Paleomagnetic evidence of synchronous emplacement of Deccan dykes along the Narmada-Son Lineament witnessing the magnetic reversal

The Deccan Continental Flood Basalts (DCFB) are associated with three major dyke swarms: the Narmada-Satpura-Tapi (N-S-T), the Western Coastal, and the Nasik-Pune swarms. The DCFB around Pachmarhi is characterized by a lower Magnesium number (Mg#) and higher TiO₂ content, suggesting a more evolved composition compared to other Deccan basalts. Located in the eastern segment of the N-S-T swarms, the Pachmarhi dyke swarms comprise approximately 244 mapped doleritic and basaltic dykes, with lengths ranging from 140 m to 22 km, averaging ~5.15 km. These dykes are emplaced along pre-existing fractures and predominantly exhibit an E-W orientation. Petrographic and rock magnetic analyses indicate that the primary remanence carriers are high- and low-titanium magnetite particles, primarily in the pseudo-single domain state, with a minor contribution from multi-domain grains.

Paleomagnetic studies have been conducted on 12 dykes, revealing that five exhibit normal polarity while seven display reverse polarity. The normal-polarity dykes are characterized by a mean ChRM direction of D_m = 332°, I_m = -39.8° (k = 90.24, α₉₅ = 8.16°, N = 32), whereas the reverse-polarity dykes exhibit D_m = 156.1°, I_m = 38.1° (k = 55.4, α₉₅ = 8.02°, N = 63). The combined mean ChRM direction has been determined as D_m ≈ 334° and I_m ≈ -38.95° (k = 72.82, α₉₅ = 8.09°, N = 95). The calculated paleopole for the Pachmarhi dykes (37.97° N, 88.38° W) closely corresponds to that of the Nandurbar-Dhule (N-D) dykes (38.3° N, 79.9° W), which represent the western segment of the N-S-T dykes. The averaged paleopole position (38.14° N, 83.84° W) aligns well with the Deccan Superpole (36.96° N, 78.7° W). This similarity suggests that the emplacement of these dykes occurred synchronously during the late stages of Deccan volcanism. The Pachmarhi dykes with normal polarity have been tentatively linked to magnetic chron 29N, while those with reverse polarity correspond to chron 29R. It is inferred that these dykes may have fed late-stage Deccan flow units, such as the Ambenali and Mahabaleshwar formations of the Wai Subgroup. The paleolatitudes of the Pachmarhi (22.4° S) and N-D (25.4° S) dykes indicate minimal latitudinal variation, supporting the hypothesis of near-synchronous emplacement across the Narmada-Son-Lineament (NSL) region.