GRAVITY AND MAGNETIC ANALYSIS OF THE SPRINGFIELD, MISSOURI REGION

The Springfield, Missouri and surrounding region is typical of southern Missouri and northern Arkansas in that it consists of mainly undeformed Mississippian through Cambrian carbonate platform sediments overlying Precambrian intrusive and extrusive lithologies. These rocks lie on the southwestern flank of the Ozark Dome whose uplift caused only minor normal faulting and jointing. The thickness of the Paleozoic units is basically unknown but varies between 1000 and 1500 feet based on widely scattered wells. The lithology of the underlying Precambrian is also unknown, so in order to determine the depth to basement and the nature of the Precambrian units, a gravity and magnetic study was undertaken. The existing gravity database is relatively sparse northeast of Springfield, so we collected in the Fall of 2005, fifty additional points and these points were merged with the existing data. Aeromagnetic data were obtained from the USGS. Bouguer gravity and magnetic anomaly maps showed that the regional anomalies trend toward the northwest with a large variation in the anomaly amplitude. This anomaly trend has been noted elsewhere with the Ozark's region and is inferred to be caused by basement topography however the variation of anomaly amplitude can also be explained by changes in lithologies (e.g., more mafic material within the large gravity and magnetic maxima within the Bassville quadrangle) within the basement. In order to further investigate these anomalies, we will construct a series of residual and horizontal derivatives maps. Also, a northeast-trending, two and one-half dimensional gravity model will be constructed in order to quantify the depth to the basement in the Springfield region.