Heterogeneous source components of intraplate basalts from NE China induced by the ongoing Pacific slab subduction
Heterogeneous source components of intraplate basalts from NE China induced by the ongoing Pacific slab subduction
复制标题
DOI：
10.1016/j.epsl.2016.11.030
复制
发表时间：
2017-02-01
影响因子：
5.3
通讯作者：
Bi, Yao
中科院分区：
文献类型：
--
作者：
Chen, Huan;Xia, Qun-Ke;Bi, Yao
人们普遍认为，大洋板片的俯冲是地幔化学不均匀性的主要原因。然而，由于可能存在重叠的印记，确定经历过多次俯冲事件的地区板块的贡献通常很困难。了解中国东部广泛分布的板内小体积玄武岩源成分的时空变化可能是研究俯冲太平洋板片影响的基础，这一点长期以来一直被假设但从未得到证实。为此，我们对中国东北地区的柴河-阿尔山火山田（包括超过35座小体积第四纪玄武岩火山）进行了调查，并分别使用二次离子质谱（SIMS）和傅里叶变换红外光谱（FTIR）测量了单斜辉石（cpx）斑晶的氧同位素和水含量。然后根据 H2O 在 cpx 和玄武岩熔体之间的分配系数来估计岩浆的含水量。 cpx斑晶的8180个（4.28%~8.57%）和岩浆的H2O含量（0.19 wt.%-2.70 wt.%）变化较大，反映了地幔源区成分的非均质性。各个样本中的 8180 值和 H2O 含量也显示出相当大的变化，表明岩浆混合，并且岩浆混合发生在喷发前不久。 cpx斑晶8180值与全岩H2O/Ce比值、Ba/Th比值和Eu异常之间的关系表明了地幔来源的三个组成部分(热液蚀变的上洋壳和海相沉积物、蚀变的下辉长岩洋壳和环境地幔)。这三个分量的比例随时间变化很大（类似于 1.37 Ma 到类似于 0.25 Ma）。太平洋板片不断地俯冲到东亚之下，不断地将回收的物质输送到地幔深处。源成分的时间异质性可能是由正在进行的太平洋板片俯冲引起的。结合中国东部其他玄武岩产地（双辽玄武岩、太行玄武岩和山东玄武岩），再循环海洋成分在其地幔来源中的贡献是不均匀的。地幔来源的这种空间异质性可能是由太平洋板片循环过程中的可变蚀变和脱水引起的。我们的研究结果表明，中国东部新生代板内小体积玄武岩的物源成分在时间和空间上均存在异质性，这可能是由太平洋板片的持续俯冲引起的。这表明，整合研究区域的地球化学特征和构造历史的时间变化可以识别俯冲的海洋板块，该俯冲的海洋板块诱发了板内玄武岩地幔源区的富集成分。 (C) 2016 Elsevier B.V. 保留所有权利。
The subduction of oceanic slabs is widely accepted to be a main reason for chemical heterogeneities in the mantle. However, determining the contributions of slabs in areas that have experienced multiple subduction events is often difficult due to possible overlapping imprints. Understanding the temporal and spatial variations of source components for widespread intraplate small volume basalts in eastern China may be a basis for investigating the influence of the subducted Pacific slab, which has long been postulated but never confirmed. For this purpose, we investigated the Chaihe-aershan volcanic field (including more than 35 small-volume Quaternary basaltic volcanoes) in NE China and measured the oxygen isotopes and water content of clinopyroxene (cpx) phenocrysts using secondary ion mass spectrometry (SIMS) and Fourier transform infrared spectroscopy (FTIR), respectively. The water content of magma was then estimated based on the partition coefficient of H2O between cpx and the basaltic melt. The 8180 of cpx phenocrysts (4.28 parts per thousand to 8.57 parts per thousand) and H2O content of magmas (0.19 wt.%-2.70 wt.%) show large variations, reflecting the compositional heterogeneity of the mantle source. The 8180 values and H2O content within individual samples also display considerable variation, suggesting the mixing of magmas and that the magma mixing occurred shortly before the eruption. The relation between the 8180 values of cpx phenocrysts and the H2O/Ce ratio, Ba/Th ratio and Eu anomaly of whole rocks demonstrates the contributions of three components to the mantle source (hydrothermally altered upper oceanic crust and marine sediments, altered lower gabbroic oceanic crust, and ambient mantle). The proportions of these three components have varied widely over time (similar to 1.37 Ma to similar to 0.25 Ma). The Pacific slab is constantly subducted under eastern Asia and continuously transports recycled materials to the deep mantle. The temporal heterogeneity of the source components may be caused by ongoing Pacific slab subduction. Combined with other basalt localities in eastern China (Shuangliao basalts, Taihang basalts and Shangdong basalts), the contributions of recycled oceanic components in their mantle source are heterogeneous. This spatial heterogeneity of mantle sources may be induced by variable alterations and dehydration during the recycling process of the Pacific slab. Our results show that the source components of Cenozoic intraplate small-volume basalts in eastern China are temporally and spatially heterogeneous, which is likely induced by the ongoing subduction of the Pacific slab. This demonstrates that integrating the temporal variations in geochemical characteristics and tectonic history of a study region can identify the subducted oceanic plate that induced enriched components in the mantle source of intraplate basalts. (C) 2016 Elsevier B.V. All rights reserved.