Geochemical studies of Ferrar Group rocks from southern ...
Geochemical studies of Ferrar Group rocks from southern Victoria Land
Steolrg,Dric sections and variat ions of selected erajoe ele,eeets of Kirkpatrick Basalt in the ereo between the Mouton and Gould Glaciers, South Victoria Land
CARAME 1-1—
PHILIP R. KYLE Institute of Polar Studies The Ohio State University Columbus, Ohio 43210
Jurassic tholeiitic Kirkpatrick Basalts and Ferrar Dolerites are geochemically unique in comparison to other tholeiitic basalts. Notably, they have extremely high 87SrI "Sr ratios and high levels of uranium, thorium, potassium, and light rare earth elements. Several models (Kyle, in press) have been proposed to account for their chemistry and include selective contamination of normal tholeiitic basalt by crustal derived components, heterogeneities in the subcontinental lithosphere due to metasomatism from the lower mantle or contamination of the lithosphere by sediment introduced into the mantle along a subduction zone.
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I6OE £ Camp site - Sledg i ng route Kirkpatrick Basalt Ei
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eror Doe and Mawson Formation Other including Ferro, Dolerte
77uS Ak
CARAPACE NUNATAK
POLA R
Hills
Ross
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\PLATEAU RShrg \EIephoc M—r, Proc
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W In NUNATAG GRIFFIN
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Figure 1. Traverse route and distribution of Kirkpatrick Basalts between the Mawson and David Glaciers.
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Figure 2. Stratlgraphic sections and variation of selected major elements of Kirkpatrick Basalts from the area between the Mawson and David Glaciers.
The purpose of our fieldwork during the 1978-79 season was to collect fresh Ferrar Group material for detailed geochemical studies to evaluate these models. We visited the area between the Mackay and David glaciers (figure 1), the Darwin Glacier area, and also Wright Valley (to sample a Ferrar Dolerite sill). We made a 33-day-long traverse using three snowmobiles from the Coombs Hills to the area between the David and Mawson glaciers, and we returned to Carapace Nunatak along much the same route (figure 1). Sections of Kirkpatrick Basalt (figure 2) were sampled at Carapace Nunatak (8 lava flows with a total thickness of 130 meters), Gorgon Peak (18 lava flows, 220 meters thick), and Brimstone Peak (20 flows, about 380 meters thick). Chilled margins, representative of the initial bulk composition of doleritic intrusives, were sampled in numerous locations. One important aspect of determining the petrogenesis of the Ferrar Group is to examine basic high-magnesium oxide basalt and dolerite. We were able to locate and sample the previously undiscovered lower chilled margin of a dolerite sill at the butte known as The Mitten that contains olivine (Skinner and Ricker, 1968; Gunn, 1966). During our traverse, we found over 200 meters of massive diamictite, probably correlative with the Mawson Formation, at the south end of Griffin Nunatak. This unit, interbedded within Kirkpatrick Basalt lava flows, is overlain by diamictite that is probably correlative with the Sirius Formation. We also determined that Twin Nunataks, Crash Nunatak, the summit of Ford Peak, and the southern end of the Ricker Hills, all previously mapped as Kirkpatrick Basalt, actually consist of intrusive dolerite. Similarly, in the Darwin Glacier area, we found that the previously reported Kirkpatrick Basalt at Westhaven Nunatak and also at Turnstile Ridge consists of doleritic intrusives. We also made a new and important discovery at Butcher Ridge, where we traced strongly deformed glassy acidic rocks for a distance of more than 4 kilometers. This is the first extensive area of "dacitic" or "rhyolitic" rocks known in the Ferrar Group. The exact means of emplacement of many of the rocks is still un25
10
it Mt Faila *Pointed Cliffs 0 Ot.y Massif C*00*I Tronsantorctic Mountains a Grosvenor MO Other North Victoria Land South Victoria Land Caron Glacier 9(99*, Eo,po.ot 0 0'O.9Q Maud Land
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base for more specialized geochemical studies. In the course of our 1978-79 fieldwork, we also discovered that Elephant Nunatak (unofficial name), a feature east of Reckling Peak previously discovered using satellite imagery, is composed entirely of moraine. In addition, we found five chondrite meteorites in the vicinity of the moraine. I was supported in the field by Kathy Cashman and Harry Keys (both from Victoria University of Wellington) and Bill McIntosh (University of Colorado). This work has been supported by National Science Foundation grant DPP 77-21590.
