皮尔巴拉和卡普瓦尔克拉通古太古代ttg比较早期的瓦尔巴拉超克拉通被评估

IF 1.2 4区 地球科学 Q2 GEOLOGY
N. Gardiner, J. Mulder, C. Kirkland, T. Johnson, O. Nebel
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引用次数: 7

摘要

支配地球最古老克拉通的大陆地壳是由早太古代至古太古代(4.0 ~ 3.2 Ga)的长英质侵入岩组成的闪长岩—闪长岩—花岗闪长岩(TTG)系列。它们既存在于代表太古宙中陆壳的高品位片麻岩地体中,也存在于代表太古宙上陆壳遗迹的低品位花岗绿岩带中。西澳大利亚皮尔巴拉克拉通的古太古代东皮尔巴拉地体(EPT)和非洲南部卡普瓦尔克拉通的巴伯顿花岗岩-绿岩带(BGGB)是最具裸露性的两个花岗岩-绿岩带。它们惊人的地质相似性导致了瓦尔巴拉的存在,一个新太古代-古元古代的超级克拉通。虽然它们各自的TTG圆顶在反映火山高原环境的共同岩石成因方面进行了比较,但它们的年龄、地球化学和同位素剖面存在重要差异。本文报道了东秦岭5个花岗岩穹窿的锆石Hf同位素数据,并比较了两个克拉通古太古代ttg的地球化学和同位素记录。稀有>3.5 Ga EPT演化岩石具有幼年εHf(t),需要球粒岩源。相比之下,较年轻的TTG穹状体发育在3.5 ~ 3.4 Ga和3.3 ~ 3.2 Ga岩浆超套中,εHf(t)向贫、富方向变化较大,微量元素特征表明其来源丰富,异晶锆石反映了TTG的混合来源,不同程度地吸收了较老的长英质地壳包体和较年轻的基性源。EPT TTG穹窿是复合的,记录了多个岩浆活动脉冲。相比之下,BGGB ttg的地球化学富集程度低于EPT,并且具有不同的年龄剖面,含有同时期的岩浆单元。铪同位素表明,在3.2 Ga北巴伯顿TTGs中,主要是一个年轻的源,在3.4 Ga南巴伯顿TTGs中,较老演化的地壳同化作用有限,但在约3.6 Ga古片麻岩杂岩TTGs中,较老(hadean - eo太古代)地壳同化作用明显。EPT的基础比东部Kaapvaal最古老的组成部分更年轻。虽然这两个克拉通形成的古太古代地质格架可能反映了相似的地球动力学机制,但这两个克拉通地体在丘顶结构和地层上的表面相似性并没有反映在它们的地球化学和年龄剖面上。两个克拉通的地壳历史既有相似之处,也有不同之处,突出表明它们是由不同时代和不同个体演化历史的不同地体形成的。瓦尔巴拉sensu lato代表了典型的古太古代克拉通地壳,不是单一的均匀克拉通,而是像今天的大陆一样多样化的克拉通。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Palaeoarchaean TTGs of the Pilbara and Kaapvaal cratons compared; an early Vaalbara supercraton evaluated
The continental crust that dominates Earth’s oldest cratons comprises Eoarchaean to Palaeoarchaean (4.0 to 3.2 Ga) felsic intrusive rocks of the tonalite-trondhjemite-granodiorite (TTG) series. These are found either within high-grade gneiss terranes, which represent Archaean mid-continental crust, or low-grade granite-greenstone belts, which represent relic Archaean upper continental crust. The Palaeoarchaean East Pilbara Terrane (EPT), Pilbara Craton, Western Australia, and the Barberton Granite-Greenstone Belt (BGGB), Kaapvaal Craton, southern Africa, are two of the best exposed granite-greenstone belts. Their striking geological similarities has led to the postulated existence of Vaalbara, a Neoarchaean-Palaeoproterozoic supercraton. Although their respective TTG domes have been compared in terms of a common petrogenetic origin reflecting a volcanic plateau setting, there are important differences in their age, geochemistry, and isotopic profiles. We present new zircon Hf isotope data from five granite domes of the EPT and compare the geochemical and isotopic record of the Palaeoarchaean TTGs from both cratons. Rare >3.5 Ga EPT evolved rocks have juvenile εHf(t) requiring a chondritic source. In contrast, younger TTG domes developed via 3.5 to 3.4 and 3.3 to 3.2 Ga magmatic supersuites with a greater range of εHf(t) towards more depleted and enriched values, trace element signatures requiring an enriched source, and xenocrystic zircons that reflects a mixed source to the TTGs, which variously assimilates packages of older felsic crust and a more juvenile mafic source. EPT TTG domes are composite and record multiple pulses of magmatism. In comparison, BGGB TTGs are less geochemically enriched than those of the EPT and have different age profiles, hosting coeval magmatic units. Hafnium isotopes suggest a predominantly juvenile source to 3.2 Ga northern Barberton TTGs, limited assimilation of older evolved crust in 3.4 Ga southern Barberton TTGs, but significant assimilation of older (Hadean-Eoarchaean) crust in the ca. 3.6 Ga TTGs of the Ancient Gneiss Complex. The foundation of the EPT is younger than that for the oldest components of the Eastern Kaapvaal. Although the broader prevailing Palaeoarchaean geologic framework in which these two cratons formed may reflect similar a geodynamic regime, the superficial similarities in dome structures and stratigraphy of both cratonic terranes is not reflected in their geochemical and age profiles. Both the similarities and the differences between the crustal histories of the two cratons highlights that they are formed from distinct terranes with different ages and individual evolutionary histories. Vaalbara sensu lato represents typical Palaeoarchaean cratonic crust, not in the sense of a single homogeneous craton, but one as diverse as the continents are today.
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来源期刊
CiteScore
3.60
自引率
5.60%
发文量
18
审稿时长
>12 weeks
期刊介绍: The South African Journal of Geology publishes scientific papers, notes, stratigraphic descriptions and discussions in the broadly defined fields of geoscience that are related directly or indirectly to the geology of Africa. Contributions relevant to former supercontinental entities such as Gondwana and Rodinia are also welcome as are topical studies on any geoscience-related discipline. Review papers are welcome as long as they represent original, new syntheses. Special issues are also encouraged but terms for these must be negotiated with the Editors.
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