(Table 1) Nd and Sr isotopic analyses of ODP Leg 127 basalts@en

Sr and Nd isotopic compositions are reported for basaltic rocks collected during ODP Leg 127 from the Yamato Basin, a rifted backarc basin in the Japan Sea. The basalts are classified into two groups in terms of Nd isotopic composition: the upper sills at Site 797 are characterized by higher 143Nd/144Nd ratios (0.513083-0.513158, epsilon-Nd = 8.68-10.14) and the basalts from Site 794 and the lower sills at Site 797 have lower 143Nd/144Nd ratios (0.512684-0.512862, epsilon-Nd = 0.90-4.37). All of the basalts show higher Sr isotopic compositions than those of the mantle array, which is attributed to seawater alteration. The basalts with lower Nd isotopic values ranging in age from 20.6 to 17.3 Ma have tapped an enriched subcontinental upper mantle (SCUM) with the minor involvement of a depleted asthenospheric mantle (AM). Subsequent change in composition through the physical replacement of SCUM by AM yielded the basalts of the upper sills of higher Nd isotopic compositions. This event within the upper mantle was associated with the breakup of the overlying lithosphere during the rifting of the Japan Sea backarc basin.本数据集报道了日本海张裂弧后盆地——大和盆地（Yamato Basin）大洋钻探计划（Ocean Drilling Program, ODP）第127航次采集的玄武岩的锶（Sr）与钕（Nd）同位素组成。根据钕同位素组成，这些玄武岩可划分为两组：797站位的上部岩床以较高的¹⁴³Nd/¹⁴⁴Nd比值（0.513083~0.513158，εNd=8.68~10.14）为特征；而794站位的玄武岩以及797站位的下部岩床则具有较低的¹⁴³Nd/¹⁴⁴Nd比值（0.512684~0.512862，εNd=0.90~4.37）。所有玄武岩的锶同位素组成均高于地幔阵列（mantle array），该特征被归因于海水蚀变作用。形成于20.6~17.3 Ma之间的低钕同位素值玄武岩，其岩浆源区为受少量亏损型软流圈地幔（asthenospheric mantle, AM）混染的富集型大陆下上地幔（subcontinental upper mantle, SCUM）。后续通过亏损型软流圈地幔对富集型大陆下上地幔的物理置换，使得岩浆同位素组成发生转变，从而形成了钕同位素组成更高的上部岩床玄武岩。这一发生于上地幔的地质事件，与日本海弧后盆地张裂过程中上覆岩石圈的破裂作用密切相关。