Influence of the architecture of magma-poor hyperextended rifted margins on orogens produced by the closure of narrow versus wide oceans

Abstract

International audienceOrogens resulting from the closure of narrow oceans, such as the Alps or the Pyrenees, usually lack voluminous synsubduction and synorogenic magmatism. Such orogenies are essentially controlled by mechanical processes in which the initial architecture of the original rifted margins strongly controls the architecture of the orogen. In this paper we first provide a synthesis of the structure, dimensions, and lithology of hyperextended rift systems and oceans, based on recent seismic and petrologic data. We then investigate how rift-related inheritance influences crustal characteristics and mantle geochemistry of orogens related to the closure of narrow oceans, and compare them to orogens resulting from the closure of wide and/or mature oceans. Our results show that narrow oceans usually lack a mature spreading system forming Penrose-type oceanic crust (i.e., 6–7-km-thick basaltic oceanic crust typical of steady-state spreading systems; see Anonymous, 1972), in contrast to wide oceans. However, there is statistically no difference in the structural and lithological architecture of their passive continental margins. Thus, the main difference between narrow and wide oceans is whether the margins are separated by a significant amount of oceanic crust and underlying depleted mantle. In addition, due to the lack of significant magmatism during the closure of narrow oceans, the mantle wedge is likely to remain relatively fertile compared to the wedge above long-lasting subduction of wide oceans. This difference in mantle composition may dictate the magmatic budget of subsequent orogenic collapse or rifting events

Necking of the Lithosphere: A Reappraisal of Basic Concepts With Thermo‐Mechanical Numerical Modeling

“…The width of necking zones ranges between 65 and 105 km in Model Series 1 (decoupled models) and between 50 and 70 km in Model Series 3 (coupled models). These ranges are consistent with both the predictions from analytical studies (14–83 km according to Schmalholz & Mancktelow, ; see also Appendix A2) and the width observed at natural rift systems/margins (10–100 km according to Chenin et al, ; see Figure b). The generally narrower width of necking zones in the coupled models with respect to decoupled models is consistent with the results of previous studies, which predict wider rift zones for weaker lithospheres (for instance, Bassi, ; Buck, ).…”

“…For several model results, the inflection in top basement is significantly laterally offset from that in the Moho (Figure ). In such cases, we placed the necking point at the onset of crustal inflection, consistent with Chenin et al () for their necking zones width measurements when the Moho was not well resolved on the seismic sections they used. In the models of Series 1, the width of the necking zones at the end of the simulation range consistently between 65 and 105 km with an average of 80 km (Figure a and Table ).…”

Thermochronological Evidence of Early Orogenesis, Eastern Pyrenees, France

“…We use 32, 20, and 28 km for present‐day Iberian, eastern North Pyrenean, and European crustal thicknesses, respectively (Chevrot et al, ; Diaz et al, ). Following Clerc et al () and inspired by modern analogs (Chenin et al, ; Reston, ; Sutra et al, ), we restore the eastern Pyrenees to a hyperextended rift in which the Agly‐Salvezines block is surrounded by depocenters recording high temperatures (113–95 Ma) and with mantle exhumation below the more distal Boucheville basin. Key thermal events integrated into this model are that the Agly‐Salvezines block (i) was affected by metasomatism from late Aptian to middle Cenomanian times followed by rapid cooling to 200–250 °C by 90 Ma and (ii) was cooled at 75 Ma during early convergence and again at 50 Ma during main collision.…”

Architecture of the Distal Piedmont‐Ligurian Rifted Margin in NW Italy: Hints for a Flip of the Rift System Polarity

“…Since during alpine compressional phases this area was only shortened N–S, perpendicular to the strike of the margin, we assume that these 50 to 60 km roughly correspond to the original width of the interpreted Adria T2. A global estimation of T2 compiled from different margins by Chenin et al () is in the order between 50 and 80 km. Moreover, restorations of the Briançonnais domain (also interpreted as a T2; Haupert et al, ) are in the order of 50–60 km (Mohn et al, , cum ref.…”