The source of A-type magmas in two contrasting settings

U-Pb, Lu-Hf and Re-Os isotopic constraints

M. J. Pankhurst*, B. F. Schaefer, S. P. Turner, T. Argles, C. E. Wade

*Corresponding author for this work

Research output: Contribution to journalArticle

27 Citations (Scopus)

Abstract

The sources of post-orogenic A-type magmas from two distinct geodynamic settings are compared. The end of the ca. 514-480. Ma Delamerian Orogeny, southeastern South Australia, was marked by ~. 10. Myr of bimodal A-type magmatism, driven by convective removal of thickened lithosphere. Initial Os and Hf isotope ratios record a heterogeneous lithospheric mantle source, with some input from aesthenospheric mantle. Mafic parental melts fractionated to produce the granites. In contrast, initial Os isotope ratios of the A-type magmas that comprise the ca. 1598-1583. Ma Mesoproterozoic Gawler Felsic Large Igneous Province, central South Australia, record a dominant evolved lower crust component. However, initial Hf isotope ratios from these samples are depleted, indicating a mantle source for lithophile elements. This voluminous, bimodal magmatism lasted for ~. 15. Myr, and ended the Wartakan Orogeny. In both cases the homogenisation of chemical (rheological) heterogeneities, inherited from terrain amalgamation and orogenic thickening, strengthened the lithosphere. The contemporaneous fusion of heterogeneous mantle. ±. crust may represent a common, stabilising influence on the lithospheric column regardless of tectono-magmatic setting.

Original languageEnglish
Pages (from-to)175-194
Number of pages20
JournalChemical Geology
Volume351
DOIs
Publication statusPublished - 2 Aug 2013

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