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1.
顽火辉石作为斜方辉石晶系的重要Mg端元矿物,是地球上地幔主要组成矿物之一。Li同位素作为重要的地幔地球化学示踪剂,在主要地幔矿物中(如橄榄石,辉石等)的扩散分馏相关性质的研究显得尤为重要。我们通过经典力学的方法,计算模拟了原子尺度下Li同位素在顽火辉石晶格以2种不同的迁移机制(填隙机制和取代空位机制)迁移的活化能和其在不同晶格位上不同温度条件下的分馏作用程度。计算结果表明,Li同位素易以填隙位机制在顽火辉石中迁移。重同位素~7Li会更多的进入晶格填隙位中,而6Li相对更多进入Mg位。温度是影响这种分馏作用的1个关键因素,相应的结果可用来解释地幔Li同位素组成特征及冷却条件下的同位素分馏等科学问题。 相似文献
2.
《矿物学报》2016,(3)
河南鹤壁地区位于太行山构造带上,该区金伯利岩中的地幔包体携带有岩石圈地幔的丰富信息。本文报道了石榴石二辉橄榄岩包体中的镁橄榄石和镁铝榴石的矿物化学特征。金伯利岩中地幔包体的镁橄榄石I(Mg~#)为91.7±0.2(n=69)。与鹤壁地区尖晶石相方辉橄榄岩相比,I(Mg~#)略偏小,指示二辉橄榄岩经历的熔融程度较低,具有过渡型地幔的特征。根据Cr_2O_3含量,镁铝榴石可以划分为高铬系列和低铬系列两类。橄榄石-石榴石矿物温压计计算表明,包体压力在1.7~2.5 GPa之间(55~80 km),温度在641~1055℃之间,对应的大地热流值为50~60m W/m~2,甚至更高。指示金伯利岩侵位时对应于较高的大地热流条件。根据Grutter的镁铝榴石划分方案,镁铝榴石主要划分为G9型、G3和G4型,其中G3和G4型镁铝榴石记录了岩石圈地幔被交代的过程。根据温压条件及岩石圈地幔性质,可以认为鹤壁地区不具有形成金刚石矿的深部地质条件。 相似文献
3.
镁铝榴石中的结构水的研究 总被引：2，自引：0，他引：2
通过对34个取自金伯利岩管中的粗晶镁铝榴石及碱性玄武岩中镁铝榴石巨晶样品的红外光谱分析发现,金伯利岩中部分镁铝榴石粗晶含有结构水,但不同颗粒之间含量差异很大,含量较高者约0.07wt%,而所研究的碱性玄武岩中的镁铝榴石不含结构水。分析发现,结构水在同一样品内分布基本均匀。在红外光谱3800—3500cm~(-1)波长范围内,分别记录到三峰谱和单峰谱两种类型,其中位于3570cm~(-1)±的吸收峰峰位明显受镁铝榴石结构中八配位阳离子(Mg~(2+)、Fe~(2+))影响,而六配位阳离子(Cr~(3+)、Al~(3+))的影响不明显。结构水在镁铝榴石晶格中的存在形式是多样的。 相似文献
4.
石榴石宝石是石榴石(garnet)族矿物的总称,岛状硅酸盐、等轴晶系矿物。根据其化学成分可划分成2个系列。铝质系列镁铝榴石:橙红色、红色铁铝榴石:橙红—红色、紫红—红紫色锰铝榴石:橙色—橙红色钙质系列钙铝榴石: 相似文献
5.
在红外光谱有关镁铝榴石中微量结构水的研究基础上,运用质子探针分析方法系统研究了辽宁50号金伯利岩管中粗晶镁铝榴石Ni、Zn、Ga、Sr、Y、Zr、Pb等微量元素的含量。根据镁铝榴石中微量元素Ni含量地质温度计,计算该岩管中镁铝榴石粗晶的形成温度,对比研究了不同含矿性的金伯利岩中粗晶镁铝榴石形成温度范围的异同,并探讨了该方法运用于金刚石找矿勘查的可能性;讨论了含结构水镁铝榴石的形成温度范围及其意义,并结合其它微量元素分析资料,探讨了镁铝榴石中微量结构水与地幔交代作用之间的成因联系。 相似文献
6.
