# Samarium-neodymium isotope map of Western Australia

Yong-Jun Lu, Michael T. D. Wingate, Dave Champion, Robert H Smithies, Simon P Johnson, Klaus Gessner, Roland Maas, David R Mole, Marc Poujol, Jian-Xin Zhao, et al.

► To cite this version:

Yong-Jun Lu, Michael T. D. Wingate, Dave Champion, Robert H Smithies, Simon P Johnson, et al. Samarium-neodymium isotope map of Western Australia. [Technical Report] State of Western Australia (Department of Mines, Industry Regulation and Safety). 2022, 8 p. insu-03817088

HAL Id: insu-03817088

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Submitted on 17 Oct 2022

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# Samarium-neodymium isotope map of Western Australia

Y Lu, MTD Wingate, DC Champion¹, RH Smithies, SP Johnson, K Gessner, R Maas², DR Mole¹, M Poujol³, J Zhao⁴ and RA Creaser⁵

1. Geoscience Australia, GPO Box 378, Canberra, ACT 2601, Australia

2. School of Earth Sciences, University of Melbourne, Parkville, VIC 3010, Australia

3. GeOHeLiS, Géosciences Rennes, UMR 6118, Université Rennes 1, 35042 Rennes cedex, France

4. Radiogenic Isotope Facility, School of Earth Sciences, University of Queensland, Brisbane, QLD 4072, Australia

5. Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, AB T6G 2E3, Canada

## Abstract

The Geological Survey of Western Australia (GSWA) released its first statewide samarium-neodymium (Sm-Nd) isotope map under the Accelerated Geoscience Program in 2021 (Lu et al., 2021). Such isotope maps have previously been used to characterize lithospheric architecture through time, and to help understand crustal evolution and mineral system distributions, and play an increasingly important role in predictive exploration targeting (Champion and Cassidy, 2007; McCuaig and Hronsky, 2014; Mole et al., 2015; Champion and Huston, 2016; Wu et al., 2022). Here we present a revised Sm-Nd isotope map of Western Australia that updates previously released data with analyses of 230 new samples, for a total of 2224 analyses (Figs 1, 2).

These Sm-Nd isotope maps (Fig. 2) are based on whole-rock Sm-Nd data for felsic igneous rocks, which provide a window into the age and compositional variation of the middle and lower continental crust where most felsic magmas are generated (Champion and Huston, 2016). Although mafic igneous and sedimentary rocks were not used in constructing the isotope maps, Sm-Nd data for those samples are also included in the data table along with data for felsic igneous rocks.

The isotope calculations are based on a chondritic uniform reservoir (CHUR) model with modern-day CHUR values of ¹⁴⁷Sm/¹⁴⁴Nd = 0.1960 and ¹⁴³Nd/¹⁴⁴Nd = 0.512630 (Bouvier et al., 2008), a depleted mantle (DM) model with modern-day DM values of ¹⁴⁷Sm/¹⁴⁴Nd = 0.2136 and ¹⁴³Nd/¹⁴⁴Nd = 0.513163, and an assumed ¹⁴⁷Sm/¹⁴⁴Nd value of 0.11 for average continental crust (Champion and Huston, 2016). The isotope maps were created using the Natural Neighbour interpolation tool in ArcGIS Spatial Analyst following Champion and Huston (2016), and are presented as both classified (natural breaks classification, Fig. 2a,c) and stretched (Histogram Equalize type, Fig. 2b,d) raster datasets.

The maps show two-stage depleted mantle model ages (T<sub>DM</sub><sup>2</sup>, proxy for the average age of the crustal source of the igneous rocks) and crustal residence time (T<sub>CR</sub>, the difference between T<sub>DM</sub><sup>2</sup> and magmatic crystallization age, i.e. the length of time the source of the igneous rocks has resided in the crust prior to melting). Strong isotope gradients are typically associated with major crustal boundaries and are potentially important for localizing mineral systems (Martin et al., 2021). However, map colours in areas with no or few samples reflect interpolated values and may have little or no relationship with underlying crust.

Some isotope gradients may not be as pronounced in the statewide map as they might be on more detailed maps of individual regions. It is therefore recommended that users download the isotope data and create their own contour maps for particular areas, to enhance the isotope gradients in those areas. An example is provided for the Archean Yilgarn Craton (Fig. 3), which provides a more detailed image of the architecture of the Kalgoorlie-Kurnalpi region, a world-class Archean gold province (Witt et al., 2020). It shows that old T<sub>DM</sub><sup>2</sup> values (>2900 Ma) are common across the Yilgarn Craton, but only occur on the western and eastern margin of the Kurnalpi Terrane, supporting the interpretation that the Kalgoorlie-Kurnalpi region developed as a rift above Youanmi-like substrate with rifting centred in the Kurnalpi Terrane (e.g. Smithies et al., 2018; Mole et al., 2019; Witt et al., 2020).

