Dengfeng He , Yunpeng Dong , Christoph A. Hauzenberger , Yuangang Yue , Bo Hui , Bo Zhou , Xiang Ren , Bin Zhang , Fubao Chong
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Samples from the <em>meta</em>-felsic unit have SiO<sub>2</sub> contents of 68.37–73.03 wt% and belong to the high-K calc-alkaline series. They exhibit similar REE distribution patterns and display enrichment in light rare earth elements (LREES) and negative Eu anomalies. Enrichments in Rb, Ba, Th, U and K, depletion in Nb, Ta, Sr, P and Ti are seen in the primitive mantle-normalized trace element pattern diagram. Magmatic zircons from different <em>meta</em>-felsic samples yield variable <em>ε</em><sub>Hf</sub>(<em>t</em>) values of −8.14 to + 9.37 corresponding to ca. 1.7–2.0 Ga two-stage Hf model ages. Samples from the <em>meta</em>-mafic unit have low SiO<sub>2</sub> concentrations of 49.87–50.43 wt%, high contents of Fe<sub>2</sub>O<sub>3</sub><sup>T</sup>, MgO, CaO and TiO<sub>2</sub>, and Mg# values of 52–58. They show low total REE concentrations of 19.8–30.4 µg/g, and depletion in LREES, flat HREES distribution patterns with (La/Yb)<sub>N</sub> of 0.27–0.53 and insignificant Eu anomalies. Flat distribution pattern of high field strength elements (HFSEs) is observed in the primitive mantle-normalized trace element pattern diagram. They display similar immobile elements’ concentrations and distribution patterns, low Ti/Y, Nb/Y, La/Yb, and high Nb/La ratios, comparable with the present-day normal middle ocean ridge basalt. Zircons from the <em>meta</em>-mafic sample have mostly positive <em>ε</em><sub>Hf</sub>(<em>t</em>) values ranging from −0.10 to + 4.10 with a single stage Hf model ages of ca. 1.7–2.0 Ga. The geochemical result implies that the <em>meta</em>-felsic unit was generated by partial melting of the Paleoproterozoic juvenile mafic lower-crustal material with mantle attributions, and the <em>meta</em>-mafic unit was probably from partial melting of the lithospheric mantle. Synthesizing the above evidences, Wulonggou Mesoproterozoic <em>meta</em>-magmatic rocks are a bimodal suite formed in a continental extensional tectonic setting which is probably related to the break-up of the Columbia supercontinent.</p></div>","PeriodicalId":49674,"journal":{"name":"Precambrian Research","volume":"412 ","pages":"Article 107551"},"PeriodicalIF":3.2000,"publicationDate":"2024-08-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"1.38 Ga magmatism and the extension tectonics in East Kunlun, northern Tibetan Plateau\",\"authors\":\"Dengfeng He , Yunpeng Dong , Christoph A. 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Samples from the <em>meta</em>-felsic unit have SiO<sub>2</sub> contents of 68.37–73.03 wt% and belong to the high-K calc-alkaline series. They exhibit similar REE distribution patterns and display enrichment in light rare earth elements (LREES) and negative Eu anomalies. Enrichments in Rb, Ba, Th, U and K, depletion in Nb, Ta, Sr, P and Ti are seen in the primitive mantle-normalized trace element pattern diagram. Magmatic zircons from different <em>meta</em>-felsic samples yield variable <em>ε</em><sub>Hf</sub>(<em>t</em>) values of −8.14 to + 9.37 corresponding to ca. 1.7–2.0 Ga two-stage Hf model ages. Samples from the <em>meta</em>-mafic unit have low SiO<sub>2</sub> concentrations of 49.87–50.43 wt%, high contents of Fe<sub>2</sub>O<sub>3</sub><sup>T</sup>, MgO, CaO and TiO<sub>2</sub>, and Mg# values of 52–58. They show low total REE concentrations of 19.8–30.4 µg/g, and depletion in LREES, flat HREES distribution patterns with (La/Yb)<sub>N</sub> of 0.27–0.53 and insignificant Eu anomalies. Flat distribution pattern of high field strength elements (HFSEs) is observed in the primitive mantle-normalized trace element pattern diagram. They display similar immobile elements’ concentrations and distribution patterns, low Ti/Y, Nb/Y, La/Yb, and high Nb/La ratios, comparable with the present-day normal middle ocean ridge basalt. Zircons from the <em>meta</em>-mafic sample have mostly positive <em>ε</em><sub>Hf</sub>(<em>t</em>) values ranging from −0.10 to + 4.10 with a single stage Hf model ages of ca. 1.7–2.0 Ga. The geochemical result implies that the <em>meta</em>-felsic unit was generated by partial melting of the Paleoproterozoic juvenile mafic lower-crustal material with mantle attributions, and the <em>meta</em>-mafic unit was probably from partial melting of the lithospheric mantle. 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引用次数: 0
