MESOZOIC-CENOZOIC CRYSTALLIZATION AND COOLING HISTORY OF THE ANTARCTIC PENINSULA

The Antarctic Peninsula consists of a Cretaceous-Cenozoic magmatic arc emplaced into Paleozoic and lower Mesozoic metasedimentary rocks, parts of a Jurassic large igneous province (LIP), and a poorly characterized basement. Presently shrouded in ice, this arc developed coevally with the adjacent Larsen basin — Earth’s southernmost Cretaceous-Paleogene sedimentary basin presently exposed on land. Thus, the arc’s history may be important for accurate interpretation of valuable high-latitude biologic, climate and chemical records preserved in the basin. Here we present new zircon (U-Pb), amphibole, biotite and feldspar (Ar-Ar) ages collected from 15 Antarctic Peninsula plutons, which we integrate with existing thermochronology from the same rocks to understand the nature of underlying crust and the tectonothermal history of the peninsula. Zircon U-Pb data reveal the dominance of Late Cretaceous arc plutons and the existence of Jurassic LIP plutons. Inherited zircons indicate a widespread and diverse crustal substructure containing zircons with crystallization ages from the mid-Paleozoic and early Mesozoic (ca. 450-200 Ma: 24% of inherited grains), the late Neoproterozoic and early Paleozoic (ca. 650-450 Ma: 10%), the early Neoproterozoic (ca. 950-750 Ma; 16%); and the late Mesoproterozoic (ca. 1.2-1.0 Ga: 18%); as well as cannibalization of slightly older Cretaceous and Jurassic arc and LIP igneous rocks (19%). Zircon U-Pb ages of arc plutons coincide with or very briefly post-date their high-, intermediate-, and some low-temperature cooling ages, suggesting very rapid (~40-100+°C/Myr) late Cretaceous cooling, followed by protracted slow cooling (~1-10°C/Myr). Such temperature-time histories are consistent with hypabyssal intrusion, followed by relative tectonic quiescence. Sparse amphibole Ar-Ar results from Jurassic plutons preclude a full assessment of early cooling rates and emplacement depths but considerably younger intermediate-temperature cooling ages suggest a more moderate early cooling history or a Cretaceous reheating event. An abundance of Late Cretaceous intermediate and low-temperature cooling ages from Jurassic plutons suggests a period of rapid cooling coincident with the rapid cooling of Cretaceous arc plutons, in possible support of the latter interpretation.