that the anomalously high latitude of the mean of the Mesa Range samples is an effect of unremoved viscous or chemical components, tectonic tilting or rotation, or incomplete averaging of paleosecular variation. In addition, an VGP
ERIC M. CHERRY and HALLAN C. NOLTIMIER 162E
Department of Geology and Mineralogy Ohio State University Columbus, Ohio 43210
-i s
Several previous paleomagnetic studies have been made of Jurassic-age antarctic igneous rocks, including (as summarized and referenced in the table): (1) Ferrar Dolerite sills from four localities along the Transantarctic Mountains; (2) Forrestal Gabbros from the Dufek Stratiform Intrusion; (3) Kirkpatrick Basalt lava flows from the Queen Alexandra Range in the central Transantarctic Mountains; and (4) tholeiites from Queen Maude Land. The results have shown generally high stabilities and predominantly normal polarities. The average virtual geomagnetic pole (vcP) is near 55°S 140°W, in good agreement with Jurassic VGP's of Africa, South America, India, and Australia in their Gondwanaland configurations (Schmidt 1976). The purpose of the present study was to investigate further the paleomagnetism of the Kirkpatrick Basalts. Oriented samples were collected from Kirkpatrick Basalts in the David Glacier Area, southern Victoria Land (55 samples from 25 sites in 24 flows), and at the Mesa Range, northern Victoria Land (60 20
I I 158E 15YE -7548'S BRIMSTONEPEAK 7 to I I I to6
Li
etop5
SECTION PEAK 1.2
c_3"\
Gorgon Itol4
li
-75303
GRIFFIN NUNATAK 10km 1
10 km
DAVID GLACIER AREA MESA RANGE AREA Figure 1. Map showing location of sample sites in the David Glacier area, southern Victoria Land, and at the Mesa Range, northern Victoria Land.
ANTARCTIC JOURNAL
Paleomagnetic results from Ferrar Supergroup igneous rocks8 Remanence
Virtual geomagnetic pole
PolarN 1 N2 AF ity DEC - INC K a95 'W 'S DP DM
Study
Kirkpatrick Basalts 15 20 60 Mesa Range (1)b David Glacier (2) 12 30-50 29 Brimstone Peak 13 30-50 26 Gorgon Peak 25 30-50 55 Mean Queen Alexandra Range (3) 12 SEP Storm Peak SEP 14 Mount Falls SEP 26 Mean Ferrar Dolerite 46 22.5 83 Wright and Victoria Valleys (4) 5 NAM 57 Ferrar Glacier (5) 7 SEP Queen Alexandra Range (6) 9 15 13 Beardmore Glacier (7) Forrestal Gabbro Dufek Intrusion (8)
- 30
Queen Maude Land Tholeiites Theron Mountains (9)
8
8 NRM
N
266
—80
174
N N N
263 274
—74 —73
156 122 141
N N N
253 225 241
—64 —71 —68
N N N N
250 255 225 244
—68 —76 —72 —75
63 52 18
150
64
3
3
4 4 7
142 130 138
56 56 55
6 6 11
7 6 12
7 4
129 137 133
44 54 49
9 7
11 8
3 3 5 11
140 142 140 139
45 58 54 59
4 5 8 18
5 5 10 20
137
60
11
11
136
54
16
16
N&R N&R
64 —68 34
12
in aAbbreviations: N, = number of samples; N 2 = number of sites; AF = alternating field demagnetization level, in milliteslas; DEC = mean declination, 05 denote percent corfidence; 'W and degrees; INC = mean inclination, in degrees; K = Fisher precision parameter; ci95 = semi-angle of the cone of 95 the position of the estimated paleomagnetic pole; DI' and DM = 95 percent probability errors in this estimate, along and at right angles to the paleomeridian, respectively; N = normal; SEP = stable endpoint; NRM = natural remanent magnetization; R = reversed.
b Numbers in parentheses indicate sources: (1) this report; (2) this report, Cherry (1981), Cherry and Noltimier (1982); (3) Ostrander (1971); (4) Bull, Irving,
and Willis (1962), Bull and Irving (1960); (5) Turnbull (1959); (6) Ostrander (1971); (7) Briden and Oliver (1963); (8) Beck, Burmester, and Sheriff (1979), Burmester and Sheriff (1980); (9) Blundell and Stevenson (1959).
c Dashes = not reported.
incremental argon-40/argon-39 (Ar 4('/Ar39 ) age obtained from a flow at the base of the Mesa Range is 174.2 ± 1.0 million years (P. R. Kyle and J . F. Sutter unpublished data, New Mexico Institute of Mining and Technology, 1982). This age is indistinguishable from reliable radiometric ages determined for other Ferrar Supergroup rocks (Kyle, Elliot, and Sutter 1981). The significance of the high-latitude VGP from the Mesa Range samples remains uncertain. It is notable, however, that similar anomalous VGP's have been reported from Tasmanian dolerites (Schmidt and McDougall 1977) that are closely related to the Ferrar Supergroup rocks in age and geochemistry. This work was supported by National Science Foundation grants DPI' 77-21590 and DPP 80-20002.
