THE MYSTERY OF THE BERMUDA RISE: ANALYSIS OF CASTLE HARBOR CAUSEWAY CORE

Bermuda, an anomalous seamount situated ~650 miles off the East Coast of the continental United States, has an enigmatic origin. While traditionally attributed to a mantle plume, evidence for such a plume is absent, as there is no discernible hotspot track and seismic imaging lacks a deep thermal anomaly (Vogt and Jung, 2007; Jackson et al., 2021). Bermuda’s basement rocks consist of bimodal foidite to basaltic lavas (Mazza et al., 2019), overlain by carbonate aeolianites.

In 2007, Golder Associates Ltd conducted coring in the Castle Harbor area, which is towards the eastern end of the island. These core holes were taken to support bridge infrastructure development, producing five boreholes at varying depths. Their analysis revealed altered porphyritic ultramafic volcanic rocks with diverse textures, mineralogy, and alteration patterns, including calcite-rich veins (Golder Associates, 2007).

Our study focuses on thin section samples from borehole 2, specifically a 130.5-foot-depth sample, suspected to contain volcanic glass. Preliminary analysis identifies orthopyroxene, clinopyroxene, calcite, titanomagnetite, albite, rutile, and apatite (in descending abundance) within a calcite matrix. Ongoing work aims to characterize the composition of volcanic glass and associated minerals to infer magma genesis conditions and the mantle source beneath Bermuda.

Works cited:

Golder Associates, 2007. Preliminary Geotechnical Assessment New Grotto Bay/Castle Harbour Crossing, Bermuda. Unpublished report submitted to the Government of Bermuda January 5th 2007.

Jackson et al., 2021 Spatial Characteristics of Recycled and Primordial Reservoirs in the Deep Mantle. Geochemistry, Geophysics, Geosystems, v. 267.

Mazza, S. E., et al., 2019. "Sampling the Volatile-Rich Transition Zone Beneath Bermuda." Nature, v. 569 no. 7756.

Vogt, P.R., and Jung, W., 2007, "Origin of the Bermuda Volcanoes and the Bermuda Rise: History, Observations, Models, and Puzzles." Special Papers, Geological Society of America.