The origin of Alpine-Himalayan K-rich orogenic lavas: an integrated experimental and geochemical approach

高山-喜马拉雅地区富钾造山熔岩的起源：综合实验和地球化学方法

• 批准号: 319239819
• 负责人: Dr. Dejan Prelevic, Ph.D.
• 金额: --
• 依托单位: Department of Earth and Planetary Sciences
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2016
• 资助国家: 德国
• 起止时间: 2015-12-31 至 2020-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/319239819?language=en
• 关键词: origin; Alpine; Himalayan; rich; orogenic

Mantle-derived magmatism that occurs within Alpine-Himalayan orogenic belts is dominantly K-rich and its origin is controversial, particularly the significance of the widespread geochemical signal typical for recycled continental crust. Three major components are recognized: i) The crustal component indicated by incompatible-element enrichment, elevated 87Sr/86Sr, 207Pb/204Pb, 187Os/188Os and low 143Nd/144Nd and 176Hf/177Hf ratios of the lavas; ii) An ultra-depleted component identified by usual presence of refractory Cr-spinel, high Fo olivine and low FeO abundances; iii) Extremely high Th/La coupled with high Sm/La points to a genetic relationship with the melange. The above observations suggest that the source of orogenic lavas cannot be realistically modelled as homogeneous peridotite. It is envisaged that the metasomatic assemblages are situated in the veins within peridotitic wall-rock of different fertility, originated through melt-mantle reaction, during three major orogenic phases: subduction, collision and postcollision. In order to simulate the melting processes within mantle source of Alpine-Himalayan orogenic magmas, which may involve a mixture of peridotite and nonperidotite-hydrous mineral assemblages, we will perform two types of experiments: i) The first one mimic recycling and re-melting of different continental crustal material that may have happened during subduction; it involves sandwich experiments up to 3 GPa including terrigenous siliciclastic sediments, marly sediments, carbonated pelites and blueshists, combined with peridotite of different fertility. ii) The second series of experiments will simulate melting events related to postcollisional stage with ultimate goal to produce melts that compositionally resemble Alpine-Himalayan orogenic lavas. It will combine i) hydrous assemblages produced in the first series of experiments, and ii) hydrous assemblages envisioned to comprise source of the orogenic lavas like phlogopite-clinopyroxenites and glimerites (MARID), again with peridotite of different fertility at pressures up to 3 GPa. By performing these experiments, we simulate major stages involved in orogenic magmatism, where first hydrous sediment melt from the slab infiltrates the overlying mantle wedge and undergoes wholesale thermal and chemical equilibration (partial to complete reactive freezing), and the second when the activation of the resulting metasomes undergoes postcollisional partial melting in the orogenic mantle. The novelty of the proposed research lies largely in the paradigm shift from melting of peridotite to the melting of combined peridotitic and non-peridotitic assemblages. This reveals immense gaps in our understanding of the melting of non-peridotitic ultramafic rocks that this project will make the first steps in filling.

发生在阿尔卑斯-喜马拉雅造山带内的幔源岩浆活动主要是富钾的，其起源是有争议的，特别是再生大陆地壳典型的广泛的地球化学信号的意义。火山岩具有3种主要成分：（1）地壳成分，表现为不相容元素富集，岩浆中87 Sr/86 Sr、207 Pb/204 Pb、187 Os/188 Os比值升高，143 Nd/144 Nd和176 Hf/177 Hf比值降低;（3）Th/La比值极高，Sm/La比值高，表明与混杂岩有成因联系。上述观察结果表明，造山熔岩的来源不可能实际地模拟为同质橄榄岩。据设想，交代组合位于静脉内的橄榄岩围岩的不同的肥力，起源于熔融地幔反应，在三个主要的造山阶段：俯冲，碰撞和碰撞后。为了模拟阿尔卑斯-喜马拉雅造山岩浆地幔源区的熔融过程，可能涉及橄榄岩和非橄榄岩-含水矿物组合的混合物，我们将进行两种类型的实验： 第一个模拟的回收和重熔不同的大陆地壳材料，可能发生在俯冲过程中，它涉及三明治实验高达3 GPa，包括陆源硅质沉积物，泥灰岩沉积物，碳酸泥质岩和blueshists，结合不同的肥力橄榄岩。ii）第二阶段 第二个系列的实验将模拟熔融事件与碰撞后阶段的最终目标，以产生熔体的成分类似于阿尔卑斯-喜马拉雅造山熔岩。它将结合联合收割机：i）第一系列实验中产生的含水组合，和ii）设想的包括金云母-单斜辉石岩和闪长岩（MARID）等造山熔岩源的含水组合， 在高达3GPa的压力下，同样具有不同肥力的橄榄岩。通过进行这些实验，我们模拟的主要阶段参与造山岩浆活动，其中第一含水沉积物熔体从板渗透覆盖地幔楔，并进行批发热和化学平衡（部分到完全反应冻结），和第二次时，所产生的变质体的激活经历碰撞后的部分熔融在造山地幔。所提出的研究的新奇主要在于从橄榄岩熔融到橄榄岩和非橄榄岩组合熔融的范式转变。这揭示了我们对非橄榄岩超镁铁质岩石融化的理解存在巨大差距，该项目将迈出填补这些差距的第一步。