根据激光探针分析含尖晶石橄榄石中矿物的氧同位素组成,反应增量法计算矿物对氧同位素分馏曲线,得到正尖晶石－矿物对氧同位素温度高于含尖晶石橄榄岩的相平衡温度,而用反尖晶石－矿物的对计算的氧同位素温度则很接近含尖晶石橄榄岩的相平衡温度,较为合理,因此地幔橄榄岩中镁铝尖晶石的氧同位素组成继承了其母体反尖晶石特征,即与橄榄石,单斜辉石和斜方辉石平衡的是反结构尖晶石,在其发生相变作用变成正结构尖晶石时未发生氧 相似文献
7.
镁铝榴石是贯穿整个地幔的重要组成矿物之一 ,携带着丰富的地幔甚至核幔边界信息。其中的包裹体是源于地幔深部最直接的样品。(1)样品描述 :镁铝榴石样品采自山东蒙阴富含金刚石的胜利一号金伯利岩岩管 ,近似椭圆形外观 ,长约 2 3mm ,最宽处约 16mm ,厚约 8mm ,主体为紫红色 ,沿裂隙有暗色的充填物。存在于镁铝榴石中的两个含有包括钾硼氯包裹体在内的多个无氧物相 (图 1和图 2中黑色部分 ,将另文讨论 )图 1 球状体背散射电子图像图 2 半球状体背散射电子图像的球状体 ,均于主晶镁铝榴石中呈清晰轮廓。球状体的主体成分为含水或其它挥发份… 相似文献
8.
9.
中国大陆科学钻探工程卫星孔PP6钻孔位于苏鲁超高压变质带的山东荣成滕家集马草夼橄榄岩体中。该橄榄岩出露于元古代花岗闪长片麻岩中,面积为300m×130m。地表岩石风化强烈,钻孔内岩石新鲜,劈理发育。孔深196m,橄榄岩厚度约110m,下部为花岗闪长片麻岩。橄榄岩主体呈块状构造,边缘呈条带状构造,靠近片麻岩的橄榄岩蛇纹石化强烈。除了10cm厚的岩脉原岩为岩浆分异的产物外,岩石主元素、微量和稀土元素地球化学显示,原岩为极亏损的地幔方辉橄榄岩。岩石主要矿物组成为橄榄石(85%~95%) 斜方辉石(3%~5%) 角闪石(3%~5%) 尖晶石(约0.5%) 镍硫化物(<0.1%),个别部位含有石榴石、单斜辉石和白云石。根据矿物的结构和成分,大体分为三个期次的组合。早期残余地幔矿物组合,由镁橄榄石、富铝顽火辉石、铬尖晶石和透辉石组成,具残余斑状结构,常含有包体,为高温低压组合;超高压变质期矿物组合,由镁橄榄石、镁铝榴石(Pyr=62~66)、低铝顽火辉石、铬尖晶石组成,具细粒变晶结构,无包体,变质温压为840~940°C、3.0~4.1GPa;麻粒岩相─角闪岩相变质期矿物组合,包括韭闪石、镁铝尖晶石、铬尖晶石、白云石、透闪石、蛇纹石,变质温度和压力为650~780℃、<1.8GPa。马草夼橄榄岩作为地幔楔,在印支期发生了超高压变质作用,并在折返过程中叠加了麻粒岩相-角闪岩相的变质作用。 相似文献
10.
中国东部新生代玄武质岩石中的超镁铁质捕虏体,主要包括五种类型:石榴石二辉橄榄岩(±少量尖晶石)、尖晶石二辉橄榄岩、尖晶石方辉橄榄岩、辉石岩和巨晶矿物。不同类型捕虏体间的共存矿物存在系统的化学成分变化。尤以Al_2O_3、Cr_2O_3变化明显。本文提出捕虏体中共存矿物的Cr~#[100Cr/(Al+Cr)]可作为分类和岩石成因的重要标志。并将五种捕虏体划分为三种地幔成因类型:饱满的或原始的地幔(石榴石二辉橄榄岩和尖晶石二辉橄榄岩),亏损的或残余的地幔(尖晶石方辉橄榄岩),地幔条件下熔浆分离的产物(辉石岩和巨晶矿物)。 相似文献
11.
