The University of Southampton
University of Southampton Institutional Repository

Thin oceanic crust and flood basalts: India-Seychelles breakup

Thin oceanic crust and flood basalts: India-Seychelles breakup
Thin oceanic crust and flood basalts: India-Seychelles breakup
Recent seismic experiments showed that separation of India from the Seychelles occurred in two phases of rifting. The first brief phase of rifting between India and the Laxmi Ridge formed the Gop Rift, which is characterized by thick oceanic crust and underplating of the adjacent continental margins. The age of the Gop Rift is uncertain, initiation of seafloor spreading being some time between 71 and 66 Ma. This was then followed by rifting and seafloor spreading between the Laxmi Ridge and the Seychelles, the onset of which is well dated by magnetic anomalies at 63.4 Ma and characterized by thin oceanic crust. Both of these rift events occurred within 1000 km of the center of the Deccan flood basalts, which formed at 65 ± 1 Ma. To constrain the age of the Gop Rift and to explore the reasons for the change in crustal structure between the Gop Rift and Seychelles-Laxmi Ridge margins, we employ a geodynamic model of rift evolution in which melt volumes, seismic velocity, and rare earth element (REE) chemistry of the melt are estimated. We explore the consequences of different thermal structures, hydration, and depletion on the melt production during the India-Seychelles breakup to understand the reasons behind the thin oceanic crust observed. Magmatism at the Gop Rift is consistent with a model in which the seafloor spreading began at 71 Ma, ca. 6 Myr prior to the Deccan. The opening occurred above a hot mantle layer (temperature of 200°C, thickness of 50 km) that we interpret as incubated Deccan material, which had spread laterally beneath the lithosphere. This scenario is consistent with observed lower crustal seismic velocities of 7.4 km s?1 and 12 km igneous crustal thickness. The model indicates that when the seafloor spreading migrated to the Seychelles-Laxmi Ridge at 63 Ma, the thermal anomaly was reduced significantly but not sufficient to explain the observed reduction in breakup magmatism. From observations here of 5.2 km oceanic crust, lower crustal seismic velocities of 6.9 km s?1 and a flat REE profile, we infer that breakup occurred in a region of mantle that became depleted by prior extension related to the Gop Rift.
1525-2027
Q0AB07
Armitage, J.J.
05d47a3a-251b-495b-ad56-a6371c435d2a
Collier, J.S.
19dfa4bb-f743-4ca8-b15f-0f72f3f7263c
Minshull, T.A.
bf413fb5-849e-4389-acd7-0cb0d644e6b8
Henstock, T.J.
27c450a4-3e6b-41f8-97f9-4e0e181400bb
Armitage, J.J.
05d47a3a-251b-495b-ad56-a6371c435d2a
Collier, J.S.
19dfa4bb-f743-4ca8-b15f-0f72f3f7263c
Minshull, T.A.
bf413fb5-849e-4389-acd7-0cb0d644e6b8
Henstock, T.J.
27c450a4-3e6b-41f8-97f9-4e0e181400bb

Armitage, J.J., Collier, J.S., Minshull, T.A. and Henstock, T.J. (2011) Thin oceanic crust and flood basalts: India-Seychelles breakup. Geochemistry, Geophysics, Geosystems, 12, Q0AB07. (doi:10.1029/2010GC003316).

Record type: Article

Abstract

Recent seismic experiments showed that separation of India from the Seychelles occurred in two phases of rifting. The first brief phase of rifting between India and the Laxmi Ridge formed the Gop Rift, which is characterized by thick oceanic crust and underplating of the adjacent continental margins. The age of the Gop Rift is uncertain, initiation of seafloor spreading being some time between 71 and 66 Ma. This was then followed by rifting and seafloor spreading between the Laxmi Ridge and the Seychelles, the onset of which is well dated by magnetic anomalies at 63.4 Ma and characterized by thin oceanic crust. Both of these rift events occurred within 1000 km of the center of the Deccan flood basalts, which formed at 65 ± 1 Ma. To constrain the age of the Gop Rift and to explore the reasons for the change in crustal structure between the Gop Rift and Seychelles-Laxmi Ridge margins, we employ a geodynamic model of rift evolution in which melt volumes, seismic velocity, and rare earth element (REE) chemistry of the melt are estimated. We explore the consequences of different thermal structures, hydration, and depletion on the melt production during the India-Seychelles breakup to understand the reasons behind the thin oceanic crust observed. Magmatism at the Gop Rift is consistent with a model in which the seafloor spreading began at 71 Ma, ca. 6 Myr prior to the Deccan. The opening occurred above a hot mantle layer (temperature of 200°C, thickness of 50 km) that we interpret as incubated Deccan material, which had spread laterally beneath the lithosphere. This scenario is consistent with observed lower crustal seismic velocities of 7.4 km s?1 and 12 km igneous crustal thickness. The model indicates that when the seafloor spreading migrated to the Seychelles-Laxmi Ridge at 63 Ma, the thermal anomaly was reduced significantly but not sufficient to explain the observed reduction in breakup magmatism. From observations here of 5.2 km oceanic crust, lower crustal seismic velocities of 6.9 km s?1 and a flat REE profile, we infer that breakup occurred in a region of mantle that became depleted by prior extension related to the Gop Rift.

Text
armitage_et_al_2011.pdf - Version of Record
Download (3MB)

More information

Published date: 2011

Identifiers

Local EPrints ID: 186105
URI: https://eprints.soton.ac.uk/id/eprint/186105
ISSN: 1525-2027
PURE UUID: dcfcb0ac-781a-4c02-abbf-285b320a7092
ORCID for T.A. Minshull: ORCID iD orcid.org/0000-0002-8202-1379
ORCID for T.J. Henstock: ORCID iD orcid.org/0000-0002-2132-2514

Catalogue record

Date deposited: 12 May 2011 10:56
Last modified: 05 Nov 2019 01:55

Export record

Altmetrics

Download statistics

Downloads from ePrints over the past year. Other digital versions may also be available to download e.g. from the publisher's website.

View more statistics

Atom RSS 1.0 RSS 2.0

Contact ePrints Soton: eprints@soton.ac.uk

ePrints Soton supports OAI 2.0 with a base URL of https://eprints.soton.ac.uk/cgi/oai2

This repository has been built using EPrints software, developed at the University of Southampton, but available to everyone to use.

We use cookies to ensure that we give you the best experience on our website. If you continue without changing your settings, we will assume that you are happy to receive cookies on the University of Southampton website.

×