Hafnium isotope data for the Simuku Igneous Complex, New Britain, Papua New Guinea

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.

References

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.

与《美拉尼西亚弧（Melanesian arc）对翁通爪哇高原（Ontong Java Plateau）碰撞的远场响应：巴布亚新几内亚新不列颠岛西穆库火成杂岩（Simuku Igneous Complex）的年代学与岩石成因》相关的铪同位素数据集。

理解新生代中期美拉尼西亚弧的演化，对于认识澳大利亚-太平洋板块边缘的区域构造演化至关重要。Holm等人（2013）针对巴布亚新几内亚新不列颠岛美拉尼西亚弧的西穆库火成杂岩发表了U-Pb定年与地球化学数据。此前的研究发现，美拉尼西亚岛弧至少自40 Ma起开始发育，其弧体渐进式生长被翁通爪哇高原的远距离碰撞事件打断，并在26 Ma左右发生俯冲作用停滞。俯冲动力学的这一转变，在美拉尼西亚弧的岩浆记录中体现为24~20 Ma期间西穆库斑岩杂岩的侵位。Holm等人（2013）还发现，岩石学与地球化学特征显示，"正常"弧火山岩与具铜-钼矿化的斑岩侵入体的埃达克质（adakite-like）地球化学属性存在成因差异。本数据集是对Holm等人（2013）研究的补充，提供了该早期研究中分析的同一批锆石（zircon）的新型铪同位素数据。

本研究于詹姆斯库克大学（James Cook University, JCU）先进分析中心，参照Holm等人（2014）提出的实验方法，使用GeoLas193-nm ArF准分子激光器与Thermo-Scientific Neptune多接收器电感耦合等离子体质谱仪（multicollector ICP-MS），对锆石开展Lu-Hf同位素（Lu–Hf isotope）的激光剥蚀（laser ablation）分析。同位素分析所用的锆石晶件依据U-Pb定年结果筛选，激光剥蚀的重复频率设为4 Hz，剥蚀光斑直径为60 μm。所有标准锆石与样品锆石的176Hf/177Hf比值均以Mud Tank参考锆石（Mud Tank reference zircon）的测试结果进行归一化校正：两次分析批次的平均测试176Hf/177Hf比值分别为0.282493 ± 8，n = 14，与0.282494 ± 8，n = 14，并以溶液标准值0.282507作为归一化基准；同时以FC1二级锆石标准物质（FC1 secondary zircon standard）作为参照，其归一化后176Hf/177Hf比值为0.282167 ± 10（Kemp等，2009）。本数据集的εHf值（epsilon Hf value）通过对应U-Pb剥蚀点位的206Pb/238U岩浆结晶年龄数据计算得到，计算时采用的176Lu衰变常数为1.867 × 10^-11 a^-1（Söderlund等，2004）。

本研究对样品SKB01、06、07、08、11以及SMD29的66、146、203、261号锆石晶件开展了Lu-Hf同位素比值分析。这些样品的选取覆盖了经U-Pb定年确定的西穆库火成杂岩的所有侵入相。相关测试结果已整理于附表与附图中。西穆库火成杂岩全演化时段（43.3 Ma至19.4 Ma）所侵位的所有火山岩样品与斑岩岩套的εHf值均集中分布于10~13的狭窄区间内，所有被测样品的εHf值均无显著差异。

参考文献
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. 《构造物理学报》（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. 《冈瓦纳研究》（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. 《化学地质学》（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. 《地球与行星科学通讯》（Earth and Planetary Science Letters）219, 311–324.