antarctica poster

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Boger S.D. 2011. Antarctica-before and after Gondwana. Gondwana Research 19, 335-371. Boger S.D., Wilson C.J.L., Fanning C.M. 2001. Early Paleozoic tectonism within the East Antarctic craton: the final suture between east and west Gondwana. Geology 29, 463-466. Corvino A.F., Boger S.D., Henjes-Kunst F., Wilson C.J.L., Fitzsimons I.C.W. 2008. Superimposed tectonic events at 2450 Ma, 2100 Ma, 900 Ma and 500 Ma in the North Mawson Escarpment, Antarctic Prince Charles Mountains. Precambrian Research 167, 281-302. Fitzsimons I.C.W. 2003. Proterozoic basement provinces of southern and southwestern Australia, and their correlation with Antarctica. Geological Society, Special Publications 206, 93-130. Harley S.L., Fitzsimons I.C.W., Zhao Y. 2013. Antarctica and supercontinent evolution: historical perspectives, recent advances and unresolved issues. Geological Society, Special Publications 383, 1-34. Mikhalsky E.V., Henjes-Kunst F., Belyatsky B.V., Roland N.W., Sergeev S.A. 2010. New Sm-Nd, Rb-Sr, U-Pb and Hf isotope systematics for the southern Prince Charles Mountains (East Antarctica) and its tectonic implications. Precambrian Research 182, 101-123. Phillips G., Wilson C.J.L., Campbell I.H. Allen C.M. 2006. U-Th-Pb detrital zircon geochronology from the southern Prince Charles Mountains, East Antarctica: defining the Archaean to Neoproterozoic Ruker Province. Precambrian Research, 148, 292-306. Phillips G., Kelsey D.E., Corvino A.F., Dutch R.A. 2009. Continental reworking during overprinting orogenic events, southern Prince Charles Mountains, East Antarctica. Journal of Petrology 50, 2017-2041. The identification of c. 500 Ma metamorphism and deformation at the East Antarctic coastline has led to the suggestion that Antarctica is crossed by a Cambrian orogen, although its path remains controversial (Fig. 1). A common proposal is that it passes through the Prince Charles Mountains, where a Cambrian suture linked with deformation and metamorphism at c. 500 Ma is inferred to pass between northern terranes with dominant orogenesis at 1000–900 Ma and a southern terrane with no evidence for this event (Fig. 2). To test this model we undertook a SHRIMP U-Pb study of gneiss in the Mount Creswell region (Fig. 3). Garnet amphibolite yields a single zircon population with a concordia age of 957 ± 18 Ma, interpreted as the age of metamorphism and indicating these rocks are part of the 1.0 Ga Rayner Complex with no evidence of a 500 Ma overprint. Two samples of garnet-biotite-quartz gneiss contain detrital zircon populations at c. 3100, 2700, 2500, 2300, and 2100 Ma, suggesting their protolith was eroded in part from the Ruker Complex before metamorphism at 1000–900 Ma. These data support suggestions that terranes in the Prince Charles Mountains had assembled by c. 1.0 Ga (Phillips et al. 2009; Mikhalsky et al. 2010) and imply that any Cambrian suture passes southeast of the Prince Charles Mountains. Preliminary age data from Mount Creswell, central Prince Charles Mountains, East Antarctica: evidence for terrane assembly at 900 Ma and not 500 Ma Levi S. Reichelt, Ian C.W. Fitzsimons, and Rich J.M. Taylor The Institute for Geoscience Research, Department of Applied Geology, Curtin University, GPO Box U1987, Perth, WA 6845 Australia Relative Probability Relative Probability Age ( 207 Pb/ 206 Pb) 1600 1800 2000 2000 2200 2400 2600 2800 3000 3200 16 12 8 4 0 16 12 8 4 0 1600 1800 2000 2000 2200 2400 2600 2800 3000 3200 1600 1800 2000 2200 2400 2600 2800 3000 3200 3400 3600 16 12 8 4 0 3400 3600 3400 3600 Relative Probability 1600 1800 2000 2200 2400 2600 2800 3000 3200 3400 3600 16 12 8 4 0 Frequency IF-02-163 Machin Nunatak (this study) n = 29 Black < 2% discordant Grey > 2% discordant IF-02-209 Mt Creswell (this study) n = 29 Black < 3% discordant Grey > 3% discordant Ruker Complex Data Compilation (Phillips et al. 2006) Black = basement rocks (n unknown) Grey = detrital ages (n = 417) Lambert Complex Data Compilation (Corvino et al. 2008) n = 118 (excluding data < 1600 Ma) Black < 5% discordant Grey > 5% discordant Figure 4: Probability density distribution of SHRIMP 207 Pb/ 206 Pb detrital zircon ages for felsic gneiss samples IF-02-163 and IF-02-209 compared with data compilations for the Ruker and Lambert complexes. Limited Archean grains in our samples have similarities with the Ruker Complex suggesting the Rayner and Ruker complexes were linked before the c. 960 Ma metamorphic event. The dominant Paleoproterozoic grains in our samples are similar age to those in the Lambert Complex, although in detail they fall between the two major zircon populations identified in previous studies of the Lambert Complex. 