Hafnium isotope data related to "Melanesian arc far-field response to collision of the Ontong Java Plateau: geochronology and petrogenesis of the Simuku Igneous Complex, New Britain, Papua New Guinea".
Understanding the evolution of the mid-Cenozoic Melanesian arc is critical for our knowledge of the regional tectonic development of the Australian-Pacific plate margin. Holm et al. (2013) presented U-Pb dating and geochemistry for the Simuku Igneous Complex of the Melanesian arc from New Britain, Papua New Guinea. The prior study found that development of the embryonic Melanesian island arc from at least 40 Ma and progressive arc growth was punctuated by distant collision of the Ontong Java Plateau and subduction cessation from 26 Ma. This change in subduction dynamics was represented in the Melanesian arc magmatic record by emplacement of the Simuku Porphyry Complex between 24 and 20 Ma. Holm et al. (2013) found that petrological and geochemical affinities highlighted genetic differences between ‘normal’ arc volcanics and the adakite-like signatures of Cu–Mo mineralised porphyritic intrusives. This dataset complements the study of Holm et al. (2013) and presents new Hf-isotope data for the same zircon crystals analysed in the earlier study.
Laser ablation analyses of zircons for Lu–Hf isotopes were carried out at the Advanced Analytical Centre, JCU, using a GeoLas193-nmArF laser and a Thermo-Scientific Neptune multicollector ICP-MS following the methods outlined in Holm et al. (2014). Zircon crystals for isotopic analysis were selected on the basis of U–Pb dating results and ablation was carried out at a repetition rate of 4 Hz and a spot size of 60 μm. All 176Hf/177Hf ratios for standard and sample zircons were normalised to measurements of the Mud Tank reference zircon (average measured 176Hf/177Hf ratios during the course of two analytical sessions were 0.282493 ± 8, n = 14, and 0.282494 ± 8, n = 14, normalised to solution value of 0.282507) and compared with the FC1 secondary zircon standard (176Hf/177Hf normalised = 0.282167 ± 10; Kemp et al., 2009). Epsilon Hf values for the data were calculated using the 206Pb/238U magmatic crystallisation age data from the corresponding U–Pb ablation spot, and used a decay constant for 176Lu of 1.867 × 10−11 y−1 (Söderlund et al., 2004).
The selected zircons from samples SKB01, 06, 07, 08, 11 and SMD29 66, 146, 203 and 261 were analysed for Lu–Hf isotopic ratios. The samples were selected to represent all intrusive phases from the Simuku Igneous Complex as established by U–Pb dating. The results are reported in the associated Table and Figures. All εHf values from all volcanic samples and porphyry suites emplaced over the period 43.3 Ma to 19.4 Ma, the entire span of the Simuku Igneous Complex, fall within a tight range between 10 and 13 with no discernible difference in εHf values between any of the measured samples.
Holm, R.J., Spandler, C., Richards, S.W., 2013. Melanesian arc far-field response to collision of the Ontong Java Plateau: geochronology and petrogenesis of the Simuku Igneous Complex, New Britain, Papua New Guinea. Tectonophysics 603, 189–212.
Holm, R.J., Spandler, C., Richards, S.W., 2014. Continental collision, orogenesis and arc magmatism of the Miocene Maramuni arc, Papua New Guinea. Gondwana Research, In Press http://dx.doi.org/10.1016/j.gr.2014.09.011.
Kemp, A.I.S., Foster, G.L., Scherstén, A., Whitehouse, M.J., Darling, J., Storey, C., 2009. Concurrent Pb–Hf isotope analysis of zircon by laser ablation multi-collector ICPMS, with implications for the crustal evolution of Greenland and the Himalayas. Chemical Geology 261, 244–260.
Söderlund, U., Patchett, P.J., Vervoort, J.D., Isachsen, C.E., 2004. The 176Lu decay constant determined by Lu–Hf and U–Pb isotope systematics of Precambrian mafic intrusions. Earth and Planetary Science Letters 219, 311–324.