Fission-track evidence for the thermotectonic evolution of a Mesozoic–Cenozoic fore-arc, Antarctica

Abstract

Zircon and apatite fission-track data from the LeMay Group accretionary complex and Fossil Bluff Group fore-arc basin sequence on Alexander Island (Antarctica) record a common regional Cretaceous and Cenozoic thermal and denudational history. With the exception of zircon data from samples closest to the trench, the apatite and zircon central ages are substantially less than known and, inferred stratigraphic ages. Thermal modelling of the data indicate cooling from maximum palaeotemperatures in the range 180-350 "C at c. 100 Ma. A younger period of accelerated cooling occurred between 40 and 35 Ma with final cooling to surface temperatures taking place at reduced rates through the Tertiary. The start of cooling was close in time to the end of deposition within the fore-arc basin and is consistent with structural evidence for Cretaceous deformation in a strike-slip setting. The accelerated, Early Tertiary cooling episode was broadly coeval with, and may have been caused by ridge-trench collisions and cessation of subduction off-shore Alexander Island.Zircon and apatite age data, from magmatic rocks emplaced in the fore-arc region in Late Cretaceous and Tertiary times, are close to their age of crystallization. This indicates rapid cooling of both fission-track systems from temperatures >350"C to <c. 60°C at high crustal levels of emplacement. The formation of these magmatic rocks, together with the cooling history of the accretionary prism, are related to changes in subduction zone parameters during Cretaceous and Cenozoic times. Slowing of subduction rates and role-back of the slab prior to cessation of subduction by ridge-trench collision may have been responsible for migration of the magmatic focus into the fore-arc region, uplift of the prism and formation of the high mountain ranges, and the extensional graben that separates Alexander Island from the Antarctic Peninsula.

Thermochronologic constraints on the tectonic evolution of the western Antarctic Peninsula in late Mesozoic and Cenozoic times

“…Metasedimentary rocks of a Mesozoic fore-arc basin yielded zircon FT ages between 129 and 78 Ma, while ages from a Mesozoic accretionary prism range from 178 to 102 Ma, always significantly younger than the ages of the host rocks, according to observations by Storey et al (1996) on Alexander Island. Apatite ages for both groups are between 62 and 27 Ma.…”

“…Also, there is no obvious correlation between ages and fault blocks associated with the fracture zones in the oceanic crust of the downgoing plate. The new data from the Anvers Island group fit into one of the episodes of (accelerated) cooling described earlier for Alexander Island in the south (Storey at al., 1996) and Livingstone Island in the north , which are around 40-35 Ma and 28 Ma, respectively. The first episode may be correlated with a major change in the plate motions in the Pacific realm around 43 Ma, including significant effects along the plate margins (Lithgow-Bertelloni & Richards, 1998), e.g.…”

“…These rocks represent a polyphase magmatic arc, since the Mid-Cretaceous related to the subduction of the Phoenix plate below the Antarctic plate. A Mesozoic fore-arc basin and an accretionary prism are preserved on Alexander Island in the south (Storey et al, 1996). The metamorphic complex associated with the southeastward subduction of the Phoenix plate is only accessible on Smith Island and in the Elephant Island Group in the north.…”

Chrono- and lithostratigraphy of a Mesozoic–Tertiary fore- to intra-arc basin: Adelaide Island, Antarctic Peninsula

“…The plutonic rocks (adamellite, granite, diorite: Rouen Intrusive Complex; Fig. 7) of Alexander Island have also been dated by several sources (Pankhurst, 1982;Storey et al 1996;McCarron & Millar, 1997) in the interval 46-75 Ma, suggesting a similar history to that seen on Adelaide Island and a similar compositional range from calc-alkaline granitoids to more mafic compositions. The plutonism on Alexander Island is also associated with late-stage mafic dykes, which cross cut the entire succession.…”

The Holocene history of George VI Ice Shelf, Antarctic Peninsula from clast-provenance analysis of epishelf lake sediments

“…The plutonic and volcanic provinces of western Palmer Land and southern Graham Land were formed by magmatic activity during the Mesozoic (Suarez, 1976;Leat et al, 1995;Storey et al, 1996;Howe, 2003). The Western Domain of Alexander Island formed in a fore-arc basin setting and is either a subduction/accretion complex of the Central Domain or a separate crustal fragment (Elliott, 1974;Vaughan and Storey, 2000).…”