Pyroxenite and peridotite xenoliths from Hexigten, Inner Mongolia: Insights into the Paleo-Asian Ocean subduction-related melt/fluid–peridotite interaction
Pyroxenite and peridotite xenoliths from Hexigten, Inner Mongolia: Insights into the Paleo-Asian Ocean subduction-related melt/fluid–peridotite interaction
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DOI：
10.1016/j.gca.2014.05.046
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发表时间：
2014-09
影响因子：
5
通讯作者：
Dongya Zou;Yongsheng Liu;Zhaochu Hu;Shan Gao;K. Zong;Rongke Xu;Lixu Deng;Detao He;Changgui Gao
中科院分区：
文献类型：
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作者：
Dongya Zou;Yongsheng Liu;Zhaochu Hu;Shan Gao;K. Zong;Rongke Xu;Lixu Deng;Detao He;Changgui Gao
通过对新疆锡盟造山带克什克腾地区橄榄岩和辉石岩捕虏体的主量、微量元素和Sr同位素组成的研究，探讨了古亚洲洋板块俯冲对岩石圈地幔改造的影响和贡献。1型辉石岩中的辉石具有较低的Mg#（67-85）和较高的87 Sr/86 Sr比值（0.7036-0.7053），表明它们是在玄武岩底侵事件中通过同化和分离结晶作用形成的。橄榄岩和2型辉石岩捕虏体采样岩石圈地幔和记录俯冲相关的交代作用。1型橄榄岩的矿物化学特征表明，该地区岩石圈地幔遭受了1-15%的熔融抽提。某些第1型橄榄岩中的单斜辉石（Cpx）具有高（La/Yb）N、高场强元素（Nb、Ta、Zr、Hf和Ti）显著亏损的特征，低Ti/Eu（Nb/La）与87 Sr/86 Sr（0.7037-0.7055）呈负相关，表明与俯冲有关的富CO2流体交代作用。第二型橄榄岩中的橄榄石（Ol）和斜方辉石（Opx）具有相对低的Mg#和高的Ni含量的特征。除了正常的不相容元素亏损的Opx，Opx与Rb，Ba，Th，U，Nb，Ta和LREE的富集，以及观察。不相容元素贫化的Opx的Mg#表现出弱的环带（即，从芯部到边缘减小）。2型辉石岩的Cpx和Opx表现出类似的高Mg#和Ni含量。Cpx的Rb、Ba、Th、U、Nb、Ta和轻稀土元素含量及87 Sr/86 Sr比值从核部向边缘逐渐增加。此外，Opx在2型橄榄岩和Cpx在2型辉石岩表现出增加的Nb/Ta比值和Ni含量相对于那些在1型橄榄岩。这些观察结果共同表明，含金红石榴辉岩衍生的榴辉岩-橄榄岩反应作为2型橄榄岩和辉石岩的起源。考虑到地质背景，熔体/流体-橄榄岩相互作用是由古亚洲洋俯冲引起的，这可能对NCC北方边缘岩石圈地幔的改造也有重要贡献。
The in situ major, trace-element and Sr-isotopic compositions of the peridotite and pyroxenite xenoliths from the Hexigten region in the Xing-Meng orogenic belt (XMOB) were examined to evaluate the influences and contributions of the Paleo-Asian Oceanic slab subduction on the lithospheric mantle transformation. Pyroxenes in the Type 1 pyroxenite exhibit low and variable Mg# (67–85) and relatively high87Sr/86Sr ratios (0.7036–0.7053), indicating that they were formed by assimilation and fractional crystallization processes during a basaltic underplating event. The peridotite and Type 2 pyroxenite xenoliths sampled the lithospheric mantle and recorded subduction-related metasomatism. The mineral chemistries of the Type 1 peridotite suggest that the lithospheric mantle beneath this area suffered 1–15% melt extraction. Clinopyroxene (Cpx) in some Type 1 peridotites are characterized by high (La/Yb)Ncoupled with marked depletions in high field strength elements (HFSE) (Nb, Ta, Zr, Hf and Ti) and negative correlations between the low Ti/Eu (Nb/La) and87Sr/86Sr ratios (0.7037–0.7055), suggesting metasomatism by subduction-related CO2-rich fluids. Olivine (Ol) and orthopyroxene (Opx) in the Type 2 peridotite are characterized by a relatively low Mg# but high Ni contents. In addition to the normal incompatible element-depleted Opx, Opx with enrichments in Rb, Ba, Th, U, Nb, Ta and LREE were observed, as well. The Mg# of incompatible element-depleted Opx exhibits weak zonations (i.e., decreasing from the cores to the rims). Cpx and Opx of the Type 2 pyroxenite exhibit similarly high Mg# and Ni contents. Rb, Ba, Th, U, Nb, Ta and LREE contents and87Sr/86Sr ratios of the Cpx increase from the cores to the rims. Moreover, Opx in the Type 2 peridotite and Cpx in the Type 2 pyroxenite exhibit increased Nb/Ta ratios and Ni contents relative to those in the Type 1 peridotites. These observations collectively suggest a rutile-bearing eclogite-derived silicic melt–peridotite reaction as the origin for the Type 2 peridotite and pyroxenite. Considering the geological setting, it is suggested that the melt/fluid–peridotite interactions were caused by the Paleo-Asian Ocean subduction, which could have contributed significantly to the transformation of the lithospheric mantle beneath the northern margin of the NCC, as well.