100 μm 200 μm 0.5 mm 1 mm 0.5 mm (g) (f) (e) (d) (c) (b) (a) 990 ±25 Ma 1009 ±29 Ma 922 ±32 Ma 2183 ±22 Ma 2773 ±30 Ma 2486 ±23 Ma Garnet amphibolite Machin Nunatak (IF-02-162) Garnet amphibolite Machin Nunatak (IF-02-162) Garnet-biotite-quartz paragneiss, Mount Creswell (IF-02-209) Garnet-biotite-quartz paragneiss, Machin Nunatak (IF-02-163) Garnet-biotite-quartz paragneiss, Machin Nunatak (IF-02-163) Figure 2: (a) Typical outcrop of interlayered amphibolite facies gneissic rocks at Mt Creswell. (b) Photomicrograph of garnet amphibolite from Machin Nunatak (sample IF-02-162). (c) Photomicrograph of garnet-biotite-quartz paragneiss from Machin Nunatak (sample IF-02-163). (d) Photomicrograph of garnet-biotite-quartz paragneiss from Mt Creswell (sample IF-02-209). (e) Cathodoluminescence image of grain separates from sample IF-02-162 with SHRIMP 206 Pb/ 238 U spot ages (1σ errors). Bright low-uranium zircon grains with patchy zonation are interpreted as metamorphic. (f) Cathodoluminescence image of grain separates from sample IF-02-163 with SHRIMP 206 Pb/ 238 U spot ages (1σ errors). Rounded zircon grains with magmatic zonation and core-rim structures are interpreted as detrital, consistent with this rock having a sedimentary protolith. IF-02-209 yielded grains of very similar appearance and age. (g) Tera-Wasserburg concordia plot of SHRIMP U-Pb zircon data from IF-02-162 providing an age of c. 960 Ma for peak amphibolite metamorphism in the Central Prince Mountains. 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.02 5.0 4.0 6.0 3.0 7.0 9.0 8.0 238 U/ 206 Pb 207 Pb/ 206 Pb 1200 1600 800 IF-02-162 Garnet amphibolite Zircon U-Pb Concordia age = 957 ±18 Ma (95% confidence, MSWD 0.95, n = 10) Data point error ellipses are ±2σ Figure 2: Geological provinces of the Prince Charles Mountains (after Boger 2011). The Cambrian suture has been inferred primarily from relationships in the Mawson Escarpment, where the boundary between the Ruker and Lambert terranes is a high-strain zone recording metamorphism and deformation at 500 Ma (Boger et al. 2001). Relationships elsewhere are poorly constrained and we have analysed samples from Mt Creswell and Machin Nunatak to determine whether these outcrops might lie on the western extension of a Cambrian suture as suggested in this model. Magmatism and metamorphism at 1.0-0.9 Ga and 0.5 Ga Magmatism and metamorphism at 1.0-0.9 Ga only 2.4 and 2.1 Ga basement and paragneiss metamorphosed at 1.0-0.9 Ga and 0.5 Ga 3.1 Ga and 2.7 Ga basement and metasedimentary rock with local metamorphism at 0.5 Ga Neoproterozoic sedimentary sequence with low-grade metamorphism at 0.5 Ga Rayner Complex Lambert Complex Ruker Complex All rocks record 1.0-0.9 Ga metamorphism No evidence of 1.0-0.9 Ga metamorphism 200 km Amery Ice Shelf Prydz Bay Mawson Grove Mountains Northern Prince Charles Mountains Southern Prince Charles Mountains 72°S 70°S 68°S 74°S 65°E 60°E 70°E 75°E 80°E 74°S 72°S 70°S 68°S 65°E 70°E 75°E Mawson Escarpment Cambrian Suture? Mt Creswell Inferred geology after Boger (2011) Machin Nunatak Figure 1: Schematic map of basement provinces in East Antarctica and adjacent parts of Gondwana , highlighting the c. 1.0 Ga (Grenville-age) and c. 0.5 Ga (Pan-African) metamorphic belts (after Harley et al. 2013). Also shown are three suggestions for how Pan-African orogenesis might continue under the Antarctic ice sheet. Path 1 passes through the Prince Charles Mountains and was proposed by Boger et al. (2001), while paths 2 and 3 were proposed by Fitzsimons (2003). In this study we have used U-Pb geochronology to investigate the age of metamorphism and terrane assembly in the Prince Charles Mountains and test the validity of path 1. 3 2 1 Pre-Grenville cratons Grenville-age belts Possible Grenville? Pan-African belts Ross Orogen East Antarctica Fig. 2

