Geochronological constraints on nickel metallogeny in the Lake Johnston belt, Southern Cross Domain

Abstract

Geochronology and stratigraphic revision of the Lake Johnston greenstone belt and adjacent granitoids and granitic gneiss provide new insight into the age of komatiites in the Southern Cross Domain of the Archean Yilgarn Craton. Roundtop Komatiites are geochemically similar to undated komatiites in the adjacent Ravensthorpe and Southern Cross—Forrestania greenstone belts, and the results can be extrapolated to improve the regional understanding and geodynamic evolution. Consequently, the further refined knowledge of the regional stratigraphy improves the understanding of the evolution and targeting of komatiite-hosted nickel deposits. A minimum age of ca 2773 Ma for the succession of the Lake Johnston greenstone belt is provided by crosscutting granitic rocks, with a maximum age for the underlying Roundtop Komatiite given by a maximum depositional age of ca 2876 Ma for felsic volcaniclastic rocks of the underlying Honman Formation. These new results suggest that komatiites of the Southern Cross Domain are significantly younger than previously assumed, which has implications for Yilgarn-wide geodynamic models regarding ‘plume activity’ and global correlations in the Meso- to Neoarchean.

约翰斯顿湖绿岩带和相邻花岗岩和花岗片麻岩的年代学和地层学修订对太古代Yilgarn克拉通南十字星域科马提岩的年龄提供了新的认识。圆顶科马提岩的地球化学特征类似于相邻的Ravensthorpe和南十字星-Forrestania绿岩带的年代未定的科马提岩带。其结果可外推，以改善对区域范围的理解和地质动力演化。因此，对该区域地层的进一步了解改善了对演化的理解和选择科马提岩中的镍矿床。切割花岗岩提供了约翰斯顿湖绿岩带地层序列的最低年龄为约2773Ma，下伏圆顶科马提岩的最大年龄的确定是根据下伏Honman组的长英质火山碎屑岩最大沉积年龄约2876Ma。这些新的研究结果表明，南十字星域的科马提岩的年龄显著小于先前所假设的，这对于Yilgarn范围的关于中-新太古代̏柱活动̋和全球对比的地球动力学模型有重大意义。

KEY WORDS:

• Archean
• greenstones
• stratigraphy
• komatiite
• zircon dating
• SHRIMP

ACKNOWLEDGEMENTS

Zircon analyses were conducted using the SHRIMP II ion microprobes at the John de Laeter Centre for Isotope Research at Curtin University, in Perth, Australia. The staff at the Geological Survey of Western Australia's Carlisle laboratory are thanked for their diligent efforts in mineral separation. The results presented were partially funded through the ARC Linkage Project LP100100647 ‘Tectonic Evolution & Lode Gold Mineralisation in the Southern Cross District Yilgarn Craton Western Australia—A Study of the Meso- to Neoarchean Missing Link.’ The authors acknowledge the facilities and scientific and technical assistance of the Australian Microscopy & Microanalysis Research Facility at the Centre for Microscopy, Characterisation & Analysis (CMCA) at The University of Western Australia, a facility funded by UWA and by WA State and Commonwealth Governments. We thank the reviewers Stephen Beresford and Andreas Mueller, and the guest editor Steffen Hagemann for their constructive comments and suggestions. This paper is published with permission of the Executive Director of the Geological Survey of Western Australia.