Data for: Mantle melting variation and refertilization beneath the Dragon Bone amagmatic segment (53°E SWIR): Major and trace element compositions of peridotites at ridge flanks

The evolution of the mantle melting regime and the process of refertilization beneath a cold lithosphere remain ambiguous at the ultraslow spreading ridges. Few previous studies were considered the temporal variation of mantle melting indicated by peridotites on the flank of a single ridge segment. Here we present in-situ major and trace geochemical analyses of harzburgite samples from the Dragon Bone Ridge Segment both near the spreading axis and from rift mountains up to tens of kilometers away from the ridge axis. We propose the Dragon Bone mantle has been depleted anciently at higher pressures, prior to the recent ascent under the ridge at lower pressures, while only a limited volume of melt was generated during recent melting beneath the ridge. This is consistent with the high degree of depletion of the Dragon Bone harzburgites with little trapped melt, and thin discontinuous igneous crust on the seafloor. Comparison of peridotites from near-ridge locations with those further out on its flanks indicates that the melting regime has progressively shrunk over time creating at present an amagmatic segment. Peridotites from segment ends are seldom affected by late-stage refertilization; while those from the segment center are highly depleted mantle residues (resembling those from fast spreading ridges) that sustained syn-melting metasomatism.超慢速扩张洋脊（ultraslow spreading ridges）下方冷岩石圈（cold lithosphere）的地幔熔融体系（mantle melting regime）演化及再富集作用（refertilization）过程目前仍存在诸多模糊之处。此前鲜有研究关注单个洋脊段侧翼橄榄岩（peridotites）所指示的地幔熔融时间变化。本文针对采自龙骨脊段（Dragon Bone Ridge Segment）扩张轴（spreading axis）附近，以及距离洋脊轴数十公里外裂谷山（rift mountains）的方辉橄榄岩（harzburgite）样品，开展了原位（in-situ）主量与微量地球化学分析。本文提出，龙骨脊下方的地幔在近期于低压下上涌之前，曾在更高压力下发生过古老的亏损作用，且近期洋脊下方的熔融过程仅产生了有限体积的熔体。这一结论与龙骨脊段方辉橄榄岩的强亏损特征、几乎无捕获熔体（trapped melt），以及海底薄而不连续的火成地壳（igneous crust）的观测结果一致。对比洋脊附近与侧翼更远区域的橄榄岩可知，熔融体系随时间逐渐收缩，当前已形成无岩浆段（amagmatic segment）。洋脊段两端的橄榄岩几乎不受后期再富集作用影响；而洋脊段中心的橄榄岩则为高度亏损的地幔残余，其特征与快速扩张洋脊的地幔残余相似，且经历了熔融同期交代作用（syn-melting metasomatism）。