Timing of Proterozoic metamorphism in the southern Curnamona Province: implications for tectonic models and continental reconstructions ∗

∗Appendix 1 [indicated by an asterisk (∗) in the text and listed at the end of the paper] is a Supplementary Paper; copies may be obtained from the Geological Society of Australia's website (www.gsa.org.au) or from the National Library of Australia's Pandora archive (http://nla.gov.au/nla.arc-25194).

Figures & data

Figure 1 Location of the southern Curnamona Province in northeastern South Australia and western New South Wales. Boxed area shows sample localities ( Figure 5).

Figure 2 Position of Australia relative to Laurentia for the SWEAT and AUSWUS tectonic reconstruction models (modified from Karlstrom et al. 2001).

Figure 3 Palaeoproterozoic and Mesoproterozoic tectonostratigraphic history of the southern Curnamona Province highlighting the timing of deposition of the Willyama Supergroup, timing of major magmatic events, and the proposed timing of tectonometamorphic events prior to this study. Data sources: Ludwig and Cooper (1984), Page and Laing (1992), Ashley et al. (1996), Nutman and Ehlers (1998), Page et al. (1998, 2000, 2003, 2005a, b), Barovich and Hand (2004), Gibson and Nutman (2004).

Figure 4 Proterozoic tectonic reconstruction highlighting the proximity of the Willyama basin to the Maronan basin in northern Australia prior to the 55° rotation of the southern Australian craton proposed by Giles et al. (2002). Both basins are situated in the backarc to convergent margins at the southern and eastern margins of the North Australian Craton (after Giles et al. 2002).

Table 1  Summary of monazite chemical age data from samples analysed in this study: distinction made between different occluding phases and the mean chemical ages of monazite included in these phases.

Sample	Lithology	Locality	Grid reference (WDS84)	Stratigraphic position	Occluding phase	Wt% Pb (avg & sd^a)	Wt% Th (avg & sd^a)	Wt% U (avg & sd)	M1 age & error (Ma)^b	n ^c	M2 age & error (Ma)^b	n ^c
Broken Hill Domain
SC2	gt-sill-bt schist	Southern Cross	539561, 6476859	Broken Hill Group	Matrix (micas)	0.54, 0.105	5.5164, 0.966	0.612, 0.363	1594 ± 17	82	–	–
RND	gt-sil-mu gneiss	Round Hill, NE of Broken Hill	549046, 6467095	Sundown Group	Sillimanite	0.479, 0.123	4.356, 0.968	0.582, 0.237	1612 ± 18	47	–	–
					Matrix (micas)	0.461, 0.025	4.397, 0.284	0.513, 0.03	1601 ± 42	13	–	–
					Garnet	0.483, 0.059	4.774, 0.625	0.526, 0.137	–	–	1570 ± 18	41
RRQ	gt-sill gneiss	Rasp Ridge Gneiss quarry	546400, 6463100	Thackaringa Group	Garnet	0.451, 0.079	4.536, 0.391	0.45, 0.24	1591 ± 17	101	–	–
RR2	Kfsp-pl-q-bt gneiss	Rasp Ridge Gneiss Block 10	542607, 6463043	Thackaringa Group	Plagioclase	0.502, 0.096	5.078, 0.937	0.517, 0.161	–	–	1571 ± 29	34
					K-feldspar	0.49, 0.036	4.834, 0.334	0.568, 0.093	–	–	1547 ± 24	44
ALM	Kfsp-pl-q-sill-gt gneiss	Airport entrance, Broken Hill	544781, 6460324	Alma Gneiss	Plagioclase	0.714, 0.05	7.213, 0.577	0.689, 0.254	1596 ± 22	31	–	–
					Sillimanite	0.683, 0.064	6.71, 1.277	0.766, 0.371	–	–	1565 ± 22	33
CUES	gt-crd-sill-pl gneiss	Airport runway, Broken Hill	546513, 6459686	Thackaringa Group	Plagioclase	0.482, 0.037	5.035, 0.474	0.423, 0.148	1591 ± 50	15	–	–
					Cordierite	0.604, 0.079	6.055, 1.328	0.612, 0.114	1587 ± 23	34	–	–
					Garnet	0.51, 0.04	5.113, 0.57	0.514, 0.134	1586 ± 20	73	–	–
					Sillimanite	0.543, 0.037	5.312, 0.517	0.591, 0.146	1585 ± 31	12	–	–
PS	gt-sill-mu-bt gneiss	Reservoir: Broken Hill	542148, 6460392	Hores Gneiss	Mica	0.579, 0.18	4.13, 1.543	1.043, 0.56	1601 ± 18	90	–	–
CB6	mu-bt-ser-pl-q schist	Copper Blow	547736, 6445055	Thackaringa Group	Quartz	0.723, 0.165	7.119, 2.074	0.849, 0.269	–	–	1554 ± 18	41
R899	gt-pl-bt-mu schist	Mingary, western BHD	490580, 6427130	Thackaringa Group	Plagioclase	0.559, 0.056	5.897, 0.786	0.525, 0.112	–	–	1560 ± 38	12
					Matrix	0.542, 0.042	5.388, 0.473	0.608, 0.195	–	–	1554 ± 17	62
					Garnet	0.516, 0.042	5.306, 0.446	0.545, 0.139	–	–	1542 ± 27	29
Olary Domain
AH5C	gt-sill-bt schist	Ameroo Hill	425230, 6444277	Saltbush Subgroup	Garnet	0.429, 0.234	2.169, 1.854	1.027, 0.485	1605 ± 30	49	–	–
NWI3	and-gt-st schist	Northern Walparuta Inlier	408070, 6439907	Wiperaminga Subgroup	Mica	0.327, 0.149	3.213, 2.164	0.357, 0.209	1589 ± 26	63	–	–
NWI5	and-gt-st schist	Northern Walparuta Inlier	408070, 6439907	Wiperaminga Subgroup	Andalusite	0.286, 0.102	2.904, 1.458	0.269, 0.112	1607 ± 17	172	–	–
OL3D	gt-mu-chl-bt schist	Northern Walparuta Inlier	404535, 6440075	Wiperaminga Subgroup	Retrograde mica	0.538, 0.153	5.194, 1.813	0.647, 0.481	–	–	1559 ± 16	101
WW18	gt-mu-bt-ser schist	Northern Walparuta Inlier	403986, 6439213	Wiperaminga Subgroup	Retrograde mica	0.439, 0.15	4.877, 2.132	0.342, 0.206	–	–	1573 ± 29	55
^aavg & sd, average and standard deviation.
^berror, 95% confidence interval.
^c n, number of analyses.
gt, garnet’ sill, sillimanite; bt, biotite; mu, muscovite; Kfsp, K-feldspar; pl, plagioclase; q, quartz; crd, cordierite; and, andalusite; st, staurolite; ser, sericite; chl, chlorite.

