A Caltech Library Service

Evolution of the Australian-Antarctic discordance since Miocene time

Marks, Karen M. and Stock, Joann M. and Quinn, Katherine J. (1999) Evolution of the Australian-Antarctic discordance since Miocene time. Journal of Geophysical Research B, 104 (B3). pp. 4967-4981. ISSN 0148-0227. doi:10.1029/1998JB900075.

PDF - Published Version
See Usage Policy.


Use this Persistent URL to link to this item:


In this study we chronicle the development of the Australian-Antarctic discordance (AAD), the crenelated portion of the Southeast Indian Ridge between ∼120° and 128°E, since anomaly 6y time (19 Ma). We reconstruct satellite-derived marine gravity fields and depth anomalies at selected times by first removing anomalies overlying seafloor younger than the selected age, and then rotating the remaining anomalies through improved finite rotations based on a very detailed set of magnetic anomaly identifications. Our gravity field reconstructions reveal that the overall length of the Australian-Antarctic plate boundary within the AAD has been increasing since 19 Ma. Concomitantly, the number of propagating rifts and fracture zones in the vicinity of the discordance has increased dramatically in recent times, effectively dividing it into its present-day configuration of five distinct spreading corridors (B1-B5) that are offset alternately to the north and south and exhibit varying degrees of asymmetric spreading. Our bathymetric reconstructions show that the regional, arcuate-shaped, negative depth anomaly (deeper than predicted by normal lithospheric cooling models) presently centered on the discordance began migrating westward before anomaly 5ad time (∼14.4 Ma), and that a localized depth anomaly low, which at time 5ad lay on the ridge axis in spreading corridor B5, has been split apart by subsequent seafloor spreading. The magnetic anomaly patterns suggest that the depth anomaly is not always associated with a particularly contorted plate boundary geometry. Although the plate boundary within the AAD has been getting progressively more crenelated with time, this effect shows little to no migration along the ridge axis since 19 Ma. Thus any geodynamic models of the evolution of the discordance must account for the following observations: (1) the crenelation of the plate boundary within the AAD has increased with time, (2) the center of the crenelated zone does not appear to have migrated along the ridge crest, and (3) both the depth anomaly and the isotopic boundary between Pacific and Indian mantle have been migrating westward along the ridge axis but at apparently different rates. We suggest that both along-axis migration of the depth anomaly and isotopic boundary, as well as temporal variation in the upwelling mantle material beneath the AAD, and local tectonic effects are required in order to explain these observations.

Item Type:Article
Related URLs:
URLURL TypeDescription
Stock, Joann M.0000-0003-4816-7865
Additional Information:© 1999 American Geophysical Union. Manuscript Accepted: 21 Oct 1998; Manuscript Received: 22 Apr 1998. Reviews from Dietmar Mueller, Donna Jurdy, and an anonymous referee improved this manuscript. We thank J. Zachariasen for working on the finite rotation parameters for Chron 6y, and Amotz Agnon and Mike Gurnis for helpful discussions. This project was partially supported by NSF grant EAR-9296102 to J. M. Stock. K. Quinn's participation was supported by the Summer Undergraduate Research Fellowship (SURF) program of the California Institute of Technology. Contribution 8535, California Institute of Technology, Division of Geological and Planetary Sciences. The magnetic anomaly identifications, finite rotation parameters, and images of the reconstructions are available on the Worldwide Web site http://
Group:Seismological Laboratory
Funding AgencyGrant Number
Caltech Summer Undergraduate Research Fellowship (SURF)UNSPECIFIED
Subject Keywords:Geodesy and Gravity: Crustal movements—interplate; Gravity anomalies and Earth structure; Seismic methods; Tectonophysics: Plate motions—present and recent; Theory
Other Numbering System:
Other Numbering System NameOther Numbering System ID
Caltech Division of Geological and Planetary Sciences8535
Issue or Number:B3
Record Number:CaltechAUTHORS:20140415-124308456
Persistent URL:
Official Citation:Marks, K. M., J. M. Stock, and K. J. Quinn (1999), Evolution of the Australian-Antarctic discordance since Miocene time, J. Geophys. Res., 104(B3), 4967–4981, doi:10.1029/1998JB900075.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:44959
Deposited On:16 Apr 2014 23:22
Last Modified:10 Nov 2021 16:58

Repository Staff Only: item control page