Origin of metasedimentary and igneous rocks from the Entia Dome, eastern Arunta region, central Australia: a U-Pb LA-ICPMS, SHRIMP and Sm-Nd isotope study

Analysis of detrital zircon from previously geochronologically unconstrained metasedimentary rocks in the eastern Arunta region, using U-Pb LA-ICPMS and SHRIMP, provides ages reconcilable with Australian sources. Maximum depositional ages of the analysed samples fall into two groups, three samples having maximum depositional ages of ca 1780-1760 Ma and two at ca 2510-2490 Ma. Metamorphic monazite from two pelitic rocks provides bimodal age populations of 1773 +/- 9 Ma and 325 +/- 8 Ma from one sample, and 1719 +/- 9 Ma and 341 +/- 5 Ma from the second. The age of 1773 +/- 9 Ma is the first direct evidence of monazite growth in the interval ca 1780-1770 Ma, and is attributed to high-grade contact metamorphism associated with the proximal emplacement of granodioritic bodies previously thought to be subduction-related. The metamorphic age of 1719 +/- 9 Ma is attributed to the Strangways Orogeny (1730-1710 Ma). The Carboniferous ages of 325 +/- 8 Ma and 341 +/- 5 Ma in both samples are attributed to partial resetting and new growth of monazite during the Alice Springs Orogeny (ca 400-300 Ma). Sm-Nd isotope systematics of the metasedimentary rocks display a large variation ranging from (epsilon)Nd(1760)= -1.4 to -8.8 and, when coupled with the detrital-zircon age populations, allow for a locally derived (North Australian Craton) source for the metasedimentary rocks. Analysis of igneous zircon from a felsic layer of the Entia Gneiss Complex intimately interlayered with the metasedimentary rocks yielded a (207)Pb/(206)Pb weighted average age of 1771 +/- 10 Ma, interpreted as the crystallisation age of the igneous precursor. This age is indistinguishable within error from that of the granodioritic intrusions (Inkamulla Granodiorite 1773 +/- 4 Ma), here thought to be responsible for the high-grade metamorphism in the metasedimentary rocks. Given that the granodioritic bodies have previously been characterised as subduction-related intrusions, the approximately coincident ages of metamorphism, deposition of at least some of the metasedimentary rocks, and the intrusion of voluminous felsic and ma. c magmas, suggests that the deposition and metamorphism of the precursor to the metasedimentary rocks may be related to active subduction along the southern margin of the Arunta region.