Transform Marginal Plateaus

Abstract

Numerous submarine plateaus form highstanding bathymetric highs at continent to ocean transitions. Due to their proximity to continents, they have been frequently labelled "marginal plateaus", although this term has not been clearly defined or associated with a specific geology or geodynamic process. Until now, these elevations have been interpreted as submerged thinned continental fragments detached from continents, basaltic buildups formed by hotspots, volcanic margins or oceanic plateaus. Many of these plateaus formed at transform margins connecting oceanic basins of contrasted ages. We propose for the first time to define and review a class of marginal plateaus related to a specific tectonic setting: "Transform Marginal Plateaus" (TMPs). Based on a compilation of 20 TMPs around the world, we show that most of them have a polyphased history and have undergone at least one major volcanic phase. Our review highlights in particular a hitherto unrecognized close link between hotspots, volcanic activity and transform margins. We also propose that, due to their polyphased history, TMPs may contain several successive basins and overlooked long-lived sedimentary archives. We finally highlight that, because these TMPs were transform plate boundaries perpendicular or oblique to surrounding rifts, many of them were close to lastcontact points during final continental breakup and may have formed land bridges or bathymetric highs between continents. Therefore, we discuss broader scientific issues, such as the interest of TMPs in recording and studying the onset and variations of oceanic currents or past biodiversity growth, bioconnectivity and lineage evolution.

Deep structure of the Demerara Plateau: From a volcanic margin to a Transform Marginal Plateau

“…They are often located at the junction between two oceanic domains of different ages (Mercier de Lepinay et al, 2016). Recently, the sub-category of Transform Marginal Plateaus (TMP) was defined, for those marginal plateaus bordered by at least one transform or oblique margin (Loncke et al, 2019). According to these authors, most of these plateaus are associated with at least one major volcanic event during their evolution.…”

Evaluating the segmented post-rift stratigraphic architecture of the Guyanas continental margin

“…The Demerara Rise and its conjugate, the Guinea Plateau, is thought to have formed a focal point for hot spot magmatism (CAMP or Bahamas hotspot related) during the early stages of the Central Atlantic opening, potentially creating a volcanic accumulation up to 21 km thick (Reuber et al, 2016;Long et al, 2018;Zinecker Mann, 2020). These submarine plateaus are clearly identifiable in present-day bathymetric maps, being a testament to the longstanding influence this basement configuration had on the bathymetry and ultimately, the segmentation of the continental margin, as observed on other TMPs worldwide (Loncke et al, 2019). The location of the volcanism in the southeastern Central Atlantic has been interpreted as creating a 'pinning point' for the final fragmentation of Gondwana and the breakup of the Equatorial Atlantic segment (Pindell, 1985;Greenroyd et al, 2007Greenroyd et al, , 2008aBasile et al, 2013).…”

“…seaward dipping. The interpreted basaltic flows have either been associated with the migrating Bahamas hotspot (Morgan, 1983) during early opening of the Central Atlantic (~158 Ma; Reuber et al, 2016), or related to the Central Atlantic Magmatic Province (CAMP) volcanism (~200 Ma; Loncke et al, 2019). Volcanism is further supported by recovered dredge samples of Jurassic-aged (173.4 ± 1.6 Ma) rhyolites and basalts from the Demerara Rise (white star -Fig.…”

Superimposed Rifting at the Junction of the Central and Equatorial Atlantic: Formation of the Passive Margin of the Guiana Shield

“…The Equatorial break‐up unconformity (EABU) and first oceanic crust are considered as Albian in age (ca. 107–100 Ma) east of the Demerara Plateau (Sapin et al., 2016; Loncke et al., 2020; Mercier de Lépinay, 2016), in the FOZ basin (Brandão & Feijó, 1994; Figueiredo et al., 2007), in the Marajo basin (Zalán & Matsuda, 2007) and along the conjugate African margin (Mascle & Blarez, 1987; Moullade et al., 1993; Ye et al., 2017). Some authors consider the oceanic crust is slightly younger (Aptian; Basile, 2015).…”