Government of Western Australia Department of Mines and Petroleum Government of Western Australia Department of Mines and Petroleum Government of Western Australia Department of Mines and Petroleum

Government of Western Australia Department of Mines and Petroleum

Geological Survey of Western Australia

Regolith geochemistry in the Kimberley Science & Conservation Strategy − links to bedrock

Paul Morris

1. Archean granites

2. c.1800 Ma granites; Salmon Gums Event

3. c.1760 Ma granites; Ngadju Event

4. c.1700 Ma granites

5. c. 1690 Ma granites

6. c. 1680 Ma granites

7. c. 1670 Ma granites

8. c. 1660 Ma granites

9. Recherche Supersuite - Stage I of the AFO (1345-1260 Ma)

10. Esperance Supersuite - Stage II of the AFO (1215-1140 Ma)

Bira

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Early

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Isolated fragments of Archean crust that remains in the Northern Foreland, Tropicana Zone and Biranup Zone can be divided between granites representative of the TTG series and Archean sanukitoids.

TTG - High Si, Al, Na, Sr, Ba; Low K, HREE - Reflection of their origin through high P melting of mafic crust - Generally very distinctive.

Sanukitoids High Mg, Mg#, Cr, Ni – high enough to infer equilibration with mantle peridotite BUT also High incompatible trace element concentrations reflecting a (subduction) enriched mantle source Form a very minor component of virtually all Archean regions forming late in the tectonic history and typically close to major structures that might be interpreted as sutures Typically a very close spatial (and perhaps genetic) relationship with gold mineralization

Geochemical and isotopic data suggest that much of the AFO crust is multiply reworked Archean crust, with juvenile mantle additions. These reworking events progressively mask, but do not destroy, the Archean compositional heritage of the crust.

Archean

Early Biranup

Late Biranup

SiO2

Mantle-like

Crustal

Bobbie Point (Tropicana Zone) - has A-type compositions reflecting high-temperature

melting of a crustal source - Hf-Nd isotopic decoupling suggests that source

earlier evolved at high P (stability field of garnet) - High Yb in the granites requires melting of that source

at low P (where garnet was no longer stable).

Significant uplift of potential source regions between the Neoarchean and c. 1780 Ma (in several events).

More mantle-like & compositionally unevolved

Crustal

Compositionally evolved

Late Biranup magmas – source apparently includes mixtures of a radiogenic and compositionally evolved component and an unradiogenic and compositionally primitive component – forming a triangular array.

A common theme from the Salmon Gums Event to the end of the Biranup Orogeny (c. 1800 to

c. 1670 Ma) is crustal recycling, more or less continuous mantle addition, with deep crustal

source components elevated to higher crustal levels and melted at high temperatures.

Dominant tectonic regime is probably extensional.

This period is thought to represent

progressive rifting of the Yilgarn

margin as it move towards an

ocean-continent transition in the

prelude to opening of the

‘Madura ocean’.

(e.g. Spaggiari et al., 2014).

Albany–Fraser Orogeny Stage I (1345–1260 Ma) [Recherche Supersuite] Stage II (1215–1140 Ma) [Esperance Supersuite]

Recherche Supersuite (1345–1260 Ma)

Highly silicic, K-rich and aluminous compositions reflecting a large component of remelted sedimentary material. Concentrated within the Fraser Zone where they represent melts of the Arid Basin rocks.

Recherche Supersuite (1345–1260 Ma) – Gora Hill Suite In terms of major and trace element concentrations, these are very difficult to distinguish from late Biranup magmas and their petrogenesis involved the same source components (i.e. recycled crust with addition of mantle-derived magmas).

Gora Hill Suite (Recherche) was co-magmatic with gabbros of the Fraser Zone. Geochemical data is consistent with the Gora Hill Suite forming through mixing of Fraser Gabbro and melts derived from the crust of Biranup and Nornalup Zones (i.e. reworked Archean crust).

Gora Hill - Systematic trends across the orogen This mixing occurred in an orogeny wide lower crustal hot zone and the active portion migrated from SE to NW with decreasing age.

Gora Hill - Systematic trends across the orogen Outcrop of Gora Hill Suite granite overstep the transition between the Nornalup Zone of the Albany–Fraser Orogen and the tectonically juxtaposed Madura Province, which must have been accreted before the earliest magmatism at c. 1330 Ma. To the southeast, the granites sample the isotopically juvenile (likely oceanic) crust of the Madura Province.

Gora Hill - Systematic trends across the orogen A sharp change in the isotopic composition of the Gora Hill granites across this boundary reflects a significant change in basement composition that also marks the present south-eastern edge of reworked Archean.

Two suites with a well defined spatial relationship (essentially mutually exclusive!) – and distinct compositions. Truslove Suite shares some characteristics of the Southern Hills Suite (Recherche) – its source possibly includes juvenile ‘sodic’ sedimentary sequences but it is perhaps better explained through melting of new mafic crust (?Fraser gabbro-like lower crust?)

Esperance Supersuite (1215–1140 Ma)

Booanya Suite granites are ferroan, alkali-calcic to alkali rocks with strong enrichments in incompatible trace elements. These are real A-type magmas resulting from very high temperature melting of anhydrous lower crust in association with significant mantle input.

Esperance Supersuite (1215–1140 Ma) Booanya Suite

Hannah

Esperance Supersuite (1215–1140 Ma) Booanya Suite Nd isotopic compositions are similar to granites of the Gora Hill Suite (Recherche) but extreme enrichments in incompatible trace elements at overlapping (or lower) silica contents means that melting of Gora Hill-type crust is not an option.

Esperance Supersuite (1215–1140 Ma) Booanya Suite The Booanya Suite rocks show rather limited influence from the old (Archean) crustal component see in spatially associated earlier (Gora Hill) granites.

Esperance Supersuite (1215–1140 Ma) Booanya Suite - Possible that a significant part of the Booanya Suite source is unique/new. - Perhaps introduced during or after AFO Stage I. - Hannah provides the clearest indication of source composition – mafic and enriched. - Enrichment trends similar to what we see from the Madura Province. Is the source highly enriched Madura Province lithosphere

Some general themes with decreasing age 1) Archean crustal signature is progressively diluted through REWORKING

and regular MANTLE INPUT

Some general themes with decreasing age 1) Archean crustal signature is progressively diluted through REWORKING

and regular MANTLE INPUT

2) Coincidence of mantle source input and melting of originally deep crustal sources at shallower crustal depths suggests magmatism accompanied periods of crustal extension

* AFO Stage I (Recherche Supersuite) continues this theme although the tectonic setting was probably different

Some general themes with decreasing age 1) Archean crustal signature is progressively diluted through REWORKING

and regular MANTLE INPUT

2) Coincidence of mantle source input and melting of originally deep crustal sources at shallower crustal depths suggests magmatism accompanied periods of crustal extension

3) Booanya Suite (Esperance Supersuite) introduces new theme – remobilized mantle lithosphere

Some general themes with decreasing age 1) Archean crustal signature is progressively diluted through REWORKING

and regular MANTLE INPUT

2) Coincidence of mantle source input and melting of originally deep crustal sources at shallower crustal depths suggests magmatism accompanied periods of crustal extension

3) Booanya Suite (Esperance Supersuite) introduces new theme – remobilized mantle lithosphere

4) There are no magmatic suites that have a strong subduction flavour – particular in the Mesoproterozoic period when the Madura Province was accreted to the AFO.