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Record 2018/49 | eCat 123951

A U–Pb Geochronology Compilation for Northern AustraliaVersion 2, 2018

S.L. Jones, J.R. Anderson, G.L. Fraser, C.J. Lewis and S.M. McLennan

A U–Pb Geochronology Compilation for Northern Australia

Version 2, 2018

GEOSCIENCE AUSTRALIA

RECORD 2018/49

S.L. Jones, J.R. Anderson, G.L. Fraser, C.J. Lewis and S.M. McLennan

Department of Industry, Innovation and Science

Minister for Resources and Northern Australia: Senator the Hon Matthew Canavan

Secretary: Dr Heather Smith PSM

Geoscience Australia

Chief Executive Officer: Dr James Johnson

This paper is published with the permission of the CEO, Geoscience Australia

© Commonwealth of Australia (Geoscience Australia) 2018

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ISSN 2201-702X (PDF)

ISBN 978-1-925848-22-9 (PDF)

eCat 123951

Bibliographic reference: Jones, S.L., Anderson, J.R., Fraser, G.L., Lewis, C.J., McLennan, S.M.,

2018. A U–Pb geochronology compilation for northern Australia: Version 2, 2018. Record 2018/49.

Geoscience Australia, Canberra. http://dx.doi.org/10.11636/Record.2018.049

Version: 1801

http://creativecommons.org/licenses/by/4.0/legalcode

mailto:[email protected]

http://dx.doi.org/10.11636/Record.2018.049

A U–Pb geochronology compilation for northern Australia: Version 2, 2018 iii

Contents

Executive Summary .................................................................................................................................. 1

1 Overview ................................................................................................................................................ 2

1.1 Introduction and aims ....................................................................................................................... 2

1.2 Outputs from this study .................................................................................................................... 2

1.3 Accessing the data compilation ....................................................................................................... 2

2 Methods ................................................................................................................................................. 3

2.1 Data compilation sources................................................................................................................. 3

2.1.1 New data added in this Record .................................................................................................. 4

2.1.2 Data compilation workflow.......................................................................................................... 5

2.1.3 Data output ................................................................................................................................. 7

2.2 Data visualisation via ArcGIS ........................................................................................................10

2.2.1 Point data maps .......................................................................................................................10

2.2.2 Contoured age maps ................................................................................................................11

3 U–Pb age thematic maps ....................................................................................................................12

3.1 Point data maps .............................................................................................................................12

3.2 Contoured age maps .....................................................................................................................15

4 Discussion & recommendations for future work ..................................................................................19

4.1 Data compilation ............................................................................................................................19

4.2 Thematic maps ..............................................................................................................................20

5 Acknowledgements .............................................................................................................................21

References .............................................................................................................................................22

A U–Pb geochronology compilation for northern Australia: Version 2, 2018 1

Executive Summary

For any given region, the age of the rocks and superimposed events is a fundamental piece of

knowledge required for geological understanding. For this reason, the minerals industry-led

UNCOVER Roadmap (AMIRA International, 2015) identified the systematic compilation of

geochronology and isotope data as a priority focus area. This Record presents a compilation of

publicly-available U–Pb geochronology from Queensland (QLD), Northern Territory (NT),

Western Australia (WA) and the most northerly parts of South Australia (SA) and New South

Wales (NSW). It represents a step towards a comprehensive U–Pb geochronology compilation

for all of Australia.

The dataset presented here expands upon the data coverage previously compiled by

Anderson et al. (2017). In particular, this compilation includes >1400 additional data points

from WA and NT, building the dataset to >3600 sample points compiled across WA, NT, QLD,

SA and NSW. Data for this compilation was sourced from Anderson et al. (2017),

geochronology databases of Geoscience Australia (GA), Geological Surveys of Western

Australia (GSWA) and Northern Territory (NTGS), and various published scientific literature.

Thematic maps created from the compiled dataset show the spatial distribution and age trends

of Igneous Crystallisation Age, Metamorphic Age and Max (maximum) Depositional Age

across northern Australia. These thematic maps have been produced in two forms: (i) as point

data, coloured according to age, and (ii) as contoured age maps.

This work can be used as both a stand–alone dataset and/or in conjunction with other

geological, geophysical, geochemical and isotopic datasets to better understand the geological

evolution of northern Australia.

