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题名:
Cooling-induced fractionation of mantle Li isotopes from the ultraslow-spreading Gakkel Ridge
作者: Gao, Yongjun1; Snow, Jonathan E.1; Casey, John F.1; Yu, Junbao2
刊名: EARTH AND PLANETARY SCIENCE LETTERS
ISSN号: 0012-821X
出版日期: 2011-01-03
卷号: 301, 期号:1-2, 页码:231-240
关键词: Li isotopes ; diffusion ; isotope fractionation ; modelling ; upper mantle
学科分类: Geochemistry & Geophysics
产权排序: [Gao, Yongjun; Snow, Jonathan E.; Casey, John F.] Univ Houston, Dept Earth & Atmospher Sci, Houston, TX 77204 USA; [Yu, Junbao] Chinese Acad Sci, Lab Coastal Wetland Ecol, Key Lab Coastal Environm Proc, Yantai Inst Coastal Zone Res, Yantai 264003, Peoples R China
通讯作者: Gao, YJ, Univ Houston, Dept Earth & Atmospher Sci, Houston, TX 77204 USA.ygao@mail.uh.edu
作者部门: 滨海湿地实验室 
中文摘要: Li isotopic compositions of magmatic rocks have gained considerable attention recently as probes of mantle-scale processes. However, the concentrations and isotopic composition of Li in mantle minerals from mid-ocean ridges remain relatively unconstrained. This is largely because of the general presence of seawater alteration in abyssal peridotites. Lithium elemental and isotopic compositions for mineral separates of coexisting olivine, clinopyroxene, orthopyroxene and bulk rocks of serpentine-free Gakkel Ridge peridotites were investigated. Bulk rocks have Li contents of 1.6 to 2.7 ppm and Ski values of 3 to 5 parts per thousand, which fall within the range of reported normal pristine "MORB mantle" values. Lithium concentrations vary in the order cpx (2.1-4.7 ppm)>opx (0.9-1.7 ppm)olivine (0.4-0.9 ppm), the opposite found in "equilibrated" mantle peridotite xenoliths (Seitz and Woodland, 2000). The Li isotopic compositions indicate a systematic mineral variation with delta Li-7(olivine) (7.14 parts per thousand-15.09 parts per thousand)>delta Li-7(opx) (1.81 parts per thousand-3.66 parts per thousand)>delta Li-7(cpx) (-2.43 parts per thousand--0.39 parts per thousand). The delta Li-7 values of cpx are negatively correlated with their Li concentrations with the lightest value for the most enriched cpx grains. There is a first order negative linear correlation between Delta(olivine-cpx) (delta Li-7(olivine)-delta Li-7(cpx)) and D-ol/cpx (Li-olivine/Li-cpx). Numerical simulations indicate that the observed systematic inter-mineral variations of Li concentrations and isotopic compositions could be explained by a cooling driven diffusive redistribution between minerals in a closed system if there is a temperature dependent partitioning of Li between olivine and clinopyroxene. The studied Gakkel Ridge abyssal peridotites may alternatively have cooled under a variable cooling rate with a rapid cooling before the Li system was closed, which is less likely given the tectonic setting. Our calculations confirm that Li systematics in minerals, especially in coexisting mineral phases could potentially be used as a mantle geospeedometer, even for slowly cooled mantle rocks. Published by Elsevier B.V..
英文摘要: Li isotopic compositions of magmatic rocks have gained considerable attention recently as probes of mantle-scale processes. However, the concentrations and isotopic composition of Li in mantle minerals from mid-ocean ridges remain relatively unconstrained. This is largely because of the general presence of seawater alteration in abyssal peridotites. Lithium elemental and isotopic compositions for mineral separates of coexisting olivine, clinopyroxene, orthopyroxene and bulk rocks of serpentine-free Gakkel Ridge peridotites were investigated. Bulk rocks have Li contents of 1.6 to 2.7 ppm and Ski values of 3 to 5 parts per thousand, which fall within the range of reported normal pristine "MORB mantle" values. Lithium concentrations vary in the order cpx (2.1-4.7 ppm)>opx (0.9-1.7 ppm)olivine (0.4-0.9 ppm), the opposite found in "equilibrated" mantle peridotite xenoliths (Seitz and Woodland, 2000). The Li isotopic compositions indicate a systematic mineral variation with delta(7)Li(olivine) (7.14 parts per thousand-15.09 parts per thousand)>delta(7)Li(opx) (1.81 parts per thousand-3.66 parts per thousand)>delta(7)Li(cpx) (-2.43 parts per thousand--0.39 parts per thousand). The delta(7)Li values of cpx are negatively correlated with their Li concentrations with the lightest value for the most enriched cpx grains. There is a first order negative linear correlation between Delta(olivine-cpx) (delta(7)Li(olivine)-delta(7)Li(cpx)) and (ol/cpx)D (Li(olivine)/Li(cpx)).
研究领域[WOS]: Geochemistry & Geophysics
关键词[WOS]: PERIDOTITE XENOLITHS ; LITHIUM ISOTOPES ; MIDOCEAN RIDGE ; OCEANIC-CRUST ; ARCTIC-OCEAN ; ABYSSAL PERIDOTITES ; OROGENIC ECLOGITES ; HIGH-TEMPERATURE ; VOLCANIC-ROCKS ; BASALT GLASS
文章类型: Article
收录类别: SCI
语种: 英语
WOS记录号: WOS:000286640400024
Citation statistics:
内容类型: 期刊论文
URI标识: http://ir.yic.ac.cn/handle/133337/4806
Appears in Collections:中科院海岸带环境过程与生态修复重点实验室_期刊论文
滨海湿地实验室_期刊论文
山东省海岸带环境过程重点实验室_期刊论文

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作者单位: 1.Univ Houston, Dept Earth & Atmospher Sci, Houston, TX 77204 USA
2.Chinese Acad Sci, Lab Coastal Wetland Ecol, Key Lab Coastal Environm Proc, Yantai Inst Coastal Zone Res, Yantai 264003, Peoples R China

Recommended Citation:
Gao, Yongjun,Snow, Jonathan E.,Casey, John F.,et al. Cooling-induced fractionation of mantle Li isotopes from the ultraslow-spreading Gakkel Ridge[J]. EARTH AND PLANETARY SCIENCE LETTERS,2011,301(1-2):231-240.
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