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4: Bushveld Igneous Complex - Geosciences

4: Bushveld Igneous Complex - Geosciences


4: Bushveld Igneous Complex - Geosciences

Studies of the Rooiberg Group, Bushveld Complex, South Africa: No evidence for an impact origin

It has been suggested that the Bushveld Complex of South Africa could be the result of multiple large meteorite or comet impacts. According to this hypothesis, part of the lower Rooiberg Group, which forms the roof of the Complex, represents a sheet of impact melt breccia and other impact breccias. The present study is an attempt to test the viability of the impact hypothesis for the Bushveld Complex by interpreting newly acquired field, geochemical, petrographic, and textural data for Rooiberg Group and associated rocks. Extensive field work throughout the Rooiberg Group and, particularly, at the contact between this unit and the underlying Pretoria Group metasediments has failed to identify any material that could be interpreted as impact-related. The Rooiberg Group is predominantly composed of individual volcanic flows and pyroclastic units representing several geochemically distinct magma types. These volcanic units are interbedded with thin, laterally extensive, sedimentary units, a few of which are sedimentary breccias. The presence of needles of quartz that may represent paramorphs after tridymite in some Rooiberg Group units has been used as evidence to support the contention that these rocks represent superheated impact melt. However, quartz paramorphs after tridymite have been recognized in terrestrial volcanic provinces (e.g., the North Shore Volcanic Group in northeastern Minnesota). Structural data, including dips of Rooiberg Group strata, suggest that the lobate shape of the Complex, which resembles several closely-spaced ring features, is the result of post-Rooiberg Group deformation. Microdeformation features in quartz from Bushveld-related rocks do not satisfy the criteria of shock metamorphic planar deformation features (PDFs) which would be characteristic of impact-induced shock pressures between ∼10 and ∼30 GPa. These data, especially the absence of macroscopic and microscopic evidence of shock deformation in pre-Bushveld rocks, are inconsistent with formation of the Bushveld Complex by impact.


4: Bushveld Igneous Complex - Geosciences

  • Maureen Feineman (Principal Investigator)
    [email protected] (814)863-7400
  • Andrew Nyblade (Co-Principal Investigator)

ABSTRACT

The over-arching goal of this Research Experience for Undergraduates (REU) site is to promote participation of undergraduate students, particularly under-represented minorities, in an international, multi-disciplinary, geosciences research project. A cohort of 6-8 undergraduates will travel to South Africa each summer to participate in a field study of the Bushveld Igneous Complex. Under the supervision of faculty from the Pennsylvania State University and the University of Witwatersrand, students will collect geophysical data and rock samples during the three-week field campaign. The raw data and samples will be brought back to Penn State for processing and analysis. Principles of Earth Science Literacy will be reinforced throughout the orientation, field work, analysis, and synthesis stages of the 10-week REU Site program. The impact of the program on the students' attitudes toward pursuing a career in the geosciences or another STEM field will be assessed through a series of surveys administered before, during, and after participating in the summer program.

2.06 Ga) is one of the largest intrusive mafic igneous bodies found in the continental crust, yet its origin and structure at depth are poorly understood. The scientific goal of this project is to determine the total volumetric and areal extent of the Bushveld Complex (BC). The BC is believed to be at least 500,000 cubic kilometers in size, and may be as large as 1,000,000 cubic kilometers, putting it on par with the largest igneous complexes in the world. The study of Large Igneous Provinces (LIPS) provides important insight into how the Earth's crust was formed, how continental landmasses are stabilized and broken apart, and perhaps into the cause of certain mass extinction events in geologic history. Over the three years of the REU Site, data will be collected and interpreted by participating students in order to better delineate the continuity (or lack thereof) between the central part of the BC and a number of outlying igneous intrusions. The data to be collected will include seismic and gravity measurements, as well as major element, trace element, and isotope ratio data for mineral separates and whole rocks.

This award was supported with co-funding from the Office of International and Integrative Activities.

PROJECT OUTCOMES REPORT

This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation NSF has not approved or endorsed its content.

Between 2015 and 2019, 31 undergraduates from universities and colleges accross the United States participated in the Penn State - AfricaArray Bushveld REU Program. All of these students participated in research projects related to the geochemistry and geophysics of the Bushveld Igneous Complex, and 30 students traveled to South Africa to conduct field work at the Bushveld Igneous Complex and the Vredefort Impact Structure. Participants presented the results of their research projects at in-house symposia at the Pennsylvania State University and the University of the Witwatersrand, the AfricaArray Diversity Forum in Houston, TX, the National Association of Black Geoscientists Conference, the Geological Society of America Annual Meeting, and the American Geophysical Union Fall Meeting.

Demographically, 42% of the REU participants were female and 67% identified as Hispanic/Latino/Mexican-American (48%) or Black/African-American (19%). As of Fall 2019, at least 12 REU participants had started MS programs in Geosciences and related fields, and at least 4 had started PhD programs in Geosciences and related fields. Of the students who entered graduate programs, five have completed their degrees and the rest are still in progress. At least seven former REU participants are currently employed as geoscientists in industry or academia. Nearly all of the former participants site the Penn State - Bushveld REU as their entry point into research in the geosciences, and credit the experience with opening avenues to subsequent employment and academic opportunities. Many also report that the REU helped them to improve their scientific communication skills and confidence.


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