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0 -50 52 54 :. 58 60 Q 14
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Figure 3. Silica variation diagrams of selected oxides for Jurassic tholeiltic rocks from the Transantarctic Mountains.
determined, but an intrusive origin appears to be the most likely method. Over 150 new major element analyses (figure 3) of Jurassic tholeiites from Antarctica will provide a data
Artesian well at Don Juan Pond LYLE D. MCGINNIS
Department of Geology Northern Illinois University De Kalb, Illinois 60115
Don Juan Pond, located in the suth fork of Wright Valley, was revisited on 9-12 December 1978 to observe the status of Dry Valley Drilling Project (DVDP) hole 13. Since its drilling on 8-13 January 1975, the borehole and pond have remained under intermittent observation (Harris and Cartwright, in press; Harris, Cartwright, and Toni, 1979). The borehole is unusual in that it contains unfrozen, concentrated brines near 200 parts per thousand. Water level in the borehole is responding to episodic, impulsive pressure changes of unproven origin (Harris and Cartwright, in press). Plans are under way to install automatically recording instrumentation at the borehole to determine the cause of the transient pressure variations and the source of the brines. After ice was cleared from the upper 10 meters of the hole at 1700 hours on 9 December, water at a temperature of - 15.50 C began flowing from the hole at a 26
References (;rn, B. M. 1966. Modal and element variation in Antarctic tholeiites. Geochimica Cosmochimica Acta, 30: 881-920. Kyle, P. R. Development of heterogeneities in the subcontinental mantle: Evidence from the Ferrar Group, Antarctica. In Contributions to Mineralogy and Petrology (in press). Skinner, D.N.B., and J . Ricker. 1968. The geology of the region between the Mawson and Priestley Glaciers, north Victoria Land, Antarctica. New Zealand Journal of Geology and Geophysics, 11: 1009- 1075.
steady rate of 4 liters per minute and continued to flow for three days before being shut off. Casing set through the sand overburden (see figure) stands 0.70 meter above ground surface and about 1 meter above Don Juan Pond. It is believed that water is flowing from the fractured and highly mineralized Ferrar dolerite, which acts as a confined aquifer in the dry valleys but may receive its water from subglacial lakes at the base of the Antarctic Ice Sheet. Geophysical logs of the borehole are also shown in the accompanying figure. A discussion of the logs is provided in McGinnis et al. (in press). This study has been supported by the Division of Polar Programs of the National Science Foundation, grant number DPP 7821112-01. References Harris, H. J . H., and K. Cartwright. In press. Pressure fluctuations in an antarctic aquifer: The freight train response to a moving rock glacier. In Third Symposium on Antarctic Geology and Geophysics, ed. C. Craddock. Madison: University of Wisconsin Press. Harris, H. J . H., K. Cartwright, and T. Toni. 1979. Dynamic chemical equilibrium in a polar desert pond: A sensitive index of meteorological cycles. Science, 264(4390): 301-3. McGinnis, L. D., J . S. Stuckless, D. R. Osby, and P. R. Kyle. In press. Gamma-ray, salinity, and electric logs of DVDP boreholes. In Dry Valley Drilling Project, ed. L. McGinnis. Antarctic Research Series. Washington, D. C.: American Geophysical Union.
