John Maurice Peckenham

John M. Peckenham
Water Research Institute
208 Sawyer Environmental Research Center
University of Maine
Orono, Maine
04469-5764
phone: (207) 581-3254
fax: (207) 581-3290

A recent (1980) 98-meter-deep drill hole on the island of Bermuda cored nearly 50 meters of submarine melilititic pillowed-lavas and associated clastic rocks which are cut by narrow anastomosing melilite-bearing intrusives. Foraminifera (Orbulina and Globigerinids) found in the interpillow sediments yield mid-Tertiary ages. The mineralogies of both igneous rock-types are similar and modes fall within these ranges: phenocrysts of titan-augite and Mg-Al titanomagnetite (5-15%), groundmass of titan-augite (5-50%), Mg-Al titanomagnetite (2-15%), melilite (1-60%), biotite (0-10%), altered sphene (0-5%), altered olivine (0-5%) and altered glassy or cryptocrystalline material (2-80%). The rocks contain abundant calcite which is evenly dispersed through the rocks and in veins. The degree of alteration varies from extensive chloritization of cooling-unit margins to relatively unaltered cooling unit interiors. Chemcially these rocks are silica undersaturated (31-39% SiO₂), titanium rich (4.1-5.6%) and volatile rich (4.4-12.5%). A paleomagnetic study yielded few stable inclinations. The stable inclinations are not reproducible using different analytical techniques. The rocks have high Curie temperatures ( 570^oC) which do not correspond to the temperatures predicted from experimental studies on Al- and Mg-bearing titanomagnetites. The correlation of the rocks with Oligocene volcaniclastic turbidites found at DSDP Site 386 and the lack of other volcanogenic horizons in the sediments on the Bermuda Rise suggest that the Bermuda Volcano was formed during a single eruptive cycle. Geological and geophysical studies are cited which indicate that the Bermuda Rise did not exist until the mid-Tertiary, approximately the same time as the eruption of the newly collected lavas.

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Pages: 320
Supervisor: James Hall