This paper reports petrology, major and trace element abundances in bulk-rocks and minerals, and clinopyroxene Sr-Nd-Hf compositions from a suite of mantle xenoliths entrained in Cenozoic Sanyitang alkali basalts, Jining County in the Inner Mongolia Suture Zone. The aim is to constrain the nature and evolution of the lithospheric mantle beneath the western North China Craton. The Sanyitang mantle xenoliths are mainly anhydrous spinel lherzolites with subordinate websterites. Petrological and geochemical features of the spinel lherzolites suggest that they are refractory mantle residues formed by variable degrees of melt extraction (3–14%), followed by silicate and carbonatite metasomatism. The Sr-Nd-Hf isotopic compositions (⁸⁷Sr/⁸⁶Sr = 0.7031–0.7037, ε_Nd = +5.2 − +11.2 and ε_Hf = +8.4 − +29.3) of clinopyroxene separates from the majority of the spinel lherzolites lie on, or close to, the mantle array defined by the composition of ocean-island basalts and mid-ocean ridge basalts. On the other hand, clinopyroxene separates from a minority of spinel lherzolites (SYT09-01, SYT09-09, SYT11-01) have high ⁸⁷Sr/⁸⁶Sr (0.7040–0.7049), εNd (+12.4 − +21.9) and εHf (+58.2 − +67.8), above the mantle array, reflecting long-term depletion of the mantle. The websterites are characterized by lower MgO (18–22 wt%) and higher Al₂O₃ contents (4.5–5.6 wt%), and lower Mg# (86.2–87.3) than the spinel lherzolites (Mg# = 89.3–90.8; Al₂O₃ = 0.9–3.6 wt%). Their convex upward rare earth element patterns, along with lower Ni contents (334–389 ppm) indicate that they were cumulates fractionated from basaltic magmas circulating through the upper mantle. The trace element patterns of clinopyroxenes from three phlogopite-free websterites show enrichment in large ion lithophile and negative anomalies for the high field strength elements. In addition, the phlogopite-free websterite clinopyroxene Sr-Nd-Hf isotope ratios plot in the enriched lithospheric field (⁸⁷Sr/⁸⁶Sr = 0.7058–0.7061, εNd = −9.2 to −8.4 and εHf = −5.2 to −3.7 respectively), which implies the contribution of recycled lower crustal materials to their source. The presence of phlogopite in some Sanyitang websterites, coupled with strong enrichments in both light rare earth elements and large ion lithophile elements, as well as high ⁸⁷Sr/⁸⁶Sr (0.7065–0.7068) and negative εNd (−1.5 to −0.3) and εHf (−6.1 to −4.8) values of clinopyroxene, provide strong evidence for the existence of subduction-related hydrous fluids/melts metasomatism. This study demonstrates that the Sanyitang mantle xenoliths and their component minerals record the complex petrological history and local heterogeneity of the subcontinental mantle lithosphere under the western North China Craton.

本文报道了内蒙古缝合线新生代三义堂碱玄武岩中夹带的一组地幔异种岩中的岩石学，块状岩石和矿物中的主要和微量元素的丰度以及斜辉石Sr-Nd-Hf组成。目的是限制华北克拉通西部下方岩石圈地幔的性质和演化。三义塘地幔中的异岩主要是无水的尖晶石锂铁矿，具有次要的维氏体。尖晶石锂铁矿的岩石学和地球化学特征表明，它们是难熔的地幔残渣，是通过不同程度的熔体萃取（3–14％），随后的硅酸盐和碳酸盐交代作用形成的。对SR-的Nd-Hf同位素组合物（⁸⁷ SR / ⁸⁶ SR = 0.7031-0.7037，ε_钕 = 5.2 - 11.2和ε_的Hf  = 8.4 - 29.3）从多数尖晶石lherzolites躺在，或接近，通过海洋岛玄武岩和洋中脊的组合物所限定的地幔阵列的单斜辉石中隔离的玄武岩。另一方面，斜生辉石与少量尖晶石锂沸石（SYT09-01，SYT09-09，SYT11-01）分离，具有较高的⁸⁷ Sr / ⁸⁶ Sr（0.7040-0.7049），εNd（+12.4-+21.9）和εHf（ +58.2-+67.8），位于地幔阵列上方，反映了地幔的长期枯竭。韦氏菱铁矿的特征在于其MgO（18–22 wt％）和Al ₂ O ₃含量较高（4.5–5.6 wt％），以及Mg＃（86.2–87.3）低于尖晶石水沸石（Mg＃= 89.3–90.8;铝₂ O ₃ = 0.9–3.6 wt％）。它们向上凸出的稀土元素形态以及较低的镍含量（334-389 ppm）表明它们是从上地幔中循环的玄武岩浆中分离出来的堆积物。来自三种不含金云母的菱镁矿中斜向辉石的痕量元素模式显示，富集大离子的亲石剂和高场强元素的负异常。此外，在富集岩石圈中，不含金云母的镁橄榄石斜辉石Sr-Nd-Hf同位素比图（⁸⁷ Sr / ⁸⁶Sr = 0.7058-0.7061，εNd= -9.2至-8.4和εHf= -5.2至-3.7），这意味着回收的下地壳物质对其来源的贡献。在三一塘韦斯特岩中存在金云母，同时在轻稀土元素和大型离子亲石元素中都有丰富的富集，以及高⁸⁷ Sr / ⁸⁶ Sr（0.7065-0.7068）和负εNd（-1.5至-0.3）和Clinopyroxene的εHf（-6.1至-4.8）值提供了俯冲相关含水流体/熔体交代作用的有力证据。这项研究表明，三义塘地幔异岩及其组成矿物记录了华北克拉通西部地区次大陆幔岩石圈的复杂的岩石历史和局部非均质性。