The final rifting evolution at deep magma-poor passive margins from Iberia-Newfoundland: a new point of view

Abstract

In classical rift models, deformation is either uniformly distributed leading to symmetric fault bounded basins overlying stretched ductile lower crust (e.g. pure shear McKenzie model) or asymmetric and controlled by large scale detachment faulting (simple shear Wernicke model). In both cases rifting is considered as a mono-phase process and breakup is instantaneous resulting in the juxtaposition of continental and oceanic crust. The contact between these two types of crusts is often assumed to be sharp and marked by a first magnetic anomaly; and breakup is considered to be recorded as a major, basin wide unconformity, also referred to as breakup unconformity. These classical models, are currently challenged by new data from deep rifted margins that ask for a revision of these concepts. In this paper, we review the pertinent observations made along the Iberia-Newfoundland conjugate margins, which bear the most complete data set available from deep magma-poor margins. We reevaluate and discuss the polyphase nature of continental rifting, discuss the nature and significance of the different margin domains and show how they document extreme crustal thinning, retardation of subsidence and a complex transition into seafloor spreading. Although our study is limited to the Iberia-Newfoundland margins, comparisons with other margins suggest that the described evolution is probably more common and applicable for a large number of rifted margins. These new results have major implications for plate kinematic reconstructions and invite to rethink the terminology, the processes, and the concepts that have been used to describe continental rifting and breakup of the lithosphere.

Oligocene–Miocene carbonates in the Reed Bank area, South China Sea, and their tectono-sedimentary evolution

“…9). Such a temporary subsidence delay has also been widely reported from either magma poor passive continental margin like the Iberia-Newfoundland (Kusznir and Karner 2007;Péron-Pinvidic and Manatschal 2009), or magma rich passive margins, such as the North-eastern Atlantic margin (Clift 1997) and Pakistan volcanic margin (Claves et al 2008). In this way, the continental margins subsides less than might be expected from the observed crustal thinning and resulting isostatic response.…”

Evidence of Late Ediacaran Hyperextension of the Laurentian Iapetan Margin in the Birchy Complex, Baie Verte Peninsula, Northwest Newfoundland: Implications for the Opening of Iapetus, Formation of Peri-Laurentian Microcontinents and Taconic – Grampian Orogenesis

“…The ultramafic rocks in such settings mainly represent inherited sub-continental lithospheric mantle exhumed onto the seafloor and the structurally interleaved sedimentary rocks represent its syn-to post-rift cover (Manatschal 2004;Péron-Pinvidic and Manatschal 2009). The complex polyphase structural history and the relatively high pressures recorded in the mafic schist (Willner et al 2012) are another feature typical of OCT zones, e.g.…”

“…In general, syn-rift magmatism is subdued and is represented by mafic intrusions of MORB-like composition; volcanic rocks commonly form a minor component of the mafic magmatism (but see Bernoulli et al 2003). These mafic intrusions record the onset of magmatic accretion within the OCT zone during distributed (delocalized) extension-related deformation, which commonly continues for a significant length of time (Jagoutz et al 2007;Péron-Pinvidic and Manatschal 2009), until the onset of true seafloor spreading and the formation of oceanic crust.…”

“…Whalen et al 1997;van Staal et al 2007;Zagorevski et al 2006) Thermal Subsidence The highly thinned continental margins of studied OCT zones commonly display significant retardation of thermal subsidence. In addition to the potentially insulating effects of a thick sedimentary blanket and the predicted slow cooling of the upper plate crust during asymmetric extension (Buck et al 1988), anomalous slow cooling and prolonged uplift of a rifted margin may also be related to the structural emplacement of hot mantle under the thinning crust Péron-Pinvidic and Manatschal 2009). Hence, a combination of these processes may have significantly delayed thermal subsidence and the resultant transgression.…”

The Ocean – Continent Transition Zones Along the Appalachian – Caledonian Margin of Laurentia: Examples of Large-Scale Hyperextension During the Opening of the Iapetus Ocean

“…A combination of modern high-quality geophysical data, deep sea drilling and comparative studies of analogue areas onshore (e.g. Manatschal 2004;Péron-Pinvidic and Manatschal 2009) has shown that the OCT of magma-poor passive margins is a zone of hyperextension characterized by extreme thinning of parts of the continental crust, resulting in exhumation of the lowermost crust and/or serpentinized continental mantle onto the seafloor (e.g. Iberian margin, Tucholke et al 2007;Sibuet and Tucholke 2013).…”