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

Abstract

Analysis of new and existing geophysical data for the Central Indian and Wharton Basins of the Indian Ocean were used to understand the formation and evolution of the Ninetyeast Ridge (NER), especially its relationship to the Kerguelen hot spot and the Wharton spreading ridge. Satellite gravity data and magnetic anomalies 34 through 19 define crustal isochrons and show fracture zones striking ∼N5°E. One of these, at 89°E, crosses the ∼N10°E trending NER, impacting the NER morphology. From 77 to 43 Ma the NER lengthened at a rate of ∼118 km/Myr, twice that of the ∼48–58 km/Myr accretion rate of adjacent oceanic crust. This difference can be explained by southward jumps of the Wharton spreading ridge toward the hot spot, which transferred portions of crust from the Antarctic plate to the Indian plate, lengthening the NER. Magnetic anomalies document a small number of large spreading ridge jumps in the ocean crust immediately to the west of the NER, especially two leaving observable 65 and 42 Ma fossil spreading ridges. In contrast, complex magnetic anomaly progressions and morphology imply that smaller spreading ridge jumps occurred at more frequent intervals beneath the NER. Comparison of the NER dates and magnetic anomaly ages implies that the hot spot first emplaced NER volcanoes on the Indian plate at a distance from the Wharton Ridge, but as the northward drifting spreading ridge approached the hot spot, the two interacted, keeping later NER volcanism near the spreading ridge crest by spreading center jumps.

Lithosphere structure and upper mantle characteristics below the Bay of Bengal

“…Earlier derived crustal models show the presence of thicker crust with and without underplating below these ridges (Detrick and Watts, 1979;Mukhopadhyay and Krishna, 1995;Subrahmanyam et al, 1999;Grevemeyer et al, 2001;Krishna et al, 2001b;Krishna, 2003;Subrahmanyam et al, 2008;Radhakrishna et al, 2010). The present analysis revealed that both ridges, in general, are earlier investigators for the ridge south of 2ºN revealed that this part of the ridge had evolved due to frequent ridge jumps in the vicinity of the Kerguelen hot spot during the rapid northward migration of the Wharton spreading ridge (Royer et al, 1991;Krishna et al, 1999;Sager et al, 2010;Krishna et al, 2012). The modeled lithosphere structure across these ridges suggests a lack of plume impact at the LAB, although there is minor eastward thinning beneath the Ninetyeast Ridge.…”

Active faulting on the Ninetyeast Ridge and its relation to deformation of the Indo‐Australian plate

“…The hot spot was often located near the spreading ridge [ Sager et al ., ; Krishna et al ., ] and changes in NER morphology may be related to the proximity of the hot spot to the spreading ridge [ Royer et al ., ]. Because of its near‐ridge location, the hot spot emplaced material on both the Indian and Antarctic plates, with most of the volcanic product ending up on the India plate owing to repeated southward ridge jumps [ Krishna et al ., ]. Nevertheless, the hot spot volcanism produced a remarkably linear age progression that ranges from 77 Ma at Ocean Drilling Program (ODP) Site 758, in the northern NER, to 43 Ma at Deep Sea Drilling Project (DSDP) Site 254 in the southern NER [ Krishna et al ., ].…”

“…Many different authors have explained the formation of the NER as a result of various tectonic anomalies [see review by Royer et al ., ], but the modern consensus is that it was created by hot spot volcanism that emplaced a ridge on the northward drifting Indian plate from Late Cretaceous to early Cenozoic time [ Royer et al ., ; Krishna et al ., ]. The hot spot was often located near the spreading ridge [ Sager et al ., ; Krishna et al ., ] and changes in NER morphology may be related to the proximity of the hot spot to the spreading ridge [ Royer et al ., ]. Because of its near‐ridge location, the hot spot emplaced material on both the Indian and Antarctic plates, with most of the volcanic product ending up on the India plate owing to repeated southward ridge jumps [ Krishna et al ., ].…”

“…Because of its near‐ridge location, the hot spot emplaced material on both the Indian and Antarctic plates, with most of the volcanic product ending up on the India plate owing to repeated southward ridge jumps [ Krishna et al ., ]. Nevertheless, the hot spot volcanism produced a remarkably linear age progression that ranges from 77 Ma at Ocean Drilling Program (ODP) Site 758, in the northern NER, to 43 Ma at Deep Sea Drilling Project (DSDP) Site 254 in the southern NER [ Krishna et al ., ]. At ~42 Ma, the large‐scale reorganization of spreading centers that brought together the India and Australia plates also moved the hot spot permanently beneath the Antarctic plate, ceasing the NER formation [ Royer et al ., ; Krishna et al ., ].…”

Ridge-push force and the state of stress in the Nubia-Somalia plate system

“…It is possible that the presence of fossil ridges may affect the thermal evolution of the oceanic lithosphere. In the Indo-Australian plate, for example, the fossil ridge segments of the Wharton and Central Indian Basins are documented to have ceased spreading between 65 and 42 Ma (Krishna et al, 2012), and the effects of the fossil ridge on the present thermal structure of the plate are not considered to be significant (unless existing fracture zones are reactivated by the occurrences of nearby earthquakes). In the Africa plate, however, there is a lack of fossil ridge segments, and therefore this effect is considered to be negligible.…”