New Paleomagnetic and ⁴⁰Ar/³⁹Ar Geochronological Results for the South Shetland Islands, West Antarctica, and Their Tectonic Implications

Abstract

To reconstruct the paleoposition of the Antarctic Peninsula relative to the South American Plate during the breakup of Gondwana, as well as the opening kinematics of the Drake Passage, we conducted detailed paleomagnetic, rock magnetic, and isotopic chronology studies of Byers Peninsula (Livingston Island) and Fildes Peninsula (King George Island) of the South Shetland Islands. The 40Ar/39Ar ages of the Agate Beach Formation to the Long Hill Formation in Fildes Peninsula range from 56.38 ± 0.2 Ma to 52.42 ± 0.19 Ma. Low natural remanent magnetization/isothermal remanent magnetization ratios, inconsistency with the polarity constrained by the paleomagnetic results and 40Ar/39Ar age constraints, as well as the widespread cation‐deficient titanomagnetite and Ti‐free magnetite of secondary origin, indicate that the volcanic and sedimentary rocks of Fildes Peninsula were remagnetized at about 55 Ma. Combining our results with previous data from the South Shetland Islands and the Antarctic Peninsula, we calculated the paleopoles for 110 Ma and 55 Ma for the South Shetland Islands and the Antarctic Peninsula. The paleomagnetic reconstruction of the relative paleoposition of the Antarctic Peninsula and South America shows that these plates were connected and experienced a southward movement and clockwise rotation from 110 to 55 Ma. Subsequently, southward translation and clockwise rotation of the Antarctic Peninsula between 55 and 27 Ma separated the Antarctic Peninsula and South America, forming the Drake Passage. Northward translation of South America after 27 Ma increased the N‐S divergence and increased the distance between the Antarctic Peninsula and the South American Plate.

Subduction initiation in the Scotia Sea region and opening of the Drake Passage: when and why?

“…Based on these paleomagnetic constraints, there is no reason to assume any relative motion between the Antarctic Peninsula and East Antarctica since the Early Cretaceous. In our reconstruction the Antarctic Peninsula is tectonically part of East Antarctica, which is in agreement with earlier conclusions (Bakhmutov and Shpyra, 2011;Gao et al, 2018;Grunow, 1993;Milanese et al, 2019;Milanese et al, 2017;Poblete et al, 2011;Watts et al, 1984).…”

“…This would render the Antarctic Peninsula also tectonically part of West Antarctica. Based on paleomagnetic studies, however, most authors interpret the Antarctic Peninsula as rigidly attached to East Antarctica since at least the mid-Cretaceous (Bakhmutov and Shpyra, 2011;Gao et al, 2018;Grunow, 1993;Milanese et al, 2019;Milanese et al, 2017;Poblete et al, 2011;Watts et al, 1984).…”

Mid Campanian‐Lower Maastrichtian magnetostratigraphy of the James Ross Basin, Antarctica: Chronostratigraphical implications

“…GPS points (Table S2) uplift recorded in the Fuegian Andes of southern South America, which by the latest Cretaceous was very close and probably in crustal continuity with the Antarctic Peninsula (e.g. Gao et al, 2018). However, the major change in SAR could also have been influenced by (glaci) eustatic changes as is coincidental with an important shift towards globally cooler waters as determined by δ0 18 during the Early Maastrichtian (C31r) that has been interpreted as causing the development of the first Antarctic ice sheet (Miller, Barrera, Olsson, Sugarman, & Savin, 1999).…”

Lithostratigraphy, age and distribution of Eocene volcanic sequences on eastern King George Island, South Shetland Islands, Antarctica

“…Carruthers Cliff Formation: The preferred age for this new formation is c. 52 Ma, which makes it potentially the oldest Eocene volcanic sequence dated in the study. Its age is similar to, but slightly younger than, the Early Eocene Fildes Formation at Fildes Peninsula (mainly c. 59-56 Ma; by K-Ar and 40 Ar/ 39 Ar; Smellie et al 1984, Kraus 2005, Haase et al 2012, Gao et al 2018 Nawrocki et al 2010, Mozer et al 2015. Thus, apart from a very few unconfirmed Late Cretaceous ages obtained on isolated volcanic outcrops with unknown affinities (e.g.…”