Geology of Waddington Bay (Kyiv Peninsula, Graham Coast of the West Antarctica)

Abstract

Background. Waddington Bay is located west of the Ukrainian Antarctic Akademik Vernadsky Station indenting the mainland coast closest to the station. The bay provides access to the largely unexplored interior of the Kyiv Peninsula. Until recently, geological understanding of this area was based on studies conducted at sites accessible for landings specifically at Tuxen Cape and Rasmussen Point. Recently geological investigations have covered the entire coastline of Waddington Bay and the adjacent areas. Field observations and the results of their subsequent analysis form the basis of this study. The aim of the research was to carry out a geological description of Waddington Bay, to identify the petrographic diversity of local rocks, determine their distribution and mode of occurrence, and establish their probable age relationships.
Methods. Field observations and sampling were conducted by geological survey in 2020, 2019 and 2017. Petrographic characteristics and mineral composition of the rocks were studied using optical polarizing microscopy, as well as electron microscopy and electron microprobe analysis.
Results. It was established that all outcrops along the coasts of Waddington Bay, as well as the nearby Mount Mill and Mount Demaria, are composed exclusively of igneous rocks. No outcrops of sedimentary or metamorphic rocks have been identified to date. The following units are distinguished among the igneous rocks: 1) Volcanic strata; 2) Rasmussen Point granites; 3) Tuxen-Rasmussen gabbroid intrusive; 4) Mount Mill granodiorites; 5) granophyric microgranites; 6) post-plutonic mafic dikes.
Conclusions. Authors demonstrate that the oldest igneous rocks among those studied are andesites and andesitic tuffs. They belong to the Volcanic formation of the Kyiv Peninsula for which a Jurassic age is tentatively assumed. Geological mapping shows that volcanic rocks are significantly less widespread than the plutonic ones in terms of areal extent. There is full range of plutonic members of the calc-alkaline orogenic series in Waddington Bay. Most plutons were determined to be of Cretaceous age, indicating that they formed during the main peak of magmatic activity of the Antarctic Peninsula Batholith. It is shown that pluton formation occurred in at least two stages. The Early Cretaceous stage is represented by the Rasmussen Point granites. The Late Cretaceous stage includes plutons forming a single gabbro-diorite-granitoid complex emplaced through several intrusive phases in a homodromous sequence. Post-plutonic mafic dykes were also intruded in at least two stages. The hypabyssal microdioritic dikes are Late Cretaceous while the subvolcanic basaltic dykes probably intruded in the Paleocene or later. A hypabyssal intrusion of granophyric microgranites has been discovered in the extreme southeastern part of Waddington Bay. Its age and origin require further investigation.