New geochemical and geochronological data lead to a fuller understanding of different aspects of the Rajmahal flood basalt province. Earlier work was on surface Rajmahal flows as well as from the nearby Bengal Traps. Samples from a ~300 m borehole near the northwestern corner of the Rajmahal lavas, analyzed herein, reveal the presence of carbonatitic (aillikitic) material. This small province, including the Bengal Traps, thus exhibits quartz and olivine tholeiites, andesitic basalts, alkali basalts as well as carbonatitic material. The Sylhet Traps, lying ~500 km to the east of the surface Rajmahal flows, show geochemical similarities, but were probably formed ~10 Myr after Rajmahal volcanism. Sr–Nd isotopic plots suggest that (a) not all lavas in the Rajmahal Traps were homogenized isotopically prior to eruption and (b) the Sylhet Traps show a much wider variety of isotopic values at eruption, possibly caused by alteration. Published and new ⁴⁰Ar/³⁹Ar ages for both the Rajmahal and other mafic rocks postulated to have been formed by the Kerguelen Hotspot in the Southern Indian Ocean, are critically examined; emphasis is placed on the freshness of the rocks dated. It is shown that a number of ‘ages’ for both the Rajmahal Province, and for rocks recovered from the Kerguelen Plateau area, should be rejected as invalid measures of the time of crystallization, as altered material was dated. For the surface Rajmahal material, valid ages span ~120 (quartz tholeiites) to ~116 Ma (andesitic basalts); alkali basalts and olivine tholeiites (Bengal Traps) as well as the aillikite were also formed within this time interval. The postulated genetic link to the Kerguelen Hotspot and basalts in the Southern Indian Ocean appears valid; in particular, a section of the southern Kerguelen Plateau (~58°S; 75°E) has strong geochemical and temporal links to the Rajmahal Traps.

新的地球化学和地质年代学数据使人们更全面地了解 Rajmahal 洪水玄武岩省的不同方面。早期的工作是在地表 Rajmahal 流以及来自附近的孟加拉陷阱。本文分析的 Rajmahal 熔岩西北角附近一个约 300 m 钻孔的样品显示存在碳酸盐质（合立克质）物质。这个小省，包括孟加拉圈闭，因此展示了石英和橄榄石拉斑矿、安山玄武岩、碱性玄武岩以及碳酸​​盐岩材料。锡尔赫特圈闭位于 Rajmahal 地表流以东约 500 公里处，显示出地球化学相似性，但可能是在 Rajmahal 火山活动后约 10 Myr 形成的。Sr-Nd 同位素图表明（a）并非所有 Rajmahal 陷阱中的熔岩在喷发前都是同位素均质化的，（b）Sylhet 陷阱在喷发时显示出更广泛的同位素值，这可能是由改变引起的。已发布和新⁴⁰氩/ ³⁹Rajmahal 和其他被认为是由南印度洋的 Kerguelen 热点形成的基性岩的年龄都经过严格检查；重点放在年代久远的岩石的新鲜度上。结果表明，拉杰马哈尔省和从凯尔盖朗高原地区回收的岩石的许多“年龄”都应作为结晶时间的无效测量而被拒绝，因为改变的材料已经过时了。对于地表 Rajmahal 材料，有效年龄跨度为~120（石英拉斑矿）至~116 Ma（安山质玄武岩）；碱性玄武岩和橄榄石拉斑玄武岩（孟加拉圈闭）以及埃利石也在这段时间间隔内形成。与南印度洋 Kerguelen 热点和玄武岩的假定遗传联系似乎是有效的。特别是凯尔盖朗高原南部的一部分（~58°S；