Partitioning Behaviors of Cobalt and Manganese along Diverse Melting Paths of Peridotitic and MORB-Like Pyroxenitic Mantle
Partitioning Behaviors of Cobalt and Manganese along Diverse Melting Paths of Peridotitic and MORB-Like Pyroxenitic Mantle
复制标题
钴和锰在橄榄岩和类 MORB 辉石质地幔不同熔解路径上的分配行为
DOI：
10.1093/petrology/egac021
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发表时间：
2022
影响因子：
3.9
通讯作者：
Christina Yan Wang
中科院分区：
文献类型：
--
作者：
Chen Chen;Zhuo-Sen Yao;Christina Yan Wang
橄榄石斑晶和寄主玄武岩的Co、Mn、Fe、Ni含量对源区地幔岩性敏感，可用于制约地幔熔融过程和鉴别玄武岩的非橄榄岩（即辉石岩）地幔源区。在这里，我们使用一个新的综合的，涉及多个参数的正演模型来模拟在不同构造环境下地幔部分熔融期间Co和Mn的分配：（1）洋中脊橄榄岩地幔的多压连续熔融可以产生随着熔融程度的增加而减少Co和Mn的熔体，因此洋中脊玄武岩（MORB）含有~39-84 μg/g的Co和~（2）俯冲带地幔楔的熔剂熔融，产生的熔体中Co含量随温度的升高从24 μg/g增加到55 μg/g，Mn含量从500 μ g/g增加到1110 μg/g;（3）由陆下岩石圈地幔等压熔融产生的熔体对升温也很敏感，约有35-160 μg/（4）与地幔柱有关的橄榄岩减压熔融产生的熔体含Co ~45-140 μg/g和Mn ~1000-2000 μg/g，且这些金属的丰度随熔融程度的增加而降低;（5）由于地幔岩石的矿物学和成分不同，类MORB辉石岩减压熔融过程中Co，Mn，Ni的配分行为与橄榄岩减压熔融过程中Co，Mn，Ni的配分行为不同，类MORB辉石岩熔体贫金属，Co ~25-60 μg/g，Mn ~290-1600 μg/g，Ni ~160-340 μg/g。虽然高镍，低锰镁橄榄石斑晶和高熔融铁/锰比已被提出作为诊断指标的辉石成分在地幔中，我们的模型表明，这些功能也可以产生熔融的橄榄岩在更大的深度（即高压和高温）。为了量化橄榄岩高压熔融对这些诊断指标的影响，我们模拟了熔体Fe/Mn和橄榄石Co、Mn和Ni含量与热羽流减压熔融路径上熔融深度的相关性，沿着。当玄武岩的Fe/Mn比值和/或橄榄石斑晶的成分显著偏离我们模拟的相关线时，橄榄岩的高压熔融不能解释这些数据，并且可能需要地幔源中的辉石组分的存在。辉石岩衍生的熔体被建模为镍贫，但混合橄榄岩衍生的熔体可以强烈增加橄榄石和混合熔体之间的分配系数的镍，从而导致在生成高镍橄榄石斑晶在羽状相关的岩浆套房。
The Co, Mn, Fe, and Ni contents of olivine phenocrysts and host basalts are sensitive to source mantle lithology, which suggests they may be used to constrain the processes of mantle melting and identify basalts formed from non-peridotitic (i.e. pyroxenitic) mantle sources. Here, we use a new comprehensive, forward model involving multiple parameters to simulate partitioning of Co and Mn during partial melting of the mantle in different tectonic settings: (1) polybaric continuous melting of peridotite mantle in mid-ocean ridges can generate melts that show decreasing Co and Mn with increasing degrees of melting so that the mid-ocean ridge basalts (MORBs) contain ~39–84 μg/g Co and ~900–1600 μg/g Mn; (2) flux-melting of the mantle wedge in subduction zones tends to produce a melt that has Co increasing from ~24 to 55 μg/g and Mn from ~500 to 1110 μg/g with increasing temperature; (3) melts produced by isobaric melting of the subcontinental lithospheric mantle are also sensitive to increasing temperature and have ~35–160 μg/g Co and ~800–2600 μg/g Mn; (4) decompression melting of peridotite related to the mantle plume generates melts containing ~45–140 μg/g Co and ~1000–2000 μg/g Mn, and the abundances of these metals decrease with increasing degrees of melting; and (5) partitioning behaviors of Co, Mn, and Ni during decompression melting of MORB-like pyroxenite contrast with those during decompression melting of peridotite due to the different mineralogy and compositions in mantle lithologies, and the MORB-like pyroxenite-derived melt is metal-poor with ~25–60 μg/g Co, ~290–1600 μg/g Mn, and ~160–340 μg/g Ni. Although high-Ni, low-Mn forsteritic olivine phenocrysts and high melt Fe/Mn ratio have been proposed as diagnostic indicators of pyroxenitic components in the mantle, our models show that these features can be also generated by melting of peridotite at greater depth (i.e. a high pressure and temperature). To quantify the effect of high-pressure melting of peridotite on these diagnostic indicators, we modeled the correlations of melt Fe/Mn and olivine Co, Mn, and Ni contents with melting depth along the decompression melting path of a thermal plume. When Fe/Mn ratios of basalts and/or compositions of olivine phenocrysts deviate significantly from our modeled correlation lines, high-pressure melting of peridotite cannot explain these data, and the existence of pyroxenitic component in the mantle source is likely required. The pyroxenite-derived melt is modeled to be Ni-poor, but mixing with a peridotite-derived melt can strongly increase the partition coefficient of Ni between olivine and mixed melt, resulting in the generation of high-Ni olivine phenocrysts in plume-associated magmatic suites.