Ages of internal granitoids in the Southern Cross region, Yilgarn Craton, Western Australia, and their crustal evolution and tectonic implications

Y. Qiu, Neal Mcnaughton, David Groves, H.J. Dalstra

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Abstract

Southern Cross, where gold deposits are sited in narrow greenstone belts surrounding granitoid domes, was one of the earliest gold mining centres in Western Australia. SHRIMP U-Pb zircon and Pb-isotope studies of the largest granitoid dome, the Ghooli Dome (80 x 40 km), provide important constraints on the crustal evolution and structural history of the central part of the Archaean Yilgarn Craton, Western Australia, which includes Southern Cross. The north-northwest-south-southeast-oriented ovoid Ghooli Dome has a broadly concentric foliation that is subhorizontal or gently dipping in its central parts and subvertical along its margins. Foliated granitoids in the dome are dated at ca 2724 +/- 5 and 2688 +/- 3 Ma using the SHRIMP U-Pb zircon and Pb-Pb isochron methods, respectively. These new data, together with the published SHRIMP U-Pb zircon age of 2691 +/- 7 Ma at another locality, 20 km from the centre of the Koolyanobbing Shear Zone, suggest that the Ghooli Dome was emplaced at ca 2.72-2.69 Ga. Because the Ghooli Dome and the other domes, which are enveloped by narrow greenstone belts, are cut by the >650 km-long and 6-15 km-wide Koolyanobbing Shear Zone, the ca 2.69 Ga age is interpreted as the maximum age of the last major movement on this structure. The pre-2.69 Ga history, if any, of the shear zone remains unknown. The shear zone is intruded by an undeformed porphyritic granitoid which has a SHRIMP U-Pb zircon age of 2656 +/- 4 Ma. This age is. thus, the minimum age of major movement along this shear zone. Post-gold mineralisation pegmatitic-leucogranite from the Nevoria gold mine has a SHRIMP U-Pb zircon age of 2634 +/- 4 Ma, with xenocrystic zircon cores of ca 2893 +/- 6 Ma, constraining the minimum age of gold mineralisation there to ca 2.63 Ga. The ca 2.72-2.69 Ga granitoids also contain ca 2.98 and 2.78 Ga xenocrystic zircon cores, suggesting an extensive crustal prehistory for their source. Whereas there is a general temporal relationship between the periods of older (ca 3.0 Ga) and younger (ca 2.80 and 2.73 Ga) volcanism and the older (2.98, 2.78 and 2.72-2.69 Ga) granitoid intrusions, there is no known volcanism temporally associated with the 2.65-2.63 Ga granitoid intrusions in the Yilgarn Craton. Other heat sources and/or tectonic processes, required for the generation of these intrusions, are interpreted to be related to a lithospheric delamination event related to continental collision.
Original languageEnglish
Pages (from-to)971-981
JournalAustralian Journal of Earth Sciences
Volume46
DOIs
Publication statusPublished - 1999

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