GEOPHYSICAL AND GEOLOGICAL INVESTIGATION OF THE MWERU RIFT, ZAMBIA: PROVIDING INTERNATIONAL RESEARCH EXPERIENCE FOR STUDENTS

This NSF-IRES project had two main goals in its third year: 1) Constrain the geometry of the Mweru Rift in northern Zambia, and 2) Provide international research experience to train the next generation of geoscientists. One of the Hypotheses to be tested was that propagation of the well developed Eastern Branch of the East African Rift System (EARS) southward gave rise to a less developed South Western Branch of which the Mweru Rift (now occupied by Lake Mweru) is a part. This was based on the shape of the lake and on preliminary data from a previous field season. ASTER remote sensing data as well as airborne gravity and magnetic data were used to identify possible rift-related faults. Based on this data the faults are deep seated structures. A 500 meter spacing for gravity profiles, a 100 meter spacing for magnetometer traverses, and field observations were used to image these proposed faults on the Northen part of the lake. The rocks in the area are all Precambrian in age. A few boulders of amphibolite could be found along the lake shore, however it was never observed in situ. Mylonite cropped out along the lake shore, and gradually graded into less deformed rapakivi granite to the East / North East. The shore line of the lake closely parallels the mylonite fabric with an average strike and dip of 214 / 070. Plunge and trend of lineations were 338 / 056, and joint measurements of 030 / 060. The results of the preliminary data suggest that the area is a Precambrian ductile shear zone. The gravity and magnetic data show an increasing anomaly to the West perpendicular to the long axis of the lake suggesting the presence of a dense body at depth, however, further modeling should be able to constrain the geometry of the graben. The gravity and magnetic data also suggest the presence of faults within the graben. The magnetic profile shows a large increase in magnetization near the shore coincident with the mylonite zone. No evidence could be found to suggest recent faulting. Nonetheless, our preliminary results suggest that the older Precambrian structure controls the structure of the lake shoreline. Any new movement is likely taking advantage of the old shear zones or zones of weaknesses.