Insights into crustal evolution can be gained by visualizing the variation with age of ε<sub>Nd</sub>(i), T<sub>DM</sub><sup>2</sup> and T<sub>CR</sub> for both mafic and felsic igneous rocks (Fig. 4). From c. 3730 to 2500 Ma, mafic and felsic igneous
rocks show overlapping εNd(i), TDM² and TCR, which is in contrast to times younger than 2000 Ma, when mafic rocks generally yield higher εNd(i), and lower TDM² and TCR than felsic rocks in any given time. Felsic rocks older than 2500 Ma record sources requiring episodic juvenile mantle input at c. 3730, 3600, 3480–3420, 3300–3200, 3100, 2950, 2800 and 2700 Ma, as well as reworking of existing crust with TDM² up to c. 3960 Ma (Fig. 4a). The data for post-2000 Ma igneous rocks, however, suggest crustal reworking is the dominant mechanism forming felsic rocks younger than 2000 Ma in Western Australia. The increasing TCR for both mafic and felsic rocks from c. 3730 to 500 Ma is consistent with secular crustal maturation observed in other isotope systems, such as zircon oxygen isotopes (Fig. 4c; Valley et al., 2005; Lu et al., 2022).

There are few mafic or felsic igneous rocks between 2500 and 2000 Ma (Fig. 4). However, xenocrystic zircons of this age are common and have mainly heavy δ¹⁸O values, implying that felsic magmatism during this interval involved significant reworking of supracrustal materials, and that those magmatic rocks were mostly emplaced at depth and not exposed at the surface (Lu et al., 2022). This may indicate that the early Paleoproterozoic may have been dominated by orogenic compression, which trapped magmas at deep crustal levels (Loucks, 2021).

<figure><img src="image_2.png" /><figcaption>**Figure 1.** Locations of new and previously released Sm–Nd isotope samples, shown on the 1:2.5 million interpreted bedrock geology map</figcaption></figure>

The Sm–Nd isotope samples and associated data were compiled as part of a collaboration between GSWA and Geoscience Australia (GA). Acquisition of GSWA's Sm–Nd isotope data was funded by
the Exploration Incentive Scheme (EIS), and involved collaboration with several university research laboratories.

## How to access

The data layer is best accessed using [GeoVIEW.WA](https://geoVIEW.WA). This online interactive mapping system allows data to be viewed and searched together with other datasets, including GSWA and GA geochronology data, geological maps, and mineral exploration datasets. The **Samarium-neodymium isotope map** digital data are also available as a free download from the [Data and Software Centre](https://datacentre.gswa.org/) via Datasets — Statewide spatial datasets — Geochronology & Isotope Geology — Samarium-neodymium isotope map, as ESRI shape files and MapInfo TAB files. These datasets are subject to ongoing updates as new data are generated.
<figure><img src="image_3.png" /><figcaption>**Figure 2.** Sm-Nd isotope maps for whole-rock samples of felsic igneous rocks in Western Australia. T<sub>DM</sub><sup>2</sup> and T<sub>CR</sub> maps are presented as classified (a and c) and stretched (b and d) raster images. Symbols show the locations of Sm-Nd samples used for isotope mapping. Major crustal boundaries (gray lines) are from Martin et al. (2021)</figcaption></figure>
<figure><img src="image_4.png" /><figcaption>**Figure 3.** Sm-Nd isotope maps for whole-rock samples of felsic igneous rocks in Yilgarn Craton. T<sub>DM</sub><sup>2</sup> and T<sub>CR</sub> maps are presented as classified (a and c) and stretched (b and d) raster images. Symbols show the locations of Sm-Nd samples used for isotope mapping. Major crustal boundaries (gray lines) are from Martin et al. (2021). Only samples older than 2600 Ma are used here to reveal the Archean crustal architecture of the craton</figcaption></figure>
<figure><img src="image_5.png" /><figcaption>Figure 4. Values of εNd(i) (a), T<sub>DM</sub><sup>2</sup> (b), and T<sub>CR</sub> (c) vs Igneous crystallization age for felsic and mafic igneous rocks in Western Australia. Samples on or close to the Depleted mantle line in (a) or the T<sub>DM</sub><sup>2</sup> = Igneous crystallization age line in (b) indicate juvenile mantle input</figcaption></figure>
## References

Bouvier, A, Vervoort, JD and Patchett, PJ 2008, The Lu-Hf and Sm-Nd isotopic composition of CHUR: constraints from unequilibrated chondrites and implications for the bulk composition of terrestrial planets: Earth and Planetary Science Letters, v. 273, no. 1-2, p. 48-57.

Champion, DC and Cassidy, KF 2007, An overview of the Yilgarn and its crustal evolution, in Proceedings of Geoconferences (WA) Inc. Kalgoorlie '07 Conference, 25-27 September 2007, Kalgoorlie, Western Australia edited by FP Bierlein and CM Knox-Robinson: Geoscience Australia, Record 2007/14, p. 8-13.