高温下非传统稳定同位素分馏 总被引：5，自引：1，他引：4
过去十几年来,非传统稳定同位素地球化学在高温地质过程的研究中取得了的重大进展。多接收诱导耦合等离子质谱(MC-ICP-MS)的应用引发了稳定同位素分析方法的重大突破,使得精确测定重元素的同位素比值成为可能。本文总结了以Li、Fe和Mg同位素为代表的非传统稳定同位素在岩石地球化学研究中的应用。Li同位素目前被广泛地用于地幔地球化学、俯冲带物质再循环和变质作用的研究中,可以用来示踪岩浆的源区性质和扩散等动力学过程。不同价态的Fe在矿物熔体相之间的分配可以产生Fe同位素分馏,可以发生在地幔交代、部分熔融、分离结晶等过程中。岩浆岩的Mg同位素则大致反映其源区的特征,地幔的Mg同位素组成比较均一,这为研究低温地球化学过程中Mg同位素的分馏提供一个均一的背景。此外,Cl,Si,Cu,Ca,U等等同位素体系也具有广阔的应用前景。对同位素分馏机制的实验研究和理论模拟为理解非传统稳定同位素数据提供了必要的指导。实验表明,高温下具有不同的迁移速度的轻、重同位素可以产生显著的动力学同位素分馏,这一分馏可以在化学扩散、蒸发和凝华等过程中发生;同位素在矿物和熔体以及流体相中化学环境的差异使得不同相之间可以发生平衡分馏。而最近的硅酸盐岩浆的热扩散和热迁移实验则揭示了一种"新"的岩浆分异和同位素分馏机制。沿着温度梯度,硅酸盐岩浆可以发生显著的元素和同位素分异,湿的安山岩可以通过这种方式演变成花岗质成分,因此这个过程可能对陆壳的产生和演化有重大影响。如果温度梯度在岩浆作用中能长期存在,热扩散就可以产生稳定同位素的分馏,这一机制有别于传统的平衡和动力学同位素分馏。 而多个稳定同位素体系的正相关关系是示踪热迁移过程的最有力证据。在热扩散过程中,流体承载的物质的浓度和它的索瑞系数有关。但是这个系数对体系的很多参数非常敏感,变化极大,因此对热扩散效应的研究产生极大的困难。对热扩散实验的镁、钙和铁同位素测量表明,同位素比值的变化与体系的化学组成以及总温度无关,只和温度变化的幅度有关,这意味着即使元素的索瑞系数变化多端,某一元素的同位素之间的索瑞系数的差别总为常数。这一发现有助于简化对热扩散和索瑞系数这一基础物理问题的研究 。 相似文献
12.
Yan-Jie Tang Hong-Fu Zhang Takuya Moriguti Ji-Feng Ying 《Geochimica et cosmochimica acta》2007,71(17):4327-4341
Li concentrations and isotopic compositions of coexisting minerals (ol, opx, and cpx) from peridotite xenoliths entrained in the Hannuoba Tertiary basalts, North China Craton, provide insight into Li isotopic fractionation between mantle minerals during melt-rock interaction in the considerably thinned lithospheric mantle. Bulk analyses of mineral separates show significant enrichment of Li in cpx (2.4-3.6 ppm) relative to olivine (1.2-1.8 ppm), indicating that these peridotites have been affected by mantle metasomatism with mafic silicate melts. Bulk olivine separates (δ7Li ∼ +3.3‰ to +6.4‰) are isotopically heavier than coexisting pyroxenes (δ7Li ∼ −3.3‰ to −8.2‰ in cpx, and −4.0‰ to −6.7‰ in opx). Such large variation suggests Li elemental and isotopic disequilibrium. This conclusion is supported by results from in situ SIMS analyses of mineral grains where significant Li elemental and isotopic zonations exist. The olivine and opx have lower Li concentrations and heavier Li isotopes in the rims than in the cores. This reverse correlation of δ7Li with Li concentrations indicates diffusive fractionation of Li isotopes. However, the zoning patterns in coexisting cpx show isotopically heavier rims with higher Li abundances. This positive correlation between δ7Li and Li concentrations suggests a melt mixing trend. We attribute Li concentration and isotope zonation in minerals to the effects of two-stage diffusive fractionation coupled with melt-rock interaction. The earliest melts may have been derived from the subducted oceanic slab with low δ7Li values produced by isotopic fractionation during the dehydration of the seawater-altered slab. Melts at later stages were derived from the asthenosphere and interacted with the peridotites, producing the Li elemental and isotopic zoning in mineral grains. These data thus provide evidence for multiple-stage peridotite-melt interaction in the lithospheric mantle beneath the northern North China Craton. 相似文献
13.
