Paleoproterozoic ultrahigh-temperature metamorphism and anatexis of the pelitic granulites in the Kongling terrane, South China

IF 3.2 2区 地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY Precambrian Research Pub Date : 2024-11-01 DOI:10.1016/j.precamres.2024.107591
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Abstract

Crustal anatexis and ultrahigh-temperature (UHT) metamorphism provide crucial insights into metamorphic evolution and tectonic process at the convergent plate margins. Pelitic granulites in the Kongling terrane record both Paleoproterozoic UHT metamorphism and anatexis, providing an ideal window to reveal the model of plate tectonic during early earth. The pelitic granulites from the Kongling terrane are mostly composed of the coarse-grained unfoliated granulite and the fine-grained foliated or migmatized granulite. The unfoliated granulite preserves a peak granulite-facies metamorphic mineral assemblage of coarse-grained garnet + sillimanite + plagioclase + K-feldspar + biotite + quartz + rutile. The foliated granulite, displaying banded structure of melanosome and leucosome, is composed of fine-grained garnet + biotite + plagioclase + quartz + rutile/ilmenite + felsic melt. The coarse-grained garnets have core-mantle-rim structures. The clean cores are rich in grossular contents and contain oriented needle-like rutile exsolution. Ti-in-garnet thermometer on the garnet cores reveals temperatures ranging from 837 to 1030 °C with a mean ± 1σ uncertainty of 943 ± 12 °C, which are consistent with ternary feldspar temperature (940 °C), suggesting a UHT granulite-facies metamorphism. The garnet ‘dirty’ mantles and rims are almandine-pyrope solutions with inclusions of felsic melt, biotite and ilmenite. Zircon grains have two groups: most of them are anatectic grains, and few of them exhibit granulite-facies core with anatectic rim. The granulite-facies zircons yield ∼2.05 Ga 207Pb/206Pb ages for peak UHT metamorphism, and the anatectic zircons give ∼2.0 Ga 207Pb/206Pb ages for anatexis. Ti-in-zircon thermometer on the anatectic zircons yields temperatures ranging from 595 to 828 °C (692 ± 4 °C), which are consistent with temperatures of the low-temperature perthite grains (670–740 °C, 705 ± 7 °C) but are lower than Ti-in-garnet temperatures of the peritectic garnets (820–916 °C, 855 ± 4 °C), suggesting a process from anatexis to melt crystallization. These results suggest that the pelitic granulites underwent crustal UHT metamorphism and subsequent anatexis during Paleoproterozoic. Together with the contemporaneous low-temperature and high-pressure metapelites from the Shuiyuesi mélange belt in the Kongling terrane, our study suggests the presence of a paired metamorphic belt at a convergent plate margin during the Paleoproterozoic orogeny.

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华南孔岭地层中的古新生代超高温变质作用和辉绿岩花岗岩的安山作用
地壳厌氧和超高温变质作用为了解板块交汇边缘的变质演化和构造过程提供了重要信息。孔岭地层中的辉绿岩花岗岩同时记录了古新生代的超高温变质作用和非晶变质作用,为揭示地球早期的板块构造模式提供了一个理想的窗口。孔岭地层中的辉绿岩主要由粗粒无叶片花岗岩和细粒叶片化或米格玛化花岗岩组成。无叶片花岗岩保留了花岗岩成因变质矿物组合的峰值,即粗粒石榴石+矽线石+斜长石+K长石+生物辉石+石英+金红石。细粒石榴石+斜长石+石英+金红石/钛铁矿+长石熔体组成的叶状花岗岩,显示出黑云母和白云母的带状结构。粗粒石榴石具有岩芯-岩幔-岩缘结构。干净的岩心含有丰富的毛玻璃成分,并含有定向针状金红石溶出物。石榴石岩芯上的钛-石榴石温度计显示温度范围为 837 至 1030 °C,平均 ± 1σ 不确定度为 943 ± 12 °C,与三元长石温度(940 °C)一致,表明是超高温花岗岩成因变质作用。石榴石的 "脏 "幔和边缘是白云石-紫云英溶液,内含长石熔体、斜长石和钛铁矿。锆石颗粒分为两类:大部分为无乳状颗粒,少数呈现花岗岩成因的核心和无乳状边缘。花岗岩成因锆石的超高温变质峰值 207Pb/206Pb 年龄为 2.05 Ga ∼2.0Ga,而无酸性锆石的无酸性 207Pb/206Pb 年龄为 2.0 Ga ∼2.0Ga。钛锆石温度计对无乳状锆石测得的温度为 595 至 828 °C(692 ± 4 °C),与低温橄榄石晶粒的温度(670 至 740 °C,705 ± 7 °C)一致,但低于透辉石榴辉岩的钛锆石温度(820 至 916 °C,855 ± 4 °C),表明从无乳状到熔融结晶的过程。这些结果表明,辉绿岩花岗岩在古新生代经历了地壳超高温变质作用和随后的无性变质作用。我们的研究与同时代孔岭地层水月寺变质岩带的低温高压玄武岩一起,表明在古近代造山运动期间,在汇聚板块边缘存在着一条成对的变质岩带。
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来源期刊
Precambrian Research
Precambrian Research 地学-地球科学综合
CiteScore
7.20
自引率
28.90%
发文量
325
审稿时长
12 months
期刊介绍: Precambrian Research publishes studies on all aspects of the early stages of the composition, structure and evolution of the Earth and its planetary neighbours. With a focus on process-oriented and comparative studies, it covers, but is not restricted to, subjects such as: (1) Chemical, biological, biochemical and cosmochemical evolution; the origin of life; the evolution of the oceans and atmosphere; the early fossil record; palaeobiology; (2) Geochronology and isotope and elemental geochemistry; (3) Precambrian mineral deposits; (4) Geophysical aspects of the early Earth and Precambrian terrains; (5) Nature, formation and evolution of the Precambrian lithosphere and mantle including magmatic, depositional, metamorphic and tectonic processes. In addition, the editors particularly welcome integrated process-oriented studies that involve a combination of the above fields and comparative studies that demonstrate the effect of Precambrian evolution on Phanerozoic earth system processes. Regional and localised studies of Precambrian phenomena are considered appropriate only when the detail and quality allow illustration of a wider process, or when significant gaps in basic knowledge of a particular area can be filled.
期刊最新文献
Paleoproterozoic ultrahigh-temperature metamorphism and anatexis of the pelitic granulites in the Kongling terrane, South China Decoding Calymmian juvenile mafic magmatism in the Ribeira Belt, Brazil: Evidence for a long-lived arc system along the margin of Columbia Detrital zircon geochronology and whole-rock geochemistry of the 1.8–1.7 Ga Xiong’er volcanic-sedimentary succession in the southern North China craton and their implications for basin evolution Syn-rift volcanism (ca. 670 Ma) in the lower Windermere Supergroup, southern Canadian Cordillera: New constraints on the syn- to post-rift transition for northwestern Laurentia Paleoproterozoic amphibolite to ultrahigh temperature granulite facies metamorphism of the Rangnim massif in the Northern Korean Peninsula and tectonic implications
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