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Improved Quantification of the Volume and Distribution of Water in Incoming Upper Oceanic Crust of Subduction Zones Using Long Offset Streamer Data

Description: 

Water carried by the downgoing oceanic plate is known to influence subduction zone processes such as megathrust slip behavior and arc magmatism. Yet, the volume and distribution of water transported into subduction zones often remain elusive despite recent progress. The water content in the oceanic crust either in the form of free water or hydrous minerals varies between subduction zones as water content depends on the full lifecycle of oceanic plates, from accretionary processes at the ridge axis to their bending outboard of the trench axis as well as their thermal structure and the thickness of the sediment cover.

Here we focus on estimating free water content present in upper oceanic crust of three subduction zones: the Sumatran, Alaska Peninsula and Mexican subduction zones. The age of oceanic lithosphere, thickness of sediments, and extent of intraplate deformation vary significantly between these locales. We use long-offset streamer data to examine the upper oceanic crust; reflection imaging is used to illuminate faulting and layer 2 properties, and downward extrapolation of the wavefield followed by traveltime tomography and differential effective medium theory is used to constrain velocities and water content. Results from the mature incoming plates offshore Alaska and Sumatra show that the uppermost crust is significantly hydrated in both areas but that the mechanisms for hydration are different. Offshore the Alaska Peninsula, the water content increases towards the trench suggesting that bending faults facilitate the ingress of water there. Offshore Sumatra, we mostly relate the high-water content in the uppermost crust (Layer 2A) and heterogeneous hydration within Layer 2B to the widespread intraplate deformation of the Indo-Australian plate. Analysis of the long streamer data from the Mexican subduction zone across the young, sediment-starved Cocos oceanic plate is ongoing. Preliminary results will be presented at this meeting and water estimates will be compared to those from Alaska and Sumatra to better understand major controls on crustal hydration prior to subduction.

Session: Subduction Zone Structure From Trench to Arc

Type: Oral

Date: 4/19/2023

Presentation Time: 08:00 AM (local time)

Presenting Author: Anne Becel

Student Presenter: No

Invited Presentation: Yes

Authors