This work has been conducted as part of Geoscience Australia’s Exploring for the Future

(EFTF) program, a four-year initiative funded by the Australian Government to better

understand the potential mineral, energy and groundwater resources under cover in northern

Australia.

http://www.amirainternational.com/WEB/site.asp?section=activities&page=ExplorationUnderCover

http://www.ga.gov.au/eftf

2 A U–Pb geochronology compilation for northern Australia: Version 2, 2018

1 Overview

1.1 Introduction and aims

Uranium–Lead (U–Pb) geochronological data have been collected in Australia for several

decades, leading to an extensive geographic coverage. The interpreted ages derived from

these data underpin the current understanding of the continent’s geological evolution. The data

and derived ages exist as both published and unpublished datasets. Published journal articles

and government survey reports, and subsets of the data, are available in a range of publicly-

accessible databases and datasets e.g. the State and Northern Territory Geological Survey

websites. Unpublished datasets typically have less accessibility and are usually found only on

an ad-hoc basis. These disparate sources of data, and the variations in reporting style, mean

that it is difficult to use the data collectively to visualise spatial and temporal patterns. The goal

of this compilation is to continue the collation of these disparate sources of data as a step

towards a single continent-wide U–Pb isotopic dataset.

The aims of this Record are to extend the data coverage of Anderson et al. (2017), and

present new thematic maps using the expanded U–Pb geochronology data across northern

Australia. It is envisaged that this U–Pb compilation can be used both as a stand–alone

dataset and integrated with other geological, geophysical, geochemical and isotopic datasets

to better understand the geology and mineral potential of northern Australia. Future versions

will expand the national coverage by incorporation of newly acquired and published U–Pb

geochronology data.

This work has been conducted as part of Geoscience Australia’s Exploring for the Future

(EFTF) program, a four-year initiative funded by the Australian Government to better

understand the potential mineral, energy and groundwater resources under cover in northern

Australia.

1.2 Outputs from this study

Expanded compilation of existing U–Pb age data across northern Australia. This

compilation is available in Appendix A as a Microsoft Excel file.

Thematic point data maps of U–Pb Igneous Crystallisation Age (including dykes and

pegmatites), Metamorphic Age, and Max (maximum) Depositional Age.

Contoured age maps of U–Pb Igneous Crystallisation Age (excluding dykes and

pegmatites), Metamorphic Age, and Max Depositional Age.

Documentation of data compilation methods and workflows, gaps and potential directions

for future versions.

1.3 Accessing the data compilation

Digital Appendix A contains an Excel spreadsheet of the U–Pb compilation and can be

accessed through the Geoscience Australia EFTF website.


http://www.ga.gov.au/eftf/minerals/nawa/geochronology-and-isotopic-mapping


2 Methods

2.1 Data compilation sources

Data attributes for this Record are based on data and modified attributes from Anderson et al.

(2017), with some fields renamed, deleted and redefined. Additional data was sourced from the

Geological Survey of Western Australia’s (GSWA) ‘Compilation of Geochronology Information

2017’ data package (Wingate et al., 2017), Geoscience Australia’s Geochron Delivery

database and various targeted published scientific literature. These additional datasets

encompass Western Australia (WA) and the Northern Territory (NT).

The data from Anderson et al. (2017) encompassed mainly the Northern Territory (NT) and

Queensland (QLD), with some datasets across the borders of South Australia (SA), Western

Australia (WA) and New South Wales (NSW). A numbered summary of the sourced datasets

of Anderson et al. (2017) are set out in Table 2.1.

Table 2.1 Summary of data sourced for Anderson et al. (2017).

State/Territory (NT, QLD, SA, WA, NSW)

Data sources 1. Arunta Orogen area compilation (McLennan et al., 2015)

2. Geochronological Synthesis and Time-Space plots for Proterozoic Australia (Neumann & Fraser, 2007)

3. Geoscience Australia Geochron Delivery Database

4. Northern Territory Geological Survey STRIKE Database

5. Geological Survey of Western Australia GeoVIEW Database

6. Geological Survey of Queensland Compilation (Withnall, 2016)

Geological region(s) 1. Arunta Orogen, Birrindudu Basin, Tanami Orogen, Tennant Creek Region

2. Etheridge Province, McArthur Basin, Mount Isa Orogen, Musgrave Province, Murphy Region, Pine Creek Orogen, Savannah Province

3. Amadeus Basin, Arnhem Province, Arunta Orogen, Bowen Basin, Davenport Province, Drummond Basin, Eromanga Basin, Etheridge Province, Iron Range Province, Kennedy Igneous Province, McArthur Basin, Millungera Basin, Mossman Orogen, Mount Isa Orogen, Murphy Region, Musgrave Province, New England Orogen, Pine Creek Orogen, Savannah Province, South Nicholson Basin, Surat Basin, Tanami Orogen, Tennant Creek Region, Thomson Orogen, Warramunga Province

4. Amadeus Basin, Birrindudu Basin, Georgina Basin, Halls Creek Orogen, McArthur Basin, Murphy Region, Musgrave Province, Pine Creek Orogen, Tanami Orogen

