Correlation and Late-Stage Deformation of Liv Group Volcanics in the Ross-Delamerian Orogen, Antarctica, from New U-Pb Ages

Abstract

We present new zircon U-Pb isotopic data for volcanic rocks from deformed metavolcanic-sedimentary successions of the widespread Ross Supergroup in the Queen Maud Mountains, Antarctica. Zircon U-Pb analyses of Liv Group volcanic rocks thought to be Neoproterozoic in age instead have early Paleozoic ages. Zircon U-Pb analyses of five samples assigned to the Fairweather Formation have yielded 524 5 9 to 514 5 9 Ma (2j) crystallization ages, whereas six samples assigned to the Taylor Formation have yielded 510 5 12 to 490 5 6 Ma (2j) crystallization ages. Although these ages imply that the Fairweather Formation is generally older than the Taylor Formation, the age uncertainties show a 17-My overlap that is consistent with previous suggestions for temporal correlation of these formations. On a regional scale, Liv Group volcanism overlapped with the emplacement of ∼535-490 Ma plutonic rocks associated with the early Paleozoic Queen Maud batholith as well as igneous rocks found elsewhere along the early Paleozoic Pacific-Gondwana margin. Collectively, these igneous rocks provide plausible zircon sources for similar age detrital zircon populations found in outboard siliciclastic rocks belonging to the Leverett, Taylor, Fairweather, Greenlee, and Starshot Formations of the Queen Maud Mountains. The youngest crystallization age yielded by the deformed Taylor Formation (∼490 Ma) assumes regional significance because it represents the youngest volcanic rock yet identified within the Ross orogen in Antarctica and provides important new evidence for latest Cambrian or younger deformation, possibly associated with orogenic collapse during slab rollback at the terminal stages of the Ross orogeny.

Outboard Onset of Ross Orogen Magmatism and Subsequent Igneous and Metamorphic Cooling Linked to Slab Rollback during Late-Stage Gondwana Assembly

“…Liv Group (Fairweather and Taylor formations) sandstones in particular show significant populations of ~530-490 Ma (Cambrian, ~Terreneuvian-Furongian) detrital zircons (Figure 10). These detrital zircon U-Pb age populations are close to Liv Group depositional ages yielded by biostratigraphic data of sedimentary rocks (Cambrian, Series 2 to Series 3, 521-501 Ma) [31,33,74], as well as U-Pb zircon crystallization ages (526-489 Ma) of volcanic rocks [33][34][35]. Siliciclastic sediments deposited in convergent margin settings are typified by high proportions of detrital zircons with U-Pb ages that approach or even overlap their depositional ages [75].…”

“…Our data record the last passage of igneous and metamorphic rocks through 40 Ar/ 39 Ar closure temperatures ranging from ~540 • C (hornblende) to 375 • C (biotite) in the Cambrian to Ordovician (Figure 8). Figure 9 shows a kernel-density-estimation diagram for all 40 Ar/ 39 Ar cooling ages (n = 28) obtained for intrusive rocks, as well as metasedimentary rocks, reported for the study area [35,45]. Density analysis shows the polymodal age distributions with primary 510 Ma, 491 Ma, and 475 Ma age peaks.…”

“…Detrital zircon ages are compiled for the Liv and Beardmore groups from [26,27,54]. Volcanic and plutonic U-Pb crystallization ages are compiled from data presented in [33][34][35][36]44,45,47,48]. 40 Ar/ 39 Ar ages for detrital muscovite from the Starshot Formation along Ramsey Glacier are from [45].…”

“…The Liv Group, in turn, includes volcanic and volcaniclastic rocks (dacites, basalts, basaltic andesites, and rhyolites) interbedded with carbonate and siliciclastic rocks [30] known as the Wyatt, Ackerman, Leverett, Taylor, Fairweather, and Greenlee formations [15,16,18,[30][31][32]. Biostratigraphic and U-Pb zircon analyses have yielded Cambrian (Terreneuvian to Furon-gian) ages for sedimentary and volcanic rocks of the Liv Group [27,[33][34][35][36]. These ages indicate that rocks belonging to the Liv Group are at least in part temporal correlatives to the Cambrian Byrd Group (Shackleton Limestone and Douglas and Starshot formations) in the central Transantarctic Mountains (Figure 3) [21,22,37,38].…”

“…These ages indicate that rocks belonging to the Liv Group are at least in part temporal correlatives to the Cambrian Byrd Group (Shackleton Limestone and Douglas and Starshot formations) in the central Transantarctic Mountains (Figure 3) [21,22,37,38]. (Terreneuvian to Furongian) ages for sedimentary and volcanic rocks of the Liv Group [27,[33][34][35][36]. These ages indicate that rocks belonging to the Liv Group are at least in part temporal correlatives to the Cambrian Byrd Group (Shackleton Limestone and Douglas and Starshot formations) in the central Transantarctic Mountains (Figure 3) [21,22,37,38].…”