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/ 201 2 1AGR Annual Convention and 9th International Symposium on Gondwana to Asia
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Paleomagnetic investigation of Lower Permian rift basalts from the Baoshan Block, SW China; insights into the Cimmerian terrane's separation from eastern Gondwana Jason R. Ali 1:, Haz M.C. Cheung 1 , Jonathan C. Aitchison 2 & Yadong Sun 3 •4 1
Department of Earth Sciences, University of Hong Kong, Pokfulam Road, Hong Kong, China 2 School of Geosc1ences, University of Sydney, Sydney, NSW 2006, Australia 3 Faculty of Earth Sciences, China University of Geosciences, Wuhan, Hubei 430074, PR China 4 School of Earth and Environment, University of Leeds, Leeds LS2 9JT, United Kingdom E-mail address:
[email protected] (JR. Ali).
We present the results of a paleomagnetic investigation was carried out on a series of rift basalts (Woniusi Formation) that accumulated on the Baoshan block (SW China) in the Early Permian . Our aim was to provide quantitative paleogeographical information on the eastern Cimmerian terrane as it detached from eastern Gondwana. Reliable data were obtained from five locations/thirty-one sites, and when combined with the findings of an earlier study (three locations/nineteen sites) indicate that breakup occurred at 42.1 os. Using this information, we fit Baoshan against Gondwana within a narrow longitudinal belt close to where northern India and northwestern Australia were once in close proximity (Fig. 1). Furthermore, we suggest that Sibumasu lay to directly the east, offshore of Australia; Qiangtang and Lhasa almost certainly sat to the west (off northern Greater lndia-SE Arabia), but we are uncertain as to their exact configuration. Our findings will be compared with several rather different models that have been published in recent years. The new paleomagnetic constraint highlights the flexibility authors currently have in reconstructing the region, principally because of the overall lack of similar highquality data from the various blocks. We explain how new data could resolve these ambiguities, thereby offering more robust explanations for eastern Gondwana's late Paleozoic development.
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2012/AGR Annual Convention and 9th lntemational Symposium on Gondwana to'-""
Ali et al. Fig. 1
Figure 1: Positionmg Baoshan alongside eastern Gondwana in the late Early Permian (-280 Ma). Note that the Cimmerian Terrane fragments east of the modelled position for Baoshan must have been separated from northern Australia by crusta/ blocks that rifled from the latter in the M1dd/e to Late Jurassic. Abbreviations: C, E, W and Z respectively refer to the Carnarvon Terrace and Exmouth, Wallaby and Zenith plateaus that sit to the W and NW of Australia Regarding the latter three, they have been "nudged" in a southeasterly direction to accommodate extension associated with the Late Jurassic-Early Cretaceous rifling that affected western Australia.
