Extensional tectonics and two-stage crustal accretion at oceanic transform faults

Abstract

Ein neuer Blick auf die Plattentektonik Nature-Studie weist Transform-Störungen eine aktive Rolle bei der Gestaltung von Ozeanböden nach 17.03.2021/Kiel. Entlang untermeerischer Gebirgszüge, der Mittelozeanischen Rücken, drücken Kräfte aus dem Erdinneren Erdplatten auseinander, bilden neuen Ozeanboden und verschieben so Kontinente. Viele Details der unter dem Begriff Plattentektonik zusammengefassten Prozesse sind aber noch unklar. Unter anderem gibt es einfach zu wenig präzise Karten der Ozeanböden. Forscher des GEOMAR-Helmholtz-Zentrums für Ozeanforschung Kiel veröffentlichen heute in der internationalen Fachzeitschrift Nature eine Studie, die Transformverwerfungen eine neue Rolle innerhalb der Plattentektonik zuweisen.

Seismic structure of the St. Paul Fracture Zone and Late Cretaceous to Mid Eocene oceanic crust in the equatorial Atlantic Ocean near 18°W

“…1c). Its younger southern edge is flanked by significantly rougher bathymetry, revealing ridge-like features aligned mostly perpendicular to the FZ that we interpret as overshooting ridges, as observed near RTIs globally (e.g., Grevemeyer et al, 2021;Lonsdale, 1986;Marjanović et al, 2020). The older northern flank of the FZ can be subdivided into two distinct domains (Fig 1c).…”

“…A recent study suggests that the crust beneath the Chain fracture zone in the equatorial Atlantic region has a nearly normal crustal thickness (Marjanović et al, 2020). This observation has been independently supported using global bathymetric observations and numerical simulation on transform fault tectonics (Grevemeyer et al, 2021) suggesting that crust is (i) initially magmatically emplaced near a ridge-transform intersection (RTI), (ii) experiences tectonic deformation, and extension while being moved along the transform fault and (iii) finally it is augmented by the second stage of magmatism as it passes the opposing RTI. If correct, the formation of crust at transform faults should occur in three distinctive phases, suggesting that the structure of crust present below the valley of an active transform fault should differ profoundly from crust found along its fracture zones.…”

“…Here, we will use the term "transform fault" for the active plate boundary offsetting the spreading axis, while with the term "fracture zone", we will refer to the inactive fossil trace where lithosphere of contrasting age meets and subsidence occurs on either side depending upon their thermal structures (e.g., Menard, 1967;Sandwell, 1984). This clear separation between the fracture zones and the transform faults are important as recent evidence suggest that crust accreted along a transform fault might be affected by processes acting at ridgetransform intersections before it converts into a fracture zone (e.g., Grevemeyer et al, 2021;Marjanović et al, 2020).…”

Thermal Effects at Continent-Ocean Transform Margins: A 3D Perspective

“…Hydrothermal circulation and volcanism within the fracture zone may change the thermal structure there and is not considered in the model [16].…”

“…Their conclusion was that the Mid Atlantic Ridge did influence the thermal state of the outermost continental crust but the thermal maturity of potential source rocks was affected only to a lesser degree. Recent studies [15,16] explore geodynamic processes including the thermal budget using 3D models but are limited to the oceanic region near the transform fault and ridge-transform intersections.…”