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文摘
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青藏高原拉萨地块广泛分布有新生代超钾质岩,岩石地球化学和Sr-Nd-Pb同位素特征表明这些超钾质岩来源于与古俯冲环境有着密切联系的含金云母的富集地幔源区,它们主要喷发于25~10 Ma. 同时在拉萨地块分布有多条南北向地堑(裂谷),且它们的切割深度可能到达下地壳的深部甚至岩石圈地幔,它们主要形成于23~8 Ma. 拉萨地块大多数超钾质岩沿着新生代的南北向地堑(裂谷)分布,并且它们在形成时代和空间分布上存在着明显的耦合性,结合沿着印度-雅鲁藏布江缝合带分布的中新世埃达克质岩,笔者认为这些超钾质岩很可能与中新世早期北向俯冲的印度岩石圈沿着印度-雅鲁藏布江缝合带附近发生断离,以及由此而引起拉萨地块东西向伸展构造活动产生的南北向地堑(裂谷)系统有关 |
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其他语种文摘
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Cenozoic ultrapotassic volcanic rocks which are widely distributed in Lhasa block of southern Qinghai-Tibetan Plateau were mainly erupted between 25 Ma and 10 Ma. These ultrapotassic volcanic rocks have typica lamproite characteristics such as high SiO_2, MgO, K_2O and TiO_2, low Al_2O_3and Na_2O, and high K_2O/Na_2O ratios. Their high abundances of incompatible trace elements like large ion lithophile elements (LILE) and ligh rare earth elements (LREE) also reach the extreme levels typical of lamproites. The lamproites show high radiogenic~87Sr/~86Sr and low unradiogenic~143Nd/~144Nd, low~206Pb/~204Pb, and elevated radiogenic~207Pb/~204Pb and ~208Pb/~204Pb ratios. Geochemical and Sr-Nd-Pb isotopic characteristics of these ultrapotassic volcanic rocks in Lhasa block suggest that they were probably derived from a phlogopite-bearing enriched mantle source related closely to metasomatism during earlier subduction events. The ultrapotassic rocks in southern Tibet may impl the uplift and extension of Tibetan plateau after the collision of Indian plate and Eurasian plate. Meanwhile, ther are a number of N-S grabens (rifts) mostly formed in 23~8 Ma in Lhasa block, which might have cut the lowe crust or lithosphere into the depth, suggesting the extension of southern Tibet in Miocene. Furthermore, thes ultrapotassic volcanic rocks are coincident with N-S grabens (rifts) in space and time. In addition, the tecton activities in western Lhasa block (such as Karakorum fault) in 17 Ma and in eastern Lhasa block (such as Jia fault and Red River-Ailao Mountain fault zone) in 23~17 Ma imply that at about 20±3 Ma the tectonic stres field in southern and southern-eastern parts of Qinghai-Tibetan Plateau underwent a considerable change from the NS-trending compression to the EW-trending extension. Combined with contemporary adakitic rocks alon the Yarlung Zangbo suture, the authors hold that the northward subducted Indian lithospheric mantle migh have experienced break-off beneath the Lhasa block along the Yarlung Zangbo suture in early Miocene, whic caused the upward and lateral migration of the asthenosphere material under the Indian lithospheric mantle alon the slab window. The upward and lateral migration of the asthenosphere material led to the rapid uplift of southern Qinghai-Tibetan Plateau as well as the eastward movement of the thickened crust, which further resulted i the EW-trending extensional deformation (23~8 Ma) of the widely distributed N-S grabens (rifts) and th eruption of the ultrapotassic magma(25~10 Ma) |
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来源
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岩石矿物学杂志
,2010,29(4):341-354 【核心库】
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关键词
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新生代
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超钾质岩
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南北向地堑(裂谷)
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拉萨地块
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青藏高原
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地址
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中国科学院广州地球化学研究所, 同位素年代学和地球化学实验室(广东), 广东, 广州, 510640
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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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1000-6524 |
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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973计划
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国家自然科学基金资助项目
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中国科学院知识创新工程重要方向项目
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文献收藏号
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CSCD:3908772
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