5. Amadeus Basin, Arunta Orogen, Canning Basin, Murraba Basin, Musgrave Province, Officer Basin, Paterson Orogen

6. Croydon Province, Drummond Basin, Kennedy Igneous Province, Mount Isa Orogen, New England Orogen, Savannah Province, South Nicholson Basin, Thalanga Base Metal Metallogenic Province, Thomson Orogen

http://www.ga.gov.au/geochron-sapub-web/geochronology/shrimp/search.htm

http://strike.nt.gov.au/wss.html;jsessionid=d2lnh8rtm6qgowqi2ule29yn

http://www.dmp.wa.gov.au/GeoView-WA-Interactive-1467.aspx


State/Territory (NT, QLD, SA, WA, NSW)

Data included/excluded from source

1. All U–Pb age data included

2. Only U–Pb age data is included. Data without location information and where the original reference cannot be accessed are excluded

3. Some attributes that were not considered essential to the compilation were excluded (e.g. session calibration information, individual analysis isotopic concentrations and ratios). Information not included in this compilation can be publicly accessed through the Geoscience Australia Geochron Delivery Database

4. Only U–Pb data is included. Zero and negative values for age data have been excluded

5. Only U–Pb data is included

6. Only U–Pb data is included

Additional Comments For additional comments refer to Tables 2.1–2.6 in Anderson et al. (2017)

2.1.1 New data added in this Record

A large proportion of WA data used to complete the coverage of northern and western

Australia was sourced from the GSWA 2017 geochronology compilation and ArcMap data

package (Wingate et al., 2017). Only U–Pb age data were extracted into Excel and the

relevant information fitted into the attribute table for this compilation (Table 2.3). Missing

attribute information was individually sourced from the original sample reports provided in the

GSWA package and entered into this compilation, where time permitted.

The WA-related datasets from Geoscience Australia’s Geochron Delivery database were

extracted as a .csv file via a SQL (Structured Query Language) script that specified relevant

compilation attributes.

Recently acquired SHRIMP data, collected under the auspices of the Northern Territory

Geological Survey-Geoscience Australia (NTGS–GA) National Collaborative Framework (NCF)

geochronology project, have been added to this compilation version (Kositcin & Carson, 2017;

Kositcin & McGloin, 2017; Kositcin et al., 2017; Kositcin et al., 2018a; Kositcin et al., 2018b;

Kositcin et al., 2018c). Finally, disparate published scientific literature sources were scoured for

original sources of U–Pb ages in WA and NT and added to this compilation. These original

sources include Blake et al. (1998); Bodorkos et al. (2000); Bodorkos et al. (1999); Page et al.

(2001); Page & Hoatson (2000) and Yang et al. (2018). Table 2.2 is a summary of data

sources used for this compilation.

Table 2.2 Summary of data sourced for this Record.

State/Territory (NT, QLD, WA)

Data sources 1. Anderson et al. (2017) Appendix A

2. GSWA ‘Compilation of Geochronology Information 2017’ package (Wingate et al., 2017)

3. Geoscience Australia Geochron Delivery database

4. NTGS-GA SHRIMP geochronology Records

5. Published scientific literature




State/Territory (NT, QLD, WA)

Geological region(s) 1. Amadeus Basin, Arnhem Province, Arunta Orogen, Birrindudu Basin, Bowen Basin, Canning Basin, Croydon Province, Davenport Province, Drummond Basin, Eromanga Basin, Etheridge Province, Georgina Basin, Halls Creek Orogen, Iron Range Province, Kennedy Igneous Province, McArthur Basin, Millungera Basin, Mossman Orogen, Mount Isa Orogen, Murphy Region, Murraba Basin, Musgrave Province, New England Orogen, Officer Basin, Paterson Orogen, Pine Creek Orogen, Savannah Province, South Nicholson Basin, Surat Basin, Tanami Orogen, Tennant Creek Region, Thalanga Base Metal Metallogenic Province, Thomson Orogen, Warramunga Province

2. Arunta Orogen, Albany-Fraser Orogen, Amadeus Basin, Capricorn Orogen, Gascoyne Province, Halls Creek Orogen, King Leopold Orogen, Musgrave Province, Lamboo Province, Paterson Orogen, Pilbara Craton, Tanami Orogen, Yilgarn Craton

3. Albany-Fraser Orogen, Arunta Orogen, Eastern Goldfields Province, Halls Creek Orogen, Kimberley Basin, King Leopold Orogen, Murchison Province, Musgrave Block, Paterson Orogen, Pinjarra Orogen, Raeside Batholith, Rudall Province, Southern Cross Province, Western Gneiss Terrane, Yilgarn Craton.

