TIMING OF CRETACEOUS MAGMATISM IN THE CHAMPLAIN VALLEY

Much of New England experienced magmatism during the Cretaceous period. Various hypotheses have been advanced to explain this magmatism including transit over a hotspot, mantle edge convection, lithospheric-scale faulting, and fluid flow. To this end, our study aims to determine the number of discrete magmatic episodes that occurred in the Champlain Valley and whether they are chemically distinct. We present 9 new ⁴⁰Ar/³⁹Ar ages, 5 new zircon U-Pb ages, and numerous geochemical analyses, which are compared with published data from the literature. Geochronology suggests three distinct episodes of magmatic emplacement in the Champlain Valley; the Burlington lobe mafic intrusions from ~136-139 Ma, the Burlington lobe felsic intrusions at 125-132 Ma, and the Taconic lobe intrusions from ~103-108 Ma. Likewise, the geochemical data is seemingly bimodal, with apparent distinctions between regional mafic intrusions and felsic rocks of the Burlington lobe. Bulk rock geochemical data suggests that the felsic rocks of the Burlington lobe and the Barber Hill pluton could have been derived from partial melting of the lithosphere.