Origin of the Bermuda volcanoes and the Bermuda Rise: History, observations, models, and puzzles

Abstract

Deep-sea drilling on DSDP Leg 43 and on Bermuda itself, together with geophysical data (anomalies in basement depth, geoid and heat flow) and modeling have long suggested the uplift forming the Bermuda Rise, as well as the initial igneous activity that produced the Bermuda volcanoes, began ca. 47-40 Ma, during the early to middle part of the Midde Eocene. Some authors attribute 65 Ma igneous activity in Mississippi and 115 Ma activity in Kansas to a putative "Bermuda hotspot" or plume fixed in the mantle below a moving North America plate. While this is more or less consistent with hotspot traces computed from 'absolute motion' models, the hotspot/plume must resemble a lava lamp, turning off for up to 25 million years at a time, and/or be heavily influenced by lithosphere structure. Moreover, Cretaceous igneous activity in Texas and Eocene intrusions in Virginia then require separate mantle "blobs".The pillow lavas forming the original Bermuda shield volcano have not been reliably dated, and the three associated smaller edifices have not been drilled or dated. A well-dated (ca. 33-34 Ma) episode of unusually titaniferous sheet intrusion in the Bermuda edifice was either triggered by plate-wide stress changes or reflects local volcanogenic events deep in the mantle source region. The high Ti and Fe of the Bermuda intrusive sheets probably relate to the very high amplitude magnetic anomalies discovered on the islands.Numerical models constrained by available geophysical data attribute the Bermuda Rise to some combination of lithospheric reheating and dynamic uplift. While the relative contributions of these two processes cannot yet be wholly separated, three features of the rise clearly distinguish it from the Hawaiian swell: 1) The Bermuda Rise is elongated at right angles to the direction of plate motion; 2) There has been little or no subsidence of the Rise and volcanic edifice since its formation-in fact, Rise uplift continued at the same site from the late Middle Eocene into the Miocene; and 3) The Bermuda Rise lacks a clear, age-progressive chain.We infer that the Bermuda Rise and other Atlantic midplate rises are supported by anomalous asthenosphere, upwelling or not, that penetrates the thermal boundary layer and travels with the overlying North America plate.The elongation, along crustal isochrons, of both the Bermuda volcanoes and the Rise and Rise development mostly within a belt of rougher, thinner crust and seismically "slower" upper mantle-implying retention of gabbroic melts at the ancient MAR axis-suggests the mantle lithosphere may have helped localize rise development-in contradiction to plume models. The Bermuda Rise area is seismically more active than its oceanic surroundings, preferentially along old transform traces and possibly reflecting a weaker upper mantle-lithosphere.We attribute the "Bermuda event" to a global plate kinematic reorganization, triggered by the closing of the Tethys and the associated gravitational collapse into the lower mantle of subducted slabs which had been ...

A sustained +21m sea-level highstand during MIS 11 (400ka): direct fossil and sedimentary evidence from Bermuda

“…The volcanic seamount is several thousand meters thick, has a pillowbasalt density equivalent to the densest lithosphere of >2.5-3.0 gm/cm 3 , is over a hundred km in circumference, and situated in the abyssal plain of the western North Atlantic on relatively thin oceanic lithosphere far away from any active plate margins (Vogt and Jung, 2007). Unless gravity fails or loci of plate tectonics shift, the seamount and its platform have been sinking, are sinking, and will continue to sink.…”

“…Unless gravity fails or loci of plate tectonics shift, the seamount and its platform have been sinking, are sinking, and will continue to sink. All subaerial volcanics have been removed either by erosion or subsidence, or both, but still exist as little as 26 m below present sea-level (Vogt and Jung, 2007). By all who have studied the surficial geology, the exposed rocks have been considered to be no older than early Pleistocene (Hearty et al, 1992;Vacher et al, 1995).…”

“…The Bermuda carbonate platform is tectonically stable and sits atop a 40 Ma volcanic pedestal. It is most likely slowly subsiding (Vogt and Jung, 2007). The Quaternary stratigraphy of the island has been mapped and described in detail (Vacher et al, 1989(Vacher et al, , 1995Hearty et al, 1992;Hearty et al, 2004), and consists of limestone and paleosol couplets correlated with early, middle, and late Pleistocene sealevel cycles (Table 1).…”

Geochronology of the Arkansas Alkaline Province, Southeastern United States

“…Additionally, the widespread occurrence of ages between 101 and 94 Ma without any apparent geographic trend does not support a hotspot trace. (2) In a carefully reasoned paper, Vogt and Jung (2007) conclude that the Bermuda rise was not the product of hotspot volcanism and that other conflicting time-space relationships for igneous activity throughout the southern United States negate the hotspot hypothesis.…”

“…Although one of the projected Bermuda hotspot traces passes through the AAP, the age progression within the AAP does not support a hotspot model. Additionally, recent studies have questioned the existence of the Bermuda hotspot (Vogt and Jung 2007). The AAP falls on the extension of the Mississippi graben and occurs between two continental blocks within a region of mid-Cretaceous uplift.…”