Geology of the Kimberley (Western Australia)

[1] The area formed in a slow tectonic plate collision during the Paleoproterozoic era, 2.5–1.6 billion years ago (Ga).

[2] During the Proterozoic and Early Phanerozoic eons up to approximately 400 million years ago (Ma), the region had phases of mountain building (orogeny), faulting and sedimentary basin formation.

[2] The Kimberley is the northernmost of the nine regions of Western Australia, with an area of 423,517 square kilometres (163,521 sq mi), about three times the size of England.

[5][6] This argument has been challenged by more recent magnetic and gravity surveys indicating that the regional lithologies incorporated recycled orogenic and volcanic arc materials.

[7][8] This incorporation suggests that, rather than having a stable basement, the Kimberley Craton was instead shaped and reshaped by stages of magmatic and mountain-building episodes.

Convergence of the two cratons could have included crustal accretion of exotic terranes (distinct fragments of earlier crust).

[9]: 21 The freshly consolidated Marboo Formation experienced metamorphism of various grades throughout the Hooper Orogeny, along with extensive mafic intrusions, which were especially prominent during its earlier stages.

[10] A passive margin developed along the edge of the North Australian Craton in the Eastern Zone, depositing siliciclastic and volcanic rocks of the Halls Creek Group.

[12][13][16] After the Hooper Orogeny, the downgoing slab, which had been deeply subducted into the asthenosphere, detached from the surface portion of the tectonic plate.

[9] Further geochemical analyses have shown that the igneous intrusions have a chemical composition similar to that of other Phanerozoic continental margins, with a strong resemblance to known subduction, back-arc spreading, and island arc systems.

[11] The geochemistry suggests that before a complete suture formed, the section of the North Australian Craton directly underlying the Kimberley Craton may have detached, instigating a short period of renewed northwest-dipping subduction (that is, the Northern Australian plate again subducting under the Kimberley plate).

[11] The Halls Creek Orogeny also resulted in silica-rich sedimentary and felsic volcanic rocks, collectively termed the Speewah Group, being eroded from the new highlands and deposited over the Kimberley Craton.

The group broadly includes the Moola Bulla, Red Rock, Texas Downs, and Revolver Creek.

An alternative model proposes an ensialic marginal basin, rather than an oceanic arc, at the time of the Early Hooper Orogeny (1865-1856 Ma).

[23] During the early deposition and consolidation stages of the Marboo Formation, there were many intrusions of mafic magma, which formed rock bodies of varying sizes.

[24][9] At 1845-1840 Ma the Tickalara Metamorphics were overlayed and encrusted with the eruption of mafic to felsic volcanic rocks, comprising the Koongie Park Formation.

[13][25] During the subsequent Halls Creek Orogeny (1835-1805 Ma), the entire Central Zone was prominently intruded by granites and gabbros, which belong to the Sally Downs Supersuite.

[14] Studies of the zircon ages of lithologies above the alkaline volcanics show that deposition of the upper sequences of the Halls Creek Group occurred at the same time as the metamorphic stages of the Central Zone.

Pre-Hooper Orogeny: Subduction and accretion of exotic terrane under the Kimberley Craton.
Early Hooper Orogeny: Convergence of the Kimberley Craton to the North Australian Craton and development of the Tickalara Oceanic Arc.
Late Hooper Orogeny: Mafic-ultramafic intrusions and deformation of the Central Zone.
Post-Hooper Orogeny: Accretion of the Tickalara Arc and development of the Koongie Park Formation.
Halls Creek Orogeny: Emplacement of the Sally Downs Supersuite and suturing of the Kimberley Craton to the North Australian Craton.
Simplified geological map of the Kimberley region, showing the three major zones of the Lamboo Complex. Inset shows the location on the continent of Australia.
Tectonic setting during the formation of the Tickalara Oceanic Arc, circa 1865 Ma before present.
Simplified time and space plot showing major tectonostratigraphic units of the three zones.