¹Pietro Demattê Avona,¹Alvaro Penteado Crósta,²Marcos Alberto Rodrigues Vasconcelos,^3,4Evan Bjonnes,¹Fernando Lessa Pereira,⁵Ana Maria Góes
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14306]
¹Institute of Geosciences, Universidade Estadual de Campinas, Campinas, SP, Brazil
²Institute of Geosciences, Federal University of Bahia, Salvador, BA, Brazil
³Lawrence Livermore National Laboratory, Livermore, CA, USA
⁴Lunar and Planetary Institute, Houston, TX, USA
⁵Institute of Geosciences, University of São Paulo, São Paulo, SP, Brazil
Published by arrangement with John Wiley & Sons

Nova Colinas, centered at 07°09′33″ S/46°06′30″ W, is the ninth confirmed complex impact structure in Brazil and the fifth in the Parnaíba Basin, with a diameter of ~6.5–7 km and a nearly circular shape. Impactites include shocked siltstones from the Pedra de Fogo Fm. found at the central peak, brecciated sandstone from the Sambaíba Fm. bearing microscopic shock features, and brecciated basalt from the Mosquito Fm. bearing shatter cones. The impact event’s age has been constrained to the interval from ~130 to ~199 Ma based on the local stratigraphy. Due to its moderate to advanced stage of erosion, geophysical modeling combined with geological field data were employed for its characterization. A new geological map was produced through field observations and remote sensing image interpretation, as well as a 3-D model based on ground gravity data and numerical modeling. iSALE2D shock physics code was employed to simulate the formation of Nova Colinas crater. The results revealed its main structural zones: the central uplift, annular basin, and outer rim, each associated with specific lithostratigraphic units from the Parnaíba Basin. Bouguer residual anomalies ranged from −3.6 to 1.2 mGal, with a nearly circular positive anomaly at the center of the structure, surrounded by a negative anomaly. 3-D gravity data inversion indicated a buried high-density body, likely due to the uplift of a diabase sill. Results of the numerical modeling point out that the final crater reached gravitational stability with a diameter of ~7 km and a depth of ~240 m, suggesting that a narrow outcrop strip of the Motuca Fm. was uplifted to a higher level compared to the Sambaíba Fm. strata, forming an antiform-like “arch” that creates an inner ring that exposes rocks of the Motuca Formation.

¹Myriam Telus,^1,2Tyler D. Wickland,^1,3Kyle Kim,⁴Steven Simon
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14299]
¹Department of Earth and Planetary Sciences, University of California Santa Cruz, Santa Cruz, California, USA
²Geological Sciences, University of Colorado Boulder, Boulder, Colorado, USA
³Department of Geology, University of Maryland College Park, College Park, Maryland, USA
⁴Institute of Meteoritics, University of New Mexico, Albuquerque, New Mexico, USA
Published by arrangement with John Wiley & Sons

Samples in which Fe and Ni isotopes have not been disturbed by secondary processing are essential for constraining the initial solar system abundance of short-lived radionuclide 60Fe, (60Fe/56Fe)SS. However, Fe- and Ni-enriched veins and fractures within chondrules in unequilibrated ordinary chondrites (UOCs) imply late-stage open-system alteration that poses a potential problem for both bulk and in situ 60Fe-60Ni systematics. This study focuses on petrologic characterization of CO3.0s, which show significantly less secondary alteration than UOCs, potentially making them better targets for studying 60Fe-60Ni systematics. We determined the petrologic type of several CO3.0 meteorites with two independent approaches, Raman spectroscopy of matrix material and Cr2O3 content of FeO-rich olivine grains. CO3 chondrites analyzed in this study range from 3.00 to 3.2 in petrologic type with slight variations between results from the two different methods. Upon analyzing two thin sections of DOM 08006, one of the most pristine CO3 chondrites known, we found a chemically anomalous region, indicative of parent body hydrothermal alteration. Using the X-ray fluorescence microscopy beamline at the Australian Synchrotron, we collected high-resolution quantitative element maps to evaluate Fe and Ni mobilization for several CO3.0s. These results indicate that late-stage Fe and Ni mobilization like that observed in UOC samples is minor for most CO3 chondrites, highly localized and mostly limited to chondrule rims. Our results support that CO3.0s are well suited for further investigation of 60Fe-60Ni systematics and that detailed characterization of both the petrologic type and late-stage Fe and Ni mobilization of samples is important for further development of this short-lived radionuclide system.