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Page 1: Antarctica Poster

Boger S.D. 2011. Antarctica-before and after Gondwana. Gondwana Research 19, 335-371.Boger S.D., Wilson C.J.L., Fanning C.M. 2001. Early Paleozoic tectonism within the East Antarctic craton: the final suture between east and west Gondwana. Geology 29, 463-466.Corvino A.F., Boger S.D., Henjes-Kunst F., Wilson C.J.L., Fitzsimons I.C.W. 2008. Superimposed tectonic events at 2450 Ma, 2100 Ma, 900 Ma and 500 Ma in the North Mawson Escarpment, Antarctic Prince Charles Mountains.

Precambrian Research 167, 281-302.Fitzsimons I.C.W. 2003. Proterozoic basement provinces of southern and southwestern Australia, and their correlation with Antarctica. Geological Society, Special Publications 206, 93-130.Harley S.L., Fitzsimons I.C.W., Zhao Y. 2013. Antarctica and supercontinent evolution: historical perspectives, recent advances and unresolved issues. Geological Society, Special Publications 383, 1-34.Mikhalsky E.V., Henjes-Kunst F., Belyatsky B.V., Roland N.W., Sergeev S.A. 2010. New Sm-Nd, Rb-Sr, U-Pb and Hf isotope systematics for the southern Prince Charles Mountains (East Antarctica) and its tectonic implications.

Precambrian Research 182, 101-123.Phillips G., Wilson C.J.L., Campbell I.H. Allen C.M. 2006. U-Th-Pb detrital zircon geochronology from the southern Prince Charles Mountains, East Antarctica: defining the Archaean to Neoproterozoic Ruker Province. Precambrian

Research, 148, 292-306. Phillips G., Kelsey D.E., Corvino A.F., Dutch R.A. 2009. Continental reworking during overprinting orogenic events, southern Prince Charles Mountains, East Antarctica. Journal of Petrology 50, 2017-2041.

