Ss. Sun et Rd. Shaw, ND ISOTOPE STUDY OF GRANITES FROM THE ARUNTA-INLIER, CENTRAL AUSTRALIA - CONSTRAINTS ON GEOLOGICAL MODELS AND LIMITATION OF THE METHOD, Precambrian research, 71(1-4), 1995, pp. 301-314
Three chemically distinct types of granite (''high Sr/low Y'' calc-alk
aline, Palaeoproterozoic ''normal'' and ''enriched'') are present in t
he Palaeoproterozoic Arunta Inlier of central Australia. Twenty-one re
presentative samples were selected for Nd isotopic analysis to complem
ent geological and geochemical data. Most samples analysed have deplet
ed-mantle Nd isotope model ages (T-DM, following McCulloch, 1987) of 2
.3 to 2.1 Ga, similar to most of Palaeoproterozoic granites of norther
n Australia (McCulloch, 1987). These ages do not show a younging trend
from the Northern to Southern provinces, although some post similar t
o 1750 Ma granites from the Central and Southern provinces, with typic
al felsic crust Sm-147/Nd-144 ratios (0.09-0.11), have younger model a
ges (less than 2.0 Ga). Post 1700 Ma, ''normal-type'' granites from th
e Southern Province have chemical compositions similar to older granit
es (1880-1760 Ma) of the same suite, even though they have younger mod
el ages (1960-1930 Ma). This implies an increase in a younger componen
t within southern source regions through melting of new underplate and
/or additional mantle input. The syn- or post-tectonic granites (1720-
1140 Ma) of the ''enriched-type'' (high heat producing granites rich i
n Th, U and K) have similar T-DM model ages to older granites of the '
'normal-type'' from the same areas. The ''enriched-type'' granite from
the Teapot Granite Complex of the Southern Province are characterised
by low Cs, Sr and high Rb/Cs (30-50), Th/U (7-20) ratios and high Y c
ontents. These chemical characteristics are consistent with magma bein
g formed through anatexis of ''normal-type'' granite sources. In contr
ast, an 1820 Ma, S-type granite from the Harverson suite in the Northe
rn Province has an older T-DM model age (2.32 Ga) than the T-DM 2.18 G
a age of the nearby Aileron Metamorphics, suggesting that the source r
ock of the granite may contain a significant Archaean component. The N
d isotope data, when integrated with geological and chemical informati
on, are compatible with the recycling of Archaean crustal material. Su
ch a process might have taken place very early in the history of the A
runta Inlier through subduction along a continental margin made up of
a stretched, dismembered, thin Archaean basement. Magmatic underplatin
g may have taken place shortly before 1850 Ma and continued episodical
ly during subsequent tectono-thermal events. Crustal melts of mixed so
urce rocks, formed during these events, could contain different amount
s of an Archaean component.