摘要
在哥伦比亚超大陆的组装、增生和解体过程中,大量古生代至中新生代岩浆岩相继问世,是说明超大陆圈的关键。本研究介绍了乌龙沟地区新发现的元长岩和元岩浆岩的地质、岩石学、地质年代和地球化学数据,以揭示中昆仑带和柴达木区块的中新生代地球动力学环境。锆石U-Pb地质年代结果表明,元长石组样品的结晶年龄为1385-1376Ma,元长石组样品的结晶年龄为1379±25Ma(MSWD=0.17)。元长石单元样品的二氧化硅含量为68.37-73.03 wt%,属于高K钙碱性系列。它们表现出类似的稀土元素分布模式,并显示出轻稀土元素的富集和负的 Eu 异常。在原始地幔归一化微量元素模式图中,可以看到 Rb、Ba、Th、U 和 K 的富集,Nb、Ta、Sr、P 和 Ti 的贫化。来自不同元长石样品的岩浆锆石的εHf(t)值从-8.14到+9.37不等,对应于约1.7-2.0 Ga的两阶段Hf模型年龄。元杂岩单元的样品二氧化硅含量较低,为49.87-50.43 wt%,Fe2O3T、MgO、CaO和TiO2含量较高,Mg#值为52-58。它们显示出较低的 REE 总浓度(19.8-30.4 µg/g)和 LREES 贫乏,HREES 分布模式平坦,(La/Yb)N 为 0.27-0.53 且 Eu 异常不明显。在原始地幔归一化痕量元素模式图中观察到高场强元素(HFSEs)的扁平分布模式。它们显示出类似的不动元素浓度和分布模式,低Ti/Y、Nb/Y、La/Yb和高Nb/La比值,与现今正常的中洋脊玄武岩相当。元黑云样品中的锆石大多具有正εHf(t)值,范围从-0.10到+4.10,单级Hf模型年龄约为1.7-2.0 Ga。地球化学结果表明,元长石单元是由古新生代稚嫩黑云母下壳物质部分熔融生成的,具有地幔属性;元黑云母单元可能是由岩石圈地幔部分熔融生成的。综合上述证据,乌龙沟中新生代元岩浆岩是在大陆伸展构造环境中形成的双峰组,可能与哥伦比亚超大陆的断裂有关。
1.38 Ga magmatism and the extension tectonics in East Kunlun, northern Tibetan Plateau
Numerous Paleo- to Mesoproterozoic magmatic rocks were emplaced during the assembly, accretion and break-up of the Columbia supercontinent, and are keys to illustrating the supercontinent circle. The geological, petrological, geochronological and geochemical data of the newly discovered meta-felsic and meta-mafic magmatic rocks from the Wulonggou area are presented in this study to shed light on the Mesoproterozoic geodynamic setting of the Central Kunlun Belt and the Qaidam Block. Zircon U-Pb geochronological results indicate that the crystallization ages of the meta-felsic samples are 1385–1376 Ma, and the meta-mafic is 1379 ± 25 Ma (MSWD=0.17). Samples from the meta-felsic unit have SiO2 contents of 68.37–73.03 wt% and belong to the high-K calc-alkaline series. They exhibit similar REE distribution patterns and display enrichment in light rare earth elements (LREES) and negative Eu anomalies. Enrichments in Rb, Ba, Th, U and K, depletion in Nb, Ta, Sr, P and Ti are seen in the primitive mantle-normalized trace element pattern diagram. Magmatic zircons from different meta-felsic samples yield variable εHf(t) values of −8.14 to + 9.37 corresponding to ca. 1.7–2.0 Ga two-stage Hf model ages. Samples from the meta-mafic unit have low SiO2 concentrations of 49.87–50.43 wt%, high contents of Fe2O3T, MgO, CaO and TiO2, and Mg# values of 52–58. They show low total REE concentrations of 19.8–30.4 µg/g, and depletion in LREES, flat HREES distribution patterns with (La/Yb)N of 0.27–0.53 and insignificant Eu anomalies. Flat distribution pattern of high field strength elements (HFSEs) is observed in the primitive mantle-normalized trace element pattern diagram. They display similar immobile elements’ concentrations and distribution patterns, low Ti/Y, Nb/Y, La/Yb, and high Nb/La ratios, comparable with the present-day normal middle ocean ridge basalt. Zircons from the meta-mafic sample have mostly positive εHf(t) values ranging from −0.10 to + 4.10 with a single stage Hf model ages of ca. 1.7–2.0 Ga. The geochemical result implies that the meta-felsic unit was generated by partial melting of the Paleoproterozoic juvenile mafic lower-crustal material with mantle attributions, and the meta-mafic unit was probably from partial melting of the lithospheric mantle. Synthesizing the above evidences, Wulonggou Mesoproterozoic meta-magmatic rocks are a bimodal suite formed in a continental extensional tectonic setting which is probably related to the break-up of the Columbia supercontinent.
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.