Discovery of a microcontinent (Gulden Draak Knoll) offshore Western Australia: Implications for East Gondwana reconstructions
Discovery of a microcontinent (Gulden Draak Knoll) offshore Western Australia: Implications for East Gondwana reconstructions
复制标题
DOI：
10.1016/j.gr.2014.08.013
复制
发表时间：
2015-10-01
影响因子：
6.1
通讯作者：
Whittaker, Joanne M.
中科院分区：
文献类型：
--
作者：
Gardner, Robyn L.;Daczko, Nathan R.;Whittaker, Joanne M.
对古尔登德拉克诺尔 (Gulden Draak Knoll) 挖掘样本的分析表明，它是位于珀斯深渊平原西部和印度洋沃顿盆地之间边界的海底裂谷大陆碎片。小丘由麻粒岩褪色基底组成，包括泥质副片麻岩和镁铁质正片麻岩，推测寒武纪花岗岩侵入其他岩石。还对具有中元古代和寒武纪原岩年龄的长英质片麻岩巨石和卵石进行了采样，这可能反映了可变沉积岩和火山岩的复杂基底。太古代和中元古代锆石中的U-Pb同位素系统受到显着干扰，反映了影响所有样本的寒武纪造山作用。原岩为石榴石-硅线石-黑云母副片麻岩，最大沉积年龄为 1163 +/- 24 Ma，包括年龄在 1000 左右的较古老的碎屑锆石颗粒。 2.65 Ga 和 1.4 至 1.1 Ga 之间。该样本中较年轻的群体被解释为新生长的变质锆石和同位素重置锆石的混合物，这意味着麻粒岩相变质作用发生在 c. 511 +/- 5 Ma。长期的寒武纪造山作用由 530 +/- 6 Ma 的镁铁质正片麻岩的变质年龄和花岗岩侵位后不久的同位素扰动（约 540 Ma，锆石年龄扰动至 509 +/- 7 Ma）和长英质正片麻岩原岩（约 528 Ma，锆石年龄扰动至 510 +/- 3）表明。 马）。寒武纪岩石中的异晶锆石颗粒包括太古代（c. 2839 +/- 9 Ma）和中元古代（1230-1370 Ma）群，在寒武纪造山作用期间也受到同位素干扰。火成系锆石颗粒的放射性 Hf 同位素组成 (Hf-i = 0.281821-0.281367) 比中元古代异晶 (Hf-i = 0.282267-0.281993) 少，表明中元古代地壳对花岗岩生产的参与有限。更可能的来源包括以 Hf-i = 0.281399-0.280863 的异晶为代表的太古代地壳。 Gulden Draak Knoll 是在冈瓦纳古陆（“Leeuwin”全拟合模型）中沿着被称为印度-澳大利亚-南极缝合线 (IAAS) 的主要结构的走向重建的，最近根据南极洲威尔克斯地的地球物理解释绘制了地图。新的同位素数据表明，Gulden Draak Knoll 的基底岩石与 IAAS 两侧暴露的地壳具有亲和力。确定该结构是否是严格意义上的缝合区仍有待测试。 (C) 2014 年国际冈瓦纳研究协会。由 Elsevier B.V. 出版。保留所有权利。
Analysis of dredged samples from the Gulden Draak Knoll demonstrates that it is a submarine rifted continental fragment that lies at the boundary between the western Perth Abyssal Plain and Wharton Basin, Indian Ocean. The Knoll comprises a granulite fades basement, including pelitic paragneiss and mafic orthogneiss, with a Cambrian granite inferred to intrude the other rocks. Boulders and cobbles of felsic gneiss with Mesoproterozoic and Cambrian protolith ages were also sampled likely reflecting a complex basement to variable sedimentary and volcanic rocks. The U-Pb isotopic system in the Archean and Mesoproterozoic zircon is significantly disturbed, reflecting Cambrian orogenesis that affected all samples. The protolith to garnet-sillimanite-biotite paragneiss has a maximum deposition age of 1163 +/- 24 Ma and includes older detrital zircon grains with populations at c. 2.65 Ga and between 1.4 and 1.1 Ga. A younger population in this sample is interpreted as a mix of newly grown metamorphic zircon and isotopically reset zircon, implying that the granulite facies metamorphism occurred at c. 511 +/- 5 Ma. Protracted Cambrian orogenesis is indicated by a metamorphic age in the mafic orthogneiss of 530 +/- 6 Ma and isotopic disturbance shortly following emplacement of granite (c. 540 Ma with zircon ages disturbed to 509 +/- 7 Ma) and the protolith to the felsic orthogneiss (c. 528 Ma with zircon ages disturbed to 510 +/- 3 Ma). Xenocrystic zircon grains in the Cambrian rocks include Archean (c. 2839 +/- 9 Ma) and Mesoproterozoic (1230-1370 Ma) populations also isotopically disturbed during Cambrian orogenesis. Igneous Cambrian zircon grains have less radiogenic Hf-isotope compositions (Hf-i = 0.281821-0.281367) than Mesoproterozoic xenocrysts (Hf-i = 0.282267-0.281993), indicating limited involvement of the Mesoproterozoic crust in granite production. A more likely source includes Archean crust represented by xenocrysts with Hf-i = 0.281399-0.280863. The Gulden Draak Knoll is reconstructed in Gondwana ('Leeuwin' full-fit model) along strike of a major structure termed the Indo-Australo-Antarctic Suture (IAAS), recently mapped from geophysical interpretations in Wilkes Land, Antarctica. New isotopic data suggest that basement rocks from the Gulden Draak Knoll have affinity to crust exposed either side of the IAAS. Determining if this structure is a suture zone sensu stricto remains to be tested. (C) 2014 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.