Geological setting and petrochemistry of early Middle Devonian volcanic and gabbroic rocks in the Guysborough area, Nova Scotia

Abstract

Mapping, petrological studies, and U-Pb dating of volcanic and plutonic units have provided a new understanding of the stratigraphy and paleotectonic setting of rocks in the Guysborough area. From base to top, the stratigraphic sequence is interpreted to consist of: (1) volcanic flows and pyroclastic rocks, with minor interlayered sedimentary rocks (Sunnyville Formation), (2) varied conglomerate (Glenkeen Formation), (3) quartz wacke with minor interlayered quartz arenite and conglomerate, and (4) massive to shaly or laminated siltstone. These volcanic and sedimentary units are intruded by small gabbroic plutons, sills, and dykes. All the units are early Middle Devonian. Based on whole-rock chemistry, the mafic volcanic and gabbroic rocks are similar, and formed in a continental within-plate setting. However, the rocks in the eastern part of the map area are more alkalic than those in the west, which are dominantly tholeiitic.