Seaward dipping reflectors along the SW continental margin of India: Evidence for volcanic passive margin

Abstract

Multi-channel seismic reflection profiles across the southwest continental margin of India (SWCMI) show presence of westerly dipping seismic reflectors beneath sedimentary strata along the western flank of the Laccadive Ridge -northernmost part of the Chagos-Laccadive Ridge system. Velocity structure, seismic character, 2D gravity model and geographic locations of the dipping reflectors suggest that these reflectors are volcanic in origin, which are interpreted as Seaward Dipping Reflectors (SDRs).The SDRs; 15 to 27 km wide overlain by ∼ 1 km thick sediment; are observed at three locations and characterized by stack of laterally continuous, divergent and off-lapping reflectors. Occurrence of SDRs along western flank of the Laccadive Ridge adjacent to oceanic crust of the Arabian Basin and 2D crustal model deduced from free-air gravity anomaly suggest that they are genetically related to incipient volcanism during separation of Madagascar from India.We suggest that (i) SWCMI is a volcanic passive margin developed during India-Madagascar breakup in the Late Cretaceous, and (ii) continent-ocean transition lies at western margin of the Laccadive Ridge, west of feather edge of the SDRs. Occurrence of SDRs on western flank of the Laccadive Ridge and inferred zone of transition from continent to ocean further suggest continental nature of crust of the Laccadive Ridge.

Structure and tectonics of the continental margins of India and the adjacent deep ocean basins: current status of knowledge and some unresolved problems

“…Chaubey et al (2002b) considered this basin to represent a failed rift with volcanism on a stretched continental regime, based on their deductions of rotated fault blocks akin to half graben. Considering the presence of seaward dipping reflectors (SDRs) west of the Laccadive Plateau and the derived crustal configuration from the forward modelling of the gravity data, Ajay et al (2010) inferred that the continent-ocean boundary in this region lies west of the Laccadive Plateau implying that the Laccadive Basin is continental in nature. Yatheesh et al (2013b) demonstrated that the Laccadive Basin region could be explained either in terms of a much thinned continental crust or as anomalously thick oceanic crust, based on forward modelling of the gravity profiles.…”

Crustal-scale architecture and segmentation of the South Atlantic volcanic margin

“…6) was constructed in order to constrain the seismic interpretation with crustal densities derived from refraction velocities obtained in the southern South Atlantic margin (Leyden et al 1971), average velocities for volcanic and igneous rocks related to the Serra Geral and Entendeka large igneous provinces, refraction from SDR edges offshore India (e.g. Ajay et al 2010), and lower crust mantle refraction velocities obtained from different sources in the oceanic realm. The gravity and magnetic anomalies cross-plotted along the profile (Fig.…”

Morphotectonic architecture of an India–Madagascar breakup related anomalous submarine terrace complex on the southwest continental margin of India

“…The average thickness of these layers in each domain, i.e., Laccadive Basin, ATTC and continental shelf/slope, were assumed using the seismic section/drill hole information as guide. The densities for these sediment layers were estimated based on the velocityedensity relationship of Ludwig et al (1970) Some researchers (Biswas and Singh, 1988) considered this region to be underlain by oceanic crust, while others Ajay et al, 2010) considered a thinned continental crust. We also noted that no dependable constraints, such as, crustal velocity structure based on seismic studies or identified seafloor spreading type magnetic anomalies, are available to resolve the ambiguity about the nature of crust underlying the Laccadive Basin.…”