Precambrian Research 101 2000 1 – 23
Tectonic implications of Palaeoproterozoic post-collisional, high-K felsic igneous rocks from the Kimberley region of
northwestern Australia
T.J. Griffin
a
, R.W. Page
b
, S. Sheppard
a,
, I.M. Tyler
a
a
Geological Sur6ey of Western Australia, Mineral House,
100
Plain Street, East Perth,
6004
WA, Australia
b
Australian Geological Sur6ey Organisation, GPO Box
378
, Canberra
2601
, ACT, Australia Received 1 March 1999; accepted 1 October 1999
Abstract
Palaeoproterozoic high-K I-type granites, high-level porphyry intrusions, and felsic volcanic rocks of the Whitewa- ter Volcanics dominate the Hooper and Lamboo Complexes in the Kimberley region of northwestern Australia. The
granites, porphyries and volcanic rocks are gradational into each other in the field, and they have the same mineralogy, similar major and trace element abundances, and indistinguishable SHRIMP U – Pb zircon ages of
1865 – 1850 Ma. There is evidence of widespread mingling between the granites and coeval gabbros. Magma mixing may be important in the formation of some of the mafic granites, but most of the rocks probably formed from felsic
parent magmas that underwent variable degrees of fractional crystallization. The felsic igneous rocks may have formed by partial melting of intermediate to felsic, calc-alkaline rocks along the southern and eastern margins of the
Kimberley Craton, following accretion of various earlier Palaeoproterozoic terranes to the craton. Therefore, models for Palaeoproterozoic high-K granites in northern Australia that invoke intracratonic rifting of a stable Archaean
craton may need to be revised. Published by Elsevier Science B.V.
Keywords
:
Palaeoproterozoic; Granites; Felsic volcanics; Geochronology; Geochemistry; Halls Creek Orogen www.elsevier.comlocateprecamres
1. Introduction
Wyborn 1988 estimated that granites and fel- sic volcanic rocks of c. 1880 – 1840 Ma age in
northern Australia cover at least 37 000 km
2
. In the Kimberley region of northwestern Australia,
I-type granites, high-level porphyry intrusions and felsic volcanic rocks of this age cover more than
11 000 km
2
. They constitute a major element of the Palaeoproterozoic Hooper and Lamboo Com-
plexes Fig. 1, and form the largest coherent felsic igneous province in northern Australia.
Some of the high-level porphyry intrusions grade into adjacent felsic volcanic rocks or coarse-
grained granites Dow et al., 1964; Gellatly et al., 1975; Griffin et al., 1993, and the similarity in
Corresponding author. Fax: + 61-8-92223633. E-mail
addresses
:
rpageagso.gov.au R.W.
Page, s.shepparddme.wa.gov.au S. Sheppard
0301-926800 - see front matter. Published by Elsevier Science B.V. PII: S 0 3 0 1 - 9 2 6 8 9 9 0 0 0 8 4 - 4
chemical compositions of the three rock types is consistent with them being cogenetic Griffin and
Tyler, 1992a. The Palaeoproterozoic granites of northern Aus-
tralia, including the pre-1840 Ma granites in the Kimberley, are mainly potassic and silicic I-types.
The high K
2
O and SiO
2
contents distinguishes them from granites at Phanerozoic convergent margins,
and Wyborn 1988 and Wyborn et al. 1992 interpreted them as being generated in a series of
linked intracratonic rifts within a stable Archaean craton. The source for these granites was thought
to be a locally fractionated mafic underplate, em- placed craton-wide at 2300 – 2100 Ma.
Fig. 1. Palaeoproterozoic geology of the Kimberley region in northwestern Australia. The inset also shows the locations of the North Australian Craton NAC and the Kimberley Craton KC.
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