Subduction zones involve many complex geological processes, including the release of slab-derived fluids, fluid/rock interactions, partial melting, isotopic fractionations, elemental transporting, and crust/mantle interactions. Lithium (Li) isotopes (6Li and 7Li) have relative mass difference up to 16%, being the largest among metal elements. Thus, Li isotopes have advantage to interprete trace various geological processes. Most importantly, during crust/mantle interactions in deep subduction zones, surface materials and mantle rocks usually have distinct Li isotopic compositions. Li isotopes can be potential tracer for subduction processes, from the onset of subduction to the release of Li from subducted slabs and interaction with mantle wedge, as well as the fate of Li in slab-derived fluids and residual slabs. Moreover, the Li isotopic composition of subducting output materials can provide useful information for understanding global Li circulation. With developments in measurement and expansion of Li isotopic database, Li isotopic geochemistry will provide more inference and be a powerful tracer for understanding subduction-related processes. This work retrospected the application of Li isotopes in tracing successive subduction processes, and made some prospects for further studies of Li isotopes. 相似文献
14.
Temperature-dependent isotopic fractionation of lithium between clinopyroxene and high-pressure hydrous fluids 总被引：2，自引：1，他引：2
Bernd Wunder Anette Meixner Rolf L. Romer Wilhelm Heinrich 《Contributions to Mineralogy and Petrology》2006,151(1):112-120
The fractionation of lithium isotopes between synthetic spodumene as representative of Li-bearing clinopyroxene and Cl- and
OH-bearing aqueous fluids was experimentally determined between 500 and 900°C at 2.0 GPa. In all the experiments, 7Li was preferentially partitioned into the fluid. The fractionation is temperature dependent and approximated by the equation
Δ7Li(clinopyroxene–fluid)=−4.61×(1,000/T [K]) + 2.48; R
2=0.86. Significant Li isotopic fractionation of about 1.0‰ exists even at high temperatures of 900°C. Using neutral and weakly
basic fluids revealed that the amount of fractionation is not different. The Li isotopic fractionation between altered basalt
and hot spring water (350°C) in natural samples is in good agreement with our experimentally determined fractionation curve.
The data confirm earlier speculations drawn from the Li isotopic record of dehydrated metamorphic rocks that fluids expelled
from a dehydrating slab carry heavier Li into the mantle wedge, and that a light Li component is introduced into the deeper
mantle. Li and Li isotopes are redistributed among wedge minerals as fluids travel across the wedge into hotter regions of
arc magma production. This modifies the Li isotopic characteristics of slab-derived fluids erasing their source memory, and
explains the absence of cross-arc variations of Li isotopes in arc basalts. 相似文献
15.
应用多接收电感耦合等离子质谱(MC-ICP-MS)等分析技术进行铊(Tl)同位素分析已成为非传统稳定同位素地球化学研究的重要内容之一.对近年来Tl同位素的实验测试方法及其地质应用的有关研究进展做了详细论述,包括Tl的地球化学行为、Tl同位素分析测试技术、同位素分馏机理、在各地质储库中的组成特征以及Tl同位素的地质应用等多个方面.这些研究表明该分析技术为行星科学、古海洋学、地幔地球化学、岩石成因以及矿床学等领域的研究提供了其他同位素分析方法难以获得的重要信息,充分展示了该分析技术在地球科学和环境科学领域的应用前景. 相似文献
16.
Iron isotope variations in spinel peridotite xenoliths from North China Craton: implications for mantle metasomatism 总被引：2，自引：1，他引：1
Xinmiao Zhao Hongfu Zhang Xiangkun Zhu Suohan Tang Yanjie Tang 《Contributions to Mineralogy and Petrology》2010,160(1):1-14
Iron isotopes, together with mineral elemental compositions of spinel peridotite xenoliths and clinopyroxenites from Hannuoba and Hebi Cenozoic alkaline basalts, were analyzed to investigate iron isotopic features of the lithospheric mantle beneath the North China Craton. The results show that the Hannuoba spinel peridotite xenoliths have small but distinguishable Fe isotopic variations. Overall variations in δ57Fe are in a range of ?0.25 to 0.14‰ for olivine, ?0.17 to 0.17‰ for orthopyroxene, ?0.21 to 0.27‰ for clinopyroxene, and ?0.16 to 0.26‰ for spinel, respectively. Clinopyroxene has the heaviest iron isotopic ratio and olivine the lightest within individual sample. No clear linear relationships between the mineral pairs on “δ-δ” plot suggest that iron isotopes of mineral separates analyzed have been affected largely by some open system processes. The broadly negative correlations between mineral iron isotopes and metasomatic indexes such as spinel Cr#, (La/Yb)N ratios of clinopyroxenes suggest that iron isotopic variations in different minerals and peridotites were probably produced by mantle metasomatism. The Hebi phlogopite-bearing lherzolite, which is significantly modified by metasomatic events, appears to be much heavier isotopically than clinopyroxene-poor lherzolite. This study further confirms previous conclusions that the lithospheric mantle has distinguishable and heterogeneous iron isotopic variations at the xenoliths scale. Mantle metasomatism is the most likely cause for the iron isotope variations in mantle peridotites. 相似文献
17.
