Temporal constraints on the timing of high-grade metamorphism in the northern Gawler Craton: implications for assembly of the Australian Proterozoic

Figures & data

Figure 1 Current distribution of tectonic elements of Proterozoic Australia that formed prior to ca 1070 Ma. Constructed from GIS datasets of Northern Territory Geological Survey, Geological Survey of Western Australia, Primary Industries and Resources South Australia, Geological Survey of Queensland. Australian coast outline adapted from topographic dataset of Geoscience Australia. Gawler Craton outline and detail interpreted from geophysical datasets (Fairclough et al. 2003).

Figure 2 Simplified solid geology of the Gawler Craton (after Fairclough et al. 2003). Inset, Total Magnetic Intensity image of the Gawler Craton overlain by interpreted domains with selected domain names: P & D, Peake and Denison Domain; CP, Coober Pedy Domain; MW, Mt Woods Domain.

Figure 3 Total Magnetic Intensity image of the Gawler Craton overlain with distribution of Kimban Orogeny metamorphic and magmatic ages on the Gawler Craton. Dashed lines represent interpreted domains with the Coober Pedy Domain (CP), Mabel Creek Ridge (MC), Peake and Denison Domain (P & D) and Mt Woods Domain (MW) and trace of the Karari Fault Zone (KFZ, bold line) marked. Metamorphic ages (black dots) are: 1, 1731 ± 8 Ma (U–Pb SHRIMP zircon: Vassallo 2001); 2, 1699 ± 15 Ma (MSWD 7.3, U–Pb SHRIMP zircon: Vassallo 2001); 3, 1693 ± 9 (MSWD 8.5, U–Pb SHRIMP zircon: Vassallo 2001); 4, 1701 ± 2.8 Ma (U–Pb zircon: Vassallo 2001); 5, 1712 ± 10 Ma (U–Pb SHRIMP monazite: Teasdale 1997); 6, 1736 ± 14 Ma (U–Pb SHRIMP zircon Daly et al. 1998); 7, 1696 ± 12 Ma (U–Pb SHRIMP zircon, 4 analyses: Daly et al. 1998); 8, 1728 ± 30 Ma (Pb–Pb garnet: Hopper 2001); 9–13, Kimban Orogeny metamorphic ages from this study; 14, 1728 ± 13 Ma (U–Pb SHRIMP monazite: Dutch et al. 2006); 15, 1720 ± 6 Ma (U–Pb SHRIMP monazite: Dutch et al. 2006). White dots represent the location of dated syn-orogenic Kimban granites; white squares represent the location of dated post-orogenic Tunkillia Suite granites: granite data from Teasdale (1997), Daly et al. (1998) and Ferris (2001).

Table 1  Sample descriptions and drillhole locations.

Sample no.	Drillhole	Location		Interval (m)(m)	Lithology
		(GDA 94, MGA Zone 53)
		Easting	Northing
650698	Mt Furner 1	447484	6891322	552.0–552.6	Quartz–plagioclase–biotite–garnet gneiss
650703	Manya 4	380974	6898335	801.9–802.1	Quartz–feldspar–biotite (garnet) gneiss
1052049	Lake Maurice East 1	738721	6721324	732.3–733.3	Garnet–biotite–sillimanite–cordierite gneiss
660856	Ooldea 2	764644	6613064	143.0–143.3	Quartz–magnetite–plagioclase–feldspar–sillimanite–(sapphirine–cordierite)
650723	AM/PB 3	391128	6806972	272.4–272.9	Quartz–plagioclase–garnet–biotite gneiss
967234	AM/PB 1	393908	6813051	351.2–351.9	Garnet–sillimanite–cordierite–biotite granulite

