A revised position for the rotated Falkland Islands microplate

Abstract

The early stages of transform margin formation are associated with crustal fragmentation and block rotation. The restricted size of the resultant microcontinental blocks precludes palaeogeographic reconstructions and reliable estimations of the amount of rotation they can undergo. An example considered here is the Falkland Plateau. This is located adjacent to the Agulhas-Falkland Fracture Zone/Transform and its westernmost province is the Falkland Islands microcontinent. The position of the plateau and the islands prior to Gondwana break-up remains contentious. This study integrates seismic reflection and gravity data to propose a revised position of the Falkland Islands microcontinent constrained by: (a) the presence of a mega-décollement, controlling the Gondwanide Orogen, described north of the Falkland Islands and underneath South Africa and Outeniqua Basin, and (b) the similar architecture of fault networks mapped north of the islands and in the northernmost Outeniqua Basin. This revised position requires a re-evaluation of the timing and rate of rotation of the Falkland Islands microcontinent and impacts the expected crustal architecture adjacent to the islands. Our model yields rotation rates between 5.5° and 8° Myr-1 , two potential times for rotation and predicts more unstretched crust beneath the basin east of the Falkland Islands than previous models.

The Malvinas (Falkland) Plateau Derived from Africa? Constraints for its Tectonic Evolution

“…In the Malvinas plateau, this décollement is dipping to the north and reaches the same depth as in the Outeniqua Basin. The opposite polarity of this décollement at both sides of the Agulhas-Malvinas transfer zone is considered as a new evidence supporting the 180º rotation of the Malvinas Islands microplate [42].…”

“…New detailed structural analyses performed north of the Malvinas Islands in the adjacent basin, combined with gravity and seismic data presented by Stanca et al [42], enhanced the importance of the occurrence of a mega-décollement formed during the Gondwanide Orogeny. This décollement has been recognized underneath the Outeniqua Basin and South Africa [41,48], associated with north-verging thrusts.…”

“…5), and Pángaro et al [19], show withou shadow of a doubt the continuity of the Ventania fold and thrust belt in the adjacent offshore area and its eastern extension in the Cape belt of South Africa (see Paton et al[20]). In those sections, what the authors considered to be the master shear is the equivalent to the mega-décollement of Stanca et al [42]. Both structures have the same north-vergence, a similar depth of detachment and equivalent offsets.…”

“…A recent study by Stanca and others [42] proposed crustal fragmentation and block rotation for the Malvinas Plateau, where the Malvinas Islands were a microcontinent; however, they state that the position of the plateau and the islands before the separation of Gondwana continues to be controversial. This work proposed a Malvinas Islands microplate, equivalent to the Lafonia microplate sensu [15,30], which underwent vertical-axis rotation during the break-up of Gondwana.…”

“…The oldest synrift deposits are not well dated in that basin, and a doubtful Upper (?) Jurassic age was assumed [42]. However, this WNW to NW-trending rift system, as seen in their Fig.…”