ZIRCON U-PB GEOCHRONOLOGY OF THE NORTHERN ANTARCTIC PENINSULA MAGMATIC ARC

Herein we present new U-Pb zircon geochronology from plutonic rocks of the northern Antarctic Peninsula to better understand the history of subduction and arc magmatism along the southern terminus of the 10,000 km long Cordilleran orogen. Whole rock samples were collected and documented in a metadatabase. These samples were then disaggregated and separated into fractions by density and magnetic characteristics, ultimately yielding a high purity zircon separate. Resulting zircons were then mounted in epoxy, polished, and analyzed using laser-ablation single-collector inductively coupled plasma mass-spectrometry (LA-SC-ICP-MS) in the Center for Elemental Mass Spectrometry at the University of South Carolina. When corrected to a Sri Lankan reference zircon (SL = 563 Ma) for downhole fractionation and instrument drift, resulting ²⁰⁶Pb/²³⁸U ages reveal a Cretaceous history of magmatism, broadly in line with previously acquired data. A tonalite from Cape Bellue yielded a weighted age of 74.3±0.8 Ma (2σ propagated errors; n = 33; MSWD 2.3), and inherited older Cretaceous grains (81.7±2.9 Ma, and 83.2±2.9 Ma). A tonalite from Hope Bay yielded a weighted age of 88.4±1.7 Ma (n = 34; MSWD 4.9), and Late Carboniferous (302 Ma, 303 Ma, 324 Ma), Devonian (363 Ma) and Neoproterozoic (578 Ma) inherited grains. A granite from the Lahille Islands yielded a weighted age of 100.1±2.0 Ma (n = 23; MSWD 3.9), as well as Early Cretaceous and late Permian inherited grains (134 Ma, 141 Ma, and 260 Ma). A granite from Sadler Point in Wilhelmina Bay yielded a weighted age of 127.1±2.4 Ma (n = 14; MSWD 4.9), and numerous Paleozoic (273-472 Ma; n = 8), Neoproterozoic (761-851 Ma; n = 4); and Mesoproterozoic (1.1-1.8 Ga; n = 6) inherited grains. A sheared granitoid from Andvord Bay yielded a weighted age of 141.7±3.3 Ma (n = 27; MSWD 7.5), and Paleozoic and Neoproterozoic inherited grains (330 Ma, 400 Ma, 651 Ma, 741 Ma and 834 Ma). In addition to these Cretaceous arc granitoids, a tonalite from Cape Roquemaurel likely derived from the silicic large igneous province associated with the break-up of Gondwana returned a poorly constrained late Jurassic age (156±28 Ma, n = 7; MSWD>100), and numerous Mesoproterozoic and Neoproterozoic (0.7-1.5 Ga; n = 24) inherited grains.