OFFSHORE RING STRUCTURES AND IGNEOUS BODIES BENEATH THE CONTINENTAL MARGIN OF THE NORTHEASTERN UNITED STATES AND THE GULF OF MAINE: EVIDENCE SUPPORTING THE NEW ENGLAND HOTSPOT TRACK BETWEEN THE WHITE MOUNTAIN MAGMA SERIES AND THE NEW ENGLAND SEAMOUNTS

Interpretations of recently available multibeam sonar data and numerous seismic reflection profiles from the National Archive of Marine Seismic Surveys (NAMSS) have revealed ring-shaped structures between the White Mountain Magma Series (WMMS) in New Hampshire and the New England seamounts (NES) and massive, Cretaceous and younger igneous intrusions beneath the continental shelf, slope and rise southeast of Nantucket Island. The concentration and collinearity of rings and intrusives between the WMMS and the NES suggests that the rings and intrusives are associated with the New England hotspot track. The presence of large positive magnetic anomalies beneath the continental shelf northwest of the NES supports this hypothesis. Two long seismic reflection profiles which traverse the southeast end of the Nantucket Shoals in this area show a 120-km-wide area of upwarped sediments, suggesting that these shoals may have formed by uplift produced by the upward emplacement of these intrusives. Some of the intrusives beneath the continental slope northwest of Bear Seamount and on trend with the hot spot track also appear to have upwarped the overlying sediments. Three 2- to 3-km-size seamounts were also discovered on the continental slope and rise and two smaller, 0.5- to 1-km-size volcanic necks were discovered on the seafloor east of Cape Ann, MA. The coincidence of two of these volcanic features with rings suggests that they erupted upward along ring fractures formed by igneous intrusives at depth.

The NAMSS seismic reflection data also revealed a large, northeast-trending area of igneous intrusives along this part of the continental margin. We postulate that these intrusives may have migrated upward along the base of the thinning continental lithosphere like an upside-down drainage pattern ahead of the mantle plume associated with the proposed New England hotspot as it approached the continental margin to the southeast during Late Cretaceous time.

Examination of numerous seismic reflection profiles also revealed evidence for a possible 200-km-wide, buried submarine landslide along the continental slope west of the New England seamounts. This large landslide appears to have occurred during late Cretaceous or early Cenozoic time.