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Evolution of the thermal and dehydration state of sediments entering the North Sumatra Subduction Zone

Evolution of the thermal and dehydration state of sediments entering the North Sumatra Subduction Zone
Evolution of the thermal and dehydration state of sediments entering the North Sumatra Subduction Zone
Shallow slip on the plate-boundary fault during the 2004 Mw 9.2 Aceh-Andaman Earthquake, offshore North Sumatra, has been linked to thick incoming sediments on the oceanic plate with advanced diagenetic and sediment property changes at the depths of plate boundary fault development. We couple age control, physical and thermal property measurements from International Ocean Discovery Program (IODP) drilling with multichannel seismic reflection data to reconstruct the thermal structure and evolution of the incoming sediment column, up to the point of accretion/subduction. Lithospheric thermal rejuvenation around 58 Ma is required to explain anomalously high heat flux at IODP Site U1480, and heat flux within the trench is suppressed by very high sediment accumulation rates during development of a thick trench wedge. Accumulation of up to ~4.5 km of thick Nicobar Fan and trench wedge sediments produces temperatures >150 °C within the basal sediments where the décollement develops, resulting in total pre-subduction diagenetic dehydration of basal sediments. The smectite-illite transformation within these basal sediments produces sufficient fluid to explain a polarity reversal on a pre-décollement reflector. We suggest that the boundary between basal-pelagic and siliclastic-fan sediments has trapped fluid over the last ~1 Myr, as a result of primary lithological properties, diagenetic fluid release and cementation, controlling décollement formation at this weakened level. Pre-subduction dehydration of large portions of the accreted sediment column strengthens the décollement beneath the prism, extending co-seismic velocity-weakening behaviour close to the trench, which may occur at other subduction zones with similar sediment compositions, thicknesses and/or temperatures.
IODP, Subduction, thermal modeling, Seismic reflection
1525-2027
Stevens, Duncan Eliott
d8a1aedd-186d-47d5-a849-6c39fc9f0a1d
Henstock, Timothy
27c450a4-3e6b-41f8-97f9-4e0e181400bb
Mcneill, Lisa
1fe6a1e0-ca1a-4b6f-8469-309d0f9de0cf
Stevens, Duncan Eliott
d8a1aedd-186d-47d5-a849-6c39fc9f0a1d
Henstock, Timothy
27c450a4-3e6b-41f8-97f9-4e0e181400bb
Mcneill, Lisa
1fe6a1e0-ca1a-4b6f-8469-309d0f9de0cf

Stevens, Duncan Eliott, Henstock, Timothy and Mcneill, Lisa (2021) Evolution of the thermal and dehydration state of sediments entering the North Sumatra Subduction Zone. G3: Geochemistry, Geophysics, Geosystems, 22 (4), [e2020GC009306]. (doi:10.1029/2020GC009306).

Record type: Article

Abstract

Shallow slip on the plate-boundary fault during the 2004 Mw 9.2 Aceh-Andaman Earthquake, offshore North Sumatra, has been linked to thick incoming sediments on the oceanic plate with advanced diagenetic and sediment property changes at the depths of plate boundary fault development. We couple age control, physical and thermal property measurements from International Ocean Discovery Program (IODP) drilling with multichannel seismic reflection data to reconstruct the thermal structure and evolution of the incoming sediment column, up to the point of accretion/subduction. Lithospheric thermal rejuvenation around 58 Ma is required to explain anomalously high heat flux at IODP Site U1480, and heat flux within the trench is suppressed by very high sediment accumulation rates during development of a thick trench wedge. Accumulation of up to ~4.5 km of thick Nicobar Fan and trench wedge sediments produces temperatures >150 °C within the basal sediments where the décollement develops, resulting in total pre-subduction diagenetic dehydration of basal sediments. The smectite-illite transformation within these basal sediments produces sufficient fluid to explain a polarity reversal on a pre-décollement reflector. We suggest that the boundary between basal-pelagic and siliclastic-fan sediments has trapped fluid over the last ~1 Myr, as a result of primary lithological properties, diagenetic fluid release and cementation, controlling décollement formation at this weakened level. Pre-subduction dehydration of large portions of the accreted sediment column strengthens the décollement beneath the prism, extending co-seismic velocity-weakening behaviour close to the trench, which may occur at other subduction zones with similar sediment compositions, thicknesses and/or temperatures.

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Stevens_et_al-2021-G-Cubed - Accepted Manuscript
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More information

Accepted/In Press date: 15 March 2021
e-pub ahead of print date: 22 March 2021
Published date: 22 March 2021
Keywords: IODP, Subduction, thermal modeling, Seismic reflection

Identifiers

Local EPrints ID: 448102
URI: http://eprints.soton.ac.uk/id/eprint/448102
ISSN: 1525-2027
PURE UUID: ec86e4d8-90d5-49e8-9215-fbfaf8d6c713
ORCID for Timothy Henstock: ORCID iD orcid.org/0000-0002-2132-2514

Catalogue record

Date deposited: 01 Apr 2021 15:58
Last modified: 27 Apr 2021 01:37

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