4. Aileron Province, Amadeus Basin, Arnhem Province, Birrindudu Basin, Limbunya Inlier, McArthur Basin, Victoria Basin.

5. Beetaloo Sub-basin , Halls Creek Orogen

Data included/excluded in this Record

Only U–Pb data is included

Additional Comments Extra information added from source or original reference, where time permitted. Some attribute fields have been renamed, deleted and redefined from Anderson et al., 2017 e.g. Superprovince and Province attributes guided by the Australian Geological Provinces 2018.01 edition (Raymond et al., 2018).

2.1.2 Data compilation workflow

An overview of the workflow undertaken for this Record is shown in Figure 2.1. Data was

sourced from Anderson et al. (2017) Appendix A, the Geological Survey of Western Australia

(GSWA) 2017 geochronology compilation (Wingate et al., 2017), Geoscience Australia’s

Geochron Delivery database (Geoscience Australia (GA), 2018) and original references: Blake

et al. (1998); Bodorkos et al. (2000); Bodorkos et al. (1999); Kositcin & Carson (2017); Kositcin

& McGloin (2017); Kositcin et al. (2017); Kositcin et al. (2018a); Kositcin et al. (2018b); Kositcin

et al. (2018c); Page et al. (2001); Page & Hoatson (2000); Yang et al. (2018).

https://ecat.ga.gov.au/geonetwork/srv/eng/catalog.search#/metadata/af11c9e2-12ac-43a2-a085-edf24cd51c94

https://ecat.ga.gov.au/geonetwork/srv/eng/catalog.search#/metadata/af11c9e2-12ac-43a2-a085-edf24cd51c94


Information fitted to compilation’s attributes

Additional attribute information sourced

Compilation excludes duplicate results

Compilation includes only onshore data

Compilation excludes results with no age or

location from original references

Anderson et al.

(2017) Appendix A

GSWA ‘Compilation of

Geochronology

Information 2017’

Additional sample

information from

original references

GA’s Geochron

Delivery database

U–Pb geochronology compilation: V2

Age interpretations from the source or

original reference are grouped into

simplified age interpretations - refer to

Table 2.4

(Total: 3629 data points)

2018 U–Pb northern Australia compilation age interpretations:

Igneous Crystallisation Age (dykes and pegmatites noted in

brackets)

Metamorphic Age

Max Depositional Age

Hydrothermal

Inheritance

Isotopic Resetting or Pb Loss

Mineralisation Age

Provenance

Recrystallisation

Significance Unknown

Thematic maps produced using age data and region of interest

Thematic maps of 2018 northern Australia compilation:

Point data maps (displaying spatial location) -

o All U–Pb age data

o Thematic: Igneous Crystallisation Age (including dykes & pegmatites),

Metamorphic Age, Max Depositional Age

Contoured age maps -

o Thematic point data: Igneous Crystallisation Age (excluding dykes &

pegmatites), Metamorphic Age, Max Depositional Age

o Restricted point data: Igneous Crystallisation Age (excluding dykes &

pegmatites) - TISA region, Metamorphic Age - Amadeus/Musgraves region,

Max Depositional Age - TISA region

Figure 2.1 Workflow of data compilation and age groupings used for thematic age maps. Data for the compilation can be found in Appendix A. TISA refers to a regional area in northern Australia, from Tennant Creek in the west to Mount Isa in the east.


2.1.3 Data output

Attributes for this compilation in Appendix A are summarised in Table 2.3. Note that some

compilation fields remain incomplete due to time constraints. Symbology and abbreviations

used in this compilation are: NA = not applicable; NR = not recorded in source document; tilde

symbol (~) = incomplete field or field not checked.

Some attribute fields have been added, deleted, renamed and redefined from Anderson et al.

(2017). Modifications to this compilation include the addition of ‘SHRIMP_Type’ attribute,

deletion of ‘Subprovince_or_domain’ attribute, and renaming of other attributes for uniformity.

These modified fields are denoted with an asterisk in Table 2.3.

Table 2.3 Compilation attributes and their definition (* denotes modification from Anderson et al., 2017).

Content

SampleID Sample identifier as it appears in the source or original reference

GASampleNo A GA system-assigned number (usually 7 digits) that uniquely defines the sample. Applicable to GA samples only

MountID Unique SHRIMP mount identifier - if applicable

GDA94_long Longitude of the sampling locality, referred to the Geocentric Datum of Australia 1994 (decimal degrees)

GDA94_lat Latitude of the sampling locality, referred to the Geocentric Datum of Australia 1994 (decimal degrees, negative for the Southern Hemisphere)

Superprovince_GA2018 * Broad geological superprovince to which the sample belongs, from the Australian Geological Provinces, 2018.01 edition (Raymond et al., 2018) - if applicable

