MAPPING AND ANALYSIS OF A DIABASE DIKE IN THE NORTH CAROLINA PIEDMONT IN AN HONORS PHYSICAL GEOLOGY CLASS

The Fall 2002 Honors Physical Geology class at N.C. State University undertook mapping and related topical studies of a large diabase dike. Several isolated segments of the dike had been mapped in previous studies, but the dike's magnitude and continuity were not previously recognized. Armed with topographic and aeromagnetic maps, and advised by grad student mentors, six student teams each mapped the dike for half a quad, tracing the dike from its southernmost exposure near Selma northward for about 54 km to just north of Rolesville. Subsequent reconnaissance shows that the dike continues at least to the Virginia border for a total of 115 km. The dike trends about N20°W in the south, becoming more N-S before swinging to about N10°E in the north.

The production and examination of a petrographic thin section enabled students to learn the preparation procedure and how minerals are distinguished using a polarized light microscope. X-ray diffraction taught sample preparation techniques, including mineral separation, the basic concept of crystal structure, and the use of a powder diffractometer. Chemical analysis by X-ray fluorescence spectrometry involved sample preparation, data collection and reduction, and permitted comparison to other igneous rock analyses in the literature. Magnetic study required students to learn the use of a portable magnetometer and the techniques of modeling to infer dike characteristics such as thickness and dip. Geomorphic analysis permitted the examination of the dike's relationship to topographic features and involved a brief investigation of the hydrologic properties of diabase. A soil and botany study included the students’ inventory of flora developed near the dike and investigation of the unique soil properties of diabase.

This assignment was extremely successful. After background research and data collection by teams, results were presented to classmates, faculty, and mentors by means of PowerPoint^TM presentation. Students achieved a firm grasp of the processes involved in a research project; synergy was evident because all projects were related. Being involved in every step of the project, students felt a greater sense of ownership and enthusiasm for their work.