MESOZOIC DIABASE DIKE NOMENCLATURE IN CONNECTICUT

Mesozoic diabase dikes in Connecticut have been referred to informally by a myriad of names in the geologic literature. The dikes form four prominent geographic trends: the Higganum set of dikes in eastern and central southern Connecticut, the Buttress set of dikes in central Connecticut, the Bridgeport set of dikes in western and central Connecticut, and the West Rock set of sills and related dikes in central Connecticut. There are also additional numerous related short dike segments scattered through the southern part of the Mesozoic Basin.

The Higganum dike segments have been referred to locally as the Ponset dike, the Higganum dike, the dikes at Fairhaven, Clintonville, and East Wallingford, and the Fairhaven dike. In Massachusetts its continuation is known as the Holden dike. The Buttress dike segments have been referred to locally as the Cheshire dike, the Blue Hills dike and the Buttress dike. In Massachusetts, its continuation is known as the Ware dike. The Bridgeport dike segments are referred to locally as the Bridgeport dike. It is known in Massachusetts as the Pelham dike. The West Rock sills and related dikes have been referred to locally as the East Rock sill, the Millbrooke dike, the Rabbit Rock sheet, Mount Carmel laccolith, Cross Rocks dike, Barndoor intrusion, and West Rock sill.

The geologic map compilation by Rodgers (1985) recognized only two categories of rocks comprising all of the Mesozoic intrusive rocks - the West Rock Dolerite and the Buttress Dolerite. Chemical analyses of the intrusive rocks indicate, however, that they fall into three distinct categories as argued by Philpotts and Martello in 1986. We present newly acquired chemical data confirming that the Mesozoic diabase rocks in Connecticut can be chemically classified into three distinct groups: (i) the Higganum-Fairhaven Dikes and West Rock intrusive bodies, (ii) the Buttress Dikes, and (iii) the Bridgeport Dikes. The three groups correspond chemically to the three extrusive lava flows preserved in the basin. We propose that the dikes be referred to according to their chemical classification, with a geographical modifier if desired, rather than to their geographic location, and that the rocks that form these bodies be referred to as (i) the West Rock Diabase, (ii) Buttress Diabase and (iii) Bridgeport Diabase respectively.