Fault were high in the crust. The coincidence of shortening directions both stages of the Albany –
Fraser Orogeny suggests that, although the two stages are temporally distinct, a single continent-
scale convergent regime was probably responsible for the entire Albany – Fraser Orogeny.
Subsequent to D
4
, rocks of the Nornalup Com- plex were folded around temporally uncon-
strained large-scale open upright D
5
structures consistent with NE-SW shortening. This fold gen-
eration is also identified in the Biranup Complex the Munglinup Terrane of Harris 1995, sug-
gesting the deformation is regionally significant. Shortening along this axis is incompatible with
the Albany – Fraser Orogeny, but occurred in the Northampton Block Bruguier et al., 1994 and in
the Musgrave Block Sun et al., 1996 at c. 1080 Ma and again in the Musgrave Block at c. 550
Ma Maboko et al., 1992; Camacho and Fanning, 1995; Clarke et al., 1995. Which, if either, of
these events relates to D
5
in the Albany – Fraser Orogen remains unclear.
5. Regional correlations on the basis of geochronology
The continental reconstruction presented in Fig. 1a suggests that the sequence of events
described in the eastern Albany – Fraser Orogen should be manifest in some form in the western
part of the Albany – Fraser Orogen and in other Australian and East Antarctic Grenville-age oro-
genic belts. Such events together should record the assembly of Mesoproterozoic Australia as
part of the supercontinent Rodinia. Geochrono- logical data from the western part of the Albany –
Fraser Orogen and other Australian and East Antarctic orogenic belts are compared with those
of the eastern Albany – Fraser Orogen below.
5
.
1
. Western part of the Albany – Fraser Orogen Until recently high-grade deformation and
metamorphism in the western part of the Al- bany – Fraser Orogen was believed to be restricted
to a narrow time interval between c. 1190 and 1170 Ma Black et al., 1992a; Clarke et al., 1995;
Harris, 1995, which is directly analogous to the intracratonic Stage II orogenesis in the east c.
1214 – 1140 Ma. However, the report of a 1289 9 10 Ma crystallisation age for an enderbite at
Albany Pidgeon, 1990, and the study of Clark 1995, provide compelling evidence for major c.
1300 Ma tectonothermal activity in the western part of the Albany – Fraser Orogen, coeval with
Stage I in the east.
Clark 1995 analysed zircons from both leuco- some and mesosome portions of a granulite facies
metasedimentary migmatite from a locality near the above-mentioned enderbite. Overgrowths on
inherited cores, interpreted to have formed in the leucosome, gave an age of 1304 9 5 Ma. Small
structureless grains, predominantly occurring in the mesosome, record an age of 1169 9 7 Ma,
believed to represent an episode of high-grade metamorphism corresponding to that defined by
earlier work Black et al., 1992a. Thus, the two- stage evolution in the eastern part of the Albany –
Fraser Orogen can be recognised throughout the entire orogen.
5
.
2
. East Antarctica The southern edge of the Albany – Fraser Oro-
gen is truncated by the Australian continental margin Fig. 1b and Fig. 2. It has long been
assumed that its counterpart may be situated in Antarctica Myers, 1990. Reconstructions of the
relative positions of Australia and Antarctica dur- ing the Mesozoic de Witt et al., 1988; Powell et
al., 1988; Veevers, 1990 place the Albany – Fraser Orogen adjacent to the Windmill Islands and
Bunger Hills regions of east Antarctica Fig. 1a. However, some uncertainty remains on the exact
Australia – Antarctica Gondwana reconstruction Black et al., 1992b; Harris, 1995.
5
.
2
.
1
. Windmill Islands The detailed history of the amphibolite to gran-
ulite facies rocks of the Windmill Islands has recently been elucidated by Post et al. 1995,
1997. The authors present SHRIMP U-Pb ages that constrain two major periods of Mesoprotero-
zoic orogenesis; a 1400 – 1310-Ma upper amphibo- lite facies event and a 1210 – 1138-Ma granulite
facies event. These ages correspond almost exactly to those reported here in the eastern part of the
Albany – Fraser Orogen. Moreover, inherited zir- con populations of c. 1800, c. 1600 and c. 1400
Ma, found in orthogneisses and melt veins in the Windmill Islands Post, personal communication,
correspond closely to those in the Albany – Fraser Orogen.
5
.
2
.
2
. Bunger Hills The basement rocks of Bunger Hills bear strik-
ing similarities in lithology and age to the Biranup Complex of the Albany – Fraser Orogen. The ig-
neous precursors of granodioritic orthogneiss in the Bunger Hills were emplaced between 1500 and
1700 Ma Sheraton et al., 1992, and were formed from early-Proterozoic or possibly very latest Ar-
chaean crust Black et al., 1992b. A Late Ar- chaean c. 2640 Ma, Sheraton et al., 1992
tonalitic orthogneiss occurring in the nearby Obruchev Hills may represent such basement
crust. This situation corresponds to c. 1600 – 1700 Ma granodioritic and granitic intrusion into c.
2630 Ma basement in the Biranup Complex Nel- son et al., 1995.
The major period of orogenesis in the Bunger Hills c. 1190 – 1140 Ma, Sheraton et al., 1992
correlates closely with the intracratonic stage of activity recognised in the Albany – Fraser Orogen.
Given the evidence for c. 1300 Ma orogeny throughout the Albany – Fraser Orogen, geometric
considerations of the fit between Australia and Antarctica suggest that the Bunger Hills region
should also contain c. 1300 Ma rocks. More detailed geochronology is needed in this area to
confirm this correlation.
5
.
3
. Musgra6e Block In the Musgrave Block, located along strike to
the northeast of the Albany – Fraser Orogen Fig. 1a, three major periods of tectonism at c. 1200 –
1150, c. 1060 and c. 550 Ma have been recognised Clarke et al., 1995. The oldest of these is
broadly correlative to the second stage of the Albany – Fraser Orogeny, involving high-grade
metamorphism and deformation at c. 1200 Ma Gray, 1978; Maboko et al., 1991; Sun and Shera-
ton, 1992 terminating with the intrusion of gran- itoids at c. 1150 Ma Camacho and Fanning,
1995. Unpublished SHRIMP zircon data White, personal communication reveal extensive high-
grade deformation and granite intrusion in the western Musgrave Block at c. 1300 Ma. Together
with the earlier data, this evidence supports conti- nuity between the Albany – Fraser and Musgrave
belts during the Mesoproterozoic assembly of Australia, as proposed by Myers et al. 1996; Fig.
1a. A U-Pb SHRIMP zircon crystallisation age of 1310 9 4 Ma on a foliated granite from the
Rudall Metamorphic Complex Nelson, 1996, and Rb-Sr ages of 1333 9 44 and 1132 9 21 Ma
Chin and de Laeter, 1981, suggest it is also part of the same Grenville-age belt.
5
.
4
. South Australia The buried Coompana Block, immediately to
the east of the Albany – Fraser Orogen, might be expected to share a common history with the
Albany – Fraser Orogen subsequent to the amalga- mation of the South Australian and West Aus-
tralian cratons. The chronology of the Coompana Block is only known from K – Ar ages of 1185 and
1159 Ma obtained on borehole samples of granitic gneiss, interpreted to reflect isotopic resetting as-
sociated with metamorphism and deformation Flint and Daly, 1993. These ages correlate with
high grade activity east of the Rodona Fault during the second stage of the Albany – Fraser
Orogeny, which implies a continuation of the Albany – Fraser Orogen beneath the cover of the
Tertiary Eucla Basin.
6. Mesoproterozoic Australia in the context of world-wide Grenville-age orogeny
