The Rift and Continent‐Ocean Transition Structure Under the Tagus Abyssal Plain West of the Iberia

I Merino,M Prada,I Grevemeyer,C R Ranero,V SallarèS

doi:10.1029/2021jb022629

Abstract

AbstractThe West Iberia margin is the focus of intense research since the 1980s, with some of the most exemplary geophysical cross‐sections and drilling expeditions. Those data sets have been used to create conceptual models of rifting used as a template to interpret margins worldwide. We present two collocated ∼350 km long lines of multi‐channel seismic (MCS) streamer data and wide‐angle seismic (WAS) data collected across the Tagus Abyssal Plain (TAP). We use travel‐times of first arrivals identified at WAS and reflected seismic phases identified at both WAS and MCS records to jointly invert for the P wave velocity (Vp) distribution and the geometry of a sediment unconformity, the top of the basement, and the Moho boundary. The Vp model shows that the TAP basement is more complex than previously inferred, presenting abrupt boundaries between five domains. Domain I under the foot of the slope and Domain III under the abyssal plain display Vp values and gradients of thin continental crust. In between, Domain II displays a steep Vp gradient and high Vp values at shallow depth that support that basement is made of exhumed partly serpentinized mantle. Domain IV and Domain V, further oceanward, have oceanic crust Vp structure. The new results support an unanticipated complex rift history during the initial separation of Iberia and America. We propose a geodynamic scenario characterized by two phases of extension separated by a jump of the locus of extension, caused by the northward propagation of the oceanic spreading center during the J‐anomaly formation, which terminated continental rifting.

Highlights

IntroductionRifted continental margins are regions where extension processes led to continental extension, breakup, and seafloor spreading with the formation of oceanic crust
We present two collocated ∼350 km long lines of multi-channel seismic (MCS) streamer data and wide-angle seismic (WAS) data collected across the Tagus Abyssal Plain (TAP)
Rifted continental margins are regions where extension processes led to continental extension, breakup, and seafloor spreading with the formation of oceanic crust

Summary

Introduction

Rifted continental margins are regions where extension processes led to continental extension, breakup, and seafloor spreading with the formation of oceanic crust. Off Iberia continental breakup is not characterized by a sharp boundary but by a ∼100 km broad (e.g., Dean et al, 2000; Pickup et al, 1996) often rather complex transition zone, called the continent-ocean transition or COT. Geophysical efforts determined heterogeneity of the structure, rock physical properties, and tectonic style of the basement at a regional scale, defining the location and nature of the COT and the oldest oceanic crust (Whitmarsh et al, 1998). The West Iberia continental margin and COT became the type example of magma-poor systems that has been used as a template to interpret the structure of many other rifted systems where less information of the nature of the basement is available.

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