Figure 5 Regional geological map of the southern Curnamona Province showing the distribution of lithological units (Jenkins & Burtt 2003), and sample localities indicated by filled circles with sample numbers/letters.

Figure 6 Pre-peak to syn-peak metamorphic monazite-hosting lithologies (M1). (a) Photomicrograph of andalusite – garnet – staurolite – mica metapelitic schist (NWI5), cross-polarised light (XPL). (b) Backscatter electron (BSE) images of monazite occluded by synkinematic andalusite in sample NWI5. (c) Photomicrograph of garnet – fibrolite – biotite – muscovite – chloritoid metapeltic schist (AH5C), plane-polarised light (PPL). (d) BSE image of monazite in AH5C. Monazite occurs as clusters in fractures dissecting the core of a polymetamorphic garnet. (e) Qualitative elemental maps (Fe, Ca) of polymetamorphic garnets from AH5C. (f) Photomicrograph of garnet – sillimanite – cordierite – mica metapelitic gneiss (RND), PPL. (g) BSE image of monazite in sample RND. (h) Photomicrograph of garnet – sillimanite – fibrolite – mica metapelitic schist (SC2), PPL. (i) BSE image of monazite occluded within matrix micas defining post-kinematic fabric (S₂). (j) Photomicrograph of garnet – sillimanite – biotite – muscovite metapelitic gneiss (PS), PPL. (k) BSE images of monazite occluded within the mica matrix of sample PS; monazite rims replaced by apatite – allanite coronas. (l) Photomicrograph of andalusite – garnet – staurolite – mica metapelitic unit (NWI3), XPL. (m) BSE image of monazite occluded within a partly retrogressed andalusite porphyroblast from sample NWI3. (n) Photomicrograph of plagioclase – quartz – biotite – garnet granitic gneiss (RRQ), XPL; monazite occluded within the fractured garnet porphyroblasts. (o) Photomicrograph of sillimanite – quartz – feldspar – garnet – biotite gneiss (ALM), XPL; monazite occluded by plagioclase and sillimanite. (p) BSE image of garnet – cordierite – sillimanite – feldspar – biotite gneissic metapelitic gneiss (CUES); monazite occluded within all major silicate phases. (q) Qualitative elemental map of Mg in garnet – cordierite decompression texture from sample CUES. Mineral abbreviations: allan, allanite; and, andalusite; apa, apatite; bt, biotite; cd, cordierite; chl, chlorite; fib, fibrolite; gt, garnet; ilm, ilmenite; Ksp, K-feldspar; mu, muscovite; mz, monazite; pl, plagioclase; q, quartz; ser, sericite; sill, sillimanite; st, staurolite.

Figure 7 Post-peak Olarian metamorphic monazite-bearing lithologies (M2). (a) Photomicrograph of quartz – feldspar – biotite granitic gneiss (Rasp Ridge Gneiss; RR2), plane-polarised light (PPL). (b) Backscatter electron (BSE) image of monazite occluded by plagioclase in sample RR2. (c) BSE image of garnet – sillimanite – biotite – feldspar – quartz metapelitic granulite (R899). (d) BSE image of monazite occluded within matrix biotite in sample R899. (e) Photomicrograph of mica – magnetite – quartz lithology (CB6), cross-polarised light (XPL). (f) BSE image of monazite located at quartz triple point in sample CB6. (g) Photomicrograph of retrograde garnet – muscovite – sericite schist (WW18), PPL.(h) BSE image of monazite analysed from within the retrograde matrix in sample WW18. (i) Photomicrograph of retrograde chlorite – sericite – muscovite – biotite schist (OL3D), PPL; monazite analysed from within strongly foliated matrix. Mineral abbreviations listed in Figure 6.

Figure 8 Probability density plots of all monazite chemical ages pooled together with regard to the two metamorphic events identified in this study.

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