Steolrg,Dric sections and variat ions of selected erajoe ele,eeets of Kirkpatrick Basalt in the ereo between the Mouton and Gould Glaciers, South Victoria Land
CARAME 1-1—
PHILIP R. KYLE Institute of Polar Studies The Ohio State University Columbus, Ohio 43210
Jurassic tholeiitic Kirkpatrick Basalts and Ferrar Dolerites are geochemically unique in comparison to other tholeiitic basalts. Notably, they have extremely high 87SrI "Sr ratios and high levels of uranium, thorium, potassium, and light rare earth elements. Several models (Kyle, in press) have been proposed to account for their chemistry and include selective contamination of normal tholeiitic basalt by crustal derived components, heterogeneities in the subcontinental lithosphere due to metasomatism from the lower mantle or contamination of the lithosphere by sediment introduced into the mantle along a subduction zone.
ç
ho
I6OE £ Camp site - Sledg i ng route Kirkpatrick Basalt Ei
;^^_
/"^
^
fl
eror Doe and Mawson Formation Other including Ferro, Dolerte
77uS Ak
CARAPACE NUNATAK
POLA R
Hills
Ross
A11- N.not.k V
p/SON G4 '
\PLATEAU RShrg \EIephoc M—r, Proc
ç
W In NUNATAG GRIFFIN
ffm
BoasPeac
SEA
RICKER HILLS
Dqo /c, rcnqe
DAVID
GLACI gouw
+ 90°E cJ
Figure 1. Traverse route and distribution of Kirkpatrick Basalts between the Mawson and David Glaciers.
!t
?
Figure 2. Stratlgraphic sections and variation of selected major elements of Kirkpatrick Basalts from the area between the Mawson and David Glaciers.
The purpose of our fieldwork during the 1978-79 season was to collect fresh Ferrar Group material for detailed geochemical studies to evaluate these models. We visited the area between the Mackay and David glaciers (figure 1), the Darwin Glacier area, and also Wright Valley (to sample a Ferrar Dolerite sill). We made a 33-day-long traverse using three snowmobiles from the Coombs Hills to the area between the David and Mawson glaciers, and we returned to Carapace Nunatak along much the same route (figure 1). Sections of Kirkpatrick Basalt (figure 2) were sampled at Carapace Nunatak (8 lava flows with a total thickness of 130 meters), Gorgon Peak (18 lava flows, 220 meters thick), and Brimstone Peak (20 flows, about 380 meters thick). Chilled margins, representative of the initial bulk composition of doleritic intrusives, were sampled in numerous locations. One important aspect of determining the petrogenesis of the Ferrar Group is to examine basic high-magnesium oxide basalt and dolerite. We were able to locate and sample the previously undiscovered lower chilled margin of a dolerite sill at the butte known as The Mitten that contains olivine (Skinner and Ricker, 1968; Gunn, 1966). During our traverse, we found over 200 meters of massive diamictite, probably correlative with the Mawson Formation, at the south end of Griffin Nunatak. This unit, interbedded within Kirkpatrick Basalt lava flows, is overlain by diamictite that is probably correlative with the Sirius Formation. We also determined that Twin Nunataks, Crash Nunatak, the summit of Ford Peak, and the southern end of the Ricker Hills, all previously mapped as Kirkpatrick Basalt, actually consist of intrusive dolerite. Similarly, in the Darwin Glacier area, we found that the previously reported Kirkpatrick Basalt at Westhaven Nunatak and also at Turnstile Ridge consists of doleritic intrusives. We also made a new and important discovery at Butcher Ridge, where we traced strongly deformed glassy acidic rocks for a distance of more than 4 kilometers. This is the first extensive area of "dacitic" or "rhyolitic" rocks known in the Ferrar Group. The exact means of emplacement of many of the rocks is still un25
10
it Mt Faila *Pointed Cliffs 0 Ot.y Massif C*00*I Tronsantorctic Mountains a Grosvenor MO Other North Victoria Land South Victoria Land Caron Glacier 9(99*, Eo,po.ot 0 0'O.9Q Maud Land
.9
9 0
7 D
1
0
• .1 D. . •0 . 4
A D0p
2 I
0
(09
A
base for more specialized geochemical studies. In the course of our 1978-79 fieldwork, we also discovered that Elephant Nunatak (unofficial name), a feature east of Reckling Peak previously discovered using satellite imagery, is composed entirely of moraine. In addition, we found five chondrite meteorites in the vicinity of the moraine. I was supported in the field by Kathy Cashman and Harry Keys (both from Victoria University of Wellington) and Bill McIntosh (University of Colorado). This work has been supported by National Science Foundation grant DPP 77-21590.
