地震地质 ›› 2024, Vol. 46 ›› Issue (6): 1227-1247.DOI: 10.3969/j.issn.0253-4967.2024.06.001

• 研究论文 • 上一篇    下一篇

中国大陆最年轻火山活动成因——来自藏北阿什库勒火山岩的同位素证据

毛翔1,2)(), 白翔3,4),*(), 于红梅3,4), 赵波3,4), 陈慧智5)   

  1. 1) 中国石化地热资源开发利用重点实验室, 北京 100083
    2) 中国石化新星石油公司能源研究院, 北京 100083
    3) 吉林长白山火山国家野外科学观测研究站, 中国地震局地质研究所, 北京 100029
    4) 中国地震局地震与火山灾害重点实验室, 北京 100029
    5) 中国石化集团中原油田分公司, 濮阳 457001
  • 收稿日期:2023-11-02 修回日期:2024-03-04 出版日期:2024-12-20 发布日期:2025-01-22
  • 通讯作者: *白翔, 男, 1987年生, 助理研究员, 主要研究方向为火山学和岩石地球化学, E-mail: baixiang@ies.ac.cn
  • 作者简介:

    毛翔, 男, 1986年生, 2014年于北京大学获构造地质学博士学位, 研究员, 主要研究方向为构造地质学, E-mail:

  • 基金资助:
    中国地震局地质研究所基本科研业务专项(IGCEA2012); 中国石化集团新星石油有限责任公司技术开发项目(P22221); 国家自然科学基金(41802204); 国家自然科学基金(41874110); 国家自然科学基金(42274136); 国家自然科学基金(42072330)

PETROGENESIS OF THE MOST RECENT VOLCANISM IN MAINLAND CHINA: EVIDENCE FROM THE ISOTOPIC CHARACTERISTICS OF ASHIKULE VOLCANIC ROCKS

MAO Xiang1,2)(), BAI Xiang3,4),*(), YU Hong-mei3,4), ZHAO Bo3,4), CHEN Hui-zhi5)   

  1. 1) Key Laboratory of Geothermal Resources Exploitation and Utilization, Sinopec, Beijing 100083, China
    2) New Energy Research Institute, SINOPEC Star Petroleum Co., Ltd., Beijing 100083, China
    3) Jilin Changbaishan Volcano National Observation and Research Station, Institute of Geology, China Earthquake Administration, Beijing 100029, China
    4) Key Laboratory of Seismic and Volcanic Hazards, China Earthquake Administration, Beijing 100029, China
    5) Sinopec Zhongyuan Oilfield, Puyang, Henan 457001, China
  • Received:2023-11-02 Revised:2024-03-04 Online:2024-12-20 Published:2025-01-22

摘要:

阿什库勒火山群位于青藏高原西北部的西昆仑地区, 记录了中国大陆最年轻的火山喷发活动。更新世以来阿什库勒火山群经历了多期次火山喷发活动, 主要产物包括粗安岩和粗面岩, 含少量响岩质碱玄岩、 玄武质粗安岩和流纹岩。火山岩锆石U-Pb及Lu-Hf同位素测试结果表明, 阿什库勒火山岩中粗安岩、 粗面岩和流纹岩的岩浆成因锆石具有接近的εHf(t)值(-9.1~-4.4), 指示其来自于富集的岩浆源区。粗安岩中存在元古代—中生代古老继承锆石, 表明岩浆源区可能经历了变质沉积岩组分的改造作用。火山岩全岩 87Sr/86Sr介于0.709 395~0.711 441, 143Nd/144Nd介于0.512 154~0.512 355, 207Pb/206Pb介于15.652~15.673, 206Pb/204Pb介于18.681~18.754, 与富集地幔 Ⅱ 型(EM Ⅱ)的同位素特征相符。结合前人发表的火山岩主微量数据, 文中开展了火山岩成因的同位素模拟研究, 结果显示阿什库勒火山岩的原始岩浆经历了岩浆混合过程。上述地球化学结果表明, 阿什库勒火山群的原始岩浆起源于EM Ⅱ 型地幔部分熔融形成的基性岩浆, 在上升至地表的过程中与古老大陆地壳物质部分熔融形成的中酸性岩浆混合后喷发, 形成现在的阿什库勒火山岩。结合青藏高原区域构造背景, 分析认为阿什库勒火山岩浆活动可能是印度板块向N俯冲作用下的产物。

