New paleomagnetic data from the Antarctic Peninsula and their tectonic implications

Abstract

New paleomagnetic data presented here further constrain the relative motion of the Antarctic Peninsula relative to East Antarctica during the Mesozoic development of the southern ocean basins. The Antarctic Peninsula (AP) is one of four crustal blocks that define West Antarctica, the others being the Ellsworth‐Whitmore Mountains (EWM), Thurston Island‐Eights Coast (TI), and Marie Byrd Land (MBL). A Jurassic pole (∼155Ma) (124°E, 64°S, A95=7.1°, N=10 VGPs) was obtained from the AP block which suggests that the AP block rotated clockwise between ∼175 and ∼155 Ma due to significant early opening in the Weddell Sea basin. A new Early Cretaceous paleomagnetic pole (182°E, 74S, A95=5.9°, N=6 site mean VGPs) indicates that the AP block was in or near to its present‐day position with respect to East Antarctica by ∼130 Ma. Between ∼155 and 130 Ma, counterclockwise rotation of the AP‐TI blocks, together with the southward motion of East Gondwanaland, probably resulted in subduction of Weddell Sea ocean floor beneath the southern AP block and initiated the Palmer Land deformational event. A ∼130 Ma pole from the TI block requires clockwise rotation of the TI and possibly the EWM blocks between 130 and ∼110 Ma producing sinsistral strike‐slip motion between the EWM block and East Antarctica and dextral transpressional motion between the TI‐EWM blocks and the AP block. New AP block ∼110 Ma and ∼85 Ma poles from this study (199°E, 74°S, A95=6.9°, N=13 VGPs; 152°E, 86°S, A95 = 7.5°, N=6 VGPs, respectively) are similar to equivalent age poles from East Antarctica and suggest little or no relative motion between the Antarctic Peninsula and East Antarctica. Northern and southern Antarctic Peninsula mid‐Cretaceous poles are very much alike suggesting that the “S” shape of the Antarctic Peninsula is not due to oroclinal bending since ∼110 Ma.