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Asymmetric Seafloor Spreading and Short Ridge Jumps in the Australian-Antarctic Discordance

Marks, Karen M. and Stock, Joann M. (1995) Asymmetric Seafloor Spreading and Short Ridge Jumps in the Australian-Antarctic Discordance. Marine Geophysical Researches, 17 (4). pp. 361-373. ISSN 0025-3235. doi:10.1007/BF01227040.

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The crenulated geometry of the Southeast Indian ridge within the Australian-Antarctic discordance is formed by numerous spreading ridge segments that are offset, alternately to the north and south, by transform faults. Suggested causes for these offsets, which largely developed since ~ 20 Ma, include asymmetric seafloor spreading, ridge jumps, and propagating rifts that have transferred seafloor from one flank of the spreading ridge to the other. Each of these processes has operated at different times in different locations of the discordance; here we document an instance where a small (~ 20 km), young (< 0.2 Ma), southward ridge jump has contributed to the observed asymmetry. When aeromagnetic anomalies from the Project Investigator-1 survey are superposed on gravity anomalies computed from Geosat GM and ERM data, we find that in segment B4 of the discordance (between 125° and 126° E), the roughly east-west-trending gravity low, correlated with the axial valley, is 20–25 km south of the ridge axis position inferred from the center of magnetic anomaly 1. Elsewhere in the discordance, the inferred locations of the ridge axis from magnetics and gravity are in excellent agreement. Ship track data confirm these observations: portions of Moana Wave track crossing the ridge in B4 show that a topographic valley correlated with the gravity anomaly low lies south of the center of magnetic anomaly 1; while other ship track data that cross the spreading ridge in segments B3 and B5 demonstrate good agreement between the axial valley, the gravity anomaly low, and the central magnetic anomaly. Based on these observations, we speculate that the ridge axis in B4 has recently jumped to the south, from a ridge location closer to the center of the young normally magnetized crust, to that of the gravity anomaly low. The position of the gravity low essentially at the edge of normally magnetized crust requires a very recent (< 0.2 Ma) arrival of the ridge in this new location. Because this ridge jump is so young, it may be a promising location for future detailed studies of the dynamics, kinematics, and thermal effects of ridge jumps.

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Stock, Joann M.0000-0003-4816-7865
Additional Information:© 1995 Kluwer Academic Publishers. Received 29 July, 1994: accepted 19 November, 1994. We wish to thank J.-C. Sempéré and B. West for providing digital bathymetry data from the SeaMARC II survey of the discordance. We also thank J.-C. Sempéré, G. Neumann, J. Weissel, and an anonymous reviewer whose suggestions led to improvements in this manuscript. This work was supported in part by the National Science Foundation grant EAR-92-96102 to J. Stock.
Group:Seismological Laboratory, Division of Geological and Planetary Sciences
Funding AgencyGrant Number
Subject Keywords:Australian-Antarctic discordance, ridge jump, asymmetric seafl oor spreading
Issue or Number:4
Record Number:CaltechAUTHORS:20140908-114127033
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:49345
Deposited By: Ruth Sustaita
Deposited On:09 Sep 2014 16:51
Last Modified:10 Nov 2021 18:42

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