Paper No. 16-5
Presentation Time: 4:20 PM
NEW ZIRCON U-PB GEOCHRONOLOGICAL DATA FROM THE MOAT VOLCANICS, WHITE MOUNTAINS, NEW HAMPSHIRE – IMPLICATIONS FOR RIFT AND/OR PLUME RELATED MAGMATISM
Jurassic volcanic and plutonic rocks within the North Conway quadrangle of New Hampshire are key to deciphering the magmatic and extensional history of the White Mountain Magma Series (WMMS) and the greater tectonic evolution of the eastern North American margin during the break-up of Pangea. The Moat Volcanics are the only plausibly extrusive component of the WMMS and are found within ring dikes associated with caldera collapse and fill sequences. Despite these important implications for the geological history of the eastern North American margin, the Moat Volcanics have received remarkably little attention since the pioneering work of Marland Billings and John Creasey, and they generally suffer from a lack of modern geochronological constraints. Here, we report new igneous zircon laser ablation-inductively coupled mass spectrometry (LA-ICPMS) and chemical abrasion-isotope dilution-thermal ionization mass spectrometry (CA-ID-TIMS) U-Pb geochronological data from comendites in the lower and upper Moat Volcanics. We also present new detrital zircon LA-ICPMS U-Pb geochronology from clasts within the Moat Volcanic breccias, including new data from the enigmatic Intervale Clay-Slate. Our findings suggest the Moat Volcanics were erupted over 10 million years earlier than previously shown by Rb-Sr geochronology, which yielded ages of ca. 168—173 Ma. These precise age constraints provide new insight into (1) the relationship between the felsic rocks of the WMMS and the mafic flood basalts of the Central Atlantic Magmatic Province (CAMP), (2) the Mesozoic apparent polar wander path of Laurentia, and (3) the style of rift- and/or plume-related magmatism associated with the early Mesozoic fragmentation of Pangea.