Lamproites and kimberlites are natural probes of the subcontinental lithospheric mantle providing insights into the Earth’s continental lithosphere. Whole-rock major-, trace-element and Sr–Nd–Pb isotopic compositions of the Paleozoic (~ 253 Ma) lamproite dikes from the Baifen zone of the Zhenyuan area in southeastern Guizhou Province (in the southern Yangtze Block, South China) are presented. The Baifen lamproites are characterized by high MgO (7.84–14.1 wt%), K 2 O (3.94–5.07 wt%) and TiO 2 (2.69–3.23 wt%) contents, low SiO 2 (41.3–45.7 wt%), Na 2 O (0.21–0.28 wt%) and Al 2 O 3 (6.10–7.20 wt%) contents. All lamproites have elevated Cr (452–599 ppm) and Ni (485–549 ppm) abundances, as well as high Ba (1884–3589 ppm), La (160–186 ppm), Sr (898–1152 ppm) and Zr (532–632 ppm) concentrations. They show uniform REE distribution patterns that are strongly enriched in light REEs relative to heavy REEs [(La/Yb) N = 71.1–87.6], and exhibit OIB-like geochemical features with obvious enrichment of both LILEs and HFSEs in the primitive mantle-normalized multi-element distribution diagram. Moderately radiogenic Sr ( 87 Sr/ 86 Sr i = 0.706336–0.707439), unradiogenic Nd ( 143 Nd/ 144 Nd i = 0.511687–0.511704 and ε Nd ( t ) = − 12.2 to − 11.9), and low initial Pb ( 206 Pb/ 204 Pb i = 16.80–16.90, 207 Pb/ 204 Pb i = 15.34–15.35 and 208 Pb/ 204 Pb i = 37.43–37.70) isotopic compositions are obtained from the rocks. They yield old model ages of T DM (Nd) = 1.48–1.54 Ga. These signatures suggest that the Baifen lamproite magmas are alkaline, ultrapotassic and ultramafic in character and mainly represent mantle-derived primary melts, which have undergone insignificant crustal contamination and negligible fractional crystallization. The Baifen lamproites originated from a veined metasomatized lithospheric mantle source. We envisage that they were derived by partial melting of old, mineralogically complex metasomatic vein assemblages in the subcontinental lithospheric mantle beneath the southern Yangtze Block. The source region experienced ancient mantle metasomatism with complex modification by enriched fluids and melts. The metasomatic agents are most likely to originate from pre-existing slab subduction beneath the southeastern margin of the Yangtze Block. Tectonically, the Baifen lamproites were emplaced at the southern margin of the Yangtze Block, and they formed in an intraplate extensional setting, showing an anorogenic affinity. In terms of time and space, the genesis of Baifen lamproites is presumably related to the Emeishan large igneous province. The Emeishan mantle plume is suggested as an effective mechanism for rapid extension and thinning of the lithosphere, followed by decompression melting of the subcontinental lithospheric mantle. Combined with the thermal perturbation from asthenospheric upwelling induced by the Emeishan mantle plume, the lamproite magmas, representing small volume and limited partial melts of ancient enriched mantle lithosphere, arose. We propose that the generation of the Baifen lamproite dikes probably was a consequence of the far-field effects of the Emeishan mantle plume.

中文翻译：

---

华南扬子地块南部古生界菱镁矿成因和岩石成因的地球化学和Sr-Nd-Pb同位素约束

Lamproites 和金伯利岩是次大陆岩石圈地幔的天然探测器，可提供对地球大陆岩石圈的深入了解。贵州省东南部镇远地区白粉带（华南扬子地块南部）古生代（~253 Ma）菱镁矿脉的全岩主、微量元素和Sr-Nd-Pb同位素组成为呈现。Baifen 菱镁矿的特点是高 MgO (7.84–14.1 wt%)、K 2 O (3.94–5.07 wt%) 和 TiO 2 (2.69–3.23 wt%) 含量，低 SiO 2 (41.3–45.7 wt%)、Na 2 O (0.21–0.28 wt%) 和 Al 2 O 3 (6.10–7.20 wt%) 含量。所有菱镁矿的 Cr (452–599 ppm) 和 Ni (485–549 ppm) 丰度，以及高 Ba (1884–3589 ppm)、La (160–186 ppm)、Sr (898–1152 ppm) 和 Zr (532–632 ppm) 浓度。它们显示出均匀的 REE 分布模式，相对于重 REE，轻 REE 富集 [(La/Yb) N = 71.1–87.6]，并表现出类似 OIB 的地球化学特征，原始地幔中 LILE 和 HFSE 均明显富集归一化多元素分布图。中度放射成因 Sr ( 87 Sr/ 86 Sr i = 0.706336–0.707439)，非放射成因 Nd ( 143 Nd/ 144 Nd i = 0.511687–0.511704 和 ε Nd ( t ) = − 126.b 至 − 126.9. / 204 Pb i = 16.80–16.90、207 Pb/ 204 Pb i = 15.34–15.35 和 208 Pb/ 204 Pb i = 37.43–37.70) 同位素组成是从岩石中获得的。它们产生了 T DM (Nd) = 1.48-1.54 Ga 的旧模型年龄。这些特征表明白芬菱镁矿岩浆具有碱性、超钾质和超镁铁质特征，主要代表地幔来源的原生熔体，它们经历了微不足道的地壳污染和可忽略的分步结晶。白粉菱镁矿起源于脉状交代岩石圈地幔源。我们设想它们是由扬子地块南部下的次大陆岩石圈地幔中古老的、矿物学复杂的交代脉组合的部分熔融产生的。源区经历了古老的地幔交代作用，并受到富集流体和熔体的复杂改造。交代因子最有可能起源于扬子地块东南缘下预先存在的板片俯冲作用。构造上，白粉菱镁矿位于扬子地块南缘，形成于板内伸展环境，显示出造山亲缘关系。在时间和空间上，白粉菱镁矿的成因推测与峨眉山火成岩大省有关。峨眉山地幔柱被认为是岩石圈快速扩张和变薄的有效机制，随后是次大陆岩石圈地幔减压熔融。结合峨眉山地幔柱引起的软流圈上涌热扰动，产生了代表古代富集地幔岩石圈体积小、部分熔融有限的菱镁矿岩浆。我们认为白芬菱镁矿脉的产生可能是峨眉山地幔柱远场效应的结果。随后是次大陆岩石圈地幔的减压熔融。结合峨眉山地幔柱引起的软流圈上涌热扰动，产生了代表古代富集地幔岩石圈体积小、部分熔融有限的菱镁矿岩浆。我们认为白芬菱镁矿脉的产生可能是峨眉山地幔柱远场效应的结果。随后是次大陆岩石圈地幔的减压熔融。结合峨眉山地幔柱引起的软流圈上涌热扰动，产生了代表古代富集地幔岩石圈体积小、部分熔融有限的菱镁矿岩浆。我们认为白芬菱镁矿脉的产生可能是峨眉山地幔柱远场效应的结果。