pre-1.8 ga crustal evolution of the mount isa fault region ... · pre-1.8 ga crustal evolution of...
TRANSCRIPT
Pre-1.8 Ga Crustal Evolution of the
Mount Isa Fault Region – Insights
from SHRIMP U-Pb and in-situ Lu-Hf
Analysis of Zircons
Frank P. Bierlein, Lance Black, Janet Hergt, Geordie Mark
predictive mineral discovery
Cooperative Research Centre
SHRIMP U-Pb age dating and laser ablation Hf-isotope analysis of zircons from pre-1.8 Ga
basement rocks on either side of the metallogenically important Mount Isa Fault indicate that
the entire region was part of the same lithospheric block, and that the Mount Isa Fault cannot
represent the surface expression of a Barramundi-aged transcrustal suture as has previously
been proposed (e.g., MacDonald et al., 1997; Hobbs et al., 2000). Magmatic ages of ca. 1.85 Ga
in samples from the Yaringa Metamorphics and from enclaves in the Kalkadoon Granite
constrain the thermo-tectonic history of the proto-Mount Isa Fault region, with ca. 2.4 – 3.2
Ga inherited zircons suggesting that Archaean crust contributed to the source of the
Palaeoproterozoic sequence.
The Lu-Hf composition of zircons analysed by SHRIMP, and the absence of evidence for
large-scale tectonism support the notion that there is no lithospheric break across the Mount
Isa Fault (e.g., Bierlein and Betts, 2004). Furthermore, the 176Hf/177Hf isotope data confirm
that Archaean – Palaeoproterozoic magmatic zircons on both sides of the Mount Isa Fault
were sourced from the same parental lithospheric reservoir which evolved over time from
more primitive mantle to more supracrustal compositions. The results of this study impact on
crustal-scale models for the development of shale-hosted massive sulphide Pb-Zn-Cu
mineralisation and whether trans-lithospheric faults are an important ingredient for the
development of this deposit type.
Frank P Bierlein
Centre for Exploration Targeting
University of Western Australia
35 Stirling Highway, Crawley WA 6009
Phone: (08) 6488 7846
Fax: (08) 64881178
Email: Your [email protected]
www.pmdcrc.com.au
1860 MaMcDonald et al. (1997)
MI-829; 1858 Ma
MI-8211; 1853 Ma
MI-827; 1847 Ma
1890 MaPage & Williams (1988)
‘magmatic’population
(= compositionof lithosphereat ca. 1.9 Ga)
inheritedzircons
(= compositionof lithosphere
between 3.4and 1.9 Ga)
(n = 169)
176/177 versus age
2.804E-01
2.806E-01
2.808E-01
2.810E-01
2.812E-01
2.814E-01
2.816E-01
2.818E-01
0 500 1000 1500 2000 2500 3000 3500 4000
Lu-Hf isotopic evolutionary trendof pre-1.9 Ga basement in
western succession east & westof Mt Isa Fault
Yaringa Creek Metamorphics
Kalkadoon Granite mafic
enclave
Kurbaya Migmatites
0.5
mm
Plum Mountain Gneiss
Yaringa Metamorphics (west of Mt Isa Fault);1858 ± 4 Ma (n = 17)
Yaringa Metamorphics (west of Mt Isa Fault);1853 ± 5 Ma (n = 17)
FBMI-829 FBMI-827FBMI-8211
Enclave in Kalkadoon Granite, NE of Mt Isa;1847 ± 3 Ma (n = 20)
References
Bierlein, F.P., Betts, P.G. (2004). The Proterozoic Mt Isa Fault Zone, northeastern Australia – is it really a ca. 1.9 Ga terrane-bounding suture? Earth and
Planetary Sciences Letters, 225, 279-294.
Hobbs, B.E., Ord, A., Archibald, N.J., Walshe, J.L., Zhang, Y., Brown, M., Zhao, C. (2000). Geodynamic modelling as an exploration tool, in: After 2000 – The
Future of Mining Conference.
McDonald, G.D., Collerson, K.D., Kinny, P.D. (1997). Late Archean and Early Proterozoic crustal evolution of the Mount Isa block, northwest Queensland,
Australia. Geology, 25, 1095-1098.
Mt Isa