DD
0 -50 52 54 :. 58 60 Q 14
lo 72
Sn2
Figure 3. Silica variation diagrams of selected oxides for Jurassic tholeiltic rocks from the Transantarctic Mountains.
determined, but an intrusive origin appears to be the most likely method. Over 150 new major element analyses (figure 3) of Jurassic tholeiites from Antarctica will provide a data
Artesian well at Don Juan Pond LYLE D. MCGINNIS
Department of Geology Northern Illinois University De Kalb, Illinois 60115
Don Juan Pond, located in the suth fork of Wright Valley, was revisited on 9-12 December 1978 to observe the status of Dry Valley Drilling Project (DVDP) hole 13. Since its drilling on 8-13 January 1975, the borehole and pond have remained under intermittent observation (Harris and Cartwright, in press; Harris, Cartwright, and Toni, 1979). The borehole is unusual in that it contains unfrozen, concentrated brines near 200 parts per thousand. Water level in the borehole is responding to episodic, impulsive pressure changes of unproven origin (Harris and Cartwright, in press). Plans are under way to install automatically recording instrumentation at the borehole to determine the cause of the transient pressure variations and the source of the brines. After ice was cleared from the upper 10 meters of the hole at 1700 hours on 9 December, water at a temperature of - 15.50 C began flowing from the hole at a 26
References (;rn, B. M. 1966. Modal and element variation in Antarctic tholeiites. Geochimica Cosmochimica Acta, 30: 881-920. Kyle, P. R. Development of heterogeneities in the subcontinental mantle: Evidence from the Ferrar Group, Antarctica. In Contributions to Mineralogy and Petrology (in press). Skinner, D.N.B., and J . Ricker. 1968. The geology of the region between the Mawson and Priestley Glaciers, north Victoria Land, Antarctica. New Zealand Journal of Geology and Geophysics, 11: 1009- 1075.
steady rate of 4 liters per minute and continued to flow for three days before being shut off. Casing set through the sand overburden (see figure) stands 0.70 meter above ground surface and about 1 meter above Don Juan Pond. It is believed that water is flowing from the fractured and highly mineralized Ferrar dolerite, which acts as a confined aquifer in the dry valleys but may receive its water from subglacial lakes at the base of the Antarctic Ice Sheet. Geophysical logs of the borehole are also shown in the accompanying figure. A discussion of the logs is provided in McGinnis et al. (in press). This study has been supported by the Division of Polar Programs of the National Science Foundation, grant number DPP 7821112-01. References Harris, H. J . H., and K. Cartwright. In press. Pressure fluctuations in an antarctic aquifer: The freight train response to a moving rock glacier. In Third Symposium on Antarctic Geology and Geophysics, ed. C. Craddock. Madison: University of Wisconsin Press. Harris, H. J . H., K. Cartwright, and T. Toni. 1979. Dynamic chemical equilibrium in a polar desert pond: A sensitive index of meteorological cycles. Science, 264(4390): 301-3. McGinnis, L. D., J . S. Stuckless, D. R. Osby, and P. R. Kyle. In press. Gamma-ray, salinity, and electric logs of DVDP boreholes. In Dry Valley Drilling Project, ed. L. McGinnis. Antarctic Research Series. Washington, D. C.: American Geophysical Union.
