| 青海玉树县南洞卡组粗面安山岩地球化学特征：岩石成因与构造背景探讨 |
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| 引用本文： | 辜平阳,何世平,计文化,董增产,时超,陈奋宁.青海玉树县南洞卡组粗面安山岩地球化学特征：岩石成因与构造背景探讨[J].地质科学,2013,48(4):1069-1082. |
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| 作者姓名： | 辜平阳 何世平 计文化 董增产 时超 陈奋宁 |
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| 作者单位： | 国土资源部岩浆作用成矿与找矿重点实验室, 西安地质调查中心 西安 710054 |
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| 基金项目： | 国家青年基金项目，青海阿尔金1∶5万打柴沟等6幅区调项目 |
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| 摘 要： | 青海玉树县南洞卡组粗面安山岩的SiO2含量为55.92%～57.85%,高Na2O、MgO和Al2O3,低K2O、TiO2和 P2O5,铝饱和指数A/CNK=0.98～1.08,具有准铝-弱过铝质的特点。岩石K2O含量低,Na2O/K2O=12.60～15.97,显示出钠质粗面安山岩特征。SiO2-K2O图解和里特曼指数(2.89～3.25),说明岩石属于钙碱性系列。稀土配分模式为轻稀土弱富集右倾型,铕弱负异常(σEu=0.90～0.96)。微量元素蛛网图显示,岩石富集Rb、Th和U等元素,亏损高场强元素Nb、Ta和大离子亲石元素Ba,样品Ce/Pb、Nb/U 并未随着MgO含量的升高而升高,样品的La/Nb、Zr/Nb、Ba/Nb比值均表现出良好的稳定性,表明岩浆在上升过程中遭受地壳物质混染的可能性不大,可能是其源区特征的反映。研究表明岩浆经历了橄榄石和单斜辉石的结晶分异,且受到俯冲板片熔体对源区的改造作用。结合234 Ma的形成年龄,说明该粗面安山岩是金沙江洋盆向西俯冲消减和斜向碰撞的地质记录,其形成时代和地球化学特征也为江达-维西火山弧的形成演化及成矿作用研究提供依据。
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| 关 键 词： | 中三叠世火山岩 地球化学 锆石U-Pb年龄 金沙江洋盆 俯冲消减 |
| 收稿时间： | 2013-05-10 |
| 修稿时间： | 2013-05-10; |
Geochemical characteristics of trachyandesite from Dongka Formation,Yushu(Qinghai) :Petrogenesis and its tectonic significance |
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| Gu Pingyang
,
He Shiping
,
Ji Wenhua
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Dong Zhengchan
,
Shi Chao
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Chen Fenning.Geochemical characteristics of trachyandesite from Dongka Formation,Yushu(Qinghai) :Petrogenesis and its tectonic significance[J].Chinese Journal of Geology,2013,48(4):1069-1082. |
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| Authors: | Gu Pingyang He Shiping Ji Wenhua Dong Zhengchan Shi Chao Chen Fenning |
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| Institution: | Key Laboratory for the Study of Focused Magmatism and Giant Ore Deposits, MLR, Xi'an Geological Survey Center, Xi'an 710054 |
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| Abstract: | The trachyandesite from Dongka Formation in Yushu county is characterized by high Na2O, MgO, Al2O3, and low K2O, TiO2, P2O5, with alumina saturation index A/CNK of 0.98～1.08.These features suggest that the trachyandesite are characteristics of Metaluminous-weak peraluminous, simultaneously, this rock belongs to sodic andesite attribute to low K2O, and Na2O/K2O=12.60～15.97.The SiO2-K2O diagram and Rittmann index(2.89～3.25)show the trachyandesite belong to the calc-alkaline series.The chondrite-normalized REE patterns are rightward inclined, with Eu weak negative anomaly(σEu=0.90～0.96).The primitive mantle normalized trace element spidergrams are characterized by enriched Rb, Th and U, depleted Nb, Ta, Ba.The ratios of CE/Pb, Nb/U do not rise, as the MgO content increase, La/Nb, Zr/Nb, Ba/Nb show a good stability, which indicates that the ascent of magma process did not suffer form crustal contamination, may be a reflection of its source region.Studies have shown that the magma experienced fractional significant crystallization of olivine and clinopyroxene during the magmatic process, and the magma source region might be converted by the subducting slab melt.It can be deduced from formation age and geochemical characteristics that the trachyandesite is a geological record of Jinsha ocean basin westward subduction and oblique collision, also provide the basis for Jomda-Weixi volcanic arc evolution and mineralization. |
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| Keywords: | Middle Triassic volcanic rocks Geochemistry Zircon U-Pb age Jinsha ocean basin Subduction |
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