The identification of c. 500 Ma metamorphism and deformation at the East Antarctic coastline has led to the suggestion that Antarctica is crossed by a Cambrian orogen, although its path remains controversial (Fig. 1). A common proposal is that it passes through the Prince Charles Mountains, where a Cambrian suture linked with deformation and metamorphism at c. 500 Ma is inferred to pass between northern terranes with dominant orogenesis at 1000–900 Ma and a southern terrane with no evidence for this event (Fig. 2). To test this model we undertook a SHRIMP U-Pb study of gneiss in the Mount Creswell region (Fig. 3). Garnet amphibolite yields a single zircon population with a concordia age of 957 ± 18 Ma, interpreted as the age of metamorphism and indicating these rocks are part of the 1.0 Ga Rayner Complex with no evidence of a 500 Ma overprint. Two samples of garnet-biotite-quartz gneiss contain detrital zircon populations at c. 3100, 2700, 2500, 2300, and 2100 Ma, suggesting their protolith was eroded in part from the Ruker Complex before metamorphism at 1000–900 Ma. These data support suggestions that terranes in the Prince Charles Mountains had assembled by c. 1.0 Ga (Phillips et al. 2009; Mikhalsky et al. 2010) and imply that any Cambrian suture passes southeast of the Prince Charles Mountains.

Preliminary age data from Mount Creswell, central Prince Charles Mountains,East Antarctica: evidence for terrane assembly at 900 Ma and not 500 MaLevi S. Reichelt, Ian C.W. Fitzsimons, and Rich J.M. TaylorThe Institute for Geoscience Research, Department of Applied Geology, Curtin University, GPO Box U1987, Perth, WA 6845 Australia

Rel

ativ

e P

roba

bilit

yR

elat

ive

Pro

babi

lity

Age (207Pb/206Pb)

1600 1800 20002000 2200 2400 2600 2800 3000 3200

16

12

8

4

0

16

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8

4

01600 1800 20002000 2200 2400 2600 2800 3000 3200

1600 1800 2000 2200 2400 2600 2800 3000 3200 3400 3600

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0

3400 3600

3400 3600

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ativ

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roba

bilit

y

1600 1800 2000 2200 2400 2600 2800 3000 3200 3400 3600

16

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Freq

uenc

yIF-02-163Machin Nunatak(this study)n = 29

Black < 2% discordantGrey > 2% discordant

IF-02-209Mt Creswell(this study)n = 29

Black < 3% discordantGrey > 3% discordant

Ruker ComplexData Compilation(Phillips et al. 2006)

Black = basement rocks(n unknown)Grey = detrital ages (n = 417)

Lambert ComplexData Compilation(Corvino et al. 2008)n = 118 (excludingdata < 1600 Ma)

Black < 5% discordantGrey > 5% discordant

Figure 4: Probability density distribution of SHRIMP 207Pb/206Pb detrital zircon ages for felsic gneiss samples IF-02-163 and IF-02-209 compared with data compilations for the Ruker and Lambert complexes. Limited Archean grains in our samples have similarities with the Ruker Complex suggesting the Rayner and Ruker complexes were linked before the c. 960 Ma metamorphic event. The dominant Paleoproterozoic grains in our samples are similar age to those in the Lambert Complex, although in detail they fall between the two major zircon populations identified in previous studies of the Lambert Complex.

100 µm 200 µm

0.5 mm1 mm

0.5 mm

(g)

(f)(e)

(d)(c)

(b)(a)

990 ±25 Ma

1009 ±29 Ma

922 ±32 Ma

2183 ±22 Ma

2773 ±30 Ma

2486 ±23 Ma

Garnet amphiboliteMachin Nunatak

(IF-02-162)

Garnet amphiboliteMachin Nunatak

(IF-02-162)

Garnet-biotite-quartz paragneiss, Mount

Creswell (IF-02-209)

Garnet-biotite-quartzparagneiss, Machin

Nunatak (IF-02-163)

Garnet-biotite-quartzparagneiss, Machin

Nunatak (IF-02-163)