Blundell, D. J . , and Stevenson, P. J . 1959. Paleomagnetism of some dolerite intrusions from the Theron Mountains and Whichaway Nunataks, Antarctica. Nature, 184, 1860. Briden, J . C., and Oliver, R. L. 1963. Paleomagnetic results from the Beardmore Glacier region, Antarctica. New Zealand Journal of Geology and Geophysics, 6, 388-394. Bull, C., and Irving, E. 1960. The paleomagnetism of some hypabyssal intrusive rocks from south Victoria Land, Antarctica. Geophysical Journal of the Royal Astronomical Society, 3, 211-214. Bull, C., Irving, E., and Willis, I. 1962. Further paleomagnetic results from south Victoria Land, Antarctica. Geophysical Journal of the Royal Astronomical Society, 6, 320-336. Burmester, R. F., and Sheriff, S. D. 1980. Paleomagnetism of the Dufek Intrusion, Pensacola Mountains, Antarctica. Antarctic Journal of the U.S., 15(5), 43-45.
References
Cherry, E. M., 1981. A paleomagnetic investigation of Jurassic Kirkpatrick Basalt flows from south Victoria Land, Antarctica. Unpublished senior thesis, Ohio State University.
Beck, M. E., Jr., Burmester, R. F., and Sheriff, S. D. 1979. Field reversal and paleomagnetic pole for Jurassic Antarctica, EOS, Transactions of
Cherry, E. M., and Noltimier, H. C. 1982. Paleomagnetic results: Kirkpatrick Basalts at Brimstone Peak and Gorgon Peak, Antarctica. EOS, Transactions of the American Geophysical Union, 63, 616.
the American Geophysical Union, 60, 818, 1982 REVIEW
21
Kyle, P. R., Elliot, D. H., and Sutter, J. E 1981. Jurassic Ferrar Supergroup tholeiites from the Transantarctic Mountains, Antarctica, and their relationship to the initial fragmentation of Gondwana. In M. M. Cresswell and P. Vella (Eds.), Gondwana Five. Rotterdam: A. A. Balkema. Ostrander, J. H. 1971. Paleomagnetic investigations of the Queen Victoria Range, Antarctica. Antarctic Journal of the U.S., 6 (5), 183-185. Schmidt, P. W. 1976. The non-uniqueness of the Australian Mesozoic paleomagnetic pole position. Geophysical Journal of the Royal Astronomical Society, 47, 285-300.
Schmidt, P. W., and McDougall, I. 1977. Paleomagnetic and potassiumargon dating studies of the Tasmanian dolerites. Journal of the Geological Society of Australia, 25, 321-328. Turnbull, C. 1959. Some paleomagnetic measurements in Antarctica. Arctic, 12, 151-157.
Figure 2. The mean virtual geomagnetic poles (vGP's) of Ferrar Supergroup rocks from eight localities form an elongate pattern extending from 45°S to 640S. The mean VGP of David Glacier samples agrees with average VGP of previous studies, but the mean VGP of Mesa Range samples is significantly different. Circles represent results of previous studies; the solid triangle is their average. Squares show the results of this study, and hollow triangles are the study localities. Ellipses of 95 percent confidence are shown for the David Glacier and Mesa Range mean VGP'S and for the average of previous studies. VGP'S and locations are numbered as In the table.
Petrographic and chemical study of orbicular rocks in western Taylor Valley, southern Victoria Land* PETER S. DAHL and DONALD F. PALMER Department of Geology Kent State University Kent, Ohio 44242
During the 1980-81 and 1981-82 austral field seasons we mapped and sampled orbicular rocks at several locations in Taylor Valley and at Granite Harbor. We are principally interested in elucidating the mechanism(s) by which orbicular rocks form and in obtaining new information regarding processes of assimilation and chemical transfer in silicate magmas. Taylor Valley is uniquely suited for such a study because orbicules in various stages of development are preserved in outcrop. In an
*Con tribu ti on 247, Department of Geology, Kent State University 22
earlier article (Dahl and Palmer 1981), we presented a detailed map showing the geometry of orbicule zones in western Taylor Valley as well as their spatial relationships with Larsen granodiorite and the nearby Skelton Group metasediments. In this article we describe the petrographical, mineral-chemical, and bulk-chemical profiles of a single representative orbicule from the western Taylor Valley area. We then use these profiles to outline the chemical transfer process involved in formation of this orbicule. A polished thin section of this orb (specimen TG81-106D) is shown in figure 1. The core of this orbicule (figure 1, left) contains the minerals biotite (dark-colored), diopside (intermediate-colored), and plagioclase (light-colored) in equigranular texture. This assemblage is identical to that in some of the gneisses found in place in the nearby Skelton metasediments. Hence, orbicule cores are thought to represent unassimilated metamorphic xenoliths. The shell structure in orbicular specimen TG81-106D consists of an inner feldspathic region and an outer shell region, the latter dominated by coarse radial hornblende (dark-colored) and plagioclase crystals (figure 1). The inner feldspathic zone contains clusters of intergrown diopside and biotite which occur as "islands" in a "sea" of coarse plagioclase. This part of the shell is thought to represent partially melted xenolith in which the present diopside-biotite clusters persist as unmelted remnants. Quartz and microcline are notably absent in both the orbicule core and shell. ANTARCTIC JOURNAL