关键词: 阿什库勒, Sr-Nd-Pb同位素, 锆石U-Pb-Hf同位素, 岩浆混合, 动力学背景

Abstract:

The Ashikule Volcanic Cluster(AVC), located in the western Kunlun region of the northwestern Tibetan plateau, represents the most recent volcanic activity on Mainland China. This volcanic cluster, which erupted continuously from the Pleistocene to the Holocene, predominantly produced trachyandesites and trachytes, with minor occurrences of phonotephrites, basaltic trachyandesites, and rhyolites. In this study, we present zircon U-Pb-Lu-Hf and whole-rock Sr-Nd-Pb isotopic analyses for volcanic rock samples from AVC. By integrating these data with petrographic, geochronological, and geochemical findings from Yu et al.(2020), we propose further constraints on the petrogenesis of the volcanic rocks and the geodynamic evolution of the western Kunlun region from the Pleistocene to the Holocene.

Zircon U-Pb-Lu-Hf isotopic analyses were conducted on five samples: Two trachyandesitic (515-01 and 518-14), two trachytic (521-1 and 521-4), and one rhyolitic(517-B-03). Together with previous 40Ar/39Ar dating, the magmatic zircon grains reveal negative εHf(t) values ranging from -8.8 to -4.4 for the trachyandesitic samples, -8.6 to -5.7 for the trachytic samples, and -9.1 to -6.7 for the rhyolitic sample, suggesting an enriched magma source. The trachyandesitic samples also contain Paleozoic to Mesozoic zircons (165-2 352Ma) with characteristics such as small oval shapes or core-rim structures, indicating that they are inherited zircons. These inherited zircons display εHf(t) values from -3.1 to 9.8, suggesting the involvement of metasedimentary components in the magma source.

Whole-rock Sr-Nd-Pb isotopic analyses were conducted on eight samples(four trachyandesitic, three trachytic, and one rhyolitic), revealing 87Sr/86Sr ratios of 0.709 395-0.711 441 and 143Nd/144Nd ratios of 0.512 154-0.512 355. In the 143Nd/144Nd-87Sr/86Sr diagram, these samples plot to the right of the EM Ⅰ region in the fourth quadrant, indicating a relationship with EM Ⅱ-type magmatism. The samples exhibit 207Pb/206Pb ratios of 15.652-15.673 and 206Pb/204Pb ratios of 18.681-18.754, aligning with EM Ⅱ-type and lower crust-derived magmatism on the 207Pb/204Pb-206Pb/204Pb diagram.

In the Rb/Nd-Rb diagram, the Ashikule volcanic rocks display an oblique distribution, indicating processes of partial melting or magma mixing, which is further supported by their alignment with the mixing trend on the 1/V-Rb/V diagram. Geochemical modeling results suggest that the Ashikule volcanic magmas formed primarily through a magma mixing process. Previous electron probe microanalysis studies have identified reverse zoning in plagioclase and orthopyroxene phenocrysts, providing additional evidence for magma mixing in the magma chamber. Consequently, these data reveal that Ashikule volcanic magmas originated from a mixing process between EM Ⅱ-type mantle-derived basic magmas and intermediate to acidic magmas from partial melting of ancient continental materials. Considering the tectonic setting of the Tibetan plateau, we propose that Ashikule volcanic activity likely formed in a subduction-dominated environment from the Pleistocene to the Holocene.

Key words: Ashikule, Sr-Nd-Pb isotopes, Zircon U-Pb-Hf isotopes, magma mixing, dynamic setting