Yan-Jie Tang Hong-Fu Zhang Eizo Nakamura Ji-Feng Ying 《Contributions to Mineralogy and Petrology》2011,161(6):845-861
Elemental and Li–Sr–Nd isotopic data of minerals in spinel peridotites hosted by Cenozoic basalts allow us to refine the existing
models for Li isotopic fractionation in mantle peridotites and constrain the melt/fluid-peridotite interaction in the lithospheric
mantle beneath the North China Craton. Highly elevated Li concentrations in cpx (up to 24 ppm) relative to coexisting opx
and olivine (<4 ppm) indicate that the peridotites experienced metasomatism by mafic silicate melts and/or fluids. The mineral
δ7Li vary greatly, with olivine (+0.7 to +5.4‰) being isotopically heavier than coexisting opx (−4.4 to −25.9‰) and cpx (−3.3
to −21.4‰) in most samples. The δ7Li in pyroxenes are considerably lower than the normal mantle values and show negative correlation with their Li abundances,
likely due to recent Li ingress attended by diffusive fractionation of Li isotopes. Two exceptional samples have olivine δ7Li of −3.0 and −7.9‰, indicating the existence of low δ7Li domains in the mantle, which could be transient and generated by meter-scale diffusion of Li during melt/fluid-peridotite
interaction. The 143Nd/144Nd (0.5123–0.5139) and 87Sr/86Sr (0.7018–0.7062) in the pyroxenes also show a large variation, in which the cpx are apparently lower in 87Sr/86Sr and slightly higher in 143Nd/144Nd than coexisting opx, implying an intermineral Sr–Nd isotopic disequilibrium. This is observed more apparently in peridotites
having low 87Sr/86Sr and high 143Nd/144Nd ratios than in those with high 87Sr/86Sr and low 143Nd/144Nd, suggesting that a relatively recent interaction existed between an ancient metasomatized lithospheric mantle and asthenospheric
melt, which transformed the refractory peridotites with highly radiogenic Sr and unradiogenic Nd isotopic compositions to
the fertile lherzolites with unradiogenic Sr and radiogenic Nd isotopic compositions. Therefore, we argue that the lithospheric
mantle represented by the peridotites has been heterogeneously refertilized by multistage melt/fluid-peridotite interactions. 相似文献
18.
锂同位素分馏机制讨论 总被引：7，自引：0，他引：7
作为一种新兴的稳定同位素示踪工具, 锂同位素地球化学的研究近年来受到了国际地学界日益广泛的关注.其应用领域涵盖了从地表到地幔的流体与矿物之间的相互作用.在地表风化作用过程中, 轻锂同位素(6Li) 优先进入固体相, 而7Li则进入流体相, 因而地表风化作用淋滤出了岩石中的重锂, 致使河水具有重的锂同位素组成, 河水又将重锂同位素组分补给海洋, 洋壳的低温蚀变作用使得海水的锂同位素组成进一步变重.在俯冲带, 由于俯冲板片释放的流体具有重锂同位素组成的特征, 它们上升并交代上覆的地幔楔和相邻的地幔, 使得地幔楔的锂同位素组成变重.同时, 深俯冲的板片由于脱水而具有较轻的锂同位素组成, 它们在地幔中可能形成一个局部轻锂的地幔储源.影响地幔橄榄岩锂同位素分馏的因素主要有3个方面: 温度、扩散机制以及外来熔体的反应.由于高温下地幔矿物之间的锂同位素分馏很小, 而单纯的扩散分馏机制不能够很好的解释我国华北汉诺坝地区地幔橄榄岩中矿物之间的锂同位素分馏.因此, 具有轻锂同位素组成的熔体与橄榄岩之间的反应是上述现象的一个合理解释.需要指出的是, 在橄榄岩-熔体反应的过程中, 锂同位素的扩散作用也对地幔矿物之间的同位素分馏有一定的贡献. 相似文献
19.