Champion, DC and Huston, DL 2016, Radiogenic isotopes, ore deposits and metallogenic terranes: Novel approaches based on regional isotopic maps and the mineral systems concept: Ore Geology Reviews, v. 76, p. 229-256.

Loucks, RR 2021, Deep entrapment of buoyant magmas by orogenic tectonic stress: Its role in producing continental crust, adakites, and porphyry copper deposits: Earth-Science Reviews, v. 220, p. 103744, 27p.

Lu, Y, Wingate, MTD, Champion, DC, Smithies, RH, Johnson, SP, Mole, DR, Poujol, M, Zhao, J, Maas, R and Creaser RA 2021, Samarium-neodymium Isotope Map of Western Australia: Geological Survey of Western Australia, digital data layer, <www.dmirs.wa.gov.au/geoview>.

Lu, Y, Wingate, MTD, Smithies, RH, Johnson, SP, Martin, L, Jeon, H, Kirkland, CL, Champion, DC, Mole, DR and Gessner, K 2022, Zircon oxygen isotope map of Western Australia: Geological Survey of Western Australia, digital data layer, <www.dmirs.wa.gov.au/geoview>.

Martin, DMcB, Murdie, RE, Cutten, HN, Kelsey, DE, Thomas, CM, Quentin de Gromard, R, Zhan, Y and Haines, PW 2021, Major crustal boundaries map of Western Australia: Geological Survey of Western Australia, digital data layer, <www.dmirs.wa.gov.au/geoview>.

McCuaig, TC and Hronsky, JMA 2014, The mineral system concept: The key to exploration targeting, in Building exploration capability for the 21st century edited by KD Kelley and HC Golden: Society of Economic Geologists, Inc, Special Publication 8, p. 153-175.

Mole, DR, Fiorentini, ML, Cassidy, KF, Kirkland, CL, Thébaud, N, McCuaig, TC, Doublier, MP, Duuring, P, Romano, SS, Maas, R, Belousova, EA, Barnes, SJ and Miller, J 2015, Crustal evolution, intra-cratonic architecture and the metallogeny of an Archaean craton, in Ore Deposits in an Evolving Earth edited by GRT Jenkin, P Lusty, I McDonald, M Smith, AJ Boyce and JJ Wilkinson: The Geological Society of London, Special Publication 393, p. 23-80.

Mole, DR, Kirkland, CL, Fiorentini, ML, Barnes, SJ, Cassidy, KF, Isaac, C, Belousova, EA, Hartnady, M and Thébaud, N 2019, Time-space evolution of an Archean craton: A Hf-isotope window into continent formation: Earth-Science Reviews, v. 196, p. 102831.

Smithies, RH, Ivanic, TJ, Lowrey, JR, Morris, PA, Barnes, SJ, Wyche, S and Lu, Y-J 2018, Two distinct origins for Archean greenstone belts: Earth and Planetary Science Letters, v. 487, p. 106-116.

Witt, WK, Cassidy, KF, Lu, YJ and Hagemann, SG 2020, The tectonic setting and evolution of the 2.7 Ga Kalgoorlie-Kurnalpi Rift, a world-class Archean gold province.: Mineralium Deposita, v. 55, p. 601-631.

Wu, C, Chen, H and Lu, Y 2022, Crustal structure control on porphyry copper systems in accretionary orogens: insights from Nd isotopic mapping in the Central Asian Orogenic Belt: Mineralium Deposita, v. 57, no. 4, p. 631-641.

## Recommended reference

Lu, Y, Wingate, MTD, Champion, DC, Smithies, RH, Johnson, SP, Gessner, K, Maas, R, Mole, DR, Poujol, M, Zhao, J and Creaser, RA 2022, Samarium-neodymium isotope map of Western Australia: Geological Survey of Western Australia, digital data layer, <www.dmirs.wa.gov.au/geoview>.

EXPLORATION INCENTIVE SCHEME

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Ge O He Li S
Géochimie Elementaire et Isotopique

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THE UNIVERSITY OF
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THE UNIVERSITY
OF QUEENSLAND

UNIVERSITY OF
ALBERTA

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Australian Government
Geoscience Australia
Disclaimer

This product uses information from various sources. The Department of Mines, Industry Regulation and Safety (DMIRS) and the State cannot guarantee the accuracy, currency or completeness of the information. Neither the department nor the State of Western Australia nor any employee or agent of the department shall be responsible or liable for any loss, damage or injury arising from the use of or reliance on any information, data or advice (including incomplete, out of date, incorrect, inaccurate or misleading information, data or advice) expressed or implied in, or coming from, this publication or incorporated into it by reference, by any person whosoever.

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© State of Western Australia (Department of Mines, Industry Regulation and Safety) 2022

With the exception of the Western Australian Coat of Arms and other logos, and where otherwise noted, these data are provided under a Creative Commons Attribution 4.0 International Licence. (https://creativecommons.org/licenses/by/4.0/legalcode)