Province_GA2018 * Geological province to which the sample belongs, from the Australian Geological Provinces, 2018.01 edition (Raymond et al., 2018) - if applicable

RegionName_source * Region name to which the sample belongs as it appears in the source or original reference, if not listed in the Australian Geological Provinces, 2018.01 edition (Raymond et al., 2018) - if applicable

Mapsheet_250K Name of the 1:250 000 scale topographic map sheet the sampling site is located in

Mapsheet_Index_250K Index number of the 1:250 000 scale topographic map sheet the sampling site is located in

UnitName_source * Rock unit name attributed to the sample as it appears in the source or original reference

Stratname_ASUD * Unique name of the stratigraphic unit to which the sample belongs, from the Australian Stratigraphic Units Database (Geoscience Australia and Australian Stratigraphy Commission, 2017)

Stratno_ASUD *

Unique numerical identifier of the stratigraphic unit to which the sample belongs, from the Australian Stratigraphic Units Database (Geoscience Australia and Australian Stratigraphy Commission, 2017)

Lithology_source * Name of the sample lithology/rock-type (e.g. granodiorite, schist, sandstone), as described in the source or original reference

Remarks Additional information regarding preceding fields e.g. rock comments from source, lat/long calculations, ASUD comments - if applicable

Age_Ma Reported age in million years (Ma)

Age_uncertainty_Ma Reported age uncertainty in million years (Ma)

Conf_level Reported confidence level of age result (e.g. 95% conf., 2)

http://www.ga.gov.au/data-pubs/data-standards/reference-databases/stratigraphic-units

http://www.ga.gov.au/data-pubs/data-standards/reference-databases/stratigraphic-units


Content

Analyses Number of analyses used in the reported age

MSWD Mean square of weighted deviates for the reported age

Age_calculation_type Statistical process (if applicable) used to generate the reported age

Isotopic_system Isotopic ratio used to calculate the reported age in the source or original reference

Target_mineral Mineral analysed for U–Pb geochronology

Technique Analytical instrument and/or technique used in analysis: SHRIMP = Sensitive high-resolution ion microprobe TIMS = Thermal ionization mass spectrometry LA-ICPMS = Laser ablation-inductively coupled plasma mass spectrometry

SHRIMP_Type * SHRIMP model used in analysis: SHRIMP–I, –RG, –II, –IIe or –UNK (unknown) – if applicable

Imaging (CL_BSE_TL_RL) Type of imaging used in analysis: CL = cathodoluminescence BSE = backscatter electron TL = transmitted light RL = reflected light

AgeInterp_source * Age interpretation from the source or original reference

SecondaryInterp_source * Secondary age interpretation from the source or original reference - if applicable

AgeComment_source * Additional comments on age interpretation from the source or original reference - if applicable

AgeInterp_simplified * Age interpretation simplified for thematic map plotting purposes – see Table 2.4 for detailed information on interpreted groups

Source Compilation, database or Record where the data was obtained for this compilation

OriginRef Original reference for the published data - if applicable

State State or Territory of Australia in which the sample is located

Ref_check Whether the data have been checked or unchecked for accuracy using original reference(s)

A wide range of slightly varying terminology is used in geological and geochronological

literature to describe essentially the same geological process that has been dated. This

variation in terminology makes it difficult to combine data from a variety of sources into

consistent thematic age maps. To overcome this, the age interpretations as described in the

source or original references (AgeInterp_source) have been simplified into a smaller number of

classifications (AgeInterp_simplified) (Table 2.4).


Table 2.4 Interpreted ages as reported in the original reference, grouped into a simplified classification, for thematic mapping purposes.

Age interpretation description from original source

[AgeInterp_source]

‘Grouped’ age interpretation

[AgeInterp_simplified]

age of igneous crystallization, crystallisation/crystallization,

crystallisation age/crystallization age, felsic magmatic age, felsic magmatic extrusive, felsic magmatic intrusive, igneous crystallisation (minimum age), igneous crystallisation age, igneous crystallisation age (extrusive), igneous crystallization (max age), magmatic, magmatic crystallization, magmatic extrusive, magmatic intrusive, magmatic intrusive (felsic) (max age), magmatic intrusive (mafic), maximum age of intrusion, protolith, time of crystallisation volcanic component, time of crystallisation volcanic rock

Igneous Crystallisation Age

Igneous Crystallisation Age (Dyke) Igneous Crystallisation Age (Dyke)

Igneous Crystallisation Age (Pegmatite) Igneous Crystallisation Age (Pegmatite)

age of metamorphism, high grade metamorphism, metamorphism, metamorphism (max age), metamorphism (peak), age of high grade metamorphism

Metamorphic Age

deposition, maximum depositional age, sedimentary depositional, sedimentary depositional (max), sedimentary maximum depositional