Figure 2: (a) Typical outcrop of interlayered amphibolite facies gneissic rocks at Mt Creswell. (b) Photomicrograph of garnet amphibolite from Machin Nunatak (sample IF-02-162). (c) Photomicrograph of garnet-biotite-quartz paragneiss from Machin Nunatak (sample IF-02-163). (d) Photomicrograph of garnet-biotite-quartz paragneiss from Mt Creswell (sample IF-02-209). (e) Cathodoluminescence image of grain separates from sample IF-02-162 with SHRIMP 206Pb/238U spot ages (1σ errors). Bright low-uranium zircon grains with patchy zonation are interpreted as metamorphic. (f) Cathodoluminescence image of grain separates from sample IF-02-163 with SHRIMP 206Pb/238U spot ages (1σ errors). Rounded zircon grains with magmatic zonation and core-rim structures are interpreted as detrital, consistent with this rock having a sedimentary protolith. IF-02-209 yielded grains of very similar appearance and age. (g) Tera-Wasserburg concordia plot of SHRIMP U-Pb zircon data from IF-02-162 providing an age of c. 960 Ma for peak amphibolite metamorphism in the Central Prince Mountains.

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.025.04.0 6.03.0 7.0 9.08.0

238U/206Pb

207Pb/206Pb

1200

1600

800

IF-02-162Garnet amphibolite

Zircon U-Pb Concordia age = 957 ±18 Ma(95% confidence, MSWD 0.95, n = 10)

Data point errorellipses are ±2σ

Figure 2: Geological provinces of the Prince Charles Mountains (after Boger 2011). The Cambrian suture has been inferred primarily from relationships in the Mawson Escarpment, where the boundary between the Ruker and Lambert terranes is a high-strain zone recording metamorphism and deformation at 500 Ma (Boger et al. 2001). Relationships elsewhere are poorly constrained and we have analysed samples from Mt Creswell and Machin Nunatak to determine whether these outcrops might lie on the western extension of a Cambrian suture as suggested in this model.

Magmatism and metamorphismat 1.0-0.9 Ga and 0.5 Ga

Magmatism and metamorphismat 1.0-0.9 Ga only

2.4 and 2.1 Ga basement andparagneiss metamorphosedat 1.0-0.9 Ga and 0.5 Ga

3.1 Ga and 2.7 Ga basementand metasedimentary rockwith local metamorphismat 0.5 Ga

Neoproterozoic sedimentarysequence with low-grademetamorphism at 0.5 Ga

Rayner Complex

Lambert Complex

Ruker Complex

All rocks record1.0-0.9 Gametamorphism

No evidence of1.0-0.9 Gametamorphism

200 km

AmeryIce Shelf

PrydzBay

Mawson

Grove Mountains

NorthernPrince

CharlesMountains

SouthernPrince CharlesMountains

72°S

70°S

68°S

74°S

65°E60°E 70°E 75°E 80°E

74°S

72°S

70°S

68°S

65°E 70°E 75°E

MawsonEscarpment

CambrianSuture?

Mt Creswell

Inferred geologyafter Boger (2011)

MachinNunatakFigure 1: Schematic map of basement provinces in East Antarctica and

adjacent parts of Gondwana , highlighting the c. 1.0 Ga (Grenville-age) and c. 0.5 Ga (Pan-African) metamorphic belts (after Harley et al. 2013). Also shown are three suggestions for how Pan-African orogenesis might continue under the Antarctic ice sheet. Path 1 passes through the Prince Charles Mountains and was proposed by Boger et al. (2001), while paths 2 and 3 were proposed by Fitzsimons (2003). In this study we have used U-Pb geochronology to investigate the age of metamorphism and terrane assembly in the Prince Charles Mountains and test the validity of path 1.

3

2

1

Pre-Grenville cratons

Grenville-age belts

Possible Grenville?

Pan-African belts

Ross Orogen

EastAntarctica

Fig. 2