Figure 4 Metamorphic mineral assemblages. (a) Mt Furner 1, showing sillimanite inclusions in garnet and late coarse-grained muscovite growth. (b) Manya 4, garnet, biotite and quartz with weathering products. (c) Lake Maurice East 1, garnet, magnetite, sillimanite with quartz ribbons. Alteration products are pseudomorphing plagioclase and cordierite. (d) Lake Maurice East 1, garnet and magnetite symplectite textures. (e) Ooldea 2, garnet and magnetite symplectite. (f) Enhanced photograph of Ooldea 2 drillcore demonstrating UHT fine-grained mylonitic fabric (taken from Teasdale 1997). (g) AM/PB 3, breakdown texture of garnet to orthopyroxene. (h) AM/PB 3, fine-grained shear fabric overprinting primary coarse-grained fabric. (i) AM/PB 1, coarse-grained garnet showing sillimanite inclusions paralleling the curved foliation enclosing the garnet in the matrix. (j) AM/PB 1, coarse-grained cordierite enclosed by quartz and sillimanite. bi, biotite; gt, garnet; mag, magnetite; mus, muscovite; opx, orthopyroxene; plg, plagioclase; qtz, quartz; sill, sillimanite; cd, cordierite; (cd), clay minerals after cordierite; (plg), clay minerals after plagioclase; wth, indeterminate weathering products.

Figure 5 BSE images of representative monazites from each sample analysed. (a) Mt Furner 1. (b) Manya 4. (c) Lake Maurice East 1: gr 1, resorption textures; gr 2, concentric zoning. (d) Lake Maurice East 1, resorption textures (e) Ooldea 2. (f) AM/PB 3, monazite with ca 1555 Ma rim. (g) AM/PB 3, monazite with inconsistent BSE zoning and ages. (h) AM/PB 1, monazite from garnet separate with two growth zones evident, highlighted by dashed white line.

Figure 6 Concordia, weighted average and probability density plots for all data from analysed samples. (a, b) Mt Furner: (a) concordia; (b) ²⁰⁷Pb/²⁰⁶Pb weighted average. (c, d) Manya 4: (c) concordia; (d) ²⁰⁷Pb/²⁰⁶Pb weighted average. (e, f) Lake Maurice East: (e) concordia; (f) ²⁰⁷Pb/²⁰⁶Pb weighted average. (g, h) Ooldea 2: (g) concordia; (h) ²⁰⁷Pb/²⁰⁶Pb weighted average. (i–k) AM/PB3: (i) concordia, all data; (j) ²⁰⁷Pb/²⁰⁶Pb weighted average, old group; (k) ²⁰⁷Pb/²⁰⁶Pb weighted average, young group. (l–n) AM/PB1: (l) concordia bulk-rock monazites and garnet-separate monazites (grey ellipses); (m) ²⁰⁷Pb/²⁰⁶Pb weighted average, garnet-separate monazites; (n) ²⁰⁷Pb/²⁰⁶Pb weighted average, bulk-rock monazites excluding monazite grain displaying two simple growth zones in BSE imaging; ²⁰⁷Pb/²⁰⁶Pb weighted average for all analyses is 1569 ± 8 Ma.

Table 2  Summary of orogenic events in the Gawler Craton.

Event	Distribution of metamorphism and deformation	Age	Metamorphic style	Peak P – T	P – T evolution	Magmatism
Sleafordian	Entire Late Archean Gawler	2460 – 2430 Ma	High heat flow, low to mod. P	850°C, 600 MPa	Unknown	Felsic and minor Mafic
Cornian	Southeast craton	ca 1850 Ma	High heat flow, mod. P	750°C, 600 MPa	Clockwise	Felsic
Kimban	Entire craton	1730 – 1690 Ma	Low-High heat flow	800 – 850°C, 700 – 900 MPa & Ooldea 900°C, 1000 MPa	Clockwise	Felsic and Mafic (large volume)
Ooldean	Ooldea Region ?	ca 1650 Ma	High heat flow, low P	800°C, 500 MPa	Isobaric cooling	Unknown
St Peter Suite deformation	Southwestern craton	ca 1620 – 1610	High heat flow	Unknown	Unknown	St Peter Suite
Hiltaba Event	Predominantly Mt Woods Domain	ca 1585 Ma	High heat flow	Estimated 750°C, 500 MPa	Unknown	Large volume felsic and mafic Hiltaba
Kararan	Northern and Western craton	1570 – 1545 Ma	Moderate heat flow	800°C, 1000 MPa	Unknown	Unknown
Late shear-zone systems	Northern and Western craton?	ca 1450 Ma?	Moderate heat flow	Estimated 500°C, <400 MPa	Unknown	None known
Information from Teasdale (1997), Daly et al. (1998), Vassallo (2001), Vassallo & Wilson (2001), Ferris et al. (2002), Dutch et al. (2006), Fraser & Lyons (2006), McFarlane (2006), Reid et al. (2006) and this study.

