Abstract NW-SE trending mafic dykes in the Bundelkhand Craton of the Indian shield manifest Palaeoproterozoic igneous activity. These dykes are Fe-rich tholeiitic basalts with compositions varying from near primary melts to more evolved magmas (Mg#: 0.64–0.35) and show enrichment of large-ion lithophile and light rare earth elements relative to primordial mantle values. Despite very subtle variations of elemental abundances and similar structural trend, at least two groups are identified, mainly based on incompatible element ratios and rare earth element patterns. Group 1 samples are characterized by relatively low Ti/Y (av. 222 ± 22) and Ti/Nb (av. 609 ± 108), high Zr/TiO2 (av. 117 ± 15), more light to heavy rare earth element fractionation (La/Yb)CN: 2.7–5.1) and mild negative Eu anomaly (Eu* = 0.77 ± 0.10). Group 2 samples possess high Ti/Y (av. 334 ± 46) and Ti/Nb (av. 1349 ± 198), low Zr/TiO2 (av. 70 ± 7) and minor light to heavy rare earth element fractionation ((La/Yb)CN: 1.5–2.7) without any Eu anomaly (Eu* = 0.97 ± 0.04). Both groups show relative depletions in Nb, Sr and P while the Group 1 also shows Ti depletion. A third group is apparent but is less certain. Group 2 dykes constitute the 1.98 Ga Jhansi swarm, whilst the Group 1 and unclassified samples are likely to be of older age (~2.18–2.20 Ga and ~2.37 Ga) based on available U-Pb ages and palaeomagnetic considerations. Despite the compositions indicate different batches of magma, the dykes have near similar petrogenetic evolutionary pattern as if the entire population constitutes a single clan. Samples of both groups (a) do not indicate significant crustal contamination (b) derived from two different batches of magmas formed by ~10–12% fractional melting of mantle near the spinel-garnet transition zone and (c) evolved through initial fractionation of olivine and thereafter clinopyroxene and plagioclase became important fractionation phases. The more primitive compositions of both groups indicate mantle potential temperatures of ~1550–1600 °C suggesting thermal anomaly. The dyke magmas inherited variably enriched compositions as a result of interaction of upwelling mantle melts with metasomatised subcontinental lithospheric mantle. Low H2O-CO2-rich silicate melts/fluids are likely the dominant metasomatic agents to develop the Indian subcontinental lithosphere in the Archaean (c. 3.0 Ga).

中文翻译：

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印度邦德尔坎德克拉通 NW-SE 走向的古元古代基性岩脉侵入体的地球化学：和次大陆岩石圈地幔过程

摘要 印度地盾邦德尔坎德克拉通 NW-SE 走向的基性岩脉表现出古元古代火成岩活动。这些岩脉是富含铁的拉斑玄武岩，其成分从接近原生熔体到更演化的岩浆（Mg#：0.64-0.35）不等，并且显示出相对于原始地幔值的大离子亲石物质和轻稀土元素的富集。尽管元素丰度的变化非常微妙，结构趋势相似，但至少确定了两组，主要基于不相容的元素比例和稀土元素模式。第 1 组样品的特点是相对较低的 Ti/Y (av. 222 ± 22) 和 Ti/Nb (av. 609 ± 108)、高 Zr/TiO2 (av. 117 ± 15)、更多的轻重稀土元素分馏(La/Yb)CN: 2.7–5.1) 和轻度负 Eu 异常 (Eu* = 0.77 ± 0.10)。第 2 组样品具有高 Ti/Y (av. 334 ± 46) 和 Ti/Nb (av. 1349 ± 198)、低 Zr/TiO2 (av. 70 ± 7) 和轻微的轻重稀土元素分馏 ((La/Yb)CN: 1.5–2.7)，没有任何Eu 异常（Eu* = 0.97 ± 0.04）。两组都显示出 Nb、Sr 和 P 的相对消耗，而第 1 组也显示出 Ti 消耗。第三组很明显，但不太确定。第 2 组岩脉构成 1.98 Ga Jhansi 群，而第 1 组和未分类的样本可能年龄较大（~2.18-2.20 Ga 和~2.37 Ga），基于可用的 U-Pb 年龄和古地磁考虑。尽管成分表明岩浆的批次不同，但这些岩脉的岩石演化模式几乎相似，就好像整个种群构成一个氏族一样。两组样品 (a) 均未表明明显的地壳污染 (b) 来自两批不同批次的岩浆，这些岩浆由尖晶石-石榴石过渡带附近约 10-12% 的地幔分馏形成，(c) 通过初始分馏演化而来橄榄石，其后单斜辉石和斜长石成为重要的分馏相。两组更原始的成分表明地幔潜在温度约为 1550-1600°C，表明存在热异常。由于上涌地幔熔体与交代的次大陆岩石圈地幔相互作用，岩脉岩浆继承了不同程度的富集成分。富含 H2O-CO2 的硅酸盐熔体/流体可能是太古宙（约 3.0 Ga）印度次大陆岩石圈发育的主要交代因子。