The relative contributions of asthenospheric mantle, lithospheric mantle, and continental crust in the genesis of the Siberian Traps Large Igneous Province (ST-LIP) remain poorly constrained. Most models invoke partial melting of asthenospheric mantle within a mantle plume with an inventory of recycled crustal material, with or without melting of subcontinental lithospheric mantle, and crustal contamination during ascend through the continental lithosphere. A greater understanding of this topic is of fundamental importance because the ST-LIP basalts are associated with the large Permian-Triassic extinction and the world’s largest magmatic Ni-Cu-platinum group element sulfide resources (Ni-Cu-PGE), the Norilsk-Talnakh mining camp. The ∼250 ± 2 Ma Siberian Traps at Norilsk contain a classic sequence of basaltic rocks that provide a spatial and stratigraphic context for changing chemistry of the eruptive products. We present a detailed geochemical and Sr-Nd-Hf-Mo isotopic investigation of ST-LIP volcanic rocks and associated sedimentary rocks, including coal and anhydrite, from the Norilsk area. The Mo/Mo isotope ratios (reported as δMo ratio relative to NIST SRM 3134) vary significantly from −0.62 to 0.07 ‰ for the older basalt formations and −0.41 to 0.03 ‰ for the younger basalt formations. The range of δMo and its correlation with the other geochemical tracers cannot be explained by post-magmatic alteration, magmatic differentiation, or sulfide fractionation as Mo behaves as a lithophile element under these magmatic conditions. We suggest that the δMo range can be explained by interaction of the plume with subcontinental lithospheric mantle modified by subduction processes. This is particularly prominent in the earlier Ivakinsky to Gudchikhinsky formations where light δMo values coupled with low Mo/Ce can be explained by contributions from a dehydrated eclogitic component, whereas more rare heavy δMo values and high Mo/Ce likely require contributions from a fluid metasomatized mantle source. Later magmas of the Nadezhdinsky formation show clear evidence of crustal contamination in their combined Mo-Sr-Nd-Hf isotope and trace element systematics, while the later more voluminous Morongovsky type magmas are shallower, large degree melts with limited crustal interaction. Our data shows the usefulness of Mo isotopes in deciphering magma sources of large igneous provinces eruptions.

中文翻译：

---

钼同位素证据对西伯利亚圈闭岩浆来源的制约


软流圈地幔、岩石圈地幔和大陆地壳在西伯利亚圈闭大型火成岩省（ST-LIP）成因中的相对贡献仍然很少受到限制。大多数模型都涉及地幔柱内软流圈地幔的部分熔融，以及回收的地壳物质的库存，有或没有次大陆岩石圈地幔的熔融，以及在上升穿过大陆岩石圈期间的地壳污染。更深入地了解这一主题至关重要，因为 ST-LIP 玄武岩与二叠纪-三叠纪大灭绝以及世界上最大的岩浆镍-铜-铂族元素硫化物资源 (Ni-Cu-PGE)——诺里尔斯克-塔尔纳赫采矿营地。诺里尔斯克 ∼250 ± 2 Ma 西伯利亚地盾包含一系列经典的玄武岩，为改变喷发产物的化学成分提供了空间和地层背景。我们对诺里尔斯克地区的 ST-LIP 火山岩和相关沉积岩（包括煤和硬石膏）进行了详细的地球化学和 Sr-Nd-Hf-Mo 同位素研究。对于较老的玄武岩地层，Mo/Mo 同位素比（报告为相对于 NIST SRM 3134 的 δMo 比值）差异显着，从 -0.62 到 0.07 ‰，对于较年轻的玄武岩地层，从 -0.41 到 0.03 ‰。 δMo 的范围及其与其他地球化学示踪剂的相关性不能用岩浆后蚀变、岩浆分异或硫化物分馏来解释，因为 Mo 在这些岩浆条件下表现为亲石元素。我们认为 δMo 范围可以通过地幔柱与俯冲过程改变的次大陆岩石圈地幔的相互作用来解释。 这在早期的 Ivakinsky 至 Gudchikhinsky 地层中尤为突出，其中轻 δMo 值与低 Mo/Ce 可以通过脱水榴辉岩成分的贡献来解释，而更罕见的重 δMo 值和高 Mo/Ce 可能需要来自流体交代的贡献地幔来源。后来的 Nadezhdinsky 岩浆在其 Mo-Sr-Nd-Hf 同位素和微量元素系统学中显示出明显的地壳污染证据，而后来体积较大的 Morongovsky 型岩浆则较浅，熔体程度较大，与地壳相互作用有限。我们的数据显示了钼同位素在破译大型火成岩省喷发的岩浆来源方面的有用性。