The Northumberland basin was initiated after eruption of alkali basalts onto the alluvial plains of the Upper Old Red Sandstone Scottish Border basin. The Birrenswark and Kelso Lavas are postulated as of upper mantle origin, produced by partial melting. Partial melting gave rise to slight upwarp and to areas of non-deposition with calcrete formation. Tensional stress in the upper crust arose locally from this upwarp and also from the regional effects of upper-mantle flow, as postulated by Bott (1964). Downfaulting along the Stublick/Ninety Fathom hinge line and basalt eruption along the pivot line of an incipient half graben led to basin initiation, Tournaisian marine transgression and southerly drainage from the Southern Uplands horst. Further volcanism, tending towards explosive central-vent activity with time, occurred along the northern basin margin in the Visean.
- Received June 7, 1973.
- Revision received September 11, 1973.
- © 1974 Scottish Journal of Geology