Geophysical dataset across the Masoke Igneous Complex in Kanye, Botswana
Description
The Masoke Igneous Complex, located in southeastern Botswana within the Kanye Basin, forms part of the larger Segwagwa–Masoke Igneous Ring Complex (SMIRC). It comprises steep-sided, elliptical intrusive bodies dominated by granite, diorite, syenite, and rhyolite. Radiometric dating places the crystallization of these rocks at approximately 2054 ± 9 million years ago, establishing a temporal link to the Bushveld Large Igneous Province in neighboring South Africa. The complex intrudes metasedimentary rocks of the upper Transvaal Supergroup and exhibits pronounced structural deformation, including E–W trending folds and N–S to NE–SW oriented fold systems. Geophysical modeling suggests that the Masoke intrusion extends to depths of nearly 5 kilometers and is associated with strong magnetic and gravity anomalies. These geophysical signatures point to magma emplacement along concentric fracture zones, likely formed during caldera collapse, reflecting a dynamic magmatic and tectonic history. To investigate the subsurface architecture of the Masoke Igneous Complex, a comprehensive geophysical survey was conducted along a single North–South oriented profile. Data were acquired at uniform 4-meter station intervals using a suite of methods: Audio Magnetotellurics (AMT), gravity measurements with a CG5 gravimeter, ground magnetic survey, MaxMin electromagnetic (EM) profiling, and seismic refraction. The AMT survey was divided into nine segments, later merged into a continuous resistivity profile to enhance structural coherence and interpretability. Gravity data reveal subsurface density variations, while magnetic measurements delineate lithological contrasts and highlight zones of magnetic enrichment. MaxMin EM readings provide high-resolution insights into shallow conductivity anomalies, particularly sensitive to mineralized zones and fluid-bearing structures, complementing the deeper resistivity data from AMT. Seismic measurements contribute stratigraphic and lithological information, offering a layered view of subsurface composition. To support regional interpretation, satellite imagery and a gridded aeromagnetic map were integrated, providing broader spatial context and aiding in the identification of structural trends and geological boundaries.
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Steps to reproduce
Field Protocol: Geophysical Survey Across Masoke Igneous Complex 1. Pre-Survey Preparation • Site Selection: Confirm North–South profile alignment across the target formation for optimal geological coverage. • Imagery Acquisition: Collect satellite imagery and gridded aeromagnetic maps to support planning and interpretation. • Survey Design: Divide the profile into segments (e.g., nine for AMT) and establish uniform 4-meter station intervals to standardize data collection. 2. Equipment Checklist Survey Type Equipment Purpose Gravity: CG5 gravimeter -- Detect subsurface density variations Magnetic: Proton magnetometer / fluxgate sensor-- Map magnetic anomalies and lithological contrasts AMT: Receiver system, electrodes-- Measure deep resistivity across segments MaxMin EM: Transmitter and receiver coils-- Detect shallow conductivity anomalies Seismic: Geophones, hammer/weight drop-- Identify subsurface layering and stratigraphy Navigation: GPS device, notebooks/tablets-- Record station coordinates and field notes 3. Data Acquisition Procedure • Station Setup: At each 4-meter interval, deploy instruments with consistent orientation (especially AMT electrodes, MaxMin coils, and geophones). Record GPS location and environmental conditions. • Measurement Collection: o Conduct gravity readings with CG5, applying drift correction. o Capture magnetic field intensity and direction. o Run AMT measurements, ensuring proper grounding and minimal interference. o Perform MaxMin EM readings using fixed coil offsets to measure in-phase and quadrature components. o Execute seismic measurements by generating wave signals and recording travel times. • Documentation: Log instrument settings, anomalies, and field conditions to ensure data integrity. Data Processing Workflow 1. Data Cleaning & Quality Control • Apply filters to reduce noise. • Verify alignment of measurements with station coordinates and timestamps. • Calibrate gravity and magnetic data using base station readings; validate MaxMin EM responses with known targets. 2. Segment Integration • Merge AMT segments into a continuous resistivity profile using spatial alignment techniques. • Integrate MaxMin EM data to enhance shallow conductivity resolution. • Align all datasets—gravity, magnetic, AMT, MaxMin EM, and seismic—spatially and temporally for coherent interpretation. 3. Visualization & Interpretation • Overlay satellite imagery and aeromagnetic maps for geospatial context. • Use modeling software (e.g., Oasis Montaj, RES2DINV, SeisImager) to generate subsurface models. • Interpret anomalies and structural features, cross-validating between datasets to refine geological models and identify zones of interest such as mineralization, faulting, or intrusions.
Institutions
- University of Botswana