Max Depositional Age

hydrothermal, hydrothermal activity Hydrothermal

age of xenocrystic component, inheritance, inherited cluster, inherited cluster (pegmatite), inherited individuals

Inheritance

isotopic resetting, Pb loss, Pb loss (dyke) Isotopic Resetting or Pb Loss

mineralisation age Mineralisation Age

Significance Unknown, Unknown Significance Unknown

provenance cluster, provenance individuals Provenance

recrystallisation Recrystallisation

The data from different sources were initially kept in separate Excel sheets while additional

attributes and edits were undertaken. The data from these spreadsheets were then combined

and checked for duplicates and invalid datasets deleted from the compilation i.e. samples

lacking latitude/longitude values, offshore points, samples lacking an interpreted age.

As there was no single attribute that could identify all true duplicates, eliminating these

duplicates was a time-consuming and manual process. Some duplicates contained key

information dispersed between each duplicate record that needed to be combined into one

record. Other duplicates had one record as ‘checked’ in the Ref_check field, while the other

record was ‘unchecked’, and to ensure the checked record was retained, a manual inspection

was needed. Straight forward duplicates were easily eliminated using Excel functions:

Conditional Formatting to identify duplicates based on the ‘SampleID’ attribute and Remove

Duplicates with cells that contained exact values in every column. The remaining identified

duplicates were manually checked, combined and/or deleted.


2.2 Data visualisation via ArcGIS

A series of U–Pb age thematic maps were generated using ArcMap 10.5, in which the data

from the compilation’s Excel sheet, outlined above, were used.

2.2.1 Point data maps

Point data maps were produced using the U–Pb interpreted ages attribute (Age_Ma), from the

compilation. Unfiltered age data was used to show the spatial distribution coverage over

Australia. The compilation was then filtered by the ‘AgeInterp_simplified’ attribute to produce

thematic point data maps.

These thematic age maps are: Igneous Crystallisation Age (2037 sample points, including

dykes and pegmatites), Metamorphic Age (303 sample points) and Max Depositional Age (866

sample points). On each thematic map, points are coloured according to a manual

classification of twenty three classes based on prior knowledge of the timing of major orogenic

events within Australia (Table 2.5).

Point data maps are plotted with the 1:2.5 M scale geological units basemap (Raymond et al.,

2012) or displayed with major crustal boundaries (Korsch & Doublier, 2015), faults and shears

2.5M (Raymond et al., 2012) layers and northern Australia EFTF (Exploring for the Future) line.

The northern Australia EFTF line refers to the southern boundary of northern Australia, as

defined in Northern Australia Infrastructure Facility Act 2016 (Pt.1, s.5), for the purposes of the

Exploring for the Future program.

Table 2.5 Age brackets assigned to major orogenic events over northern Australia and used to define the 23 classification classes in point data maps, coloured according to age (Figure 3.1 to Figure 3.4).

Age Bracket (Ma) Event

> 2801 –

2800 – 2501 –

2500 – 2301 –

2300 – 2051 –

2050 – 1881 –

1880 – 1841 Barramundi

1840 – 1801 Stafford

1800 – 1771 Yamba

1770 – 1736 –

1735 – 1691 Strangways

1690 – 1651 –

1650 – 1601 Leibig

1600 – 1561 Chewings

1560 – 1501 mid–late Isan

1500 – 1401 –



Age Bracket (Ma) Event

1400 – 1271 early Musgrave

1270 – 1001 late Musgrave

1000 – 541 –

540 – 471 Larapinta/Delamerian

470 – 431 Benambran

430 – 381 Tabberabberan

380 – 351 Kanimblan

< 350 –

2.2.2 Contoured age maps

Contoured maps were produced through spatial analysis of the thematic point data (Igneous

Crystallisation Age, excluding dykes and pegmatites, Metamorphic Age and Max Depositional

Age), using ArcMap’s ‘Natural Neighbor’ interpolation tool with the ‘Age_Ma’ attribute as the ‘Z

value’ to build a raster dataset. These datasets were classified into ten ‘Natural Breaks (Jenks)’

classes to produce the final contoured visualisations.

All contoured maps were clipped to the Australian coast or smaller example region and display

the spatial distribution of sample points restraining the interpolation. Additional ArcMap layers

added are the northern Australia EFTF (Exploring for the Future) line, as defined in Northern

Australia Infrastructure Facility Act 2016 (Pt.1, s.5), major crustal boundaries (Korsch &

Doublier, 2015), geological units 2.5M, and faults and shears 2.5M (Raymond et al., 2012).



3 U–Pb age thematic maps

A key aim of this Record was to produce a series of thematic maps to demonstrate the

information that may be obtained from spatially visualising geological age information at

regional to continental scale. The following maps are indicative of thematic U–Pb age maps

that may be produced when data are compiled in a consistent format.

