New insight into the thermal-tectonic history of the southern Antarctic Peninsula: (Uranium-Thorium-Samarium)/Helium and fission-track thermochronologic results from northwest Palmer Land and Alexander Island.

摘要

This study examines the thermal history of the southern Antarctic Peninsula through the application of thermochronometry, and presents the first high-resolution thermochronologic dataset for arc rocks of northwest Palmer Land. I present 19 new thermochronologic ages obtained via (U-Th-Sm)/He and fission-track analyses of apatite and zircon from arc granitoids of northwest Palmer Land and fore-arc rocks of the LeMay and Fossil Bluff Groups of Alexander Island. These data were modeled via Monte Carlo simulations to generate time-temperature pathways. Thermal models generated for arc granitoids of northwest Palmer Land reveal a Late Cretaceous-Early Cenozoic episode of accelerated cooling from ca. 78--55 Ma not previously recognized in the southern Antarctic Peninsula. Here, faster cooling at an average rate of ∼15°C/Myr is bracketed by slower cooling at rates 3°C/Myr. Modeled thermal histories of metamorphosed fore-arc sedimentary rocks of Alexander Island reveal rapid cooling throughout the Eocene at an average rate of ∼13°C/Myr, preceded and followed by slower rates of cooling on the order of 3°C/Myr. The spatial and temporal distribution of the observed cooling trends may reflect localized variations in the thermal regime due to regional changes in plate kinematics, subduction dynamics, and related magmatism, but the cooling rates are also within range of those typical of exhumational processes such as normal faulting, ductile thinning, and erosion.