Abstract
AbstractNineteen large (2348–4285 m above sea level) central polygenetic alkaline shield-like composite volcanoes and numerous smaller volcanoes in Marie Byrd Land (MBL) and western Ellsworth Land rise above the West Antarctic Ice Sheet (WAIS) and comprise the MBL Volcanic Group (MBLVG). Earliest MBLVG volcanism dates to the latest Eocene (36.6 Ma). Polygenetic volcanism began by the middle Miocene (13.4 Ma) and has continued into the Holocene without major interruptions, producing the central volcanoes with 24 large (2–10 km-diameter) summit calderas and abundant evidence for explosive eruptions in caldera-rim deposits. Rock lithofacies are dominated by basanite and trachyte/phonolite lava and breccia, deposited in both subaerial and ice-contact environments. The chronology of MBLVG volcanism is well constrained by 330 age analyses, including 52 new40Ar/39Ar ages. A volcanic lithofacies record of glaciation provides evidence of local ice-cap glaciation at 29–27 Ma and of widespread WAIS glaciation by 9 Ma. Late Quaternary glaciovolcanic records document WAIS expansions that correlate to eustatic sea-level lowstands (MIS 16, 4 and 2): the WAIS was +500 m at 609 ka at coastal Mount Murphy, and +400 m at 64.7 ka, +400 m at 21.2 ka and +575 m at 17.5 ka at inland Mount Takahe.
Highlights
The age progression is consistent with the degree of dissection: Mount Rees is much more eroded than Mount Steere, and both of these two Late Miocene volcanoes are more eroded than the Pliocene Mount Frakes
The third and ongoing stage of Mount Berlin volcanism is recorded in explosively-erupted pyroclastic deposits dating back to 25.9 ka and preserved in the summit caldera that is up to 3478 m asl
Englacial tephra found at Mount Moulton and in ice cores records highly-explosive Mount Berlin volcanism during the Merrem Peak and Berlin summit caldera stages (Dunbar et al 2021)
Summary
The published descriptions of Mount Murphy have largely focused on volcanic sequences along the lower SW flank of Mount Murphy, at Sechrist Peak, and at three satellite nunataks, west and SW of the central volcano (McIntosh et al 1985; LeMasurier et al 1994; Smellie 2001; Wilch and McIntosh 2002) (Fig. 7) Stratigraphic sequences at these localities are composed of intercalated volcanic and glacial deposits that provide evidence of higher palaeo-ice levels during Miocene–Pleistocene times (LeMasurier et al 1994; Wilch and McIntosh 2002). Interpreting regional ice-sheet levels from the lower Sechrist Peak–Bucher Peak Ridge sequence
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