01-05 December 2025
INCOIS, Hyderabad, India.
| Abstract Submission No. | ABS-06-0204 |
| Title of Abstract | Geochemistry of basement lavas in the Laxmi Basin, NW Indian Ocean: Implications for regional tectonics in South Asia during Late Cretaceous |
| Authors | Sibin Sebastian*, Jyotiranjan S Ray |
| Organisation | Physical Research Laboratory, Ahmedabad |
| Address | Physical Research Laboratory, Navrangpura Ahmedabad, Gujrat, India Pincode: 380009 E-mail: sibinpaulseb@gmail.com |
| Country | India |
| Presentation | Oral |
| Abstract | The Laxmi Basin is a prominent geomorphic feature and a marginal depression in the Northwest Indian Ocean. This ~300 km wide basin separates the western Indian continental margin from the Laxmi Ridge (LR), which is believed to be continental. The exact nature of the basin's basement remains debated, with different views suggesting it to be either a stretched continental crust with continental rift-related magmatic intrusions or a pre-Paleogene oceanic crust. Additionally, a geochemical study of the basin's igneous rocks, collected during IODP 355, proposes that these rocks formed in a subduction zone setting. Here, we present new geochemical and Nd-Sr-Pb isotopic data for the basaltic lava samples from this basement, recovered during IODP 355, to settle the controversy. The Primitive Mantle (PM)-normalized multi-element and chondrite-normalized rare-earth-element (REE) patterns of the lavas resemble those of typical mid-ocean ridge basalts (MORB). Their Nd and Sr isotopic compositions (εNd(t) = +5.6 to +6.2 and 87Sr/86Sr(t) = 0.7037 to 0.7039 at t = 72 My) fall within the depleted quadrant and overlap with those of present-day Central Indian Ridge (CIR) field on the εNd vs. 87Sr/86Sr diagram. Pb isotopic compositions (206Pb/204Pb = 17.571 to 17.944, 207Pb/204Pb = 15.469 to 15.674, and 208Pb/204Pb = 37.391 to 38.141) are also similar to CIR and preclude significant involvement of crustal materials. They are distinctly different in chemistry from the Deccan flood basalts and Reunion hotspot lavas. All our findings point to the presence of an MORB basement (oceanic crust) beneath the Laxmi Basin, making it a paleo- or extinct MOR. Considering earlier geophysical results, we infer that the formation of oceanic crust in the Laxmi Basin was driven by pre-Deccan rift-to-drift tectonics. The spreading in the basin likely ceased, possibly due to the separation of Seychelles and LR that led to the formation of the Carlsberg Ridge. |
| Are you part of IIOE-2 endorsed project | no |
| Keywords | Laxmi Basin, IODP, geochemistry, Nd-Sr-Pb isotopes, mid-oceanic ridge |
| For Awards | no |