Lithostratigraphy and petrology of Lachman Crags and Cape Lachman lava-fed deltas, Ulu Peninsula, James Ross Island, north-eastern Antarctic Peninsula: Preliminary results

Abstract

This paper presents the preliminary results regarding the lithostratigraphy, petrography and petrology of James Ross Island Volcanic Group dominating the Lachman Crags and Cape Lachman lava-fed deltas in the Ulu Peninsula, James Ross Island north-eastern Antarctic Peninsula. Studied lava-fed deltas were produced via Late Miocene to Pleistocene sub-marine and sub-glacial volcanism and made up four main lithofacies: a- bottomset pillow lavas, peperites and associated volcanoclastic/siliciclastic deposits; b- foreset-bedded hyaloclastite breccias; c- intrusions (feeder dykes, sills, and plugs) and d- topset subaerial lavas. Collectively these lithofacies record the transition from an effusive subaqueous to an effusive subaerial eruption environment. All lava samples and dykes from bottomset, foreset and topset lava-fed delta associations are olivine-phyric alkali basalts and are mineralogically and geochemically homogeneous. These eruptive products display significant enrichments in alkali contents and have ocean island basalt (OIB)-type, intra-plate geochemical signatures characterized by enrichments in all highly to moderately incompatible trace elements relative to basaltic rocks from ocean ridge settings. Volcanic products from a number of different eruptive periods display limited variations in major and trace element relative abundances, indicating derivation from a relatively homogeneous mantle source. The results of quantitative modelling of geochemical data is consistent with the view that the primary melts from which these mafic alkaline rocks were originated are the products of relatively small degrees (~3-7%) of partial melting of a volatile-bearing, metasomatized mantle source. The magmatism is likely the result of extension-driven mantle upwelling.

High‐latitude dust deposition in snow on the glaciers of James Ross Island, Antarctica

“…() and Altunkaynak e t al . () show the K/Ca ratio being in the range 0.063–0.485, coinciding with our XRF‐based K/Ca ratio of JRIVG basalts (0.040–0.355) and hyaloclastites (0.088–0.424). This is similar to the values calculated for aeolian deposition on the studied glaciers (0.463–0.639), but the samples from individual glaciers differ in Fe/Ti ratio, as can be seen in Figure .…”

“…The results were validated by the analysis of certified reference material CH‐4 (Natural Resources Canada), because of the similar proportions of the main elements and most of the trace elements analysed both in the snow samples as well as in the background geological samples (volcanic and sedimentary rocks). The comparison of XRF‐based trace element proportions and elemental ratios with ICP‐based geochemical data from James Ross Island Volcanic Group (JRIVG) basaltic rocks (Košler et al, ; Altunkaynak et al, ) proved the suitability of the XRF spectrophotometry for our study. Replicate measurements of the same sample showed differences of <1% for all assessed elements.…”

“…The high Rb/Sr ratios (0.425–0.703) for all the HLD on the glaciers exclude the JRIVG rocks (Nelson, ) as the source material for aeolian transport on the glaciers. The Rb/Sr ratios of volcanic rocks lie in the range of 0.007–0.040 (Košler et al ., ; Altunkaynak et al ., ). Higher values are found in the sedimentary rocks of the Santa Marta Formation (0.235–0.300, see Figure ).…”