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首页> 外文期刊>Journal of Asian earth sciences >Detrital zircon and igneous protolith ages of high-grade metamorphic rocks in the Highland and Wanni Complexes, Sri Lanka: Their geochronological correlation with southern India and East Antarctica
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Detrital zircon and igneous protolith ages of high-grade metamorphic rocks in the Highland and Wanni Complexes, Sri Lanka: Their geochronological correlation with southern India and East Antarctica

机译：斯里兰卡高地和万尼地区的高级变质岩碎屑锆石和火成岩原岩时代：它们与印度南部和南极东部的年代学相关性

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摘要

The high-grade metamorphic rocks of Sri Lanka place valuable constraints on the assembly of central parts of the Gondwana supercontinent. They are subdivided into the Wanni Complex (WC), Highland Complex (HC) and Vijayan Complex (VC), but their correlation with neighbouring Gondwana terranes is hindered by a poor understanding of the contact between the HC and WC. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) U-Pb dating of remnant zircon cores from 45 high-grade metamorphic rocks in Sri Lanka reveals two domains with different age characteristics that correlate with the HC and WC and which help constrain the location of the boundary between them. The HC is dominated by detrital zircon ages of ca. 3500-1500 Ma from garnet-biotite gneiss, garnet-cordierite-biotite gneiss, some samples of garnet-orthopyroxene-biotite gneiss and siliceous gneiss (interpreted as paragneisses) and igneous protolith ages of ca. 2000-1800 Ma from garnet-hornblende-biotite gneiss, other samples of garnet-orthopyroxene-biotite gneiss, garnet-two-pyroxene granulite, two-pyroxene granulite and charnockite (interpreted as orthogneisses). In contrast, the WC is dominated by detrital zircon ages of ca. 1100-700 Ma from paragneisses and igneous protolith ages of ca. 1100-800 Ma from orthogneisses. This clearly suggests the HC and WC have different origins, but some of our results and previous data indicate their spatial distribution does not correspond exactly to the unit boundary proposed in earlier studies using Nd model ages. Detrital zircon and igneous protolith ages in the HC suggest that sedimentary protoliths were eroded from local 2000-1800 Ma igneous rocks and an older Paleoproterozoic to Archean craton. In contrast, the WC sedimentary protoliths were mainly eroded from local late Mesoproterozoic to Neoproterozoic igneous rocks with very minor components from an older 2500-1500 Ma craton, and in the case of the WC precursor sediments there was possibly additional detritus derived from early to middle Neoproterozoic metamorphic rocks. The relic zircon core ages in the HC are comparable with those of the Trivandrum Block and Nagercoil Block of southern India. In contrast, those ages in the WC match the Achankovil Shear Zone and Southern Madurai Block of southern India. These comparisons are also supported by Th/U ratios of detrital zircon cores from paragneisses (Th/U ratios of 0.10 for the former and not only 0.10 but also = 0.10 for the latter). Comparisons with the Liitzow-Holm Complex of East Antarctica indicate that the geochronological characteristics of the HC and WC broadly match those of the Skallen Group, and the Ongul and Okuiwa Groups, respectively.
机译：斯里兰卡的高级变质岩对冈瓦纳超大陆中央部分的组装构成了宝贵的约束。它们被细分为Wanni复合体（WC），Highland复合体（HC）和Vijayan复合体（VC），但是由于对HC和WC之间的接触了解不足，阻碍了它们与邻近的Gondwana地形的相关性。斯里兰卡45个高级变质岩中残留锆石岩心的激光烧蚀-电感耦合等离子体质谱（LA-ICP-MS）U-Pb测年显示出与HC和WC相关的两个年龄特征不同的区域，其中帮助限制它们之间边界的位置。 HC的碎屑锆石年龄大约为。 3500-1500 Ma来自石榴石-黑云母片麻岩，石榴石-堇青石-黑云母片麻岩，一些石榴石-邻苯二茂铁-黑云母片麻岩和硅质片麻岩（被解释为Paragneisses）和火成岩的原生石时代。石榴石-角闪石-黑云母片麻岩，石榴石-邻苯二茂铁-黑云母片麻岩，石榴石-二-辉石花岗石，二-辉石花岗石和菱镁矿（解释为正长片麻岩）的其他样品。相比之下，WC的碎屑锆石年龄约占16％。大约从1100-700 Ma的石蜡和火成岩的原石年龄。直生片麻的1100-800 Ma。这清楚地表明了HC和WC的起源不同，但是我们的一些结果和先前的数据表明它们的空间分布与在使用Nd模型年龄的早期研究中提出的单元边界不完全一致。 HC中的碎屑锆石和火成原生岩年龄表明，沉积的原生岩从局部2000-1800 Ma火成岩和较老的古元古代到太古代克拉通被侵蚀了。相比之下，WC沉积原生质岩主要从局部中元古代晚期到新元古代火成岩侵蚀，其中少量成分来自较老的2500-1500 Ma克拉通，而在WC前体沉积物的情况下，可能还有从早期到中期的碎屑。新元古代变质岩。 HC中的遗物锆石核心年龄与印度南部的Trivandrum街区和Nagercoil街区相当。相比之下，WC中的年龄与印度南部的Achankovil剪切带和南部的Madurai街区相匹配。这些对比也得到了石蜡型碎屑锆石芯的Th / U比值（前者的Th / U比> 0.10，不仅> 0.10，而且<= 0.10）。与南极东部的Liitzow-Holm复杂区的比较表明，HC和WC的年代学特征大致上与Skallen组，Ongul组和Okuiwa组相匹配。

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