The Watonga formation and tacking point gabbro, Port Macquarie, Australia: insights into crustal growth mechanisms on the eastern margin of Gondwana
The Watonga formation and tacking point gabbro, Port Macquarie, Australia: insights into crustal growth mechanisms on the eastern margin of Gondwana
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DOI：
10.1016/j.gr.2014.02.013
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发表时间：
2015-08
影响因子：
6.1
通讯作者：
S. Buckman;A. Nutman;J. Aitchison;J. Parker;Sarah Bembrick;Tom Line;H. Hidaka;Tomoyuki Kamiichi-Tomoyuki-Kamii
中科院分区：
文献类型：
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作者：
S. Buckman;A. Nutman;J. Aitchison;J. Parker;Sarah Bembrick;Tom Line;H. Hidaka;Tomoyuki Kamiichi-Tomoyuki-Kamii
在澳大利亚东部新英格兰造山带东端麦夸里港的蛇纹岩混杂岩中，出现了各种增生杂岩、岛弧、蛇绿岩和高压低温变质岩的组合。新的野外观测、锆石U-Pb定年、岩石学和地球化学研究为这些岩石建立了更可靠的年代学和解释。此前，麦夸里港的所有玄武岩、硅质岩和火山碎屑砂岩都归入Watonga组。奥陶纪至中泥盆世的放射虫和牙形刺来自‘Watonga’硅质岩-玄武岩组合，表明它们比‘Watonga’火山碎屑岩更古老，但与之无关，如Green Mound的火山碎屑岩，其中含有来自石炭纪弧的火山/碎屑锆石，年龄早至335 Ma。火山碎屑与枕状熔岩在蛇纹岩混杂岩中形成块体，产生452 Ma±10.10 Ma的火成岩锆石，表明其时代为奥陶纪。粘结点辉长岩的年龄为390 Ma±17.7 Ma(泥盆纪)，与大洋内弧状火成岩具有地球化学亲缘关系。它被侵入瓦通加组的变形硅质岩中，从而在空间上将奥陶纪-泥盆纪？增生杂岩及其邻近的泥盆纪岛弧。Watonga组和泥盆纪接合点辉长岩的类MORB玄武岩-硅质岩组合代表了冈瓦纳的中古生代异地组合，可能与位于新英格兰造山带以西的Djugati地体和Gamilaroi地体有关。锆石测年结果表明，后蛇纹岩-镁铁长英质岩墙侵位于麦夸里港蛇纹岩中，形成于247 Ma±320 Ma，并进一步受到破坏。因此，影响蛇纹岩的构造作用一直延续到早三叠世，最后的运动发生在Hunter-Bowen造山期。我们来自Port Macquarie的结果与新英格兰造山带的构造模型相一致，该造山带包括幕式岛弧碰撞事件(Gamilaroi地体和Gymbie地体)以及沿冈瓦那东部的大陆边缘“安第斯类型”岩浆活动和吸积时期。
A diverse assemblage of accretionary complex, island-arc, ophiolitic and high-pressure, low-temperature metamorphic rocks occurs within the serpentinite mélange at Port Macquarie on the eastern extremity of the New England Orogen of eastern Australia. New field observations, U–Pb zircon dating, petrography and geochemistry presented here establish a more robust chronology and interpretation of these rocks. Previously, all basalt, chert and volcaniclastic sandstones at Port Macquarie were grouped into the Watonga Formation. Ordovician to middle Devonian radiolarians and conodonts from ‘Watonga’ chert-basalt associations shows that they are older than, and unrelated to, ‘Watonga’ volcaniclastic rocks like those at Green Mound which contain volcanic/detrital zircons as young as 335 Ma that were derived from a Carboniferous arc. Volcanic detritus with pillow lava forming a block within the serpentinite mélange yielded 452 ± 10 Ma igneous zircons, indicating an Ordovician age. The Tacking Point Gabbro has an age of 390 ± 7 Ma (Devonian) and geochemical affinities with intra-oceanic arc igneous suites. It was intruded into deformed cherts of the Watonga Formation giving a spatial link between an Ordovician–Devonian? Accretionary complex and adjacent Devonian island-arc. The MORB-like basalt-chert association of the Watonga Formation and the Devonian Tacking Point gabbro represents a mid-Paleozoic assemblage allochthonous to Gondwana, which possibly correlates with the Djungati and Gamilaroi terranes respectively located further west in the New England Orogen. Zircon dating shows that post-serpentinite mafic–felsic dykes were emplaced into the Port Macquarie serpentinite at 247 ± 20 Ma and further disrupted. Therefore, tectonism affecting the serpentinite continued into the Early Triassic, with final movement during the Hunter-Bowen Orogeny. Our results from Port Macquarie are compatible with a tectonic model for the New England Orogen that involves episodic island-arc collisional events (Gamilaroi and Gympie terranes) interspersed with periods of continental margin “Andean-type” magmatism and accretion along eastern Gondwana.