The Shackleton Range (East Antarctica): an alien block at the rim of Gondwana?

Abstract

The Shackleton Range is a truncated Pan-African Orogen situated at the Weddell Sea margin of East Antarctica. It almost exclusively consists of basement rocks exposed at an elevated, escarpment-bound palaeosurface and is covered locally by patchy remnants of Ordovician, Permian and, controversially, Jurassic terrestrial deposits. This inventory does not match the geological record of any other place in Antarctica. Here we reconstruct the Phanerozoic evolution of the Shackleton Range by means of a multi-disciplinary approach combining petrological, geochemical and geochronological data with thermal history models of zircon and apatite fission track (ZFT, AFT) and (U–Th–Sm)/He (AHe) data. Petrographic, geochemical and 40Ar/39Ar analyses of a sedimentary cover sequence identify volcaniclastic rocks related to the Ferrar/Karoo magmatic event. Thermal history modelling of ZFT ages of 160–215 Ma, AFT ages of 124–225 Ma, AHe ages of 95–169 Ma and kinematic proxies in combination with geological information indicates a complex thermal history comprising at least three cooling episodes interrupted by reheating pulses. Thermal history refers to inversion of part of the Carboniferous–Triassic Transantarctic Basin prior to the 180 Ma Ferrar/Karoo Event and formation of an up to 3.4 km deep extensional Jurassic – Early Cretaceous basin due to Weddell Sea rifting. Basin depth was diminished by regional middle Cretaceous stress field changes. Final basin inversion and surface uplift were likely triggered by far-field tectonics and climatic influence. This history represents a typical example for the transition from an active to passive margin setting along the outer rim of Gondwana.

Thurston Island (West Antarctica) Between Gondwana Subduction and Continental Separation: A Multistage Evolution Revealed by Apatite Thermochronology

“…This scenario implies that parts of the present‐day landscape of Thurston Island formed already in the Jurassic and thus >80 Myr prior to the mid‐Cretaceous landscape architecture of Marie Byrd Land. Between the Early Jurassic and Early Cretaceous, Thurston Island was characterized by heating, which we interpret as burial resulting from back‐arc basin development following widespread Early Jurassic volcanism. Basin development on Thurston Island shows striking similarities with the Mesozoic basins in the Shackleton Range (Krohne et al, ) and the Transantarctic Mountains (Lisker & Läufer, ). All these basins initiated by the Early Jurassic and thus indicate that Mesozoic intra‐Gondwana extension extended over larger areas than previously thought. All basement units in the Thurston Island area experienced cooling at ~135–125 Ma, corresponding with crustal thickening and rapid erosion of almost the complete Early Jurassic‐Early Cretaceous basin deposits due to basin inversion until ~95 Ma.…”

Uplift and tilting of the Shackleton Range in East Antarctica driven by glacial erosion and normal faulting

“…Another option is that the observed asymmetry in the topography is the result of spatially variable erosion rather than spatially variable uplift. However, this is unlikely to be the case, since the tilt is observed in the mesa/plateau surfaces (Figure ), which have experienced negligible incision and cut different geological units [ Kerr and Hermichen , ; Sugden et al ., ; Krohne et al ., ]. The presence of surfaces that all tilt away from the region of unloading and have slopes that are not the same as geological dip slopes is strong evidence for flexural tilting [ Watts et al ., ].…”

“…The timing and mechanism(s) responsible for the uplift of the Shackleton Range and Theron Mountains and the subsidence of the Recovery, Slessor, and Bailey troughs remain outstanding questions. Apatite fission track and (U‐Th)/He dating indicate multiple phases of denudation and burial of the Shackleton Range in the Mesozoic before final uplift and formation of the present landscape since EAIS inception at 34 Ma [ Krohne et al ., ]. Previous studies have suggested that the uplift of the mountain ranges and subsidence of the troughs are inherently coupled.…”

Subglacial Geology and Geomorphology of the Pensacola‐Pole Basin, East Antarctica

“…The second commenced in the Jurassic following emplacement of the Ferrar Large Igneous Province, the onset of rifting in the Weddell Sea, and the subsequent breakup of Gondwana and onset of seafloor spreading between Africa and East Antarctica (Jordan et al, 2017;Leinweber & Jokat, 2012). AFT data indicate that up to 4 km of post-Jurassic sediments were deposited in a "Mesozoic Victoria Basin" that extended from Coats Land to Victoria Land (Krohne et al, 2016;Lisker et al, 2014;Lisker & Läufer, 2013;Prenzel et al, 2018), although such rocks have not been directly observed in East Antarctica.…”

“…Apatite fission track (AFT) and (U-Th)/He thermochronology data, alongside thermal history modeling, have been interpreted as reflecting two phases of burial of the basement along the East Antarctic margin from Victoria Land to Coats Land by sedimentary successions since the mid-Paleozoic (Krohne et al, 2016;Lisker et al, 2014;Lisker & Läufer, 2013;Prenzel et al, 2018). The first phase was associated with the deposition of Beacon Supergroup strata along the subduction-dominated Panthalassan margin of Gondwana in a series of basins referred to collectively as the Transantarctic Basin (Collinson et al, 1994).…”