藏南早侏罗世新特提斯洋俯冲过程中壳幔混合作用:来自日喀则东嘎闪长质岩体的证据
Mixing of Early Jurassic crustal and mantle-derived magmas induced by subduction of the Neo-Tethyan Ocean: Evidence from the Dongga dioritic pluton, South Tibet
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文摘
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大陆地壳的总体成分是闪长质的,闪长岩的成因是理解大陆地壳形成的关键。发育在青藏高原南部的冈底斯岩基,其总体成分是闪长质的,但是前人的研究主要集中在讨论镁铁质和长英质岩石的成因,很少涉及闪长岩。本工作选取冈底斯岩基中部东嘎闪长质岩体作为研究对象,以揭示冈底斯带闪长岩的成因及其与地壳生长的关系。锆石U-Pb定年显示东嘎闪长岩形成于(176.5±1.2) Ma,并且有(191.3±1.2) Ma的继承锆石,指示有早期地壳组分的加入。这些闪长岩具有相对较高的Mg#(0.40~0.44),亏损的Sr((~(87)Sr/~(86)Sr)_i=0.703570~ 0.703595)、Nd(ε_(Nd)(t)=+6.1~+6.5)和锆石Hf (ε_(Hf)(t)=+12.0~+14.7)同位素组成,以及较高的~(147)Sm/~(144)Nd值,表明岩浆源区有地幔物质贡献。岩相学上,闪长岩中镁铁质聚晶团块附近的针状磷灰石,以及东嘎岩体中广泛发育的镁铁质包体,暗示闪长岩为岩浆混合成因。岩浆混合的地球化学检验,也证实东嘎闪长岩是由幔源和壳源岩浆混合形成。东嘎闪长岩的壳幔混合成因表明在早侏罗世新特提斯洋俯冲过程中发生了垂向大陆地壳生长。 |
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其他语种文摘
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The geochemical composition of bulk continental crust is dioritic and therefore the petrogenesis of diorite is key to understanding the formation of continental crust. The Gangdese batholith in southern Tibet is dominated by dioritic rocks. However, previous studies mostly focused on the petrogenesis of mafic and felsic rocks instead of diorites. Thus, we carry out researches on the Dongga dioritic pluton in the central Gangdese batholith in order to decipher the petrogenesis of Gangdese diorite and its relationship with crustal growth. Zircon U-Pb dating reveals that the Dongga diorites were crystallized at (176.5±1.2) Ma. The abundant (191.3±1.2) Ma inherited zircons in the dated sample imply that crustal materials were involved in the magma source. These diorites have relatively high Mg# values, depleted (~(87)Sr/~(86)Sr)_i ratios (0.703570 - 0.703595), ε_(Nd)(t) values (+6.1 - +6.5) and zircon ε_(Hf)(t) values (+12.0 - +14.7), and relatively high ~(147)Sm/~(144)Nd ratios, thereby indicating non-negligible mantle contributions. In petrography, acicular apatite crystals surrounding mafic clots in the Dongga diorites, together with the abundant mafic enclaves in the neighbouring coeval pluton, imply a magma mixing origin for the diorites. The geochemical simulation of the magma mixing also confirms that the Dongga diorites were formed by mixing of crustal and mantle-derived magmas. In addition, the petrogenesis of magma mixing supports vertical continental crustal growth during the subduction of the Neo-Tethyan Ocean at the Early Jurassic. |
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来源
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地球化学
,2018,47(5):478-490 【核心库】
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DOI
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10.19700/j.0379-1726.2018.05.003
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关键词
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冈底斯岩基
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闪长岩
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岩浆混合
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地壳生长
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青藏高原
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地址
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1.
中国科学院广州地球化学研究所, 同位素地球化学国家重点实验室, 广东, 广州, 510640
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中国科学院大学, 北京, 100049
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西北大学地质学系, 大陆动力学国家重点实验室, 陕西, 西安, 710069
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语种
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中文 |
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文献类型
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研究性论文 |
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ISSN
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0379-1726 |
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学科
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地质学 |
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基金
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国家自然科学基金
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文献收藏号
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CSCD:6333161
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