Zircon geochronology and Hf isotopes of the Dwalile Supracrustal Suite, Ancient Gneiss Complex, Swaziland: Insights into the diversity of Palaeoarchaean source rocks, depositional and metamorphic ages
Zircon geochronology and Hf isotopes of the Dwalile Supracrustal Suite, Ancient Gneiss Complex, Swaziland: Insights into the diversity of Palaeoarchaean source rocks, depositional and metamorphic ages
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斯威士兰古片麻岩杂岩 Dwalile 地壳套的锆石年代学和 Hf 同位素：深入了解古太古代烃源岩、沉积和变质时代的多样性
DOI：
10.1016/j.precamres.2017.04.025
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发表时间：
2017
影响因子：
3.8
通讯作者：
C. Lana
中科院分区：
文献类型：
--
作者：
V. Schijndel;G. Stevens;A. Zeh;D. Frei;C. Lana
本文报道了对采自东秦岭Dwalile表壳岩套（DSS）的各种变质火山-沉积岩中碎屑和变质锆石颗粒进行U-Pb和Lu-Hf同位素联合分析的结果。3.66到斯威士兰的3.20 Ga古片麻岩杂岩（AGC）。结果表明，该盆地是由古、中太古代岩石组成，这些岩石在新太古代受到多变质叠加作用的影响而形成构造组合。最古老的Dwalile岩石形成于长英质到中等火山作用的一个阶段，大约在2000年。3.46 Ga，与Tsawela片麻岩来自同一岩浆源。根据U-Pb-Hf同位素组合数据，可以区分出两组变质沉积岩：一组较老的Dwalile I组，其年龄与Hooggenoeg组和Kromberg组（3.46-3.40 Ga）相似，但源区不同。一个年轻的Dwalile第二组是同时代的无花果树和可能穆迪集团U-Pb-Hf同位素数据和岩石学观察表明，深圳湾盆地经历了3期变质叠加作用：3.23Ga的事件，3.15Ga的普遍角闪岩相变质作用，2.99Ga的低磷麻粒岩相变质作用。角闪岩相岩石中的变质锆石是在3.15 Ga的水溶液中新生长的，而麻粒岩相岩石中的新锆石是在熔体的存在下形成的。3.23 Ga事件与巴伯顿绿岩带（BGB）最后一次重要的变质叠加事件相吻合，而两次较年轻的事件仅限于AGC。3.23佐治亚州此外，他们需要地壳增厚在AGC的地壳厚度在约。3.15 Ga，在DSS中引起Barrovian型变质，在Luboya-Kubuta地体中引起麻粒岩相变质。低磷麻粒岩相变质作用。2.99 Ga很可能与Pongola盆地裂谷开始期间的地壳伸展有关，导致地幔上涌、镁铁质岩浆作用以及从地幔到薄地壳的热量传递。
We report the results of combined U-Pb and Lu-Hf isotope analyses of detrital and metamorphic zircon grains from a variety of metavolcano-sedimentary rocks of the Dwalile Supracrustal Suite (DSS) from the ca. 3.66 to 3.20 Ga Ancient Gneiss Complex (AGC) in Swaziland. The results indicate that the DSS is made up by Palaeo- and Mesoarchaean rocks which have been affected by a polymetamorphic overprint and became tectonically assembled during the Neoarchaean. The oldest Dwalile rocks were formed during a phase of felsic to intermediate volcanism at ca. 3.46 Ga, and are derived from the same magma source as the Tsawela Gneisses. Based on the combined U-Pb-Hf isotope data, two groups of metasedimentary rocks can be distinguished: an older Dwalile Group I that is similar in age to the Hooggenoeg and Kromberg Formations (3.46–3.40 Ga), but with a different source area. A younger Dwalile Group II is coeval with the Fig Tree and possibly Moodies Groups (<3.23 Ga) and the data suggest there was a similar provenance.The U-Pb-Hf isotope data and petrological observations demonstrate that the DSS was affected by three stages of metamorphic overprint: an event at 3.23 Ga, pervasive amphibolite-facies metamorphism at 3.15 Ga, and low-P granulite-facies metamorphism at 2.99 Ga. Metamorphic zircon in the amphibolite-facies rocks resulted from new growth in aqueous fluids at 3.15 Ga, whereas in the granulite-facies rocks new zircon was formed in the presence of melt. The 3.23 Ga event coincides with the last significant metamorphic overprint documented in the Barberton Greenstone Belt (BGB), whereas as two younger events are restricted to the AGC.The data support the model suggesting amalgamation between the AGC and BGB terranes at ca. 3.23 Ga. In addition, they require crustal thickening in the AGC terrane at ca. 3.15 Ga, causing Barrovian-type metamorphism in the DSS and granulite-facies metamorphism in the Luboya-Kubuta Terrane. Low-P granulite-facies metamorphism at ca. 2.99 Ga is most likely related to crustal extension during the onset of Pongola Basin rifting, causing mantle upwelling, mafic magmatism, and heat transfer from the mantle into the thinned crust.
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