Academic Affiliation: University of Puerto Rico, at Mayagüez
Diana Prado Garzón was born in Caracas, Venezuela, and moved to Puerto Rico as a child for access to a better education. Her secondary educational years were spent at the American Military Academy in Guaynabo, PR. Diana is working on her bachelor’s degree in geology and geophysics, and teaches yoga on the side. In her senior research project, she is studying crater impacts in South Africa. She hopes to go the University of Colorado at Boulder to study geophysics and geochemistry at the graduate level.
Zircons from the middle Proterozoic (CA. 1.81 GA) Sudbury impact structure, Ontario, Canada
The Sudbury Igneous Complex (SIC) forms the central part of the Sudbury impact structure and comprises three layers: norite (bottom), quartz gabbro, and granophyre (top). To determine the impact’s precise timing and the crust’s subsequent thermal behavior, an experimental approach was formulated to directly assess the associated impact energies. Zircon’s slow diffusional response at different temperatures makes this mineral an ideal recorder of postcrystallization thermal regimes. Furthermore, zircon’s titanium content is a function of temperature, which renders this relationship a useful thermometer.
The zircon grains were extracted from SIC norite and granophyre samples by using standard heavy-mineral techniques. Samples were prepared by hand-picking grains under an optical microscope and casting them in epoxy, or entire heavy-mineral aliquots were cast without biased hand-picking. A JEOL JSM-6480LV low-vacuum scanning electron microscope operating in secondary- and back-scattered electron imaging mode was used to identify zircon, apatite, and other minerals; many of the norite zircons displayed sets of planar deformation features attributable to shock-wave deformation from impact (Figure 1). The largest and least altered grains were removed and recast in epoxy with standard zircon AS-3 in anticipation of titanium thermometry and uranium and lead isotope measurements by high-resolution ion microprobe in depthprofile mode.
Depth profiling can reveal relationships between zircon growth time and the geochemical environment during crystallization and cooling after impact. This study aims to quantify the conditions for secondary zircon growth and recrystallization after a large impact and provides a quantitative means to define impact conditions and timing for ancient terrestrial and lunar samples.