ALBERT

Description: Dove Basin is situated in the south-central Scotia Sea, between Pirie and Bruce banks, and was formed during the development of the Scotia Arc. The basin has a roughly sigmoidal shape, with a prominent NNE?SSW elongated ridge located in its central part, the Dove Ridge, which is considered as an extinct spreading axis. A NE?SW elongated tectonic high, the Dove Seamount, is located in the north-eastern region of the basin, bounded by a normal fault dipping to the southeast. Dredged rocks and geophysical data were collected during the SCAN2004 and SCAN2008 cruises. Dredged samples were recovered from three positive features in the center of the basin, two from Dove Ridge, and one from Dove Seamount. Igneous rocks along the Dove Ridge are mainly tholeiitic basalts, derived from asthenospheric upper mantle within an extensional supra-subduction back-arc tectonic setting, which evolved over time from back-arc basin basalts (BABB) toward Mid Oceanic Ridge Basalts (MORBs). Altered olivine-bearing fine- and medium-grained basaltic rocks were also dredged from Dove Ridge and the seamount, together with minor oceanic island arc basalts and basaltic andesites. The mantle source was affected, up to early Miocene times, by a subducted oceanic slab related to an arc to the east, with Dove Basin forming in a back-arc position. Minor alkaline oceanic island basalts dredged at the seamount might represent a final extensional stage, genetically related with the dying Dove Ridge volcanism or, less probably, to a later, late Miocene?Pliocene extensional stage, producing incipient volcanism deriving from a deeper mantle source. 40Ar/39Ar dating of MORB samples dredged from the Dove Ridge provided ages of 20.4 ± 2.6 to 22.8 ± 3.1 Ma. These outcrops were later coated by Fe?Mn crusts with Co-Chronometer ages ranging from at least 12.6 Ma and probably up to 18 Ma. Analysis of magnetic anomaly profiles shows the best fit in the central profile, corresponding to chrons C6B (21.7 Ma) to C7 (24.5 Ma), although alternative ages may be proposed due to the short length. This interpretation supports the 40Ar/39Ar dating of a late Oligocene to early Miocene age. The spreading was asymmetrical, the asynchronous age of extinction of spreading in the basin being confirmed by the variable character of magnetic anomalies. The western part extended faster than the eastern part, suggesting an eastward location for a westward deepening subduction zone. The age obtained for the Dove Basin is older than the age previously proposed for the Protector Basin located to the west, thus suggesting an opposite polarity for the development of some small oceanic basins of the southern Scotia Sea with respect to others generated by an eastward migrating arc over subducted Atlantic oceanic floor. This apparent contradiction could be explained by considering the Dove Basin as originated from an Oligocene to early Miocene arc?back-arc spreading system, which would contribute to the eastward general development of the Scotia Arc, meanwhile Protector Basin was formed by a middle Miocene extensional phase, not genetically related with the main oceanic spreading along the Dove Basin.