Seismic velocity structure of seaward-dipping reflectors on the South American continental margin

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Title: Seismic velocity structure of seaward-dipping reflectors on the South American continental margin
Authors: McDermott, C
Collier, JS
Lonergan, L
Fruehn, J
Bellingham, P
Item Type: Journal Article
Abstract: Seaward dipping reflectors (SDRs) are a key feature within the continent to ocean transition zone of volcanic passive margins. Here we conduct an automated pre-stack depth-migration imaging analysis of commercial seismic data from the volcanic margins of South America. The method used an isotropic, ray-based approach of iterative velocity model building based on the travel time inversion of residual pre-stack depth migration move-out. We find two distinct seismic velocity patterns within the SDRs. While both types show a general increase in velocity with depth consistent with expected compaction and alteration/metamorphic trends, those SDRs that lie within faulted half grabens also have high velocity zones at their down-dip ends. The velocity anomalies are generally concordant with the reflectivity and so we attribute them to the presence of dolerite sills that were injected into the lava pile. The sills therefore result from late-stage melt delivery along the large landward-dipping faults that bound them. In contrast the more outboard SDRs show no velocity anomalies, are more uniform spatially and have unfaulted basal contacts. Our observations imply that the SDRs document a major change in rift architecture, with magmatism linked with early extension and faulting of the upper brittle crust transitioning into more organised, dike-fed eruptions similar to seafloor spreading.
Issue Date: 1-Sep-2019
Date of Acceptance: 31-May-2019
ISSN: 0012-821X
Publisher: Elsevier
Start Page: 14
End Page: 24
Journal / Book Title: Earth and Planetary Science Letters
Volume: 521
Copyright Statement: © 2019 Elsevier Ltd. All rights reserved. This manuscript is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International Licence
Keywords: 02 Physical Sciences
04 Earth Sciences
Geochemistry & Geophysics
Publication Status: Published
Embargo Date: 2020-06-17
Online Publication Date: 2019-06-17
Appears in Collections:Earth Science and Engineering

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