RE-EVALUATING THE WHITE MOUNTAIN MAGMA SERIES THROUGH HIGH-PRECISION ZIRCON U-PB GEOCHRONOLOGY AND TRACE ELEMENT GEOCHEMISTRY: A PRELIMINARY REPORT

The intrusive White Mountain Magma Series (WMS) represents an anomalous feature on the eastern North American Margin (ENAM). Comparative studies between the WMS and other features/events on the ENAM (e.g., the Central Atlantic Magmatic Province, opening of the Atlantic Ocean, the Monteregian Hills, etc.) fundamentally depend on accurate and precise age determinations. Our work seeks to modernize the geochronology of the WMS and reinforce the foundation necessary for unraveling the complex tectonic history of the region. Here we report preliminary results from an LA-ICP-MS survey of zircons from both the Jurassic and Cretaceous plutons of the WMS. Our initial geochronological work will measure zircon U-Pb content, allowing us to select the best grains for high-precision analyses. Additionally, we will report preliminary trace element measurements, including Hf and Ti, which will aid the development of petrogenetic and geodynamic models. Ultra-high precision dating using the ID-TIMS method will be conducted during winter 2015-2016 on units from both age groupings, focusing on the early Mesozoic White Mountain Batholith and a selection of Cretaceous plutons. These high precision ages (on the order of 100k kyr), coupled with zircon trace element geochemistry, will allow us to thoroughly investigate and address the following. 1) What is the relationship of the Central Atlantic Magmatic Province (implicated in the end-Triassic mass extinction) to the Jurassic Plutons of the WMS? 2) Did the emplacement of the White Mountain Batholith really span ~50 Myr? 3) Is the lack of a ‘classic’ age progression for the WMS and nearby Monteregian Hills related to imprecise or erroneous geochronology or does it imply something fundamental about its geodynamic setting? 4) What do the various ages of the WMS mean for the question of true polar wander and the plate position of North America? 5) How are intrusive and extrusive phases of the WMS related? 6) Do the pyroclastic deposits found in the lacustrine strata of the Newark and Hartford basins originate from the eruptive phases of the early Jurassic WMS plutons?