Evolution of the Late Cretaceous crust in the equatorial region of the Northern Indian Ocean and its implication in understanding the plate kinematics

Abstract

S U M M A R YAnalysis of 3100 km of newly acquired marine magnetic data, constrained by satellite and shipborne free air gravity anomalies, in the corridor between the 86 • E fracture zone (FZ) and Ninetyeast Ridge, north of the equator reveals the evolutionary history of the Late Cretaceous crust characterized by anomaly 34 through 31 (83.5-68.7 Ma) under complex tectonic settings. Seafloor spreading model studies suggest that the crust, particularly between the chrons 33R and 33 (79.0-73.6 Ma), was formed with variable and slightly higher half-spreading rates (4.8-7.1 cm yr −1 ) than the crust of similar age either in the regions west of 86 • E FZ or east of the Ninetyeast Ridge or the Southern Crozet Basin. Further, the interpretation of magnetic anomalies suggests the presence of fossil spreading ridge segments and extra oceanic crust on the Indian plate that has been transferred from the Antarctica plate by discrete southward ridge jumps. These ridge jumps are caused by thermal instability of the spreading centre as the Indian plate moved northward over the Kerguelen mantle plume. The present study indicates that the spreading ridge-plume interaction is the prime mechanism for these ridge jumps, which have occurred since 75.8 Ma. The newly identified magnetic anomalies 34 through 31 and the inferred ∼N3 • E trending FZs refined the plate reconstruction models for that period.

Large fault fabric of the Ninetyeast Ridge implies near‐spreading ridge formation

“…Moreover, repeated small ridge jumps would give the appearance of a linear age progression with coarse age sampling. This hypothesis fits with a trend that more detailed studies of magnetic lineations have defined smaller southward ridge jumps within NER [Krishna et al, 1999;Desa et al, 2009]. Unfortunately, it is currently impossible to confirm this hypothesis with magnetic anomalies alone because magnetic data are sparse in the region and anomalies over NER are difficult to interpret [Krishna et al, 1999;Desa et al, 2009].…”

“…Clearly the ridge has had a complex tectonic history. It has already been hypothesized that NER evolution was complicated by ridge jumps [Royer et al, 1991;Pilipenko, 1996;Krishna et al, 1999;Desa et al, 2009] and this mechanism may explain the observed faulting as well as the discrepancy between the length of the NER and the observed linear age trend [Pringle et al, 2008].…”

Tectonics of the Ninetyeast Ridge derived from spreading records in adjacent oceanic basins and age constraints of the ridge

“…Our interpretation of the magnetic data set in basins adjacent to the NER is a small number of larger ridge jumps. However, both Krishna et al [1999] and Desa et al [2009] have mapped smaller southward ridge jumps near the NER at ∼76 and 54 Ma, respectively. Sager et al [2010]concluded, on the basis of identification of extensive faulting within the NER structure, that numerous small‐scale ridge jumps may have occurred and that the hot spot and Wharton spreading ridge may have remained in close proximity.…”

Late Cretaceous bioconnections between Indo-Madagascar and Antarctica: refutation of the Gunnerus Ridge causeway hypothesis

“…(2010) have recently questioned this general interpretation, and instead contend that the seafloor there began forming sometime after M0. Such a revision inevitably also challenges the anomaly assignments proposed for the conjugate basin southeast of Sri Lanka (Desa et al. , 2006, 2009).…”