内蒙古集宁新生代玄武岩中橄榄岩包体矿物化学特征及其地幔演化意义
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国家自然科学基金项目(90714002, 40821061)


Peridotite xenoliths in Jining Cenozoic basalts: mineral-chemistry and significance for lithospheric mantle evolution beneath the North China Craton
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    摘要:

    在无水“干"体系的四矿物相橄榄岩中,单斜辉石由于熔点低而通常记录着丰富的部分熔融作用和地幔交代作用信息。在详细岩相学特征和组成矿物主元素分析基础上,重点对内蒙古集宁玄武岩中橄榄岩包体的单斜辉石进行了激光原位微量元素研究。通过与新生代时华北具古老克拉通地幔特征(如鹤壁)和具新生岩石圈地幔特征(如山旺)的橄榄岩对比,讨论了新生代时集宁地区陆下岩石圈地幔性质及其形成和演化机制。集宁地区岩石圈地幔是相当于原始地幔经过较低程度的部分熔融抽取形成的,除个别样品的部分熔融程度<5%外,多数样品为5%~10%。橄榄岩的平衡温度与橄榄石Mg#关系表明新生代时集宁地区的陆下岩石圈地幔是不均一的,无明显分层现象,表现为饱满与过渡型地幔的共存。这种主体饱满并兼有过渡型地幔的不均一现象,可能是软流圈物质对古老地幔进行不均匀侵蚀、改造和置换作用的结果。

    Abstract:

    In four-facies peridotite, clinopyroxene (Cpx) contains abundant information concerning partial melting and mantle metasomatism due to its low melting point. Based on detailed studies of petrographic characteristics and major elements of minerals, the authors analyzed trace elements of Cpx in the peridotitic xenoliths from Jining area, Inner Mongolia. The properties and evolution of the subcontinental lithosphere mantle (SCLM) beneath Jining area in Cenozoic period have been discussed in comparison with things of lithospheric mantle (SCLM) beneath Hebi and Shanwang areas in the North China Craton. The peridotitic xenoliths from Hebi and Shanwang areas represent samples from the Archean (relict) and Phanerozoic (new accreted) mantle, respectively. The Jining peridotitic xenoliths are dominated by spinel-lherzolites. The lherzolites have mineral assemblage of olivine (42%~72%)+orthopyroxene (12%~50%)+clinopyroxene (5%~20%)+spinel (<5%). Compared with Hebi (coarse-grained) and Shanwang (fine-grained) peridotites,Jining peridotitic xenoliths mainly display the transitional porphyroclastic texture. The olivine Mg# values of Jining peridotitic xenoliths range from 89.4 to 91.4, quite consistent with the data obtained by previous researchers, and are fairly close to the values of peridotitic xenoliths from Shanwang and Yangyuan xenoliths. The samples were collected from a fertile lithospheric mantle.The Jining SCLM was formed from the relics after low partial melting of the primitive mantle. Most of the samples have a partial melting degree of 5%~10% with only a few lower than 5%. The Jining SCLM has undergone silicate melt/fluid metasomatism, quite similar to things experienced by Shanwang SCLM. The relationship between the Ol-Mg# and the equilibrium temperature of the peridotites suggests the coexistence of fertile mantle and refractory-transitional mantle beneath the study area in Cenozoic period. Such phenomena might be attributed to the reformation of the cratonic SCLM by the upwelling asthenospheric materials and the eventual replacement resulting from the cooling of the upwelled asthenosphere under heterogeneous conditions.

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周媛婷,郑建平,余淳梅,等, 2010. 内蒙古集宁新生代玄武岩中橄榄岩包体矿物化学特征及其地幔演化意义[J]. 岩石矿物学杂志, 29(3):243~257.
ZHOU Yuan_ting, ZHENG Jian_ping, YU Chun_mei, et al, 2010. Peridotite xenoliths in Jining Cenozoic basalts: mineral-chemistry and significance for lithospheric mantle evolution beneath the North China Craton[J]. Acta Petrologica et Mineralogica, 29(3): 243~257.

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