Figure 7 (a) TMI data of the Gawler Craton overlain with locations of Kimban Orogeny metamorphic age data. Black dots represent metamorphic ages; white dots and squares represent syn- and post-Kimban magmatism. Dashed trendlines represent structural trends interpreted to have formed during the Kimban Orogeny. (b) TMI data of Gawler Craton overlain with location and ages of metamorphic mineral geochronology in the ca 1585–1545 Ma interval. Black dots represent U–Pb metamorphic ages in the interval 1590–1570 Ma; White dots represent U–Pb metamorphic ages in the 1570–1550 Ma interval; the white square represents metamorphic age in the 1550–1540 Ma interval. See text for data sources.

Table 3  U – Pb Isotopic composition of MAdel by TIMS.

^206Pb/^238U				^207Pb/^235U				^207Pb/^206Pb
Ratio		Age (Ma)		Ratio		Age (Ma)		Ratio		Age (Ma)
	2σ		2σ		2σ		2σ		2σ		2σ
Analysis conducted at Massachusetts Institute of Technology
0.083681	41	518.06	0.24	0.657679	434	513.19	0.27	0.057001	26	491.6	1.0
0.083611	44	517.64	0.26	0.657445	502	513.05	0.31	0.057029	31	492.6	1.2
0.083138	39	514.83	0.23	0.653150	453	510.42	0.28	0.056979	29	490.7	1.1
Analysis conducted at University of Adelaide
0.082973	51	513.8	0.3	0.6535159	1456	510.6	0.85	0.057039	101	495.7	3.9

Table 4  Representative compositions of MAdel monazite standard.

Element	MAdel a (ppm)	MAdel b (ppm)	MAdel c (ppm)	Average (ppm)
Mg	0.05	0.0338	0.023	0.04
Si	12 384	9760	12 289	11 478
Sc	0.45	0.40	0.41	0.42
Ti	18.37	19.91	17.60	18.63
Mn	0.86	0.81	0.85	0.84
Sr	1.377	0.0553	0.0727	0.50
Y	8816.1	9152.1	8579.1	8849.1
Zr	3.41	4.2	3.59	3.73
Nb	0.377	0.459	0.443	0.43
La	71474	75 795	73 197	73 489
Ce	203 895	215 658	206 011	208 521
Pr	31226	33 180	31 438	31 948
Nd	133 777	142 217	134 126	136 707
Sm	39 599	41 974	39200	40 258
Eu	5.57	5.99	5.62	5.73
Gd	18 331	19 533	18134	18 666
Tb	12 84.7	1358.9	1268.6	1304.1
Dy	2483.6	2612.1	2456.5	2517.4
Ho	160.14	168.86	160.45	163.15
Er	157.48	166.20	157.35	160.34
Tm	10.62	10.91	10.32	10.62
Yb	44.95	47.03	43.27	45.08
Lu	3.65	3.69	3.36	3.57
Hf	0.36	0.38	0.37	0.37
Ta	0.05	0.06	0.06	0.06
Compositions obtained by LA-ICPMS using Ca as internal standard.

Fairclough , M. C. , Schwarz , M. and Ferris , G. M. 2003 . Interpreted Crystalline Basement Geology of the Gawler Craton, South Australia , (Special Map 1:1 000 000 scale) Primary Industries and Resources South Australia, Adelaide

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