Geochemical characteristics of Shatsky Rise Cretaceous basalts and implication on the interaction between mantle plume and mid-ocean ridge

Shatsky Rise is a large igneous province in the Northwest Pacific that was formed in the Early Cretaceous, and its formation genesis and evolution process are still controversial. This study analyzes the bulk-rock major elements, trace elements, and Sr-Nd-Pb isotopic compositions of Shatsky Rise Cretaceous basalts. Shatsky Rise volcanic rocks mainly belong to tholeiite and are characterized by the depletion of large ion lithophile elements and light rare earth elements (LREEs), the enrichment of heavy rare earth elements (HREEs), and the absence of obvious Eu anomaly (delta Eu =0. 99 similar to 1. 29), which is similar to the distribution pattern of normal mid-ocean ridge basalt (N-MORB). However, these basalts have relatively enriched Sr-87/Sr-86 (0. 702986 similar to 0. 703991) and Nd-143/Nd-144 (0. 513034 similar to 0. 513194) isotopic ratios, and relatively enriched Pb-207/Pb-204 (15. 439 15. 508) and Pb-208/Pb-204 (37. 853 similar to 38. 488) isotopic ratios, which are similar to the isotopic compositions of enriched ocean island basalt (OIB) and island arc volcanic rocks, and have the involvement of enriched mantle components with high U/Pb ratio (HIMU). The REE partial melting model proves that Shatsky Rise volcanic rocks may originate from a relatively shallow magma source where the spinet iherzolite exists stably, and experience a relatively high degree of partial melting (> 10%). We attempt to use the mantle plume-mid ocean ridge interaction model to explain the special geochemical characteristics of Shatsky Rise volcanic rocks with the depleted incompatible element compositions and enriched isotopic compositions. Due to the influence of strong ridge tensile forces, the mantle plume magma would flow to the ridge axis and undergo decompression melting, resulting in the depletion of the highly incompatible elements but the invariability of the isotopic compositions due to the relatively long half-life of the radiogenic elements (Sm, Rb, and U). We speculate that these Shatsky Rise isotopically enriched N-MORB-type tholeiites may be an exclusive product of a mid-ocean ridge-mantle plume interaction.