Mantle formation and evolution, Slave Craton: constraints from HSE abundances and Re–Os isotope systematics of sulfide inclusions in mantle xenocrysts
Mantle formation and evolution, Slave Craton: constraints from HSE abundances and Re–Os isotope systematics of sulfide inclusions in mantle xenocrysts
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DOI：
10.1016/j.chemgeo.2004.04.006
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发表时间：
2004-08
期刊：
影响因子：
3.9
通讯作者：
S. Aulbach;W. Griffin;N. Pearson;S. O’Reilly;K. Kivi;B. Doyle
中科院分区：
文献类型：
--
作者：
S. Aulbach;W. Griffin;N. Pearson;S. O’Reilly;K. Kivi;B. Doyle
主元素，微量元素，包括高度亲铁元素（HSE）和铼-锇同位素比值进行了分析，在现场的个别硫化物颗粒和一个铁金属颗粒封闭在新鲜的捕虏橄榄石和辉石金伯利岩在Lac de Gras地区，中央奴隶的。将低温组合重建为高温前体硫化物表明，有两种主要的硫化物群：含镍的单硫化物固溶体（mss）和一组独特的缺硫富镍和富钴硫化物（（Ni，Co，Fe）3 − xS2）。包裹体组是不寻常的，因为所有的（Ni，Co，Fe）3-xS2，一个mss的亚组，和Fe金属包裹体都具有高的W浓度（分别高达3400，2600和24，000 ppm），并且因为（Ni，Co，Fe）3-xS2具有更高的Ni和Co浓度（平均47和6.8 wt. %，与文献报道的大多数幔源硫化物相比，它们具有更高的金属/硫（平均Me/S = 1.1）。钙橄榄石温度表明，主机橄榄石和硫化物来自分层岩石圈的深层下面的Lac de Gras。收集了24个mss包裹体的Re-Os同位素数据，187 Re/188 Os的范围为0.006 - 2.71，187 Os/188 Os的范围为0.1002 - 0.4732，对应的γ Os为− 21 - 272。硫化物在~2.8Ga时以TRD-TCHUR-TRD-TCHUR-TCHUR-TCHUR-TCHUR-TCHUR-TCHUR-TCHUR-TCHUR-TCHUR-TCHUR-TCHUR-TCHUR-TCHUR-TCHUR-TCHUR-TCHUR-TCHUR-TCHUR-TCHUR-TCHUR-TCHUR-TCHUR-TCHUR-TCHUR-TCHUR-TCHUR-TCHUR-TCHUR-TCHUR-TCHUR-TCHUR-TCHUR-TCHUR-TCHUR-TCHUR-TCHUR-TCHUR-TCHUR-TCHUR-TCHUR-TCHUR-TCHUR-TCHUR-TCHUR-TCHUR-TCHUR-TCHUR-TCHUR-TCHUR-TCHUR-TCHUR-TCHUR-TCHUR-TCHUR-TCHUR-TCHUR-TCHUR-TCHUR 11个样品在t = 3.27 ± 0.34Ga处具有等时线，初始187Os/188Os在t = 0.10725 ± 0.00014处富集（γ Os，i = 2.53 ± 0.13; MSWD = 0.75）。Os含量和187Re/188Os与寄主橄榄石Mg/（Mg + Fe）的弱协变与含硫化物橄榄岩熔体亏损程度的变化一致。不相容的元素丰度的不连贯的行为，不相关的富集在流体流动元素W，As和Zn，和无支持的放射成因的Os和最近的重新富集在一些硫化物建议重复交代过程熔融后。不寻常的（Ni，Co，Fe）3-xS2的形成可能与地幔硫化物的交代或蚀变有关。然而，mss和（Ni，Co，Fe）3 − xS2的主要元素组成也与岩浆起源一致，这是由富含镍的硫化物熔体分馏而来，而这些硫化物熔体与下地幔中的含硫金属熔体分离。尽管有与流体相互作用的证据，但一些硫化物能够保留古老的熔体耗尽特征。模式年龄和等时线年龄在深Lac de Gras下面的岩石圈超过了上覆地壳的Contowyto的年龄。如果在这两个实体碰撞过程中，相邻的较老的中央奴隶基底复合体（CSBC）下的岩石圈地幔被推到年轻的Contowyto岩下，导致translithospheric东北倾斜缝合线，那么这种“年龄悖论”可能会得到调和。
Major elements, trace elements including highly siderophile elements (HSE) and Re–Os isotope ratios were analysed in situ on individual sulfide grains and one Fe metal grain enclosed in fresh xenocrystic olivine and pyroxenes from kimberlites in the Lac de Gras area, central Slave Craton. Reconstruction of low-temperature assemblages to high-temperature precursor sulfides shows that there are two major sulfide populations: nickeliferous monosulfide solid solution (mss), and a distinct group of S-deficient Ni- and Co-rich sulfides ((Ni,Co,Fe)3−xS2). The inclusion suite is unusual because all (Ni,Co,Fe)3−xS2, a subgroup of mss, and Fe metal inclusion have high W concentrations (up to 3400, 2600 and 24,000 ppm, respectively) and because (Ni,Co,Fe)3−xS2have higher Ni and Co concentrations (mean 47 and 6.8 wt.%, respectively) combined with higher metal/sulfur (mean Me/S=1.1) than the great majority of mantle-derived sulfides reported in the literature. Ca-in-olivine temperatures indicate that the host olivine and included sulfides are derived from the deep layer of the stratified lithosphere beneath Lac de Gras. Re–Os isotope data were collected for 24 mss inclusions.187Re/188Os ranges from 0.006 to 2.71, and187Os/188Os from 0.1002 to 0.4732, corresponding to γOsfrom −21 to 272. The sulfides show a major mode of TRDat ∼2.8 Ga, extending to 3.9 Ga, and of TCHURat ∼2.9 Ga. Eleven samples define an isochron at t=3.27±0.34 Ga, with an enriched initial187Os/188Os at t of 0.10725±0.00014 (γOs,i=2.53±0.13; MSWD=0.75). Weak covariations of Os contents and187Re/188Os in mss with Mg/(Mg+Fe) of host olivine are consistent with variable degrees of melt depletion of sulfide-bearing peridotite. The incoherent behaviour of incompatible element abundances, the unrelated enrichment in the fluid-mobile elements W, As and Zn, and the unsupported radiogenic Os and recent Re-enrichment in some sulfides suggest repeated metasomatic processes subsequent to melting. The formation of the unusual (Ni,Co,Fe)3−xS2could be related to metasomatism or alteration of mantle sulfide. However, the major element compositions of mss and (Ni,Co,Fe)3−xS2would also be consistent with an igneous origin, by fractionation from extremely Ni-rich sulfide melts that unmix from S-bearing metal melts expected in the lower mantle. Despite the evidence for interaction with fluids, some sulfides were able to preserve ancient melt-depletion signatures. Model ages and the isochron age in the deep lithosphere beneath Lac de Gras exceed the age of the overlying crust of the Contwoyto terrane. This “age paradox” may be reconciled if the lithospheric mantle beneath the adjacent older Central Slave Basement Complex (CSBC) was thrust beneath the younger Contwoyto terrane during collision of these two entities, resulting in a translithospheric northeast-dipping suture.