Xinmiao Zhao Hongfu Zhang Xiangkun Zhu Suohan Tang Yanjie Tang 《Contributions to Mineralogy and Petrology》2010,160(1):15-14
Iron isotopes, together with mineral elemental compositions of spinel peridotite xenoliths and clinopyroxenites from Hannuoba
and Hebi Cenozoic alkaline basalts, were analyzed to investigate iron isotopic features of the lithospheric mantle beneath
the North China Craton. The results show that the Hannuoba spinel peridotite xenoliths have small but distinguishable Fe isotopic
variations. Overall variations in δ57Fe are in a range of −0.25 to 0.14‰ for olivine, −0.17 to 0.17‰ for orthopyroxene, −0.21 to 0.27‰ for clinopyroxene, and −0.16
to 0.26‰ for spinel, respectively. Clinopyroxene has the heaviest iron isotopic ratio and olivine the lightest within individual
sample. No clear linear relationships between the mineral pairs on “δ-δ” plot suggest that iron isotopes of mineral separates
analyzed have been affected largely by some open system processes. The broadly negative correlations between mineral iron
isotopes and metasomatic indexes such as spinel Cr#, (La/Yb)N ratios of clinopyroxenes suggest that iron isotopic variations in different minerals and peridotites were probably produced
by mantle metasomatism. The Hebi phlogopite-bearing lherzolite, which is significantly modified by metasomatic events, appears
to be much heavier isotopically than clinopyroxene-poor lherzolite. This study further confirms previous conclusions that
the lithospheric mantle has distinguishable and heterogeneous iron isotopic variations at the xenoliths scale. Mantle metasomatism
is the most likely cause for the iron isotope variations in mantle peridotites. 相似文献
20.
Li isotope fractionation in peridotites and mafic melts 总被引：4，自引：0，他引：4
A.B. Jeffcoate T. Elliott S.A. Kasemann K. Cooper 《Geochimica et cosmochimica acta》2007,71(1):202-218
We have measured the Li isotope ratios of a range of co-existing phases from peridotites and mafic magmas to investigate high-temperature fractionations of 7Li/6Li. The Li isotopic compositions of seven mantle peridotites, reconstructed from analyses of mineral separates, show little variation (δ7Li 3.2-4.9‰) despite a wide range in fertility and radiogenic isotopic compositions. The most fertile samples yield a best estimate of δ7Li ∼ 3.5‰ for the upper mantle. Bulk analyses of olivine separates from the xenoliths are typically ∼1.5‰ isotopically lighter than co-existing orthopyroxenes, suggestive of a small, high-temperature equilibrium isotope fractionation. On the other hand, bulk analyses of olivine phenocrysts and their host melts are isotopically indistinguishable. Given these observations, equilibrium mantle melting should generate melts with δ7Li little different from their sources (<0.5‰ lighter). In contrast to olivine and orthopyroxene, that dominate peridotite Li budgets, bulk clinopyroxene analyses are highly variable (δ7Li = 6.6‰ to −8.1‰). Phlogopite separated from a modally metasomatised xenolith yielded an extreme δ7Li of −18.9‰. Such large Li isotope variability is indicative of isotopic disequilibrium. This inference is strongly reinforced by in situ, secondary ion mass-spectrometry analyses which show Li isotope zonation in peridotite minerals. The simplest zoning patterns show isotopically light rims. This style of zoning is also observed in the phenocrysts of holocrystalline Hawaiian lavas. More dramatically, a single orthopyroxene crystal from a San Carlos xenolith shows a W-shaped Li isotope profile with a 40‰ range in δ7Li, close to the isotope variability seen in all terrestrial whole rock analyses. We attribute Li isotope zonation in mineral phases to diffusive fractionation of Li isotopes, within mineral phases and along melt pathways that pervade xenoliths. Given the high diffusivity of Li, the Li isotope profiles we observe can persist, at most, only a few years at magmatic temperatures. Our results thus highlight the potential of Li isotopes as a high-resolution geospeedometer of the final phases of magmatic activity and cooling. 相似文献