Geochemical characteristics of lava-field basalts from eastern Australia and inferred sources: Connections with the subcontinental lithospheric mantle? |
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Authors: | Suzanne Y O’Reilly Ming Zhang |
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Institution: | (1) Centre for Petrology and Lithospheric Studies, School of Earth Sciences, Macquarie University, Sydney, NSW 2109, Australia, AU |
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Abstract: | A large new database of major, trace elements and Sr-Nd isotopic ratios from 11 lava-field provinces in New South Wales and
Queensland, eastern Australia allows detailed interpretation of the origin of these basaltic magmas. Isotopic signatures and
trace element patterns identify an OIB-type (oceanic island basalt) source as a dominant component for most of these and some
provinces appear to have additional significant components derived from the subcontinental lithospheric mantle (SCLM). The
SCLM components have geochemical characteristics that overlap those observed in spinel lherzolite xenoliths (samples of shallow
lithospheric mantle) from eastern Australia. These SCLM components show geochemical provinciality that indicates the occurrence
of distinct geochemical lithospheric domains reflecting the timing and style of tectonic evolution of different regions. One
component reflects modification by subduction-related processes during the late Paleozoic and Mesozoic, one records enrichment
by fluids during old metasomatic events and another suggests a metasomatic event involving a distinctive amphibole and apatite-style
enrichment. The composition and age distribution of volcanic lava-field provinces older than 10 Ma are consistent with a model
involving a regional upwelling (elongated N–S along eastern Australia) of deep hot mantle related to marginal rifting and
with OIB-type source geochemical characteristics. Thermal inhomogeneities within this plume swath resulted in small diapirs
which may have undergone melt segregation at about 100 km and incorporated varying amounts of SCLM components there or from
higher levels of the SCLM during ascent. Subsequent hot-spot generated central volcanoes overprinted this lava-field volcanism,
tapped a similar OIB-type source component and truncated the thermal events.
Accepted: 15 March 1995 |
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