3.1 Point data maps

The spatial distribution of unfiltered U–Pb age data is displayed in Figure 3.1. Filtered Igneous

Crystallisation Age (including dykes and pegmatites), Metamorphic Age, and Max Depositional

Age data are displayed in Figure 3.2 to Figure 3.4. These geologically meaningful maps

provide direct age constraints and general trends across large regions of Australia and reflect

regional tectonothermal events. They also serve to highlight areas where the data is sparse

and therefore provide information on potential areas for future data collection.

Layers in all point data maps include: Northern Aust. EFTF Line, which refers to the southern

boundary of northern Australia, as defined in Northern Australia Infrastructure Facility Act 2016

(Pt.1, s.5), for the purposes of the Exploring for the Future program; Major Crustal Boundaries

– 2015 from Korsch & Doublier (2015) and Faults & Shears 2.5M from Raymond et al. (2012).

Background image in Figure 3.1 is the 1:2.5M scale geological units map layer from Raymond

et al. (2012).

Figure 3.1 Spatial distribution of all U–Pb geochronology age data in this compilation. This includes all age interpretations displayed in Table 2.4. Number of data points = 3632.



Figure 3.2 Point data map of U–Pb Igneous Crystallisation Age (including dykes and pegmatites). Number of data points = 2037.

Figure 3.3 Point data map of U–Pb Metamorphic Age. Number of data points = 303.


Figure 3.4 Point data map of U–Pb Max Depositional Age. Number of data points = 866.


3.2 Contoured age maps

The following contoured age maps were produced using filtered thematic age data as

presented in 3.1 – Igneous Crystallisation Age (excluding dykes and pegmatites),

Metamorphic Age, and Max Depositional Age. For spatial demonstration over different sized

areas, the first map illustrates broad trends at the continental scale using all filtered thematic

age data, while the second map is confined to a smaller region of interest and shows finer

details of spatial and temporal heterogeneity that may be revealed with such thematic maps

(Figure 3.5 to Figure 3.10).

Layers in the contoured age maps include: Northern Aust. EFTF Line, which refers to the

southern boundary of northern Australia, as defined in Northern Australia Infrastructure

Facility Act 2016 (Pt.1, s.5), for the purposes of the Exploring for the Future program; Major

Crustal Boundaries – 2015 from Korsch & Doublier (2015) and Faults & Shears 2.5M from

Raymond et al. (2012).



Figure 3.5 ‘Natural Neighbor’ interpolation of Igneous Crystallisation Ages (excluding dykes & pegmatites) using ten Natural Breaks (Jenks) intervals. Inset map: spatial distribution of point data constraining interpolation.

Figure 3.6 Interpolated spatial comparison of Igneous Crystallisation Ages using restricted points for smaller focus area: Tennant Creek–Mount Isa (TISA) region. Note the different age range used here compared with Figure 3.5. Inset map: Regional location and spatial distribution of point data constraining interpolation.


Figure 3.7 ‘Natural Neighbor’ interpolation of Metamorphic Ages using ten Natural Breaks (Jenks) intervals. Inset map: spatial distribution of point data constraining interpolation.

Figure 3.8 Interpolated spatial comparison of Metamorphic Ages using restricted points for smaller focus area: Amadeus–Musgrave region. Note the different age range used here compared with Figure 3.7. Inset map: regional location and spatial distribution of point data constraining interpolation.


Figure 3.9 ‘Natural Neighbor’ interpolation of Max Depositional Ages using ten Natural Breaks (Jenks) intervals. Inset map: spatial distribution of point data constraining interpolation.

Figure 3.10 Interpolated spatial comparison of Max Depositional Ages using restricted points for smaller focus area: Tennant Creek–Mount Isa (TISA) region. Note the different age range used here compared with Figure 3.9. Inset map: Regional location and spatial distribution of point data constraining interpolation.


4 Discussion & recommendations for future work

As identified in the UNCOVER Roadmap (AMIRA International, 2015), this work

demonstrates the value of a single, comprehensive, consistently-compiled and classified

geochronology dataset. In part, this value comes from being able to immediately visualise the

spatial coverage of available data (e.g. Figure 3.1) and draw attention to regions where new

data acquisition will have high impact. In addition, such a dataset facilitates convenient

production of thematic maps that illustrate spatio-temporal trends, and may be readily

compared with geological maps and geophysical images to understand the timing and origin

of major geological features. Amongst other applications, these thematic age maps may be

used as input layers for mineral prospectivity analysis.

