The Palaeoproterozoic Hooper and Lamboo Complexes of the Kimberley region of Western
Australia were interpreted by Hancock and Rut- land 1984 and Page and Hancock 1988 as an
intracratonic rift. This model was largely based on the assumption that turbidite deposition was con-
temporaneous throughout the Hooper and Lam- boo Complexes. However, Tyler et al. 1999
showed that turbidites in the eastern part of the Lamboo Complex were deposited at least eight
million years after turbidites in the Hooper Com- plex and western part of the Lamboo Complex
were deformed, metamorphosed and intruded by granite. Recent systematic regional mapping of
the Palaeoproterozoic rocks in the Kimberley re- gion indicates that the two complexes consist of
three fault-bounded zones terranes with different geological histories Tyler et al., 1995, 1999. The
presence of tectonostratigraphic terranes suggests that the evolution of the Hooper and Lamboo
Complexes can be explained by modern-style plate tectonic processes. The data outlined below
also argue against ensialic rifting of a stable Ar- chaean craton, and are consistent with a post-col-
lisional setting for the felsic magmatism. Here we present SHRIMP U – Pb zircon data and whole-
rock geochemical data, which show that the vol- canic rocks, porphyries and older granites in the
Kimberley region form an 1865 – 1850 Ma felsic magmatic association. Large volumes of younger
granite of 1835 – 1790 Ma age Page and Sun, 1994; Sheppard et al., 1995 also intruded the
Lamboo Complex Fig. 1 but they are not con- sidered in this paper.
2. Regional geology
The Hooper and Lamboo Complexes initially formed in the Palaeoproterozoic between the
Kimberley and North Australian Cratons Fig. 1. The two complexes form a belt of crystalline
rocks about 700 km long and at least 100 km wide along the southern and eastern margins of the
Kimberley Craton. The Lamboo Complex con- sists of three parallel north-northeast trending
zones Fig. 1, which Tyler et al. 1995 inter- preted
as tectonostratigraphic
terranes. The
Hooper Complex is a continuation of the Western zone of the Lamboo Complex Tyler et al., 1995.
The 1865 – 1850 Ma felsic igneous rocks described here dominate the Hooper Complex and the
Western zone of the Lamboo Complex. They predated final collision and suturing of the two
cratons at c. 1820 Ma, which was marked by granite intrusion into all three zones of the Lam-
boo Complex Fig. 1.
2
.
1
. Hooper Complex and Western zone of the Lamboo Complex
The oldest rocks exposed in the Hooper Com- plex and Western zone of the Lamboo Complex
are low- to high-grade turbiditic metasedimentary rocks of the Marboo Formation Figs. 2 and 3.
These rocks have a maximum age of 1870 Ma constrained by U – Pb ages of detrital zircons
Tyler et al., 1999. The Marboo Formation was intruded by a series of mafic sills collectively
referred to as the Ruins Dolerite Griffin et al., 1993. The Marboo Formation and the Ruins
Dolerite were deformed and metamorphosed be- fore being overlain by felsic volcanic and volcani-
clastic rocks of the Whitewater Volcanics. All three units were intruded by porphyries, granites,
and gabbros.
High-level, fine-grained porphyry and micro- granite intruded the Whitewater Volcanics, but
local gradational contacts suggest that the high- level intrusions are very closely related to the
volcanic rocks e.g. Gellatly et al., 1974, 1975; Griffin et al., 1993. In addition several of the
porphyries strongly resemble massive, thickly bed- ded crystal-rich ignimbrites of the Whitewater
Volcanics Gellatly et al., 1974; Griffin et al., 1993; Sheppard et al., 1997b. Coarse-grained
granites dominate the Hooper Complex and the Western zone of the Lamboo Complex. Gabbro
intrusions are abundant in the northern half of the Lamboo Complex, but in the southern half,
and in the Hooper Complex, they are only a minor component. Contacts between the granites
and gabbros are commonly marked by net-vein complexes, and other textures and structures in-
dicative of limited hybridization in situ of mafic and felsic magmas are widespread Blake and
Fig. 2. Simplified geology of the central part of the Hooper Complex in the west Kimberley. Also shown are the locations and numbers of samples dated in this paper.
Hoatson, 1993; Sheppard, 1996. The granites and porphyry intrusions have been placed into the
Paperbark supersuite along with the gabbro intru- sions, owing to their close temporal, spatial, and
probably, genetic associations Sheppard et al., 1997a.
Bennett and Gellatly 1970 obtained Rb – Sr isotopic data that were recalculated by Page
1976, to yield isochrons of 1912 9 107 Ma for the Whitewater Volcanics and associated por-
phyries, and 1840 9 50 Ma from the granites of the Hooper Complex. Page et al. 1995 obtained
a SHRIMP U – Pb zircon date of 1855 9 2 Ma from the Toby Gabbro, an intrusion of massive
quartz-biotite bearing gabbro in the Western zone of the Lamboo Complex. Contacts between this
gabbro intrusion and adjacent coarse-grained granites are marked by net-vein complexes, indi-
cating that the gabbro and granites were coeval. A second episode of deformation and metamor-
phism occurred either before, or during granite intrusion. Metamorphic grade was generally low,
although in the central part of both the Hooper Complex and the Western zone of the Lamboo
Complex, high-grade migmatitic metasedimentary rocks and rare anatectic S-type granites are
present Griffin et al., 1993; Tyler et al., 1997.
The Hooper Complex and Western zone of the Lamboo Complex were unconformably overlain
by sedimentary and mafic volcanic rocks of the Speewah and Kimberley Basins between 1835 and
1800 Ma Page and Sun, 1994.
2
.
2
. Central zone of the Lamboo Complex The oldest rocks in the Central zone are the
Tickalara Metamorphics, the protoliths to which were deposited at c. 1865 Ma Page and Sun,
1994; Bodorkos et al., 1999. Basement to these
rocks is not recognized. Protoliths to the Tick- alara Metamorphics mainly consist of mafic vol-
canics and
turbiditic sediments.
They were
intruded by the sheet-like Rose Bore Granite at c. 1863 Ma Tyler and Page, 1996. At c. 1850 – 1845
Ma the volcanic and sedimentary rocks were in- truded by sheets of tonalite and minor trond-
hjemite, and metamorphosed at high grade Page and Sun, 1994; Bodorkos et al., 1999. Following
high-grade metamorphism and deformation, the Tickalara Metamorphics were overlain by sedi-
ments and mafic and felsic volcanics of the Koongie Park Formation at c. 1845 – 1840 Ma.
The Central zone was extensively intruded by granite and gabbro at 1835 – 1805 Ma Sheppard
et al., 1997b.
2
.
3
. Eastern zone of the Lamboo Complex The
Eastern zone
consists of
low-grade metasedimentary and mafic metavolcanic rocks of
the Halls Creek Group Griffin and Tyler, 1992b, which unconformably overlie 1920 – 1900 Ma
granite and volcanic rock Blake et al., 1999. Fluvial quartz sandstone at the base of the Halls
Creek Group was overlain by mafic and minor felsic volcanic rock at c. 1880 Ma. These were in
turn overlain disconformably by alkaline, in- traplate-type volcanic rocks dated at 1857 – 1848
Ma Blake et al., 1999. Detrital zircons from a thick sequence of turbidites above the alkaline
volcanic rocks indicate deposition after c. 1847 Ma Blake et al, 1999. Therefore, the upper part
of the Halls Creek Group was being deposited while rocks of the Central zone were metamor-
phosed at high grade Tyler et al., 1995. This suggests that the Eastern and Central zones were
not adjacent to each other at this time.
3. Geology and SHRIMP geochronology
