| 青藏高原北部白榴碧玄岩年代学及地球化学研究 |
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| 引用本文： | 杨迪,丁林.青藏高原北部白榴碧玄岩年代学及地球化学研究[J].地质科学,2013,48(2):449-467. |
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| 作者姓名： | 杨迪 丁林 |
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| 作者单位： | 1. 中国科学院青藏高原研究所大陆碰撞与高原隆升重点实验室 北京 100101;
2. 中国科学院大学 北京 100049 |
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| 基金项目： | 中国科学院资环局国际合作项目，中国科学院战略性先导科技专项，科技部"973"项目 |
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| 摘 要： | 本文在可可西里北部边缘银顶山地区首次发现含橄榄石的高镁高钾质超基性火山岩。火山岩在阿尼玛卿-昆仑-木孜塔格缝合带南侧呈熔岩残丘形式产出,分布面积约为0.2 km2,其形成时代为上新世(5～4 Ma),是岩浆的快速侵位-喷溢的结果。斑晶主要为橄榄石(10%～12%)+白榴石(21%～27%)+霞石(13%～16%)±透辉石(29%～31%),基质主要为透辉石+云母+Fe-Ti氧化物+玻璃,定名为白榴碧玄岩。对3个样品51个点的橄榄石电子探针数据计算显示,橄榄石牌号为Fo74-87Fa13-26,属贵橄榄石,岩石中的橄榄石均不存在扭折带,表明这些橄榄石很可能是岩浆结晶的产物,而非岩浆捕获体。通过计算,银顶山地区橄榄石的结晶温度大约在1 226 ℃～1 234 ℃左右。白榴碧玄岩的化学组分:SiO2<45%,MgO>10%, Na2O+K2O>8%,Mg#(68.84～70.80),而Cr(149×10-6～156×10-6)和Ni(138×10-6～151×10-6),87Sr/86Sr(约0.708 6)和143Nd/144 Nd(约0.512 4),处于EMII源区范围内。初步认为藏北地区上新世超基性火山岩来自于较深的源区,最有可能是软流圈顶部地幔的局部熔融,并受到俯冲地壳物质的交代。
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| 关 键 词： | 高镁-高钾质 白榴碧玄岩 上新世 软流圈 青藏高原 |
| 收稿时间： | 2012-11-28 |
| 修稿时间： | 2012-11-28; |
Geochronology and geochemistry of the high magnesium and high potassium ultrabasic leucite basanite in northern Tibetan Plateau |
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| Yang Di
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Ding Lin.Geochronology and geochemistry of the high magnesium and high potassium ultrabasic leucite basanite in northern Tibetan Plateau[J].Chinese Journal of Geology,2013,48(2):449-467. |
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| Authors: | Yang Di Ding Lin |
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| Institution: | 1. Key Laboratory of Continental Collision and Plateau Uplift, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100101;
2. University of Chinese Academy of Sciences, Beijing 100049 |
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| Abstract: | The high magnesium and high potassium ultrabasic leucite basanites were first found in the Silver Mountain region of northern Tibet.Leucite basanites are located in the south of A'nyemaqen-Kunlun-Muztag suture zone,covering an area of about 0.2 km2 and the age of the volcano eruption is about 5～4 Ma dated by Ar-Ar method.The phenocrysts are mainly composed of olivine(10%～12%),leucite(21%～27%),nepheline(13%～16%) and diopside(29%～31%),and the groundmass(～30%) is composed of fine grain of diopside,biotite,Fe-Ti oxide and glass.The composition of the olivine phenocrysts are Fo74-87Fa13-26,without obvious kink band,which suggests that the olivine phenocrysts were crystallized from magma rather than xenoliths captured from mantle.The estimated crystallization temperature ranges from 1 226 ℃ to 1 234 ℃.Leucite basanites contain SiO2<45%,MgO>10%,Na2O+K2O>8%,higher Mg#(68.84～70.80),high concentration of some compatible elements,such as Cr(149×10-6～156×10-6) and Ni(138×10-6～151×10-6).The ratios of 87Sr/86Sr(～0.708 6) and 143Nd/144Nd(～0.512 4) are within a typical EMII source area.Therefore,we argued that these ultrabasic leucite basanites were originated from the partial melting of the mantle rocks at the top of the asthenosphere,and probably contaminated by the subducted crust material. |
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| Keywords: | magnesium and high potassium Leucite basanite Pliocene Asthenosphere Tibetan Plateau |
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