Compilations of geochronology data within Australia have been produced by numerous

previous studies, at a variety of regional scales and with varying levels of detail, with respect

to the underlying isotopic and sample metadata. Some level of compilation and review of

existing geochronological knowledge is carried out by almost every regional geological study

conducted by government, industry or academia. The compilation presented here is an

attempt to scale-up such compilations to the semi-continental scale and to provide a template

for future compilations. These future compilations would represent a balance between

sufficient detail to assess the quality and geological meaning of the ages, while being simple

enough to allow relatively easy extraction of the relevant information from published

geological literature.

In future, a freely available and comprehensive continental-scale compilation of this nature

would largely remove the need for regional-scale literature searches and data compilations at

the project scale. The challenge will be to keep the dataset up to date, consistent in format,

and free of duplicate data. While simple in concept, in practise the compilation of these data

has been a time-consuming task and some of the challenges are discussed below.

4.1 Data compilation

Compiling the dataset, matching disparate sources of data with the compilation attributes, and

sorting through the data to delete ‘true’ duplicates continues to be the most time consuming

task. When merging source data from pre-existing compilations or databases, duplicate

datasets are found. The main challenge is finding and deleting ‘true’ duplicates as there is no

single uniquely identifying attribute. Some ‘true’ duplicates were easily identified and

eliminated if the duplicate contained exactly the same information. Most identified duplicates,

however, had to be individually interrogated as differing attribute information was found in

each duplicate and the information had to be merged into one complete record, if deemed

important.

Some preliminary pseudo-code was written to try to simplify the duplicate identification and

elimination process. This work is currently in progress and further investigation and coding

input is required to advance a potential solution to this time-consuming task. However, it may



still remain the case that some duplicate datasets can only be eliminated after manual

interrogation of the datasets.

Stratigraphic nomenclature also remains a challenge as stratigraphy is a dynamic science,

constantly being redefined and renamed. As an example, given time constraints the GSWA

dataset used the cited stratigraphic name given in the source document. If required, the user

will be able to interrogate the Australian Stratigraphic Units Database (ASUD) and follow the

index trail to the most current stratigraphic name and relationship to the cited stratigraphic

name.

The development of a single national repository for all Australian U–Pb geochronology (and

possibly other isotopic data), is a consideration worth pursuing. If the repository was in the

form of a database, then it could potentially link with the ASUD, GA’s Geochron Delivery, and

the State and Northern Territory geological survey geochronology databases. This could lead

to a comprehensive and continuously-updated continent-wide dataset being available, and

would likely lead to cost savings in ‘person-hours’ spent compiling the dataset in the current

manner.

4.2 Thematic maps

Once the data has been compiled and quality checked, the map productions are a (relatively)

quick and simple process. The U–Pb thematic maps presented in this Record demonstrate

what may be visualised using the datasets from this compilation. These example maps were

visualised in ArcMap 10.5 along with geological units, fault and shear lines and major crustal

boundary layers, however, any number of other datasets might be used alongside this point

data to enhance geological insights. These might include specific solid geology map layers,

outcrop geological maps, other isotopic data (e.g. Sm–Nd, Lu–Hf, Ar–Ar) and/or geophysical

data (e.g. gravity, aeromagnetic, radiometric).

Obvious features in the continental-scale point data and contoured thematic maps are the

older ages in the west i.e. Pilbara and Yilgarn Craton regions, and the progressive “younging”

of ages towards the east coast of Australia. The regional-scale maps demonstrate how

limiting the dataset to a narrower region of interest may assist with highlighting trends within a

particular region via a different colour stretch, or different contour interval. The patterns in

these contoured age maps should, however, be considered in the context of the underlying

data density. The geological meaning of such contours in regions of low data density should

be treated with caution.

Further expansion of this U–Pb compilation through the addition of existing data from South

Australia, New South Wales, Victoria and Tasmania is clearly desirable to complete the

continental-scale coverage. The data coverage would also clearly benefit from new data

acquisition in regions of sparse data. In many cases areas of poor data coverage are in

regions where ‘basement’ rocks are not exposed at the surface, and new age information is

dependent on the availability of rock samples from drill-holes.

This compilation remains a work in progress. Some additional recommendations include 1)

continually checking and adding new datasets, 2) continue to screen for duplicate datasets, 3)

populating incomplete attribute fields and 4) identification of samples from drill-cores and their

relative depth measurement(s).

http://www.ga.gov.au/data-pubs/datastandards/stratigraphic-units


5 Acknowledgements

This work has been conducted as a part of the Exploring for the Future program. The authors

acknowledge the Geological Survey of Western Australia for providing their GSWA Geochron

2017 data package to expand this compilation. Thank you to our colleagues within the Mineral

Systems Branch at Geoscience Australia for their support, encouragement and advice, with

special thanks to Jane Thorne and Natalie Kositcin for reviewing this Record and its dataset.


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