Evidence of a Cenomanian carbonatite emplacement linked with the Marion mantle plume and breakup of India–Madagascar: Constraints from 40Ar-39Ar geochronology and geochemistry of carbonatite xenolith within the Ambadungar–Saidivasan carbonatite breccia, Western India

A carbonatite xenolith from a carbonatite breccia exposure within the Ambadungar-Saidivasan alkaline carbonatite complex in western India has been examined for its emplacement age, mineral chemistry, and whole-rock geochemistry. Although this complex is generally linked with magmatic activities of the Réunion plume, which produced the ca. 66.0–65.5 Ma Deccan large igneous province, the studied xenolith yields phlogopite ⁴⁰Ar/³⁹Ar weighted plateau age of 97.0 ± 2.2 Ma. This age predates the arrival of the Réunion plume and likely reflects the crystallization and emplacement age of the xenolith. The timing coincides with the main India-Madagascar breakup, driven by the Marion hotspot, which occurred between 92 and 88 Ma. However, evidence suggests that the Marion hotspot was active along the rifted eastern margin of Madagascar as early as 120 Ma, continuing until the breakup at ca. 88 Ma. Several magmatic events with ages ranging from 93 Ma to 86 Ma from both the Indian and Madagascar plates highlight a connection to the Marion plume. The new ⁴⁰Ar/³⁹Ar date for the carbonatite xenolith, previously unreported from this region, along with its geochemical characteristics, suggests an association with early magmatic activity of the Marion plume, likely predating the rift and breakup phases. In addition to the older age, the carbonatite xenolith is distinguished from the other associated carbonatites by its higher Rb content (20 ppm) and a spoon-shaped HREE. These findings, along with existing geochronological and geophysical evidence, support the presence of the Marion hotspot beneath the western margin of the Indian Shield and the eastern margin of the Madagascar plate, driving widespread magmatism beginning as early as 120 Ma or potentially earlier.