Transtensional Reactivation of Suture Zones: Insights from 3D Numerical Modelling of Pull-Apart Basins

Suture zones mark the final closure of oceanic domains through subduction and subsequent continental collision [1]. These zones are typically characterized by inherited crustal shear zones and the fossil subduction interface in the mantle lithosphere. The orientation of the suture reflects the preceding subduction polarity. While the presence of hydrated lithosphere in older sutures is somewhat contested, the upper plate peridotite portion of the lithosphere certainly involves significant hydration and metasomatism.

Reactivation of suture zones triggered by post-collisional extensional episodes can result in lithospheric thinning, rifting and associated magmatic activity. Large-scale suture reactivation linked to continental breakup is well-documented [2], whereas localized post-collisional extension is sometimes invoked in order to explain less voluminous magmatic events. An example of the latter is the enigmatic Late Cretaceous magmatism along Sava-Vardar suture Zone (e.g. Klepa, Ripanj, Jelica) which is recently argued to be the product of a transtensional regime imposed onto the suture that lead to opening of pull-apart basins alongside lithospheric thinning and emplacement of basaltic magma [3].

Here, we present our results of numerical 3D modelling of a transtensionally reactivated suture. To this end we use the petrological-thermo-mechanical code I3VIS [4]. The code implements a marker-in-cell approach with conservative finite differences and a multigrid method. The model consists of upper and lower continental crust, lithospheric and sublithospheric mantle down to 250 km depth. Two continental blocks are translated along the transfer zone in the middle of the model domain resulting in transtension. The suture consists of a fossil slab represented by oceanic lithosphere and a hydrated mantle wedge in the upper plate.

Our results demonstrate that the step-over distance between the two weak crustal zones governs the development of the pull-apart basins accompanied by crustal and lithospheric thinning and asthenospheric uplift. Partial melting of the suture's metasomatized mantle yields primary melts which ultimate derivatives are emplaced at the surface. The model provides important new insights into magmatic processes assosciated with suture reactivation in the Sava-Vardar Zone and in other similar tectonic settings.

[1] J. F. Dewey, “Suture zone complexities: a review,” Tectonophysics, vol. 40, no. 1-2, pp. 53–67, 1977.

[2] S. J. Buiter and T. H. Torsvik, “A review of wilson cycle plate margins: A role for mantle plumes in continental break-up along sutures?,” Gondwana Research, vol. 26, no. 2, pp. 627–653, 2014.

[3] D. Prelević, S. Wehrheim, M. Reutter, R. L. Romer, B. Boev, M. Božović, P. van den Bogaard, V. Cvetković, and S. M. Schmid, “The late cretaceous klepa basalts in macedonia (fyrom)—constraints on the final stage of tethys closure in the balkans,” Terra Nova, vol. 29, no. 3, pp. 145–153, 2017.

[4] T. V. Gerya and D. A. Yuen, “Characteristics-based marker-in-cell method with conservative finite-differences schemes for modeling geological flows with strongly variable transport properties,” Physics of the Earth and Planetary Interiors, vol. 140, no. 4, pp. 293–318, 2003.